The anterior cruciate ligament. One of the major ligaments in the knee joint, connecting the femur bone in the thigh to the tibia bone in the shin. This ligament is infamous in sports, and you may have seen headlines of athletes devastated by injuries to their ACL. Derrick Rose, the youngest MVP in NBA history, was touted to be the second coming of Michael Jordan, before his ACL tear in the 2011/12 season halted his career. Michael Owen, Tom Brady, Klay Thompson, and Anne Keothavong are all examples of high-class athletes who have suffered this same injury. How is this important? To answer this, we must delve into what an ACL is, the manner in which it is injured, and the repercussions.
The ACL is a joint in the knee, the Anterior Cruciate Ligament. It forms a pair with the posterior cruciate ligament, crossing over each other, hence its name – cruciate (cross).
It attaches anteriorly towards the middle of the tibia and connects it to the posterior region of the femur, in the intercondylar fossa (a groove in the back of the femur bone). In anatomy, the structure of a ligament is pivotal to its function. The ACL prevents the tibia from dislocating anteriorly. It also stabilises the knee joint. So, what happens when this ligament is torn?
We have established that the role of the ACL is to keep the tibia from dislocating anteriorly (forwards), thus keeping it in line with the femur. Hence, a torn ACL will not be functional, and allow the tibia to dislocate anteriorly. A simple test for this is the ‘anterior drawer test’. If a doctor or physician attempts to pull the tibia of a patient forwards and it moves, we can conclude the ACL is torn as it is no longer serving its function of preventing such movement. The ACL can be torn if the knee and lower leg are twisted. It can be torn if the knee is hyperextended (where the knee is extended beyond its normal range of motion), or if a large force is applied to the back of the knee while the knee is partly flexed (bent), a movement which encourages anterior tibial dislocation. This can be seen in the image below:
The ACL tear is a very common injury in sports, especially those involving sudden changes of direction (which may lead to situations where the knee and lower leg are twisted in opposite ways). The usual treatment for an ACL tear is reconstructive surgery, and athletes can be out injured for periods as long as a year. 25% of people also injure the ligament again. With a less than optimal prognosis, it is a big area of research in sports health and therapy.
New evidence suggests that rehabilitation exercises could be just as effective as reconstructive surgery. The study examined active adults in Sweden between the ages of 18 to 35 who had torn ACLs. The randomised trial either had participants undergo surgery or rehabilitation. Surprisingly, 16 people out of the 54 who were chosen for rehabilitation had signs of healing within two years, using only strengthening exercises. In the future, larger MRI studies could help doctors decide at the three-month mark which ACL tears need surgery, and which ones will heal with rehabilitation. Not all ACL tears are equal, and reconstructive surgery may be a better treatment for injuries involving ligaments that have been ripped off the bone, for example.
Studies are also exploring the use of a knee brace which pushes the torn ligament back together to promote healing. As more and more evidence piles up, one thing is for certain: we are getting closer and closer to shifting the narrative of the ACL tear being a potentially career-ending injury, to one that can be mitigated and healed.
References
British Journal of Sports Medicine, DOI: 10.1136/bjsports-2022-105473
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