Review Question - QID 217355

Apex volar malunion of a proximal phalanx fracture results in extensor lag of the proximal interphalangeal joint.

Transverse proximal phalangeal fractures deform secondary to the central slip and lumbrical insertions. The central slip inserts distally on the distal fragment pulling it into extension, while the lumbrical insertions flex the proximal fragment resulting in overall apex volar angulation of the fracture. If this is not corrected and maintained through conservative or operative means, apex volar malunion is common with these fractures. Extension through the fracture effectively shortens the dorsal cortex compared to the extensor tendon resulting in loss of extension at the proximal interphalangeal joint. Sagittal deformity of 15 degrees results in 12 degrees of extensor lag per millimeter shortening.

Gajendran et al. wrote a comprehensive review on the management of complications from hand fractures. They describe malunions of phalangeal fractures and their effect on the range of motion. Specifically, they cite a 15-degree apex volar malunion results in a 12-degree extensor lag per millimeter. Malunions greater than 25 degrees will affect both flexion and extension. Treatment should be corrective osteotomies at the level of the fracture. Historically union rates are excellent, while rates of tendon adhesions and joint contractures are high.

Vahey et al. published a cadaveric biomechanical study investigating malunion on extensor tendon function in the proximal phalanx. They found a linear relationship between proximal phalangeal shortening and extensor lag. A similar linear relationship was found between the lengthening of the extensor tendon and the resulting extensor lag. Their calculations demonstrated a 12 degree lag per 1 mm of phalanx shortening.

Figure A demonstrates AP and oblique Xrays of the index finger with a transverse fracture of the base of the proximal phalanx with apex volar angulation. Figure B demonstrates a lateral fluoroscopic image of the index finger proximal phalanx with an apex volar malunion.

Illustration A shows the corrective osteotomy to the malunion in Figure B with percutaneous fixation with Kirschner wires.

Incorrect Answers:
Answer 1&2: Malunion of the proximal phalanx would affect the proximal interphalangeal joint.
Answer 3: Apex volar angulation less than 15-degrees results in loss of extension, not flexion. Once the angulation is greater than 25-degrees, both flexion and extension are affected.
Answer 5: There is no evidence of rotational malunion of the fracture which would result in cross-over of his fingers.