Epidemiology

Approximately 300,000 hip fractures occur each year in the United States,¹ and this number is projected to increase significantly as the population ages. The major cause of hip fractures is ground-level falls in elderly patients with osteoporosis. Hip injuries are a major cause of morbidity and mortality, especially in the elderly, in whom 1-year mortality after a hip fracture is approximately 25%. Femoral shaft and distal femoral fractures are usually the result of high-energy trauma such as motor vehicle collisions and falls from heights, and thus open wounds and associated traumatic injuries are common.

Pathophysiology

The leading cause of hip fractures is falls in elderly people with underlying osteoporosis. Osteoporosis is a common condition in the elderly, and its incidence increases with advancing age. After about the age of 30, bone resorption slowly begins to exceed bone formation, and as a result bone mass and bone strength lessen. The lifetime risk of fracturing a hip is about 17% in white women and 5% in white men.²

The major cause of hip dislocations is motor vehicle collisions. A great deal of force is required to dislocate a hip, and thus associated injuries are common. Up to 88% of hip dislocations will be accompanied by an associated fracture.³ Patients with hip dislocations have about a 25% risk for osteoarthritis and a 20% risk for avascular necrosis. In addition, sciatic nerve injuries occur in approximately 10% to 14% of patients with posterior hip dislocations.⁴ These risks may be decreased by prompt diagnosis and treatment in the emergency department (ED).

Osteonecrosis (also known as aseptic necrosis, ischemic necrosis, or avascular necrosis) may be caused by acute disruption of the blood supply to the femoral head as a result of a hip fracture or dislocation. Fractures of the femoral neck can also disrupt the blood supply and result in osteonecrosis. Other causes are sickle cell disease, barotrauma, radiation therapy, chemotherapy, atherosclerosis, and Gaucher disease. Associated conditions include steroid use, excessive alcohol consumption, smoking, connective tissue diseases, pancreatitis, and chronic liver and renal diseases.⁵ The incidence of osteonecrosis after hip dislocation depends on the degree of trauma involved and the duration of the dislocation. Some data suggest that reduction of the hip within 6 hours after dislocation decreases the incidence of osteonecrosis.⁶ Therefore, every effort must be made to relocate dislocated hips as soon as possible. Femoral neck fractures are also associated with a high incidence of osteonecrosis. It is thought that the synovial fluid around the fracture site interferes with normal bone healing. Intertrochanteric fractures and other more distal fractures of the femur are rarely complicated by osteonecrosis.

Anatomy

The hip joint is a ball-and-socket articulation located between the femoral head and the acetabulum. The ligamentum teres, the capsular ligaments, and the proximal muscles of the leg make the hip a stable joint that requires very strong force to dislocate it. The femur is the largest and strongest bone in the body. The femoral neck is about 8 to 10 cm in length. The intertrochanteric line is an oblique line that connects the greater trochanter and the lesser trochanter and marks the junction of the femoral neck and the shaft.

The muscles of abduction (gluteus medius and gluteus minimus) insert on the laterally located greater trochanter, and the muscles of flexion (iliopsoas) insert on the medially located lesser trochanter. The major blood supply to the head and neck of the femur is the medial and lateral circumflex arteries, which are branches of the femoral artery.

The hip region has approximately 18 bursae. The most common source of hip pain and inflammation is the deep trochanteric bursa, which lies between the gluteus maximus and the greater trochanter.

Presenting Signs and Symptoms

Pain is the most common complaint in patients with hip problems.⁷ The location and character of the pain are very helpful in making a diagnosis. Increased pain during and after weight bearing and improvement with rest suggest a structural joint problem such as osteoarthritis. Constant pain, unrelated to use, suggests an infectious, inflammatory, or neoplastic process.

Lateral hip pain, especially with tenderness over the greater trochanter, suggests trochanteric bursitis. Lateral hip pain with paresthesias suggests meralgia paresthetica—lateral femoral cutaneous nerve entrapment. This condition is characterized by a local area of pain (often burning or dysesthesia) that is not influenced by direct pressure on the hip or back movement.

Anterior hip or groin pain made worse by joint motion suggests a problem with the hip joint, such as osteonecrosis, occult fracture, synovitis, or a septic joint. Anterior hip pain that is not made worse by hip motion or weight bearing suggests an inguinal hernia, lower abdominal pathology, or referred lumbar nerve root pain. Posterior hip pain suggests sacroiliac joint inflammation, lumbar radiculopathy, or herpes zoster. Anterior thigh pain may be secondary to injury to the hip joint or femur, stress fracture of the femoral neck, or lumbar radiculopathy.