The much-loathed news that an athlete has torn his or her ACL is unfortunately not an uncommon occurrence at any level of athletics. In fact these “season-ending” injuries are seemingly so common that it is almost as if one cannot turn on ESPN without hearing about an ACL injury, be it football, soccer, basketball, or whatever sport may be in season. It’s also not uncommon to see young children on Saturday mornings sitting on their teams’ respective bench with that telltale, bulky brace strapped to their leg. But despite the ever-present nature of these knee injuries, many athletes, coaches, and parents are still left with many questions regarding the nature of these injuries and wonder what to expect throughout the somewhat lengthy rehabilitation process.
To even begin a discussion regarding an ACL injury it’s imperative to have a basic understanding of the architecture of the knee. Without this basic knowledge to build upon, it is difficult to grasp the actual dynamics of the injury and significant role that the ligament play in producing many of the movements that we use in athletics and exercise.
The knee joint, as commonly considered, is an articulation between the femur (the bone in the thigh) and the tibia (the shin bone). It’s considered primarily a hinge joint, which means that it permits flexion and extension like the opening of a door by a hinge mechanism. The surfaces at this joint are unique in that they provide large communicating planes, but unfortunately, the surfaces are discrepant and lead to a somewhat less stable joint when compared to many of the other large joints. To better visualize the inherent instability of the knee joint in a more exaggerated manner, one could visualize trying to balance a bowling ball upon a coffee table without the ball rolling off. This analogy helps us to visualize the necessity for other stabilizing factors in the knee joint to help prevent unwanted slipping and dislocation.
These stabilizing factors include the external fibrous capsule that surrounds the joint as well as the muscles and ligaments that hold the bones in place. Most commonly noted are:
· Lateral collateral ligament (LCL) and medial collateral ligament (MCL), which both prevent side-to-side movement at the joint
· Oblique popliteal ligament
· Arcuate popliteal ligament
· The menisci that serve as cartilaginous cushions for shock absorption and stabilization
· Posterior Cruciate Ligament, which limits anterior/forward rolling of the femur on the shin (tibia) during extension of the knee.
· Anterior Cruciate Ligament, which is the weaker of the two cruciate ligaments and prevents the posterior or backwards movement of the femur upon the shin (tibia) as well as hyperextension at the joint.
Although it may seem arduous to review the anatomy of the joint, it’s helpful in understanding why the knee is such a commonly injured area. After seeing how inherently unstable the bony components of this articulation are, we can appreciate that the knee requires many fibrous ligaments to hold the two bones in place. Furthermore, one can begin to visualize why the ACL is one of the more commonly injured elements of the knee given its role in preventing hyperextension/backwards movement of the femur.
To further investigate ACL injuries, it’s helpful to quickly “walk-through” a common example of this injury mechanism. ACL injuries are most commonly seen in sports such as soccer, football, and basketball because these sports require participants to stop quickly, and cut/change directions very sharply. This kind of motion on the knee makes individuals more prone to decelerate, twist, or hyperextend their knees even without contact from another player. When you add in the physicality of contact some of these, one can easily see how ligaments may be strained to the point of tearing. In fact, when a player is hit from the side of the knee, many times we will see what is dubbed the “unhappy triad.” This involves a torn ACL, a torn MCL, and a torn medial meniscus.
Some researchers have shown that a major role in ACL injury involves something known as ground reactive forces (GRFs). These are the forces that must be absorbed by the body when our foot strikes the ground. In one particular video analysis that was done in 2009, it was shown that athletes who ruptured their ACLs tended to land more often on their hind foot or in a flat foot position when compared to the individuals who did not injure their ACLs. Furthermore, the athletes who sustained ACL injuries reached their flat-footed position 50% sooner than their control counterparts. Essentially what this showed is that the calf muscle (Gastrocnemius), which plays a role in reducing the GFRs that we transmit to the knee by allowing a slower transition to a flat foot position, may influence our foot strike and thus possibly influence risk for injury of an ACL.
Another interesting mechanical point regarding ACL injuries that should be noted is the fact that female athletes have a significantly increased incidence of ACL injury due to the inherent higher Q-angle in the female body. This Q-angle is essentially an imaginary line that can be drawn from the hip to the kneecap. The angle of this line is measured as a way to examine various forces on the knee. As the Q-angle is increased, as we commonly see in women, this increases the inherent lateral (outside) compressive force on the knee. Because of this increase in inherent lateral compression, the GRF needed to injure the ACL is effectively lowered which makes women more prone to injuring their ACLs as compared to their male counterparts.
What are the symptoms of a torn ACL?
When an athlete tears his or her ACL, there are a number of common signs and symptoms that he or she will likely experience. It is common that upon the movement or hit that causes the damage, that an athlete may even hear a popping sound. This may be followed by pain on the lateral/outside of the knee or even in the back of the knee. Many times there is an immediate instability of the knee in which the athlete may complain of a “wobbly” feeling knee that buckles out from underneath when attempting to cut sharply or jump. Lastly, the knee will typically swell during the first few hours after the injury, which may be attributed to the normal inflammatory process or more serious bleeding within the joint. It is not uncommon for this swelling to limit the flexibility of the joint as it worsens.
Typically, on-field testing is done as a preliminary assessment of the ligament’s integrity. This test is called the anterior draw test. After the athlete is taken to a medical facility, the diagnosis will be confirmed with an MRI to examine the structural components of the knee.
Treatment options for ACL injuries most commonly include:
· Nonsurgical rehabilitation
· Surgical reconstruction
For the nonsurgical treatment of an ACL injury, the patient has most likely only sprained his or her ACL, or has elected to not have surgery because the instability of their knee does not affect their daily quality of life. This kind of treatment typically includes an initial immobilization of the knee via the use of crutches and/or splint that is followed up by physical therapy treatment to strengthen the surrounding muscles of the knee to help stabilize the joint.
The surgical treatment of the knee is typically done via the use of a surgical instrument called the arthroscope, which allows the surgeon to enter the joint in a minimally invasive way by using a microscopic camera. There are several techniques that may be applied to surgical reconstruction of the ACL such as the use of cadaver tissue or the use of the patient’s own tissue from another site to harvest as a graft. These techniques allow the surgeon to drill holes into the bones to form tunnels in which the graft can be anchored in. After the surgery, the patient will likely take 4-6 months to complete physical therapy and fully recover from the injury. It has been shown that 60% of patients achieve a full recovery to their former athletic performance prior to the injury, while 80-90% of patients report a great improvement in pain and stability as compared to their pre-surgical status.
While the field of orthopedics is constantly evolving, the management and treatment of ACL injuries is a particular area of interest to many individuals given the magnitude of impact an ACL injury can have on an athlete’s career as well as the sheer number of injuries that are reported each year. It is simply amazing some of the progress that we have seen in sports medicine throughout the years. In fact, in the near future we may be using spider silk to help strengthen ACL grafts in patients in order to reduce the number of recurring injuries to the ligament. Furthermore, rehabilitation science and less invasive surgical procedures are allowing for quicker recovery time and less functional deficits. The human body is a truly amazing machine that runs in such an intricate and fine-tuned manner. As sports science pushes this machine to it’s limits, sports medicine is right there following behind to help provide the appropriate treatments to help us excel and raise the bar of human limits.
For local sports medicine orthopedics and more information on ACL injuries and treatment check out the great resources at our own:
Brigham and Women's Orthopedics
Mass General Orthopedic Surgery
Please feel free to leave me any comments, feedback, concerns, or insight on this page or email me at c_meltsakos@nymc.edu. Also, if you like what you've read subscribe to the feed to get my articles sent directly to your inbox!
References:
1. Boden BP, Torg JS, Knowles SB, Hewett TE: Video analysis of anterior cruciate ligament injury: Abnormalities in hip and ankle kinematics. Am J Sports Med 2009;37(2):252-259.
2. Hewett TE, Torg JS, Boden BP: Video analysis of trunk and knee motion during non-contact anterior cruciate ligament injury in female athletes: Lateral trunk and knee abduction motion are combined components of the injury mechanism. Br J Sports Med 2009;43(6):417-422.
3. Meyer EG, Haut RC: Excessive compression of the human tibiofemoral joint causes ACL rupture. J Biomech 2005;38(11):2311-2316.
4. Plowman, SA., Smith, DL. Exercise Physiology for Health, Fitness, and Performance. 2008: Philadelphia, PA: Lippincott Williams & Wilkin.
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