Charcot (Neuropathic) Arthropathy of the Shoulder

The painless destroyed shoulder. The defining feature of a Charcot shoulder is destruction out of proportion to pain. The joint is hot, grossly swollen and disorganised, often unstable, yet relatively painless, because the underlying problem is loss of protective sensation and proprioception.

Why the joint breaks down. Two theories are combined. The neurotraumatic theory holds that loss of protective sensation allows repetitive, unperceived microtrauma and progressive destruction; the neurovascular theory adds autonomic dysregulation that increases blood flow and bone resorption. Together they produce fragmentation, resorption and disorganisation of the joint.

The cause. Syringomyelia is the leading cause of an upper-limb neuropathic joint, at the elbow and the shoulder. A painless destroyed shoulder should therefore prompt MRI of the cervical spinal cord to find a syrinx, which is often associated with a Chiari malformation.

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Let the joint point to the cause. Syringomyelia is the classic upper-limb cause, but the joint distribution usually points to the underlying neurological disease. A destroyed shoulder or elbow is syringomyelia until proven otherwise.

Each of these is developed separately in syringomyelia, Chiari malformation, Charcot neuroarthropathy, diabetic neuropathy, spinal cord injury, myelomeningocele, hereditary motor and sensory neuropathies and, for the elbow, Charcot neuropathic joint of the elbow.

The bedside sign that makes the diagnosis is the sensory pattern, not the joint. A cervical syrinx expands first through the crossing spinothalamic fibres in the anterior commissure, so it produces dissociated sensory loss: pain and temperature sensation are lost while light touch, vibration and proprioception are preserved. The loss lies over the shoulders and upper trunk in the classic "cape" or "shawl" distribution.

The rest of the neurological examination. Look for wasting and weakness of the small muscles of the hand (anterior horn involvement) and for lost upper-limb reflexes. A patient who cannot feel a pinprick over the shoulder but can feel light touch there has declared the cause of their destroyed joint.

Radiographs. The humeral head is resorbed and fragmented, with bony debris, in a disorganised 'bag of bones', and the shoulder is often grossly swollen with effusion. Classic teaching summarises the changes as the 6 Ds.

Atrophic versus hypertrophic. Charcot joints take two radiographic forms, and the limb predicts which. The upper limb, and syringomyelic joints in particular, tend to the atrophic pattern: pure osteolysis and resorption of the humeral head with little new bone, so the head appears to dissolve or be "licked" away. The hypertrophic pattern, with exuberant sclerosis, osteophyte and periosteal new bone and the full 6 Ds, is more characteristic of the weight-bearing lower limb, as in the diabetic Charcot foot. At the shoulder, expect resorption and do not be reassured by the absence of florid new bone.

Exclude the dangerous mimics first. The grossly swollen, destroyed, fluid-filled shoulder can look like a tumour (an expansile mass) or infection (septic arthritis or osteomyelitis). Image appropriately and, when there is doubt, aspirate and/or biopsy before attributing the destruction to neuropathy.

Infection can coexist with a neuropathic joint rather than merely mimic it. A raised inflammatory response therefore does not exclude the diagnosis, and it does not excuse skipping the aspirate.

Milwaukee shoulder is the other destroyed shoulder to know: a rapidly destructive cuff-tear arthropathy driven by basic calcium phosphate crystals, in an elderly patient with a large effusion and a massive cuff tear. It is distinguished by the absence of a neurological deficit and by pain that fits the destruction, where the Charcot shoulder is painless out of proportion. It is developed in the Milwaukee Shoulder and Rotator Cuff Arthropathy topics.

Find and treat the cause. The cervical-cord MRI looks for the syrinx, and neurosurgical decompression may be indicated for a progressive one.

Support the joint. Joint care is largely supportive and is the default: protect the joint, modify activity, manage symptoms and maintain function, with a role for bracing.

Why surgery fails. The 'bag of bones' gives poor bone stock for fixation or fusion. More important, the neuropathy persists, so protective sensation is still absent and continued unperceived loading drives recurrent destruction, implant loosening and non-union. Rates of infection and instability are high, and the painless instability is often surprisingly well tolerated.

When surgery is considered. Surgery is selective and unreliable, with high complication and failure rates. It is considered for intractable pain, gross instability or functional loss, and is best undertaken only after the neurological process has been addressed and is quiescent, within a multidisciplinary team. The options all carry guarded outcomes and high complication rates:

• Resection arthroplasty
• Arthrodesis - technically difficult, with a high non-union rate in the neuropathic joint
• Arthroplasty - reserved for carefully selected cases, typically a constrained or reverse total shoulder replacement for the unstable, often cuff-deficient neuropathic shoulder

Counselling. The aim is function and symptom control, and the patient should not expect a normal joint. The procedures themselves are developed in the Shoulder Arthrodesis and Reverse Total Shoulder Arthroplasty topics.