In vivo validation of in vitro testing of hallucal flexor mechanics

Objective. The purpose of this study was to validate an in vitro method of testing first metatarsophalangeal joint mechanics. Design. We compared the orientation of the resultant moment of hallucal plantarflexion in cadaveric specimens undergoing loading of the flexor hallucis longus to the plane of the active great toe plantarflexion moment in normal volunteers. Background. Frontal plane deviation of hallucal plantarflexion is a fundamental component of the altered biomechanics in hallux valgus. Methods. The cadaveric model utilized dynamic loading of the flexor hallucis longus and static loading of the remaining muscles of the great toe. The in vivo method involved measurement of force output with isometric hallucal plantarflexion in the standing position. The medial-lateral and superior-inferior forces as well as the angle of the resultant moment in the clinically relevant frontal plane for both groups were quantified. Results. We found no significant difference between the frontal plane forces of each group. The directional orientations in the frontal plane also displayed a marked similarity, with an average lateral deviation of 0.63 ° (P = 0.99) for each group. Conclusions. The lack of a significant difference between the cadaveric and clinical methods of finding the resultant hallucal moment indicates that the cadaveric method accurately simulates in vivo internal flexor muscular loading of the great toe.