The knee is the largest joint in your body and one of the most complex. Three bones meet to form the knee joint: the thighbone (femur), shinbone (tibia), and kneecap (patella). The kneecap sits in front of the joint to provide some protection. Knee ligaments connect the thighbone to the lower leg. The four primary ligaments in the knee act like strong ropes, holding the bones together and keeping the knee stable.
One of the most common knee injuries is an ACL sprain or tear. Athletes who participate in high demand sports like soccer, football and basketball are more likely to injure their anterior cruciate ligaments. About half of all ACL injuries occur along with damage to other structures in the knee, such as articular cartilage, meniscus, or other. Most ACL injuries are complete or near complete tears, while partial tears are quite rare. If you have injured your ACL, you may require surgery to regain full function of your knee. This will depend on several factors, such as the severity of your injury and your activity level.
An injured ligament is considered a sprain, and is graded on following severity scale:
When injuring your ACL, you may hear a "popping" noise and feel your knee give out from under you. Within 24 hours most people experience swelling of the knee and many have pain as well. Other typical symptoms include: loss of full range of motion, tenderness along the joint line, and discomfort while walking. If ignored, the swelling and pain may resolve on its own, however, if you attempt to return to sports, your knee will probably be unstable and you risk causing further damage to the cushioning cartilage (meniscus) of your knee.
An ACL injury can occur in various ways, including: rapidly changing direction; stopping suddenly; slowing down while running; landing incorrectly after a jump; and direct contact or collision, such as a football tackle. In fact, 70-80% of ACL tears occur without a collision with another person/player. Several studies have shown that female athletes have a higher incidence of ACL injury than male athletes in certain sports. It has been proposed that this is due to differences in physical conditioning, muscular strength, and neuromuscular control. Other suggested causes include differences in pelvis and lower extremity (leg) alignment, increased looseness in ligaments, and the effects of estrogen on ligament properties.
Your physician will examine all the structures of your injured knee and compare them to your uninjured knee. Most ligament injuries can be diagnosed with a thorough physical examination. Other tests which may help confirm your diagnosis include magnetic resonance imaging (MRI), and X-rays, which can reveal any injury to the bone. It is possible, however, for these images to appear normal, especially if the injury occurred more than three months prior to testing.
A torn ACL will not heal without surgery. However, nonsurgical treatment may be effective for patients who require a lower activity level which may allow them to recover to a quieter lifestyle without surgery. In the latter case, if the overall stability of the knee is intact, your doctor may recommend simple, nonsurgical options. Patients with a higher activity level, especially young athletes, often require surgical treatment to stabilize the knee and allow return to normal activity levels.
ACL tears cannot be sutured (stitched) back together. However, unless the ACL reconstruction is treatment for a combined ligament injury, it is not typically performed immediately. This delay gives the inflammation a chance to resolve and allows a return of motion before surgery. Performing an ACL reconstruction too early greatly increases the risk of arthrofibrosis, or scar forming in the joint, which would risk a loss of knee motion.
To surgically repair the ACL and restore knee stability, the ligament must be reconstructed with a tissue graft. This graft will act as scaffolding for a new ligament to grow on. Grafts can be obtained from several sources, including: the patellar tendon, which runs between the kneecap and the shinbone; the hamstring tendon at the back of the thigh; or the quadriceps tendon, which runs from the kneecap into the thigh. Cadaver graft (allograft) can also be used. There are advantages and disadvantages to all graft sources, and you should discuss these with your orthopaedic surgeon to help determine which is best for you. For more information, read Dr. Stewart's Frequently Asked Questions About ACL Injuries/Tears.
This is typically an arthroscopic surgery. Knee arthroscopy is performed using small incisions. The benefits of this less invasive technique include less post-surgery pain, less time in the hospital, and quicker recovery times. Because the regrowth takes time, it is typically six months or more before an athlete can return to sports after surgery.
Whether your treatment involves surgery or not, rehabilitation plays a vital role in helping you regain knee strength and motion, and getting you back to normal activities. If you undergo surgery, your physical therapy will first focus on returning motion to the joint and surrounding muscles. This will be followed by a strengthening program designed to protect the new ligament by gradually increasing stress. The final phase of rehabilitation is aimed at a functional return tailored to your sport.