Abstract
Category:
Hindfoot; Midfoot/Forefoot
Introduction/Purpose:
The cavovarus deformity of Charcot-Marie-Tooth (CMT) disease typically presents with hindfoot varus and forefoot valgus. This seemingly paradoxical relationship is poorly understood. Better insight into this complex three- dimensional alignment under physiologic load-bearing conditions is possible using weight-bearing computed tomography (WBCT). This is the first study to examine the extreme rotational deformity in the midfoot of CMT patients, and thereby provides a key to the successful operative correction of the CMT cavovarus foot.
Methods:
We retrospectively reviewed the WBCTs of patients with CMT who presented to a single surgeon. Those with history of bony surgical correction, severe degenerative joint disease, or open physes in the foot, were excluded. Scans were analyzed using three-dimensional analysis software (Disior Bonelogic) to generate axes of select bones and their relationship relative to the tibial plafond anterior-posterior axis in the axial plane. The coronal alignment of the foot involved angular measurements of the calcaneus, talar dome, midfoot and forefoot relative to the ground. We reported quantitative alignment parameters and compared the measurements to WBCT of 20 controls.
Results:
17 WBCT scans from 15 CMT patients (average age 24 years) met criteria for inclusion. In the axial plane, external rotation of the distal tibia accounted for the varus heel position rather than subtalar malalignment. The greatest change in axial alignment occurred between the talar neck and navicular (26 degrees). The average talonavicular (TN) medial uncoverage angle was -15 degrees for CMT patients, indicating medial overcoverage, compared to +11 degrees for controls, (p<0.01). Coronal plane analysis revealed varus rotational deformity at the calcaneus (23 degrees), a peak of 61 degrees varus across the navicular and cuboid, then compensatory rotation of the cuneiforms and metatarsals to achieve a plantigrade forefoot (11 degrees varus). In comparison, controls averaged 9 degrees coronal valgus at the calcaneus and 34 degrees varus at the naviculo-cuboid level, (p<0.01). Figure 1 shows the WBCT scans of a representative CMT patient and control case.
Conclusion:
This three-dimensional WBCT analysis is the first to characterize and quantify the axial and coronal rotational deformity in CMT. Axial plane deformity had a center of rotational angulation at the talonavicular joint, associated with medial ’overcoverage’ of the talar head, likely from chronic tibialis posterior over-pull. The peak coronal deformity was localized at the navicular and cuboid, which measured nearly twice as much as controls. These observations suggest dorsiflexion osteotomy of the 1st metatarsal would fail to address the coronal rotation; releases through the talonavicular joint may be necessary to abduct and de-rotate the midfoot to achieve a plantigrade foot.
