Ask the Doctor: ACL Injuries

Adam Senk was sidelined by a left ACL tear in the spring. The same injury occurred to Rodney Kinlaw two summers ago. Last week freshman Brennan Coakley tore an ACL. Potentially career-ending, a tear of the anterior cruciate ligament is a success story in the discipline of sports medicine. This injury, which once could end a career in a fraction of a second, is now felt to be fully recoverable.

Let's take a look at the ACL, how the injury occurs, how it is repaired and rehabilitated, and the outlook for the player.

What is an ACL injury?

The anterior cruciate ligament (also called the ACL) is one of four ligaments that are critical to the stability of the knee joint. A ligament is made of tough fibrous material and functions to control excessive motion by limiting joint mobility.

The ACL injury is the most common knee ligament injury. The knee is essentially a modified hinge joint located where the end of the femur (thigh bone) meets the top of the tibia (shin bone). There are four main ligaments connecting these two bones:

  • medial collateral ligament (MCL) — runs along the inner part of the knee and prevents the knee from bending inward.
  • lateral collateral ligament (LCL) — runs along the outer part of the knee and prevents the knee from bending outward.
  • anterior cruciate ligament (ACL) — lies in the middle of the knee. It prevents the tibia from sliding out in front of the femur, and provides rotational stability to the knee.
  • posterior cruciate ligament (PCL) — works in concert with the ACL. It prevents the tibia from sliding backward under the femur.

    ACL tears may be due to contact or non-contact injuries. A blow to the side of the knee, which may occur during a football tackle, may result in an ACL tear. Alternatively, coming to a quick stop, combined with a direction change while running, pivoting, landing from a jump or overextending the knee joint, can cause injury to the ACL.

    Rodney Kinlaw suffered a non-contact ACL tear. ACL injuries can be associated with simultaneous injuries to the MCL and the medial meniscus (one of the shock-absorbing cartilages in the knee). This type of injury is most often seen in football players and skiers.

    Women are more likely to suffer an ACL tear than men. The cause for this is not completely understood, but may have to do with differences in anatomy as well as muscular functioning.

    When an ACL injury occurs, the knee becomes less stable. The ACL injury is a problem because this instability can make sudden, pivoting movements difficult, and it may make the knee more prone to developing arthritis and cartilage tears. Many sports require a functioning ACL to perform common maneuvers such as cutting, pivoting and sudden turns. There are certainly other sports, but football is one of these high-demand sports.

    Early symptoms include a "pop" sound at the time of injury, severe pain, knee swelling within six hours of injury and sudden giving way of the knee.

    An ACL injury should be treated with a splint, ice, elevation of the joint (above the level of the heart) and pain relievers such as nonsteroidal anti-inflammatory drugs. The patient should not continue to play until evaluation and treatment has taken place.

    An ACL tear may be difficult to diagnose immediately after the injury because of associated pain and swelling. There may also be muscle spasm that contributes to making the knee difficult to examine. In the orthopedist's office, knee instability can be assessed by specific maneuvers performed by the physician. These maneuvers test the function of the ligament to determine if an ACL tear is present. A complete examination of the knee is also necessary to determine if other injuries may have occurred. The physician will also evaluate X-rays of the knee to assess for any possible fractures and a MRI may be ordered to evaluate for ligament or cartilage damage.

    Virtually all athletes undergo surgery, with the hope of returning to normal function and competitive level. The term "ACL repair" is actually a misnomer. The ACL, as it pertains to sports related injuries and therefore the return of the athlete to a competitive level, cannot be repaired. It cannot be sewn together. In actuality, the torn ends of the tendon almost always appear frayed when visualized after an ACL tear. The torn ends of the ACL are removed and replaced with a different structure (a graft). To secure the graft into the position of the normal ACL, tunnels are made in the shin bone (tibia) and thigh bone (femur), and the graft is passed through these tunnels to reconstruct the ligament. The important issue in reconstruction is the source of the graft to use for the reconstruction.

    ACL reconstruction can be done with several different graft choices. These include patellar tendon, hamstring tendon, and donor tissue (allograft). Each of these choices has advantages and disadvantages.

    Patellar Tendon

    The patellar tendon is the structure on the front of your knee that connects the kneecap (patella) to the shin bone (tibia). The patellar tendon averages between 25 to 30 mm in width. When a patellar tendon graft is taken, the central 1/3 of the patellar tendon is removed (about 9 or 10 mm) along with a block of bone at the sites of attachment on the kneecap and tibia.

    Advantages: Many surgeons prefer the patellar tendon graft because it closely resembles what needs reconstruction. The length of the patellar tendon is about the same as the ACL, and the bone ends of the graft can be placed in to the bone where the ACL attaches. This allows for "bone to bone" healing, something many surgeons consider to be stronger than any other healing method.

    Disadvantages: When the patellar tendon graft is taken, a segment of bone is removed from the kneecap, and about 1/3 of the tendon is removed. There is a risk of patellar fracture or patellar tendon rupture following this surgery. Also, the most common problem following this surgery is pain on the front of the knee. In fact, patients sometimes say they have pain when kneeling, even years after the surgery.

    Hamstring Tendon

    The hamstring muscles are the group of muscles on the back of your thigh. When the hamstring tendons are used in ACL surgery, two of the tendons of these muscles are removed, and "bundled" together to create a new ACL.

    Advantages: The most common problem following ACL surgery using the patellar tendon is pain over the front of the knee. Some of this pain is known to be due to the graft and bone that is removed. This is not a problem when using the hamstring tendon. The incision is also smaller, and the pain both in the immediate post-operative period, and down the road, is thought to be less.

    Disadvantages: The primary problem with these grafts is the fixation of the graft in the bone tunnels. When the patellar tendon is used, the bone ends heal to the bone tunnels ("bone to bone" healing). With the hamstring grafts, a longer period of time is necessary for the graft to become rigid. Therefore, people with hamstring grafts are often protected for a longer period of time while the graft heals into place.

    Allograft (Donor Tissue)

    Allograft is most commonly used in lower demand patients, or patients who are undergoing revision ACL surgery (when an ACL reconstruction fails). Biomechanical studies show that allograft (donor tissue from a cadaver) is not as strong as a patient's own tissue (autograft). For many patients, however, the strength of the reconstructed ACL using an allograft is sufficient for their demands. Therefore this may be an excellent option for patients not planning to participate in high-demand sports (e.g. soccer, basketball, etc.).

    Advantages: Performing the surgery using allograft allows for decreased operative time, no need to remove other tissue to use for the graft, smaller incisions and less post-operative pain. Furthermore, if the graft were to fail, revision surgery could be performed using either the patellar tendon or hamstring grafts.

    Disadvantages: Historically, these grafts were of poor quality and carried a significant risk of disease transmission. More recently, techniques of allograft preparation have improved dramatically, and these problems have greatly improved. However, the process of graft preparation (freeze-drying) kills the living cells, and decreases the strength of the tissue. There is also the concern of disease transmission. While sterilization and graft preparation minimizes this risk, it does not eliminate it entirely.

    Many surgeons have a preferred technique for different reasons. The strength of patellar tendon and hamstring grafts is essentially equal. There is no right answer as to which is best, at least not one that has been proven in orthopedic studies. The strength of allograft tissue is less than the other grafts, but the strength of both the patellar tendon and hamstring tendon grafts exceed the strength of a normal ACL.

    ACL reconstruction is usually not performed until several weeks after the injury. Studies have shown improved results when ACL reconstruction surgery is delayed several weeks to allow swelling to decrease, inflammation to subside and range of motion to improve. Resolution of swelling and stiffness prior to ACL reconstruction surgery improves the post-operative function of the joint.

    Anterior cruciate ligament rehabilitation has undergone considerable changes over the past decade. Intensive research into the biomechanics of the injured and the operated knee have led to a movement away from the techniques of the early 1980s characterized by post operative casting and delayed rehabilitation, to the current early rehabilitation program.

    Many rehabilitation programs are divided into four phases. In the first one to two weeks the aims of therapy are to decrease pain and swelling, and increase the range of motion of the knee. A post-operative brace is ranged from 30 to 90 degrees and is used until there is adequate quadriceps control. Crutch-walking with partial weight bearing is allowed and the usual modalities are used to reduce pain and swelling.

    During the second phase, from two to six weeks, the emphasis is on increasing the range of motion, increasing weight bearing and gaining hamstring and quadriceps control. The patient is usually out of the brace by the third to fourth week

    During the third stage, from six to twelve weeks, emphasis is placed on improved muscular control, proprioception and general muscular strengthening. Proprioceptive work progresses from static to dynamic techniques including balance exercises on the wobble board and eventually jogging on a mini-tramp. The patient should have a full range of motion during this stage and gentle resistance work should be added. By the end of this period the patient should be able to cycle normally, swim with a straight leg kick and be able to jog freely on the mini-tramp.

    The fourth phase of rehabilitation from twelve weeks to six months involves the gradual re-introduction of sports specific exercises aimed at improving agility and reaction times and increasing total leg strength.

    Over 90 percent of patients are able to resume their previous level of activity after ACL reconstruction. A small percentage of patients will be limited by persistent pain or instability; however, changes in activity level following ACL reconstruction surgery are often due to choice rather than limitations of the knee joint. An elite athlete who has had a technically well-performed early reconstruction of the anterior cruciate ligament followed by an adequate and successful rehabilitation program should be able to return to the field of his chosen sport between six and nine months.


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