Anterior cruciate ligament (ACL) tears are a common knee injury in the United States. Without surgery to repair the damage, most athletes can’t remain active. The damage is fixed by replacing the torn ligament with a piece from some other ligament. The graft is usually taken from either the quadriceps or the hamstring muscle.
Getting the right graft tension is a challenge. At first the graft tissue loses strength while the body is accepting it. If the graft is set too tight it may lose its blood supply. Healing will be delayed. If it’s too loose the result can be a loose knee with too much motion.
Most grafts will stretch to some extent after surgery. The perfect amount of graft tension hasn’t been decided yet. In this study, doctors used a special machine to measure the sliding motion of the knee joint. They tested this movement, called joint laxity, right before surgery. They also measured it during the operation and again six months later.
There was no link between joint laxity right after the operation and joint laxity six months later. In all cases the graft loosened up after six months. But the doctors couldn’t use the amount of laxity at the time of the operation to tell how much laxity patients would have six months later.
The authors conclude that joint laxity after ACL repair is based on more than one factor. It’s likely that the patient’s overall joint laxity makes a difference. So does the rehab program, how the bones line up to form the knee, and the healing process itself.