The plantar support of the navicular cunieform joint - a major component of the medial longitudinal arch
E. Swanton, A. Fisher, L. Fisher, A. Molloy, L. Mason
Introduction: Weight bearing radiographic analysis of pes planus deformities show, with varying degree of severity, a break in Mearys line, uncovering of the talar head and in increase in talar first metatarsal angle. Work by Alsousou (BOFAS 2016) has shown the break in Mearys line to occur not only at the talanavicular joint (2/3rds of cases) but also at the navicular cuneiform joint (1/3rd of cases), which is distal to the spring ligament and reported tibialis posterior insertion. There are currently no anatomical studies analysing the medial longitudinal arch distal to the spring ligament insertion. We aimed to examine this area and assess the anatomy.
Methods: We examined 10 cadaveric lower limbs that had been preserved for dissection at the Human Anatomy and Resource Centre at Liverpool University in a solution of formaldehyde. The lower limbs were carefully dissected to identify the plantar aspect of the medial longitudinal arch.
Results: In all specimens, the tibialis posterior tendon inserted into the plantar medial aspect of the navicular with separate slips to the intermediate and lateral cuneiforms. Following insertion on the navicular, a tendon like structure extends from this navicular insertion point to the medial cuneiform. This structure is statically inserted between the navicular and medial cuneiform allowing the pull of tibialis posterior to act on the navicular and medial cuneiform in tandem. A separate smaller plantar ligament is also present between the navicular and medial cuneiform.
Conclusion: The tibialis posterior tendon inserts into the navicular and continues onto medial cuneiform to provide a static restraint between two bony insertions, thus supporting the distal aspect of the medial longitudinal arch. This structure is not addressed in classical tibialis posterior reconstructions.
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