Risk factors for ACL tears have been studied for many years. The following risk factors were identified in a 2000 article from the Journal of the American Academy of Orthopedic Surgery from the year 2000.
How ACL tears occur.
Research shows that only 30% of ACL tears are from a direct blow or contact. The other 70% occur without contact – when athletes pivot or cut or “land wrong” on a jump. A question that we will tackle in the future is, “What can we do to reduce the risk of this 70% of tears?”
Anatomic Risk Factors
The way our bodies are structured – or individual anatomy – can be identified as risk factors for ACL tears. Here’s what we do know:
ACL tears are more common in females than males.
Differences in structures of the female body include a large “Q angle”. In simple terms this means the hips are wider than the knees and thus the angle from the hip to knee is greater. This puts increased stress on the knee joint.
Women are more “lax” than men. Meaning females tend to have more mobility throughout their bodies.
Another factor is called the “notch”. This is part of the big thigh bone (the femur), right where it joins to make the knee. The ACL connects in the notch. In general, the smaller the width of the notch, the more likely people are to tear their ACLs.
These factors continue to be researched and we continue to attempt to understand WHY they change the stress on the ACL.
Hormonal Risk Factors
This continues to be an area that medical professionals continue to research. There have been studies to look at the interaction between female hormones and how these may affect the ACL. Some people speculate that during some phases of the menstrual cycle the ACL may be weakened. Much more research is needed in this area.
Terms such as “proprioception” and “neuromuscular control” are often deemed risk factors for ACL tears. Neuromuscular control essentially means the ability of your nerves to control your muscles. This is an unconscious process that happens in the body, although there is some research to support it can be trained. Proprioception is a term that refers to the ability of our bodies to provide information from the body to the brain to assist with a good response to provide proper neuromuscular control.
Hip and Trunk Contributions
In simple terms – the ability to generate proper forces at both the hip and trunk – including from the hamstrings and gluteus medius (a hip muscle) – is being studied more and more as risk factor for non-contact ACL tears. When people are unable to stabilize their trunk and hips they are found to have increased forces on the knee and altered muscle activation in the leg. The changed mechanics tend to put more force on the ACL and thus risk of tearing is increased.
There are many other factors being studied and there is more current research than that provided. The article reviewed in this blog does show that the risk of ACL tears has been a large area of research and the continued attempted to find risk factors in order to better reduce the risk of ACLs is at the forefront of the orthopedic world!
Our next blogs will cover: Ways to reduce the risk of ACL tears, Advances in PT follow ACL injuries, and Returning to Sport after an ACL tear.
REFERENCE (this entire blog is a review of the follow article)
1. Griffin LY et al. Noncontact Anterior Cruciate Ligament Injuries: Risk Factors and Prevention Strategies. Journal of the American Academy of Orthopaedic Surgeons. 2000, 8(3). 141-150.