THA Leg Length Discrepancy

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.

Identify calibration object on radiograph (femoral head diameter, marker ball). Set scale in PACS to match known size. Verify calibration by measuring known anatomic structure.

Draw reference lines (teardrop or ischial). Measure to lesser trochanters. Software calculates difference in millimeters accounting for magnification.

Overlay acetabular and femoral components. Adjust cup position, stem size, and head/neck length. Measure predicted postoperative leg length and offset.

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.

Sciatic nerve palsy from overlengthening - decompress and revise to shorten immediately. Do not delay - permanent foot drop risk increases with time.

Consider revision if: (1) LLD over 20mm with failed conservative management, (2) Documented functional impairment (gait analysis, energy expenditure), (3) Component malposition contributing to LLD, (4) Patient fully informed of risks and benefits.

Do not revise if: (1) LLD under 15mm, (2) Conservative management not attempted, (3) Patient perception exceeds measured LLD (psychological issue), (4) Medical comorbidities prohibit surgery, (5) Litigation pending (wait for resolution).

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.

Pelvic landmark: ASIS, pubic symphysis, or iliac crest. Femoral landmark: lesser trochanter, medial epicondyle, or medial malleolus. Mark with pen or place towel clip.

Measure distance with sterile ruler or calibrated calipers. Record baseline measurement on both operative and contralateral sides.

Reduce trial components. Reposition limb identically. Remeasure from same landmarks. Compare to baseline and contralateral.

If discrepancy detected, adjust head size, stem depth, or offset as needed. Remeasure after each adjustment until within 5mm of target.

Acetabular pin: Into anterior column or iliac wing - stable fixed reference. Femoral pin: Into greater trochanter or femoral shaft - moves with femur.

Before dislocation, attach measuring device between pins. Record baseline distance. This represents preoperative hip anatomy.

After trial reduction, reconnect device. Read distance change. Positive = lengthening, negative = shortening. Adjust components accordingly.

Place K-wire horizontally across sacrum or pubic symphysis. Secure with tape. Ensure wire is truly horizontal on AP fluoroscopy.

AP pelvis fluoroscopy showing K-wire and both lesser trochanters. Measure vertical distance from wire to lesser trochanter bilaterally. Save image.

After trial reduction, repeat AP fluoroscopy with identical patient position. Remeasure to lesser trochanter. Compare to baseline and contralateral.

After final component implantation, take final AP image. Confirm LLD within acceptable range. Save all images for record.

Absolute: Nerve palsy from overlengthening (decompress urgently). Relative: LLD over 20mm with failed conservative management, patient demands, documented functional impairment, litigation threat.

Identify cause: Was it cup position, femoral offset, neck cut level, or stem depth? Template revision strategy. Ensure adequate bone stock for reconstruction. Consent for persistent LLD risk.

If too long: Lower cup position (limited by bone), shorten femoral neck cut (modular neck), downsize head diameter, revise to shorter stem. If too short: Distal femoral strut allograft (rarely), constrained liner, accept discrepancy.

Success rate 70-80% for LLD correction. Risk of new complications (infection, dislocation, loosening). May not fully resolve patient dissatisfaction. Document thoroughly to protect against further litigation.

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.

Before prepping: Measure baseline leg lengths with limbs in neutral. Mark measurement points on skin. Document baseline fluoroscopic image if using. Place calibrated pins if using that method.

Restore hip center: Position cup at anatomic center (not high and medial). Check templated cup size and position. Avoid medialization (shortens) or lateralization (lengthens). Confirm inclination and anteversion targets.

Follow template exactly: Use templated neck cut level (usually 1cm above lesser trochanter). Measure from lesser trochanter with ruler before cut. Consider head diameter when planning cut height. Too distal = lengthening; too proximal = shortening.

Restore offset first: Template stem size and offset. Prepare femur to templated depth. Check version. Use offset broaches if needed to restore anatomy. Do not sink stem excessively (shortens).

Measure with multiple methods: Shuck test, direct measurement, calibrated device, and fluoroscopy if available. Compare to contralateral and preoperative baseline. Adjust head size, stem depth, or offset as needed.

Systematic approach: If too long, try smaller head or deeper seating. If too short, try larger head or less deep seating. Recheck offset - inadequate offset forces lengthening. Trial again after each adjustment.

Implant definitive components. Reduce final construct. Recheck measurements one last time. Perform stability testing. Document final LLD in operative note.