Pelvic avulsion fractures are common in youth athletes; many of these injuries can be treated conservatively. This article reviews the etiology, presentation, and management of the more common pelvic avulsion fractures, including anterior superior iliac spine, anterior inferior iliac spine, ischial tuberosity, and iliac crest avulsions. Adolescent pelvic avulsion fractures rely on the amount of fracture displacement to guide treatment. Conservative management includes rest and avoiding use of the muscle(s) that attach to the avulsed fragment. Operative treatment is reserved for widely displaced fractures or symptomatic nonunions. With appropriate treatment, young athletes frequently return to their same level of sport.
Key points
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Apophyseal avulsion fractures are seen almost exclusively in the setting of pediatric sports participation. The apophysis is at risk during the time between the formation of the secondary ossification center and its closure.
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Older adolescents are more likely to sustain injuries to the iliac crest and anterior superior iliac spine (ASIS), and younger adolescents tend to sustain injuries at the anterior inferior iliac spine (AIIS) and ischium.
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The history and physical examination are excellent clues as to the diagnosis and usually confirmed with plain radiographs. Ischial avulsion fractures may require advanced imaging to evaluate the extent of hamstring tendon involvement.
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Pelvic avulsion fractures rely on the amount of fragment displacement to guide treatment. Conservative management is appropriate in most cases with recommendations of rest and avoiding use of the muscle(s) that attach to the avulsed piece. Operative treatment is typically reserved for widely displaced fractures or symptomatic nonunions.
Introduction
Growing numbers of children in the United States participate in sports each year. There are concerns that current trends placing higher demands on young athletes and a push toward earlier single sport specialization may contribute to greater risk of injury. , Physiologic differences in the pediatric skeletal system compared with that of an adult lead to differences in the types of injuries sustained during sporting activity. One class of injuries unique to the pediatric population are apophyseal avulsion fractures, an entity almost exclusively seen in the setting of pediatric sports participation.
Apophyseal avulsion injuries are rare injuries that occur in the setting of sudden, forceful, eccentric contraction of the lower extremity. Tensile force ultimately leads to avulsion of the musculotendinous attachment with fracture at the secondary apophysis. Apophyseal avulsions in the pediatric pelvis tend to occur with sudden eccentric forces, as seen in sprinting, jumping, swinging a bat, or kicking. In the pelvis, avulsion fractures are most commonly seen at the anterior superior iliac spine (ASIS), anterior inferior iliac spine (AIIS), and ischial tuberosity. Avulsions from the iliac crest and pubic symphysis also can be seen.
The pediatric pelvis is at risk of avulsion fractures due to tensile stress on the apophyseal growth plate. The cartilaginous growth plate tends to fail in tension before the musculotendinous unit, leading to avulsion fractures at the level of the apophysis. The apophysis is at risk of injury in the time between the formation of the secondary ossification center and its closure. Formation of the secondary ossification center typically begins in girls around age 10 at the AIIS, with closure ranging from age 11 to 16. The remainder of the iliac crest closes between 16 to 25 years of age.
In a 2015 review of 228 pediatric pelvic avulsion fractures, it was determined that 49% were AIIS avulsions, 30% ASIS avulsions, 11% ischial tuberosity avulsions, and 10% iliac crest avulsions. The most common mechanisms were running (39%) and kicking (29%), with the most common sports during which these injuries occurred being soccer (32%), track and field (24%), and football (14%).
Age, skeletal maturity, and sex have been found to be associated with specific types of avulsion fractures of the pelvis. , Older adolescents are more likely to sustain injuries to the iliac crest and ASIS, whereas younger adolescents tend to sustain injuries at the AIIS and ischium. Overall, boys are more likely than girls to sustain pelvic apophyseal avulsion fractures. Due to their earlier skeletal maturity and physeal closure, girls tend to sustain these injuries at a younger age than boys.
Anterior superior iliac spine avulsion injury
Etiology
ASIS avulsions occur secondary to eccentric force at the hip with avulsion of the sartorius muscle. Although the tensor fascia lata also originates from the ASIS, these avulsions tend to cause iliac crest avulsion fractures instead of ASIS avulsions. ASIS avulsions are typically seen between age 11 and 16 in girls and 12 and 18 in boys. This injury is most commonly sustained in activities that involve running and kicking. ASIS avulsions are more likely to occur in the setting of a closed triradiate cartilage compared with AIIS avulsions.
Presentation and Evaluation
Patients with ASIS avulsions will typically present with pain at the anterior pelvis and point tenderness over the ASIS. Patients will frequently report feeling or hearing a “pop” at the time of injury. Weight bearing may be limited secondary to pain. In acute injuries, swelling and ecchymosis also may be present over the ASIS. On physical examination, resisted hip flexion will likely be painful and weaker compared with the contralateral side.
Initial workup includes radiographs of the pelvis. Typically, an anterior-posterior (AP) and frog-leg lateral view of the pelvis will sufficiently demonstrate the avulsion from the ASIS while including the contralateral side for comparison ( Fig. 1 ). Of note, ASIS avulsion injuries can be mistaken for AIIS avulsions due to lateral and inferior displacement of the avulsed fragment on radiographs. In children with delayed presentation, callus formation already may be present. Advanced imaging with computed tomography (CT) or MRI is rarely needed, but may assist in confirming the diagnosis.
Management
Nonoperative treatment with rest, protected weight bearing, and nonsteroidal anti-inflammatory drugs is the standard treatment for most ASIS avulsion injuries. Partial weight bearing with crutches is typically allowed at 0 to 3 weeks, with full weight bearing starting at 3 to 6 weeks. Return to sport is usually permitted approximately 3 months postinjury. Some studies report a longer delay in return to sport with conservative treatment when compared with surgical fixation.
Surgical treatment for ASIS avulsions is typically reserved for fractures with more than 20 mm of displacement or in the setting of a chronic, painful nonunion. Some studies suggest a cutoff of 15 mm of fragment displacement for consideration of operative fixation. Surgical fixation is most commonly performed with screws, with k-wires and plates less commonly used. The rate of nonunion for pelvic apophyseal avulsion fractures has been demonstrated to be lower with surgical fixation (0% vs 2.4%); however, there is a greater risk of heterotopic ossification reported after surgery in some studies (8.2% vs 2.4%).
Postoperatively, patients are typically kept non–weight bearing for 7 to 10 days. Some literature suggests that it is safe to begin immediate partial weight bearing, with full weight bearing approximately 4 to 6 weeks after surgery. Return to sport is between 6 to 12 weeks based on patient recovery and radiographic healing. ,
Anterior inferior iliac spine avulsion injury
Etiology
AIIS avulsion fracture involves the direct head of the rectus femoris tendon. The direct head of the rectus femoris originates from the AIIS, whereas the indirect head originates from the anterior superior acetabular rim and is rarely affected by avulsion injuries. Avulsion injury of the AIIS typically occurs with eccentric force at the hip, such as seen in sprinting and kicking a ball.
AIIS injuries are more commonly seen in boys (82%) than girls, with greater gender disproportion than that seen in ASIS avulsions. AIIS avulsion fractures are also seen more commonly in sports played with a ball (70%) compared with ASIS avulsions, which are seen more equally between ball sports and other athletic activities. Due to the earlier age at formation of the AIIS apophysis, these injuries are usually seen in younger patients who consequently have a greater rate of open triradiate cartilage at the time of injury.
Presentation and Evaluation
Similar to ASIS avulsions, patients with AIIS injuries may describe feeling or hearing a “pop” at the time of injury. Swelling and ecchymosis may be present. Physical examination will demonstrate tenderness at the AIIS. Pain and weakness with hip flexion, knee extension, or a resisted straight leg raise also may be present.
Initial diagnostic workup includes plain radiographs with AP and frog-leg lateral of the pelvis and hip ( Fig. 2 ). As with ASIS avulsions, CT or MRI are rarely needed for diagnosis but may assist if the diagnosis is unclear on initial radiographic evaluation.
