Assessing Axial Instability of Bennett Fractures and Direct Comparison of Two K-wire Fixation Constructs: A Paired Cadaveric Biomechanical Analysis.

Abstract

There is no clear consensus regarding optimal surgical management of Bennett fractures of the thumb carpometacarpal joint. We aimed to assess the initial displacement of such fractures and directly compare the stability of 2 different Kirschner-wire (K-wire) fixation constructs, hypothesizing that both constructs would confer substantial stability and that a pin crossing the fracture site would be more resistant to subsidence at the joint than suspensory fixation alone. Bennett fractures were recreated using a sagittal saw in 8 paired fresh-frozen cadaveric specimens. Axial subsidence was then measured under a 100 N load of applied force. Specimens were then assigned to one of two 0.064" K-wire fixation methods: (1) an intermetacarpal suspensory method with 2 parallel K-wires between the diaphyses of the first and second metacarpals; and (2) an interfragmentary pin directly spanning the fracture site at the base of the first metacarpal with a second suspensory intermetacarpal pin. Specimens were then tested with cyclic loading to 25 N, 50 N, and 100 N. Axial subsidence between the two fragments was measured followed by paired statistical analysis. The average axial subsidence of the fractures prior to fixation was 3.1 mm. There was less subsidence for the fracture-spanning fixation at 25 N and 50 N compared to suspensory fixation (<i>P</i> = .0156 and <i>P</i> = .0078, respectively) but no difference at 100 N (<i>P</i> = .37). Bennett fractures without fixation demonstrate clinically significant step off greater than 2 mm indicating a benefit from operative fixation. Both percutaneous K-wire fixation methods conferred acceptable stability, with interfragmentary fixation providing increased stability at lower loads.