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What is a potential complication of an amputation at the level of the distal interphalangeal joint?
Central slip rupture
Swan neck deformity
Lumbrical plus finger
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A lumbrical plus finger is descibed as paradoxical extension of the IP joints while attempting to flex the fingers. In the case a lumbrical plus finger secondary to a DIP amputation, the PIP will extend upon attempted finger flexion.
The review article by Parkes describes how the lumbricals originate from the FDP. When the FDP is lacerated or amputated, FDP contraction leads to pull on the lumbricals. This leads to shortening of the lateral bands and paraodoxical PIP and DIP extension. (Illustrations A-C). There are several causes of lumbrical plus finger including (1) FDP laceration or rupture distal to the lumbrical origin, (2) amputation of the DIP distal to central slip insertion, and (3) excessively long flexor tendon graft. Treatment consists of lumbrical release at the level of the flexor sheath in the palm, which then prevents paradoxical PIP extension.
Quadrigia may occur when the profundus is advanced of greater than 1 cm in repair. The FDP tendons share a common muscle belly, and distal advancement of one tendon will effect the flexion strength of the adjacent digits.
J Bone Joint Surg Br. 1971 May;53(2):236-9. PMID: 5578219 (Link to Abstract)
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Demonstrates a lumbrical plus after flexor tendon laceration. When the FDP is l...