Many conditions and types of injuries can cause hip or knee pain. Click a link below to learn more about common hip and knee conditions.

Anterior cruciate ligament (ACL) tear

Arthritis

Bursitis

Cartilage tears

Collateral ligament tears

Dislocated kneecap

Fractures

Knee instability

Ligament injuries

Meniscus tears

Osteoarthritis

Osteoporosis

Osteonecrosis

Rheumatoid arthritis

Sprains/strains

Tendonitis

Anterior cruciate ligament (ACL) tear is a common athletic injury. The anterior cruciate ligament (ACL) is the major stabilizing ligament of the knee. It runs from the thighbone to the shinbone through the center of the knee where it prevents the knee from buckling. Tears usually occur with a sudden change in direction or when something stops a person abruptly.

ACL tears are season-ending injuries. In these MRI studies, Panel A shows a healthy anterior cruciate ligament (see arrow). In Panel B, you can’t see the band, indicating a torn ACL.

Arthritis is the wearing away of the protective tissue layer that covers the bone ends inside joints. This layer acts as a shock absorber. As it wears, the joint becomes achy, swollen and eventually deformed. Arthritis can occur at any age after an injury to a joint.

Bursitis is inflammation of bursae — small sacs located between bone and other moving structures such as muscles, skin or tendons. The bursa allows smooth gliding between these structures. Bursae are all over the body, but the ones closest to joints (hips, knees, shoulders, elbows) tend to become irritated more often. Bursitis is usually temporary and occurs mainly as result of overuse.

Cartilage tears affect the protective tissue between joints such as knees, elbows and shoulders. See also meniscus tears.

Collateral ligament tears can affect the medial collateral ligament (on the inside of the knee joint), or rarely, the lateral collateral ligament (attached outside the knee joint). These ligaments supply stability to your knee for side-to-side movement, even during normal walking. Injury to these areas usually occurs after a strike from the side such as a football tackle.

Dislocated kneecap is what happens when your kneecap pops out of place, usually to the outside of the knee.

Fractures are breaks in bones. Broken bones can result from falls, accidents or traumatic injuries. Severe breaks may require surgery to repair. However, most fractures are treated by immobilizing broken bones in casts or splints until they have grown back together.

Knee instability is a condition usually caused by an anterior cruciate ligament injury. This ligament is a major stabilizer of the knee.

Ligament injuries are common in athletes and active people. Ligaments on either side of a bone can be strained or torn by overuse or by a fall or traumatic injury. Sometimes a "snap" or "pop" is heard and the joint attached to the ligament feels loose or wobbly.

Meniscus tears are tears in knee cartilage (meniscus) – a small, horseshoe-shaped, mobile shock absorber between the bone ends inside the knee joint. There are two in each knee on either side of the knee. Meniscus tears are extremely common with ACL injuries.

Osteoarthritis is the most common form of arthritis (Osteo is Greek for bone; arthritis means joint inflammation.) Osteoarthritis (OA) is an inevitable part of aging and can affect any joint. It usualy develops after age 45; about half of men and women over age 65 have it to some degree. OA is caused in part by wear and tear on a joint over time. It develops as cartilage – smooth tissue that cushions bones and keeps them from rubbing against each other – breaks down. This leads to joints becoming painful, warm to the touch, reddened and swollen. When the cushioning system of the joint is lost, the bones may grind painfully against each other. The joint can begin to stiffen, and movment is impaired. OA typically strikes the weight-bearing joints (knees, hips, back, feet); hands; and spine. The knee is the most commonly affected joint.

Osteoporosis (brittle bones) is a condition in which bones lose calcium, causing them to become fragile and more likely to break. If left untreated, osteoporosis can progress painlessly until a bone does break, such as a hip, spine or wrist or rib. This disease affects more women than men; 80 percent of those with osteoporosis are female. You may be at increased risk for osteoporosis if you have a family history of brittle bones; suffer from autoimmune disorders such as diabetes, rheumatoid arthritis or asthma; are extrmemly thin; or are a postmenopausal woman or a man with low testosterone levels. Children with such conditions as cystic fibrosis, celiac disease and inflammatory bowel disease are also at increased risk of osteoporosis because they can not absorb nutrients such as calcium properly. There are steps you can take to help prevent osteoporosis. These steps include getting enough calcium in your diet or through supplements, as well as Vitamin D to ensure your body absorbs the calcium. Getting regular exercise, especially weight-bearing or resistance exercise, builds stronger, denser bones. Avoiding smoking and heavy drinking can also improve bone health. Long-term use of some medicines (cortcosteroids, anticonvulsants) can speed up bone loss.

Osteonecrosis (bone death) is what happens when a segment of bone within the joint suddenly loses its blood supply and ‘dies.’ This condition usually affects older patients; the cause is not always known but high-dose steroid treatments for other medical conditions can cause osteonecrosis.

Rheumatoid arthritis is a form of arthritis in which excessive inflammation wears away the protective tissue between joints.

Sprains/strains are two different injuries, although both are the result of forcing a joint past its normal range of motion. Sprains occur when ligaments that connect bone to bone are overstretched, resulting in swelling, pain and even bruising. Jammed fingers, twisted knees, and twisted ankles are common examples of sprains. Strains, also called muscle pulls, refer to an overstretching of a muscle or tendon that causes the muscle to actually tear. Strains usually occur when a muscle is stretched too fast.

Tendonitis is inflammation or irritation of a tendon. Tendons are the thick fibrous cords that attach muscles to bones. They transmit the power generated by a muscle contraction to move bones. Tendonitis is usually temporary and occurs mainly as result of overuse.

Reviewed for clinical accuracy by Anthony S. Puglisi, MD, and John T. Williams Jr., .