Locked versus nonlocked plate fixation for first metatarsophalangeal arthrodesis: a biomechanical investigation.

BACKGROUND: First metatarsophalangeal (MTP) arthrodesis using dorsal plate fixation is a common procedure for painful conditions of the great toe. Locked plates have become increasingly common for arthrodesis procedures in the foot, including the hallux MTP joint. The biomechanical advantages and disadvantages of these plates are currently unknown. The purpose of this study was to compare locked and nonlocked plates used for first MTP fusion for strength and stiffness.

MATERIALS AND METHODS: The first ray of nine matched pairs of fresh-frozen cadaveric feet underwent dissection, preparation with cup-and-cone reamers, and fixation of the MTP joint with a compression screw and either a nonlocked or locked stainless steel dorsal plate. Each specimen was loaded in a cantilever fashion to 90 N at a rate of 3 Hz for a total of 250,000 cycles. The amount of plantar MTP gap was recorded using a calibrated extensometer. Load-to-failure testing was performed for all specimens that endured the entire cyclical loading. Stiffness was calculated from the final load-to-failure test.

RESULTS: The locked plate group demonstrated significantly less plantar gapping during fatigue endurance testing from cycle 10,000 through 250,000 (p < .05). Mean stiffness was significantly greater in the locked plate group compared with the nonlocked plate group (p = .02). There was no significant difference in load to failure between the two groups (p = .27).

CONCLUSION: Compared with nonlocked plates, locked hallux MTP arthrodesis plates exhibited significantly less plantar gapping after 10,000 cycles of fatigue endurance testing and significantly greater stiffness in load-to-failure testing.

CLINICAL RELEVANCE: As the use of locked plate technology is becoming increasingly common for applications in the foot, a thorough understanding of the biomechanical characteristics of these implants may help optimize their indications and clinical use.