ACL degeneration after an excessive increase in the medial proximal tibial angle with medial open wedge high tibial osteotomy.

PURPOSE: This study examined the influence of the mechanical medial proximal tibial angle (MPTA) on anterior cruciate ligament (ACL) degeneration following open wedge high tibial osteotomy (OWHTO). It was hypothesised that an excessive increase in MPTA would be associated with ACL degeneration following OWHTO.

METHODS: Seventy-four knees treated with OWHTO were retrospectively examined. Arthroscopic ACL grading [0 (intact) to 4 (complete rupture)], anterior tibial translation (ATT) test at the time of OWHTO with the index arthroscopy and at plate removal with the second-look arthroscopy, clinical assessments using the Knee Society Score (KSS), and radiographic evaluations of MPTA were performed. The relationship between MPTA and the ACL condition was analysed using Spearman's correlation.

RESULTS: The time from the index arthroscopy to the second-look arthroscopy was 15.0 ± 4.4 months; the total follow-up was 31.0 ± 6.5 months. ACL grade significantly increased from 0.6 ± 0.8 (index arthroscopy) to 1.1 ± 1.2 (second-look arthroscopy) (p < 0.0018). ATT on the operated side significantly decreased from 7.1 ± 2.6 mm preoperatively to 5.3 ± 2.3 mm at the time of plate removal (p < 0.001). No significant difference was observed in KSS for ACL grades in the steady and progression groups. Changes in MPTA from the preoperative to postoperative period were significantly higher in the progression group (p = 0.0155). Changes in ACL grades were significantly correlated with preoperative MPTA and changes in MPTA (r = - 0.365 and 0.343, respectively; p < 0.01).

CONCLUSIONS: Excessively increased MPTA led to ACL degeneration following OWHTO. ACL degeneration was not associated with short-term clinical outcomes. Excessive correction of MPTA should be avoided to prevent ACL degeneration following OWHTO.

LEVEL OF EVIDENCE: Therapeutic case series, Level IV.