Foot Pain After Knee Replacement: 6 Potential Causes and When to See Your Surgeon

Foot pain after total knee arthroplasty (TKA) is not "normal" but occurs in 10–20% of patients. It usually reflects referred pain, nerve injury, or biomechanical chain effects.

Differential Diagnosis

Cause	Mechanism	Typical Presentation	Workup
IT band syndrome	Tight ITB → lateral knee/foot pain; altered gait	Lateral knee → lateral foot; worse on stairs	Clinical; US/MRI if unclear
Saphenous nerve injury	Medial retinaculum release/retraction	Medial calf/ankle/foot numbness, burning	EMG/NCS; Tinel's at medial knee
Common peroneal nerve palsy	Compression at fibular head (positioning, tourniquet)	Foot drop, lateral leg/foot numbness	EMG/NCS urgent; MRI if compressive
Complex regional pain syndrome (CRPS)	Neuroimmune dysregulation	Burning, allodynia, edema, color/temperature changes	Budapest criteria; bone scan
Referred lumbar/hip pain	L4–S1 radiculopathy; hip OA	Radiating, positional; pre-existing	Lumbar/hip imaging; selective blocks
Vascular: DVT / popliteal artery injury	Stasis, trauma; rare (<1%)	Calf swelling, pain, pallor, pulselessness	Duplex US; CTA/angiogram
Biomechanical: gait compensation	Quadriceps avoidance → vaulting, circumduction	Plantar fascia, metatarsalgia, Achilles	Gait analysis; PT evaluation

Red Flags — Urgent Evaluation

• Foot drop (peroneal nerve)
• Calf swelling + pain (DVT)
• Pulseless/cool foot (arterial)
• Signs of infection (fever, wound drainage, erythema)
• CRPS signs (disproportionate pain, autonomic changes)

Management Approach

1. Orthopedic surgeon evaluation (incision check, neurovascular)
2. Physical therapy: gait retraining, hip/core strengthening, modalities
3. Neuropathic pain medications (gabapentin, duloxetine) if nerve injury
4. Orthotics/AFO if foot drop
5. CRPS: early multidisciplinary (PT, OT, pain psychology, blocks)

Don't assume foot pain is "just referred." New or worsening foot symptoms post-TKA deserve a thorough workup.