Retro-tubercular gap widening can be caused by inappropriate anterior osteotomy and large opening gap in the medial biplanar open-wedge HTO.

PURPOSE: The purpose of this study was to investigate the causes of retro-tubercular gap widening and to confirm whether this widened gap causes instability of the osteotomy configuration during open-wedge high tibial osteotomy (OWHTO). METHODS: Operative records and radiologic findings of patients who underwent biplanar medial OWHTO between 2014 and 2016 were retrospectively evaluated. To identify the osteotomy configuration including lateral hinge fracture, postoperative simple radiographs and CT images were analyzed. Postoperative CT scan was used to evaluate the widening of the retro-tubercular gap, thickness, and axial angle of retro-tubercular osteotomy, as well as the ratios of anterior and posterior osteotomy, and hinge length. The correlation of each factor was evaluated and analyzed in accordance with the lateral hinge fracture (LHF). RESULTS: Widening of the retro-tubercular gap showed a significant correlation with the axial angle of retro-tubercular osteotomy, anterior osteotomy ratio, and opening gap distance, but not with the thickness of retro-tubercular osteotomy, posterior osteotomy ratio, and hinge length ratio. The LHF group showed significantly larger value than the non-LHF group with respect to the thickness of retro-tubercular osteotomy (P = 0.003), axial angle of retro-tubercular osteotomy (P = 0.033), retro-planar gap distance (P = 0.001), anterior osteotomy ratio (P = 0.000), and opening gap distance (P = 0.003). The hinge length ratio was smaller in the LHF group than in the non-LHF group (P = 0.001). However, the posterior osteotomy ratio was not different between the two groups (n.s.). CONCLUSION: Retro-tubercular gap widening can be caused by inappropriate anterior osteotomy and large opening gap distance, which can be related to LHF. Therefore, anterior cortical osteotomy may also be an important factor for preventing instability of the proximal fragment in biplanar OWHTO. LEVEL OF EVIDENCE: Case-control study, Level III.