Biomechanical comparative study of the JuggerKnotTM soft anchor technique with other common mallet finger fracture fixationtechniques

Abstract

Introduction

Mallet finger is a common injury involving either an extensor tendon rupture at its insertion or an avulsion fracture involving the insertion of the terminal extensor tendon. It is usually caused by a forceful blow to the tip of the finger causing sudden flexion or a hyperextension injury. Fracture at the dorsal aspect of the base of the distal phalanx is commonly associated with palmar subluxation of the distal phalanx. Most mallet finger injuries are recommended to be treated with immobilization of the distal interphalangeal joint in extension by splints. However, surgical fixation is still indicated in certain conditions such as open injuries, avulsion fracture involving at least one third of the articular surface with or without palmar subluxation of the distal phalanx and also failed splinting treatment. This study was designed to identify the strongest peak load resistance among four mallet finger fracture fixation methods, namely Kirschner wire fixation, pull-out wire fixation, tension-band wire fixation and the JuggerKnot? (Biomet) soft anchor fixation and to assess the role of the JuggerKnot? technique in mallet finger fixation.

Materials and method

Four different fixation techniques were assigned among twenty-four specimens (all fingers, no thumbs) from six cadaveric human hands in a randomized block fashion. Only one technique was performed on each finger. A downward load was applied to flex the distal phalanx and the maximum loading force was recorded. The load was tested at 30 degrees, 45 degrees and 60 degrees of flexion of the distal interphalangeal joint. Two separate data sets were performed for each finger before and after the osteotomy and fixation. The data underwent Shapiro-Wilk normality testing before analysis. The values of the mean peak load of the four groups were compared using the one-way analysis of variance test in SPSS version 19.0.

Result

All data points passed the Shapiro-Wilk test for normality. The mean peak load of the tension-band wiring group was 67.8N at 60 degrees of flexion which was significantly higher than the other three groups (p=0.008). The JuggerKnot? fixation had mean peak loads of 13.35N (30°), 22.51N (45°) and 32.96N (60°) which were all above the required load for mobilization. No complications of implant failure or fragmentation of the dorsal fragment was noted.

Discussion

The tension-band wire fixation was the strongest fixation method among the four. However it was cumbersome and it had the most soft tissue trauma among the four. No major difficulty was encountered during the testing. No fragmentation of the dorsal fragment was encountered during the procedures. The JuggerKnot? soft anchor fixation was a simple and easy technique and did not require trans-articular Kirschner wire fixation for protection. It could reduce and immobilize a grossly displaced dorsal fragment easily and allowed for safe immediate mobilization of the joint after operation as indicated by the peak load results. This fixation technique was a viable option for treating mallet finger injuries with a dorsal bony fragment size at least one-third of the articular surface with or without palmar subluxation of the distal phalanx.