Radiological morphology of peritalar instability in varus and valgus tilted ankles.

BACKGROUND: Varus and valgus talar tilt in weight-bearing ankles can be explained by loss of peritalar stability allowing the talus to shift and rotate on the calcaneal and navicular surfaces. Little is known about the underlying destabilization process or the resulting talar malpositions. The purpose of this study was to determine talar position in 3 radiographic planes of varus and valgus tilted ankles. METHODS: Standard weight-bearing radiographs of 126 varus ankles (118 patients [mean age 62 ± 12 years]) and 81 valgus ankles (75 patients [mean age 65 ± 10 years]) were retrospectively evaluated. The tibiotalar surface angle, sagittal talocalcaneal inclination angle, and horizontal talometatarsal I angle were used to determine the frontal, sagittal, and horizontal position of the talus. A control group was used for comparison. RESULTS: Isolated talar varus malposition was found in 33.3% of the ankles (42/126), and malposition in 1 or both additional planes was found in 49.2% (62/126) and 17.5% (22/126), respectively. In valgus ankles, the percentages were 52% (42/81), 43% (35/81), and 5% (4/81), respectively. Seven out of 9 possible varus and 5 out of 9 possible valgus talar malposition configurations were found. The 4 predominant varus malposition configurations (89.7%, or 113/126) were dorsiflexion or neutral (sagittal plane) combined with neutral/external rotation and neutral/internal rotation (horizontal plane), respectively. The 3 predominant valgus malposition configurations (95%, or 77/81) were neutral or plantar flexion (sagittal plane) combined with neutral/external rotation and neutral (horizontal plane), respectively. CONCLUSION: In varus and valgus tilted ankles, talar frontal plane alignment does not predict talar sagittal and horizontal position, indicating that peritalar instability leads to various talar malpositions. Prior to operative treatment of varus and valgus tilted ankles, thorough 3-dimensional analysis of talar position may minimize failure in properly balancing the talus within the ankle mortise. LEVEL OF EVIDENCE: Level III, retrospective comparative series.