Factors Related to Distal Interphalangeal Joint Extension Loss After Extension Block Pinning of Mallet Finger Fractures.

PURPOSE: To identify factors related to postoperative extension loss when treating mallet finger fractures with extension block pinning.

METHODS: We reviewed 31 consecutive patients with a mallet finger fracture treated with extension block pinning. We measured range of motion of the distal interphalangeal (DIP) joint including extension lag. We investigated the injury mechanism and checked radiographic factors such as DIP joint subluxation, fixation angle, fragment size index, fracture angle, and amount of articular involvement. We performed statistical analyses such as correlation analysis, multiple regression analysis, and independent t test to investigate factors related to postoperative extension loss.

RESULTS: Mean voluntary extension loss at final follow-up was 5° (range, 0° to 20°) and mean active flexion of the DIP joint was 84° (range, 75° to 90°). Sixteen patients had a forceful flexion injury and 15 had a simple blow injury. Fixation angle was not associated with postoperative extension loss. Postoperative extension loss increased significantly in the forceful flexion group compared with that in the simple blow injury group. Fragment size index, fracture angle, and amount of articular involvement decreased significantly in the forceful flexion group compared with that in the simple blow injury group and were negatively linearly correlated with postoperative extension loss. Multiple regression analysis showed that sex and injury mechanism affected postoperative extension loss.

CONCLUSIONS: Sex, injury mechanism, fragment size index, fracture angle, and amount of articular involvement should be considered to anticipate postoperative extension loss even though mallet finger fractures were successfully reduced and healed using extension block pinning.

TYPE OF STUDY/LEVEL OF EVIDENCE: Therapeutic III.