MCQs – Knee Recon 1

Modern Study Review (AI-Generated)

High-Yield Summary

High Tibial Osteotomy (HTO), unicompartmental knee arthroplasty, and total knee arthroplasty (TKA) are core topics in orthopaedic board exams, emphasizing patient selection, implant positioning, and biomechanical principles. The single most critical clinical decision often hinges on alignment thresholds (e.g., <15° varus for HTO) and implant constraint levels, which directly influence longevity and complication rates. While classic teachings emphasize strict contraindications (e.g., ACL deficiency for HTO), modern practice recognizes broader indications and nuanced biomechanical factors such as adductor moment and femoral rollback. Advances in implant technology and surgical technique have improved survivorship, but challenges remain in infection diagnosis and revision surgery.

High-Yield Decision Matrix

Active Recall Q&A

High Tibial Osteotomy (HTO)

Q: What are the indications for High Tibial Osteotomy (HTO) in knee reconstruction?
A: Young active patients with less than 15° varus, less than 10° flexion contracture, and primarily unicompartmental changes.
Related Pearl: ACL deficiency is not a contraindication for HTO, expanding its applicability in ligament-deficient knees.

Q: Is ACL deficiency a contraindication for HTO?
A: No, the lack of an ACL is NOT a contraindication to HTO.
Related Pearl: HTO can provide stability and offload compartments even in ACL-deficient knees.

Posterior Cruciate Ligament (PCL) Retention

Q: What should be monitored in patients with PCL-retaining knees postoperatively?
A: Watch for posterior sag, as their PCL may be insufficient, leading to significant anteroposterior instability.
Related Pearl: PCL insufficiency can compromise knee stability despite retention, requiring close follow-up.

Porous Bone Ingrowth

Q: What factors influence porous bone ingrowth in implants?
A: Avoidance of micromotion, approximation of surfaces, and pore size between 150-400 microns.
Related Pearl: Optimal pore volume fraction porosity is 30-40%, critical for osteointegration.

Q: Does titanium promote better bone ingrowth than cobalt chrome?
A: No, titanium has not been shown to be more conducive to bone ingrowth than cobalt chrome.
Related Pearl: Material choice should consider mechanical properties and biocompatibility, not just ingrowth potential.

Cement and Implant Fixation

Q: What causes cement failure in femoral components?
A: Microfracture and fragmentation of cement lead to failure.
Related Pearl: Cement integrity is crucial for implant longevity; microfractures can propagate under cyclic loading.

Q: How does cement porosity affect its mechanical properties?
A: Reducing cement porosity improves compressive modulus and increases strength.
Related Pearl: Cement handling techniques can optimize implant fixation strength.

Postoperative Knee Range of Motion (ROM)

Q: What predicts the ultimate postoperative knee range of motion (ROM)?
A: The preoperative knee ROM is the best predictor of postoperative ROM.
Related Pearl: Pre-op physiotherapy to maximize ROM can improve surgical outcomes.

Medial Unicompartmental Knee Arthroplasty

Q: What alignment is recommended for medial unicompartmental knee replacement to maximize prosthesis longevity?
A: Slight mechanical varus is acceptable; valgus alignment is not recommended due to risk of lateral compartment deterioration.
Related Pearl: Proper alignment prevents uneven wear and tibial component loosening.

Q: What is critical about tibial component positioning in medial unicompartmental knee replacement?
A: The component should not “yawn” anteriorly during knee flexion to avoid tibial loosening.
Related Pearl: Stability of the tibial component is the biggest challenge in unicompartmental knee arthroplasty.

Bilateral vs Staged Total Knee Arthroplasty (TKA)

Q: How do simultaneous bilateral and staged total knee replacements compare?
A: They differ only in duration and cost of hospitalization; no significant difference in pulmonary embolism, ROM, infection, or component loosening.
Related Pearl: Patient selection and perioperative care are more important than timing for complication rates.

PCL Retention in TKA

Q: What is the effect of PCL retention in total knee arthroplasty?
A: PCL retention improves femoral rollback during knee flexion.
Related Pearl: Improved rollback enhances knee kinematics and functional flexion.

Rheumatoid Arthritis and Joint Replacement Sequence

Q: In rheumatoid arthritis patients, which joint should be replaced first: hip or knee?
A: The hip should be replaced before the knee for easier rehabilitation.
Related Pearl: Hip replacement improves gait mechanics, facilitating subsequent knee rehab.

TKA Survivorship in Younger Patients

Q: How does age <55 years affect 10-year survivorship of total knee arthroplasty?
A: Survivorship is good and comparable to older patients, but better than in very young patients.
Related Pearl: Younger patients have higher activity levels but modern implants show improved durability.

HTO Outcome Predictors

Q: What predicts a poor response to HTO in varus knees?
A: The presence of varus alignment combined with a high adductor moment predicts poor response.
Related Pearl: Biomechanical loading plays a critical role in osteotomy success.

Infection Diagnosis in TKA

Q: What is the false negative rate of aspiration in diagnosing infected total knee arthroplasty?
A: Approximately 25% false negative rate; clinical suspicion must guide diagnosis.
Related Pearl: Negative aspiration does not exclude infection; consider multiple diagnostic modalities.

TKA Constraint and Loosening

Q: How does the degree of constraint in TKA affect component loosening?
A: Higher constraint increases the rate of tibial component loosening; hinged > TCIII > regular TKA.
Related Pearl: Constraint should be minimized to reduce mechanical stress on fixation interfaces.

Factors Reducing TKA Failure Risk

Q: Which factors are associated with a significantly lower risk of TKA failure?
A: Primary TKA, rheumatoid arthritis, age over 60, and use of metal backing on the tibial component.
Related Pearl: Metal backing improves load distribution and implant longevity.

Osteochondral Allografting

Q: What type of osteochondral allograft produces the best incorporation for femoral condyle lesions?
A: Tissue-matched fresh osteochondral grafts produce excellent incorporation.
Related Pearl: Cryopreserved grafts lose chondrocytes; non-matched grafts are immunogenic and degrade.

Osteonecrosis Diagnosis

Q: How is osteonecrosis of the femoral condyle identified on MRI?
A: Loss of high intensity signal from marrow fat on T1-weighted MRI indicates osteonecrosis.
Related Pearl: Early MRI changes precede radiographic findings, aiding early diagnosis.

Patellar Management in Inflammatory Arthritis

Q: Should the native patella be resurfaced in patients with inflammatory arthritis undergoing TKA?
A: Yes, resurfacing reduces peripatellar pain compared to leaving the native patella.
Related Pearl: Inflammatory arthritis increases patellar cartilage degeneration, justifying resurfacing.

Reconstruction After Previous Sepsis

Q: What is the recommendation for reconstruction in patients with previous sepsis, especially pseudomonas?
A: Avoid reconstruction; arthrodesis is preferred.
Related Pearl: Persistent infection risk and poor soft tissue conditions contraindicate reconstruction.

Femoral Rotation and Patellar Tracking

Q: How does external rotation of the femur affect patellar tracking?
A: External rotation improves patellar tracking.
Related Pearl: Femoral rotational alignment is critical in preventing patellofemoral complications.

Revision TKA Failure Causes

Q: What are the most common causes of failure in revision TKA?
A: Extensor mechanism or patellar problems are most common, followed by component loosening and sepsis.
Related Pearl: Addressing patellar alignment and extensor mechanism integrity is essential in revisions.

TKA Longevity

Q: What is the 10-15 year survival rate of total knee arthroplasty?
A: Approximately 90%.
Related Pearl: Modern implant designs and surgical techniques have improved long-term survival.

HTO Surgical Technique

Q: What is a critical technical point to avoid destabilization during HTO?
A: Do not cut the medial cortex.
Related Pearl: Preserving the medial cortex maintains stability and promotes bone healing.

Classic Clinical Notes

• HTO – young active patients with less than 15° of varus, less than 10° flexion contracture, and primarily unicompartmental changes. The lack of an ACL is NOT a contraindication to HTO.

• Watch out for posterior sag in patients with PCL retaining knees – their PCL may not be so good and they may develop significant AP instability.

• Porous ingrowth is dependent on a few things: avoidance of micromotion; approximation of the surfaces; and size of pores (150-400 microns). The optimal pore volume or volume fraction porosity is 30-40%. Obtaining intimate bone contact and avoiding micromotion are the most important factors for bone ingrowth. Titanium has not been shown to be more conducive to bone ingrowth than cobalt chrome.

• Cement failure in femoral components is caused by microfracture and fragmentation of cement.

• Ultimate postop knee ROM is most predicted by PRE-OP knee ROM.

• For medial unicompartmental knee replacement, to maximize longevity of the prosthesis it should neither rock nor tilt as the knee is put through a range of motion. The principles of uni’s are different from total knee. It is NOT recommended to put the knee in valgus, as this can lead to deterioration of the lateral side. Slight mechanical varus is acceptable, especially with implants that rest on cortical bone. Tibial loosening is the biggest problem with uni’s, so it is important that the component be well-positioned – it should not “yawn” anteriorly with knee flexion.

• Comparing simultaneous bilateral vs staged total knee replacements: the only significant difference has been duration and cost of hospitalization. There is no significant difference in P.E., ROM, infection, or component loosening.

• PCL retention supposedly improves femoral rollback in flexion.

• In rheumatoids, do their hips before knees – it is easier to rehab after the total hip.

• In patients less than 55 yrs, the 10 year survivorship is actually pretty good – comparable to older patients. They are better than those in really young though.

• Reducing cement porosity improves the compressive modulus of cement (increases its strength).

• The presence of a varus alignment with a high adductor moment actually predicts a poor response to HTO.

• In aspirating TKA – there is a 25% false negative result rate – need to go by clinical history and suspicion!

• The more constrained the TKA, the higher the rate of component loosening – particularly the tibia. Thus, a hinged component would be worse than a TCIII, which would be worse than a regular TKA.

• There are four independent factors that are associated with a significantly LOWER risk of failure: PRIMARY total knee arthroplasty, rheumatoid arthritis, age over 60, and the use of metal backing for the tibial component.

• For osteochondral allografting of the femoral condyle lesions – tissue matched fresh osteochondral grafts produce excellent incorporation; cryogenically preserved grafts unfortunately lose most of the chondrocytes. Non-matched fresh grafts are immunogenic and are broken down.

• When looking for osteonecrosis of the femoral condyle, look on T1 MRI for loss of the high intensity signal from the marrow fat.

• Patients with inflammatory arthritis should not be left with their native patella in TKA. They should be resurfaced because they will have significantly less peripatellar pain than in those who do not undergo resurfacing.

• Beware trying to do any reconstruction in a patient with previous sepsis, especially pseudomonas! Do arthrodesis instead.

• External rotation of the femur is a good thing for patellar tracking.

• The most common cause of failure in revision TKA are patellar malalignment, component loosening, and sepsis. The most common is extensor mechanism or patellar problems.

• 10-15 year survival of TKA is about 90%.

• When doing an HTO, make sure you don’t cut the medial cortex – you’ll destabilize the thing!

Last Updated on January 25, 2026 by Christian Veillette