Growth influences knee laxity after anterior tibial spine fracture: a study on rabbits

An anterior tibial spine (ATS) fracture, with or without displacement, was created in the right knee of 8-week and 22-23-week-old rabbits. After 4 weeks of cast immobilization and 8 weeks of free cage activities, the animals were killed. A method to measure anterior knee laxity in rabbits was developed using a material testing machine. The laxity of the right knee was compared to the unoperated left knee in each rabbit. The difference was found to have increased in the adult rabbits after the healing of a displaced ATS fracture (median 0.5 mm, range 0.3-0.9), but not in the young rabbits (median 0.2 mm, range 0.0 -0.4). The ultimate load of the anterior cruciate ligament (ACL) was reduced after healing of the ATS fracture. The results support the theory that further growth may compensate for the functional elongation of the ACL caused by healing of a displaced ATS fracture. The study also indicates that an ATS fracture may affect the mechanical properties of the ACL.