Few sporting activities capture the graceful movement of the human body like gymnastics and cheerleading do. These sports are generally safe; however, the potential exists for injury during both training and performance. Some injuries occur because the participant's bones have not yet fully developed, while others are due to overuse, poor technique, and a lack of warm-up.

The knee functions as the prime shock absorber of forces created by jumping and landing activities. Lower extremity impact forces incurred from a double backward somersault, for example, can result in peak vertical ground reaction forces of 8 to 14 times the body's weight.¹

Absorbing these forces, however, can lead to microtrauma and acute trauma to the ligaments, tendons, and bones that make up the knee joint. By far, the most common knee injury involves the patella (kneecap), which represents approximately 60% of gymnastic and cheerleading knee disorders. These injuries range from tendinitis and inflammation of the growth plate, to patellar instability, to dislocation of the kneecap.

As an athlete runs, jumps, and lands, the power of these activities is largely generated by the quadriceps, the group of large muscles in front of the thigh (Fig.1). As the quadriceps contracts, it pulls on the patella, thereby transmitting force to the femur (thighbone). This creates a powerful extension force at the knee, which can be used to jump or to resist flexion (bending) of the knee during jumping and landing. The tendon that attaches the patella to the tibia (shinbone) delivers the power across the knee to the tibia. In a child, who is still growing, this tendon is attached to the tibia at the growth plate. Because the plate has not fully fused with the tibia, it is weak and can be injured by the repetitive pulling that occurs when a gymnast lands.

Osgood Schlatter's disease, which occurs in active growing children, usually occurs between ages 10 to 13. Children often present with pain and swelling at the tuberosity of the tibia (a bony projection below the kneecap) to which the patellar tendon attaches (Fig. 2).

Patellar tendinitis, or jumper's knee, is an inflammation of the patellar tendon. It most commonly occurs at the lower portion of the patella where the tendon attaches to the kneecap. Symptoms include pain, swelling, and varying degrees of hamstring tightness.

Rest, anti-inflammatory medication (such as ibuprofen or aspirin), and icing the area should help reduce the pain and swelling caused by Osgood Schlatter's disease and patellar tendinitis. Stretching the hamstring muscle also helps to reduce the strain on the knee. The athlete can return to practice and competition once the injury has healed and there is no more pain.

Patellar subluxation and patellar dislocation are two conditions in which there is a problem with the kneecap tracking in the groove on the end of the femur (Fig. 3). Subluxation refers to minor slippage or partial movement of the kneecap out of the femoral groove; a dislocation often occurs during an acute event that causes the kneecap to completely displace from its normal position in the femoral groove. Normally, soft tissues and muscles around the knee help to stabilize the kneecap allowing it to glide smoothly up and down. However, if the muscles are weak or the soft tissues are loose, the kneecap can slide out of the femoral groove causing pain and swelling. A dislocated patella can occur when an athlete lands off balance, forcing the patella out of position. Patellar subluxation and dislocations are usually treated nonoperatively with a patellar stabilizing brace, rest, and physical therapy to restore strength to the joint. Early treatment tends to minimize wear and tear on the joint, which can affect future sports participation and the development of arthritis later in life. Some athletes have structural problems with their knees, and despite proper conservative care they may require surgery.

Plica syndrome, or inflammation of the fold, can also cause anterior knee pain and weakness in gymnasts and cheerleaders. The fold is a part of the soft tissue lining of the knee joint (Fig. 4). This horseshoe shaped band can become thick and cause snapping and popping sounds as the knee bends. Athletes may also complain of anterior knee pain when they sit with their knee flexed for too long. The treatment involves rest and exercises to strengthen the muscles that keep the plica pulled back and stretching the hamstrings so the knee does not have to work as hard.

Injuries to the meniscus (cartilage) of the knee comprise approximately 20% of gymnastic and other athletic knee injuries. These injuries are usually the result of significant trauma. The meniscus is a good shock absorber that helps stabilize the knee. However, sudden, considerable force across the knee can produce a tear in the meniscus. These injuries should be evaluated by a sports medicine professional. Treatment may be either nonoperative or may require surgery to repair the damage. An MRI (magnetic resonance imaging) scan that shows bones, muscles, tendons, and ligaments often helps to diagnose the extent of these injuries.

Significant force can also produce damage to the ligaments of the knee. These injuries represent approximately 20% of all gymnastic and cheerleading knee injuries. The ligaments are bands of tissue on both the inside and the outside of the knee, and they are the major stabilizers of the knee. An off-balance landing or dismount can produce a major force on these bands, and one or more ligaments can tear either partially or completely. The anterior cruciate and the medial collateral ligaments are the most commonly injured, and the posterior cruciate and lateral collateral ligaments are injured less often. These injuries should be evaluated promptly and diagnosed so treatment can begin. Most athletes recover from these injuries with the appropriate treatment of bracing or surgery and, most often, return to their sport.

Treatment is important, not only to reduce the immediate swelling and discomfort, but also to reduce the risk of a more serious injury that can prevent the athlete's return to the sport. Early diagnosis and treatment helps reduce the time away from the sport, allowing for a quicker return to high performance activities. For this reason, "playing through the pain" should be avoided, but, more importantly, an injury to the knee can lead to arthritis later in life if it is not allowed to heal properly.

Kurt E. Jacobson, MD
Columbus, Georgia

References:
1. Panzer VP, Wood GA, Bates BT, Mason BR. In: de Groot, G. et al, eds. Biomechanics XI-B. Amsterdam: Free University Press; 1988:727-735.