Peritalar Kinematic Changes Associated with Increased Spring Ligament Tear in Cadaveric Flatfoot Model

Category: Hindfoot Introduction/Purpose: Adult Acquired Flatfoot Deformity (AAFD) is a complex and progressive deformity characterized by abduction of the midfoot and valgus alignment of the hindfoot. Spring ligament tear is often present in advanced stages of the AAFD. Previous anatomic studies have demonstrated that the superficial deltoid ligament blends with the superomedial spring ligament to provide both medial tibiotalar and talonavicular stability aiding in coronal plane stability. Given that the spring ligament blends with the superficial deltoid ligament, we sought to investigate the kinematic effect of spring ligament tear in development of peritalar instability in cadaveric flatfoot model. We hypothesized that increased spring ligament tear size will result in increased talonavicular joint abduction (axial) and plantarflexion (sagittal), and increased valgus alignment of the tibiotalar and subtalar joints (coronal). Methods: Seven fresh-frozen cadaveric foot specimens were employed. Reflective markers were mounted on the tibia, talus, navicula, calcaneus and the first metatarsus. Kinematics of the peritalar joints were captured by multiple camera motion capture system. A flatfoot model was created by sectioning the medial and inferior talonavicular interosseous ligament, followed by cyclic axial load of 1150 N under a hydraulic loading frame with 350 N load applied to the Achilles tendon. The talo-first metatarsus (T- 1MT) abduction angle was calculated and cycles were applied until abduction of 5-10° (mild flatfoot) was achieved. Spring ligament sectioning was extended 1 cm proximally along the superomedial ligament followed by cyclic loading until 10-15° (moderate) of T- 1MT abduction was achieved. The spring ligament was sectioned for another 1 cm followed by cyclic loading until >15° (severe) abduction was noted. The relative kinematic changes were compared among the initial, mild, moderate, and severe flatfoot model using two-way ANOVA. Results: The average T-1MT abduction angles in the mild, moderate, and severe flatfoot were 7.79°+/-2.27°, 11.47°+/-2.82°, and 15.46°+4.15°. Meary’s angle increased with progression of the flatfoot (mild 6.17°+/-2.92°, moderate 9.71°+/-3.4°, severe 12.46°+/-4.13°). Hindfoot valgus angle also increased. The mild, moderate, and severe flatfoot showed 2.4°+/-3.85°, 4.13°+/-3.9°, and 4.75°+/-3.79° of tibiotalar valgus angle. The subtalar joint exhibited 2.94°+/-3.41°, 5.52°+/-4.34°, and 6.97°+/-4.83° valgus angle in the mild, moderate, and severe models. The T-1MT abduction angle and Meary’s angle were significantly different in all flatfoot models compared to the initial condition (p