Photo Quiz

Right hip pain in a high school football player
A 15-year-old boy complains of right hip pain that began the day before, when he felt a "pop"during football practice. His medical history is significant only for several ligamentous injuries in both ankles and fractures of the right lateral malleolus and the left medial malleolus, which healed uneventfully. He denies anabolic steroid use and alcohol use. The patient is in significant distress because of his hip pain. Temperature is 37.2C (99F); heart rate, 67 beats per minute with normal rhythm; respiration rate, 16 breaths per minute; and blood pressure, 122/76 mm Hg. Head and neck are normal; lungs are clear. Examination of the lower extremities reveals strong pulses and intact sensation. Active range of motion in the right hip is limited-particularly when the hip is flexed. Passive range of motion in the same hip remains intact despite considerable pain. You order radiographs of the right hip. What are the findings, and what would you do next to clinch the diagnosis? Right hip pain in a high school football player Close inspection of the frontal (A) and lateral (B) radiographs of the right hip reveals displacement of the apophysis of the lesser trochanter in a cephalad direction (A, arrow), which is consistent with a fracture through the physis of the lesser trochanter. Note the following normal findings:

• The femoral head is intact and unremarkable.
• The physis through the femoral neck is intact.
• No osseous fragments are identified adjacent to the normal structures.

The normal appearance of the femoral head helps rule out avascular necrosis, and the intact physis of the femoral neck excludes a slipped capital femoral epiphysis. Avulsion fractures are seen frequently in adolescent athletes. In this type of fracture, the bone is pulled apart during active motion as a result of stress placed on it by a ligament or tendon that is stronger than the bone to which it attaches. Avulsion fractures are more common in adolescents because their bones are not as strong as those of adults-especially at the physis, which contributes to the growth of a bone but is also a point of weakness. In addition, adolescents tend to be very physically active and to have strong muscles. Commonly involved origins and insertion sites include:

• The anterior superior iliac spine- origin of the sartorius muscle.
• The anterior inferior iliac spine- origin of the rectus femoris muscle.
• The pubic symphysis and along the inferior medial aspect of the pubic bones-origin of the adductor muscles.
• The greater trochanter-insertion site of the gluteus medius and minimus muscles.
• The lesser trochanter-insertion site of the iliopsoas muscle.

Typically, avulsion fractures can be diagnosed based on the radiographic findings in conjunction with a working knowledge of the relevant muscular and tendinous anatomy. In some instances, it may be advisable to obtain an MRI scan as well. Here an MRI scan is ordered to confirm the diagnosis. A coronal T2-weighted image with fat suppression using inversion recovery technique shows fluid signal between the avulsed osseous fragment and the parent bone (C, arrow), which indicates the site of the fracture. A slightly more anterior image from the same T2-weighted series (D) shows slight retraction of the iliopsoas muscle (yellow arrow) with fluid signal interdigitating between the tendon fibers (red arrow). An axial T2-weighted image also shows fluid interdigitating between tendon fibers of the retracted iliopsoas muscle (E, arrow). These MR images delineate the relationship between the involved muscle and its insertion site on the lesser trochanter; they also demonstrate clearly that stress was placed on both the muscle and the bone, with the break occurring at the weakest "link" in the kinetic chain-the physeal plate. The patient was sent for orthopedic consultation. He was encouraged to rest and take NSAIDs for pain. After 8 weeks, his ability to flex the injured hip significantly improved; the improvement continued during the next 6 months until he had reached full recovery.