Accuracy of the correction obtained after tibial valgus osteotomy. Comparison of the use of the Hernigou table and the so-called classical method

'One millimetre equals one degree' is a major source of inaccuracy in planning osteotomies around the knee for metaphyseal deformities compared to the digital planning

PURPOSE

The objective of this study was to compare the accuracy of virtually performed osteotomies around the knee. The comparison was made between the Miniaci method (method 1), considered the gold standard planning, with the widely held dogma that one degree of correction required equates to one millimetre of opening/closing (method 2).

METHODS

This retrospective cross-sectional study was conducted between December 2018 and September 2022 in patients aged at least 15 years with metaphyseal knee deformity. Osteotomy planning was performed in methods 1 and 2 utilising calibrated long-leg alignment X-rays in the frontal plane. In both methods, the desired correction was defined by the Fujisawa point. The error % in measurement (ratio method 1/method 2) and the difference in millimetres (method 1 - method 2) between the two methods were analysed.

RESULTS

A total of 107 osteotomies with 27 (25.2%) distal femoral osteotomies, 54 (50.5%) proximal tibial osteotomies and 26 (24.3%) double-level osteotomies were performed virtually with a mean hip-knee-ankle angle of 176.4 ± 6.6. In distal femur osteotomy, the mean error % between methods 1 and 2 was 38.9 ± 16.7% and 22.4 ± 16.8% for the opening and closing groups, respectively. In proximal tibial osteotomies, the mean error % was 22.7 ± 15.6% and 9 ± 10.8% for the opening and closing groups, respectively. In double-level osteotomy, the mean error % of femur-based corrections was 34.9 ± 19% and 19.5 ± 21% for the opening and closing groups, respectively, and the mean error of the tibial-based corrections was 26.4 ± 12.1% for the opening group and 10.8 ± 10% for the closing group, respectively.

CONCLUSION

Planning one millimeter per degree of desired correction for osteotomies around the knee in metaphyseal deformities is a major source of error when compared with digital planning using the Miniaci method. This was seen most frequently with osteotomies of the distal femur and all opening wedge osteotomies.

LEVEL OF EVIDENCE

Level Ⅲ, retrospective cross-sectional study.

Slope-decreasing anterior closing wedge proximal tibial osteotomies using the freehand technique are accurate to within 2̊

INTRODUCTION

Anterior cruciate ligament (ACL) reconstruction requires a detailed analysis of the posterior tibial slope (PTS) as excessive values may cause the reconstruction to fail and require a slope-decreasing anterior closing wedge tibial osteotomy combined with revision of the failed ACL reconstruction. The main purpose of this study was to assess the accuracy of correction after slope-decreasing anterior closing wedge tibial osteotomy in cases of chronic anterior instability caused by ACL rerupture.

MATERIALS AND METHODS

This single-center retrospective study included 19 patients (20 knees) operated on by slope-decreasing anterior closing wedge tibial osteotomy combined with a second revision ACL reconstruction. The mean age was 22.4±3.3 years and the mean follow-up was 12.7±4.4 months. The preoperative planning was based on lateral calibrated X-rays of the entire tibia. The height of the closing wedge, which corresponded to the base of the osteotomy, was measured in millimeters. The procedure was performed using the freehand technique. The accuracy of the correction was defined as the difference between the desired preoperative PTS and the postoperative PTS achieved. An inter- and intraobserver analysis was performed.

RESULTS

The mean preoperative PTS was 13.9±2̊ and the mean postoperative PTS was 4.0±1.7̊. The mean PTS correction was 10.1±2.1̊ with a planned target of 5.4±1.8̊. The accuracy obtained between the planned target and the postoperative corrections was 1.7±1.1̊. The regression analysis showed that the accuracy of the PTS correction was not influenced by the patient's age, BMI, excessive preoperative PTS, or degree of correction achieved (p>0.05).

CONCLUSION

Slope-decreasing anterior closing wedge tibial osteotomies performed using the freehand technique for ACL graft rerupture can correct an excessive PTS within 2̊ of the planned slope correction. This accuracy is not determined by demographic factors, excessive preoperative PTS or degree of correction achieved.

LEVEL OF EVIDENCE

IV; retrospective cohort study.

"One millimetre equals one degree": a simple way to achieve in 92% of cases the desired correction after opening proximal tibial osteotomy for genu varum

INTRODUCTION

When performing a high tibial osteotomy (HTO) for genu varum deformity, it is not always easy to obtain the correct amount of overcorrection. The aims of this study were to review the results of a simple and reproducible method of correction that we have called "1 mm equals 1°". We have applied this technique to the medial opening wedge osteotomy. Our hypothesis was that one degree of correction corresponded with one degree of opening.

METHODS

97 proximal medial opening wedge osteotomies were measured intraoperatively with a navigation system and at 3 months with long-leg X-rays. The hip-knee-ankle (HKA) angle preoperatively was on average 173.8 ± 2.3° (170°-177°). In most cases, an opening of 4° greater than the initial varus was performed using our formula that one degree varus was equal to 1 mm of opening. In other words, when the varus was 6°, an opening of 10 mm was performed. The void left by the opening wedge was filled with a calcium triphosphate wedge and the construct fixed and held with a locking plate.

RESULTS

Aiming for a knee axis of 184 ± 2°, which corresponds to 2°-6° of overcorrection, we obtained the following results: HKA intraoperatively measured angle with navigation was on average 183.5 ± 0.9° (182°-184°) and HKA radiologically postoperatively angle was 182.5° ± 1.6° (179°-189°). We therefore achieved the desired overcorrection of 2°-6° in 92% of cases based on our postoperative radiographs and in 100% cases based on intraoperative measurements with computer navigation.

CONCLUSION

The method of "1 mm equals 1°" is a simple, reliable, and reproducible method to achieve in 92% of cases the desired overcorrection (i.e., 184 ± 2°) with valgising proximal medial opening wedge osteotomy in genu varum.