What is an ACL tear?
The knee is essentially a hinged joint made of the femur (thigh bone) and the tibia (shin bone). The ACL is one of the ligaments within the knee that helps to connect the two bones.
The ACL prevents the tibia from sliding too far forward relative to the femur, but it is also important in rotational stability of the knee. It runs diagonally in the middle of the knee and is one of the most commonly injured ligaments in the knee. Annually, there are approximately 200,000 ACL injuries in the United States. In general, the incidence of ACL tears is higher in athletes involved in pivoting, cutting sports such as football, soccer, and basketball.
The mechanism of injury in ACL tears is usually a deceleration with a pivoting or cutting maneuver. For instance, a soccer player who is planting and cutting directions to get around an opponent. Seventy percent of ACL injuries occur in a non-contact manner, whereas 30% are a contact injury with another player.
Several studies have shown that female athletes have a higher incidence of ACL injuries than male athletes. The reason for this isn’t entirely known, but proposed theories include differences in bony anatomy, muscle strength, and neuromuscular control. Currently, a biomechanical study is ongoing in conjunction with The Center and OSU Biomechanics Laboratory at Therapeutic Associates looking at landing patterns of athletes and its connection to ACL injuries.
Usually an ACL injury is one in which the athlete pivot, cuts, lands awkwardly, or has contact with another player, and feels immediate pain in the knee and an abnormal shifting or motion during the injury. Usually, the knee becomes swollen fairly quickly and it is difficult to walk afterwards.
During the physical examination with your sports medicine orthopedic surgeon, we will look for several physical findings. First, the amount of fluid within the knee is assessed. When the ACL is torn, the artery that supplies the ACL tears is torn as well, and the knee gets filled with blood. This fluid can be detected by the exam. Range of motion is usually limited. The outside back of the knee (lateral posterior aspect of the tibia) is tender to the touch and corresponds to the bone contusion (bruise) that usually occurs with this injury. At the same time, an orthopedic surgeon will assess the knee for other injuries, such as meniscus tears. Testing the ACL ligament is done by the Lachman’s test and pivot shift test. The Lachman test is performed by assessing the translation, or motion forward, of the tibia on the femur. It is compared to the amount of translation the other knee. The pivot shift test assesses the rotation stability of the knee. The other ligaments of the knee are tested as well during a complete exam.
X-rays are usually taken as a screening exam to make sure there is no fracture. Sometimes x-rays will show a “Segond fracture” which is a pathognomonic sign on an x-ray of an ACL tear. Usually, your sports medicine orthopedist can diagnose an ACL tear by history and physical exam alone. Many orthopedists will order an MRI to assess all concomitant injuries that can occur with ACL injuries to refine the treatment plan.
Treatment plans should be tailored to each individual patient. Non-operative treatment is definitely an option and should be considered in low demand patients. It is also the preference in partial ACL tears without instability, athletes without instability symptoms, athletes who are willing to modify their sports, and those who desire to try non-operative treatment. Brace treatment tend to lessen “instability episodes” or feeling like the knee is shifting in recreational athletes.
In general, younger athletes in pivoting, cutting sports have a higher incidence of electing ACL reconstructive surgery. Many of the middle-aged recreational athletes in Central Oregon also fit into this category, due to their desire to continue their active lifestyle with a stable knee. The goal of ACL reconstruction is to provide the athlete with a stable knee so they can return to their previous level of function. Orthopedic surgeons are successful in this pursuit approximately 82-95% of the time.
ACL reconstructive surgery involves making a new ligament to take the place of the torn ACL. When the ACL tears, it disrupts the blood supply to the ligament and it is not able to repair itself. The surgery involves taking new tissue called a graft and using it to replace the ACL. This is done in an arthroscopic surgery in which small drill holes, about the size of a pencil, are drilled in the locations of the native ACL. Then the graft is passed through these drill holes and fixed on either end to form the new ligament. The graft tissue used is determined by the individual patient and surgeon preferences.
The recovery after surgery is dictated by your body’s repair capabilities. It takes your body at least six months for a new ACL to fully incorporate, so you need to protect the graft for this amount of time. Initially, patients will use a brace and crutches for a variable time period, usually 2-6 weeks. A graduated activity program is implemented over the six month period until full return to activity without limitations is allowed six months after surgery. Brace treatment after return to full activity is optional. There is some evidence showing that bracing helps reduce the incidence of ACL graft tears only in alpine skiing.