Define Charcot (Neuropathic) Joint. Describe its causes and investigations.
Definition
A Charcot (neuropathic) joint is a progressive, destructive arthropathy occurring in a joint that has lost its protective pain and proprioceptive sensation. Repeated unperceived trauma to the insensate joint leads to gross destruction, disorganisation and instability that is characteristically painless or far less painful than the appearance suggests.
Causes
Any condition causing sensory neuropathy: diabetes mellitus (now the commonest cause, typically the foot/ankle), tabes dorsalis (syphilis — classically the knee/hip), syringomyelia (shoulder/upper limb), leprosy, and peripheral neuropathies.
CLINICAL PEARL
The clinical paradox is a grossly destroyed, swollen, unstable joint that is relatively painless — the mismatch between the dramatic radiograph and the modest symptoms is the clue to a neuropathic joint.
Features & Management
The joint is swollen, warm, unstable and deformed, with abnormal mobility and effusion; radiographs show the ‘5 Ds’ — joint Destruction, Density increase (sclerosis), Debris (loose bodies), joint Disorganisation and Dislocation. Management centres on treating the underlying neuropathy, protecting the joint (offloading, total-contact casting and bracing for the diabetic foot to prevent ulceration), and surgery (arthrodesis or reconstruction) only in selected cases, as results are compromised by the neuropathy.
Investigations
Radiographs show the florid destruction, sclerosis, fragmentation and disorganisation described by the ‘͟5 Ds’, often with large effusions and heterotopic bone. Because a neuropathic joint can be complicated by, or mistaken for, infection (particularly in the diabetic foot), distinguishing Charcot change from osteomyelitis is a common and important challenge, aided by MRI and sometimes labelled-white-cell studies. Investigation of the underlying neuropathy (blood glucose, syphilis serology, MRI of the cord for syringomyelia) is essential.
DANGER / REMEMBER
In the diabetic foot, an acute red, warm, swollen Charcot foot is frequently misdiagnosed as cellulitis or infection. Offloading and protecting the foot early prevents the collapse and ulceration that lead to amputation.
Destruction is grossly out of proportion to the pain felt.
KEY POINT
Key points TO remember
- Destructive arthropathy in a joint that has lost pain/proprioception.
- Causes: diabetes (commonest, foot), tabes dorsalis (knee), syringomyelia (shoulder).
- Paradox: gross destruction but relatively painless; X-ray ‘5 Ds’.
- Treat the neuropathy + protect/offload the joint; surgery selectively.
EXAM TIP
Sources: Maheshwari's Essential Orthopaedics; Apley & Solomon's System of Orthopaedics and Trauma; AO Principles of Fracture Management.
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