Knee-ankle joint line angle: a significant contributor to high-degree knee joint line obliquity in medial opening wedge high tibial osteotomy.

BACKGROUND: Medial opening wedge high tibial osteotomy (MOWHTO) changes the knee joint inclination in the coronal plane, which can be compensated by the ankle joint. Once there is a decompensated knee joint obliquity, it can induce excessive shear force on the articular cartilage. This study aimed to investigate the capacity of the compensation by analyzing the correlation of the knee-ankle joint line angle (KAJA) and the knee joint line obliquity (KJLO). PATIENTS AND METHODS: Ninety-six patients undergoing MOWHTO were included. We measured potential predictors including preoperative or postoperative body mass index (BMI), weight-bearing line (WBL) ratio/correction amount, knee-ankle joint line angle(KAJA), mechanical lateral distal femoral angle (mLDFA), medial proximal tibia angle (MPTA), ankle joint line obliquity (AJLO), mechanical hip-knee-ankle angle (mHKA) and joint line convergence angle (JLCA). The correlations of these predictors and postoperative KJLO were determined using Pearson correlation coefficient. The contribution of significant predictors was further analyzed using multiple linear regression. Finally, the cutoff value of the most contributing factor resulting in decompensated KJLO was derived with receiver operating characteristic (ROC) curve analysis. RESULTS: Preoperative AJLO, JLCA, MPTA, mHKA and KJLO and postoperative KAJA and MPTA correlated with postoperative KJLO. After multiple linear regression, only preoperative AJLO and JLCA and postoperative KAJA still showed significant contribution to postoperative KJLO. Postoperative KAJA made the greatest contribution. The cutoff value of postoperative KAJA was at 9.6° after ROC analysis. The incidence rate of high-grade KJLO was 69.6% when postoperative KAJA exceeded 9.6°. CONCLUSIONS: Postoperative KAJA is a significant contributor to high-grade KJLO after MOWHTO. The incidence was increased at angles greater than 9.6°. The results suggest that KAJA should be carefully assessed during preoperative planning or intraoperative evaluation. Postoperative KAJA < 9.6° can lower the rate of early high-degree KJLO.

Focal proximal fibular angle: A potential indicator of the tibial mechanical axis in opening-wedge high tibial osteotomy.

BACKGROUND: For opening-wedge high tibial osteotomy, correct alignment is essential for a better prognosis. It is difficult to evaluate the mechanical axis of the lower extremity or tibia using a single fluoroscopic image. This study aimed to discuss the use of focal proximal fibular angle (FPFA), which can be assessed by a single fluoroscopic image, as an intraoperative indicator. METHODS: Eligible for analyses were 111 consecutively treated patients; for the final analyses 96 patients were included. The preoperative and postoperative medial proximal tibial angle (MPTA) and FPFA were measured. The relationship between these two angles, correction amount, weight-bearing line ratio and patient characteristics were analyzed. RESULTS: The preoperative FPFA and MPTA were 96.5 ± 3.8° (mean ± standard deviation, SD) and 84.8 ± 3.0°, while the postoperative FPFA and MPTA were 87.6 ± 4.1° and 94.0 ± 3.5°, respectively. The preoperative and postoperative sums of the MPTA and FPFA were constant. The discrepancy was less than 3° in all knees, less than 2° in 92.7% knees and less than 1° in 68.8% knees. It was not correlated with age, sex, weight-bearing line ratio, or correction amount. CONCLUSION: The study findings confirmed the constancy of the sum of the MPTA and FPFA. The FPFA can be easily evaluated on a single fluoroscopic image of the knee. Use of the FPFA as guidance may simplify the procedure of opening-wedge high tibial osteotomy and approximately predict the tibial mechanical axis.