• S K Lee, Y H Kim, K H Moon, and W S Choy.
• Department of Orthopedic Surgery, Eulji University College of Medicine, 1306, Dunsan-dong, Seo-gu, 35233 Daejeon, Republic of Korea. Electronic address: sklee@eulji.ac.kr.
• Orthop Traumatol Sur. 2018 Feb 1; 104 (1): 127-132.

IntroductionExtension-block pinning represents a simple and reliable surgical technique. Although this procedure is commonly performed successfully, some patients develop postoperative extension loss. To date, the relationship between extension-block Kirschner wire (K-wire) insertion angle and postoperative extension loss in mallet finger fracture remains unclear.HypothesisWe aimed to clarify this relationship and further evaluate how various operative and non-operative factors affect postoperative extension loss after extension-block pinning for mallet finger fracture.Materials And MethodA retrospective study was conducted to investigate a relationship between extension block K-wire insertion angle and postoperative extension loss. The inclusion criteria were: (1) a dorsal intra-articular fracture fragment involving 30% of the base of the distal phalanx with or without volar subluxation of the distal phalanx; and (2) <3 weeks delay from the injury without treatment. Extension-block K-wire insertion angle and fixation angle of the distal interphalangeal (DIP) joint were assessed using lateral radiograph at immediate postoperative time. Postoperative extension loss was assessed by using lateral radiograph at latest follow-up. Extension-block K-wire insertion angle was defined as the acute angle between extension block K-wire and longitudinal axis of middle phalangeal head. DIP joint fixation angle was defined as the acute angle between the distal phalanx and middle phalanx longitudinal axes.ResultsSeventy-five patients were included. The correlation analysis revealed that extension-block K-wire insertion angle had a negative correlation with postoperative extension loss, whereas fracture size and time to operation had a positive correlation (correlation coefficient for extension block K-wire angle: -0.66, facture size: +0.67, time to operation: +0.60). When stratifying patients in terms of negative and positive fixation angle of the DIP joint, the independent t-test showed that mean postoperative extension loss is -3.67° and +4.54° (DIP joint fixation angles of <0° and ≥0°, respectively, P=0.024). When stratifying patients in terms of extension-block K-wire insertion angle (30°, 30°-40°, >40°), ANOVA showed significantly less postoperative extension loss for higher insertion angles (>40°) than for medium insertion angles (30°-40°). Mean postoperative extension loss difference between higher insertion angle (>40°) and medium insertion angle (30°-40°) was 11° (P=0.002).DiscussionUsing an insertion angle of the extension-block K-wire of 40°-45° and a slightly hyperextended position of the DIP joint may help reducing postoperative extension loss.Level Of EvidenceTherapeutic level III.Copyright © 2017 Elsevier Masson SAS. All rights reserved.

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