Posteromedial vertical capsulotomy selectively expands the intraoperative extension gap in cruciate-retaining total knee arthroplasty

Purpose Effective soft-tissue balancing procedures for expanding the extension gap (EG) are needed in cases of gap mismatch in total knee arthroplasty (TKA). A posteromedial vertical capsulotomy (PMVC) is performed to restore mobility in a knee with a flexion contracture. The purpose of this study was to evaluate the effectiveness and safety of PMVC for intraoperative gap adjustment in cruciate-retaining TKA. Methods A total of 120 consecutive knees undergoing cruciate-retaining TKA for varus osteoarthritis were examined. The EG and flexion gap (FG) with a trial femoral component were measured using spacer blocks before and after PMVC. PMVC was performed when the first FG was larger than the first EG by > 2 mm. Results Sixty-five knees underwent PMVC, and the mean EG significantly increased by 2.4 mm ( p < 0.001). This increase was significantly larger than that of the FG by 2.0 mm ( p < 0.001). The preoperative extension range of motion (ROM) was negatively correlated with the EG change after PMVC ( r = − 0.39, p = 0.001). A receiver operating characteristic (ROC) curve indicated a preoperative extension ROM cut-off of -10° for predicting PMVC (sensitivity 72.3%, specificity 56.4%). No associated complications were observed during a minimum 2-year follow-up period, and there was no difference in the postoperative Knee Society Score between the PMVC and non-PMVC groups. Conclusion PMVC may be a useful soft-tissue treatment for gap adjustment with a selective EG expansion in TKA, especially in cases of a limited preoperative extension of − 10° or less. Level of evidence Therapeutic study, level III.