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Developing Presurgical Conversion Formulas to Predict Miniaci Angle for Personalized Realignment Targets in
Hongyu Chen1, Liang Chen1, Yuan Zhang2
1Department of Orthopedic Surgery, Shanghai Jiao Tong University of Medicine affiliated Ninth People's Hospital, Shanghai, China.
Background:
The correlation between the Miniaci angle and presurgical hip-knee-ankle (HKA) angle, weightbearing line (WBL) percentage, and changes in the HKA angle (ΔHKA angle) and WBL percentage (ΔWBL percentage) is significant in opening-wedge high tibial osteotomy (OWHTO). The conversion formulas that interrelate the Miniaci angle with pre-HKA angle (formula 1), pre-WBL percentage (formula 2), ΔHKA angle (formula 3), and ΔWBL percentage (formula 4) have been derived through the linear regression analysis. However, the accuracy of conversion formulas has not been validated.
Purpose:
To validate the precision of conversion formulas targeting various surgical objectives for OWHTO planning in the varus knee patient population.
Study Design:
Cross-sectional study; Level of evidence, 3.
Methods:
A retrospective study of 155 lower limbs of 112 patients with medial unicompartmental knee osteoarthritis was conducted. A computer simulation of OWHTO was performed to calculate the Miniaci angle by delivering the WBL to the Fujisawa point (group 1), at 65% WBL percentage (group 2), and 4.5° of valgus (group 3). Spearman correlation and Bland-Altman analyses were conducted between the computer simulation and formula calculation.
Results:
Upon evaluating the widely accepted Fujisawa point as a postoperative target, all formula results demonstrated a strong correlation with computer simulation outcomes (r = 0.962-0.999). Compared with the simulated Miniaci angle, the mean bias of the calculated angles derived from formulas 1 to 4 was 0.098° (formula 1), -0.268° (formula 2), 0.065° (formula 3), and -0.246° (formula 4). Notably, the formula based on the ΔHKA angle exhibited an ideal correlation with the simulated Miniaci angle (r = 0.998-0.999). In the 3 groups with varying postoperative targets, the mean bias of this formula in predicting the Miniaci angle was 0.065° (group 1), 0.070° (group 2), and 0.080° (group 3).
Conclusion:
Formulas based on the presurgical HKA angle and WBL percentage showed perfect accuracy for measuring the Miniaci angle targeting the Fujisawa point. The formula based on ΔHKA angle achieved the best accuracy and may be a valuable tool for measuring the Miniaci angle in broader surgical targets.
