Preoperative joint line convergence angle correction is a key factor in optimising accuracy in varus knee correction osteotomy

Purpose This study aimed to identify and prevent preoperative factors that can be influenced in preoperative planning to reduce postoperative malcorrections. Methods The method used in this study was a retrospective two-centre analysis of 78 pre and postoperative fully weight-bearing radiographs of patients who underwent valgus osteotomy correction due to symptomatic medial compartment osteoarthritis. A computer software (TraumaCad (R)) was used to aim for an intersection point of the mechanical tibiofemoral axis (mTFA) with the tibia plateau at 55-60% (medial = 0%, lateral = 100%). Postoperative divergence +/- 5% of this point was defined as over- and undercorrection. Preoperative joint geometry factors were correlated with postoperative malcorrection. Planning was conducted using the established method described by Miniaci (Group A) and with additional correction of the joint line convergence angle (JLCA) using the formula JLCA-2/2 (Group B). Additionally, in a small clinical case series, planning was conducted with JLCA correction. Statistical analysis was performed using (multiple) linear regression analysis and analysis of variance (ANOVA) with p < 0.05 considered significant. Results In 78 analysed cases, postoperative malcorrection was detected in 37.2% (5.1% undercorrection, 32.1% overcorrection). Linear regression analysis revealed preoperative body mass index (BMI, p = 0.04), JLCA (p = 0.0001), and osteotomy level divergence (p = 0.0005) as factors correlated with overcorrection. In a multiple regression analysis, JLCA and osteotomy level divergence remained significant factors. Preoperative JLCA correction reduced the planned osteotomy gap (A 9.7 +/- 2.8 mm vs B 8.3 +/- 2.4 mm; p > 0.05) and postoperative medial proximal tibial angle (MPTA: A 94.3 +/- 2.1 degrees vs B 92.3 +/- 1.5 degrees; p < .05) in patients with preoperative JLCA > 4 degrees. The results were validated using a virtual postoperative correction of cases with overcorrection. A case series (n = 8) with a preoperative JLCA >= 4 revealed a postoperative accuracy using the JLCA correction of 3.4 +/- 1.9%. Conclusion Preoperative JLCA >= 4 degrees and tibial osteotomy level divergence were identified as risk factors for postoperative overcorrection. Preoperative JLCA correction using the formula JLCA-2/2 is proposed to better control ideal postoperative correction and reduce MPTA. The intraoperatively realised osteotomy level should be precisely in accordance with preoperative planning.

Automated summary

The purpose of this study was to reduce postoperative malcorrections by identifying and addressing preoperative factors in the planning stage. The analysis of 78 patients undergoing valgus osteotomy correction revealed that preoperative factors such as body mass index, joint line convergence angle, and osteotomy level divergence were correlated with postoperative overcorrection. Correction of the joint line convergence angle was found to be effective in achieving ideal postoperative correction. Precise alignment with preoperative planning during osteotomy was emphasized.