A knee that resists bending fully can be a concerning symptom, indicating various underlying issues. This limitation, whether sudden or gradual, can significantly impact daily activities. Understanding the potential causes, from acute injuries to chronic conditions, is important for identifying when to seek professional help and what management options are available.
Sudden Mechanical Issues and Injuries
Sudden knee flexion limitations often stem from acute injuries and mechanical obstructions. A torn meniscus, especially a “bucket-handle” tear, can “lock” the knee when cartilage fragments become trapped, preventing full movement. Forceful twisting or rotation, particularly when bearing weight, often causes this, leading to pain, swelling, and a popping sensation.
Ligament sprains or tears, such as those affecting the anterior cruciate ligament (ACL) or posterior cruciate ligament (PCL), also limit knee bending. An ACL tear, often accompanied by a “popping” sound at injury, can cause instability and difficulty straightening the knee. Knee joint fractures, including patellar (kneecap) fractures, directly impede movement due to bone displacement, pain, and swelling. Acute bursitis (inflammation of fluid-filled sacs cushioning the knee) or significant trauma-related swelling can also restrict bending due to increased joint pressure.
Underlying Medical Conditions
Chronic medical conditions can cause a gradual or persistent inability to bend the knee. Osteoarthritis, a degenerative joint disease, involves cartilage wearing down, causing bones to rub, leading to pain, stiffness, and reduced range of motion. Rheumatoid arthritis, an autoimmune condition, causes the immune system to attack the joint lining, leading to inflammation, swelling, and stiffness that limits movement and can damage cartilage and bone over time.
Chronic tendonitis, like patellar tendonitis, involves inflammation of tendons connecting muscles to bones, causing pain and tenderness that worsens with knee bending. Patellofemoral pain syndrome, often called “runner’s knee,” involves pain around or behind the kneecap, especially during activities like squatting or climbing stairs. Plica syndrome occurs when a normal tissue fold in the knee becomes irritated or inflamed, causing pain, swelling, and a catching or popping sensation that restricts motion. Loose bodies, small fragments of cartilage or bone floating within the joint, can also cause mechanical locking or catching sensations.
When to Seek Professional Help
Knowing when to consult a healthcare professional for knee issues is important. Seek immediate medical attention if you experience severe pain, a visible deformity, or a “popping” sound at the time of injury. An inability to bear weight on the affected leg or sudden, significant swelling also warrants urgent evaluation.
Other warning signs include a knee that is “locked” and cannot be straightened or bent, persistent pain not improving with self-care, or signs of infection like warmth, redness, and fever around the joint. Any stiffness or instability affecting daily activities or feeling like the knee might give way should also prompt a medical consultation.
Diagnosis and Management
Diagnosis for a knee that won’t bend starts with a thorough physical examination. A doctor inspects the knee for swelling, tenderness, warmth, and assesses its range of motion. The joint may also be manipulated to check ligament and other structural integrity.
Imaging tests visualize the knee’s internal structures. X-rays detect bone fractures and degenerative changes; MRI is useful for visualizing soft tissues like ligaments, tendons, and cartilage. A CT scan can identify subtle bone problems. In some cases, joint aspiration (fluid removal from the knee for analysis) may be performed to check for infection or inflammation.
Management options vary by diagnosis. Non-surgical treatments include rest, ice, compression, and elevation (RICE protocol) to reduce pain and swelling. Physical therapy often strengthens surrounding muscles, improves flexibility, and restores range of motion. Medications like pain relievers or anti-inflammatory drugs are prescribed. For severe cases, surgical interventions like arthroscopy (a minimally invasive procedure to repair or remove damaged tissue) or joint replacement surgery are considered.