Introduction
The Medial opening wedge high tibial osteotomy (MOWHTO) targeting the Fujisawa point is represented as the gold standard treatment for medial knee osteoarthritis combined with varus malalignment. In this study, through digital planning and three dimensional (3D) printed patient-specific instruments (PSI), we hypothesized that the postoperative medial proximal tibial angle (MPTA) of less than or equal to around 93° would be the most ideal for MOWHTO, with factors such as clinical outcomes and overcorrection prevention considered.
Methods
From August 2018 to July 2021, PSI-guided MOWHTOs (Anatomic Precision PSI HTO; A-plus Bio., New Taipei City, Taiwan) targeting MPTA around 93° were performed on a total of 35 patients and 36 knees. All patients suffered from mild to moderate medial compartment osteoarthritis (grade 1 to 3 on the Kellgren–Lawrence Classification), varus alignment of knee was defined by the weight-bearing line (WBL) passing through medial to the medial tibial spine with a medial proximal tibial angle less than 85°, which was indicated for the surgery. Parameters such as MPTA, lateral distal femoral angle (LDFA), hip-knee-ankle angle (HKA), joint line convergence angle (JLCA) and WBL were measured by preoperative and postoperative radiographs through a digital planning software (OsteoMaster; 2017 Luo Chu An, Taiwan). The results of clinical outcomes were evaluated using the KOOS scoring system.
Results
The mean postoperative MPTA and WBL was 92.5° ± 2.2° and 57.8% ± 6.6%, respectively. All varus malalignment cases had been corrected to a mean HKA of 2.3 ± 1.1°. No significant changes of posterior tibial slope were observed (P<0.05). This technique leads to high accuracy outcomes around the target with less than 1% of MPTA and WBL error between preoperative plannings and postoperative results. The average KOOS of all patients was improved from 34% to 65% (P>0.05). Through digital planning, our study demonstrated that up to 22 cases (63%) would be overcorrected (simulated postoperative MPTA > 93°) if the conventional method was used (target at the Fujisawa point).
Discussion
Targeting the MPTA at less than or equal to 93° as the primary planning angle could achieve a more favorable outcome and avoid overcorrection. With the help of a digital planning software, the postoperative results could be accurately estimated by simulating the mentioned parameters preoperatively. Moreover, the 3D printed PSI guide was also proven as a safe and valid method for performing an accurate MOWHTO.
Conclusion
Our study demonstrates satisfactory outcomes through the digital planning of the postoperative MPTA as the correction target. We concluded that by setting the MPTA to less than or equal to 93°, accurate and reliable outcomes could be achieved in OWHTOs.