Or Boxer’s Knuckle. This is a rupture of the sagittal band of the MCPJ joint, most commonly of the middle finger.
This shouldn’t be confused with boxer’s fracture.
It is not a common presentation in my experience but certainly not unheard of.
Typical injury is from a fist strike onto a solid surface such as a punch bag, or due chronic inflammatory process such as rheumatoid arthritis. Pt might report some sensation of tearing around the knuckle region.
It may or may not present with swelling to MCPJ region, usually swelling is relatively slow in developing (overnight say). If there isn’t excess swelling, especially if the patient presents promptly, it may be possible to see the extensor tendon subluxing over the head of metacarpal. You can see it really well demonstrated in this tweet.
Patients generally report the sensation of this subluxing, and may well have observed (or even videoed) it prior to the swelling developing.
It is generally tender over the dorsal MCPJ.
Other than this there may or may not be some extensor lag at the MCPJ, and pain and poor resistance in extension.
X-Ray is recommended to rule out associated fracture or joint deterioration.
Treatment
Recommended treatment is in a yoke orthosis in order to limit flexion at the MCPJ. Although we don’t keep these, or formable splinting material, I have had some success in crafting one from Zimmer splint. The position and process is demonstrated in the video below.
Usual self-care and precautionary advice should be given to the patient.
Referral and prognosis
Closed injuries can be referred to face to face fracture clinic. Splinting time is around 6 weeks.
Open injuries should be referred for on call opinion (hands).
You can advise the patient that acute closed tears are usually managed conservatively.
Chronic, open, and in elite sports or other professional considerations are usually managed surgically.
