Finite element analysis of the effects of gap filling and tuberosity union for stability in open-wedge distal tuberosity tibial osteotomy.

Background: Open-wedge distal tuberosity tibial osteotomy is a joint-preserving surgical procedure that minimally affects the patellofemoral joint. Although it is considered less stable than other osteotomy procedures, few studies have evaluated its stability. Therefore, here, we categorized cases according to the state of bone union and performed a finite-element stability analysis. Methods: Computed tomography (CT) data from a patient (63-year-old female) scheduled for osteotomy at our hospital were analyzed. We created a model with 10 patterns by dividing the progression of gap filling into five stages (0 %, 25 %, 50 %, 75 %, and 100 %) and further subdividing them into two groups based on the presence or absence of descending cut union. The maximum von Mises stress and displacement of the osteotomy site were calculated using specialized software. Results: The maximum Mises stress decreased by approximately 90 % at 50 % gap filling compared with baseline (0 %), regardless of whether the descending cut had healed. Conversely, under gap filling conditions of 0 % and 25 %, the tibial tuberosity fused, resulting in a 66.7 % reduction in maximum von Mises stress under the 0 % condition and a 66.2 % reduction under the 25 % condition. Similarly, displacement decreased by 87.9 % under the 0 % condition and by 65.1 % under the 25 % condition owing to descending-cut union. Conclusion: When gap filling reached 50 %, both maximum stress and displacement decreased significantly compared with baseline, regardless of whether the descending cut had fused. Furthermore, there was a significant difference in stability depending on whether the descending cut had fused, particularly when gap filling was insufficient. Therefore, in cases where descending cut healing is not achieved, it may be recommended to wait until gap filling reaches close to 50 % before removing the implants; moreover, when considering removal at approximately 25 %, it may be necessary to use tuberosity bone healing as a criterion in the decision.