Common Muscle and Tendon Related Causes
Pain behind the knee often originates from the muscles and tendons surrounding the joint, frequently due to overuse, strain, or injury. Hamstring strain or tendinopathy commonly presents as pain in the back of the thigh or closer to the knee. This condition can result from sudden acceleration, insufficient warm-up, or repetitive activities like running, leading to sharp pain, tenderness, and sometimes bruising or weakness.
A calf strain, particularly affecting the gastrocnemius muscle, can refer pain to the back of the knee. This injury typically occurs with forceful pushing off actions or sudden starts and stops, causing sudden sharp pain, tenderness, and swelling in the upper calf.
The popliteus muscle, a small, deep muscle at the back of the knee, plays a role in knee rotation and stability. Inflammation of its tendon, known as popliteus tendinopathy, can cause pain behind the knee, often aggravated by downhill walking or running due to increased stress.
Issues Within the Knee Joint
Structural problems or conditions affecting the knee joint can also manifest as pain behind the knee. A Baker’s cyst, also known as a popliteal cyst, is a fluid-filled sac at the back of the knee. This cyst often develops from underlying knee problems like arthritis or meniscus tears, causing a feeling of fullness, tightness, or swelling, particularly with knee extension. In some instances, a Baker’s cyst can rupture, leading to sudden, sharp pain, inflammation, and bruising down the calf.
Meniscus tears, specifically affecting the posterior horn, can cause discomfort behind the knee. The meniscus is a C-shaped cartilage that functions as a shock absorber and stabilizer within the knee. Tears in its posterior portion can result in localized pain, clicking, locking sensations, or instability at the back of the knee.
Knee osteoarthritis, characterized by the “wear and tear” of protective cartilage, can also contribute to pain behind the knee. When the posterior compartment of the knee is affected, individuals may experience deep, aching pain, stiffness, and reduced range of motion, often worsening after activity or in the morning.
Less Common But Serious Conditions
While less common, certain conditions causing pain behind the knee require immediate medical attention due to their severity. Deep vein thrombosis (DVT) involves a blood clot in a deep vein, most frequently in the leg. Symptoms often include sudden onset of pain, swelling, warmth, redness, or tenderness in the calf or behind the knee. DVT is considered a medical emergency due to the risk of the clot traveling to the lungs, leading to a pulmonary embolism.
Nerve entrapment can also cause pain behind the knee. Nerves passing through this region, such as the sciatic or common peroneal nerve, can become compressed or irritated. This type of issue typically presents with symptoms distinct from localized musculoskeletal pain, including radiating pain down the leg or into the foot. Individuals may also experience numbness, tingling, or weakness in the affected area, indicating nerve involvement.
When to Seek Professional Medical Advice
Certain symptoms associated with pain behind the knee warrant prompt medical evaluation. Immediate attention is advised for sudden, severe pain, significant swelling, or inability to bear weight on the affected leg. Signs indicative of deep vein thrombosis, such as redness, warmth, or tenderness in the calf, also necessitate urgent medical consultation.
Additional red flag symptoms include fever or chills, or any new onset of numbness, tingling, or weakness in the foot or lower leg, which could suggest nerve involvement or infection. If pain behind the knee persists for more than a few days, worsens despite rest and self-care, or significantly interferes with daily activities, seeking medical help is recommended. A proper diagnosis from a healthcare professional is important for effective treatment and appropriate management.