The hip joint attaches the leg to the torso of the body. In the hip joint, the head of the thigh bone (femur) swivels in a socket, called the acetabulum, that is made up of pelvic bones. While many causes of hip pain can arise from the joint itself, there are numerous structures surrounding the hip that can also be the source of pain.
Trauma is often the cause of hip pain, but any source of inflammation may cause pain in the hip area. Pain is one of the symptoms of inflammation, along with swelling, warmth, and redness; together these are signals that a problem may exist.
Pain can arise from structures that are within the hip joint or from structures surrounding the hip. The hip joint is a potential space, meaning that there is a minimal amount of fluid inside it to allow the femoral head to glide in the socket of the acetabulum. Any illness or injury that causes inflammation will cause this space to fill with fluid or blood, which stretches the hip capsule and results in pain.
The femoral head and the acetabulum are lined with articularcartilage that allows the bones to move in the joint with less friction. Also, the socket area of the acetabulum is covered with tough cartilage called the labrum. Just like any other joint cartilage, these areas can wear away or tear and be the source of pain.
There are thick bands of tissue that surround the hip joint, forming a capsule. These help maintain joint stability, especially with movement.
Movement at the hip joint is possible due to the muscles that surround the hip and the tendons that attach across the hip joint, allowing motion in different directions. Aside from controlling movement, these muscles act in concert to maintain joint stability. There are large bursas (closed fluid-filled sacs) that surround areas of the hip where muscles intersect and allow the muscle and tendon to glide more easily. Any of these structures can become inflamed.
Pain from other sources can be referred to the hip, meaning that while the hip hurts, the problem originates elsewhere. Inflammation of the sciatic nerve as its arises from the back can cause hip pain, especially if the L1 or L2 nerve roots are involved. Other types of nerve pain may manifest as hip pain, including pain arising in the lateral femoral cutaneous nerve of the thigh, which is often inflamed inpregnancy. Pain from an inguinal hernia can also cause pain that is felt in the hip.
Hip pain is a nonspecific complaint that requires the health-care practitioner to find the underlying cause, from injury to illness. Without specific trauma, the approach to the diagnosis of hip pain requires an open mind.
Falls are the most common reason that elderly people break a hip. The fracture is due to a combination of two effects of aging, osteoporosis (thinning of bones) and a loss of balance. These two risk factors precipitate many falls. In some cases, the bone may break first due to osteoporosis and cause the fall
When health-care practitioners talk about a hip fracture, they really mean a fracture of the proximal or upper part of the femur.
The precise location of the fracture is important, because it guides the decision of the orthopedic surgeon as to which type of operation is needed to repair the injury.
Aside from a fall, any trauma can potentially cause a hip fracture. Depending upon the mechanism of injury, the femur may not break; rather, a portion of the pelvis(often the pubic ramus) may be fractured. The initial pain may be in the hip area, but examination and X-rays may reveal a different source of the injury. Trauma can also cause a hip dislocation, in which the femoral head loses its relationship with the acetabulum. This is almost always associated with an acetabular (pelvic bone) fracture.
Contusions (bruises), sprains, and strains may occur as a result of trauma, and even though there is no broken bone, these injuries can still be very painful. Sprains are due to ligament injuries, while strains occur because of damage to muscles and tendons. Because of the mount of force required to walk or jump, the hip joint is required to support many times the weight of the body. The muscles, bursas, and ligaments are designed to shield the joint from these forces. When these structures are inflamed, the hip cannot function and pain will occur.
Hip pain may also arise from overuse injuries in which muscles, tendons, and ligaments can become inflamed. These injuries may be due to routine daily activities that may cause undue stress on the hip joint or because of one specific strenuous event. Overuse may also cause gradual wearing away of the cartilage in the hip joint, causing arthritis (arth=joint + itis=inflammation).
Certain other structures should be mentioned as a cause of hip pain because they become inflamed. The iliotibial band stretches from the crest of the pelvis down the outside part of the thigh to the knee. This band of tissue may become inflamed and cause hip pain, knee pain, or both. This is a type of overuse injury that has a gradual onset associated with tightness of the muscle groups that surround the knee and hip. Piriformis syndrome, in which the piriformis muscle irritates the sciatic nerve in the buttock, can also cause significant posterior hip pain.
The trochanteric bursa is a sac on the outside part of the hip that serves to protect muscles and tendons as they cross the greater trochanter (a bony prominence on the femur). Trochanteric bursitis describes the inflammation of this bursa. The bursa may become inflamed for a variety of reasons, often due to minor trauma or overuse.
Hip pain may be caused by a variety of illnesses. Anything that causes systemic inflammation in the body may also affect the hip joint. The synovium is a lining tissue that covers those parts of the hip joint not covered by cartilage. Synovitis(syno=synovium + itis= inflammation), or inflammation of this lining tissue, causes fluid to leak into the joint, resulting in swelling and pain.
Hip pain may not originate in the hip itself but may be caused by problems in adjacent structures.
Children who complain of leg or hip pain should not be ignored. If the pain is persistent, if a limp is present, or if a fever exists, a health-care practitioner should be contacted
Potential concerns in children with hip pain include