Unstable metatarsal-phalangeal joints (MTPJ): what went wrong? A description of a novel technique to stabilize it

F. Alam, G. Chami, T. Drew

Introduction: MTPJ instability is very common yet there is no consensus of best surgical technique to repair it. The current techniques range from extensive release, K-wire fixation or plantar plate repair, which requires release of remaining intact plantar plate and all collaterals. Such varieties reflect a controversy regarding its aetiology. The aim of this study was to assess how much each structure contributes towards the stability of MTPJ and describing a simple technique designed by the senior author that can anatomically reconstruct all contributing structures to the pathology.

Methods: Eleven cadaveric toes in two groups (five in group 1 and six in group 2) were included. Dorsal displacement (drawer test) was used to measure instability in an intact MTPJ followed by two different series of sequential sectioning of each part of collateral ligament (PCL and ACL) and part or complete plantar plate.

Results: Group 1 result showed that after incising PCL dorsal displacement was 0.51mm, PCL+ACL was 0.8mm and PCL+ACL+50% plantar plate was 2.39mm. Group 2 results showed that after incising 50% plantar plate dorsal displacement was 0.48mm, after full plantar plate 0.62mm, plantar plate +PCL was 0.74mm and plantar plate +PCL+ACL was 1.06mm. To produce significant instability, both collaterals on one side with combination of 50% plantar plate tear was needed. An isolated 50% tear of plantar plate caused less displacement of MTPJ compared to isolated collaterals. PCL contributed more towards the stability of MTPJ when the plantar plate was intact. Whereas, ACL contributed more stability when plantar plate was sectioned.

Conclusions: The current practice of releasing the collaterals to gain access for repairing plantar plate by indirect method should be re-evaluated. A new technique of proximal tenotomy of extensor digitorum brevis tendon looped around the transverse ligament and attached to the neck of metatarsal reconstructs both structures (plantar plate and collaterals).