The hip is a common area of pain resulting from a myriad of conditions ranging in levels of severity and complexity. The hip is also an area where pain is felt that is generated from distant sources (referred pain).
The hip joint is classified as a ball-and-socket joint, similar in makeup to that of the shoulder. The structure known as the “ball” is the head of the femur (thigh bone) and the “socket” is comprised of an area on the pelvis known as the acetabulum. Similar to the shoulder, the stability of the hip joint is not created by a marked degree of bone-bone contact, but rather from the integrity and strength of surrounding muscle, ligament, and cartilage structures. Additional stability is provided by a strong joint capsule, the dense and fibrous structure which includes the iliofemoral, pubofemoral, and ischiofemoral ligaments. The need for such a high degree of stabilization of the joint limits excessive and possibly damaging movement. If you think of the hip joint in layers, the deepest layer is bone and cartilage, next are the ligaments of the joint capsule, with the tendons and muscles completing the final layer.
The main cartilage structures of the hip are the articular cartilage surrounding the head of the femur and the labral cartilage that surrounds the socket of the hip the acetabulum. Damage to these structures can lead to further damage of the underlying bone which can result in the need for a hip replacement.
The muscles of the thigh and hip work together to keep the hip stable, aligned, and allow for the basic movements of the hip: flexion – bringing the hip up towards the stomach; extension – moving the hip back away from the front of the body; abduction – moving the leg away from the midline of the body; adduction – bringing the leg back towards the midline of the body. There are a large number of muscles that connect directly to the bones that make up the hip or whose contraction causes movement of the hip. These muscles include the quadriceps (assist with hip flexion and abduction), hamstrings (assist with hip extension and adduction), adductors (move the hip into adduction and assist with internal rotation), gluteal musculature including the gluteus maximus (extension), medius and minimus (abduction and external rotation), the deep external rotators of the hip including the piriformis, the gamelli, the obturators, and the quadratus femoris, and the tensor fascia latae (abduction).
Due to the complexity of the joint, there are many causes of hip pain which can result from a number of conditions and/or injuries. One of the more common causes of hip pain results from osteoarthritis, which is damage and weakening of the bony structures of the hip. Although there are many contributing factors to the development of osteoarthritis, one injury that people with osteoarthritis are at an increased risk of is a hip fracture secondary to a fall or of a spontaneous nature. Another common cause of hip pain is of mechanical or musculoskeletal nature. This type of hip pain is generated directly from dysfunction of the joint itself, dysfunction of joints that act upon the hip (ankle, knee, and lower/mid back), or by the musculature surrounding and acting upon the hip. Because the hip is a major weight-bearing joint, changes in the hip from mechanical defect can significantly affect gait (walking) and place abnormal stress on joints above and below the hip. Weight bearing stresses on the hip during walking alone can be five times a person’s body weight.
Other conditions that can be a cause of hip pain and dysfunction include trochanteric bursitis, femoroacetabular impingement (FAI), labral tears, osteonecrosis, dislocation, and fracture. Common symptoms of hip dysfunction include pain and sensation abnormalities surrounding the hip, groin pain, pain in the buttocks, popping or snapping around the hip joint, decreased ability to move the hip, and difficulty bearing weight. Regardless of the severity of the condition responsible for pain and dysfunction surrounding the hip, proper diagnosis is vital when formulating any kind of rehabilitation program be it conservative or invasive in nature.