Radiographic Evaluation of Plantar Plate Injury: An In Vitro Biomechanical Study

Background: The term turf toe has been generally applied to athletic dorsiflexion injuries of the hallux metatarsophalangeal (MTP) joint. Variations in injury patterns coupled with the complexity of the MTP joint makes the diagnosis of more severe injuries challenging and may lead to a failure in recognition of an unstable joint and a subsequently prolonged recovery. Although the proximal migration of one or both sesamoids has been previously identified with a plantar plate disruption, the current study proposes a quantitative grading system based on dorsiflexion stress radiographs, providing a predictable and reproducible test for evaluating the extent of injury to the first MTP joint. Methods: Twenty-four nonpaired fresh-frozen foot/ankle specimens with no history or physical evidence of prior injury were used in this study. The specimens were randomly assigned into 4 cutting groups, and the 4 main distal ligaments of the plantar plate were identified and sectioned. Lateral dorsiflexion fluoroscopic stress images were obtained in the intact state and with each subsequent cut. With each image, measurements from the distal margin of the sesamoids to the most proximal margin of the proximal phalanx were taken. Images were obtained at 45 degrees with both a fibrous loop wrapped around the interphalangeal joint and applying 15 N and also with a manual dorsiflexion stress. Statistical testing performed was a repeated-measures analysis of variance with Tukey post hoc to compare measurements between each group to determine if movement of the sesamoid bones relative to the phalanx quantitatively increased with each structure that was cut. Results: Our results demonstrate a relationship between the number of ligaments injured in the turf toe simulation and an increase in sesamoid phalangeal distance. We found that an increase of 3 mm in the distance from the sesamoids to the proximal phalanx was significant and predictive of a severe injury to the plantar plate. Conclusion: Injuries producing differences of 3 mm or greater from the intact state have a high likelihood of having sustained injury to at least 3 of the 4 ligaments of the plantar plate complex. This study is the first to establish a quantitative grading scale for evaluating turf toe injuries radiographically based on changes in movement of the sesamoids relative to the intact state. Clinical Relevance: In assessing a turf toe injury, historically the evaluation has been qualitative, but our study provides quantifiable data for evaluation of the severity of plantar plate injuries, which may provide guidance to physicians for treatment decisions.