Anterior Cruciate Ligament Injuries of the Knee

by Terry Habig, M.D.

Anterior cruciate ligament (ACL) injuries of the knee have become more publicized over the past few years because of newspaper articles and injury reports of high school, collegiate and professional athletes. The anterior cruciate ligament is one of the major ligaments in the knee and it provides stability to the knee, particularly in preventing the lower leg or tibia from abnormal anterior movement on the femur. Disruption of the ACL often can cause functional disability and, therefore, prevent an athlete from returning to his or her athletic event. The injury usually occurs with a non-contact injury: the athlete suddenly decelerates (comes to a quick stop); this is followed by a sudden change in direction while running, pivoting or landing from a jump. The stress applied to the ACL exceeds the threshold of strength, and the ACL tears. The athlete describes a sudden giving way or shifting associated with a pop and frequently a rather sudden onset of swelling and pain. The most common sports with a higher incidence of ACL injuries include basketball, soccer and volleyball.

Female athletes have a much higher incidence of ACL injuries than do male athletes, particularly in basketball. The number of female athletes participating in sports at all levels has risen dramatically over the past several years. The style of play in the different sports also has changed in that females are playing sports more often with higher speed and greater power. Several theories regarding the increased risk of ACL disruption in females include: smaller muscle mass about the knee to protect the ACL, smaller opening around the ACL within the knee, which could cause some impingement and perhaps increased rate of tear, hormonal differences and the effect of hormones on muscle imbalance, and "loose jointedness." No one knows for sure why female athletes have an increased risk of tearing the ACL.

A simple explanation of exactly what happens inside the knee at the moment of injury is that the anterior cruciate ligament tears completely or is stretched such that it no longer provides stability to the knee. Symptoms such as a fairly sudden onset of swelling and pain are quite typical of an ACL tear. Because of the swelling and pain it is not unusual that the athlete is unable to fully extend the knee and, therefore, tends to limp because of a combination of lack of full extension and pain.

Physical examination by a physician may show signs of an ACL injury. Specific tests performed to evaluate the ACL include the Lachman test, the anterior drawer test and the pivot-shift test. The Lachman test is performed with the athlete lying down and the physician pulling forward on the tibia below the knee while holding the thigh in place. Increased forward movement of the tibia bone is indicative of an ACL injury. This test is performed with the knee bent about 20^o or 30^o. The anterior drawer test is similar but the knee is bent 90^o and the physician puts his or her hands behind the proximal tibia and once again pulls forward. Increased anterior displacement of the tibia on the thighbone indicates a torn anterior cruciate ligament. The pivot-shift test is a maneuver in which the knee is moved slowly through a range of motion while a lateral stress is applied to the knee .The physician can oftentimes produce a sudden pivoting of the knee while this maneuver is performed but it depends on the patient being able to relax the involved extremity.

Plain x-rays of the knee will not show a torn anterior cruciate ligament but oftentimes a small chip fracture on the lateral side of the knee is associated with a torn anterior cruciate ligament. An MRI of the knee is the gold standard for diagnostic testing to determine a torn anterior cruciate ligament. Unfortunately, no test is 100% accurate.

Treatment options consist of conservative management as well as surgical intervention. Certain sports such as basketball, soccer, volleyball, racquetball and tennis put more demand on the knee than other sports. Physical therapy for rehabilitation of the knee and bracing of the injured knee for sports sometimes can allow patients to function normally; however, a young athlete who wants to return to a high demand sport has a much greater risk of having problems of instability in a knee that has had an ACL injury. Surgical intervention is appropriate, therefore, for the athlete or patient who has symptoms of instability or who plans to return to a "high demand" sport.

Surgical treatment of ACL injury of the knee has evolved into reconstruction of the anterior cruciate ligament. Borrowing tissue from either the patient’s own knee or from a cadaver’s (a dead person) has been the treatment of choice for ACL reconstructions. The gold standard is to borrow the central third of the patellar tendon with a piece of bone from the patella and a piece of bone from the tibia. The tendon that is borrowed becomes the new ligament inside the knee and the bone plugs at each end fit into a drill hole that is made in the tibia and femur respectively. The bone plugs are secured by a variety of fixation devices but the most common device is a screw. Different tissue options other than the patellar tendon include hamstring tendon or patellar tendon from a cadaver.

Usually, range of motion of the knee is started immediately after surgery. Frequently, a continuous passive motion (CPM) machine is used to move the knee passively. The patient usually is discharged from the hospital within 24 hours and is started on weightbearing as tolerated with crutches and physical therapy. The first six weeks are used to regain full range of motion and to diminish the swelling within the knee and to wean off of the crutches. It is not uncommon for the athlete to be able to run by 10 weeks and to return to sports by six months. The functional abilities of the athlete improve over the first one to two years during this period of time.

Unfortunately, all operations have some risk, and this certainly is true with ACL reconstructions. It is not uncommon to have some soreness in the front of the knee, particularly if the patellar tendon is used to reconstruct the anterior cruciate ligament. Patients will have some soreness, popping and sometimes an area of numbness around the front of the knee. These symptoms usually improve and subside over the first year. The risk of rupture of the patellar tendon or fracture of the patella is very small. Additional risk includes the risk of not regaining full range of motion. This risk of stiffness is diminished if the surgery is not performed until the patient has regained almost full range of motion preoperatively. The risk of stiffness also is diminished by starting motion immediately and by attending physical therapy. It is unusual for the reconstructed ACL to provide the same stability to the knee as existed preoperatively. Generally, an 85% success rate for return of athletes to all activities can be expected. Improved techniques of performing the surgery have increased successful results, diminished hospital stays and decreased complication rates.

An ACL injury can be a disappointing injury to an athlete, causing functional limitations and difficulty with the return to sports. But currently, an athlete’s chance of returning to his or her sport following reconstruction for an ACL injury is excellent.

For further information please contact us for assistance in arranging an appointment, (504) 897-6351.