What is the management approach for foot dorsum numbness after total knee replacement (TKR)?

Management of Foot Dorsum Numbness After Total Knee Replacement

Foot dorsum numbness after TKR requires urgent evaluation for common peroneal nerve palsy (CPNP), which presents with weakness or inability to dorsiflex the ankle and decreased sensation on the dorsum of the foot, typically manifesting on postoperative day 0 or 1. 1

Immediate Assessment

Distinguish between benign incisional numbness versus nerve injury:

• Check motor function immediately: Test ankle dorsiflexion strength and toe extension to rule out CPNP, which has an incidence of 0.3% to 4% after TKR 1
• Assess timing of onset: CPNP typically presents on postoperative day 0 or 1, while benign incisional numbness develops more gradually 1
• Evaluate pre-operative risk factors: Patients with pre-operative valgus deformity are at higher risk for CPNP 1

Diagnostic Workup

If motor weakness is present (foot drop):

• Obtain plain radiographs of the knee to assess component positioning and alignment as the initial imaging study 2
• Consider CT knee without IV contrast (rated 7/9 appropriateness) if component malrotation is suspected, as excessive internal rotation can alter lower extremity biomechanics and create abnormal stress patterns 3
• Urgent orthopedic surgery consultation for consideration of acute peroneal nerve decompression within the first 90 days postoperatively 1

If only sensory changes without motor weakness:

• This likely represents benign incisional numbness from saphenous or infrapatellar nerve injury, which occurs in 68% of patients after TKR 4
• No urgent intervention is required, as this is common and not associated with worse patient-reported outcomes 4

Treatment Algorithm

For CPNP with Motor Deficit:

Acute surgical decompression is the recommended treatment:

• Timing is critical: Return to operating room electively within the first 90 days for common peroneal nerve decompression 1
• Expected outcomes: At average 12-week follow-up, all patients showed return of motor and sensory function with average motor strength of 4.6 out of 5 1
• Surgical approach: Dissection, release, and decompression of the common peroneal nerve at the fibular head 1

For Isolated Sensory Numbness Without Motor Deficit:

Conservative management with reassurance:

• Natural history: Most patients recover sensation over time, with the short incision group showing only 8% residual numbness at 6 months and most patients recovering by 1 year 5
• Patient education: Numbness after knee replacement is common (68% of patients) but does not correlate with worse functional outcomes or quality of life 4
• Monitor for progression: If numbness persists beyond 6 months or worsens, consider referral to peripheral nerve specialist 6

For Persistent Neuropathic Pain with Numbness:

If conservative management fails after 3+ months:

• Peripheral nerve surgery options include saphenous or infrapatellar branch neurectomy with targeted muscle reinnervation (TMR) or regenerative peripheral nerve interface (RPNI) for medial knee pain 6
• Common peroneal nerve decompression for lateral knee pain and/or foot drop 6
• Expected outcomes: 95.5% of patients report improvement after peripheral nerve surgery, with mean quality of life scores returning to general population norms 6
• Median time to surgery: 29.5 months after TKA in patients who ultimately require peripheral nerve intervention 6

Key Clinical Pearls

Critical distinction: The presence or absence of motor weakness determines urgency—motor deficit requires immediate surgical evaluation, while isolated sensory changes can be managed conservatively 1

Timing matters: Neuropathic pain peaks between 6 weeks and 3 months post-operatively, with high correlation between pain scores and neuropathic pain scores (r > 0.7) at these time points 7

Kneeling difficulty: While numbness correlates with difficulty kneeling (correlation 0.36), this does not predict worse overall outcomes 4

Pre-operative factors: Pre-operative pain scores, anxiety, depression, or neuropathic pain scores do not predict post-operative numbness or pain at any time point 7