ANTERIOR CRUCIATE LIGAMENT INJURIES The volleyball match has been going on for over an hour. Both teams have been trading points and side-outs. The ball is set high outside so that the big outside hitter can put the ball away. She comes in hard, plants, leaps into the air and smashes the ball down the line in a twisting motion. As she lands on her right leg, a POP is heard and down she goes. What has just happened is occurring more and more often in athletics, the athlete has just torn the anterior cruciate ligament (ACL). In this paper I will describe ACL, how it is injured and diagnosed, how it be repaired and what is being done to prevent ACL injuries. The Anterior Cruciate Ligament (ACL) is one of the two cruciate ligaments of the knee, the other being the Posterior Cruciate Ligament (PCL). These ligaments are the stabilizers of the knee. The ACL is a strip of fibery tissue, which is located deep inside the knee joint. It runs from the posterior side of the femur (thigh bone) to the anterior side of the tibia (shin bone) deep inside of the knee. The ligament is a broad, thick cord the size of a person's index finger. It has long collagen strands woven together in a fashion that permits forces of up to 500 pounds to be exerted. The function of the ACL is to prevent the tibia from moving in front of the knee and femur. The ACL also prevents hyperextension (or extreme stretching of the knee backward) and helps to prevent rotation of the tibia. The amount of knee ligament injuries have been on the rise in recent years. Over the last 15 years, ankle sprains have decreased by 86% and tibia fractures by 88%, but knee ligament injuries have increased by 172%. The injury usually occurs in either a slow twisting fall, a sudden hyperextension, or a sudden hyperflexion as when landing from jumping. When the injury occurs the athlete usually hears a "pop" and they will have immediate swelling of the knee. When the person tries to put weight on the leg it will feel like the knee isn't underneath the athlete. With most injuries the type of movement will help to determine the injury: "I twisted to the right." etc. When ACL injuries occur there is a "popping" sound at the time of injury and swelling within six hours. An experienced clinician can diagnose an ACL tear with relative accuracy by a manual examination. X-ray examination and Magnetic Resonance Imaging (MRI) is also used in diagnosing ACL injuries. The knee joint will be instable and the athlete will have joint pain on the inner (medial) side of the knee. Doctors or trainers can use three different types of physical examinations: Lachman's test, Anterior drawer test and Pivot shift test of MacIntosh. Lachman's test is performed by having the athlete lie on his/her back, then passively flexing the knee of the athlete to between 20 degrees and 30 degrees. Make sure that the hamstring is relaxed or it can produce a false test result. Holding the lower part of the athlete's thigh in one hand and the upper part of the athlete's calf in the other, slowly pull the tibia forward. Increased looseness in the knee joint is indicative of an ACL injury. During the Anterior drawer test the athlete lies on his/her back with the knee bent to 90 degrees and the foot resting on the table. Stabilizing the foot either by sitting on it or having someone else hold it down, the doctor will place his/her hands around the upper part of the calf with thumbs on the end of the thigh bone (tibal condyles), slowly appling pressure on the posterior side of the proximal tibia. Any looseness in the joint could indicate ACL injury. The Pivot shift test of MacIntosh is done by having the athlete lay on his/her back. The foot of the injured side is lifted with the leg straight and the foot turned inward. Pressure is applied to the outside of the knee while the knee joint is slowly bent. An ACL injury is detected if the tibia moves out of joint at 30-40 degrees or if a clunk is