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We read with interest the very rare case report of Lam et al on volar metacarpophalangeal joint dislocation.1
However, the subluxed and locked MCP joint is often confused with a dislocation of the MCP joint. We have seen three similar cases in our department over the past few years.
For example, a 78 year old former miner was referred to us by his general practitioner with a suspected dislocated MCP joint of the left middle finger. He had spontaneously developed pain in the finger two days previously. He was unable to move it. Past medical history included diabetic macular degeneration, myocardial infarction, ruptured aortic aneurysm, and hypertension. He was taking aspirin, nifedipine and glibenclamide.
On examination, the left middle finger was in flexed position at about 40° and he was unable to extend it. There was no swelling. He was unable to flex the MCP joint any further. There was slight movement of the PIP and DIP joint, actively and passively. The PIP and DIP joints were in full extension. Radiographs of the left middle finger showed volar subluxation of the MCP joint, with marginal osteophytes (fig 1). Under an intermetacarpal block with lignocaine (lidocaine) 1%, 2 ml on each side, the MCP joint was relocated with click. The patient was able to move the joint freely after the manipulation. A check radiograph revealed a normal joint space (fig 2). The patient was treated with neighbour strapping and advised to do active exercises after three days. He was reviewed four weeks later, there was a full range of movements of the finger. There was no tenderness and the patient had resumed his gardening.
A locked MCP joint is an unusual entity, characterised by a moderate flexion deformity. It must be differentiated from stenosing flexor tenosynovitis and volar dislocation of the MCP joint. Most commonly, the index and middle fingers are involved because of their prominent metacarpal heads. The condition is generally manifested in one of two ways, degenerative and spontaneous.2 In the former group the patients generally tend to be older and radiographs will, as in this case, usually reveal marginal osteophytes.3 Middle fingers are generally affected. In the spontaneous group, the patients are younger, and the condition tends to affect the index finger with the pathological structure being a very prominent radial condylar margin of the metacarpal head impaling the lateral collateral ligament.2
It is difficult to recognise all these conditions in a busy emergency department, and when in doubt, a trial of gentle manipulation should be tried before referral to the hand surgeon for an operation.4
We note with interest the comments made by Muthu and Fraser-Moodie. They discuss the occurrence of a locked metacarpophalangeal joint that is usually caused by snagging of the collateral ligaments over an adjacent osteophyte in older patients, which is obviously a condition that should be brought to the attention of accident and emergency staff. The main differential diagnosis being a trigger finger.
However, it is an entirely different condition to the one in our case report,1 which is a serious injury and one that is associated with serious and characteristic radiological changes requiring the early input of the hand surgery service.
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