Avulsion Fractures of the Hip and Pelvis

Patient information — Dr Christopher Spelman, Orthopaedic Surgeon

Overview

An avulsion fracture occurs when a strong tendon or muscle suddenly pulls a small piece of bone away from the pelvis at the point where it attaches. These injuries are seen most often in adolescent and young adult athletes, whose growth areas (apophyses) are weaker than the attached tendons. They typically happen during an explosive movement such as sprinting, kicking or jumping, and cause sudden, sharp pain in the hip, groin or buttock.

Common sites

The site of the avulsion depends on which muscle is involved. The most common locations are:

●      Anterior inferior iliac spine (AIIS) – the attachment of the rectus femoris (a quadriceps muscle), often injured during kicking

●      Anterior superior iliac spine (ASIS) – the attachment of the sartorius and tensor fascia lata, injured during sprinting

●      Ischial tuberosity – the attachment of the hamstrings, injured during sprinting or the splits

●      Iliac crest – the attachment of the abdominal muscles

Diagnosis and treatment

The diagnosis is usually made on x-ray, though occasionally further imaging (ultrasound, CT or MRI) is needed to size the fragment or clarify the injury. The great majority of pelvic avulsion fractures heal well without surgery. Treatment follows a graduated programme: initial rest and protected weight-bearing with crutches, pain relief, then a gradual return of movement, stretching and strengthening, before a staged return to sport – typically over six to twelve weeks depending on the site.

When surgery is considered

Surgery is only occasionally required – usually when the fragment is pulled a considerable distance from its origin (generally more than about 2 cm), or when a fracture fails to heal (nonunion) and remains painful. Ischial tuberosity (hamstring) avulsions in particular are more prone to nonunion and to ongoing symptoms, and are the ones most likely to be considered for fixation.

Outcomes and what the evidence shows

A large review of 228 pelvic apophyseal avulsion fractures found that 97% were managed successfully without surgery. Persistent pain beyond three months occurred in about 14% of patients, and was more likely with AIIS avulsions, while ischial tuberosity avulsions carried the highest risk of nonunion. Fracture displacement of more than 20 mm substantially increased the risk of nonunion.

Complications

Most avulsion fractures heal without any lasting problem, but families should be aware of the following:

●      Chronic pain – ongoing symptoms beyond three months occur in around one in seven patients, most often with AIIS injuries.

●      Non-union – the fragment occasionally fails to unite, particularly at the ischial tuberosity and with larger displacement, and may require surgery if painful.

●      Excess bone formation (exuberant callus or exostosis) – a bony prominence can form at the healing site, occasionally causing irritation or, at the ischial tuberosity, symptoms when sitting or with nerve irritation.

●      Weakness or re-injury – returning to sport too early risks re-avulsion or a muscle strain; a graduated rehabilitation programme reduces this.

●      Rare surgical risks – if surgery is needed, the usual risks of infection, bleeding and nerve irritation apply.

Summary

Pelvic avulsion fractures are common sporting injuries in young athletes and nearly always heal well with rest and staged rehabilitation. A small number – particularly widely displaced or hamstring-origin injuries – may develop ongoing pain or nonunion and occasionally need surgery. Dr Spelman will guide the return-to-sport programme and advise if any further treatment is required.