A Too-Long Anterior Process of the Calcaneus: Defining Normative Values for the Calcaneonavicular Distance Using MRI in a Pediatric Population.

BACKGROUND The calcaneonavicular distance has yet to be definitively defined on the basis of morphological studies and thus remains a somewhat elusive value for orthopaedists. The purposes of the present study were to measure the calcaneonavicular distance with use of magnetic resonance imaging (MRI) in a control pediatric population and to assess whether sex and age affected this distance. METHODS We retrospectively reviewed 363 MRI scans of the feet of healthy controls and measured calcaneonavicular distances (i.e., the distance between the bone margins of the anterior process of the calcaneus and the navicular and the distance between the cartilaginous margins of the anterior process of the calcaneus and the navicular) in the axial and sagittal planes. RESULTS Interobserver and intraobserver agreements were better for the bone measurements than for the cartilaginous measurements. The mean calcaneonavicular distance was 5.6 mm for values based on bone margins and 4.5 mm for those based on cartilaginous margins. On the basis of current criteria, the distributions of these distances were such that 41% to 46% of participants presented with values that defined them as having a too-long anterior process of the calcaneus. Furthermore, age seemed to play a major role in males, with calcaneonavicular distances narrowing with bone maturation. CONCLUSIONS The mean physiological calcaneonavicular distances measured in healthy pediatric controls are much shorter than reported previously. In almost 50% of cases, the calcaneonavicular distance measurements between the bone margins presented values that defined them as having a too-long anterior process of the calcaneus. Age played a major role in the calcaneonavicular distances in males, and we hypothesize that the calcaneonavicular distance narrows with bone maturation. We believe that it is essential to establish normative calcaneonavicular distance values based on sex and age so that they can be used as guidelines when diagnosing and treating patients suspected of having a too-long anterior process of the calcaneus. LEVEL OF EVIDENCE Prognostic Level III. See Instructions for Authors for a complete description of levels of evidence.