Neuropathic joint disease
Description
- Charcot joint - progressive destructive arthropathy in a joint that has lost PROTECTIVE SENSATION
- *The cardinal paradox: gross destruction with disproportionately little pain*
- Two phases
- ACTIVE (acute) Charcot - hot, red, swollen, oedematous foot; skin temperature typically >2 degrees C warmer than the contralateral side
- CHRONIC (coalescence/reconstruction) - deformity, ROCKER-BOTTOM foot, midfoot collapse, ulceration
- Eichenholtz stages: 0 (inflammation, normal X-ray) -> 1 (fragmentation) -> 2 (coalescence) -> 3 (consolidation/remodelling)
Epidemiology
- *Diabetes is by far the commonest cause in Australia - ~0.1-0.4% of all people with diabetes; ~10-13% of those with established peripheral neuropathy*
- Typically 50-60 years old, with diabetes of >10 years' duration and established neuropathy
- Bilateral in ~10-20%
- Tarsal and tarsometatarsal (midfoot, Lisfranc) joints are the commonest sites in diabetes
- *Misdiagnosed as cellulitis, gout or osteomyelitis in a large proportion at first presentation* - median delay to diagnosis is months
Aetiopathogenesis
Two classical theories, now understood as one process
- Neurotraumatic - loss of protective pain and proprioception -> repetitive unrecognised microtrauma -> fracture and joint subluxation
- Neurovascular - autonomic neuropathy -> arteriovenous shunting -> hyperaemia -> osteoclastic bone resorption -> bone that fractures under normal load
The unifying mechanism
- Trauma or surgery -> local inflammation -> inc TNF-alpha and IL-1 -> inc RANKL -> inc NF-kB -> OSTEOCLAST activation -> bone resorption
- -> further fracture -> more inflammation -> a self-sustaining loop
- *Preserved or increased blood supply is REQUIRED - Charcot does not develop in a critically ischaemic limb*
- Palpable, often bounding, pulses in a hot swollen foot is a diagnostic clue
- Bisphosphonates were used on this rationale - but the evidence is weak and they are not standard therapy
Causes - by site
| Cause | Typical joints |
|---|---|
| *Diabetes mellitus* | Tarsal and tarsometatarsal (midfoot), ankle |
| Tabes dorsalis (tertiary syphilis) | Knee, hip, lumbar spine |
| Syringomyelia | *SHOULDER, elbow, cervical spine (upper limb Charcot is syringomyelia until proven otherwise*) |
| Leprosy | Foot, hand |
| Hereditary sensory and autonomic neuropathy, amyloid, CMT | Foot, ankle |
| Spinal cord injury, myelomeningocele | Below the level of the lesion |
| Chronic alcohol use, B12 deficiency, chemotherapy neuropathy | Foot |
| Repeated intra-articular corticosteroid injection | The injected joint |
Diagnosis
Clinical
- *Suspect active Charcot in ANY person with neuropathy and a hot, swollen foot*
- Unilateral warmth, erythema, swelling - erythema that resolves on elevating the limb for 5-10 minutes suggests Charcot; cellulitis does not blanch
- Pain is absent or disproportionately mild - but ~50% report some discomfort; painlessness is not required
- Bounding pulses, distended dorsal veins (hyperaemia)
- Absent ankle jerks, absent 10 g monofilament and vibration sense
- Deformity: midfoot collapse, rocker-bottom sole, medial convexity, ankle instability
- Joint effusion, crepitus, gross instability with a remarkably comfortable patient
Imaging
- *X-ray is NORMAL in Eichenholtz stage 0 - a normal film does not exclude it*
- X-ray (later): the "6 Ds" - Destruction, Debris, Disorganisation, Dislocation, Density increase (sclerosis), Distension
- Fragmentation, subluxation, periarticular new bone, joint disorganisation out of proportion to symptoms
- *MRI is the investigation of choice - bone marrow oedema and microfracture in stage 0*, and the best test to separate Charcot from osteomyelitis
Charcot vs osteomyelitis - the central difficulty
| Charcot | Osteomyelitis | |
|---|---|---|
| Skin | *Intact* | Ulcer, usually overlying the affected bone |
| Probe-to-bone | Negative | *Positive - strongly suggests osteomyelitis* |
| Distribution | Multiple bones, midfoot, periarticular | Single bone, usually a pressure point (forefoot, heel, malleolus) |
| MRI | Subchondral/periarticular oedema, joint-centred, deformity | Bone-centred, with a sinus tract, cortical destruction, adjacent ulcer |
| CRP/ESR | Normal or mildly raised | Often markedly raised |
| Systemic features | Absent | Fever, leucocytosis |
| Nuclear medicine | Bone scan positive in both | Labelled WCC scan or WCC-SPECT/CT favours infection |
- *The two coexist* - a Charcot foot that ulcerates can become infected
- Bone biopsy/culture is the definitive answer where the distinction changes management
Other investigations
- HbA1c, UEC, FBE, CRP/ESR
- B12, syphilis serology (if upper limb or knee/hip), MRI cervical spine for SYRINGOMYELIA if a shoulder or elbow is affected
- Vascular assessment (ABI, toe pressures, duplex) - heavily calcified vessels make the ABI falsely high in diabetes
Management
1. OFFLOADING AND IMMOBILISATION - the treatment
- *The single intervention that alters outcome; start on clinical suspicion, before imaging confirms it*
- Total contact cast (non-removable), changed 1-2 weekly initially (swelling reduces quickly, so the cast loosens)
- Then a removable walker / Charcot restraint orthotic walker (CROW) as the foot consolidates
- Non-weight-bearing or strictly protected weight-bearing on the affected limb
- *Protect the CONTRALATERAL foot* - it now takes all the load and is at high risk
- Duration: typically 3-6 months, often longer
- Endpoint: clinical and radiological resolution - skin temperature difference <2 degrees C, resolution of oedema, and radiographic consolidation
- Transition gradually to bespoke footwear and orthoses; return to unprotected walking too early causes relapse
2. Multidisciplinary care
- High-risk foot service: endocrinology, podiatry, orthotics, vascular and orthopaedic surgery, wound care
- Glycaemic optimisation, smoking cessation, vascular assessment
- Ulcer prevention and treatment - the ulcer, not the deformity, is what leads to amputation
3. Drugs - limited role
- Bisphosphonates, calcitonin, denosumab - used on the RANKL rationale, but evidence is weak; not routine
- Analgesia; treat the neuropathic pain if present (amitriptyline, duloxetine, pregabalin)
- Antibiotics only for proven infection - not for the inflammation of active Charcot
4. Surgery - avoided where possible
- *Corrective osteotomy and arthrodesis heal poorly in a neuropathic joint* - non-union, hardware failure and infection rates are high
- Reserve surgery for:
- Unstable deformity that cannot be braced
- Recurrent or non-healing ulceration over a bony prominence (exostectomy)
- Established osteomyelitis
- Impending or actual joint dislocation
- Achilles tendon lengthening may reduce forefoot pressure
- Operate in the consolidated (quiescent) phase where possible, not during active fragmentation
5. Prevention and follow-up
- Annual foot screening in everyone with diabetes; 3-6 monthly in those with neuropathy
- Patient education: daily foot inspection, never walk barefoot, check footwear
- *Lifelong protective footwear and podiatry review* - recurrence rates are high
Associations
- Diabetic peripheral and autonomic neuropathy, retinopathy and nephropathy (Charcot marks advanced microvascular disease)
- Diabetic foot ulceration and osteomyelitis
- Syringomyelia - upper limb Charcot
- Tabes dorsalis (tertiary syphilis) - knee, hip, spine
- Leprosy, hereditary sensory and autonomic neuropathy, Charcot-Marie-Tooth, amyloid neuropathy
- Spinal cord injury, myelomeningocele, spina bifida
- Alcohol-related and B12 deficiency neuropathy, chemotherapy-induced neuropathy
- Renal transplantation and CKD in diabetes - a recognised risk period
- Repeated intra-articular corticosteroid injection
Natural history & complications
- Active phase burns out over 6-12 months into a deformed but stable foot
- *The deformity is permanent - the goal of treatment is a plantigrade, braceable, ULCER-FREE foot*, not a normal one
- Recurrence in ~20-30%, either in the same foot or the contralateral one
- Ulceration in ~35-50% of chronic Charcot feet -> infection -> amputation
- Major amputation rate ~10-15%
- *Mortality is high - ~25-30% at 5 years - reflecting the advanced diabetic disease it signals, not the foot itself*
- Early diagnosis and early offloading are the only factors that reliably improve outcome - hence: a hot swollen foot in a neuropathic patient is a Charcot foot until proven otherwise
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