Defining and Differentiating Congenital Vertical Talus and Congenital Oblique Talus: It's Not Primarily About the Talus.

Background: Congenital vertical talus (CVT) and congenital oblique talus (COT) are rocker-bottom foot deformities that have similar names and no objective definitions. This has led to confusion for practitioners, as well as scientific challenges for researchers. Our goal was to provide objective radiographic criteria to define and differentiate CVT and COT.

Methods: We evaluated 62 pairs of maximum dorsiflexion and plantar flexion lateral radiographs of infant feet that had been clinically diagnosed with CVT. The dorsiflexion tibiotalar angle, the plantar flexion talus-first metatarsal angle, and the plantar flexion foot center of rotation of angulation (foot-CORA) were measured using transparent overlay tools. Freehand measurements were made on a subset of 10 pairs of radiographs to confirm clinical applicability. Nine contralateral pairs of radiographs of normal feet were measured for comparison.

Results: Specific values for the radiographic measurements were identified that, together, reliably differentiated the shapes of rocker-bottom feet with CVT, COT, and flexible flatfoot with a short tendo-Achilles (FFF-STA), as well as the shape of the normal foot. More severe and rigid rocker-bottom foot deformities were diagnosed with CVT. Less severe and more flexible deformities were diagnosed with COT.

Conclusions: CVT, COT, FFF-STA, and normal feet can be reliably differentiated using 2 angular measurements and 1 bone position measurement on dorsiflexion and plantar flexion lateral radiographs. Our data indicated that the differentiation of CVT and COT is based primarily on the rigidity of the navicular dislocation rather than the verticality of the talus. The data further supported the proposition that COT is a foot deformity along a spectrum of valgus/eversion deformities of the hindfoot that requires early treatment. Application of these diagnostic criteria should lead to clinical studies that identify a specific treatment, treatment outcome, and prognosis for each deformity.

Level of evidence: Diagnostic Level II. See Instructions for Authors for a complete description of levels of evidence.