osteomyelitis of the pelvis can be a difficult condition to diagnose and can present in a number of different ways . the ilium is the bone most frequently affected and staphylococcus aureus is the organism most commonly responsible . this case report describes a six year old girl , who presented with right sided hip pain , fevers and altered weight bearing . she was initially diagnosed with septic arthritis of the hip and underwent open joint washout . a magnet resonance imaging scan was subsequently performed which confirmed the diagnosis of iliac osteomyelitis with abscesses of the iliopsoas and iliacus . the patient underwent further operative debridement and required prolonged antibiotic therapy but she eventually made a full recovery . pelvic osteomyelitis can present very similarly to hip septic arthritis and early magnetic resonance imaging is beneficial in diagnosing the condition . surgical intervention can be required if there is abscess formation , although recovery is usually very good and the incidence of long term complications is rare . it is usually caused by haematogenous spread of organisms ; in most cases staphylococcus aureus but multiple other organisms have also been identified as causative agents . the disease can mimic many different pathologies including the acute abdomen , septic arthritis , typhoid fever , nephrolithasis , osteomyelitis of the proximal end of the femur , discitis and neoplasia . this case report highlights the similarity in presentation of iliac osteomyelitis to septic arthritis of the hip . a six year old girl presented to the orthopaedic department with a five day history of right hip pain , fevers and difficulty weight bearing . the patient was of somail origin but there was no recent history of travel or infectious contacts and no significant past medical history . on examination she had a temperature of 39.5 degrees celsius and the right hip was held in flexion , with localised anterior joint line tenderness . blood tests showed a neutrophilia with left shift and a raised c - reactive protein ( crp ) and erythrocyte sedimentation rate ( esr ) . she was diagnosed with hip septic arthritis and an open washout of the hip joint was performed . two millilitres of blood stained fluid was aspirated and the patient was commenced on intravenous ( iv ) antibiotics . the following day the patient remained pyrexial and the crp and esr continued to be raised . a second open washout of the right hip was performed but no pus or fluid was aspirated . a magnetic resonance imaging ( mri ) scan of the right hip was performed which showed collections of the right iliacus and distal iliopsoas , with abnormal marrow signal in the right iliac wing consistent with osteomyelitis ( fig 1 ) . t1 weighted axial mri image demonstrating collections of the right ilicus and distal right iliopsoas and a collection on the other side of the iliac wing extending into the gluteus minimus and medius . there is also abnormal marrow signal in the right iliac wing consisitent with osteomyelitis the patient was diagnosed with iliac osteomyelitis and transferred to manchester children s hospital were she underwent exploration of the right iliopsoas abscess . this revealed a large collection of pus and some necrotic muscle , which was thoroughly washed out and debrided . she gradually made a recovery and was eventually discharged home after a total of 30 days . oral antibiotics were continued on an outpatient basis for a further 28 days . on follow - up , one month later she had made a full recovery , with a normal gait and a full range of movement of her right hip . pelvic osteomyelitis is an uncommon condition but accounts for approximately 1% to 11% of haematogenous osteomyelitis . the most common location is the ilium due its larger size and abundant blood supply . the average age of onset tends to be between 7 and 14 years , with a slight male preponderance . the most frequent causative organism is staphylococcus aureus , present in 38% to 46% of cases , but other organisms include salmonella , streptococcus pneumoniae and gram negative bacilli . clinical features associated with pelvic osteomyelitis include hip or thigh pain , present in 98% of cases , fever present in 57% and altered weight bearing in 46% . in addition there is often tenderness on palpation of the sacro - iliac joint , decreased straight leg raising and pain on lateral pelvic compression . flexion of hip may occur as a result of irritation of the iliopsoas muscle by abscess formation . passive movement of the hip joint is usually preserved , with pain solely at the extremes of motion . right iliac fossa tenderness can also occur secondary to spread of inflammation from the inner cortex of the pelvis . blood tests typically show raised inflammatory markers , with an elevated esr present in 90% of cases and a raised white cell count in 59% to 66% of cases . blood and tissue cultures are positive in only 50% to 78% of cases and negative cultures do not exclude infection . initial radiographs are usually normal , as the typical radiographic features of osteomyelitis usually take two to three weeks to become visible . ultrasound scans can demonstrate deep soft tissue swelling in pelvic osteomyelitis   and radionuclide bone scans can indicate pyogenic infection at an early stage . computed tomography can also allow early diagnosis , demonstrating the site and extent of infection , as well as the presence of lytic lesions , sequestrum or traumatic fractures . mri is , however the gold standard investigation and is reported as being 97% sensitive and 94% specific for the diagnosis of pelvic osteomyelitis . it is able to demonstrate marrow oedema and hyperaemia of the infected bone early in disease onset , as well as the presence of soft - tissue and intra - osseous abscess . treatment of pelvic osteomyelitis usually consists of iv antibiotics alone , as the good blood supply to the pelvis means the risk of sequestrum is reduced and the ligamentous structure minimises the spread of infection . surgery is generally only advocated if there is extensive osseous involvement , failure to respond to antibiotic therapy or abscess formation requiring drainage . prognosis is normally good with prompt treatment , with 95% to 97% of patients making a full recovery . complications can , however occur if treatment is delayed and include the development of chronic osteomyelitis , growth arrest , fusion of the sacro - iliac joint and irregularity of the acetabulum . this case report highlights the difficulty in diagnosing pelvic osteomyelitis and the similarity in presentation to septic arthritis of the hip . the most common clinical features of pelvic osteomyelitis include hip or thigh pain , fever and altered weight bearing . mri is the gold standard investigation and can diagnose the disease at an early stage . in general antibiotic therapy alone is adequate but if there is abscess formation then this will require operative debridement . pelvic osteomyelitis can be difficult to diagnose and can mimic several different conditions , including hip septic arthritis . a high index of clinical suspicion is required and mri scanning should be performed early to prevent delays in diagnosis .
introduction : osteomyelitis of the pelvis can be a difficult condition to diagnose and can present in a number of different ways . 
 the ilium is the bone most frequently affected and staphylococcus aureus is the organism most commonly responsible.casereport:this case report describes a six year old girl , who presented with right sided hip pain , fevers and altered weight bearing . 
 she was initially diagnosed with septic arthritis of the hip and underwent open joint washout . 
 a magnet resonance imaging scan was subsequently performed which confirmed the diagnosis of iliac osteomyelitis with abscesses of the iliopsoas and iliacus . 
 the patient underwent further operative debridement and required prolonged antibiotic therapy but she eventually made a full recovery.conclusion:pelvic osteomyelitis can present very similarly to hip septic arthritis and early magnetic resonance imaging is beneficial in diagnosing the condition . 
 surgical intervention can be required if there is abscess formation , although recovery is usually very good and the incidence of long term complications is rare .