CHAPTER 5: Imaging the Hip

1. INTRODUCTION: FAST HIP FACTS

❑ The Pathologies

• Newborns

  • ◗ Developmental dysplasia of the hip (DDH) covers a range of hip instability, from laxity to dislocation. Estimates are 1 in 100 births present with hip subluxation, 1 in 1,000 with dislocation. The left hip is more often affected owing to intrauterine positioning of the hip in adduction against the mother's spine.

• Children—remember that hip problems often present as referred pain in the thigh or knee.

  • ◗ Transient synovitis is an inflammatory reaction of the joint that often occurs after an upper respiratory infection.

  • ◗ Legg-Calvé-Perthes is an expression of avascular necrosis of the femoral head; boys are more often affected than are girls.

  • ◗ Juvenile rheumatoid arthritis covers a subset of conditions that may be self-limiting or chronic. Peak ages of presentation are from 7 to 12 years. Girls are more often affected than are boys.

  • ◗ Septic arthritis, septic bursitis, and osteomyelitis are terms for infection in the joint, bursa, or bone.

• Teenagers

  • ◗ Slipped femoral capital epiphysis is a posteromedial displacement of the femoral head resulting from a weakening of the growth plate at the femoral head-neck junction. It is most common in adolescent boys during growth spurts at puberty.

  • ◗ Snapping hip syndrome is the audible “snap” of tendons gliding abnormally over bone. The most common cause is the iliotibial band moving over the greater trochanter. The iliopsoas tendon moving over the iliopectineal eminence at the anterior acetabulum and the rectus femoris tendon gliding over the femoral head may both also cause snapping hip syndrome.

  • Femoroacetabular impingement results from abutment of the femoral neck with the acetabulum. Pain is exacerbated in the athlete as a result of repetitive movements and the greater amount of flexion incurred during activities. Tears of the acetabular labrum are highly associated with this condition.

• Adults

  • Osteoarthritis is the most common form of joint disease in humans and is a leading cause of disability among the elderly. More than 300,000 total hip replacements are performed annually in the United States.

  • Osteoporosis: The most devastating sequela of osteoporosis is fracture. Falls cause 90% of all hip fractures. Most often affected are elderly females, both because they tend to have less bone density and longer life spans than do males. Mortality rates increase significantly in the first year after a hip fracture.

❑ The Imaging Choices

• Radiographs adequately demonstrate most fractures and dislocations at the hip and pelvis as well as nontraumatic disorders such as the various arthritides.

• Computed tomography (CT) provides optimal visualization of complex fracture characteristics especially in distinguishing fractures of the acetabulum or in localizing the position of fracture fragments.

• Magnetic resonance imaging (MRI) is the best choice for evaluating injuries to the acetabular labrum and articular cartilage; assessing femoroacetabular impingement; and assessing and staging avascular necrosis of the femoral head.

• Musculoskeletal ultrasound (MSUS) is the ...