What causes pain in the back of the knee when squatting or standing up?

Leg pain when bending the knees upon standing up from a squatting position may be caused by meniscus injury, ligament damage, osteoarthritis, knee synovitis, popliteal cyst, or other reasons. A detailed medical examination at a hospital is recommended to identify the exact cause and allow for targeted treatment. Specific causes are analyzed as follows:

1. Meniscus Injury

During physical activity, sudden twisting or rotating of the knee while in a half-squatting position may result in meniscus injury, causing knee joint pain and discomfort when bending the leg. Applying ice packs to the knee can help reduce pain and swelling.

2. Ligament Injury

Ligament injuries can also cause leg pain when rising from a squatting position, often accompanied by knee swelling, limited mobility, joint instability, deformity, or functional impairment. If the ligament is only partially torn, follow medical advice to immobilize the knee at 20°–30° flexion using a plaster splint applied anteriorly and posteriorly to the knee joint.

3. Osteoarthritis

Obesity increases joint stress and accelerates joint degeneration, while metabolic or endocrine abnormalities may trigger local aseptic inflammation, leading to osteoarthritis and causing leg pain upon standing from a squat. It is recommended to undergo treatments such as infrared light therapy or transcutaneous electrical nerve stimulation (TENS) under professional medical guidance to improve local blood circulation, protect the joints, and relieve symptoms.

4. Knee Synovitis

Knee synovitis is often caused by joint degeneration or trauma, primarily manifesting as dull or hidden knee pain. The pain intensifies especially after prolonged squatting or excessive fatigue. Additional symptoms may include joint swelling, restricted movement, and limping. Under medical guidance, oral anti-inflammatory and analgesic medications such as ibuprofen tablets or diclofenac sodium sustained-release capsules may be used.

5. Popliteal Cyst

Increased intra-articular pressure can force joint fluid through weak areas of the joint capsule into the popliteal region, forming a popliteal cyst that causes pain when bending the leg. Under professional medical care, cyst aspiration can be performed to drain the fluid, reduce cyst size, and alleviate compression symptoms.

In addition, conditions such as rheumatoid arthritis, rheumatic arthritis, or gout may also lead to similar symptoms. Active treatment under the guidance of a qualified physician is necessary to prevent disease progression and worsening of symptoms.