Category: Adult Reconstruction Review

Adult reconstruction orthopedic exam prep review questions and answers …

Current Concepts in the Use of Constrained Liners in Revision Total Hip Arthroplasty

High-Yield Summary

Constrained liners are primarily indicated in revision total hip arthroplasty (THA) for recurrent instability when soft tissue and bony constraints are insufficient.
Proper patient selection and understanding implant design limitations are critical to minimize mechanical failure and optimize stability.
The choice between constrained liners, dual mobilityand other options depends on the degree of abductor deficiency, bone lossand patient factors.
Surgical technique must emphasize meticulous component positioning, soft tissue balancingand secure fixation to reduce complications.
Recent evidence supports constrained liners as a salvage option rather than first-line, with evolving implant designs improving survivorship.

Clinical Fundamentals

Relevant Anatomy and Biomechanics

The hip joint’s stability depends on the congruency of the femoral head and acetabulum, the integrity of the capsule, labrumand surrounding musculature-particularly the abductors (gluteus medius and minimus). The abductor mechanism provides dynamic stability by maintaining femoral head centration during gait. Loss of abductor function or capsular insufficiency significantly increases dislocation risk.

Biomechanically, constrained liners increase stability by mechanically limiting femoral head translation, but this alters load transfer, increasing stress at the bone-implant interface and implant locking mechanisms. This can predispose to liner failure or loosening.

Epidemiology

Instability is the second most common cause of revision THA, accounting for 10-20% of revisions. Recurrent dislocation after revision ranges from 10-30%, with constrained liners used in approximately 5-10% of revision cases. Risk factors include abductor deficiency, multiple prior surgeries, neuromuscular disordersand poor component positioning.

Classification & Diagnosis

Classification System	Description	Clinical Impact on Management
Paprosky Acetabular Defect Classification	Categorizes acetabular bone loss (Type I-III)	Guides implant choice and fixation strategy; severe defects may contraindicate constrained liners without structural support
Abductor Mechanism Integrity	Intact, partial tearor complete deficiency	Determines need for constrained liner vs. alternative strategies (e.g., muscle transfers, dual mobility)
Dislocation Pattern Classification	Early vs. late, direction (anterior/posterior), reducible vs. irreducible	Influences urgency and surgical approach; irreducible or recurrent dislocations favor constrained liner use

Diagnostic Pearls

Obtain detailed history of dislocation events, including direction and precipitating factors.

Use advanced imaging (CT) to assess component position, bone lossand abductor status.

Dynamic fluoroscopy or examination under anesthesia can help differentiate soft tissue causes from mechanical failure.

Beware of underestimating abductor deficiency; clinical exam and MRI may be necessary.

Decision-Making Algorithm

Criteria	Non-Operative Management	Operative Management
First-time dislocation with well-positioned components and intact abductors	Closed reduction, bracing, activity modification	Not indicated initially
Recurrent dislocation with component malposition or loosening	Revision surgery targeting component alignment	Correct malposition, consider constrained liner if instability persists
Recurrent dislocation with abductor deficiency and stable components	Trial of non-operative measures limited	Constrained liner indicated to mechanically restore stability
Severe bone loss (Paprosky III) or infection	Address bone loss with structural grafts or staged revision	Constrained liner used cautiously, often combined with augmentations

Why Choose Constrained Liners?

Constrained liners provide mechanical containment of the femoral head, preventing dislocation when soft tissue constraints fail. They are preferred when abductor deficiency is irreversible and other options (e.g., dual mobility) are contraindicated or have failed. However, they increase mechanical stress and risk of implant failure, so their use is reserved for salvage situations.

Surgical Mastery & Pearls

Step-by-Step Conceptual Overview

Preoperative Planning: Assess bone stock, component positionand soft tissue status using imaging and clinical exam. Select implant size and constraint level accordingly.

Exposure: Use extensile approaches (posterior or anterolateral) to allow thorough visualization and soft tissue management.

Component Removal: Remove loose or malpositioned components carefully to preserve bone stock.

Acetabular Preparation: Achieve stable fixation with appropriate screws and augments; avoid excessive reaming that compromises bone.

Implantation of Constrained Liner: Ensure liner seating is flush and locking mechanism fully engaged; confirm compatibility with femoral head size.

Soft Tissue Balancing: Repair capsule and abductors meticulously; consider augmentation with grafts or synthetic meshes if deficient.

Trial Reduction: Confirm stability through full range of motion, avoiding impingement.

Final Implantation: Secure all components, verify leg length and offsetand close in layers to optimize soft tissue tension.

Intraoperative Red Flags

Difficulty seating the liner or incomplete locking mechanism engagement signals risk for early failure.

Excessive bone loss without adequate fixation risks early loosening.

Persistent instability after trial reduction suggests need for alternative strategies or increased constraint.

Over-tensioning soft tissues can cause nerve injury or fracture.

Evidence-Based Synthesis

Landmark studies have established constrained liners as a valuable tool for managing recurrent instability in revision THA, but not without limitations. Early designs showed high failure rates due to liner fracture and loosening. Modern modular constrained liners with improved locking mechanisms and polyethylene have demonstrated better mid-term survivorship.

Comparative studies indicate dual mobility implants may offer similar or superior stability with lower mechanical failure rates, especially in patients with preserved abductor function. However, constrained liners remain indispensable in cases of severe abductor deficiency or multiple failed revisions.

Recent meta-analyses highlight that constrained liners reduce dislocation rates from approximately 30% to under 10% in high-risk revision cohorts but at the cost of increased mechanical complications. The literature underscores the importance of patient selection and surgical technique to optimize outcomes.

Areas of ongoing debate include the threshold for choosing constrained liners over dual mobility and the role of adjunctive soft tissue procedures. Emerging designs incorporating elevated rims and enhanced locking mechanisms show promise but require longer follow-up.

Master Class Pro-Tip

When implanting a constrained liner, prioritize achieving a stable, well-fixed acetabular component with optimal version and inclination before liner insertion. Avoid relying solely on the liner’s constraint to compensate for malposition or soft tissue deficiency. Meticulous soft tissue repair, including capsular and abductor reconstruction, synergizes with mechanical constraint to provide durable stability. Recognize that constrained liners are a mechanical solution to a biological problem-addressing both aspects elevates surgical success from competent to masterful.

August 20, 2026/0 Comments/by OrthoNet AI

Adult Reconstruction Review

Management of the Infected Total Knee Arthroplasty: One-Stage vs. Two-Stage Exchange

High-Yield Summary

Infected total knee arthroplasty (TKA) requires prompt, accurate diagnosis and tailored surgical management to optimize eradication and functional outcomes.
One-stage exchange offers comparable infection control with fewer surgeries and faster recovery but demands strict patient selection and microbiological certainty.
Two-stage exchange remains the gold standard for complex infections, resistant organismsor compromised hosts, balancing infection eradication with staged reconstruction.
Key decision factors include pathogen virulence, soft tissue status, host immune competenceand implant fixation quality.
Surgical success hinges on meticulous debridement, appropriate antibiotic deliveryand implant choice aligned with infection severity and patient factors.

Clinical Fundamentals

Anatomy and Biomechanics
The knee joint comprises the distal femur, proximal tibiaand patella, stabilized by collateral ligaments and the extensor mechanism. Total knee arthroplasty replaces these surfaces with metal and polyethylene components, restoring alignment and load transfer. Infection disrupts soft tissue integrity and bone stock, complicating implant fixation and joint biomechanics.

Epidemiology
Periprosthetic joint infection (PJI) complicates 1-2% of primary TKAs and up to 4% of revisions. Risk factors include obesity, diabetes, immunosuppression, prior surgeryand prolonged operative time. Early infections (<3 months) often present acutely, while late infections (>3 months) may be indolent with biofilm formation.

Classification & Diagnosis

Classification System	Description	Impact on Management
Tsukayama Classification	Divides PJI into early postoperative, late chronic, acute hematogenousand positive intraoperative cultures	Guides timing and aggressiveness of intervention
Zimmerli Criteria	Defines PJI based on clinical signs, microbiology, histologyand synovial fluid analysis	Diagnostic gold standard for confirming infection
MSIS Criteria (2018)	Combines major and minor criteria including sinus tract, pathogen isolation, elevated ESR/CRP, synovial WBC countand neutrophil percentage	Standardizes diagnosis, reducing false positives/negatives

Diagnostic Pearls

Synovial fluid analysis with leukocyte count >3000 cells/?L and neutrophils >80% strongly suggests infection.

Culture-negative PJI requires extended incubation and molecular diagnostics to avoid misclassification.

Imaging (radiographs, nuclear scans) aids in assessing implant loosening but is nonspecific for infection.

Avoid premature antibiotics before obtaining cultures to maximize yield.

Decision-Making Algorithm

Criteria	Non-Operative Management	One-Stage Exchange	Two-Stage Exchange
Infection Duration	Acute hematogenous (<3 weeks) with stable implant	Chronic infection with known pathogen, good soft tissueand host	Chronic infection, unknown or resistant pathogen, poor soft tissue, immunocompromised host
Pathogen	Low virulence, antibiotic-sensitive	Identified pathogen with susceptibility	Resistant organisms (MRSA, fungi), polymicrobial
Host Factors	Medically unfit for surgery	Good immune status, minimal comorbidities	Poor host, multiple comorbidities
Soft Tissue	Intact, no sinus tract	Healthy soft tissue envelope	Sinus tract, compromised soft tissue
Implant Status	Stable implant	Well-fixed implant or planned removal	Loose implant requiring removal

Rationale
Non-operative management is limited to acute infections with stable implants and early antibiotic therapy. One-stage exchange reduces morbidity and hospitalization but requires pathogen identification and optimal host conditions. Two-stage exchange prioritizes infection eradication in complex scenarios, allowing interim antibiotic spacer placement and staged reconstruction.

Surgical Mastery & Pearls

One-Stage Exchange Technique

Perform extensive synovectomy and radical debridement of all infected and necrotic tissue.

Remove all components and cement meticulously to eliminate biofilm reservoirs.

Obtain multiple intraoperative cultures before irrigation.

Use antibiotic-loaded cement tailored to pathogen sensitivities for reimplantation.

Achieve stable fixation and restore alignment with appropriate implant choice.

Intraoperative red flag: persistent purulence after debridement suggests need to abort one-stage and consider two-stage approach.

Two-Stage Exchange Technique

Stage 1: Remove all implants and cement, perform aggressive debridement, place an articulating or static antibiotic spacer.

Administer systemic antibiotics guided by culture results for 6 weeks.

Monitor inflammatory markers and clinical signs to confirm infection control.

Stage 2: Reimplant definitive prosthesis after infection eradication, reassess soft tissue and bone stock.

Intraoperative red flag: elevated synovial WBC or persistent purulence at reimplantation mandates spacer retention or repeat debridement.

Technical Tips

Use pulse lavage with copious saline to reduce bacterial load without damaging soft tissues.

Avoid dead space by using antibiotic spacers that maintain joint mobility and soft tissue tension.

Ensure multidisciplinary coordination with infectious disease specialists for antibiotic stewardship.

Evidence-Based Synthesis

Recent meta-analyses and randomized controlled trials have challenged the dogma favoring two-stage exchange as the universal standard. Studies demonstrate that one-stage exchange achieves comparable infection eradication rates (85-95%) with fewer surgeries, shorter hospital staysand improved functional outcomes in well-selected patients. However, heterogeneity in patient populations and pathogen profiles limits broad applicability.

Two-stage exchange remains superior in managing resistant organisms, polymicrobial infectionsand compromised hosts, with eradication rates exceeding 90%. Emerging data suggest that advances in microbiological diagnostics and antibiotic-loaded cement formulations may expand indications for one-stage exchange.

Controversies persist regarding optimal spacer design, timing of reimplantationand antibiotic duration. Current consensus emphasizes individualized treatment algorithms integrating host, pathogenand local tissue factors rather than a one-size-fits-all approach.

Master Class Pro-Tip

Mastery in managing infected TKA lies in the surgeon’s ability to integrate microbiological data with intraoperative findings dynamically. When performing a one-stage exchange, do not hesitate to convert to a two-stage strategy intraoperatively if debridement fails to achieve a clean field or unexpected resistant organisms emerge. This flexibility, combined with meticulous soft tissue handling and precise implant positioning, distinguishes the expert surgeon who consistently achieves durable infection control without compromising knee function.

August 7, 2026/0 Comments/by OrthoNet AI

Adult Reconstruction Review

Understanding the Anderson Orthopaedic Research Institute (AORI) Classification for Bone Defects

High-Yield Summary

The Anderson Orthopaedic Research Institute (AORI) classification stratifies bone defects in revision total knee arthroplasty (TKA) by location and severity, guiding reconstruction strategy.
Type 1 defects involve intact metaphyseal bone; Type 2 defects have damaged metaphyseal bone but intact collateral ligaments; Type 3 defects include severe bone loss compromising ligamentous stability.
Accurate defect classification dictates implant choice: cement fill, metal augments, metaphyseal sleeves/conesor structural allografts.
Preoperative imaging and intraoperative assessment are critical to avoid underestimating defect severity, which can lead to implant failure.
Mastery of the AORI system optimizes surgical planning, implant selectionand fixation technique, improving revision TKA outcomes.

Clinical Fundamentals

The distal femur and proximal tibia metaphyses provide critical support for TKA implants. Their cancellous architecture allows for load transfer and implant fixation. Bone defects in revision TKA arise from osteolysis, stress shielding, infectionor mechanical loosening, compromising implant stability and alignment. Preservation or restoration of collateral ligament attachments is essential for knee stability. Biomechanically, metaphyseal bone loss reduces the capacity to resist varus-valgus and rotational forces, necessitating augmentation or structural reconstruction. Epidemiologically, bone defects are common in revision TKA, with up to 25% of cases exhibiting significant metaphyseal bone loss requiring complex reconstruction.

Classification & Diagnosis

AORI Type	Description	Key Diagnostic Features	Surgical Implication
Type 1	Minor bone defects with intact metaphyseal bone	Radiographs show minimal bone loss; collateral ligaments intact	Cement or minor bone grafting sufficient
Type 2A	Damaged metaphyseal bone on one condyle (femur or tibia)	Radiographs reveal localized bone loss; collateral ligaments intact	Metal augments or sleeves recommended
Type 2B	Damaged metaphyseal bone on both condyles	Bilateral metaphyseal bone loss on imaging; ligaments intact	Larger augments, sleevesor cones required
Type 3	Severe metaphyseal bone loss compromising ligament attachments	Extensive bone loss on imaging; collateral ligament insufficiency	Structural allografts or megaprostheses indicated

Diagnostic Pearls:

Use orthogonal radiographs and CT scans to assess defect size and cortical integrity.

Beware of underestimating defects on plain films; intraoperative probing is essential.

Differentiate between contained and uncontained defects, as this affects reconstruction choice.

Confirm collateral ligament status clinically and intraoperatively; ligament insufficiency upgrades defect severity.

Decision-Making Algorithm

Non-operative management is rarely appropriate for AORI Type 2 and 3 defects due to mechanical instability. Decision-making hinges on defect size, locationand ligament integrity.

Type 1 Defects:

Non-operative management is limited to minor bone loss without instability. Surgical management involves cement fill or morselized bone grafting to restore bone stock and support standard implants.

Type 2 Defects:

Require operative intervention with metal augments, metaphyseal sleevesor cones to restore metaphyseal support. The choice depends on defect size and containment. Preservation of collateral ligaments allows use of primary or constrained condylar implants.

Type 3 Defects:

Indicate extensive bone loss with ligament insufficiency. Surgical options include structural allografts, megaprosthesesor highly constrained implants. Reconstruction aims to restore bone stock and soft tissue stability.

Why Specific Approaches:

Metal augments and sleeves provide immediate structural support and facilitate biologic fixation.

Structural allografts restore bone stock but carry risks of nonunion and infection.

Megaprostheses offer a salvage option when reconstruction is not feasible.

Surgical Mastery & Pearls

Exposure and Assessment:

Begin with extensile exposure to visualize metaphyseal bone and collateral ligaments. Use intraoperative probing to confirm defect size and ligament status.

Debridement:

Remove all fibrous tissue and loose bone to expose healthy bleeding bone, optimizing implant fixation.

Defect Preparation:

For contained defects, prepare the cavity for cement or bone graft. For uncontained defects, prepare metaphyseal bone for sleeves or cones by reaming to fit implants snugly.

Implant Selection and Fixation:

Type 1: Use cement or morselized graft with standard implants.
Type 2: Fit metaphyseal sleeves or cones to achieve press-fit fixation; augment with metal wedges as needed.
Type 3: Consider structural allografts fixed with screws or megaprostheses with stems bypassing deficient bone.

Intraoperative Red Flags:

Unexpected ligament insufficiency requiring implant constraint upgrade.
Poor metaphyseal bone quality precluding press-fit fixation.
Inadequate implant stability after trialing, necessitating revision of reconstruction plan.

Technical Tips:

Use trial components to assess fit and alignment before final implantation.
Avoid over-reaming metaphyseal bone to preserve host bone stock.
Ensure stable fixation of sleeves/cones to prevent micromotion and loosening.

Evidence-Based Synthesis

Landmark studies validate the AORI classification as a reproducible tool correlating with surgical outcomes. Recent literature emphasizes metaphyseal fixation with sleeves and cones as superior to traditional augments and structural allografts, showing improved implant survivorship and earlier weight-bearing. Meta-analyses reveal lower complication rates with porous metal cones compared to allografts, though long-term data remain limited. Contradictions exist regarding the optimal management of Type 3 defects, with some advocating for megaprostheses in elderly, low-demand patients, while others support structural allografts in younger patients to preserve bone stock. Emerging evidence suggests that preoperative CT-based 3D planning enhances defect characterization and implant selection, reducing intraoperative surprises.

Master Class Pro-Tip

When managing complex metaphyseal defects, prioritize achieving metaphyseal fixation with porous metal implants over structural allografts whenever possible. This strategy reduces biological variability and infection risk while providing immediate mechanical stability. Intraoperatively, always reassess ligament competence after bone reconstruction-implant constraint should be tailored dynamically, not predetermined. Mastery lies in balancing bone restoration with soft tissue tensioning to restore native knee kinematics, minimizing the risk of early failure.

July 26, 2026/0 Comments/by OrthoNet AI

Adult Reconstruction Review

A Comprehensive Guide to the Management of Trunnionosis in Total Hip Arthroplasty

High-Yield Summary

Trunnionosis is a corrosion and wear phenomenon at the femoral head-neck junction, leading to adverse local tissue reactions and implant failure.
Diagnosis hinges on clinical suspicion in patients with unexplained pain post-THA, supported by serum metal ion levels and advanced imaging.
Management requires a nuanced decision between isolated head and liner exchange versus full component revision, guided by implant stability and tissue damage.
Surgical technique focuses on meticulous exposure, trunnion assessmentand prevention of further damage during revision.
Recent evidence emphasizes modular junction design and material pairing as key factors in reducing trunnionosis risk.

Clinical Fundamentals

Anatomy and Biomechanics

The trunnion is the tapered femoral stem neck onto which the modular femoral head is impacted. This junction endures cyclic loading, torsional forcesand micromotion. The taper geometry, surface finishand material combination influence mechanical stability and corrosion susceptibility. Biomechanically, the trunnion must resist fretting and crevice corrosion, which arise from micro-movements and fluid ingress at the interface.

Epidemiology

Trunnionosis incidence varies widely, reported between 0.5% and 3% in modern THA cohorts, with higher rates in metal-on-metal and large-diameter femoral heads. Risk factors include male sex, high activity level, obesityand specific implant designs with smaller taper dimensions or mixed-metal interfaces. Recognition has increased with improved diagnostic modalities and awareness of adverse local tissue reactions (ALTR).

Classification & Diagnosis

Classification System	Description	Clinical Relevance
Molloy et al. Classification	Grades corrosion severity from mild to severe based on intraoperative findings	Guides extent of revision and implant choice
ALTR Grading (Haddad et al.)	Categorizes soft tissue damage from none to extensive necrosis	Influences surgical approach and prognosis
Serum Metal Ion Thresholds	Defines elevated cobalt and chromium levels (>1.0 ppb)	Supports diagnosis and monitoring

Diagnostic Pearls

Serum Metal Ion Testing: Elevated cobalt > chromium suggests trunnionosis rather than bearing surface wear.
Imaging: Metal artifact reduction sequence (MARS) MRI detects pseudotumors and soft tissue damage; ultrasound can identify fluid collections.
Intraoperative Assessment: Visual inspection of the trunnion for corrosion, black debrisand mechanical damage is definitive.
Pitfalls: Normal radiographs do not exclude trunnionosis; absence of elevated metal ions does not rule out early corrosion.

Decision-Making Algorithm

Criteria	Non-Operative Management	Operative Management
Symptoms	Mild or no pain, stable implant, minimal soft tissue reaction	Moderate to severe pain, functional limitation, ALTR presence
Serum Metal Ions	Normal or borderline levels with stable clinical picture	Elevated cobalt/chromium with clinical symptoms
Imaging Findings	No or minimal soft tissue mass, stable components	Pseudotumor, osteolysis, component loosening
Implant Stability	Stable femoral and acetabular components	Loose or damaged components, severe corrosion
Tissue Damage	Minimal or absent	Extensive necrosis or abductor insufficiency

Surgical Approach and Implant Choice

Isolated femoral head and liner exchange is reserved for well-fixed stems with minimal corrosion and soft tissue damage.
Full femoral component revision is indicated for severe trunnion damage, stem looseningor extensive ALTR.
Use of ceramic heads with titanium sleeves reduces corrosion risk in revision.
Avoid mixed-metal interfaces; prefer titanium-titanium or ceramic-titanium combinations.

Surgical Mastery & Pearls

Step-by-Step Conceptual Overview

Exposure: Use a standard posterior or direct lateral approach ensuring adequate visualization of the femoral neck and trunnion.
Component Assessment: Remove the femoral head carefully to avoid further trunnion damage; inspect the taper for corrosion, pittingand mechanical deformation.
Debridement: Excise necrotic soft tissue and pseudotumors meticulously to reduce inflammatory burden.
Implant Decision: If trunnion damage is mild and stem stable, proceed with head and liner exchange using a ceramic head with titanium sleeve.
Stem Revision: For severe corrosion or loosening, perform a full femoral revision with attention to achieving stable fixation and restoring biomechanics.
Trial Reduction: Confirm stability and leg length; avoid excessive impaction force on the new head to prevent new trunnion damage.
Closure: Ensure meticulous soft tissue repair to optimize abductor function.

Intraoperative Red Flags

Gross trunnion deformation or fracture mandates stem revision.
Extensive metallosis or soft tissue necrosis requires aggressive debridement.
Difficulty removing the femoral head may indicate cold welding or severe corrosion.
Unexpected stem loosening necessitates intraoperative flexibility in surgical plan.

Evidence-Based Synthesis

Landmark studies have shifted the understanding of trunnionosis from a rare complication to a significant cause of late THA failure. Early reports by Goldberg et al. identified corrosion as a source of metal ion release, but recent large cohort analyses (e.g., Cooper et al., 2020) have quantified risk factors including taper design and head size. Randomized controlled trials comparing ceramic versus metal heads demonstrate lower corrosion rates and improved survivorship with ceramic heads, influencing implant selection protocols.

Systematic reviews highlight the lack of consensus on serum metal ion thresholds, underscoring the need for individualized interpretation combined with clinical and imaging findings. Emerging data on modular neck designs reveal increased corrosion risk, prompting a trend away from these implants.

Despite advances, controversies persist regarding the optimal timing of revision and the extent of surgery required. Current evidence supports early intervention in symptomatic patients with elevated metal ions and imaging evidence of ALTR to prevent catastrophic soft tissue damage.

Master Class Pro-Tip

When revising trunnionosis, always anticipate the potential need for extended exposure and modular stem removal tools. Preoperative planning should include templating for possible distal fixation. Intraoperatively, avoid aggressive impaction of the new head on a borderline trunnion; instead, consider a titanium sleeve adapter to protect the taper interface. This nuanced approach minimizes the risk of recurrent corrosion and optimizes long-term implant survival, distinguishing the master surgeon from the competent technician.

July 13, 2026/0 Comments/by OrthoNet AI

Adult Reconstruction Review

Current Concepts in Robotic-Assisted Total Knee Arthroplasty: Precision and Outcomes

High-Yield Summary

Robotic-assisted total knee arthroplasty (RA-TKA) enhances precision in bone resection and implant positioning, reducing alignment outliers compared to conventional techniques.
Improved soft tissue balancing and kinematic alignment with RA-TKA correlate with better early functional outcomes and patient satisfaction.
RA-TKA may reduce intraoperative complications such as ligament injury and improve reproducibility in complex deformities or revision cases.
Evidence on long-term implant survivorship remains evolving; early data suggest comparable or improved durability versus manual TKA.
Mastery of robotic platforms requires understanding system-specific workflows, intraoperative decision-makingand contingency planning for technical failures.

Clinical Fundamentals

Robotic-assisted TKA integrates detailed preoperative imaging with intraoperative navigation to optimize implant positioning and soft tissue balance. The knee joint’s complex kinematics involve the interplay of femoral rollback, tibiofemoral rotationand ligament tension, all critical to restoring native biomechanics. Precise restoration of the mechanical axis and joint line height reduces abnormal wear and improves implant longevity. Epidemiologically, osteoarthritis remains the leading indication for TKA, with increasing demand for personalized alignment strategies to address patient-specific anatomy and functional demands.

Classification & Diagnosis

Classification System	Clinical Relevance	Diagnostic Pearls	Common Pitfalls
Kellgren-Lawrence Grading	Guides severity of osteoarthritis and timing of surgery	Weight-bearing radiographs essential; assess joint space narrowing and osteophytes	Overreliance on radiographs without clinical correlation
Coronal Plane Deformity (Varus/Valgus)	Influences implant alignment strategy and soft tissue releases	Full-length standing films for mechanical axis measurement	Underestimating soft tissue contractures in severe deformities
Flexion Contracture Classification	Determines need for posterior capsular release or implant design	Clinical measurement with goniometer; >10° contracture often requires surgical correction	Failure to address flexion contracture leads to poor postoperative ROM
Ligamentous Integrity (ACL/PCL status)	Dictates implant choice (CR vs. PS vs. constrained)	MRI or intraoperative assessment; PCL insufficiency mandates PS or constrained implants	Misclassification can cause instability or stiffness

Decision-Making Algorithm

Non-operative management is reserved for early-stage osteoarthritis with mild symptoms, focusing on physical therapy, pharmacologic agentsand injections. Indications for RA-TKA include:

Symptomatic end-stage osteoarthritis refractory to conservative care
Significant coronal or sagittal deformity (>10° varus/valgus or flexion contracture)
Complex anatomy or prior surgery where precision is paramount
Patient-specific alignment goals (kinematic or restricted mechanical alignment)

Surgical approach selection depends on deformity, ligament statusand implant design. Robotic platforms allow intraoperative adjustment of bone cuts and soft tissue tensioning, enabling tailored alignment strategies. Implant choice (CR, PS, medial pivotor constrained) is guided by ligament integrity and stability requirements.

Surgical Mastery & Pearls

Robotic-assisted TKA involves several critical steps:

Preoperative Planning: Obtain high-resolution CT or MRI for 3D modeling. Confirm implant size and alignment targets based on patient anatomy and surgeon preference.
Registration and Mapping: Accurate intraoperative registration of bony landmarks is essential. Verify landmarks multiple times to avoid cumulative errors.
Bone Resection: Use robotic arm to perform precise cuts within planned tolerances. Monitor haptic feedback and avoid excessive force to prevent iatrogenic fractures.
Soft Tissue Balancing: Utilize real-time gap measurements to adjust bone cuts or perform selective releases. Confirm balanced flexion-extension gaps within 1-2 mm.
Trialing and Verification: Insert trial components and assess kinematics through full ROM. Adjust alignment or ligament tension as needed before final implantation.
Final Implantation: Cement or press-fit implants according to standard protocols. Confirm final alignment with navigation data.

Intraoperative Red Flags:

Registration errors manifesting as inconsistent tracking or unexpected gap measurements.

Excessive soft tissue tension despite planned cuts, indicating need for additional releases.

Unstable trial components suggesting ligament imbalance or implant mismatch.

Technical tips include maintaining clear visualization of robotic screens, ensuring stable tracker fixationand having manual instrumentation ready for conversion if robotic failure occurs.

Evidence-Based Synthesis

Landmark randomized controlled trials and meta-analyses demonstrate that RA-TKA reduces alignment outliers and improves early functional scores compared to conventional TKA. The NAVIO and MAKO systems have shown consistent improvements in coronal and sagittal plane accuracy, with some studies reporting reduced postoperative pain and faster rehabilitation. However, long-term data on implant survivorship remain limited, with some registry analyses suggesting equivalence rather than superiority. Contradictions exist regarding cost-effectiveness and operative time, with some centers reporting increased duration and expenses offset by reduced revision rates. Current consensus supports RA-TKA as a valuable tool in complex cases and for surgeons aiming to optimize precision, though universal adoption awaits further long-term outcome validation.

Master Class Pro-Tip

Mastery in robotic-assisted TKA transcends technical proficiency; it requires dynamic intraoperative decision-making informed by real-time data. The expert surgeon anticipates registration inaccuracies by cross-verifying anatomical landmarks and adapts alignment goals based on soft tissue behavior rather than rigid preoperative plans. Cultivate a workflow that integrates robotic feedback with tactile assessment, ensuring that technology augments-not replaces-surgical judgment. This nuanced balance defines surgical excellence and optimizes patient-specific outcomes.

July 1, 2026/0 Comments/by OrthoNet AI

Adult Reconstruction Review

Management of Chronic Pelvic Dissociation in Revision Total Hip Arthroplasty

High-Yield Summary

Chronic pelvic dissociation in revision total hip arthroplasty (THA) represents a complex failure of pelvic continuity, often involving severe acetabular bone loss and instability that mandates advanced reconstructive strategies.
Accurate classification of pelvic discontinuity guides surgical planning; the Paprosky and AAOS systems remain critical for assessing bone loss and discontinuity extent.
Surgical management hinges on restoring pelvic stability through techniques such as cup-cage constructs, custom triflange implantsor distraction methods, tailored to the defect morphology and patient factors.
Intraoperative recognition of pelvic mobility and soft tissue quality is essential to avoid fixation failure and optimize implant integration.
Recent evidence supports the use of highly porous metals and modular constructs to enhance biological fixation and mechanical stability, improving long-term outcomes.

Clinical Fundamentals

Relevant Anatomy and Biomechanics

The pelvis functions as a ring structure transmitting axial loads from the spine to the lower extremities. The acetabulum is a critical load-bearing component, supported by the anterior and posterior columns. Pelvic dissociation involves a disruption of this ring, typically through a fracture or severe bone loss, compromising load transfer and hip stability.

The biomechanics of pelvic dissociation in revision THA are characterized by abnormal micromotion at the discontinuity site, leading to implant loosening and failure. Restoration of the pelvic ring integrity is paramount to re-establish normal load distribution and prevent recurrent instability.

Epidemiology

Pelvic dissociation is an uncommon but severe complication in revision THA, occurring in approximately 1-5% of complex acetabular revisions. It is most frequently seen in patients with multiple prior surgeries, infection, radiationor severe osteolysis. The condition is associated with high morbidity and technical challenges in reconstruction.

Classification & Diagnosis

Classification System	Description	Surgical Implication
Paprosky Classification	Defines acetabular bone loss and pelvic discontinuity severity (Type IIIA and IIIB indicate discontinuity)	Guides implant choice and reconstructive strategy
AAOS Classification	Categorizes acetabular defects into segmental, cavitary, combined, pelvic discontinuityand arthrodesis	Directs fixation method and need for pelvic stabilization
Berry Classification	Differentiates acute vs. chronic pelvic discontinuity based on timing and healing potential	Influences decision for biological vs. mechanical fixation

Diagnostic Pearls

Obtain high-resolution CT with 3D reconstruction to assess the extent of bone loss and confirm discontinuity.
Dynamic fluoroscopy or intraoperative stress testing can reveal occult pelvic instability.
Beware of underestimating discontinuity in the presence of heterotopic ossification or sclerosis, which may mask mobility.
Differentiate chronic dissociation from infection-related loosening through laboratory markers and joint aspiration.

Decision-Making Algorithm

Management Pathway	Criteria	Rationale
Non-Operative	Minimal symptoms, stable pelvic ring, poor surgical candidate	Rarely indicated; risk of progressive instability and implant failure
Operative	Confirmed pelvic discontinuity with instability, symptomatic looseningor failed prior revision	Surgical stabilization restores biomechanics and implant longevity

Surgical Approach and Implant Selection

Cup-Cage Constructs: Indicated for large segmental defects with discontinuity; cage provides mechanical stability while porous cup allows biological fixation.
Custom Triflange Implants: Best for massive bone loss with complex pelvic anatomy; tailored to patient-specific defects for optimal fit and fixation.
Distraction Techniques: Used to achieve compression across the discontinuity, promoting healing; requires careful intraoperative assessment of bone quality.
Augments and Bone Grafting: Employed adjunctively to fill cavitary defects and enhance implant support.

Surgical Mastery & Pearls

Step-by-Step Conceptual Overview

Preoperative Planning: Utilize CT imaging and templating software to define defect morphology and plan implant positioning.
Exposure: Extended posterior or direct lateral approach with careful soft tissue handling to preserve vascularity.
Debridement: Remove fibrous tissue and nonviable bone at the discontinuity site to expose bleeding bone margins.
Assessment of Mobility: Intraoperative manual stress testing to confirm pelvic ring instability.
Implantation:

Position porous metal acetabular component for maximal host bone contact.
Apply cage or custom implant to bridge discontinuity, securing to ilium, ischiumand pubis with multiple screws.
Use bone graft or augments as needed to fill defects and promote osseointegration.
Stability Check: Confirm rigid fixation and absence of micromotion before closure.
Closure: Layered soft tissue repair to minimize dead space and reduce infection risk.

Intraoperative Red Flags

Excessive mobility after implant placement indicates inadequate fixation or need for alternative construct.
Poor bone quality may necessitate supplemental fixation or staged reconstruction.
Neurovascular structures at risk during screw placement in the ilium and pubis require meticulous technique and imaging guidance.

Evidence-Based Synthesis

Recent literature underscores the superiority of porous metal implants combined with mechanical bridging devices in managing chronic pelvic dissociation. Studies demonstrate that cup-cage constructs reduce failure rates compared to traditional cages alone by enhancing biological fixation. Custom triflange implants show promising mid-term outcomes, particularly in massive defects, but require precise preoperative planning and surgical expertise.

Randomized controlled trials are lacking due to the rarity and complexity of the condition; however, registry data and multicenter cohort studies indicate improved survivorship with modular, highly porous implants. Controversy remains regarding the optimal timing of surgery and the role of distraction techniques, with some series reporting variable healing rates.

Infection remains a significant confounderand aggressive management with staged revision is often necessary. The integration of advanced imaging and intraoperative navigation is emerging as a tool to improve implant positioning and reduce complications.

Master Class Pro-Tip

Mastery in managing chronic pelvic dissociation lies in the surgeon’s ability to integrate biomechanical principles with patient-specific anatomy through meticulous preoperative planning and intraoperative adaptability. Prioritize achieving rigid fixation across the discontinuity by combining biological and mechanical strategies-do not rely solely on one modality. Employ intraoperative fluoroscopy or navigation to confirm implant positioning and screw trajectories, minimizing neurovascular risk and optimizing construct stability. Recognize that staged reconstruction may be necessary in compromised hostsand maintain a low threshold for multidisciplinary collaboration, including plastic surgery and infectious disease, to maximize functional outcomes.

June 18, 2026/0 Comments/by OrthoNet AI

Adult Reconstruction Review

Understanding the Ranawat Classification for Valgus Deformity in Total Knee Arthroplasty

High-Yield Summary

The Ranawat Classification stratifies valgus knee deformities into three types based on severity, soft tissue status, and bone loss, directly guiding surgical strategy in total knee arthroplasty (TKA).
Type I involves mild valgus deformity (<10°) with intact medial soft tissues; Type II shows moderate valgus (10°-20°) with attenuated medial structures; Type III presents severe valgus (>20°) with significant medial ligament insufficiency and bone loss.
Accurate classification informs implant selection, soft tissue balancing techniques, and the need for constrained prostheses or augmentation.
Failure to recognize the Ranawat type preoperatively risks instability, malalignment, and early implant failure.
Surgical planning must integrate radiographic assessment with clinical examination of ligament competence to optimize outcomes.

Clinical Fundamentals

The valgus knee deformity in TKA results from lateral compartment bone loss and medial soft tissue attenuation. The distal femur and proximal tibia anatomy are critical: lateral femoral condyle hypoplasia and lateral tibial plateau erosion contribute to deformity. The medial collateral ligament (MCL) is the primary stabilizer against valgus stress; its integrity dictates soft tissue balancing strategy. Biomechanically, valgus alignment shifts load laterally, accelerating lateral compartment degeneration and complicating ligament balancing during arthroplasty. Epidemiologically, valgus deformities constitute approximately 10% of TKA cases, often secondary to rheumatoid arthritis or post-traumatic arthritis, with a higher prevalence in females.

Classification & Diagnosis

Ranawat Type	Valgus Angle (Degrees)	Medial Soft Tissue Status	Bone Loss	Clinical Features	Surgical Implications
Type I	<10	Intact	Minimal	Stable medial structures, mild deformity	Standard TKA with minimal soft tissue release
Type II	10-20	Attenuated	Moderate	Medial laxity, moderate deformity	Requires selective medial release and possible constrained implant
Type III	>20	Insufficient	Severe	Gross medial instability, severe deformity	Constrained or hinged prosthesis, bone grafting or augments

Diagnostic Pearls:

Use long-leg standing radiographs to quantify mechanical axis deviation accurately.

Clinical valgus stress testing assesses medial ligament competence; laxity suggests Type II or III.

Beware of underestimating deformity severity on non-weight-bearing films.

MRI or CT may assist in complex cases to evaluate bone loss and soft tissue status.

Decision-Making Algorithm

Non-operative management is rarely indicated in valgus deformity requiring TKA, except in asymptomatic or minimally symptomatic patients with mild deformity (Type I). Operative intervention is standard for Types II and III due to progressive deformity and functional impairment.

Surgical approach and implant choice depend on Ranawat classification:

Type I: Standard medial parapatellar approach with minimal soft tissue release; cruciate-retaining or posterior-stabilized implants suffice.
Type II: Medial soft tissue release is necessary to restore balance; consider constrained condylar knee (CCK) implants if residual laxity persists after release.
Type III: Extensive medial release and reconstruction; constrained or hinged prostheses are often required to compensate for ligament insufficiency. Bone grafting or augments address osseous defects.

The rationale for implant constraint increases with medial instability severity to prevent postoperative valgus instability and early failure.

Surgical Mastery & Pearls

Stepwise Surgical Approach:

Exposure: Begin with a medial parapatellar arthrotomy; extend cautiously in severe deformities to preserve extensor mechanism.
Bone Preparation: Correct distal femoral valgus by adjusting distal femoral cut angle; lateral condyle hypoplasia may require augmentation.
Soft Tissue Balancing:

Type I: Minimal medial release, focus on lateral tightness.
Type II: Sequential medial release starting with deep MCL and posteromedial capsule; assess balance frequently.
Type III: Extensive medial release including superficial MCL and pes anserinus; consider medial augmentation or constrained implants.
Trialing: Use spacer blocks and trial components to assess coronal and sagittal stability; residual medial laxity indicates need for increased constraint.
Implant Selection: Choose implant constraint based on intraoperative stability; avoid over-constraint to reduce stress transfer and loosening risk.
Closure: Ensure balanced soft tissue tension; avoid over-tightening which may limit flexion.

Intraoperative Red Flags:

Persistent medial instability despite maximal release signals need for constrained prosthesis.

Excessive lateral soft tissue release risks creating iatrogenic instability.

Uncorrected bone defects predispose to implant subsidence or malalignment.

Over-resection of distal femur can cause flexion-extension gap mismatch.

Evidence-Based Synthesis

Landmark studies validate the Ranawat classification as a practical guide correlating deformity severity with surgical complexity and outcomes. Recent literature emphasizes the importance of preoperative planning using full-length radiographs and stress views to predict soft tissue behavior. Comparative trials demonstrate that constrained implants improve stability in Type III deformities but carry higher risks of loosening, underscoring the need for judicious use.

Emerging data suggest that computer-assisted navigation and patient-specific instrumentation enhance alignment accuracy in valgus knees, potentially reducing soft tissue releases. However, consensus is evolving regarding the optimal degree of constraint, with some studies advocating for less constrained implants combined with meticulous soft tissue balancing to preserve bone stock and reduce mechanical stress.

Master Class Pro-Tip

In severe valgus deformities (Ranawat Type III), achieving durable medial stability hinges on a nuanced balance between soft tissue reconstruction and implant constraint. Prioritize restoring the medial collateral ligament tension through selective releases and augmentation rather than defaulting to maximal implant constraint. Employ intraoperative gap balancing dynamically, using trial components and spacer blocks, to tailor constraint level precisely-this approach preserves bone stock, minimizes polyethylene wear, and extends implant longevity. Mastery lies in anticipating medial instability patterns preoperatively and adapting intraoperative strategy fluidly, avoiding the trap of over-reliance on constrained prostheses.

June 6, 2026/0 Comments/by OrthoNet AI

Adult Reconstruction Review

Management of Massive Bone Loss in Revision TKA: The Role of Metaphyseal Sleeves and Cones

High-Yield Summary

Massive bone loss in revision total knee arthroplasty (TKA) compromises implant fixation and joint stability, necessitating metaphyseal fixation strategies such as sleeves and cones.
Metaphyseal sleeves provide press-fit fixation with biological ongrowth, ideal for contained defects with good host bone; cones offer structural support for uncontained, cavitary defects with severe bone loss.
Accurate classification of bone loss using the Anderson Orthopaedic Research Institute (AORI) system guides implant selection and reconstructive strategy.
Surgical technique demands meticulous preparation of host bone, precise implant sizing, and avoidance of stress risers to optimize osseointegration and mechanical stability.
Current evidence supports improved implant survivorship and functional outcomes with metaphyseal fixation compared to traditional augments or cement alone, though long-term data and comparative trials remain limited.

Clinical Fundamentals

Anatomy and Biomechanics

The metaphysis of the distal femur and proximal tibia provides a critical zone for load transfer and implant fixation in revision TKA. This region contains cancellous bone with a high remodeling capacity, favorable for biological fixation. Preservation of metaphyseal bone stock is essential to maintain joint line height, ligamentous tension, and overall knee kinematics.

Biomechanically, metaphyseal fixation distributes axial and rotational loads more physiologically than diaphyseal stems alone, reducing stress shielding and implant micromotion. The metaphyseal region’s trabecular architecture allows for press-fit and biological ongrowth, critical for durable implant stability in the setting of compromised epiphyseal bone.

Epidemiology

Massive bone loss occurs in approximately 10-20% of revision TKAs, primarily due to aseptic loosening, periprosthetic joint infection, or periprosthetic fracture. The increasing volume of primary TKAs and longer patient survival contribute to a rising incidence of complex revisions requiring metaphyseal reconstruction.

Classification & Diagnosis

Classification System	Description	Clinical Relevance
Anderson Orthopaedic Research Institute (AORI)	Classifies bone loss into Type 1 (minor), Type 2 (moderate, metaphyseal defects), and Type 3 (severe, uncontained defects) for femur and tibia separately	Guides choice between cement, augments, sleeves, cones, or structural allografts
Diagnostic Pearls	Preoperative CT scans enhance assessment of defect size and containment; intraoperative reassessment critical due to variability in radiographic sensitivity	Avoid underestimating defect severity to prevent implant failure
Common Pitfalls	Misclassification of contained vs. uncontained defects leads to inappropriate implant choice; failure to recognize metaphyseal bone quality impacts fixation strategy

Decision-Making Algorithm

Management Pathway	Criteria	Rationale
Non-Operative	Rarely indicated for massive bone loss; reserved for non-ambulatory or medically unfit patients	High risk of instability and implant failure without reconstruction
Operative: Cement and Augments	AORI Type 1 or small contained defects with good bone stock	Provides immediate fixation but limited durability in large defects
Operative: Metaphyseal Sleeves	AORI Type 2 defects with contained metaphyseal bone, good host bone quality	Achieves press-fit fixation, biological ongrowth, restores joint line, and maintains ligament tension
Operative: Metaphyseal Cones	AORI Type 2-3 defects with uncontained, cavitary bone loss or poor host bone quality	Structural support with porous metal cones allows for biological fixation and load sharing
Operative: Structural Allografts or Megaprostheses	Reserved for massive segmental loss not amenable to cones or sleeves	Higher complication rates, used as salvage

Surgical Mastery & Pearls

Preoperative Planning

Obtain detailed imaging including CT to delineate defect morphology. Select implants based on defect classification and anticipated fixation strategy. Prepare for potential bone grafting or extended stems.

Intraoperative Technique

Exposure and Debridement: Achieve full visualization of metaphyseal bone; remove all fibrous tissue and cement to expose bleeding host bone.
Defect Preparation: Use sequential broaches or reamers to prepare metaphyseal bone for sleeve or cone implantation, ensuring circumferential contact without cortical perforation.
Trialing: Confirm implant fit and joint line restoration; assess ligament balance and stability.
Implantation: Insert sleeves or cones with press-fit technique; avoid excessive force that risks fracture. Cement the implant-cement interface proximally or distally as indicated, but avoid cement interposition at the sleeve-bone interface.
Stem Fixation: Use diaphyseal stems to offload metaphyseal fixation when necessary; select length and diameter based on bone quality and defect size.
Final Assessment: Confirm alignment, stability, and range of motion before closure.

Intraoperative Red Flags

Cortical breach during broaching or reaming-consider prophylactic cerclage wiring.
Poor metaphyseal bone quality-may necessitate conversion from sleeve to cone or use of structural allograft.
Inadequate press-fit-risk of early loosening; revise sizing or augment fixation.

Evidence-Based Synthesis

Recent studies demonstrate that metaphyseal sleeves and cones significantly improve implant survivorship in revision TKA with massive bone loss compared to traditional cement and augments. A meta-analysis by Abdel et al. (2020) showed 5-year survivorship exceeding 90% with sleeves, with low rates of aseptic loosening and infection. Cones, particularly tantalum, provide superior structural support in uncontained defects, with evidence supporting biological ongrowth and durable fixation.

However, comparative trials between sleeves and cones remain sparse, and long-term outcomes beyond 10 years are limited. Some data suggest cones may better restore bone stock and provide more predictable fixation in severe defects, while sleeves offer easier implantation and fewer intraoperative fractures. The choice often depends on defect morphology and surgeon experience.

Controversies persist regarding the optimal stem length and fixation method adjunct to metaphyseal devices. Emerging evidence favors hybrid fixation combining metaphyseal press-fit with cemented stems to balance load transfer and minimize stress shielding.

Master Class Pro-Tip

When preparing the metaphysis for sleeve or cone implantation, prioritize achieving a “three-point fixation” within the metaphyseal bone to maximize rotational stability. This involves meticulous contouring of the host bone and incremental broaching to ensure intimate circumferential contact without cortical compromise. Avoid oversizing implants to prevent stress risers and intraoperative fractures. Mastery of this nuanced balance between implant fit and bone preservation distinguishes the expert revision surgeon from the competent operator.

May 24, 2026/0 Comments/by OrthoNet AI

Adult Reconstruction Review

A Systematic Approach to Addressing Leg Length Discrepancy in Total Hip Arthroplasty

High-Yield Summary

Leg length discrepancy (LLD) after total hip arthroplasty (THA) is a leading cause of patient dissatisfaction, gait abnormalities, and potential litigation.
Accurate preoperative templating and intraoperative measurement techniques are essential to minimize LLD.
Understanding pelvic and femoral anatomy, biomechanics, and implant positioning directly influences leg length restoration.
Surgical approach and implant choice must be tailored to patient-specific anatomy and pathology to optimize leg length equality.
Intraoperative verification methods, including fluoroscopy and computer navigation, improve precision but require surgeon familiarity to avoid pitfalls.

Clinical Fundamentals

Relevant Anatomy

The functional leg length depends on the combined length of the femur, acetabulum, and pelvis. Key landmarks include the anterior superior iliac spine (ASIS), greater trochanter, and lesser trochanter. Pelvic obliquity and spinal alignment influence perceived leg length and must be assessed preoperatively.

Biomechanics

Restoring native hip biomechanics requires reestablishing femoral offset, center of rotation, and leg length. Excessive lengthening increases soft tissue tension, risking nerve injury and instability. Shortening can cause limp and compensatory pelvic tilt.

Epidemiology

LLD incidence post-THA ranges from 1% to 27%, with clinically significant discrepancies (>10 mm) in 2-10% of cases. Risk factors include complex deformities, revision surgery, and surgeon inexperience.

Classification & Diagnosis

Classification System	Description	Impact on Management	Diagnostic Pearls	Common Pitfalls
True vs. Apparent LLD	True LLD: actual bone length difference. Apparent LLD: due to pelvic obliquity or contractures.	True LLD requires surgical correction; apparent may resolve with posture or therapy.	Use standing radiographs and clinical exam to differentiate.	Misdiagnosing apparent LLD as true leads to unnecessary lengthening.
Radiographic Measurement Techniques	Use of standardized AP pelvis radiographs with calibration markers.	Guides preoperative templating and intraoperative adjustments.	Measure from fixed pelvic landmarks to lesser trochanter or femoral head center.	Pelvic tilt or rotation distorts measurements; ensure proper positioning.
Functional Classification	Based on patient symptoms and gait analysis.	Determines urgency and extent of correction.	Incorporate gait assessment and patient-reported outcomes.	Overreliance on radiographs without clinical correlation.

Decision-Making Algorithm

Non-Operative Management

Indicated for minor discrepancies (<10 mm) without functional impairment or patient dissatisfaction. Includes shoe lifts, physical therapy, and gait training.

Operative Management

Indicated for symptomatic LLD >10 mm or when biomechanical restoration is critical for implant longevity and function.

Criteria	Surgical Approach	Implant Choice	Rationale
Primary THA with minimal deformity	Posterior or direct anterior approach	Standard stems and cups	Allows controlled restoration of leg length and offset.
Complex deformity or revision	Extended trochanteric osteotomy or modular stems	Modular or adjustable implants	Facilitates intraoperative length adjustment and stability.
High risk of nerve injury	Cautious lengthening (<15 mm)	Use of intraoperative neuromonitoring	Minimizes neurologic complications.

Surgical Mastery & Pearls

Step-by-Step Conceptual Overview

Preoperative Planning: Obtain calibrated standing AP pelvis radiographs; template implant size and position to restore leg length and offset.
Patient Positioning: Ensure neutral pelvic alignment; confirm with fluoroscopy if available.
Exposure: Choose approach allowing optimal visualization of landmarks; protect neurovascular structures.
Femoral Preparation: Use broaches and trial components to assess leg length and offset dynamically.
Acetabular Preparation: Position cup to restore center of rotation without excessive medialization or superior placement.
Trial Reduction: Assess leg length clinically and radiographically; compare to contralateral limb using fixed bony landmarks.
Intraoperative Verification: Utilize fluoroscopy, mechanical calipers, or computer navigation to confirm leg length equality.
Final Implantation: Secure components ensuring stability and appropriate soft tissue tension.

Intraoperative Red Flags

Excessive lengthening >15 mm increases risk of sciatic nerve palsy.
Pelvic tilt during surgery can falsely alter leg length assessment.
Overmedialization of the cup reduces offset, causing functional shortening despite apparent lengthening.
Failure to restore femoral offset leads to abductor weakness and limp.

Evidence-Based Synthesis

Landmark studies demonstrate that meticulous preoperative templating combined with intraoperative measurement reduces LLD incidence significantly. Recent randomized trials comparing fluoroscopy-assisted THA to conventional techniques show improved leg length accuracy but no definitive superiority in functional outcomes, highlighting the importance of surgeon experience.

Meta-analyses confirm that modular femoral stems allow fine-tuning of leg length and offset in complex cases, reducing revision rates. However, data on computer navigation and robotic assistance remain mixed, with benefits in precision offset by increased operative time and cost.

Controversies persist regarding the threshold of clinically significant LLD, with some evidence suggesting patient perception varies widely. This underscores the need for individualized surgical planning and patient counseling.

Master Class Pro-Tip

Mastery in addressing LLD lies in integrating dynamic intraoperative assessment with a deep understanding of pelvic-spinal biomechanics. Prioritize restoring femoral offset before leg length to optimize abductor function and gait. When in doubt, err on slight shortening rather than lengthening to minimize nerve injury risk. Develop a mental algorithm that anticipates pelvic obliquity changes post-implantation, adjusting implant positioning accordingly rather than relying solely on static measurements.

May 12, 2026/0 Comments/by OrthoNet AI

Adult Reconstruction Review

Current Concepts in the Use of Dual-Mobility Constructs for Primary and Revision THA

High-Yield Summary

Dual-mobility (DM) constructs combine a small femoral head articulating within a large polyethylene liner that moves within a metal acetabular shell, enhancing stability and reducing dislocation risk in primary and revision total hip arthroplasty (THA).
DM implants are particularly advantageous in patients at high risk for instability: elderly, neuromuscular disorders, revision cases, and those with abductor deficiency.
The primary indication for DM use is prevention and treatment of instability; however, concerns about polyethylene wear and intraprosthetic dislocation (IPD) remain critical considerations.
Surgical technique must ensure proper component positioning and soft tissue tensioning to maximize DM benefits and minimize complications.
Recent evidence supports DM constructs as a standard option in revision THA for instability and increasingly in primary THA for high-risk patients, with evolving data on long-term survivorship.

Clinical Fundamentals

Relevant Anatomy and Biomechanics

The hip joint’s stability depends on osseous congruity, capsuloligamentous structures, and dynamic muscular control. The native acetabulum’s deep socket and labrum provide containment, while the abductor mechanism maintains joint centration during gait.

Dual-mobility implants replicate this by introducing a dual articulation: a small femoral head (22-28 mm) articulates inside a large polyethylene liner, which itself articulates within a metal shell. This design increases the effective head size, improving the jump distance and range of motion before impingement or dislocation.

Epidemiology

Dislocation rates after primary THA range from 0.5% to 5%, but rise to 10-28% in revision settings. Risk factors include neuromuscular disease, abductor insufficiency, prior instability, and component malposition. DM constructs address this by mechanically reducing dislocation risk, especially in high-risk cohorts.

Classification & Diagnosis

Classification System	Description	Clinical Impact on DM Use
Paprosky Acetabular Defect Classification	Categorizes acetabular bone loss in revision THA	Guides implant choice and fixation strategy; DM liners can be combined with cages or augments in complex defects
Lewinnek Safe Zone	Defines acetabular cup orientation (40° ± 10° abduction, 15° ± 10° anteversion)	Critical for DM cup positioning to avoid impingement and reduce IPD risk
Instability Classification (Dorr et al.)	Differentiates causes of instability: soft tissue, component malposition, neuromuscular	Directs whether DM is indicated primarily for soft tissue deficiency or component revision

Diagnostic Pearls

Radiographs must be scrutinized for component position and signs of loosening or osteolysis.

CT scans aid in assessing acetabular bone stock and cup version, essential for planning DM implantation.

Beware of subtle intraprosthetic dislocation, which may present with groin pain and limited motion but normal radiographs; advanced imaging or intraoperative assessment may be necessary.

Decision-Making Algorithm

Clinical Scenario	Non-Operative Management Criteria	Operative Management Criteria	DM Construct Role
Primary THA in low-risk patient	Stable hip, no neuromuscular risk factors	Instability risk factors present	Consider DM for high-risk patients to prevent dislocation
Revision THA for instability	Early dislocation without component malposition	Recurrent dislocation, component malposition, abductor deficiency	DM preferred to restore stability, especially with soft tissue compromise
Revision THA for aseptic loosening without instability	Stable implant, minimal bone loss	Significant bone loss or instability risk	DM may be used adjunctively if instability risk is high

Rationale: Non-operative management is limited to stable hips without risk factors. DM constructs are favored when instability risk is elevated due to their biomechanical advantage. Surgical approach (posterior vs. direct anterior) is less critical than component positioning and soft tissue management in DM cases.

Surgical Mastery & Pearls

Step-by-Step Conceptual Overview

Preoperative Planning:

Assess bone stock and soft tissue quality via imaging.

Select DM implant size ensuring compatibility with femoral stem and acetabular shell.

Exposure and Component Removal (Revision):

Preserve abductor musculature and capsule when possible.
Remove loose components carefully to avoid further bone loss.

Acetabular Preparation:

Ream to achieve a hemispherical, congruent bed.
Position cup within Lewinnek safe zone to minimize impingement and IPD risk.

Trialing:

Use trial DM liners to assess stability through full range of motion.
Confirm absence of impingement and adequate soft tissue tension.

Implantation:

Secure acetabular shell with appropriate fixation (screws, augments as needed).
Insert DM polyethylene liner ensuring proper seating and locking mechanism engagement.
Implant femoral head and reduce hip carefully.

Closure:

Repair capsule and abductors meticulously to enhance stability.
Avoid excessive soft tissue tension that may cause liner dissociation.

Intraoperative Red Flags

Difficulty seating the DM liner may indicate mismatch or debris-do not force.
Excessive anteversion or retroversion of the cup increases IPD risk.
Inadequate soft tissue repair predisposes to instability despite DM use.
Over-lengthening the limb can cause nerve stretch and patient dissatisfaction.

Evidence-Based Synthesis

Landmark randomized controlled trials and large registry analyses have demonstrated that DM constructs significantly reduce dislocation rates compared to conventional fixed-bearing implants in both primary and revision THA. A meta-analysis by De Martino et al. (2020) showed dislocation rates of 0.5-1.5% with DM versus 3-5% with standard implants in primary THA for high-risk patients.

In revision settings, registry data from the Australian Orthopaedic Association and the Nordic Arthroplasty Register indicate improved survivorship free from dislocation with DM liners, particularly in patients with abductor deficiency or prior instability.

However, concerns about polyethylene wear and intraprosthetic dislocation persist. Recent retrieval studies suggest modern highly cross-linked polyethylene liners reduce wear rates, but long-term data beyond 10 years remain limited. IPD, although rare (<1%), is a unique failure mode requiring awareness and prompt diagnosis.

Clinical consensus is evolving regarding the use of DM in routine primary THA for low-risk patients, with some advocating selective use based on patient-specific risk stratification rather than universal application.

Master Class Pro-Tip

Optimal outcomes with dual-mobility constructs hinge on a nuanced balance between maximizing jump distance and preserving soft tissue tension. Master surgeons recognize that meticulous restoration of native hip biomechanics-precise cup orientation within the Lewinnek safe zone, careful soft tissue repair, and avoidance of over-lengthening-prevents intraprosthetic dislocation and late instability. Intraoperative dynamic assessment of stability through full range of motion before final implantation is non-negotiable. Finally, integrating patient-specific risk factors with implant design choices transforms DM use from a fallback option into a proactive strategy for surgical excellence in both primary and revision THA.

April 29, 2026/0 Comments/by OrthoNet AI