High tibial osteotomy in medial compartment osteoarthritis of knee: functional outcome of medial open wedge and lateral closing wedge osteotomies-How does the outliers fare in the medium term?

BACKGROUND AND AIM OF THE STUDY

Our study aimed to compare the functional outcome of HTO performed via lateral closing wedge osteotomy and medial open wedge osteotomy followed up for a mean period of 6 years using Lysholm knee score. Secondary objective was to find out whether an achievement of 2°-6° of mechanical axis had a significant impact in the outcome and how the outliers of 2°-6° (177°-182° (straight knees) and greater than 186° (overcorrection) performed in the medium term and how patients who lost correction to more than - 3° (persistent varus) performed in the medium term.

STUDY DESIGN

This is a prospective observational study.

MATERIALS AND METHODS

Sixty-two consecutive patients who had undergone HTO by a single surgeon from 2012 to 2015 were followed up. The final follow-up visit was from August 2019 to December 2019. Nine were lost to follow-up, and 53 presented for the follow-up visit. Case records were noted for the preoperative LKS scores, preoperative mechanical axis, ROM, and preoperative tibiofemoral angle. Post-operative mechanical axis in full-length weight bearing at 4 months was also noted. During the latest visit, patients underwent LKS scoring, full-length weight-bearing X-rays to assess mechanical axis, and assessment of tibiofemoral angle. The results were grouped into excellent, good, fair, and poor outcomes based on LKS scale. The mechanical axes attained at surgery and at the follow-up were grouped into less than 177° as varus, 177°-182° as straight 182°-186° as required correction, and more than 186° as overcorrection. Lysholm knee score was dichotomised using LKS 84 as the cut-off (LKS ≥ 84 high LKS; LKS 84 low LKS).

RESULTS

A total of 53 patients with a median age of 56 years (SD 4.23) were included in this study. There were 8 (15.1%) males and 45 (84.9%) females. The mean ± SD of BMI of patients was 28.10 ± 2.66 kg/m. Medial opening wedge osteotomy was performed in 27 (50.9%) cases, and lateral closing wedge osteotomy was performed in 26 (49.1%). Median duration between the time of surgery and the follow-up was 72 months (IQR 32.5). Preoperatively, the mean LKS score of the patients was 50.25 ± 12.43 (88.68% had poor score and 11.32% had fair score), and the mean mechanical axis of the knee was 172.54 ± 3.78 (all had varus deformity). The mean (SD) preoperative LKS score of the 53 participants before the surgery was 50.25 (12.43). Poor score was reported by 47 (88.68%) and fair score by 6 (11.32%) patients, respectively. At the time of final follow-up, the mean (SD) LKS score of 53 patients was 77.81(17.11). At the time of final follow-up (when compared with the score before surgery), 41(77.36%) patients had improvement in the LKS score, 10 (18.87%) patients had no improvement in the score, and 2 (3.77%) patients worsened from fair to poor. The difference between the LKS score before surgery and at the final follow-up was significantly greater for patients who underwent medial opening wedge osteotomy [median (IQR)35 (26-38)] than for the patients who underwent lateral closing wedge osteotomy [median (IQR) 30 (23-34)], U226.5, p 0.026. Knees with desired valgus angle within 2°-6° and knees which remained straight at the final follow-up showed a good or excellent outcome at the final follow-up (23 out of 53 knees). Those knees with had varus HKA axis had a poor or fair outcome at the final follow-up (23 out of 53 knees). Those knees that were overcorrected also had poor outcomes.

CONCLUSION

Our study shows that both medial open wedge osteotomy and lateral closing wedge osteotomy are capable of improving knee function in medial compartment osteoarthritis of knee. Medial open wedge with locking plates is a biomechanically more stable construct compared with lateral closing wedge osteotomy. Irrespective of the two techniques chosen, the aim of the osteotomy should be to achieve an overcorrection of 2°-6° of valgus or at least to keep the knee straight (normal mechanical axis). This will give a satisfactory medium-term result. However, varus alignment  and valgus alignment of more than 6° can result in a deterioration of function of knee. The results of the osteotomy are found to deteriorate with obesity, severe varus in  preop mechanical axis and longer duration of follow-up.