The Biomechanical Evaluation of Revision First Metatarsophalangeal Arthrodesis: A Cadaveric Study.

Background: 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 to (1) investigate stiffness of a dual mini-plate construct versus a standard MP arthrodesis plate in the setting of severe bone loss and (2) evaluate arthrodesis interface motion when an interpositional graft is used.

Methods: Twelve matched cadaveric samples were used in this study. In a given pair, both dual mini-plate fixation and standard MP arthrodesis plate were used. Interpositional graft was used in 6 of the specimen pairs. After implantation, soft tissues were dissected away and specimens were placed into a cantilever bending setup. A cantilever load was applied at a rate of 6 mm/min until catastrophic failure of the test construct or 5-mm plantar gapping of either bone block interface.

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.

Conclusions: 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.

Clinical Relevance: This is the first biomechanical study investigating the stiffness of multiple constructs for MP arthrodesis in the setting of severe bone loss. Furthermore, this is the first study to introduce a biomechanical rationale for difficulties in healing for this particular clinical scenario.

Levels Of Evidence: Level V: Bench testing.