A 13-year-old boy with a common athletic injury

CASE

A 13-year-old boy presented to the clinic for the evaluation of right hip pain. He stated that he was playing soccer and felt a “pop” after kicking the ball. On physical examination, his vital signs were normal. He was able to stand but experienced mild right hip pain with walking; no swelling or bruising was visible. There was tenderness with palpation about the right hip. Internal and external rotation of the hip was normal, but there was mild pain.Radiographs of the pelvis were obtained (see Figure 1). What does the radiograph reveal?

DISCUSSION

Figure 1 demonstrates an avulsion fracture of the anterior inferior iliac spine. In this type of injury, a fracture occurs at the insertion or origin of a tendon or ligament on the bone. The fracture usually results from sudden or forceful contraction or pulling on the ligament or tendon. In children, the injury is usually associated with athletic activity, such as running, jumping, or kicking, when it occurs in the pelvis. Although avulsion injuries can occur at almost any tendon or ligament insertion site, this article discusses avulsion fractures of the pelvis in children.

The diagnosis of an avulsion injury is usually suggested by the history and physical examination and is confirmed with radiographs. The child may complain of a sudden, sharp pain or “pop.” There may be focal tenderness and swelling at the injury site. Palpation and movement may exacerbate the pain. A hematoma may be present. Occasionally, the avulsed fragment may be palpable.

Children involved in sports, particularly cheerleaders, football players, gymnasts, soccer and baseball players, and track and field athletes, are prone to these types of injuries. Trauma can also cause an avulsion fracture. Avulsion injuries of the pelvis appear to be more prevalent in the second decade of life and more common in males than females.

Tendons in children usually insert on an apophysis, which is a secondary ossification center related to the size or shape of a bone and not associated with length. As a person ages, the apophyses eventually fuse with the remainder of the bone. In adolescents, the apophysis is an area that, when put under stress, is weaker than the tendon attached to it and therefore is more susceptible to fracture. The characteristic sites for avulsion fractures of the pelvis are demonstrated in Figure 2.

The ischial tuberosity, the area where the hamstring muscles originate, is the most common fracture site involved. This fracture may cause buttock pain or difficulty walking. An example of this fracture is seen in Figure 3. Fracture of the ischial tuberosity usually heals well with conservative treatment, but sometimes exuberant callous formation can occur during healing. This can mimic a more aggressive process, such as osteomyelitis or Ewing's sarcoma. If the history and diagnosis are not clear, CT may prove useful. Ischial tuberosity fractures are more common in runners, cheerleaders, and dancers.

The anterior superior iliac spine is the attachment site for the tensor muscle of the fascia lata and the sartorius muscle. When avulsed, this can present as pain below the anterior aspect of the iliac crest. This fracture usually results from forceful hip extension, such as when sprinting.

The rectus femoris muscle originates from the anterior inferior iliac spine. An avulsion fracture in this area can also be caused by forceful hip extension. The recovery period for avulsion fractures of the anterior inferior iliac spine and anterior superior iliac spine is usually shorter than the recovery period for an ischial tuberosity fracture. Avulsion fractures of the anterior inferior iliac spine and anterior superior iliac spine are also usually less disabling.

Avulsion fractures of the greater trochanter are uncommon in children. The gluteus medius, gemelli, obturator internus, and pyriformis muscles insert at this location. The lesser trochanter is the insertion site of the iliopsoas muscle. The iliac crest is also a less common site for avulsion injury, which usually occurs at its lateral aspect; the transverse abdominus and internal oblique muscles originate here, and the external oblique muscles insert here.

Treatment of avulsion fractures of the pelvis is usually conservative. Open reduction and internal fixation are rarely necessary. Many patients are able to return to their usual level of athletic activity within a few months. Surgery may be required if motion at the fracture site occurs as a result of incomplete union or fibrous union with associated pain, or if there is significant distraction of the fracture fragment from its site of origin. JAAPA

Julie Vajnar is the department editor for Diagnostic Imaging Review and practices in a radiology group at North Oaks Health System, Hammond, Louisiana. She has indicated no relationships to disclose relating to the content of this article.