avulsion fractures of the pelvis are rare injuries that occur when a tendon or ligament contracts suddenly and forcefully to remove a part of the bone it is attached to .
they are most commonly seen affecting the growing apophyses of adolescents , and are often missed on initial presentation .
an apophysis , an outgrowth , can be defined as a growth centre where a tendon attaches to bone . as would be expected ,
its cartilaginous growth plate remains weaker than the attached musculotendinous unit until it fuses at the time of skeletal maturation , and thus is more prone to fracture when the musculotendinous unit is suddenly and vigorously contracted .
adolescents involved in athletic pursuits such as football , sprinting and gymnastics are more likely to suffer from apophyseal avulsion injuries due to the sudden powerful muscular contractions that are required in these activities , as well as the abrupt directional changes of motion performed . the anterior superior iliac spine , which develops from an anterior apophysis of the iliac crest , is the site of origin of the sartorius muscle and part of the tensor fasciae latae . therefore , an avulsion fracture of the anterior superior iliac spine is most commonly due to forceful contraction or sudden repetitive actions of these muscles , as occurs when running or kicking a ball [ 3 , 4 ] .
the treatment of choice for this injury remains conservative : rest , analgesia , anti - inflammatories and rehabilitation ; however , surgical treatment has been utilised depending on the degree of fracture displacement and the individual s rehabilitation requirements [ 5 , 6 ] .
a 14-year - old male patient presented with a 1  week history of pain in his anterior right thigh and anterior pelvic region , which was exacerbated by walking .
he was kicking a football when a severe pain in his right thigh developed , which rendered him unable to walk , and he had to crawl off the football pitch . on examination his gait
was affected by pain in the right thigh , there was tenderness to the anterior superior iliac spine on palpation , and all hip movements were limited by pain .
plain film radiographs were reported by a local district general hospital radiologist as showing a faint ossification within the soft tissues immediately inferior and adjacent to the right anterior inferior iliac spine , suggestive of a rectus femoris avulsion fracture . however , when reviewed in clinic the consultant orthopaedic surgeon noted that there was some calcification around the anterior superior iliac spine which did not collaborate with the time since injury , and a magnetic resonance imaging ( mri ) scan was performed .
the imaging reported an abnormality in the anterior right iliac crest with an avulsion fracture and a surrounding soft tissue mass ( fig .  1 ) .
this solid mass was centred on the anterior superior iliac spine and measured 3    4    5  cm in size .
the signal intensity of this mass was mildly hyperintense on t1-weighted images ( figs . 
at the referring hospital , these findings were thought not to correspond to a simple trauma , and suggested a possible underlying bone tumour.fig . 
note the sharp anterior superior iliac spine fracture line ( long white arrow ) with retracted sartorius tendon margin ( short white arrow ) .
also note that the signal intensity of haematoma is slightly hyperintense ( as compared to skeletal muscle , indicated by the chevron mark ) , which is suggestive of a haemorrhagic product rather than a tumour massfig . 
note the sharp anterior superior iliac spine fracture line ( long white arrow ) with retracted sartorius tendon margin ( short white arrow ) .
also note that the signal intensity of haematoma is slightly hyperintense ( as compared to skeletal muscle , indicated by the chevron mark ) , which is suggestive of a haemorrhagic product rather than a tumour mass coronal t1-weighted image .
signal is compared to skeletal muscle ( long white arrow ) the patient was referred to our sarcoma unit for an opinion , where the images were reviewed at a multi - disciplinary meeting . on the review of radiology performed by our specialist musculoskeletal radiologist , it was felt that there was an avulsion fracture of the anterior superior iliac spine with anterolateral displacement of the apophysis and a large surrounding haematoma ( figs .  1 , 2 , 3 ) .
there was mild enhancing marrow oedema present in the anterior third of the iliac blade , but the signal intensity in the bone was otherwise normal .
note that the surrounding haematoma shows a bright signal indicating haemorrhagic components ( short white arrow ) axial t1 fat - saturated pre - gadolinium image .
note that the surrounding haematoma shows a bright signal indicating haemorrhagic components ( short white arrow ) radiological features which were supportive of the diagnosis of a fracture rather than a tumour were : presence of a clear fracture with avulsed tendon of sartorius.bone marrow signal in the anterior superior iliac spine was relatively normal with only a subtle oedema seen.the haematoma showed a slightly hyperintense t1 signal intensity and bright t2 fat - saturated ( fs ) signal .
tumour masses generally show low t1 and bright t2 fs signals ( see fig .  4 ) .
bone marrow signal in the anterior superior iliac spine was relatively normal with only a subtle oedema seen .
the haematoma showed a slightly hyperintense t1 signal intensity and bright t2 fat - saturated ( fs ) signal .
tumour masses generally show low t1 and bright t2 fs signals ( see fig .  4 ) .
based upon the clinical history , examination and radiological findings , the mdt decision was that this was an avulsion fracture of the anterior superior iliac spine apophyses .
a biopsy was not felt necessary at this stage , but a careful , regular clinical follow - up was ensured .
the initial haematoma was smaller , the degree of marrow oedema was significantly less , and there were no features of bone marrow oedema.fig . 
bone tumours with surrounding mass usually show marrow infiltration indicated by low t1 and bright t2 signals in bone that enhance with gadoliniumfig . 
5axial proton density images obtained 3  months after the first scan indicate that the avulsion fracture shows signs of healing .
6fat - saturated images obtained 3  months after the first scan show signs of fracture healing axial post - intravenous gadolinium t1 fat - saturated image .
there is , however , no enhancement in bone ( long white arrow ) . bone tumours with surrounding mass usually show marrow infiltration indicated by low t1 and bright t2 signals in bone that enhance with gadolinium axial proton density images obtained 3  months after the first scan indicate that the avulsion fracture shows signs of healing .
bone marrow signal is also normal fat - saturated images obtained 3  months after the first scan show signs of fracture healing at 1  year follow - up , the patient had normal gait , there was no tenderness of the anterior superior iliac spine on palpation , and he had pain - free full range of movement of the hip .
whilst apophyseal avulsion fractures are rarely seen , avulsion fractures of the anterior superior iliac spine are found more commonly in adolescents undergoing vigorous activity .
this injury usually occurs as a result of sudden , vigorous or repetitive contraction of the sartorius muscle and tensor fasciae latae .
it is sprint athletes , football players and gymnasts that are most often affected , due to the range of movements they perform and sudden changes in direction required . 
 
diagnosis can be achieved by clinical examination with plain radiograph , and mri or computed tomography ( ct ) as determined by availability .
treatment is usually conservative , with rest , analgesia and anti - inflammatories yielding good reported results [ 7 , 8 ] .
surgical intervention may be required in selected cases when it is desirable to have as short a rehabilitation time as possible , such as in professional athletes , and in those with significantly displaced fractures [ 5 , 6 ] .
these avulsion injuries usually have an associated haematoma and develop excessive callus with post - fracture osteolysis , which on radiological investigation may be mistaken for an osteosarcoma , ewing s sarcoma , or an infective process .
if the suspicion of a bone tumour has been raised , this must be ruled out before instigating a management plan for the fracture .
if there is any doubt the case should be referred to a specialist sarcoma unit for an opinion , ideally in a multi - disciplinary team setting . 
 
features that support a diagnosis of possible underlying malignancy are relatively trivial traumas resulting in excessive bone injury . on imaging , plain films can show permeative destruction of bone , aggressive new bone formation ( indicating osteosarcoma  shown by a sun - ray appearance , codman s triangle and cumulus cloud osseous matrix ) .
mr features suggestive of a tumour are poorly defined oedema in bone , surrounding solid soft tissue mass that usually shows low t1 and bright t2 signal intensity mass which is disproportionally large compared to bone involvement ( especially in cases of ewing s sarcoma and lymphoma ) .
myositis ossificans is soft tissue ossification that develops after trauma and is characterised by a rim of new bone formation .
mri features of this entity can be confused with a soft tissue tumour , especially because there can be surrounding oedema .
the typical rim - shaped mineralization is , however , appreciated on careful analysis of mri and ct scan , and is pathognomonic for myositis ossificans .
the authors feel it is vital that in such cases surgical reduction and fixation should not be performed until an opinion has been sought from a specialist tumour centre .
there are helpful signs on various imaging studies which point towards the diagnosis of a fracture vis -  - vis tumour .
careful clinical and radiological follow - up is important to ensure that the initially observed lesion is demonstrating signs of healing .
 avulsion fractures of the anterior superior iliac spine are rare . this injury is usually seen in adolescents , as an avulsion fracture of the apophyses , a result of sudden vigorous contraction or repetitive contraction of the sartorius and tensor fasciae latae muscles . 
 treatment for this injury is usually conservative ; however , surgical management has been reported in those with significant displacement . 
 we present a 14  year old male patient who was referred to our unit for biopsy of a possible pathological fracture of his right ilium . 
 the authors feel it is essential to understand the importance of ruling out a bone tumour , if the possibility has been raised , before managing a suspected fracture . 
 if there is any doubt , the case should be referred to an appropriate sarcoma unit for review prior to any intervention . 
Introduction
Case report
Discussion