ACL Tears
The anterior cruciate ligament (ACL) is one of the key stabilizing ligaments in the knee, that plays a vital role in maintaining balance and coordination during movement. Injuries to this ligament, known as ACL tears, are among the most common knee injuries, particularly among athletes and individuals who participate in sports requiring sudden stops, pivots, or changes in direction. For patients treated by Dr. Kevin Collon, a respected orthopedic surgeon at Keck Medicine of USC, expert evaluation and management ensure optimal recovery and return to activity.
The ACL is a strong band of connective tissue located in the center of the knee joint, connecting the femur (thighbone) to the tibia (shinbone). It works in conjunction with the posterior cruciate ligament (PCL) to control the knee’s forward and backward movements and to prevent the tibia from sliding too far forward. An ACL injury occurs when this ligament is stretched beyond its limit or torn.
ACL tears are categorized as partial or complete, depending on the extent of the damage. A partial tear means some fibers of the ligament remain intact, while a complete tear indicates a total rupture. In many cases, ACL injuries occur alongside damage to other knee structures, such as the meniscus, cartilage, or additional ligaments, which can complicate the injury and recovery process.
Most ACL tears occur during athletic activities that involve quick pivots, cutting movements, or awkward landings from jumps. Sports such as soccer, basketball, football, skiing, and volleyball have a higher incidence of these injuries. The mechanism of injury often involves a sudden deceleration combined with a twisting motion of the knee, leading to excessive strain on the ligament.
Direct contact injuries, such as a collision or tackle, can also cause ACL tears, though these are less common than non-contact mechanisms. Poor neuromuscular control, weak core or hip muscles, and imbalances in lower extremity strength can increase susceptibility to ACL injuries. Anatomical factors—such as the shape of the knee joint, ligament laxity, or hormonal influences in female athletes—can further elevate the risk.
An ACL tear often occurs suddenly and is usually accompanied by a distinct “popping” sound or sensation in the knee at the moment of injury. Most patients experience immediate pain, swelling, and instability. Common symptoms include:
- A loud pop or snapping sensation at the time of injury
- Immediate swelling within hours due to bleeding inside the joint
- Severe pain that limits walking or weight-bearing
- Inability to put weight on the knee, the knee giving out or a feeling of looseness or instability
- Reduced range of motion or difficulty fully extending or bending the knee
Over time, untreated ACL tears can lead to repeated episodes of instability, which may cause additional injury to the meniscus or cartilage and accelerate the onset of knee arthritis.
Dr. Collon will take a detailed history and perform a thorough physical examination. During the exam, he will evaluate the stability of the affected knee using specific maneuvers, such as the Lachman test, anterior drawer test, and pivot shift test, which assess the integrity of the ACL.
Imaging studies will help confirm the diagnosis and evaluate associated injuries. An MRI (magnetic resonance imaging) is the most accurate tool for visualizing ligament tears, cartilage damage, or meniscal injuries. X-rays are often taken to rule out fractures or bone-related injuries that may accompany the ligament tear.
Certain individuals are more prone to ACL injuries due to anatomical, biological, and activity-related factors. These include:
- Athletes in pivoting sports: Soccer, basketball, and football players are at greater risk because of frequent cutting and jumping movements.
- Female athletes: Studies have shown that women experience ACL tears more often than men, possibly due to differences in anatomy, hormonal influences, and neuromuscular control patterns.
- Previous knee injuries: A history of ACL injury increases the risk of re-injury, especially if rehabilitation was incomplete or return to sports was premature.
- Poor biomechanics: Improper landing mechanics, weak core and hip muscles, or imbalances in quadriceps and hamstring strength increase stress on the ACL.
- Environmental factors: Playing on artificial turf or wearing footwear with excessive traction can also elevate the risk of ACL tears.
Beyond the immediate pain and instability, an ACL tear can have lasting consequences if not properly treated. Instability in the knee can lead to further damage to the meniscus and articular cartilage, potentially resulting in early-onset osteoarthritis. For athletes, an untreated ACL tear can compromise performance and make it difficult to return to pre-injury levels of activity. Recurrent instability can also lead to chronic knee pain, swelling, and loss of confidence in movement.
Even after surgical reconstruction, patients must undergo extensive physical therapy to regain strength, flexibility, and coordination. The recovery process can take several months, emphasizing the importance of early diagnosis, individualized treatment planning, and adherence to rehabilitation protocols.
While not all ACL injuries can be prevented, incorporating proper training techniques and conditioning programs can significantly reduce risk. Preventive strategies include improving core and hip strength, enhancing balance and proprioception, and practicing correct jumping and landing mechanics. Many athletic programs now integrate ACL injury prevention exercises, which have been shown to lower the rate of injury, especially among young athletes.
Anyone who experiences a popping sensation in the knee, sudden swelling, or feelings of instability following an injury should seek evaluation by an orthopedic surgeon. Early diagnosis is crucial in determining the extent of the injury and the appropriate treatment approach, whether non-surgical rehabilitation or surgical reconstruction.
At Keck Medicine of USC, Dr. Kevin Collon provides advanced, evidence-based care for patients with ACL tears and other complex knee injuries. Fellowship-trained in sports medicine, Dr. Collon uses the latest diagnostic techniques and treatment approaches to help athletes and active individuals recover strength, stability, and confidence in their knee function.
ACL tears are a serious but treatable condition that can greatly affect an individual’s mobility and athletic performance. Recognizing the symptoms early, seeking prompt evaluation, and following a personalized treatment plan are key to achieving a successful recovery. With expert care from Dr. Kevin Collon and the multidisciplinary orthopedic team at Keck Medicine of USC, patients in Los Angeles can expect comprehensive support throughout every stage of healing, from diagnosis to full return to activity. Schedule an appointment with Dr. Kevin Collon at Keck Medicine of USC in Los Angeles for an expert diagnosis and personalized treatment plan that supports full and lasting recovery.
At a Glance
Dr. Kevin Collon
- Fellowship-Trained Sports Medicine Surgeon
- Team Physician – LA Kings, USC Athletics
- Cutting-edge, Evidence-based Treatment
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