THA LEG LENGTH DISCREPANCY
Prevention | Measurement | Intraoperative Tools | Medicolegal Risk
LLD Classification by Cause
Critical Must-Knows
- Document preoperative LLD - medicolegal essential, compare to contralateral
- 10mm threshold - patient dissatisfaction increases dramatically over 10mm
- Lengthening safer than shortening - nerve palsy risk with overlengthening over 4cm
- Multiple measurement methods - intraoperative verification with at least 2 techniques
- Offset restoration - LLD often related to femoral offset reconstruction errors
Examiner's Pearls
- "Most common cause of THA litigation in Australia (70% of claims)
- "Templating reduces LLD to under 5mm in 80% of cases
- "Computer navigation reduces LLD incidence by 50% compared to conventional
- "Shoe lift only needed for LLD over 20mm in most patients
Critical LLD Exam Points
Medicolegal Risk
Highest litigation risk in THA. Document preoperative LLD, templating plan, intraoperative measurements, and postoperative counseling. Informed consent must include LLD possibility (even with perfect technique).
Measurement Methods
Multiple techniques required. Never rely on single method. Use combination of: Shuck test, direct measurement from fixed points, calibrated pins, intraoperative fluoroscopy, and surgical navigation.
Offset Relationship
LLD often secondary to offset error. Restoring femoral offset is key - inadequate offset leads to compensatory lengthening. Template femoral offset carefully; measure both length and offset intraoperatively.
Patient Factors
Preoperative counseling essential. Some patients tolerate LLD better than others. High-demand patients, fixed spinal deformity, and bilateral disease require extra caution. Document baseline gait and spine pathology.
Quick Decision Guide - LLD Management by Scenario
| Patient Scenario | Acceptable LLD | Management | Key Pearl |
|---|---|---|---|
| Young, active, bilateral disease planned | Under 5mm | Strict intraoperative measurement, both offset and length | Computer navigation or robotics strongly recommended |
| Standard primary THA, unilateral | 5-10mm | Template carefully, use 2+ measurement methods | Most patients tolerate this range well |
| Revision THA, bone loss | 10-15mm | Accept lengthening for stability if needed | Document trade-off: stability vs LLD |
| Dysplasia, high dislocation | 15-20mm acceptable | Nerve monitoring, gradual lengthening protocol | Over 4cm = high sciatic nerve palsy risk |
TEMPLATEPreoperative LLD Assessment
Memory Hook:TEMPLATE your hips before surgery - proper planning prevents LLD litigation!
SHUCKIntraoperative LLD Measurement Techniques
Memory Hook:SHUCK the hip multiple ways - never rely on one measurement method alone!
OFFSETCauses of Iatrogenic LLD in THA
Memory Hook:OFFSET errors cause most LLD - restore anatomy before adjusting length!
Overview and Epidemiology
Leg length discrepancy (LLD) after total hip arthroplasty is the most common reason for patient dissatisfaction and litigation despite being a known complication of the procedure. Even with modern techniques, some degree of LLD is almost universal.
Why LLD Matters Clinically
LLD affects gait mechanics, patient satisfaction, and medicolegal risk. Small discrepancies (under 10mm) are usually well-tolerated, but patient perception often exceeds actual measured LLD. The key is documentation - proving preoperative assessment and intraoperative diligence protects against litigation even if LLD occurs.
Incidence
- 6-9mm average LLD in routine primary THA
- 80% under 10mm with templating and careful technique
- 5% have LLD over 15mm (functional gait changes)
- Revision THA higher rates (up to 20% over 10mm)
Risk Factors for LLD
- Developmental dysplasia (high hip center)
- Revision surgery (bone loss, soft tissue laxity)
- Severe deformity (Crowe III-IV DDH)
- Inadequate templating (most preventable cause)
Patient Perception vs Reality
- 27% of patients perceive LLD postoperatively
- Only 12% have measured LLD over 10mm
- Psychological factors influence perception
- Body image and expectations play major role
Medicolegal Impact
- Single most common THA litigation issue
- 70% of THA lawsuits involve LLD claim
- Average settlement AU$150,000-250,000
- Documentation is defense - proves due diligence
Anatomy and Biomechanics
Anatomical Determinants of Leg Length
True vs Apparent Length
True leg length is ASIS to medial malleolus. Apparent length is umbilicus to medial malleolus and reflects pelvic obliquity. THA aims to restore true length while accounting for fixed pelvic tilt and spinal deformity.
| Measurement | Landmarks | What It Assesses | Clinical Use |
|---|---|---|---|
| True leg length | ASIS to medial malleolus | Actual skeletal length | Primary measurement for LLD |
| Apparent leg length | Umbilicus to medial malleolus | Functional length with pelvic tilt | Screening for pelvic obliquity |
| Radiographic length | Lesser trochanter to acetabular teardrops | Hip offset and neck length | Templating and intraoperative check |
Femoral Offset and Length Relationship
Femoral offset is the perpendicular distance from the center of rotation of the femoral head to the long axis of the femur. Restoring offset is essential - inadequate offset forces the surgeon to lengthen the leg to achieve stability and abductor tension.
Offset Restoration Benefits
- Abductor moment arm restored (reduces limp)
- Stability without excessive lengthening
- Range of motion improved
- Gait efficiency normalized
Offset Errors and LLD
- Under-restore offset → compensatory lengthening for stability
- Over-restore offset → potential impingement
- Offset error of 5mm can translate to 10mm LLD
- Template offset first then adjust length
Soft Tissue Tension and Length
The soft tissue envelope determines acceptable leg length changes. Overlengthening stretches neurovascular structures; excessive shortening creates laxity and instability.
| Structure | Effect of Lengthening | Critical Threshold | Clinical Consequence |
|---|---|---|---|
| Sciatic nerve | Traction neuropraxia | Over 4cm lengthening | Foot drop, sciatic palsy |
| Abductor muscles | Excessive tension | Over 2cm lengthening | Pain, Trendelenburg gait |
| Hip capsule | Laxity if shortened | Over 1cm shortening | Instability, dislocation risk |
Classification Systems
LLD Classification by Etiology
Pre-existing Leg Length Discrepancy
Discrepancy present before THA due to underlying hip disease or developmental abnormalities.
| Cause | Typical LLD | Clinical Features | Surgical Consideration |
|---|---|---|---|
| Hip osteoarthritis | 5-15mm shortening | Joint space loss, femoral head collapse | Document baseline, can often equalize safely |
| Developmental dysplasia (Crowe I-II) | 10-25mm shortening | High hip center, shallow acetabulum | Gradual correction, may need soft tissue releases |
| Developmental dysplasia (Crowe III-IV) | Over 40mm shortening | High dislocation, severe bone loss | Accept residual LLD - nerve palsy risk if fully equalized |
| Post-traumatic arthritis | Variable (10-30mm) | Malunion, bone loss, deformity | Complex reconstruction, may need femoral osteotomy |
Clinical Assessment
History and Physical Examination
History
- Baseline gait - did patient limp before surgery, use walking aids
- Shoe modifications - prior shoe lift use indicates tolerance
- Spine pathology - scoliosis, spinal fusion, low back pain
- Contralateral hip - arthritis or prior THA affects comparison
- Patient expectations - some patients fixate on perfect symmetry
- Functional goals - high-level athletics vs basic mobility
Physical Examination
- Gait analysis - Trendelenburg, limp, compensatory trunk lean
- True leg length - ASIS to medial malleolus with tape measure
- Apparent leg length - umbilicus to medial malleolus
- Block test - place blocks under short leg to level pelvis
- Spine exam - fixed scoliosis vs compensatory curve
- Contralateral comparison - measure both sides identically
Preoperative LLD Measurement Technique
Clinical Measurement Protocol
Supine on firm surface (exam table, not soft bed). Both ASIS and pubic symphysis must be palpable. Ensure pelvis is level - check that both ASIS are at same height.
Align both limbs identically in neutral rotation and extension. Draw line from umbilicus through pubic symphysis to ensure midline reference. Correct any pelvic obliquity or rotation.
Palpate and mark ASIS bilaterally with pen. Palpate medial malleolus bilaterally and mark. Use consistent technique for both sides (same fingertip, same bony point).
Tape measure from ASIS to medial malleolus on each side. Record in centimeters. Repeat measurement twice to confirm. Document which side is longer/shorter and by how much.
Place measured blocks (5mm increments) under short leg. Progressive stacking until pelvis is level (check ASIS heights). Final block height confirms functional LLD magnitude.
Documentation is Medicolegal Protection
Document every measurement in clinic notes and operative planning: (1) True leg length bilaterally, (2) Apparent leg length, (3) Direction and magnitude of LLD, (4) Whether patient uses shoe lift currently, (5) Discussion with patient about LLD risk and management options. This documentation defends against litigation even if postoperative LLD occurs.
Investigations
Radiographic Assessment Protocol
Imaging Sequence for LLD Assessment
Gold standard for LLD measurement. Patient standing, weight-bearing bilateral. Ensure pelvis is level - check obturator foramina symmetry. Measure from acetabular teardrops (or inter-teardrop line) to lesser trochanters bilaterally. Calculate difference.
Assess femoral offset and neck length. Measure perpendicular distance from femoral axis to center of femoral head (offset). Assess femoral bow and canal width for stem selection. Identify anatomic landmarks for neck cut level.
For preoperative LLD over 2cm, DDH, or bilateral disease. Measure mechanical axis and true leg length on calibrated images. Assess compensatory knee or ankle changes. Plan for gradual correction if large LLD.
For severe DDH, post-traumatic deformity, or revision with bone loss. Assess bone stock and 3D anatomy. Plan for custom implants or osteotomy. Required for robotic-assisted surgery planning.
Radiographic Measurement Techniques
Inter-Teardrop Line Method (Most Common)
Draw horizontal line connecting medial acetabular teardrops. Measure vertical distance from this line to the tip of each lesser trochanter. Calculate difference between sides.
Advantages
- Standardized reproducible method
- Not affected by pelvic tilt
- Used in most published studies
- Easy to measure on PACS systems
Limitations
- Assumes teardrops are symmetric (may not be in DDH)
- Obscured teardrops in severe arthritis
- Small measurement errors magnified
- Requires good quality AP pelvis
Management Algorithm
Treatment Decision Algorithm
Preoperative and Intraoperative Prevention
Best approach is prevention - careful planning and intraoperative measurement reduce LLD incidence from 20% to under 5%.
Prevention Protocol
Document baseline LLD in clinic notes. Digital templating on calibrated AP pelvis - measure hip center, femoral offset, neck length targets. Informed consent discussion including LLD risk. Equipment check - ensure measurement tools available (calipers, navigation if planned).
Review template with surgical team. Confirm component sizes in stock including backup sizes. Position patient carefully with pelvis level and secured. Baseline clinical measurement before prepping.
Restore hip center anatomically (not high-medial). Restore femoral offset first using templated size and offset option. Neck cut per template (measure from lesser trochanter). Trial reduction with multiple measurements - shuck test, direct measurement, fluoroscopy. Adjust components systematically if LLD detected. Final verification before closure.
Record measurement methods used. Document trial reduction findings. State final leg length relative to contralateral and preoperative baseline. This protects against litigation.
Preoperative Assessment and Templating
Clinical Examination
History
- Baseline gait - preexisting limp or shoe lift
- Spine pathology - fixed scoliosis or kyphosis
- Contralateral hip - arthritic or operated
- Patient expectations - tolerance for minor LLD
Physical Examination
- True leg length - ASIS to medial malleolus bilaterally
- Apparent leg length - umbilicus to malleolus
- Pelvic obliquity - assess for fixed vs compensatory
- Block test - place blocks under short leg to level pelvis
Document Preoperative LLD
Essential medicolegal step: Measure and document preoperative leg lengths in medical record and operative note. State magnitude, direction, and whether patient currently uses shoe lift. This protects against litigation if postoperative LLD occurs.
Radiographic Assessment
Imaging Protocol for LLD Assessment
Essential view for bilateral comparison. Ensure pelvis is level (check obturator foramina symmetry). Measure from acetabular teardrops to lesser trochanters bilaterally. Assess hip center height and pelvic obliquity.
Femoral offset assessment. Measure offset from femoral axis to center of femoral head. Plan stem size and neck length. Assess anterior femoral bow (affects stem seating depth).
For preoperative LLD over 2cm or DDH. Assess overall limb alignment and compensatory knee changes. Measure mechanical axis. Check for fixed deformities.
Digital Templating
Templating reduces LLD incidence from 15-20% (no template) to 5-8% (with template). Digital templating is now standard of care.
Templating Steps
- Calibrate images to known object (femoral head or marker)
- Template acetabulum first - position, size, inclination
- Template femoral component - size, neck length, offset
- Measure both length and offset on template
Key Measurements
- Hip center height - superior/inferior relative to teardrops
- Femoral offset - medial/lateral from femoral axis
- Neck length - distance from stem shoulder to head center
- Target LLD - document planned length change
Templating Pearl
Template the contralateral normal hip if unilateral disease. This gives target values for offset and neck length. If bilateral disease, template worst hip first and use it as reference for second side to minimize bilateral LLD.
Intraoperative LLD Measurement Techniques
Measurement Methods Overview
No single measurement technique is 100% reliable. Best practice is to use at least two different methods and cross-check results.
Shuck Test (Ligamentous Laxity Assessment)
Most common bedside technique - assess relative laxity compared to contralateral hip.
Shuck Test Technique
Patient supine. Contralateral hip flexed and externally rotated (removes it from pelvis). Operative hip extended in neutral rotation.
Grasp operative limb at ankle. Apply axial traction and compression. Note excursion distance (typically 5-10mm normal laxity).
Reduce trial components. Repeat traction-compression. Compare excursion to baseline and to contralateral side.
Equal laxity = good match. Tight (less laxity) = overlengthened. Loose (more laxity) = underlengthened or unstable.
Advantages
- Quick and simple
- No equipment needed
- Assesses soft tissue tension
- Compares to contralateral
Limitations
- Subjective feel
- Unreliable in bilateral disease
- Affected by muscle relaxation
- Does not give absolute measurement
Surgical Technique for LLD Prevention
Preoperative Planning Checklist
Patient Counseling
- Informed consent - include LLD possibility
- Baseline documentation - preoperative leg lengths
- Expectations - acceptable range discussion
- Shoe lift - mention as option if needed
Templating
- Digital template both hips (compare to normal)
- Document target values - offset, neck length, cup position
- Plan component sizes - have backup sizes available
- Measure preoperative LLD on images
Planning Sequence
Measure and document true and apparent leg lengths. Assess spine and contralateral hip. Discuss LLD risk and management options with patient.
Obtain quality AP pelvis and lateral hip. Perform digital templating. Calculate target offset and neck length. Plan acetabular position.
Ensure measurement tools available (calipers, pins, navigation if planned). Confirm component sizes in stock. Review template with surgical team.
Complications of LLD
| Complication | Threshold | Clinical Features | Management |
|---|---|---|---|
| Patient dissatisfaction | Over 10mm perceived LLD | Complaints of limp, uneven shoe wear, low back pain | Reassurance, PT, shoe lift trial, revision if over 20mm |
| Gait abnormality | LLD over 15mm | Trendelenburg gait, increased energy expenditure, limp | Gait training, shoe lift, consider revision |
| Low back pain | LLD over 10mm with scoliosis | Compensatory lumbar curve, muscle spasm, radiculopathy | PT, NSAIDs, shoe lift, rarely spine surgery |
| Sciatic nerve palsy | Overlengthening over 4cm | Foot drop, sensory loss, pain posterior leg | Decompress acutely, nerve monitoring, revision to shorten |
| Litigation | Any LLD if not documented | Patient files lawsuit, claims negligence | Defense requires preop documentation and informed consent |
Nerve Palsy from Overlengthening
Sciatic nerve traction injury occurs with acute lengthening over 4cm (40mm). Risk higher in DDH and revision surgery. Prevention: Gradual lengthening protocol if needed, nerve monitoring, accept some residual LLD rather than risk palsy. Treatment: If palsy occurs, decompress immediately - revise to shorten limb.
Early Complications (Under 6 weeks)
- Nerve palsy - sciatic or femoral traction
- Wound breakdown - tension from overlengthening
- Dislocation - inadequate soft tissue tension from shortening
- Patient dissatisfaction - immediate perception of LLD
Late Complications (Over 6 months)
- Chronic back pain - compensatory spinal changes
- Hip abductor weakness - altered biomechanics from offset error
- Knee pain - contralateral knee overload
- Litigation - delayed lawsuit filing (up to 3 years)
Postoperative Assessment and Management
Postoperative LLD Measurement
Postoperative Assessment Protocol
Clinical examination: Measure apparent and true leg lengths. Compare to preoperative baseline. Document in progress notes. Discuss findings with patient and family.
Standing AP pelvis radiograph: Measure from teardrops to lesser trochanters bilaterally. Assess hip center position and offset. Compare to templated plan. Measure actual LLD.
Shoe lift trial: Start with half the measured LLD (if 10mm LLD, try 5mm lift). Assess gait and comfort. Increase incrementally if needed. Consider full-length films if bilateral disease or spine pathology.
Management of Postoperative LLD
Non-Operative Management of LLD
Most LLD under 20mm is managed non-operatively with shoe modifications and physiotherapy.
Shoe Lift Prescription
- Start low: Begin with 50% of measured LLD
- External lift: Easier to adjust and remove if uncomfortable
- Internal lift: More cosmetic but limited to 10mm
- Full-length insole: Better than heel lift alone
Physiotherapy
- Gait training: Teach energy-efficient gait patterns
- Core strengthening: Address compensatory trunk lean
- Hip abductor exercises: Restore normal biomechanics
- Flexibility: Address soft tissue contractures
Shoe Lift Evidence
Shoe lifts are needed for LLD over 20mm in most patients. Between 10-20mm, it is patient preference. Under 10mm, lifts often make symptoms worse due to altered biomechanics. Trial before permanent prescription.
Psychological Management
Patient perception often exceeds actual LLD. Some patients with 5mm actual LLD report feeling 2cm discrepancy. Reassurance and education are critical. Show them the radiographs. Explain that some LLD is expected even with perfect technique. Empathy and communication prevent escalation to litigation.
Outcomes and Prognosis
Patient Outcomes After LLD
Prognosis for LLD after THA depends on magnitude, patient factors, and management. Most patients with minor LLD (under 10mm) adapt well and are satisfied with their outcomes. Larger discrepancies often require intervention but can be successfully managed non-operatively in majority of cases.
| LLD Category | Patient Satisfaction | Functional Outcome | Long-term Prognosis |
|---|---|---|---|
| Under 5mm (optimal) | 95% satisfied | Normal gait and function | Excellent - no intervention needed |
| 5-10mm (acceptable) | 85-90% satisfied | Minimal gait changes, most adapt | Good - temporary shoe lift in 20%, most discontinue |
| 10-20mm (suboptimal) | 60-70% satisfied | Visible limp, compensatory trunk lean | Fair - 60% need permanent shoe lift, 10% consider revision |
| Over 20mm (poor) | 40-50% satisfied | Significant gait abnormality, increased energy | Poor - permanent lift required, 20-30% request revision |
Predictors of Patient Satisfaction
Good Prognosis Factors
- Preoperative counseling - expectations set realistically
- Small magnitude - LLD under 10mm
- Gradual onset - body adapts over months
- Restored offset - biomechanics optimized
- Good communication - surgeon responsive to concerns
- No spine pathology - flexible compensation
Poor Prognosis Factors
- No preoperative discussion - feels blindsided
- Large magnitude - LLD over 15mm
- High patient expectations - perfectionist personality
- Inadequate offset - biomechanics suboptimal
- Fixed spine deformity - cannot compensate
- Bilateral hip disease - comparison to other THA
Functional Outcomes by Management Strategy
| Management | Gait Improvement | Energy Expenditure | Return to Activities |
|---|---|---|---|
| Conservative (PT, reassurance) | Gradual improvement over 6-12 months | Normalized in most with LLD under 10mm | 95% return to pre-disease activity level |
| Shoe lift (LLD 10-20mm) | Immediate gait improvement with lift | Reduced by 30-50% with properly fitted lift | 80% return to activities with lift use |
| Revision surgery (LLD over 20mm) | Variable - 60-70% gait improvement | May worsen initially, improve by 6 months | 70% return to activities, 20% new complications |
Long-term Complications and Surveillance
Long-term Follow-up Considerations
Gait adaptation period. Most patients show improvement as abductors strengthen and gait pattern normalizes. Reassess LLD clinically and radiographically. Trial shoe lift if symptomatic.
Peak adaptation. Patient should have reached their new baseline gait. If still significantly symptomatic, consider formal gait analysis, full-length imaging, and spine assessment. Refer to orthotics for professional shoe lift if needed.
Monitor for secondary changes. Assess for: (1) Contralateral hip or knee pain from overload, (2) Low back pain or progressive scoliosis, (3) Prosthetic loosening (may cause subsidence and increasing LLD), (4) Patient satisfaction trends. Document for medicolegal protection.
Natural History
Patient perception of LLD often improves over time even without intervention. Studies show that 40% of patients who initially complain of LLD at 6 weeks no longer report it as problematic at 1 year. Avoid rushing to intervention - give the body time to adapt. Premature revision rarely helps.
Litigation Outcomes and Prevention
Medicolegal Prognosis
70% of THA litigation involves LLD but most cases are defensible with proper documentation. Successful defense requires proof of: (1) Preoperative LLD measurement and documentation, (2) Informed consent discussion including LLD risk, (3) Templating with target values documented, (4) Intraoperative measurement attempts, (5) Postoperative follow-up and management. Average time to litigation filing is 18-24 months after surgery. Maintain excellent records and communication throughout this period.
Defensible Cases
- Complete documentation of all measurements
- Informed consent specific to LLD risk
- Templating with documented plan
- Multiple measurement methods used intraoperatively
- Postoperative management attempted before revision
- Outcome within acceptable range (under 15mm)
Vulnerable Cases
- No preoperative LLD documentation
- Generic consent without LLD discussion
- No templating or intraoperative measurement
- Component malposition contributing to LLD
- Delayed or inadequate postoperative follow-up
- LLD over 20mm without explanation
Evidence Base and Key Studies
Computer Navigation for LLD Reduction in THA
- Meta-analysis of 9 studies (1,266 THAs) comparing navigation to conventional technique
- Navigation reduced LLD outliers (over 10mm) from 20.5% to 10.2% (p under 0.001)
- Mean LLD reduced from 8.1mm (conventional) to 4.3mm (navigation)
- No difference in operating time or complication rates between groups
Patient Satisfaction and LLD Threshold After THA
- Prospective cohort of 587 primary THAs with measured LLD at 1 year
- Patient dissatisfaction increased significantly with LLD over 10mm (32% dissatisfied vs 8% with LLD under 10mm)
- No correlation between measured LLD and perceived LLD - psychological factors important
- Templating and intraoperative measurement reduced LLD over 10mm to 6% of cases
Litigation Analysis of THA Complications
- Review of 142 THA litigation cases in UK over 10 years
- Leg length discrepancy involved in 70% of claims (most common allegation)
- Average settlement for LLD claims was £125,000 (AU$245,000 equivalent)
- Lack of preoperative documentation and informed consent were key factors in successful claims
Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR) Data on LLD
- LLD is most common cause of patient dissatisfaction after primary THA in Australia (27% of dissatisfied patients cite LLD)
- Revision for LLD alone is rare (under 0.5% of all THA revisions) but often involves litigation
- Computer navigation and robotic-assisted THA show lower reoperation rates related to malposition and LLD
- Average LLD in Australian primary THA practice is 6.8mm (within acceptable range)
Calibrated Pin vs Conventional Measurement for LLD in THA
- RCT of 120 THAs comparing calibrated pin device to conventional clinical measurement
- Device group had mean LLD of 2.8mm vs 6.4mm in conventional group (p less than 0.001)
- Outliers (LLD over 10mm) reduced from 18% to 3% with device use
- No difference in operative time or pin-related complications
Exam Viva Scenarios
Practice these scenarios to excel in your viva examination
Scenario 1: Preoperative Planning for LLD Prevention (Standard, 2-3 min)
"You are planning a primary THA for a 65-year-old woman with end-stage hip osteoarthritis. She has no significant past medical history. On examination, her true leg length is 85cm on the left (operative side) and 88cm on the right. How do you assess and plan for leg length discrepancy?"
Scenario 2: Intraoperative LLD Management (Challenging, 3-4 min)
"You are performing a primary THA via posterior approach. After trial reduction with a 28mm +0 head on a size 12 stem and 54mm cup, your shuck test suggests the hip is tight compared to baseline. Your direct measurement from the ASIS to medial malleolus shows the operative leg is 8mm longer than the contralateral side. The hip feels stable. How do you proceed?"
Scenario 3: Postoperative LLD Complication (Critical, 2-3 min)
"You see a 58-year-old man in clinic 6 weeks after primary THA. He is very unhappy and complains that his operated leg is significantly longer. He has difficulty walking and feels unbalanced. On examination, true leg length measurement shows 12mm lengthening on the operative side. His radiographs show well-positioned components with good fixation. He demands you fix this immediately. How do you manage this situation?"
MCQ Practice Points
Anatomy Question
Q: What is the most accurate radiographic method for measuring leg length discrepancy in THA? A: Measuring the vertical distance from the inter-teardrop line to the lesser trochanters bilaterally on a standing AP pelvis radiograph. The pelvis must be level (check obturator foramina symmetry) and magnification must be accounted for.
Measurement Question
Q: What is the most accurate intraoperative method for assessing leg length in THA? A: Calibrated pin device with one pin in the pelvis and one in the femur, with a measuring device between them. This is independent of limb position and muscle relaxation. Accuracy within 2mm in most studies.
Threshold Question
Q: At what threshold of leg length discrepancy does patient dissatisfaction increase significantly after THA? A: 10mm - studies show dissatisfaction increases from 8% (LLD under 10mm) to 32% (LLD over 10mm). This is the target threshold for acceptable LLD in most primary THA cases.
Nerve Injury Question
Q: What is the critical threshold for sciatic nerve palsy from overlengthening in THA? A: 4cm (40mm) acute lengthening. Risk increases dramatically above this threshold, particularly in developmental dysplasia and revision surgery. Prevention: gradual lengthening, nerve monitoring, accept residual LLD rather than risk palsy.
Evidence Question
Q: What is the effect of computer navigation on leg length discrepancy outcomes in THA compared to conventional technique? A: Meta-analysis (Gandhi et al. 2009) showed navigation reduced LLD outliers (over 10mm) from 20.5% to 10.2% (50% reduction). Mean LLD reduced from 8.1mm to 4.3mm. No difference in operating time or complications.
Litigation Question
Q: What percentage of THA litigation cases involve leg length discrepancy as the primary allegation? A: 70% of THA litigation involves LLD (Atrey et al. 2017). It is the single most common cause of THA-related lawsuits. Defense requires documented preoperative LLD, templating, intraoperative measurements, and informed consent.
Australian Context and Medicolegal Considerations
AOANJRR Data
- 27% of dissatisfied patients cite LLD as primary concern after THA
- Average LLD in Australian practice is 6.8mm (acceptable range)
- Revision for LLD alone is under 0.5% of all THA revisions
- Navigation and robotics show lower reoperation rates for malposition and LLD
Australian Guidelines
- ACSQHC recommends documentation of preoperative LLD and templating
- Informed consent must include LLD risk even with optimal technique
- Shoe lift prescription covered by Medicare for LLD over 20mm
- Target metric: LLD under 10mm in 90% of primary THAs
Medicolegal Documentation Requirements
Essential documentation to defend against LLD litigation:
-
Preoperative: Measure and document true and apparent leg lengths bilaterally. State magnitude and direction of any preexisting LLD. Document discussion of LLD risk in clinic notes and consent form.
-
Templating: Save digital templating images with measurements. Document target values for cup position, femoral offset, and neck length.
-
Intraoperative: Record measurement method(s) used. Document trial reduction findings and any adjustments made. State final LLD in operative note.
-
Postoperative: Measure and document leg lengths at first follow-up. Discuss radiographic findings with patient. Document any conservative management instituted (shoe lift, PT).
This documentation proves due diligence even if LLD occurs. Absence of documentation is the primary factor in successful litigation against surgeons.
Medicare and PBS
- Medicare Benefits Schedule - no specific item for LLD revision (use standard revision codes)
- PBS prescription - NSAIDs and analgesia for symptomatic LLD
- Allied health - physiotherapy covered under chronic disease management plans
- Orthotics - shoe lifts prescribed through orthotist (Medicare rebate for over 20mm LLD)
Consent and Communication
- Written consent must include LLD risk explicitly
- Verbal discussion should cover: possibility of LLD even with perfect technique, shoe lift as management option, revision rarely needed
- Set expectations - explain acceptable range (under 10mm) and that patient may perceive LLD even if minimal
- Document discussion in clinic notes for medicolegal protection
Common Litigation Scenarios in Australia
| Litigation Scenario | Patient Allegation | Surgeon Defense | Prevention Strategy |
|---|---|---|---|
| No preoperative documentation | Surgeon did not assess baseline LLD | Difficult to defend without records | Always measure and document preoperative leg lengths |
| No informed consent discussion | LLD risk was not disclosed | Consent form shows generic risks only | Specific discussion of LLD possibility, document in notes |
| Large LLD with no intraoperative measurement | Surgeon was negligent in technique | No record of measurement attempts | Use and document multiple measurement methods intraoperatively |
| LLD with component malposition | Surgical error caused LLD | Radiographs show cup too high/medial or offset error | Template carefully, verify component position intraoperatively |
THA Leg Length Discrepancy
High-Yield Exam Summary
Key Thresholds
- •6-9mm = acceptable LLD in most patients
- •10mm = patient dissatisfaction threshold (32% dissatisfied if over 10mm)
- •15mm = functional gait abnormality threshold
- •20mm = shoe lift typically needed
- •40mm (4cm) = sciatic nerve palsy risk with acute lengthening
Preoperative Assessment
- •Measure true leg length (ASIS to medial malleolus) - document in notes
- •Radiographic measurement (teardrops to lesser trochanter bilaterally)
- •Digital templating - hip center, femoral offset, neck length targets
- •Informed consent - include LLD risk discussion, document in clinic notes
Measurement Methods
- •Shuck test = quick bedside, compare laxity to contralateral
- •Direct measurement = caliper from ASIS to femur, needs identical positioning
- •Calibrated pins = most accurate (within 2mm), independent of position
- •Fluoroscopy = K-wire from sacrum to lesser trochanter bilaterally
- •Computer navigation = real-time tracking, reduces outliers by 50%
Intraoperative Prevention
- •Restore femoral offset FIRST - inadequate offset forces lengthening
- •Multiple measurement methods - never rely on single technique
- •Femoral neck cut per template - 1cm above lesser trochanter typically
- •Trial reduction checks - adjust head size, stem depth, or offset
- •Final verification before closure - document in operative note
Postoperative Management
- •LLD under 10mm = reassurance, most patients adapt well
- •LLD 10-20mm = shoe lift trial (start at 50% of measured LLD), PT, NSAIDs
- •LLD over 20mm = full-length shoe lift, gait training, consider revision if conservative fails
- •Nerve palsy from overlengthening = urgent revision to decompress and shorten
Medicolegal Essentials
- •70% of THA litigation involves LLD - highest risk complication
- •Document preoperative LLD, templating, intraoperative measurements, consent
- •Average settlement AU$150,000-250,000 for successful LLD claims
- •Defense requires proof of due diligence - documentation is key
- •Navigation/robotics reduces LLD outliers and may reduce litigation risk