What causes foot numbness after total knee replacement surgery?

Foot Numbness After Total Knee Replacement

Foot numbness after total knee replacement is most commonly caused by peroneal nerve injury (occurring in approximately 0.37% of cases), which typically resolves spontaneously within 1 year without intervention, though surgical decompression should be considered for persistent symptoms beyond 3 months that interfere with function. 1

Immediate Diagnostic Approach

• Obtain plain radiographs of the knee first to exclude mechanical complications such as component malposition, periprosthetic fracture, or hardware issues that could cause nerve compression 2, 3
• Perform a focused neurological examination to determine the specific nerve distribution affected:
  • Peroneal nerve (most common): foot drop, lateral leg numbness, inability to dorsiflex foot 1, 4
  • Tibial nerve: plantar foot numbness, tarsal tunnel syndrome symptoms 5
  • Saphenous nerve: medial knee and leg numbness 6
• Order electrodiagnostic testing (EMG/NCS) if symptoms persist beyond 2-4 weeks to confirm nerve involvement and localize the lesion 1, 4

Common Causes and Mechanisms

• Peroneal nerve dysfunction accounts for the majority of post-TKA neuropathies (37 of 54 cases in one series), typically from stretch injury during surgery, tourniquet use, or compression from postoperative swelling 1
• Tibial nerve compression can occur from tarsal tunnel syndrome developing secondary to altered biomechanics or positioning during surgery 5
• Saphenous or infrapatellar nerve injury causes medial knee and leg numbness, often from direct surgical trauma 6
• Sciatic nerve involvement is less common but can present with combined peroneal and tibial symptoms 1

Management Algorithm

Initial Conservative Management (First 3-12 Months)

• Observe and reassure patients that motor recovery typically occurs within 1 year and is complete or near-complete in the vast majority of cases 1
• Physical therapy focusing on range of motion and gait training, as some patients cannot achieve adequate ROM due to nerve dysfunction 4
• Symptomatic treatment with gabapentin or pregabalin for neuropathic pain symptoms while awaiting spontaneous recovery 6

Surgical Intervention Criteria (After 3+ Months)

• Consider common peroneal nerve decompression for lateral knee pain and/or foot drop that persists beyond 3 months and interferes with rehabilitation 6, 4
• Perform saphenous nerve neurectomy with targeted muscle reinnervation (TMR) or regenerative peripheral nerve interface (RPNI) for medial knee neuropathic pain unresponsive to conservative care 6
• Tarsal tunnel release for confirmed tibial nerve compression at the ankle with positive electrodiagnostic findings 5
• Surgical decompression resulted in mean ROM improvement of 40° and resolution of pain in patients with persistent symptoms 4

Critical Pitfalls to Avoid

• Do not assume numbness alone requires intervention: 68% of patients report numbness around the TKR scar at 1 year, but this does not correlate with worse patient-reported outcomes or quality of life 7
• Rule out infection first if numbness is accompanied by pain, as infection occurs in 0.8-1.9% of TKAs and can present with atypical neurological symptoms 2, 3
• Do not delay electrodiagnostic testing beyond 4 weeks if motor weakness is present, as this confirms the diagnosis and guides surgical planning 1, 4
• Recognize that anesthesia type does not correlate with post-TKA neuropathy, so this should not factor into diagnostic reasoning 1

Expected Outcomes

• 95.5% of patients report improvement after peripheral nerve surgery for post-TKA neuropathic symptoms, with quality of life scores returning to general population norms 6
• Motor recovery is typically complete within 1 year without intervention in the majority of cases 1
• Sensory numbness may persist but does not significantly impact function or patient satisfaction in most cases 7