Overview of Knee Pain
Knee pain is a common condition that often results from overuse, injury, or medical conditions, such as arthritis. Incidence of knee pain increases with age. In the United States, about 20 million people seek medical care for knee pain each year. The condition can develop suddenly (acute knee pain) or gradually over time (chronic knee pain).
The knees are the largest joints in the body. The lower end of the thighbone (femur), the upper end of the shinbone (tibia), and the knee cap (patella) are the bones that make up the knee joints. Bands of connective tissue in the knees (called ligaments) connect the bones, allow mobility, and help prevent abnormal movement within the joints. Cartilage in the knees cushions the ends of the bones and helps absorb impact.
Knee Pain Causes
The knees are complex joints that often are damaged as a result of injury (trauma) or "wear and tear." In people over the age of 50, osteoarthritis is the most common cause for pain in the knees. Common causes in younger people include overuse and injury. Knee pain also can result from infections (e.g., osteomyelitis, septic bursitis) and certain medical conditions.
Common types of knee injuries include the following:
- Fractures (broken bone; e.g., fractured knee cap [patella], upper tibia, or lower femur)
- Torn ligaments (e.g., anterior cruciate ligament [ACL] tear, medial collateral ligament [MCL] tear)
- Torn cartilage (e.g., meniscus tear)
- Knee sprains or strains (injury to ligaments or muscles)
- Dislocated knee cap (patella)
Medical conditions that can cause knee pain include the following:
- Arthritis (e.g., osteoarthritis, rheumatoid arthritis)
- Bursitis (e.g., anserine bursitis, housemaid's knee [prepatellar bursitis])
- Baker's cyst (fluid-filled sac that develops as a result of excess fluid production within the joint)
- Chondromalacia patella (softening of the cartilage in the knee)
- Gout (often causes pain in the big toe, but also can affect the knees)
- Osgood-Schlatter disease (condition that usually develops in children during periods of rapid growth)
- Osteochondritis dissecans (condition in which fragments of cartilage and bone in the knee become detached and inflamed)
- Reiter's syndrome (inflammatory condition that also causes swelling and stiffness)
- Synovitis (type of inflammation within the knee joint)
- Tendonitis (e.g., jumper's knee [patellar tendonitis])
Abnormal alignment in the legs (e.g., bowlegs, knock-knees) and bone tumors also can result in knee pain. Bone tumors can be benign (i.e., do not spread) or malignant (cancerous). Benign tumors include osteomas, osteoblastomas, and osteochondromas. Types of malignant bone tumors that can result in knee pain include osteosarcoma, chondrosarcoma (develops in cartilage), and Ewing's tumor.
Knee Pain Risk Factors
The main risk factor for knee pain is age. Over time, wear and tear can cause pain, stiffness, and inflammation in the knees. People who are overweight are at increased risk.
Athletes often develop knee pain as a result of overuse or injury. Work-related factors, such as frequent heavy lifting, kneeling, stair climbing, and standing for long periods of time, also can increase the risk. Participation in physical activities and sports increases the risk for knee pain, especially if improper techniques (e.g., not warming up or cooling down correctly, poor body mechanics) are used.