Supplementary axial Kirschner wire fixation for crescentic and Ludloff proximal metatarsal osteotomies: a biomechanical study

BACKGROUND: Loss of reduction of proximal metatarsal osteotomies may result from poor bone quality, suboptimal fixation, and limitations inherent in the bony geometry of the osteotomy. This study evaluated the mechanical benefit of adding two supplementary Kirschner wires to the crescentic and Ludloff osteotomies. METHODS: Eleven and 10 matched pairs of cadaver foot specimens were used for the Ludloff and the proximal crescentic metatarsal osteotomies, respectively. Each metatarsal head specimen was then loaded to failure using a servohydraulic MTS Mini Bionix test frame (MTS Systems Corp, Eden Prairie, MN), and the failure gap was measured with an extensometer. To account for variable bone quality in the study specimens, the failure loads were normalized with the measured bone mineral density (BMD) values of the metatarsal specimens. A paired Student's t-test analysis was used to compare the failure loads between the specimens with the conventional osteotomies and the osteotomies supplemented with two axial Kirschner wires. RESULTS: The load-to-failure of the Ludloff osteotomy with two screws and with one proximal screw and two Kirschner wires was 858.5 N cm(2)/gm and 692.3 N cm(2)/gm, respectively (p > 0.05). The average load-to-failure of crescentic osteotomy with one screw and two axial Kirschner wires (458.8 N cm(2)/gm) was significantly higher than the strength of crescentic osteotomy fixed with one screw only (367.5 N cm(2)/gm) (p = 0.05). For the Ludloff osteotomy, 16 specimens (72.7%) failed by more than 2 mm of gapping. The crescentic osteotomy failures included 16 2-mm gap failures (80%). The Ludloff osteotomy showed a trend toward increased fixation stability as compared with both crescentic osteotomy constructs. CONCLUSION: The use of two supplemental axial Kirschner wires offers a simple and effective means to improve the initial mechanical stability of the proximal crescentic osteotomy and can be used in the standard Ludloff osteotomy to replace the second screw when screw purchase is poor without significant loss of fixation strength. The possible advantage of Kirschner wire flexibility in restoring position after gapping of the osteotomy site should be investigated.