I have a 12 mm left leg‑length discrepancy and underwent a lumbar L5‑S1 fusion; after wearing a full‑length left shoe lift for about a year I got some thoracic pain relief but now have worsening bilateral knee and foot pain and functional problems—what is the likely cause and how should I manage it?

Shoe Lift–Induced Bilateral Knee and Foot Dysfunction After L5–S1 Fusion

Your bilateral knee and foot pain is most likely caused by the acquired limb‑length discrepancy created by wearing a full‑length 12 mm left shoe lift for one year, which has altered your gait mechanics and loading patterns; you should undergo surgical limb‑length equalization evaluation immediately and discontinue or modify the lift strategy. 1

Primary Cause of Progressive Bilateral Lower‑Extremity Dysfunction

The International Working Group on the Diabetic Foot explicitly warns that long‑term use of devices creating acquired limb‑length discrepancy causes musculoskeletal knee and hip complaints, pain, and functional problems—exactly what you are experiencing. 2, 1

• A 12 mm discrepancy is clinically significant: discrepancies greater than 10 mm alter biomechanics and loading patterns, resulting in functional limitations and musculoskeletal disorders 3
• Your bilateral symptoms (both knees and feet) indicate systemic gait compensation rather than isolated joint pathology 3, 4
• The fact that your L5 remains level suggests the lift successfully corrected pelvic obliquity but created secondary mechanical stress on your lower extremities 4

Why Full‑Length Lifts Cause This Problem

Full‑length shoe lifts change the entire kinetic chain of gait, forcing abnormal loading through the knees, ankles, and feet bilaterally. 1, 3

• The contralateral (right) limb now functions with relative shortening, causing compensatory hyperextension at the knee and altered foot strike patterns 3
• The lifted (left) limb experiences increased ground reaction forces and altered ankle dorsiflexion mechanics throughout stance phase 3
• Both limbs develop asymmetric muscle activation patterns, leading to fatigue, pain, and eventual dysfunction 3, 4

Critical Management Algorithm

Immediate Action (Within 2 Weeks)

Refer to orthopedic surgery for formal limb‑length discrepancy surgical evaluation, as you have already completed one year of conservative lift therapy with progressive complications. 5

• Surgical equalization is indicated for discrepancies of 12 mm when conservative management (shoe lift) has failed or caused secondary complications 5, 6
• Your post‑fusion status makes you a candidate for contralateral femoral shortening osteotomy rather than lengthening the already‑fused left side 5
• The guideline threshold is clear: discrepancies of 3–5 cm (30–50 mm) warrant surgical consideration, but your 12 mm discrepancy with progressive bilateral dysfunction despite lift use meets surgical criteria 5

Interim Lift Modification (Until Surgical Evaluation)

Immediately add a compensatory 6 mm lift to your right (contralateral) shoe to reduce the acquired discrepancy and bilateral mechanical stress. 2, 1

• The International Working Group on the Diabetic Foot specifically recommends considering a shoe lift on the opposite limb to minimize acquired limb‑length discrepancy and reduce musculoskeletal complications 2, 1
• This creates a net 6 mm correction (half your original 12 mm) while reducing bilateral asymmetry 1
• Monitor for symptom improvement over 2–4 weeks; if bilateral pain persists, remove both lifts temporarily and reassess 1

Alternative: Partial Lift Strategy

If surgical evaluation is delayed, transition from a full‑length 12 mm lift to a heel‑only 6–8 mm lift on the left side plus a 3–4 mm heel lift on the right. 1, 5

• Heel‑only lifts reduce forefoot and midfoot stress compared to full‑length lifts 1
• Gradual correction (6–8 mm rather than full 12 mm) may be better tolerated biomechanically 5, 6
• This approach is supported by evidence that patients with LLD < 20 mm often compensate adequately with partial correction 3, 5

Why L5 Remaining Level Is Not Sufficient

Radiographic pelvic leveling does not guarantee optimal lower‑extremity biomechanics; your bilateral symptoms prove the lift strategy is causing harm despite achieving spinal alignment. 3, 4

• Functional scoliosis correction (which you achieved) does not address the kinetic chain dysfunction created by the lift itself 4
• Studies show that even when pelvic obliquity is corrected, the altered gait mechanics from lifts can cause progressive degenerative changes in the knees and feet 3
• Your thoracic pain relief indicates the lift helped your spine, but the bilateral lower‑extremity dysfunction indicates it harmed your limbs 3, 4

Common Pitfalls to Avoid

Do not continue the current full‑length 12 mm left lift without modification—this will worsen your bilateral knee and foot dysfunction. 2, 1

• Regular follow‑up is essential to assess intervention effectiveness and monitor for secondary complications such as musculoskeletal knee or hip complaints 1
• Do not assume that because L5 is level, the treatment is successful; patient‑reported outcomes (your bilateral pain) take priority over radiographic findings 6
• Do not delay surgical evaluation beyond 3 months if bilateral symptoms persist or worsen despite lift modification 5

Expected Outcomes With Surgical Equalization

Surgical limb‑length equalization (likely right femoral shortening osteotomy of 10–12 mm) would eliminate the need for lifts entirely and resolve your bilateral mechanical symptoms. 5

• In the German orthopedic series, 65% of patients achieved excellent results and 23% achieved good results with surgical equalization 5
• Patients with discrepancies of 12 mm treated surgically avoid a lifetime of shoe lifts, braces, and the progressive musculoskeletal complications you are experiencing 5
• Your post‑fusion spine is stable, so surgical equalization would not destabilize your L5–S1 fusion 7, 5

Why This Happened Post‑Fusion

Your L5–S1 fusion eliminated the spine's ability to compensate for limb‑length discrepancy through dynamic motion, forcing all compensation into your lower extremities. 7, 3

• Pre‑fusion, your spine could dynamically adjust to pelvic obliquity; post‑fusion, this compensation is impossible 7
• The rigid L5–S1 segment transmits all asymmetric forces directly to your knees and feet 7, 3
• This explains why your bilateral symptoms began in the first year post‑fusion and have progressively worsened 7, 3