With every movement of the knee, from a simple step forward in line to an ice skater’s leap, a complicated network of tendons and ligaments help stabilize and support this major joint. Unfortunately, these structures, particularly the anterior cruciate ligament (ACL) are vulnerable to injury during athletic activity, or even as the result of impact.
Tears of the anterior cruciate ligament are quite common, with between 70,000 to 80,000 reported each year in the United States.1 These injuries, which may be partial or complete, usually occur during athletic activity when a person stops suddenly, and changes direction as when running, pivoting or landing after a jump. Sudden impact to the knee may also result in a torn ACL. Without an intact ACL there is instability of the knee resulting in a sudden sense of shifting or bucking, and individuals can not jump and land on the knee, accelerate and then change directions, or rapidly pivot on the knee.
Sagittal MR image demonstrates intact anterior cruciate ligament
In some cases patients report hearing a popping sound at the moment that the tear occurs. Pain, swelling and a feeling of instability to the knee may occur within the immediate period after the injury, however, in some cases, the symptoms may be mild. When the tear to the ACL is the only injury present, and if the patient’s lifestyle does not require the performance of the movements described, non-surgical treatment is a viable option. Immediately after the injury, the patient is advised to stay off the leg and elevate it, apply ice, and to take medication such as ibuprofen to reduce pain and inflammation. A course of physical therapy is prescribed to strengthen surrounding muscles, and a brace may be fitted for use during activities that would place special stress on the knee.
Sagittal MR image demonstrates a complete tear of the ACL
Many people with torn ACLs treated with conservative measures continue to lead an active lifestyle that includes the use of most equipment found at the gym or health club, swimming, jogging, and possibly skiing up to an intermediate level.
However, long-term outcome for patients who are treated non-surgically varies. Those who return to unrestricted activity are likely to experience some instability. Pain may be associated with the physical therapy regimen. In the absence of an intact ACL—even when no other injury is present—the menisci (pads of cartilage that cushion the bones that meet at the knee joint) are at greater risk of injury. Once the menisci are torn, pain and swelling may occur, and with it, a greater risk for developing osteoarthritis.
The decision to proceed to surgical repair is usually dictated by lifestyle rather than age. According to Thomas L. Wickiewicz, MD, Attending Orthopedic Surgeon at HSS, "An active 60-year-old who feels constrained after their injury should consider surgery; similarly, a 20-year-old who fits the appropriate profile can go ahead and opt for non-surgical treatment."
Because the ACL cannot be reattached once it is torn, surgical reconstruction requires the grafting of replacement tissue in its place. Multiple sources are used including the patient’s own hamstring tendons, bone-tendon-bone patellar tendon, the quadriceps tendon, or an allograft (human donor tissue). The type of graft used is determined on a case-by-case basis.
Sagittal MR image demonstrates intact anterior cruciate ligament reconstruction.
ACL reconstruction is performed using arthroscopic techniques, in which a combination of fiber optics, small incisions, and small instruments are used. (A somewhat larger incision is needed to obtain the tissue graft.) Patients undergoing ACL reconstruction at the Hospital for Special Surgery (HSS) are given an epidural—the same type of anesthesia that many women receive during childbirth—so that they may be awake during their surgery if they so choose. An overnight stay in the hospital is not necessary.
Reconstructive surgery is generally scheduled between three and six-weeks after the injury occurs in order to allow inflammation in the area to subside. If surgery is performed too early, patients may develop arthrofibrosis, a profound scar response. Orthopaedic surgeons gauge the appropriate timing of surgery based on the presence of other injuries (which may require more prompt attention), physical appearance of the knee, and the patient’s level of pain, degree of range of motion, and the quality of muscle control.
Following surgery, the patient enters a rehabilitation program to restore strength, stability, and range of motion to the knee. Recovery time varies, with a period from about 6 to 9 months representing the average. However, cautions Dr. Wickiewicz "I advise patients not to regard rehabilitation as a race. People heal differently from one another and a variety of factors influence recovery, including the presence of associated injury or disease and the amount of time the patient has to commit to a physical therapy program."
Assessment of recovery is based on restoration of muscle strength, range of motion, and proprioception or joint position sense. The degree of pain associated with ACL recovery also varies and can be addressed successfully with medication.
People of all ages and physical abilities and conditioning can tear their ACLs. In recent years, many investigators have noted the high incidence of ACL injuries among women. A number of theories—none of them confirmed—have been presented including: greater laxness in the ligaments, anatomical differences, and hormonal fluctuations.
ACL injuries are also not uncommon in children, for whom treatment, including non-operative measures, proves more difficult. "Restriction of physical activity can be next to impossible in young children," notes Dr. Wickiewicz. "The movements the child needs to avoid are a part of his or her everyday play." Moreover, braces are not particularly effective since the child must wear them virtually all the time and they must be replaced often, to accommodate growth. In addition, if the ligament is not repaired, the child risks doing greater injury to the meniscus and cartilage in the joint.
Owing to concern for preserving normal growth, treatment for children has traditionally been non-operative. However, more recently developed techniques have made surgical repair an option at some institutions, such as HSS. The success rate for the surgery in children is somewhat lower than that for adults, owing to the different stresses placed in the knee among children.
Much of what is known about the function of the ACL and early attempts to repair this ligament can be attributed to the late John Marshall, MD, the Director of Sports Medicine at HSS in the late 1970s. Building on his legacy, physicians in the HSS Sports Medicine service have participated in more than 20 years of research on ACL reconstruction, from primary repairs to current, state-of-the art arthroscopic techniques. Results from this research have appeared in numerous publications.
Working with a dedicated team of experienced nurses, and specialists in rehabilitation and pain management, the orthopaedic surgeons at HSS are well-prepared to respond to the clinical needs of a wide range patients with ACL tears, including those with multiple injuries and/or pre-existing disease. To date they have performed more than 2000 ACL reconstructions and have considerable experience with pediatric patients (a population for whom surgical reconstruction is not considered to be an option at some institutions.)
Summary Prepared by Nancy Novick • Diagnostic imaging examinations provided by HSS Radiologists