Metatarsophalangeal Joint Instability as a Basis for Ultrasound Diagnosis of Plantar Plate Rupture: A Cadaveric Study

Research Type: Level 2 - Prospective comparative study, Meta-analysis of Level 2 studies or Level 1 studies with inconsistent results Introduction/Purpose: Plantar plate rupture is a significant contributor to metatarsophalangeal (MTP) joint instability, frequently resulting in forefoot pain and deformity. Accurate and timely diagnosis is essential for appropriate and timely management. Ultrasound is an accessible, no-radiation, and inexpensive imaging modality, however, the findings associated with plantar plate integrity are not well-established. This study aims to evaluate MTP joint instability in cadaveric specimens to identify the ability of ultrasonic markers to identify plantar plate rupture. Methods: In this experimental study, nineteen MTP joints (Including 2nd, 3rd, and 4th MTP) from nine fresh-frozen cadaveric feet were analyzed to evaluate MTP joint stability under controlled conditions. Ultrasound imaging was used to measure MTP joint widening in response to four stages with different axial traction forces (0N, 25N, 50N, and 75N). Measurements were performed in three states of the plantar plate (intact, partially ruptured, and completely ruptured) and two joint positions (neutral and 40-degree dorsiflexion). Changes in MTP joint widening relative to the baseline (0N traction) were compared among the three states, and the percentage increase in joint space was statistically analyzed using ANOVA test with interactions, Tukey HSD as a post-hoc with P< 0.05 as significance threshold. Results: Under neutral MTP position, 25N axial traction force was only statistically significant in the complete rupture plantar plate state with a MTP joint widening of 34% (p < 0.001). With 50 N traction force, MTP joint widening increased 30% in the partial rupture state (p=0.01), and 52% at the complete rupture state (p < 0.001). The same significant trend was observed with 75N. Additionally, dorsiflexion of the MTP joint did not affect joint widening in all plantar plate conditions under ultrasound imaging. Conclusion: This cadaveric study provides valuable insights into the relationship of quantitative ultrasound measurements between increased MTP joint widening under axial tensile forces and the presence of a plantar plate tear. These findings could help develop accurate diagnostic criteria for assessing plantar plate integrity using ultrasound modality. This study suggests that a force of 25 N is necessary to reliably visualize joint widening in the setting of plantar plate injury.