Pes Cavovarus in Charcot-Marie-Tooth Compared to the Idiopathic Cavovarus Foot: A Preliminary Weightbearing CT Analysis

Abstract

Category: Ankle, Hindfoot Introduction/Purpose: Charcot-Marie-Tooth disease (CMT) is an inherited sensory motor peripheral neuropathy progressively leading to cavovarus deformity of the foot. Conversely, the idiopathic cavovarus foot represents a non-neurological condition, with a spectrum from subtle to markedly deformed. Our aim was to investigate morphological differences between CMT pes cavovarus (CMT-PC), idiopathic pes cavovarus (I-PC) and normally aligned feet using three-dimensional (3D) cone beam weightbearing computed tomography (WBCT) measurements. We hypothesised that the hindfoot alignment was significantly different between the three groups. Methods: Retrospectively, we compared 17 CMT-PC (15 patients) with 24 I-PC and 24 clinically normally aligned feet. Patients were comparable by age, sex and body mass index. All WBCTs were performed during routine investigation. Exclusion criteria included previous ipsilateral foot/ankle surgery and inability to heel weightbear. Three measurements were made by one orthopaedic surgeon: foot and ankle offset (FAO), a three-dimensional calculation describing the relationship between the centre of gravity of the tripod of the foot and the centre of the ankle; calcaneal offset (CO), measuring the distance between a theoretically neutral position of the calcaneus and its true position; and hindfoot angle (HA), an estimative of coronal angular hindfoot alignment. These measurements were all repeated twice for intraobsever reliability calculation (Pearson correlation). The mean values were compared using one-way ANOVA (values normally distributed after Shapiro-Wilk test) with the Bonferroni test. Results: Intraobserver reliability was excellent for all the three measurements (r=0.98 for FAO, CO and HA). Mean FAO value ± standard deviation in CMT-PC group (-14.1% ± 7.2) and in I-PC group (-9.6% ± 5.2) both differed from normal feet (1.6% ± 3.3) (p< .001). Of note, a difference was found between mean FAO in CMT-PC and I-PC feet (p .025). Furthermore, the mean CO (- 23.6 mm ± 11.3 in CMT-PC, -16.7 mm ± 8.2 in I-PC and 3.1 mm ± 6 in normal feet) and the mean HA (-44.9° ± 21.7 in CMT-PC; - 30.3° ± 16.9 in I-PC; 5.1° ± 10.1 in normal feet) significantly differed in three groups (p< .001) and specifically between CMT-PC and I-PC feet (p .032 and p .02 for CO and HA, respectively). Conclusion: This study confirms our hypothesis. Hindfoot alignment in patients diagnosed with CMT cavovarus and idiopathic cavovarus feet significantly differed between them and from normal controls, with a more accentuated varus deformity in CMT patients. This probably reflects the presence of a known neuromuscular imbalance driving the deformity over time in CMT feet. We therefore propose using a reliable method of quantifying heel varus and seeking a potential neurological diagnosis in the more severe.