Interrelations Between the Too-Long Anterior Calcaneal Process, Hind and Mid-tarsal Bone Volumes, Angles and Osteochondral Lesion of the Dome of the Talus: Analysis by Software Slicer of 69 CT Scan of Feet.

INTRODUCTION: Although the association between Too-Long Anterior Calcaneal Process (TLACP) and osteochondral lesion of the dome of the talus (OCL) has been hypothesized, no study has investigated the interrelations between TLACP, hind and mid-tarsal volumes and angles and the development of OCL. The main goals of this work are: (1) to measure the volume of the calcaneum, talus, navicular and cuboid in subjects with and without TLACP; (2) to evaluate the angular relationships between talus, calcaneum and navicular in subjects with and without TLACP; (3) to assess whether TLACP has an effect on the volume of OCL.

METHODS: This is a retrospective study of 69 CT scans of 54 consecutive children aged 11-15 years who had undergone a CT scan due to symptomatology suggestive of TLACP. The 3D Slicer software allowed to calculate the volume of the talus, calcaneum, navicular, cuboid, TLACP and OCL (in cm3 ). The PACS system was used to perform the angular measurements (in degrees) between talus, calcaneum and navicular in the frontal, axial and sagittal plane.

RESULTS: Amid the 69 CT scans, 49 were found to have pathologies related to TLACP (71%, TLACP Group) and 20/69 were normal (29%, Control Group). The mean hind and mid-tarsal bone volumes of the TLACP group were comparable to those of the control group. There were 40 (81.6%) OCLs detected exclusively in pathological feet (TLACP group); 32 lesions were medial (80%), and 8 lesions were lateral (20%). According to Ferkel and Sgaglione CT Staging System, there were 22 (55%) stage 1 lesions, 5 (12.5%) stage 2A, 3 (7.5%) stage 2B and 10 (25%) stage three lesions. Only the angle between the talus and calcaneum in the frontal plane was significantly lower in pathological feet with respect to the control group ( p  < 0.001). In pathological feet, the talus was supinated, and the calcaneus pronated.

CONCLUSIONS: TLACP tend to stiffen the foot, modifying its biomechanics and leading to supination of the talus and pronation of the calcaneum. This induces an overpressure at the medial side of the talus where we observed a greater frequency of medial OCL with larger volume than lateral OCL.

LEVEL OF EVIDENCE: III.