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Deep Transverse Metatarsal Ligament and Static Stability of Lesser Metatarsophalangeal Joints

Background: The static support that guides motion around the lesser metatarsophalangeal joints (MTPJs) is complex. Biomechanical studies revealed important roles of both the plantar plane and collateral ligaments. Since part of the plantar plate is attached to the deep transverse metatarsal ligament (DTML), we hypothesized that the transection of the DTML in the intermetatarsal space may substantially reduce the MTPJ stability. Methods: The second, third, and fourth MTPJ stabilities of 6 fresh-frozen human cadaveric foot specimens were measured under load control. Both dorsiflexion and dorsal subluxation conditions were tested. After the intact condition was assessed, the DTML was sequentially transected such that each MTPJ had a unilateral and then a bilateral DTML transection. Stiffness data were calculated using the loading range in each test condition. Paired Student t tests were performed to test for statistical significance (P value less than .05). Results: In intact specimens, the mean stiffness with dorsiflexion of the second, third, and fourth toes was 0.52 ± 0.15 N/deg. When the DTML was operatively transected on one side, the dorsiflexion stiffness significantly decreased 17.3% to an average of 0.43 ± 1.00 N/deg (P < .001). Subsequent transection of the DTML on the other side of each joint resulted in a further significant decrease of 5.8% to an average of 0.40 ± 0.08 N/deg (P < .001). The mean stiffness with dorsal subluxation of the intact second, third, and fourth toes was 3.55 ± 0.66 N/mm. When the DTML was operatively transected on one side, the dorsal subluxation stiffness significantly decreased 16.1% to an average of 2.98 ± 0.64 N/mm (P < .001). Subsequent transection of the DTML on the other side of each joint resulted in a further significance decrease of 7.6% to an average of 2.71 ± 0.48 N/mm (P = .016). Conclusion: The DTML has a significant role in maintaining lesser MTPJ ligament stability. Both unilateral and bilateral DTML transections caused substantial instability of the lesser MTPJ. Clinical Relevance: The DTML is part of the natural static restraint to dorsiflexion or dorsal subluxation of the lesser MTPJ. Operative transection, injury, or degeneration of this ligament may predispose the adjacent MTPJ to instability.