Poor Accuracy of Intraoperation Medial Proximal Tibial Angle Measurement Compared to Alignment Rod Methods in Open-Wedge High Tibial Osteotomy for Medial Knee Osteoarthritis

The alignment rod is widely used as an index for intraoperative alignment but alignment error is inevitable. The purpose of this study was to verify the accuracy of lower limb alignment correction by measurement of mechanical medial proximal tibial angle (MPTA) as an index in open-wedge high tibial osteotomy (OWHTO). This study was retrospective case series. This study involved 152 patients undergoing OWHTO for primary medial osteoarthritis. Alignment rod or MPTA measurement board was used as an index of optimal correction in OWHTO. Alignment rod was used from October 2013 to May 2017, and MPTA measurement board was used from June 2017 to April 2020. The correction using an alignment rod was that the weight-bearing line ratio (WBLR) passed through 62.5% of the tibial plateau which was defined as Fujisawa's point under intraoperative fluoroscopy (A rod group). The correction using MPTA measurement board was aligning the intraoperative MPTA to the preplanned angle (MPTA group). Preplanned optimal alignment was defined as Fujisawa's point in all patients. Knee injury and osteoarthritis outcome measure (KOOS), Knee Society scoring system objective knee score (KSS), 3-m timed up-and-go test (TUG), single-limb standing test (SLS), and isometric muscle strength of quadriceps and hamstrings were assessed as clinical results. WBLR, MPTA, joint-line convergence angle (JLCA), and joint-line obliquity (JLO) were assessed as radiological results preoperatively and at 1 year after surgery. The clinical and radiological results after OWHTO were compared with both groups. Postoperative WBLR in A rod group was closer to the target alignment (Fujisawa's point: 62.5) than in the MPTA group at all stage (A rod group vs. MPTA group: 63.1 vs. 54.6 at 6 months; 62.0 vs. 53.4 at 1 year; p < 0.001). There were no significant differences in the clinical results between both groups. The intraoperative measurement of medial proximal tibial angle has a risk of undercorrection after OWHTO. His study is a retrospective case series and reflects level of evidence IV.