The four main ligaments of the knee are the anterior and posterior cruciate ligaments and the medial and lateral collateral ligaments. The anterior cruciate (cruciate means “cross”) is the front cross ligament of the knee. It prevents the tibia, or lower leg bone, from coming forward. Injury to this ligament is so common that Sports Illustrated once devoted an entire article to this ligament.
A first-degree sprain (left) causes tenderness and pain, but ligament function is unchanged. With a second-degree sprain (center), joint laxity is present along with pain. A third-degree sprain (right) brings dramaticinstability and complete disruption to ligament function. Pain with a third-degree sprain may be less than in others because nerves may be severed, making pain intensity an unreliable guide to ligament damage.
The posterior cruciate ligament is the strongest ligament in the knee. It runs opposite to the anterior cruciate ligament and prevents the shinbone from going backward. Since it is so strong, it takes a much stronger blow to tear this ligament. The medial and collateral ligaments are on the sides of the knee. They are long, flat bands that prevent the limbs from becoming too knock-kneed or too bowlegged. We call these ligaments varis and valgus, respectively. If an athlete gets hit on the outside of the knee, it puts stress and pressure on the medial, or inside, collateral ligament. The opposite stress would cause injury or stress to the lateral collateral ligament. Ligament sprains are measured in degrees. Imagine your interlocked fingers as the ligament, and a first-degree sprain can be likened to pulling flatly and having your fingers stay in place. The length of the ligament fibers has not changed, but there is some injury, if only microscopic. A second-degree tear would be similar to pulling your interlocked fingers apart a bit. A slight lengthening of the ligaments results in some loosening of the joint in the direction the ligament protects. A third-degree injury would be similar to pulling your hands completely apart. Your fingers (the ligament fibers) would then be disconnected and a complete tear would exist. The degree of pain and swelling usually increases as the grade increases; however, in a complete, third-degree tear of the ligament, the pain fibers are also torn. Since they are torn or disconnected, many times this tear does not hurt as much as when the pain fibers are only stretched, as in the first- and second-degree injuries. For this reason, pain cannot be the sole guide to how badly a ligament is torn.
Ligaments can be strained by a traumatic or definite event or a chronic overload. In a traumatic injury, for example, the skier’s tip gets caught, the binding does not release, and the knee goes inward. The ligament on the medial side of the knee (the medial collateral ligament) then sustains an immediate injury. A chronic overload would be caused by a person who is flatfooted and knock-kneed and goes running. Day after day there is increased stress on that ligament because of imbalance of alignment. Eventually stretching of the ligament and pain result because of chronic overload. Thus the mechanisms of injury can be very different.
Ligament strains can happen at work (when the floor is uneven and your foot falls into an unexpected depression) or on the sports field—especially in football, soccer, or rugby.
Pain is the foremost symptom of ligament strain and may vary from severe to excruciating. The knee will feel unstable and, if untreated, may be identified as a “trick” knee. A snap or an audible pop may accompany the injury. Afterward, if the pain disappears, it does not mean that all is well. It may mean that the nerves have also been damaged. When swelling immediately follows the injury, it indicates that blood has flowed into the joint, a natural consequence of the ligament’s being ruptured or torn. The damage can vary from a slight overstretching to a complete rupture, detaching the ligament from the thighbone above it or from the shinbone below it. If you hear a pop and the telltale swelling follows within four hours, ice your knee, take acetaminophen (Tylenol)—not aspirin (it will facilitate bleeding)—and see a doctor.
Injuries to the separate ligaments produce different symptoms. When the collateral ligament is injured, patients usually describe a definite blow or twist and resulting pain along the ligament’s course. If the anterior posterior ligament is injured, the pain, sometimes overwhelming, will be deep inside the knee. When this ligament is torn, though, pain may be absent or minimal if other ligaments are not injured. Injury to the anterior cruciate ligament produces blood inside the knee and swelling within 24 hours in 70% of cases. Therefore, immediate swelling after a knee injury is an ominous sign that there may be ligament damage. When the posterior cruciate ligament is injured, it often bleeds in the back of the knee, and the blood does not pool within the joint.
Exercises for strengthening the muscles may be an integral part of the rehabilitation process. Swimming, for example, is an excellent means of regaining functionality because it helps strengthen the muscles and restore stability without the strain of gravity.
If the ligaments fail to regain their strength, a brace designed for activity may be necessary if the patient wishes to continue sports known to produce these kinds of injuries. These specially made braces encircle the calf and the thigh, and they support the knee’s top, bottom, and sides.
This is a section from Dr. Jack E, Jensen’s book The One Stop Knee Shop. Read the next section Meniscus Tear.