Why does the kneecap catch or lock when bending and straightening the leg, and what should be done about it?

Under normal circumstances, a catching sensation when bending or straightening the leg may be caused by factors such as joint laxity, muscle imbalance, patellar chondromalacia, meniscus injury, or partial patellar dislocation. If abnormalities occur, it is recommended to seek medical attention promptly. Detailed explanations are as follows:

1. Joint Laxity

Joint laxity may result from reduced elasticity of ligaments and soft tissues around the joint due to age, gender, or other factors, causing the patella to shift or catch during flexion and extension. Mild joint laxity can be improved by strengthening surrounding muscles to enhance joint stability. Severe cases may require using supportive braces or undergoing professional physical therapy.

2. Muscle Imbalance

If there is an imbalance between muscle groups in the leg—such as certain muscles being overly tight or weak—it may cause abnormal pulling forces on the patella during movement, leading to a catching sensation. An individualized exercise program, including strengthening the quadriceps and hamstrings combined with stretching tight muscles, can help correct this imbalance.

3. Patellar Chondromalacia

Patellar chondromalacia occurs when the cartilage surface of the patella wears down or becomes damaged, resulting in an uneven contact surface between the patella and femur during movement, which causes a catching sensation and may be accompanied by knee pain. In early stages, wearing knee braces or applying hot/cold compresses may help relieve symptoms. In severe cases, surgical intervention such as cartilage repair or transplantation might be necessary.

4. Meniscus Injury

A meniscus injury typically results from twisting motions or external impact to the knee joint. Fragments of the injured meniscus may become trapped during knee movement, causing a catching sensation, often accompanied by knee pain, swelling, and a locking feeling. Initial management includes rest, ice application, and compression with elastic bandages to alleviate symptoms. In cases of severe tears, arthroscopic surgery may be required to repair or remove the damaged meniscal tissue.

5. Partial Patellar Dislocation

This condition involves instability of the patella during knee flexion and extension, where the patella partially or completely moves out of its normal track, causing a catching sensation. It is usually associated with pain and a sense of joint instability. Treatment options include conservative methods such as manual reduction, casting, or bracing. Patients experiencing recurrent dislocations or those unresponsive to conservative treatment may require surgery to restore patellar stability.

It is recommended to maintain regular exercise, ensure a balanced diet, and support bone health in daily life. Additionally, always pay attention to safety during physical activities, and perform proper warm-up and stretching exercises before and after workouts.