Guest commentary: The ins and outs of ACL injuries
October 18, 2016
The ACL (anterior cruciate ligament) is one of the four major ligaments in the knee. The ACL helps connect the femur to the tibia and is very important for normal knee stability. Its main function is to prevent front-to-back motion between the femur and tibia, but it also is important for rotational stability.
Women, in particular high school and collegiate volleyball, basketball and soccer players, are most susceptible to tearing the ACL. Skiing, mainly from the torque placed on the knee by a long lever (ski), is a very common cause of ACL injury in our community. The incidence of ACL injury in skiing is similar to that of collegiate football.
When one tears the ACL, they will often feel a "pop" and develop pain, swelling and instability. Active individuals often lack confidence in the knee and have difficulty getting back to high-end activities. ACL-deficient knees also are more vulnerable to further injury to the meniscal or articular cartilage. When this happens, subsequent arthritis is likely. Physical therapy and bracing may help restore motion and strength but not normal stability. Though ACL-prevention programs have been very successful in reducing the likelihood of injury in high-risk individuals (female volleyball, basketball, and soccer players) once injury does occur, surgery is the recommended treatment.
We know from previous experience that repairing the ACL is not effective. Though other ligaments in the knee (medial collateral ligament) heal without surgery when injured, the location of the ACL in the knee joint (intra-articular) makes it unlikely to heal when injured or when repaired. Thus, reconstruction is the procedure of choice for restoring normal knee stability. Reconstruction means using other tissue to act as a substitute for the torn ACL.
ACL substitutes (grafts) are generally divided into autografts and allografts. Autografts are tissue taken from the patient at the time of surgery. The most common autografts are the middle one-third patellar tendon, hamstring tendon, and quadriceps tendon. Autografts are most commonly used in young, active individuals. Some studies have shown a higher graft failure rate when using allografts (tissue from a cadaver) in young, active patients. The decision to use one autograft over another is based on several factors, including patient age, gender, laxity, harvest site morbidity, previous surgery and surgeon preference. All autograft tissue is stronger at the time of insertion (2,400 to 4,000 newtons) than the native ACL (2,100 newtons).
Allografts are most commonly used in older patients who may not place as much stress on their knee. Advantages of allografts include no harvest site morbidity, shorter surgery, smaller incisions and quicker initial rehab (less pain). However, because of the patient's immune response to the allograft, final healing takes longer than an autograft. Secondary to the ability to obtain larger (and stronger) tissue, allografts are commonly used in revision ACL surgery. In general, studies comparing long-term outcomes of auto and allograft tissue show similar results.
ACL reconstruction is an arthroscopic procedure. Other associated pathology (usually cartilage injury) is addressed at the same time. The surgery takes about an hour and is done as an out-patient procedure. Tunnels (holes) are drilled into the femur and tibia to reapproximate the normal ACL anatomy. The graft tissue of choice is then passed through the tunnels and fixed to the bone (with screws, etc.) until biological healing occurs (usually six to 12 weeks). The technical aspects of the procedure vary among surgeons and are beyond the scope of this discussion. Though double-bundle reconstruction — the native ACL has an antero-medial and a postero-lateral bundle — has been advocated by some surgeons, it is technically demanding and has not proven to be clinically superior. Most surgeons today perform a single-bundle anatomic reconstruction.
Rehabilitation following ACL reconstruction is aggressive yet guarded. Patients leave the hospital on crutches and wearing a brace. Crutches are usually discontinued after one to two weeks and the brace after three to six weeks, depending on other associated injuries. Most patients are on a stationary bike in one week and ambulating comfortably within a week. Activities are increased as swelling decreases and motion and strength improves. By 12 weeks, patients are able to jog on level surfaces, hike, bike and swim. Unlimited activity occurs at a minimum of six months. It takes that long to regain sufficient muscular strength and control of the limb and for the graft to mature (ligamentization) enough to allow aggressive activities. No evidence exists to recommend the routine use of functional braces post-op.
Though ACL injuries can be devastating in terms of limiting an individual's ability to work and recreate, modern medicine and technology give us the ability to anatomically reconstruct a torn ACL. By doing so, patients are able to regain their knee function and get back to pre-injury activity levels.
Tom Pevny is a physician who specializes in orthopedic sports medicine, trauma and partial and total knee replacement at OrthoAspen.