What causes the left knee joint to make a snapping sound and feel sore, weak, and无力 when going downstairs?

Clicking sounds in the left knee joint accompanied by soreness, pain, and weakness when descending stairs may be caused by the following possible factors:

1. Meniscus injury: The meniscus is an important structure within the knee joint that helps to absorb joint pressure. When the meniscus is damaged, clicking sounds may occur during flexion and extension of the joint. Particularly when going downstairs, increased pressure on the knee joint can cause pain and a feeling of weakness.

2. Osteoarthritis: With aging, the joints may undergo degenerative changes leading to cartilage wear and abnormal friction within the joint. This can result in clicking sounds during walking, accompanied by pain and weakness.

3. Patellar chondromalacia: This condition is primarily caused by the wearing away of cartilage beneath the kneecap. It is common among athletes and middle-aged or elderly individuals, mainly manifesting as pain and clicking sounds in the front of the knee. Long-term damage to the cartilage surface of the patella may lead to cartilage swelling and breakdown, causing knee weakness, pain, and clicking sounds.

4. Lactic acid buildup: After intense exercise or prolonged physical activity, leg muscles may produce excessive lactic acid that accumulates around the knee joint, leading to soreness, weakness, and clicking sounds.