By: Kate Fast B.Sc (Kin), B.Sc (PT), Dip. Sport (PT)
In 1999, there were 102,000 Anterior Cruciate Ligament (ACL) reconstructions in the United States (3),
By: Kate Fast B.Sc (Kin), B.Sc (PT), Dip. Sport (PT)
In 1999, there were 102,000 Anterior Cruciate Ligament (ACL) reconstructions in the United States (3), and over 130 in Saskatoon. According to the NCAA injury Surveillance System, the ACL is the most common severe ligamentous injury (3). Although there may be some debate as to whether ACL injuries are on the rise or that they are being identified more often, the number of athletes with known ACL injuries is clearly increasing. As a result, coaches and therapists are more likely to be involved in the rehabilitation of ACL injures, and in the management of ACL injured athletes as they return to sport.
Although the high number of reconstructions being performed may give the impression that the management and rehabilitation of this injury is routine, a careful review of the literature supports the opposite conclusion. In fact, the ACL injured knee should command the utmost care and attention given it’s natural history.
This is the first in a series of three articles regarding ACL injuries and rehabilitation. The purpose of this article is to provide some background in terms of function, mechanism of injury, and injury classification. The natural history and management of the complete (3rd degree) ACL tear will also be described. The next article will present some current rehabilitation approaches following ACL reconstruction. The last paper in the series is devoted to the rehabilitation of the female ACL injured athlete.
ACL Function, Mechanisms of Injury and Classification
The anterior cruciate ligament is one of a matched pair of ligaments in the middle of the knee. It’s function is to stop the tibia (calf) from slipping forward under the femur (thigh) during pivoting and twisting motions.
Men and women tend to injure their knee ligaments in different ways. Men frequently injure their ACL because of contact with another player or piece of equipment. The knee is struck from the outside, with the foot planted and the knee straight. On the other hand, women hurt their ACLs most often during non-contact events. Landing from a jump onto a straight knee, or rapid planting and cutting are the most common mechanisms of ACL injuries in women (8).
The classification of ACL injuries follows traditional definitions. A first-degree ligament injury is characterized by a minimal amount of microscopic disruption of the ACL fibers. The length of the ligament, and therefore it’s function, remains intact. A second degree ACL sprain causes a moderate amount of tearing of the fibers. As a result, the ligament lengthens, and consequently, the knee becomes slightly loose. A third degree ACL sprain is a complete disruption of fibers. Tearing the ligament fibers causes bleeding into the joint space, commonly know as a hemarthosis. Because the fibers are completely torn, the ACL does not function to prevent forward sliding of the tibia under the femur. The knee becomes unstable during pivoting and twisting motions.
Consequences of ACL Tears
ACL injuries occur when significant forces are transmitted through the joint, and such extreme forces can damage many structures within the knee, including other ligaments, menisci and the articular cartilage.
When the ACL tears, other ligaments sustain a 2nd or 3rd degree sprain in 20 to 40% of reported cases (3,4). Most often, the medical collateral ligament (MCL) and occasionally the posterior cruciate ligament (PCL) may be damaged. These ligaments work in concert with each other to limit the motion of the knee. While the ACL limits the slide of the tibia from under the femur, the MCL stops the knee from hinging sideways. Significant damage to two ligaments leads to abnormal movement in two directions, and thereby, a profoundly unstable knee.
Over 40% of 3rd degree ACL tears sustain significant meniscal injury (3). The menisci are two washer-like fibrous discs which function to maintain ideal alignment between the bones of the knee. They also bear and distribute body weight and forces through the joint. Unfortunately, there is a direct relationship between meniscal damage and the development of arthritis (7). It is because of this association that surgeons now spare and repair as much of the meniscus as possible.
In addition to multiple ligament and meniscal trauma, ACL deficient knees show significant signs of articular cartilage damage. Articular cartilage is the layer of cells which line the bony surfaces of the joint. It’s function is to decrease friction within the joint, and to absorb and distribute forces acting on the joint. A recent MRI study showed that knees with acute (newly acquired) 3rd degree tears had evidence of bone bruising in 80% of cases examined (2). Such bruising indicated significant trauma to the articular cartilage and underlying bone. Even more disconcerting is evidence that this kind of damage is still present on MRI 6 years after the injury (2). It appears that 3rd de