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.
