While viewing a sports event, you may have seen an athlete who suddenly falls and is removed from the game because of knee pain. The coach or trainer later reports that this athlete suffered a knee ligament injury, like an ACL tear. Although this is a common occurrence, the exact details are rarely discussed. Outside of the realm of sports, motor vehicle accidents are one of the most common causes of knee injury. A patient with a knee ligament injury will usually be referred to an orthopedist.
The knee is a complex joint that consists of four bones held together by attachments called ligaments. These ligaments are called: anterior cruciate, posterior cruciate, medial collateral, and lateral collateral. These ligaments connect the lower portion of the femur or thigh bone, with the upper portion of the shin bones (tibia and fibula), and a small central bone called the patella or knee cap.
In addition, the muscles of the thigh and lower leg attach to these bones via elastic-type bands called tendons. A “cushion” between the femur and tibia called the meniscus prevents the bones from scraping together. All of these components work together to enable the knee joint to function properly and effectively.
Unlike tendons, ligaments have limited flexibility. While this keeps the knee joint stable, the lack of flexibility increases the likelihood of injury. The type and severity of a ligament injury will dictate the amount of impairment and course of treatment necessary.
Anterior cruciate ligament or ACL sprains or tears are commonly caused by motor vehicle accidents and falls. The ACL is located inside the knee, and prevents sliding of the bones. When the ACL is injured, one may hear or feel the knee pop.
This is immediately followed by pain, swelling, and a reduced ability to extend or flex the leg. If it is still possible to walk, the affected knee may feel like it slides out of place.
The posterior cruciate ligament injury is another type of ligament injury that can be caused by trauma. Like the ACL, the posterior cruciate ligament, or PCL, is located inside the knee joint. Mild cases often go unnoticed until pain gradually develops.
The pain associated with a PCL injury can also be immediate, following a traumatic event. For example, a patient can damage the PCL when the knee is caused to strike a hard surface inside a vehicle as a result of the forces associated with a car accident. In these cases, pain, swelling, and difficulty walking are usually immediately evident.
The medial and lateral collateral ligaments are the support system for the sides of the knee joint. Medial refers to the inner side of the knee, while lateral refers to the outer side. These ligaments prevent the bones of the knee from dislocating to the left or right.
Any blow to the side of the knee can cause either a sprain or tear in one or both of these ligaments. Injuries to these ligaments usually produce immediate pain, swelling, and difficulty walking.
A thorough physical examination is the first step to diagnosing a knee ligament injury. The exam will usually include an assessment of the ability to walk, squat, and stand up. In addition to assessing mobility and swelling, your doctor may perform several tests during the physical examination to assess the knee’s ligaments. These include Lachman’s test, the Drawer’s test, and the Pivot test.
The Lachman test is a simple test that can be performed by your doctor during the physical examination to determine whether the ACL and PCL are intact. With the knee flexed at 30 degrees, your doctor will pull the lower leg forward and backward. If the lower leg slides forward, it is likely that the ACL is torn. If it slides backward, this indicates a PCL injury.
Similarly, the Drawer’s test is conducted in the same manner, but with the knee flexed at 90 degrees. In cases where the pain is minimal, a Pivot test is done. During the Pivot test, the lower leg is turned slightly inward while flexing the affected leg. Any knee laxity further confirms the presence of an ACL injury.
After a thorough exam, imaging studies help to determine the extent of ligament damage. X-rays reveal any associated bone fractures, and an MRI gives closer look at ligament, tendon, and muscle problems. Most injuries can be viewed via these modalities, but more complicated injuries may require surgical exploration.
The treatment plan for these types of knee ligament injuries is determined by their severity. For partial tears of a single ligament, conservative measures are the norm. If, however, the knee has sustained multiple ligament tears and fractures, surgery may be necessary early in the treatment.
Initial management of most knee injuries includes rest, application of ice, and frequent leg elevation to reduce swelling. Crutches may be needed to reduce weight bearing on the injured knee. Stabilization is important to prevent additional ligament damage.
An elastic wrap may be sufficient for single collateral ligament injuries, but ACL and PCL tears may require a hinged-type of brace for better support. Non-steroidal anti-inflammatory medications are generally recommended for pain management.
Once the initial swelling has resolved, physical therapy is the next step in the treatment plan. It can further reduce knee pain, and improve mobility as the ligaments heal. Because many simple injuries heal without surgery, an 8 to 12-week course of physical therapy is typically recommended. In severe knee ligament cases, where surgery is needed, physical therapy will usually be ordered post-operatively. This helps a patient regain knee mobility and leg muscle strength.
For refractory cases or those with multiple ligament tears, arthroscopic surgery is sometimes the best option. This surgical technique involves making small incisions in the knee and inserting a fiberoptic camera to visualize the inside of the joint. Surgical instruments access the knee through one or two incisions. In this way, the orthopedic surgeon can remove bone fragments and torn pieces of cartilage or ligament.
Partial ligament tears can be repaired, but complete tears must be replaced. A “new ligament” can be made from a piece of muscle tendon that is grafted into the location of the damaged ligament. The graft replicates the job of the ACL, and the knee joint becomes stable again. With post-operative physical therapy, the prognosis and outcome is typically good.