Bilateral anterior superior iliac spine apophysis avulsion fractures in a skeletally mature patient: case report and literature review

Abstract

We present a case of bilateral anterior superior iliac spine avulsion fractures in an adult patient who was involved in a road traffic collision. Her injuries were managed conservatively and she has had an uncomplicated recovery with a good outcome. This is, to our knowledge, the only reported case of bilateral simultaneous anterior superior iliac spine apophyseal avulsion fractures in an adult.

Background

An avulsion fracture of the anterior superior iliac spine (ASIS) apophysis is a rare injury and accounts for only 1.4% of injuries to the pelvis.¹ They typically occur in adolescents while sprinting and may often present chronically due to being undiagnosed or misdiagnosed as muscular injuries.^1,2 Simultaneous bilateral ASIS avulsion fractures are rarer still, accounting for just 3% of all ASIS avulsion injuries.³ To our knowledge, this case is the only instance of bilateral simultaneous ASIS avulsion fractures in a skeletally mature individual.

Case history

A fit and well 51-year-old woman was the restrained driver of a car involved in a head-on road traffic collision with another car travelling at around 40 mph. She was alert at the scene and the airbags were deployed. She was brought to the local emergency department by emergency road ambulance. There were two other passengers in the car, and they were conveyed to the local major trauma centre as a result of their injuries.

Primary examination was unremarkable and secondary survey demonstrated right anterior pelvic pain, exacerbated by hip extension, and a step deformity of the midshaft of her right clavicle.

A plain anteroposterior radiograph of the pelvis illustrated bilateral ASIS injuries (Figure 1). Trauma series computed tomography showed a displaced midshaft fracture of the right clavicle and bilateral avulsions of the ASIS apophyses (Figure 2). The left fragment was displaced inferiorly by 12mm and the right fragment was displaced inferiorly by 34mm and anterolaterally by 36mm. No other injuries were detected on tertiary survey and she was admitted under trauma and orthopaedics. Her case and injuries were discussed and deemed suitable for conservative management. She was discharged home the next day with analgesia, one walking stick, seat-raisers and a broad-arm sling for her clavicle injury.

Figure 1 .

Coronal computed tomography displaying displacement of bilateral avulsed anterior superior iliac spine fragments

Figure 2 .

Anteroposterior plain pelvic radiograph displaying displacement of bilateral anterior superior iliac spine fragments

The patient was reviewed in the outpatient clinic one week after the accident. At this time that she reported areas of paraesthesia over the anterolateral aspects of each thigh, with a larger area affected on the right. This was managed expectantly and has largely resolved except for intermittent occurrence when lying on her right side.

Our patient was able to mobilise without a walking stick at two months after her injury. She returned to work after six weeks and was able to recommence badminton and swimming after three months. At six months post-injury, she was mildly troubled by stiffness over the right thigh on waking and with intermittent mild paraesthesia over the anterolateral thigh, she reports that her pelvis and hip function is 90–95% of its pre-injury levels.

Discussion

The typical mechanism for avulsion of the ASIS is a forceful contraction of sartorius and tensor fascia lata against a hyperextended hip joint.² In the immature skeleton, the ASIS epiphysis has not yet fused, meaning that this is a point of structural weakness that a muscular contraction can overcome. Our patient’s case is unusual because the avulsion injuries were not as a result of weakness associated with immature epiphyses as reported in previous cases.²

Another unusual aspect of this case is that there was no corresponding injury to her lower limbs to suggest that her hip joint was extended by an external force in the impact. The mechanism is likely to have been an avulsion by forcible eccentric contraction of the above-described muscular unit, perhaps in anticipation of the impact, but the precise mechanism remains unclear.

Our patient’s bilateral proximal thigh numbness is thought to be due to a neurapraxia of the lateral cutaneous nerve of the thigh. This nerve is closely related to the ASIS and therefore its displacement could damage the nerve. It may also occur by compression from a secondary haematoma. In our patient’s case, she experienced bilateral meralgia paresthetica, with a greater deficit on the right anterolateral thigh, which could be attributed to the greater degree of displacement of the right fragment.

There is no consensus in the literature regarding the management of ASIS avulsion injuries.² This may well be due to their rarity and the subsequent lack of any randomised control trials on the subject. Conservative management strategies involve bed rest followed by progressive weight bearing and permitted range of motion over a period of weeks.¹ This approach has been associated with a greater risk of non-union and pseudoarthrosis, especially with displaced fragments.² However, the majority of these are asymptomatic.³

Described operative techniques for managing epiphyseal avulsions include use of cannulated screws, suture anchors or tension band wiring to reduce and fix the avulsed fragments.^1,4 This approach has been recommended if the fragments are displaced by greater than 20–30mm or if the patient demands a more rapid return to activity, such as in elite athletes^{1, 3} There is a risk of iatrogenic injury to the lateral cutaneous nerve of the thigh, as well as an increased incidence of heterotopic ossification.² Overall, there is no significant difference in long-term outcomes between surgical and conservative management of these ASIS avulsion injuries.¹ In the case of our patient, the avulsed fragments were likely to be too small to be amenable to surgical fixation.

Our patient did not require any extended period of bed rest and was able to mobilise with one walking aid within 24 hours of her injury, despite the degree to which the avulsed fragments were displaced, and the associated injury to the lateral cutaneous nerve of the thigh. She continues to experience a good recovery from her injuries.