1. Epidemiology and aetiology
A variety of conditions can lead to pain in the hip area during childhood.
Septic arthritis of the hip joint is the single most important diagnosis to consider and rule out first, as it can rapidly lead to irreversible damage to the articular cartilage and long-term disability.
Haematogenous septic arthritis can occur at any age but is more common in young children, from birth to five years of age. Staphylococcus aureus remains the most common organism involved with this infection.
Transient synovitis of the hip or 'irritable hip syndrome' can present with a similar clinical picture. The aetiology is unclear but it often follows viral illness or minor trauma. It is a lot more common than septic arthritis. It typically affects children between the ages of three and 10 years.
Perthes' disease is a disorder of the femoral head of unknown aetiology. It involves temporary interruption of the blood supply to the femoral head, which leads to bone necrosis and increased density. The necrotic bone is replaced by new bone but the femoral head becomes flattened and enlarged. Remodelling follows to restore the anatomy of the femoral head.
Perthes' disease affects approximately one in 1,000 children, with boys affected four times more often than girls. Age at presentation varies between two and 12 years with a peak between four and eight years.
Slipped upper femoral epiphysis
Slipped upper femoral epiphysis (SUFE) is a condition affecting adolescents most often between the ages of 12 and 15, which involves relative displacement of the femoral head in relation to the femoral neck through the growth plate.
Both mechanical and endocrine factors play a role in the aetiology: obesity and delay in skeletal maturation are common in this condition. The incidence is low at two in 100,000. SUFE is classified according to the degree of the slippage as mild, moderate or severe.
More useful in predicting prognosis is the classification in stable SUFE, where the patient is still able to weight bear on the affected side and unstable SUFE, where weight bearing is not possible.
Typically a child with septic arthritis of the hip presents with systemic illness, including pyrexia and malaise, as well as severe pain and limping or inability to weight bear.
However, a more subtle onset is not uncommon and differential diagnosis with transient synovitis can be challenging.
Children with Perthes' disease usually present with a history of intermittent limping over several weeks or even months, while pain is not severe.
Patients with stable SUFE can also present with a relatively long history of mild-to-moderate pain, an externally rotated leg and a more recent deterioration of the pain. Unstable SUFE causes severe pain and inability to weight bear.
A simple clinical test to identify pain arising from the hip joint involves gently 'rolling' the extended leg on the bed with the patient supine.
Any hip pathology would be associated with resistance to this rolling movement.
This test should also be part of the knee examination in any child, since 50 per cent of children presenting with knee pain have hip pathology.
In septic arthritis the hip is typically 'rigid' and held in flexion, abduction and external rotation.
In transient synovitis the range of hip movement is globally reduced but some movement is still possible.
In Perthes' disease, hip abduction as well as adduction in the flexed position are typically reduced.
In SUFE the typical finding is the spontaneous abduction and external rotation of the hip during flexion.
Blood inflammatory indices are important when sepsis is considered. Plain pelvic radiographs, including anteroposterior and frog lateral views, help establish the diagnosis in the vast majority of patients with Perthes' disease and SUFE.
Various diagnostic criteria have been suggested for the differentiation between septic arthritis and transient synovitis.
However, the only safe way to rule out joint sepsis is by hip aspiration under X-ray or ultrasound control.
This is the investigation of choice in the presence of clinical suspicion of septic arthritis.
MRI can be helpful when diagnosis is unclear but rarely in the acute presentation.
Bone infection - mosteomyelitis - tumour, rheumatological conditions and referred pain from the pelvis and spine should also be considered in the differential diagnosis, although these conditions are not discussed here.
3. TREATMENT AND PROGNOSIS
Septic arthritis of the hip has an excellent prognosis when treated adequately and promptly. Surgical washout of the joint and IV antibiotic treatment are usually recommended.
Delay in diagnosis of over 24-48 hours can lead to permanent damage to the joint.
Transient synovitis is a self-limiting condition with no long-term consequences. It requires only symptomatic treatment and usually settles within a few days.
Approximately 60 per cent of children with Perthes' disease have a good prognosis and do not require specific treatment other than temporary activity modification. Identifying the children with a suboptimal prognosis, who might benefit from treatment, is very challenging.
Therefore, all children with Perthes' disease require close monitoring in the orthopaedic clinic during the active phase of the disease.
Stable SUFE treated with surgical stabilisation has an excellent prognosis.
Patients with moderate and severe SUFE with continuing symptoms after fusion of the growth plate would be candidates for reconstructive surgery to re-align the proximal femur.
Unstable SUFE is often complicated by avascular necrosis of the femoral head and chondrolysis, involving early articular cartilage degeneration and a poor prognosis.
SUMMARY OF PAINFUL HIP CONDITIONS
| Septic arthritis|| Systemic illness, pyrexia|| Rigid joint, severe pain|| Joint aspirate|| IV antibiotics, surgical washout|
|Transient synovitis|| Limping and pain|| Reduced range of motion|| History,?joint aspirate|| Symptomatic|
| Perthes' disease|| Long history of limping|| Limited abduction|| X-ray|| Observation, surgery in 30%|
|SUFE|| Acute deterioration of longer symptoms|| Externally rotated leg, abducts during flexion|| X-ray|| Surgical stabilisation|