One of the most common orthopedic injuries in the United States is an anterior cruciate ligament (ACL) sprain or tear. Recreational and professional athletes of all ages who participate in popular sports like soccer, football, and basketball are more likely to injure their anterior cruciate ligaments. ACL tears are the most common orthopedic injuries in the United States with more than 100,000 ACL reconstructions are performed annually. Depending on the severity of the injury to the ACL, surgery may be required in order to restore full knee stability and function.
Anatomy of the Knee
The knee joint is the largest and most complex joint in the body. It is formed from the junction of three bones: the kneecap (patella), the upper thigh (femur), and the shin bone (tibia). The ACL connects the top of the shin bone to the bottom of the thigh bone to run diagonally through the middle of the knee. It provides the knee joint with stability and rotational control during and prevents the shin bone from sliding out in front of the thigh bone. Because half of all injuries to the anterior cruciate ligament occur along with damage to other structures in the knee, such as articular cartilage, meniscus, or other ligaments, preventing injury or recurrence is essential to the keep the knee joint healthy throughout life.
When ACL Injuries Occur Most Often
Certain sports, such as basketball and soccer, have higher incidents rates of injury. Injury can occur to the anterior cruciate ligament can occur under several common conditions:
Changing direction rapidly
Stopping suddenly
Slowing down while running
Landing from a jump incorrectly
Direct contact or collision, such as a football tackle or car accident
Gender is also believed to play a large role in ACL injury risk, especially in adolescent athletes. Female athletes in particular are at higher risk of ACL injury than male athletes in certain sports. This may be due to differences in physical conditioning, muscular strength, reproductive hormones, 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. Additionally, a woman’s ACL may be smaller than a man’s, which may make it more susceptible to fraying or becoming injured. Some experts suggest that relatively weak hamstrings may also pose problems for women. When the hamstrings contract, they help stabilize the knee, so if the hamstrings are weaker or don’t activate fast enough, injury may
result. Anatomic alignment differences, especially the quadriceps angle (Q-angle), have been cited as the cause of the higher ACL injury rate in women, but this has not yet been confirmed by the research. Other findings have shown a difference in neuromuscular control in women when landing jumps, as women appear to have less hip and knee flexion than men.
ACL and other lower-extremity injuries occur most commonly during planting and cutting maneuvers. This is due to insufficient neuromuscular control of lower limb mechanics, particularly in the frontal plane. The most common movement pattern occurring at the time of non-contact ACL and other lower-extremity injury is an internally rotated femur moving the knee position inward (known as a valgus position) and externally rotated lower leg. This unstable position places great strain on the ACL, which may be sufficient enough to cause spontaneous rupture of the ligament (2). Through proper movement assessments, like NASM’s Overhead Squat Assessment and the Single Leg Squat Assessment, we can identify these same compensation patterns in a controlled environment and begin to correct them.
Underlying Causes and Interventions
Imbalances in lower body neural-muscular-skeletal control increase the risk of ACL strains and tears. Individuals with weak knee support muscles or imbalances or weaker hip flexor strength are particularly vulnerable. Unfortunately, no single exercise can prevent injury to the ACL. The good news is that you can give yourself some protection by developing and maintaining strength and endurance in your lower extremities. To promote stability in the knee, perform closed-chain exercises (for example, bridges, side-leg raises, leg presses, squats, lunges) as part of your strength-training program. Also, do some cross-training in your cardiovascular workout using the stairclimber, stationary bike, elliptical trainer or ski machine. You can also avoid an ACL injury by preparing for your favorite sport in the preseason. Plan for at least four weeks of endurance training before your basketball, tennis, or racquetball league begins, or prior to ski season. Have fun, but be sensible when playing your sport. Whenever you find that you must stay away from your regular routine for two or three weeks due to travel or illness, ease up for several workouts to give your body time to recondition.
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