Biomechanical Comparison of Metatarsal Head Designs in First Metatarsophalangeal Joint Arthroplasty

Background: Arthritis of the metatarsophalangeal (MTP) joint is characterized by loss of MTP joint range of motion (ROM) and pain. Joint arthroplasty is one treatment option, and while results can be satisfactory, there is still room for improvement. The aim was to use cadaveric model to compare the sagittal kinematics and articulating contact properties of 4 different first metatarsal head designs of an MTP joint implant. Methods: Six cadaveric feet were each prepared with a single modular first MTP joint total arthroplasty. A standard cyclic load, which induced hallux dorsiflexion, was applied and motion measured from high resolution images. Contact behavior was collected simultaneously using a pressure transducer. Data collected compared the native joint with 4 different reconstructed cases. Each reconstructed joint used a different metatarsal-head-component while reusing the same phalangeal component to compare the 4 alternative metatarsal head designs. Results: All reconstructed joints displayed greater ROM compared with the intact joint. Of the 4 metatarsal head components, the grooved, anatomical design demonstrated the greatest dorsiflexion when compared to the standard design, 31.6 degrees (SD +/- 8.6 degrees), P < .05. All reconstructed joints displayed contact areas lower than the intact (similar to 50%, P < .001). The grooved metatarsal-head-component experienced the least contact force (P < .015), and the eccentric component underwent the greatest contact pressure (P < .05) when compared to the intact case. Conclusions: In this study of a first metatarsophalangeal joint replacement design, ROM was shown to be better for the more anatomically designed metatarsal head, while contact properties did not vary across different designs.