Pelvic avulsion injuries

Ben, a 14-year-old competitive sprinter, limps into your emergency department complaining of sudden onset severe pain and a “pop” felt in his left hip shortly after the start of his National Athletics 100m Final. He points to a specific area on his pelvis and walks with an antalgic gait. Further examination reveals pain on left hip flexion and an appreciable weakness on active flexion compared to his right side. Mum tells you that Ben has complained of pain during and after heavy training for the last few weeks, but this seems to settle with rest and icing after each session.

Ben and Mum are keen to know what you think of his x-ray.
 
What is his diagnosis, how are you going to manage it and what are his chances of making the International Schools Team trials in 3 weeks’ time?

Introduction

Injuries to the apophysis range from recurring painful episodes of apophysitis to avulsion fractures of these secondary ossification centres. Avulsions often present with reports of a “pop” followed by severe pain and weight-bearing difficulties. There is a reported injury predominance in adolescent males of over 70%, with sports involving kicking or sprinting most likely to be involved.

As the participation of adolescents in competitive sport increases so too are reports of apophyseal avulsion injuries. The young athlete is becoming more powerful with stronger muscle groups enhancing physical abilities. Coupled with weaker apophyses, these factors lead to a higher incidence of avulsion fractures in this group.

Early diagnosis and appropriate management is necessary to reduce the risk of chronic pain, disability and reduced participation in physical activity. Apophyseal injuries can be misdiagnosed as “muscle strains” due to a failure to appreciate the anatomical uniqueness of this population making their injury pattern distinct from that of adults. The impact of a delay to diagnosis on long-term health, sports participation and development could be profound.

Anatomy and Mechanics

The apophysis (also known as a traction epiphysis) is a secondary ossification centre that serves as a site for musculotendinous attachment. It arises as a separate bony outgrowth and fuses with the main bone over time. These helpful table illustrations from a publication by Moeller in 2003 highlight the various expected ages of opening and closing of the various pelvic apophyses:

Tensile forces from strong muscular contractions are experienced at the pre-pubescent and adolescent apophysis during sporting activities. We know of several factors which make these structures more susceptible to avulsion injury:

• Ligaments, tendons and muscles are stronger than their bony apophyseal outgrowths.
• Pubescent bone is subject to transient deficiencies in minerals during periods of rapid growth. The resulting porous bone is weaker and more susceptible to injury.
• Chronic repetitive physical loading and tensile stresses across the musculotendinous attachment to an apophysis can predispose to acute avulsion type injuries.

The mechanism of injury in avulsion fractures is based on sudden ballistic movements that are experienced during “explosive” type activities like sprinting, kicking, twisting or jumping. Sudden forceful muscular contractions lead to eccentric loading of the tendon insertion at the apophysis. This then results in the separation and retraction of the apophysis away from its origin at the pelvis or femur.

Ischial tuberosity (54%) and anterior inferior iliac spine (22%) avulsions are the most common types of fractures reported in the adolescent population. Although rare, 5 patients from a study by Rossi and Dragoni in 2001  were reported as having two fractures so be sure to review all apophyseal sites before committing to a final diagnosis.

The various muscles and their corresponding apophyses are shown in the image below:

Radiographic Examples

Management, Prognosis and Recovery

Most injuries are managed conservatively with initial rest and symptomatic support in the form of ice, protected weightbearing and analgesia. Gradual reintroduction to weightbearing with early range of motion (ROM) and strengthening should be progressed under the guidance of a physiotherapist.

While specifics may vary, a good conservative approach to managing these injuries could be:

• Protected weightbearing with crutches for 2-4 weeks until painless normal gait is achieved.
• Gentle ROM and strengthening exercises from weeks 4-8 with physiotherapy.
• Consider return to sport at 8-10 weeks if pain is minimal with squatting and jumping.
• Return to full sporting activity should only be considered once the patient is pain free doing sports-specific movements.

Open reduction and internal fixation is considered for fractures with displacement of >2cm or those with chronic pain secondary to painful non-unions. The goal of surgery is to reduce the time to return to pre-injury level of physical activity. Fracture displacement of >2cm has been reported to increase the risk of non-union by up to 26 times, with AIIS and ischial tuberosity fractures also being an increased risk of developing nonunion complications. Sundar and Carty reported significant difficulty in returning to sport in 75% of ischial tuberosity avulsion cases with 25% of these athletes dropping out of sport altogether. A large case series by Schuett et al highlighted that 14% of all patients reported pain more than 3 months post injury, with patients with AIIS avulsions much more likely to report chronic pain.

It is important to counsel patients and parents about the small risk of chronic pain or non-union before disposition from ED and the potential need for delayed surgical intervention in the future.

Thanks to your keen eye for x-rays and knowledge of adolescent sports hip pathology, you diagnose Ben with a left sided ASIS avulsion (“Hip pointer”). You reassure Ben and Mum that this injury is unlikely to require surgery but explain that it will need rehabilitation with his local physiotherapist over the next few weeks. Ben’s devastation is clear for all to see after you express worry that he may not make his important International Schools Trial in three weeks’ time…but thankfully he quickly reassures himself as he has two more years at this age group and fancies his chances next year!

References

Moeller JL. Pelvic and Hip Apophyseal Avulsion Injuries in Young Athletes. Current Sports Medicine Reports. 2003; 2:110–115

Rossi F and Dragoni S. Acute avulsion fractures of the pelvis in adolescent competitive athletes: prevalence, location and sports distribution of 203 cases collected. Skeletal Radiol. 2001; 30:127–131.

Schuett DJ, Bomar JD, Pennock AT. Pelvic Apophyseal Avulsion Fractures: A Retrospective Review of 228 Cases. Journal of Pediatric Orthopaedics. 2015; 35(6): 617–623

Sundar M and Carty H. Avulsion fractures of the pelvis in children: a report of 32 fractures and their outcome. Skeletal Radiol. 1994; 23:85–90.

www.orthobullets.com/pediatrics/3000/pelvis-fractures–pediatric