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Findings When comparing the radiographs, there is an interval medial or tibial displacement of the second toe in this patient with an elongated 2nd metatarsal. MRI demonstrates a poorly defined and disrupted plantar plate of the second toe that extends to injury of the capsule/collateral ligaments. The degree of abnormality is greater laterally where an associated soft tissue mass extends into the second intermetatarsal (IM) space. Joint effusion and synovitis are present of the second MTP but with the vast majority of the second MTP cartilage still present.
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Diagnosis: Lesser MTP Joint Instability MTP joint instability typically occurs in middle aged women and involves the second MTP most frequently and less so the third and remainder of the MTP’s. Predisposing factors relate to an elongated metatarsal as well as wearing high heels and shoes with a narrow toe box. The pathology tends to occur in a typical progression with first degeneration and early tearing of the lateral aspect of the plantar plate at its insertion to the proximal phalanx of the toe. This insertion is a conjoined insertion of the plantar plate and lateral collateral ligament. With further injury, there is scarring and contracture of the medial capsule and dynamic stabilizers. This helps render the medial subluxation of the proximal phalanx relative to the metatarsal. With progressive degeneration, there is a complete disruption of the plantar plate that yields a dorsal subluxation/dislocation of the proximal phalanx relative to the metatarsal. As a part of the injury of the lateral structures there can be a marked amount of scarring that will be present about the deep intermetatarsal ligament that can mimic a Morton’s neuroma. However, this scarring tends to be asymmetric relative to the webspace as compared to centered more directly on the webspace in the setting of neuroma. This difference is important as relates to treatment and prognosis for the two different entities. In this situation, a shortening metatarsal osteotomy was performed and can be combined with soft tissue balancing/other osseous procedures deemed necessary or preferred by the treating physician.
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Resources MRI of lesser metatarsophalangeal joint plantar plate tears and associated adjacent interspace lesions.Umans H1, Srinivasan R, Elsinger E, Wilde GE. Skeletal Radiol. 2014 Oct;43(10):1361-8. Lesser Metatarsophalangeal Joint Instability. Leland Y. Tsao. Radsource.us. MTP Dislocations. Jason McKean. orthobullets.com
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