Extensor mechanism slide for the treatment of proximal interphalangeal joint extension lag: an anatomic study.

PURPOSE: We describe a technique for correction of proximal interphalangeal joint (PIP) extensor lag secondary to angulation and/or shortening of proximal phalanx fractures.

METHODS

Proximal phalanx fracture malunions with 2.5 mm of shortening, 5.0 mm of shortening, and apex volar angulation of 40 degrees were simulated in 15 cadaver fingers, creating PIP extensor lags. The metacarpophalangeal (MCP) joint was pinned in neutral. Transection of the ulnar and radial sagittal bands, the extensor digitorum communis (EDC) insertion on the MCP joint capsule, and the juncturae tendinae then was performed. The PIP extensor lag before and after each of the earlier-noted releases was recorded. The MCP joint then was freed and MCP hyperextension was recorded. With the MCP joint in neutral position the sagittal bands then were reapproximated with sutures and MCP extension was measured.

RESULTS

The 2.5 mm of axial shortening, 5.0 mm of axial shortening, and 40 degrees of apex volar angulation fracture models produced an average extensor lag of 6.2 degrees , 25.8 degrees , and 42.5 degrees , respectively. Maximal correction of PIP extensor lag required transection of both sagittal bands, EDC insertion on the MCP capsule, and the juncturae tendinae with an average residual extensor lag of -0.8 degrees for the 2.5-mm shortening model, 0.7 degrees for the 5.0-mm shortening model, and 3.2 degrees for the 40 degrees -angulation model. The MCP joint hyperextension increased by 20 degrees to 30 degrees after the releases but decreased to only 1.8 degrees if the sagittal bands were reapproximated to the EDC tendon at their new resting position with the MCP joint in neutral position.

CONCLUSIONS

In the cadaver model the PIP extensor lag can be improved substantially by transection of the sagittal bands, release of the EDC insertion on the MCP capsule, transection of the juncturae tendinae, and reapproximation of the sagittal bands to the EDC tendon.