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

Management of Foot Dorsum Numbness After Total Knee Replacement

Foot dorsum numbness after total knee replacement is most commonly a benign sensory phenomenon related to surgical nerve injury (typically the infrapatellar branch of the saphenous nerve), but you must first rule out serious complications including peroneal nerve injury causing foot drop, compartment syndrome, or vascular compromise through immediate clinical examination and plain radiographs. 1

Initial Evaluation and Workup

Immediate Assessment

• Obtain plain radiographs of the knee first to assess component positioning, alignment, and exclude periprosthetic fracture or other mechanical complications that could cause nerve compression 1
• Perform a focused neurological examination to differentiate between:
  • Sensory-only numbness (benign nerve injury) versus motor weakness (peroneal nerve injury requiring urgent intervention) 2
  • Assess for foot drop, which occurs in 3.7-7.4% of cases requiring nerve surgery 2
  • Check for signs of compartment syndrome (severe pain, tense compartments, pain with passive stretch)

Clinical Context

• Numbness around the TKR scar is extremely common, occurring in 56.9-86% of patients 3, 4
• Most numbness is lateral or medial to the incision and relates to injury of cutaneous nerves during surgical approach 5, 6
• 68% of patients report subjective numbness, but this does not correlate with worse patient-reported outcomes or quality of life 3

Diagnostic Algorithm Based on Clinical Presentation

If Sensory Numbness Only (No Motor Weakness)

• Reassure the patient that numbness is common and typically improves over time 3, 5
• The numb area decreases significantly from 2 weeks (51.7 cm²) to 1 year (2.1 cm²) postoperatively 6
• 69% of patients have complete resolution of numbness by 1 year 6
• No additional imaging beyond initial radiographs is needed 1

If Motor Weakness or Foot Drop Present

• Obtain CT of the knee without IV contrast to evaluate for component malposition, periprosthetic fracture, or other structural causes of nerve compression 1
• Consider urgent orthopedic consultation for possible:
  • Common peroneal nerve decompression if lateral knee pain and/or foot drop present 2
  • Surgical exploration if acute onset suggests hematoma or compartment syndrome

If Neuropathic Pain Accompanies Numbness

• Differentiate from infection (most serious complication occurring in 0.8-1.9% of cases) by assessing for night pain, pain at rest, warmth, and erythema 1
• Perform joint aspiration after reviewing radiographs if infection suspected 1
• If neuropathic pain persists beyond 3 months without improvement, consider referral for peripheral nerve surgery evaluation 2

Management Strategies

Conservative Management (First-Line for Isolated Sensory Numbness)

• Observation with serial clinical assessments as 62% of patients report improvement in numbness over time 3
• Numbness does not significantly correlate with joint-specific patient-reported outcome measures (WOMAC, KOOS) 3
• Counsel patients that numbness may affect kneeling ability (correlation coefficient 0.36, p=0.020) but does not impact overall function 3

Surgical Intervention (For Persistent Neuropathic Symptoms)

• Median time from TKR to nerve surgery is 29.5 months for patients who ultimately require intervention 2
• Surgical options based on location and symptoms:
  • Saphenous or infrapatellar branch neurectomy with targeted muscle reinnervation (TMR) or regenerative peripheral nerve interface (RPNI) for medial knee pain (48.1% of cases) 2
  • Common peroneal nerve decompression for lateral knee pain and/or foot drop (40.7% of cases) 2
  • Combination procedures (11.1% of cases) 2
• 95.5% of patients report improvement after peripheral nerve surgery with quality of life scores returning to general population norms 2

Key Clinical Pitfalls to Avoid

• Do not dismiss foot dorsum numbness without assessing motor function - foot drop requires urgent evaluation and potential surgical decompression 2
• Do not attribute all post-TKR numbness to benign nerve injury - always obtain radiographs first to exclude mechanical complications 1
• Do not rush to surgical nerve intervention - most sensory numbness improves spontaneously over 12 months 6
• Do not confuse neuropathic pain with infection - infection presents with systemic signs and requires joint aspiration 1

Follow-Up Recommendations

• Serial clinical assessments at 2 weeks, 3 months, 6 months, and 1 year to document improvement in numbness area 6
• Annual weight-bearing radiographs for routine surveillance even in asymptomatic patients 1
• Refer to peripheral nerve surgeon if neuropathic symptoms persist beyond 3 months without improvement or if motor weakness develops 2