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

OBJECTIVES: 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. METHODS: 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. RESULTS: 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. CONCLUSION: 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.

Apex posterior angulation of the humerus: A characterization of normal sagittal plane anatomy with implications for surgical fixation.

INTRODUCTION: An understanding of the sagittal plane morphology of the humerus is relevant during surgical fixation of humeral fractures but is not well described in the literature. The purpose of this study was to better characterize the native sagittal plane morphology of the humerus. MATERIALS AND METHODS: 170 patients with uninjured full length lateral humerus radiographs were retrospectively evaluated. The angle between the proximal humeral diaphyseal axis and the distal humeral diaphyseal axis was identified and measured. The proximal axis was defined by two points equidistant from the anterior and posterior cortex 10 mm and 100 mm distal to the metaphyseal flare, and the distal axis by two points at 10 mm and 50 mm proximal to the capitellum/trochlea. The relative location of the center of rotation of angulation (CORA) was calculated as a percentage of humeral length. RESULTS: 114 radiographs were included in the analysis (66 right humeri, 48 left humeri). The average apex posterior angulation was 6.5 +/- 2.9°. The CORA occurred at an average of 80% (SD+/-13%) of the length of the humerus (proximal to distal). Total humeral length and absolute distance to CORA were greater in males compared to females (364 ± 50 mm versus 326 ± 30 mm; p<0.001; 290 ± 68 mm versus 260 ± 48 mm; p=0.003), but there were no significant sex differences with respect to magnitude of the apex posterior angulation (p=0.077) or location of CORA as a percentage of total humeral length (p=0.916). There were no statistically significant associations between age and total humeral length (p=0.056), distance to CORA (p=0.130), location of CORA as percentage of total humeral length (p=0.753), or magnitude of angulation (p=0.075). CONCLUSION: An apex posterior bow consistently exists in the distal one-quarter of the humerus that is consistent across ages and between sexes. This normal anatomic bow is important to recognize to avoid an extension malreduction and has implications for implant fit and contouring.