Stress fractures of the lateral tibial plateau after open wedge high tibial osteotomy could be delayed type III lateral hinge fractures

Abstract

Purpose: To examine the condition and triggers of stress fractures of the lateral tibial plateau (LTP) similar to type III lateral hinge fractures (LHFs) after open wedge high tibial osteotomy (OWHTO). Methods: OWHTO was performed in 118 knees. They were examined for LHFs by computed tomography (CT). Patients were divided into the stress fracture group (Group SF) if they showed fracture lines on CT performed after starting weight-bearing walking and the normal group (Group N) for others. Results: The mean age was significantly older in Group SF (P = 0.022). Preoperatively, Group SF showed a significantly higher tibio-femoral angle (TFA, P = 0.014). No significant differences were observed in TFA and weight-bearing line ratio after surgery. Correction angle was significantly higher in the SF group. And all of the SF were more than 13 degrees. There was no significant difference in LHF incidence between groups, whereas stress fracture incidence differed significantly for each type of LHF (chi-squared test, P = 0.0001): 14.6% of type I cases, 100% of type II cases, 0% of type III cases, and 6.1% of those without LHF. Discussion: The load on the LTP is assumed to act as a shearing force in type II fractures, which may contribute greatly to stress fractures. In type III, stress fractures may not occur because of the load dispersed at the fracture part. The stress fracture site is similar to type III LHF, and this kind of fracture is thought to be a delayed type III because it occurs after patients start weight-bearing walking. Moreover, they are observed in type I cases with a stable hinge and in 6% of cases without LHF. This study showed that high varus knees corrected with a large correction angle may develop stress fractures. OWHTO requires attention to stress fractures of the LTP, which can be regarded as delayed type III, in those developing LHFs postoperatively or having a high varus knee preoperatively. Conclusion: These results indicated the possibility of stress fracture in LTP during weight-bearing exercise after OWHTO, which was regarded as a delayed type III fracture. The results showed that Correction angle was more than 13 degrees, and lateral hinge fracture type II of the Takeuchi classification was an inducement of this stress fracture. Level of evidence: Level IV.