Hip Tendonitis and Bursitis 

Hip overuse injuries such as tendinitis and bursitis occur commonly in active individuals who participate in running, cycling, and cutting sports such as football, hockey, soccer, etc.^{[1, 2, 3, 4, 5, 6, 7, 8]} These injuries can occur after an acute injury, such as an adductor strain from soccer, or present as a chronic pain, such as a hamstring tendinopathy from repetitive activities such as running. Training errors, biomechanical issues, and sudden increases in activity levels are also risk factors. In the adolescent age group, traction injuries such as avulsion fracture and apophysitis can occur and cause difficulties with training and performance.^[9]

The investigation into the cause and treatment of hip overuse injuries can often be frustrating for clinicians and patients alike. Many musculoskeletal injuries can cause referred pain into the hip area, but so can intra-abdominal, gynecologic, urologic, and spinal disorders.^{[1, 3, 4, 5, 6, 7, 8, 10]}

For excellent patient education resources, visit eMedicine's Foot, Ankle, Knee, and Hip Center, Sports Injury Center, and Sprains and Strains Center. Also, see eMedicine's patient education articles Repetitive Motion Injuries and Muscle Strain.

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Hip overuse syndrome is a relatively common condition, particularly in people who are physically active.

The hip joint can be imagined as a ball and socket. The ball, called the femoral head, is seated within the acetabulum of the pelvic bone (the socket). Both of these bones are covered by articular cartilage, a lubricating and cushioning layer that helps to prevent damage to the underlying bones. Likewise, the labrum is a cushion of fibrocartilage deep within the socket that helps to aid articulation and provide further cushioning.

The hip joint is subject to strong forces (which can be multiple times the body weight) with all weight-bearing activities, from walking to running, as well as jumping and cutting sports. This is due to the long, lever-arm mechanism of the lower extremity, with the hip joint being the fulcrum. Thus, the hip joint is often the location of degenerative arthritis as people age.

The capsular ligaments of the hip joint, which act like ropes, are formed from thickened portions of the joint capsule, helping to keep the 2 bones together and aid in articulation. These ligaments provide stability and tension to the joint with movement.

Anteriorly, the rectus femoris, iliopsoas, gracilis, and sartorius muscles connect the pelvic bone to the femur and help aid in flexion of the femur, bringing the leg up toward the body. These muscles, along with the rest of the quadriceps muscles, which extend the knee, are the largest and most powerful muscles in the body, responsible for producing large concentric, isometric, and eccentric forces. Because of this, these muscles are subject to traumatic injuries and tears from sudden starts (concentric contraction), stops (eccentric contractions), and direct trauma, as well as overuse injuries from repetitive activities (microtrauma).

Medially, the set of 3 adductor muscles and the pectineus connect the inner aspect of the femur to the front and inferior aspect of the pelvis; contracting these muscles adducts the femur back to midline and across the body (ie, crossing the legs). From the outside, the tensor fasciae latae and biceps femoris (toward the back) aid in abduction, moving the legs outward from the body. Posteriorly, the semitendinous and semimembranous muscles (the hamstrings), the biceps femoris, and the large gluteus maximus extend the leg backward from the body.

The gluteus medius, another posterior muscle of the hip and buttocks, aids in internal rotation and abduction of the thigh. The piriformis, quadratus, and superior and inferior gemelli work in tandem to perform external rotation of the hip.

All of the previously mentioned muscle groups are subject to increased loads in athletic and recreational activity (see Functional Anatomy). Tendons, which attach muscle directly into bone, are structures that are subject to high tensile strength, meaning they must stretch as the muscles shortens, but they do not provide strength. Inflammation of a tendon from injury or repetitive stress is called tendinitis.

Several tendons are cushioned from the underlying bone by a lubricating and cushioning sac called a bursa. The largest bursa in the hip joint is between the iliopsoas muscle and the pelvic brim and is called the iliopsoas bursa. Between the tensor fasciae latae and gluteus medius muscles and the greater trochanter of the femur, a portion of bone that juts out laterally from the proximal femur, lies the greater trochanteric bursa. Any bursa within the body can be inflamed from repetitive stress of the overlying muscles, direct trauma, or a spreading infection.

The tendinous portion of the muscle has poor blood flow, so injury or stress at the attachment of the tendon onto the bone can lead to degeneration of the area. This degeneration is associated with the disorientation of collagen fibers, increased cellularity, and angiofibroblastic degeneration. Pathology examination of these tendons fails to reveal inflammatory cells or increased blood supply to the area. These "scars" within the tendon are difficult to treat because of decreased blood flow into the injured area.

In the pelvic bones of children, adolescents, and young adults, the tendons attach onto a secondary growing portion of bone. This connection between the larger pelvic bone and smaller secondary growth area is called the apophysis, and in this age group it is the weakest link from the musculature to the bone. Consequently, the apophysis can be the direct source of pain from irritation (apophysitis), or it can be broken apart by a strong force on the tendon and pulled away from the larger pelvic bone (avulsion fracture).

Avulsion fractures around the pelvis occur in prepubertal athletes as the result of an actively contracting muscle encountering abrupt resistance such as a misstep, rapid acceleration, or eccentric movements. The treatment of most smaller avulsion fractures is similar to the treatment of strains of the muscle-tendon unit.