The Biomechanical Evaluation of Revision First Metatarsophalangeal Arthrodesis

Abstract

Category: Midfoot/Forefoot Introduction/Purpose: First metatarsophalangeal (MP) arthrodesis in the setting of bone loss is a difficult problem. Bone loss may compromise stability of implant fixation. Union rates may be adversely affected by these circumstances. The primary goals of this cadaveric, biomechanical study were as follows: 1) To investigate stiffness of a dual mini-plate construct versus a standard MP arthrodesis plate in the setting of severe bone loss, 2) To evaluate arthrodesis interface motion when an interpositional graft is used. Methods: Twelve matched pairs of fresh, frozen cadaveric foot/ankle specimens were utilized in this study. Pairs were randomized to fixation constructs via computerized randomization (Excel, Microsoft, WA). Within a matched pair one construct used the dual mini plate fixation technique while the other was secured with a standard MP arthrodesis plate. (Fig 1) A revision MP fusion construct with structural bone graft was simulated on six of the specimen pairs, while the remaining constructs did not utilize any interpositional graft. Results: Based on load to failure data, there were no differences between the various constructs in terms of stiffness. There was a high degree of calculated plantar gapping with the placement of a bone block, irrespective of the fixation type. In the presence of an interpositional graft, regardless of plating construct, the calculated proximal interface strain was an average of 26%. Subsequently, failure was most commonly seen at the proximal interface of the interpositional graft group (83%, 10 out of 12). Distal interface strain in the interpositional graft group was calculated to be 11%. The proximal interface strain was significantly larger than the distal interface strain (26% vs 11%) (p < 0.05). Conclusion: Although no construct differences were observed in terms of stiffness, the dual mini-plate is an alternative option for fixation when asymmetric bone loss is either seen on the phalangeal or metatarsal head side. The high degree of plantar gapping of the proximal interface with the placement of the bone block may have implications for healing potential across the arthrodesis site.