Charcot Arthropathy

Charcot arthropathy (neuropathic osteoarthropathy) is a progressive destructive disease of the bones and joints in a limb with loss of protective sensation and autonomic neuropathy. It most often affects the foot and ankle (midfoot in about 60%, hindfoot and ankle in 20 to 30%, forefoot in 10 to 15%).

The most common cause is diabetes (0.1 to 0.4% of diabetic patients, and over 13% of those with neuropathy), then syphilis (tabes dorsalis), syringomyelia, leprosy, spinal cord injury, alcoholic neuropathy, congenital insensitivity to pain, and peripheral nerve injury.

It affects patients aged 40 to 60 years with long standing neuropathy, and is bilateral in 10 to 30%. It is often misdiagnosed as cellulitis, gout, deep vein thrombosis or osteomyelitis, with a delay in diagnosis of weeks to months.

The Eichenholtz classification describes three stages: stage 0 (prodromal; swelling, warmth, normal radiographs), stage 1 (development/fragmentation: bone destruction, joint dislocation), stage 2 (coalescence: resolution of oedema, bone healing) and stage 3 (reconstruction/consolidation: remodelling and stable deformity). The Brodsky classification divides the foot into type 1 (tarsometatarsal and naviculocuneiform, midfoot), type 2 (hindfoot: subtalar, talonavicular, calcaneocuboid), type 3A (ankle) and 3B (calcaneus), and type 4 (forefoot).

Complications are rocker bottom deformity, ulceration and infection (osteomyelitis), amputation, instability, and reduced quality of life, with a 5-year mortality of 30 to 40% in those with associated ulceration.

Pathophysiology.

Two theories combine. In the neurotraumatic theory, loss of pain sensation allows repetitive microtrauma and unrecognised fractures, with continued walking. In the neurovascular theory, autonomic neuropathy increases blood flow through arteriovenous shunting, which causes bone resorption (osteoclast activation through RANKL, inflammatory cytokines, and osteoprotegerin imbalance). The two mechanisms cause progressive fragmentation, joint dislocation and loss of the arch.

A warm, swollen, erythematous foot (temperature difference over 2 degrees Celsius (4 degrees Fahrenheit) compared with the other foot), often with mild or no pain, in a patient with neuropathy, after minor trauma or none. Later, deformity (rocker bottom, collapsed arch, prominent plantar bony prominence), instability and ulceration under the bony prominence.

Examine the neuropathy (10 g monofilament, vibration, reflexes), pulses (ankle brachial index; arterial calcification may falsely raise values), skin and ulcers (probe to bone), temperature (infrared thermometer), deformity, and range of motion. Check footwear, the contralateral foot and glucose control.

• Radiographs: weight bearing views of the foot and ankle. Early films are normal (stage 0). Later, the "5 Ds": distension (effusion), density (sclerosis), debris, dislocation and disorganisation. Measure the calcaneal pitch, lateral talar first metatarsal angle and cuboid height.
• MRI is the most sensitive in the early stage (bone marrow oedema, subchondral cysts, joint effusion) and distinguishes Charcot from osteomyelitis (osteomyelitis: bone marrow changes next to an ulcer or sinus, ghost sign, abscess).
• White cell labelled scan or positron emission tomography when osteomyelitis is suspected; bone biopsy for culture and histology is the reference method.
• Blood tests: full blood count, C-reactive protein, erythrocyte sedimentation rate (raised in osteomyelitis; a value over 60 mm/h is suggestive), HbA1c, creatinine, calcium and 25-hydroxyvitamin D.
• Vascular assessment (toe pressures, Doppler) before surgery.

Differential diagnosis.

• Osteomyelitis and cellulitis.
• Deep vein thrombosis and gout.
• Acute fracture or sprain and osteoarthritis.
• Rheumatoid arthritis, septic arthritis and complex regional pain syndrome.

Early recognition and offloading are the main treatments, and any warm swollen foot in a neuropathic patient is treated as Charcot until proven otherwise.

Acute phase (stages 0 and 1).

• Strict offloading with a non-removable total contact cast (changed weekly at first, then every 2 to 4 weeks) until the temperature difference is under 2 degrees Celsius (4 degrees Fahrenheit), radiographs show consolidation and oedema has resolved. This usually takes 3 to 6 months (can be up to 12 months).
• Use crutches, a wheelchair or a knee scooter to avoid weight bearing.
• Replace by a removable cast walker boot, then custom made therapeutic footwear with a rigid rocker sole and custom insoles (lifelong).
• Control diabetes, nutrition (vitamin D), blood pressure and smoking.
• Bisphosphonates and calcitonin have not shown consistent benefit in controlled studies and are not advised routinely.
• Optimise vitamin D: colecalciferol 800 to 2000 IU orally daily with dietary calcium to a total of 1000 to 1200 mg daily (maximum total 2000 mg daily); correct deficiency first.

Ulceration and infection. Debride, offload, and treat osteomyelitis (bone resection or culture directed antibiotics for 6 weeks). For example, amoxicillin clavulanic acid 625 mg orally every 8 hours (or 1.2 g intravenously every 8 hours) with ciprofloxacin or a regimen directed by culture. Check liver function. Adjust at creatinine clearance under 30 mL/min.

Surgery.

• Indications: unstable or progressive deformity that cannot be braced, recurrent ulceration under a bony prominence, instability of the ankle or hindfoot, and failed non-operative treatment.
• Exostectomy (removal of a plantar prominence) for stable deformity with ulceration.
• Reconstruction (arthrodesis) with a superconstruct: extended fusion beyond the zone of injury, bone resection, large screws, plates, beams, intramedullary bolts or a circular external fixator. Tendo-Achilles lengthening or gastrocnemius recession is often added to reduce midfoot load.
• Ankle and hindfoot: tibiotalocalcaneal arthrodesis with a nail. Amputation (transtibial) for uncontrolled infection, failure of reconstruction or a nonreconstructable limb.
• Postoperative: non-weight bearing for 8 to 12 weeks in a cast, then protected weight bearing, then custom footwear.

Operative antibiotic prophylaxis. Cefazolin 2 g intravenously (3 g when weight is 120 kg or over) within 60 minutes before incision as a single dose (repeat after 4 hours or blood loss over 1500 mL).

With severe penicillin allergy, use vancomycin 15 mg/kg intravenously starting 90 to 120 minutes before incision as a single dose, with levels and creatinine checked in prolonged cases.

Thromboprophylaxis. Enoxaparin 40 mg subcutaneously once daily for the period of immobilisation and restricted weight bearing (usually 4 to 6 weeks) in patients with a lower limb cast or non-weight bearing, started within 24 hours of injury or after surgery.

Dose adjustments: 20 mg once daily at creatinine clearance under 30 mL/min; adjust by anti-Xa level in obesity and renal impairment. Check the platelet count on days 5 to 14 for heparin induced thrombocytopenia. Add mechanical prophylaxis as needed.

Analgesia.

• Paracetamol 1 g orally every 6 hours as needed for up to 5 to 7 days (maximum 4 g daily; 3 g daily when weight is under 50 kg, with chronic alcohol use or hepatic impairment).
• Neuropathic pain (a minority have pain): gabapentin 300 mg orally at night, increased by 300 mg every 1 to 3 days to 300 to 600 mg three times daily (maximum 1800 mg daily; reduce at creatinine clearance under 60 mL/min); monitor sedation and dizziness. Pain does not reflect the severity of destruction.
• Avoid NSAIDs in patients with diabetic kidney disease.

Monitoring. Skin temperature of both feet at each visit (every 1 to 4 weeks in the active phase). Radiographs every 4 to 8 weeks until consolidation, then every 3 to 6 months. HbA1c every 3 months. Daily foot inspection by the patient, and ulcer surveillance every 1 to 3 months for life. Footwear review every 3 to 6 months. The contralateral foot is at high risk (up to 30%).

Referral and escalation. Refer any suspected acute Charcot foot to a multidisciplinary diabetic foot service within 24 hours. Emergency referral for a foot ulcer with spreading infection, abscess, gangrene, critical ischaemia or sepsis.

Special groups.

• Diabetes: the main group; lifelong foot protection and glucose control.
• Syringomyelia and spinal cord injury: shoulder and spine joints are affected as well.
• Obese patients: higher failure rates of casting and reconstruction; need stronger fixation.
• Kidney impairment: avoid NSAIDs, adjust antibiotics, and reduce gabapentin.