Reduction of initial tension in the in situ frozen anterior cruciate ligament.

The purposes of this study were to develop a new method to measure in situ tension in the anterior cruciate ligament, and to show degradation changes in the tension applied to the in situ frozen-thawed anterior cruciate ligament during a 12-week period postoperatively. Eighteen mature Beagles were used in the current study. Each dog had the in situ freeze and thaw treatment to its anterior cruciate ligament, and an initial tension of 20 N was applied to the anterior cruciate ligament. The in situ tension in the anterior cruciate ligament was measured immediately after surgery (n = 4) and at 6 and 12 weeks (n = 5, respectively) with a method developed specifically for this study. A commercially available force transducer, the utility and the validity of which were established in previous studies, was inserted into the anterior cruciate ligament, and the transducer was calibrated in situ using a tensile tester after sacrifice. The four remaining animals were used for histologic examinations. The average tension in the anterior cruciate ligament decreased from 19.1 N immediately after surgery to 14.2 N and 4.7 N at 6 and 12 weeks, respectively. There were significant differences among the times. At 12 weeks, histologically, degenerative changes were seen with asteroid-shaped cells and vacuoles in the anterior cruciate ligament. The current study showed that the high initial tension applied to the in situ frozen anterior cruciate ligament gradually decreased with time until 12 weeks.