Paediatric ImagingAvulsion fracture
a pull-off
fracture at a musculotendinous or ligamentous insertion site caused by sudden forceful muscle contraction or
ligament traction. Such fractures are relatively common in athletic adolescents. The child characteristically describes acute onset of pain during muscle contraction. There is usually
focal tenderness, although the exact site may be difficult to localize when the injury is deep, e.g. around the
pelvis. Common sites of avulsion fractures include:
the anteroinferior iliac
spine: insertion of straight head of rectus femoris
anterosuperior iliac
spine: insertion of sartorius and tensor fasciae latae,
lesser trochanter: insertion of iliopsoas
ischial tuberosity: insertion of hamstrings and part of adductor magnus
greater trochanter: insertion of gluteal muscles
iliac crest: insertion of
abdominal tensor fasciae latae, gluteus medius, latissimi dorsi, gluteus maximus
medial epicondyle distal humerus: insertion of flexor pronator muscle
volar aspect of phalanges: insertion of flexor
tendon dorsal aspect of phalanges: insertion of extensor
tendonAt most of these sites the fracture plane is through the physis of an apophysis as an apophysis acts as the insertion site for muscle and the physis represents a weak link in the immature skeleton.
Conventional radiographs generally confirm the diagnosis by demonstrating a bony fragment displaced at variable distance from the parent bone (Fig.1). For situations where radiographs are inconclusive, ultrasound may be helpful. Ultrasound can show displacement of the apophysis (Fig.2) and dynamic examination allows confirmation that this corresponds with the site of tenderness. Ultrasound may also demonstrate associated haematoma within the adjacent muscle. Ultrasound is particularly advantageous in the young child in whom the apophysis may be unossified and, therefore, not visible on radiographs. The MR imaging appearances of avulsion injury can appear aggressive and it is, therefore, important to recognize the entity by its characteristic site and radiographic appearance so as to avoid misdiagnosis.
Management is usually conservative and the prognosis is generally good although at certain sites, such as the tibial tuberosity, there may be deformity secondary to growth arrest. Avulsion of the ischial tuberosity may heal with abundant callus, particularly if compounded by repetitive trauma, and this may cause compression of the sciatic nerve with long-term morbidity. Avulsion of the medial epicondyle of the distal humerus (Fig.3) is an important injury as the fragment may be avulsed into the joint and require open reduction and fixation. Unless absence of the medial epicondyle from its normal site is recognized on radiographs there is a danger of the displaced fragment being overlooked leading to long-term morbidity. For this reason it is important to remember that the medial epicondyle ossification centre usually becomes visible radiographically from 59 years of age (mean 7 years) and precedes ossification of the trochlea, olecranon and lateral epicondyle.
GL