Variations in the Anatomic Morphology of the Lateral Distal Tibia Surgical Implications for Distal Tibial Allograft Glenoid Reconstruction

Background: Distal tibial allograft glenoid augmentation has been introduced as a viable treatment approach for glenoid bone loss in conjunction with shoulder instability. No previous study, however, has assessed the morphologic variation of the distal tibia at the incisura as it relates to graft dimensions for glenoid augmentation. Increased concavity at the lateral distal tibia necessitates removal of the lateral cortex to obtain a flat surface, which may have implications for the strength of surgical fixation. Purpose: To assess the morphologic variation of the distal tibia at the incisura as it relates to graft dimensions for glenoid augmentation. Study Design: Descriptive laboratory study. Methods: Magnetic resonance images of the ankle were reviewed for morphology assessment of the appearance and depth of the distal tibia. A classification system was created reflecting the suitability for glenoid augmentation. Type A tibias contained a flat contour of the lateral tibia at the articular surface, indicative of an ideal graft. Type B tibias had slight concavity with a central depth <5 mm and were deemed acceptable grafts. Type C tibias had deep concavity with a central depth.5 mm and were deemed unacceptable. Statistical analysis was performed via univariate analyses to compare patient demographics against acceptable morphology for glenoid augmentation. Results: Eighty - five study patients met inclusion criteria (53 male, 32 female; mean age +/- SD, 35.1 +/- 10.3 years). Overall, 12 patients (14.1%) demonstrated type A morphology, with 61 patients (71.8%) having type B morphology for a total of 85.9% of acceptable grafts for glenoid augmentation. The interrater reliability was moderate to strong between observers (kappa value = 0.841). On univariate analysis, sex was the only variable significantly associated with an acceptable graft, with 100% of female patients having acceptable morphology, as compared with 77% of male patients (P =.004). Conclusion: Variable morphology of the distal tibia at the incisura was found: 14.1% of patients demonstrated an ideal morphology for glenoid augmentation; an additional 71.8% were deemed suitable for graft usage; and 14.1% of tibias had unacceptable morphology. Sex was a significant factor for predicting acceptable grafts.