What is the management approach for foot dorsum numbness without weakness after total knee replacement (TKR)?

Management of Foot Dorsum Numbness Without Weakness After Total Knee Replacement

Foot dorsum numbness without weakness after TKR is most likely a sensory nerve injury (common peroneal nerve distribution) that warrants initial conservative management with close monitoring for motor function deterioration, but if symptoms persist beyond 3-6 months or significantly impact quality of life, referral for peripheral nerve surgery should be considered.

Initial Assessment and Diagnosis

Confirm the diagnosis through clinical examination:

• Assess the specific distribution of numbness on the foot dorsum to localize the nerve involved (typically common peroneal nerve or its branches) 1
• Document baseline motor function carefully, particularly ankle dorsiflexion and toe extension, to ensure true absence of weakness 1
• Evaluate for any associated neuropathic pain symptoms using validated tools 1

Obtain appropriate imaging:

• Start with plain radiographs of the knee to rule out component malposition or other mechanical causes 2
• If nerve impingement is suspected, MRI of the knee without IV contrast (rating 7) or ultrasound (rating 7) are equally appropriate for evaluating soft tissue abnormalities including nerve impingement 2
• Consider CT of the knee without IV contrast if component malrotation is suspected, as this is the most accurate method for measuring component positioning 3

Conservative Management (First-Line Approach)

Reassure the patient about the natural history:

• Numbness around the knee and lower leg is extremely common after TKR, occurring in 68-86% of patients 4, 5
• Importantly, numbness does not correlate with worse patient-reported outcomes or quality of life measures 4
• Improvement occurs with time in approximately 62% of patients who experience numbness 5
• The area of numbness typically decreases, particularly in the first 25 weeks following surgery 5

Implement watchful waiting with serial examinations:

• Monitor motor function closely at regular intervals to detect any progression to foot drop 1
• Document any changes in the distribution or severity of numbness 1
• Assess for development of neuropathic pain, which would change management 1

Indications for Surgical Referral

Consider peripheral nerve surgery if:

• Symptoms persist beyond 3-6 months without improvement 1
• Neuropathic pain develops in addition to numbness 1
• Any motor weakness emerges (foot drop), which requires urgent evaluation 1
• Quality of life is significantly impacted despite conservative management 1

Surgical options based on clinical scenario:

• For lateral knee symptoms with or without foot drop: common peroneal nerve decompression at the fibular head 1
• For medial knee symptoms: saphenous nerve management with targeted muscle reinnervation (TMR) or regenerative peripheral nerve interface (RPNI) 1
• Combined procedures may be necessary based on the distribution of symptoms 1
• Surgical outcomes show 95.5% of patients report improvement, with quality of life scores returning to general population norms 1

Common Pitfalls to Avoid

Do not dismiss isolated sensory symptoms:

• While numbness alone has good prognosis, it can herald more serious nerve injury 1
• Failure to monitor for motor progression can result in delayed treatment of foot drop 1

Do not attribute all numbness to surgical incision:

• Numbness on the foot dorsum is in a different distribution than typical incisional numbness (which is usually lateral to the knee) 5, 6
• Foot dorsum numbness suggests common peroneal nerve involvement, not just cutaneous nerve injury from the incision 1

Do not delay imaging if component malposition is suspected:

• Excessive internal rotation of tibial or femoral components can alter lower extremity biomechanics and create nerve compression 3
• CT without IV contrast is the gold standard for measuring component rotation if this is suspected 3

Recognize that kneeling difficulty may be multifactorial:

• While numbness correlates with kneeling difficulty, pain and range of motion are stronger predictors 4, 6
• Address all contributing factors rather than attributing kneeling problems solely to numbness 6

Timeline for Decision-Making

Immediate (0-6 weeks):

• Obtain baseline imaging and document motor function 2
• Provide reassurance about natural history 4, 5

Short-term (6 weeks to 6 months):

• Continue monitoring for improvement 5
• Watch closely for any motor deterioration 1

Long-term (>6 months):

• If persistent symptoms without improvement, consider referral to peripheral nerve surgeon 1
• Median time to nerve surgery in successful cases was 29.5 months, but earlier intervention may be appropriate for severe symptoms 1