Effect of Medial Osteophyte Removal on Correction of Varus Deformity in Total Knee Arthroplasty

Preoperative valgus-corrected hip-knee-ankle angle and medial meniscal extrusion are useful for evaluating postoperative alignment in mobile-bearing UKA

Purpose

The purposes of the study were to analyze the correlation between preoperative variables (valgus corrected hip-knee-ankle angle (vcHKA), medial osteophyte areas of the tibia and femur, and medial meniscus extrusion (MME)) and the postoperative alignment in mobile-bearing unicompartmental knee arthroplasty (UKA).

Methods

This study enrolled 109 patients (118 knees) who underwent mobile-bearing UKA between January 1, 2019 and January 1, 2023, retrospectively. Radiographic parameters, including the HKA, hip-knee-shaft angle (HKS), and valgus-corrected femorotibial angle (vcFTA), were measured using preoperative radiographs. The vcHKA was calculated as vcFTA - HKS. The medial osteophyte areas of the tibia and femur and MME were measured using knee magnetic resonance imaging (MRI). Simple and multiple linear regression analyses, univariate and multivariate logistic regression analyses, and receiver operating characteristic (ROC) curves were performed.

Results

In total, 109 patients (118 knees) were enrolled in this study. In the multiple linear regression analysis, vcHKA (β = 0.732, 95 % confidence interval (95%CI) = 0.582 to 0.881; p < 0.001) and MME (β = 0.203, 95%CI = 0.001 to 0.405; p = 0.049) were positively correlated with postoperative HKA, and postoperative HKA was modeled according to the following equation: 45.420 + (0.732° * vcHKA) + (0.203 mm × MME). In the multivariate logistic regression analysis, vcHKA (odds ratio (OR) = 2.007, 95 % CI = 1.433 to 2.810, p < 0.001) was associated with postoperative valgus malalignment independently. In the ROC curve, vcHKA (cutoff value: 180°) was predictive of postoperative valgus malalignment, with an accuracy (95%CI) of 0.862 (0.780-0.944).

Conclusion

Overcorrection of a varus knee under valgus stress radiograph (VSR) and excessive MME on preoperative MRI increase the possibility of overcorrection of postoperative alignment in mobile-bearing UKA.

The relationship between severity of varus osteoarthritic knees and contracture of the medial structures

BACKGROUND

Severe varus osteoarthritic knee has possibility of medial structure contracture. There is no report concerning the relationship between severity of varus deformity and contracture of medial structure. We aimed to reveal a threshold angle that could be corrected in proportion to the width of medial osteophyte removal, and to examine correction differences between larger and smaller than the threshold angle in total knee arthroplasty.

METHODS

This study included 27 varus osteoarthritic knees scheduled for total knee arthroplasty (TKA). Each knee was measured the hip-knee-ankle angles (HKA) using a navigation system, at maximum extension, 30˚ and 60˚ flexion before and after osteophyte removal, with and without external 10 N-m valgus torque loads. Subsequently, resected osteophyte widths were measured. Mean correction angle per 1 mm osteophyte removal was calculated, and the threshold angle was calculated using the receiver operating characteristic curve. HKA differences were compared against larger and smaller deformity than the threshold angle.

RESULTS

Mean osteophyte width was 7.1±2.20 mm. Osteophyte removal produced a mean 3.1° correction, which equaled a 0.4° correction per 1 mm osteophyte width removal. The varus deformity threshold angle was 9.5°, however, when comparing the groups larger and smaller than the threshold, there were no significant differences in HKA differences between each step and flexion angle.

CONCLUSIONS

The threshold angle for expected correction with medial osteophyte removal was 9.5˚. However, with no differences in correction between those with larger or smaller than this angle, medial structure contracture seemed to be unrelated to severity of deformity.