Foot length - A reliable predictor of posterior tibial tendon thickness: A cadaveric study.

BACKGROUND: Tibialis posterior tendon, deltoid ligament and spring ligament are the three most important structures on the medial aspect of the foot. They contribute to the stability of the foot and ankle and also to the maintenance of the arches of the foot. These structures get affected and dimensions get disrupted in various traumatic and degenerative conditions. Normal range of dimensions of these structures has not been studied in an Indian population. Our objective is to define the normal thicknesses of these structures using a cadaveric model. We also hypothesize that longer the foot, higher stresses on these structures and hence thicker they will be. We aim to assess this hypothesis as well.

METHODS: Dissection of the medial aspect of the foot was done on twenty cadaveric below knee specimens. Tibialis posterior tendon was identified and its thickness was measured. Deltoid and plantar calcaneonavicular ligaments were identified. Their lengths and thicknesses were measured. Length of the feet was also measured prior to dissection. Statistical analysis was done using the data obtained.

RESULTS: Mean tibialis posterior thickness was 7.0165 ± 0.387 mm. Mean deltoid thickness was 5.124 ± 0.28 mm. Its mean length was 21.328 ± 2.22 mm. Mean plantarcalcaneonavicular ligament thickness was 2.491 ± 1.120 mm. Thicknesses of the tibialis posterior tendon and plantarcalcaneonavicular ligament correlated significantly with the length of the foot.

CONCLUSION: The thicknesses of the tibialis posterior tendon and plantar calcaneonavicular ligament are shown to be a function of and significantly proportional to the length of the foot. This helps the surgeon to estimate the thicknesses which the structures had prior to the pathology, in order to recreate the non-pathological anatomy after a tendon transfer or a reconstruction procedure. The normal thicknesses of tibialis posterior, deltoid and plantar calcaneonavicular ligaments are described for an Indian setting and deviations can be used to assess various pathologies of the foot and ankle affecting these structures.