The purpose of this study was to clarify the relationship between posterior tibial slope angle (PTSA) and anterior cruciate ligament (ACL) status in medial open wedge high tibial osteotomy (OWHTO). Our hypothesis was that even though OWHTO may improve anteroposterior laxity of the knee, an increase in PTSA after OWHTO would be associated with ACL degeneration.

Seventy-five patients treated with OWHTO were retrospectively analyzed. PTSA were evaluated radiographically pre- and postoperatively. The ACL was evaluated during the index arthroscopy at the time of OWHTO and a second-look arthroscopy during the plate removal, and scored from 1 (normal ACL) to 4 (complete tear). An anterior tibial translation (ATT) test was performed.

The mean time period from the index to second-look arthroscopy was 15.0±4.4months. PTSA significantly increased from 5.3±3.4° preoperatively to 7.5±4.0° postoperatively (p<0.001). The average ACL score significantly increased from 1.9±0.5 at the index arthroscopy to 2.2±0.5 at the second-look arthroscopy (p=0.0025). The average ATT on the operated side significantly decreased from 7.1±2.6mm preoperatively to 5.3±2.3mm at the second-look arthroscopy (p<0.0001). There was a significant positive correlation between the increase in PTSA and the change of ACL grade [correlation coefficient (r)=0.221, p<0.05].

Even though OWHTO reduces anteroposterior knee laxity, an increase in PTSA is associated with ACL degeneration. It is important for the surgeon to avoid an increase in PTSA during the intervention to prevent ACL degeneration after OWHTO.

IV, therapeutic retrospective case series.