Knee pain in adults refers to discomfort or pain localized to the knee joint. It affects a significant portion of the adult population, with an approximate incidence that increases with age. This condition is important to understand due to its impact on mobility and quality of life, often necessitating medical attention to address underlying causes and prevent long-term complications.
The anatomy of the knee
The knee joint is a complex structure that connects the thigh bone (femur) to the shin bone (tibia). It also includes the kneecap (patella), which sits over the front of the joint. Ligaments, tendons, cartilage, and fluid-filled sacs (bursae) support and stabilize the knee, allowing for its pivotal functions in movement and weight-bearing.
The femur’s rounded end, known as the femoral condyles, articulates with the flat surfaces of the tibia, forming the main knee joint. These surfaces are covered with smooth, protective cartilage that cushions the bones and allows for smooth movement. The patella, or kneecap, is embedded within the quadriceps tendon above the knee joint. It acts as a fulcrum, increasing the leverage of the quadriceps muscles as they straighten the knee. The patella also protects the front of the knee joint and assists in maintaining joint stability.
Several ligaments provide stability to the knee joint. The anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL) cross within the joint, controlling the forward and backward movement of the tibia relative to the femur. Medial and lateral collateral ligaments, located on the inner and outer sides of the knee, respectively, prevent excessive sideways movement. Two wedge-shaped pieces of cartilage, known as the medial and lateral menisci, sit between the femur and tibia. These act as shock absorbers, distributing weight and reducing friction during movement. They also enhance joint stability by deepening the joint surfaces.
Muscles surrounding the knee joint, such as the quadriceps and hamstrings, provide dynamic stability and movement. Tendons connect these muscles to bones, transmitting forces and facilitating joint motion. Fluid-filled sacs called bursae are located around the knee joint. They reduce friction between tendons, ligaments, and bones during movement. Common bursae include the prepatellar bursa in front of the kneecap and the pes anserinus bursa on the inner side of the knee.
What is the most common cause of knee pain in adults?
Osteoarthritis
Osteoarthritis is the most common cause of knee pain in adults. It involves degeneration of joint cartilage and underlying bone, leading to pain, stiffness, and reduced function. Incidence increases with age, typically presenting after age 50. Distinguishing features include worsening pain with activity, joint stiffness, crepitus, and bony enlargement. Diagnosis relies on clinical evaluation, imaging (X-ray), and sometimes joint aspiration. Management includes weight management, physical therapy, analgesics (NSAIDs), and surgical options like arthroplasty in severe cases.
Other common medical conditions associated with knee pain in adults
Rheumatoid arthritis
Rheumatoid arthritis is an autoimmune disorder affecting synovial joints, including the knee. Its pathogenesis involves inflammation, joint erosion, and systemic manifestations. The typical age of onset is between 30 and 50 years. Additional symptoms include morning stiffness, symmetric joint involvement, and rheumatoid nodules. Diagnostic clues include positive rheumatoid factor and anti-CCP antibodies. Treatment includes disease-modifying antirheumatic drugs (DMARDs) and biologics.
Patellofemoral pain syndrome
Patellofemoral pain syndrome is characterized by anterior knee pain exacerbated by activities like squatting or stair climbing. It is common in young adults, especially athletes. The pathogenesis involves abnormal patellar tracking and overuse. The diagnosis is based on clinical history and physical exam showing pain with patellar compression or movement. Management includes physiotherapy, NSAIDs, and activity modification.
Meniscal tears
Meniscal tears are commonly caused by trauma or degeneration. They cause localized pain, swelling, and mechanical symptoms (locking or catching). They typically affect adults of all ages, with incidence peaking in middle age. Diagnosis is via clinical history, physical exam (McMurray’s test), and MRI. Treatment includes rest, physical therapy, and surgical repair or partial meniscectomy as needed.
Ligamentous injuries
Ligamentous injuries, such as ACL and PCL tears, cause acute knee pain, swelling, and instability, often with a history of sports or physical activity. ACL tears are more common in younger adults, while PCL injuries may occur with direct trauma or dashboard injuries. Diagnosis involves a physical exam (Lachman test, Pivot shift test) and MRI. Management varies from conservative measures to surgical reconstruction based on severity and patient goals.
Bursitis
Bursitis is the inflammation of knee bursae due to overuse, trauma, or underlying arthritis. It presents with localized pain, swelling, and tenderness over the affected bursa (e.g., prepatellar bursitis). It is diagnosed by clinical exam and sometimes imaging to exclude other causes. Treatment includes rest, ice, NSAIDs, and addressing underlying factors like repetitive stress.
Medical conditions associated with prolonged or recurrent knee pain in adults
Gout
Gout is a crystal-deposition arthritis that causes recurrent acute attacks of severe joint pain, swelling, and redness. It typically affects older adults, and risk factors include diet and genetics. The diagnosis is based on clinical presentation, joint aspiration showing monosodium urate crystals, and elevated serum uric acid levels. Treatment includes lifestyle modifications, NSAIDs, colchicine, and urate-lowering therapies.
Septic arthritis
Septic arthritis is a joint infection that causes the sudden onset of severe joint pain, swelling, and systemic symptoms like fever. It can affect adults of any age, often with predisposing factors (e.g., joint surgery, immunosuppression). The diagnosis is via joint aspiration showing purulent fluid and culture positivity. It requires urgent antibiotic therapy and sometimes surgical drainage.
Osteochondritis dissecans
Osteochondritis dissecans is a condition where a fragment of cartilage and underlying bone detaches from the joint surface, causing intermittent knee pain, swelling, and mechanical symptoms. Common in adolescents and young adults, especially athletes. Diagnosis via imaging (MRI or CT) showing fragment and surrounding bone involvement. Treatment includes rest, immobilization, and sometimes surgical fixation or removal of loose bodies.
Reactive arthritis
Reactive arthritis, also known as Reiter’s syndrome, is an inflammatory arthritis following infection (e.g., gastrointestinal or genitourinary). It presents with asymmetric arthritis, often affecting the knee, along with urethritis, conjunctivitis, and mucocutaneous lesions. Diagnosis is based on clinical criteria and the exclusion of other causes. Management includes treating the underlying infection, NSAIDs, and sometimes DMARDs in persistent cases.
Iliotibial band syndrome
Iliotibial band syndrome is an overuse injury that causes lateral knee pain during running or repetitive activities. It is common in runners and athletes, typically young adults. The pathogenesis involves friction over the iliotibial band insertion. The condition is diagnosed by clinical history and physical exam (Ober’s test, Noble’s test). Treatment includes rest, stretching, NSAIDs, and addressing biomechanical factors.
Additional symptoms
- Locking: Mechanical symptoms suggest a meniscal tear or loose body.
- Pain worse with prolonged sitting or inactivity: Suggests patellofemoral pain syndrome or osteoarthritis.
- Systemic symptoms (fever, chills): Indicative of septic arthritis.
- Morning stiffness: Seen in inflammatory arthritis like rheumatoid arthritis.
Advice for patients
Mild knee pain that does not significantly limit activities may not require immediate medical attention. However, severe pain, pain that persists for several days, or pain that significantly limits mobility should prompt a visit to a healthcare provider. Treatment varies based on the underlying cause but may include rest, physical therapy, medications (such as pain relievers and anti-inflammatories), and in some cases, surgical intervention. It’s important to seek medical evaluation for persistent or severe symptoms to ensure appropriate management and to prevent potential complications.
Summary
Knee pain in adults encompasses a range of conditions, from osteoarthritis to ligamentous injuries and systemic inflammatory diseases like rheumatoid arthritis and gout. Each condition presents distinctively with specific diagnostic clues and management strategies. Early diagnosis and appropriate treatment are crucial to alleviate pain, restore function, and prevent long-term complications, emphasizing the importance of medical evaluation for persistent or severe symptoms.