Distal Tibia Apex Posterior Angulation: A Normal Anatomic Variant Related to Hindfoot Alignment With Side-to-Side Symmetry.

Abstract

The sagittal plane of the distal tibia has not been well-described. This study sought to characterize sagittal plane morphology, determine symmetry from side to side, and identify differences based on hindfoot alignment. One hundred twelve bilateral lateral weight-bearing ankle radiographs were retrospectively evaluated (224 ankles). Hindfoot alignment was classified as neutral, planus, or cavus using the Meary angle. The angle between the diaphyseal and distal tibia axes was measured, and the apex location relative to the plafond was recorded. A mean distal tibia apex posterior angulation (DTAPA) of 2.0° (range -2° to 7°, SD = 2.06°) was located 8.0 cm proximal to the plafond. No difference was observed from side to side in DTAPA magnitude (P = 0.36) or location (P = 0.90). Planus alignment was associated with a significantly greater DTAPA (3.05°) as compared with neutral (1.89°) (P = 0.002) and cavus (1.25°) (P < 0.001) alignment. The distal tibia has an apex posterior angulation, suggesting that the true anatomic axis of the tibia terminates just posterior to the plafond center. Hindfoot alignment is related to distal tibia morphology. DTAPA symmetry indicates that contralateral imaging can be used to guide reconstruction of patient-specific anatomy and alignment. Knowledge of the DTAPA may help mitigate sagittal malalignment during distal tibia fracture surgery.