Experiencing pain behind the knee while walking is a common complaint with diverse origins. This discomfort can range from mild to severe, often impacting daily activities and mobility. Understanding these potential causes is the first step toward effective treatment.
Common Muscular and Tendon Causes
Pain behind the knee often stems from issues with the muscles and tendons. Hamstring strains are a frequent culprit, involving one or more of the three muscles at the back of the thigh: the biceps femoris, semitendinosus, and semimembranosus. These strains occur when muscles are overstretched or overloaded, leading to microscopic tears. Symptoms include sudden, sharp pain in the back of the thigh, which may radiate to the knee, along with tenderness, swelling, and bruising, making it difficult to bend or straighten the leg. Severe strains can also cause a popping sensation and significant weakness.
Another source of discomfort is popliteus tendinitis, an inflammation of the popliteus tendon located at the outer and back part of the knee. This small muscle helps unlock and stabilize the knee during movement, especially when walking downhill or on uneven surfaces. Pain from popliteus tendinitis is worse when standing with the knee slightly bent, or during the push-off phase of walking or running. Localized tenderness, swelling, and sometimes a crackling sound (crepitation) with movement can occur.
Calf muscle strains, particularly involving the gastrocnemius muscle, can also cause pain behind the knee. The gastrocnemius is one of the two main calf muscles, extending from behind the knee down to the heel, and is susceptible to injury from sudden accelerations or changes in direction. A calf strain presents with sudden pain in the back of the lower leg or behind the knee, accompanied by a tearing or popping sensation. Other symptoms include stiffness, weakness when trying to rise onto the toes, and bruising or swelling in the calf.
Structural Issues and Cysts
Beyond muscle and tendon issues, structural problems within the knee joint can lead to pain behind the knee. A common example is a Baker’s cyst, also known as a popliteal cyst. This fluid-filled sac forms behind the knee, often due to underlying knee conditions like arthritis or a meniscus tear. The cyst can cause a noticeable bulge or swelling, a feeling of tightness, and pain that worsens with activity or when fully bending or straightening the knee. Some individuals also experience an ache in the calf, stiffness, or a clicking noise in the knee.
Tears to the meniscus, particularly the posterior horn of the medial meniscus, are another cause of pain. The menisci are C-shaped cartilage pads that act as shock absorbers between the thigh and shin bones. A posterior horn tear results from twisting the knee and can lead to pain along the joint line and at the back of the knee, especially with deep squatting. Other symptoms include swelling, stiffness, and a sensation of catching or locking in the knee, which can impede full extension or bending.
Posterior Cruciate Ligament (PCL) injuries can also cause pain behind the knee. The PCL is a strong ligament that prevents the shin bone from sliding too far backward on the thigh bone. Injuries occur due to a direct impact to the front of a bent knee or hyperextension. Symptoms include immediate or delayed pain at the back of the knee, swelling that develops over hours, and a feeling of instability or looseness in the knee, especially when walking or bearing weight.
When to Seek Professional Medical Advice
While some pain behind the knee might resolve with rest and home care, certain signs indicate the need for professional medical attention. If you experience severe pain that prevents you from bearing weight on the affected leg, seek prompt evaluation. Significant swelling, especially if it appears rapidly or is accompanied by warmth, redness, or bruising, requires a doctor’s visit.
A popping sound heard at the time of injury can suggest a more severe issue, such as a ligament tear, and should be assessed by a healthcare provider. If you develop a fever alongside knee pain, or if the pain worsens progressively or does not improve after a few days of rest and self-care, consult a doctor. This article provides general information and should not replace personalized medical diagnosis or treatment from a qualified healthcare professional.