[Healing of ligaments and tendons]

Regeneration of ligaments and tendons is a slow process, compared with the healing of other connective tissues (e.g., bone). Healing starts from the surrounding soft tissues ("extrinsic healing"), but also from the ligament or tendon itself ("intrinsic healing"). Regeneration is poor when there is little surrounding soft tissue available, as is the case in the anterior cruciate ligament. Regeneration of the medial collateral ligament of the knee is examined best. Mechanical and ultrastructural properties are not completely normal even 1 year after dissection of the ligament irrespective of whether it was sutured or not. Our own experiments on rabbit anterior cruciate ligaments showed that there is no regeneration after complete transection of the ligament. After incomplete transection there is regeneration, but maximum load of the ligament reaches only about 3/4 of the values of the sham-operated contralateral side. An additional experiment showed that regeneration is significantly better with the application of continuous passive motion, and elongation of the ligament can be avoided. If the healing tissue is not loaded, regeneration results in unstructured scar tissue. Under functional load, the collagen fibers are oriented in a longitudinal direction and the mechanical properties are optimized. There are no fundamental differences in the healing process between tendons and ligaments.