The hip is a ball-in-socket joint that provides the movements of flexion, extension, abduction, adduction, internal and external rotation and circumduction.
The head of the femur sits in the acetabulum, joined centrally by the ligamentum teres (ligament of the head of the femur), carrying the acetabular branch of the obturator artery.
The acetabular fossa is lined by the acetabular labrum, joined inferiorly by the transverse acetabular ligament. Surrounding these structures is the synovial joint capsule (Figure 1).
Three external ligaments support the hip, the iliofemoral, ischiofemoral and pubofemoral ligaments. These are named respectively for the part of the hip bone from which they originate, and their insertion into the femur.
Developmental dysplasia of the hip (DDH)
DDH is a disorder of abnormal development resulting in dysplasia and potential subluxation or dislocation of the hip secondary to capsular laxity and mechanical factors.4,5
DDH is the most common abnormality in newborn infants. Due to the nature of how the baby sits in the womb, the left hip is more commonly affected.4,5
The exact cause of DDH is unknown but risk factors for DDH include:
Family history of DDH
Fixed foot deformity
There is no singular way to prevent DDH. The incidence of DDH may be influenced by local child-rearing practices, as certain swaddling and baby-carrying techniques have been shown to correlate with a decline in this disorder.6
If DDH is suspected, an examination of the hip should be undertaken. In addition, screening examinations are performed as part of routine baby checks.
Findings in 3-6-month-olds include leg length discrepancy and limitations in hip abduction due to contractures.
Ultrasound: can be performed in infants less than 4-6months old
AP pelvic X-ray: should be performed in children greater than 4-6months old, when the femoral head ossification centre is visible (Figure 3)
Management of DDH depends on the age of the patient:7
Under 6 months: Pavlik harness
6 – 18 months (or failure of Pavlik harness): closed reduction and spica casting
Greater than 18 months (or failure of closed reduction): operative management (open reduction and hip reconstruction)
Complications of DDH include:
Transient femoral nerve palsy with excessive flexion during Pavlik bracing
Avascular necrosis: due to retrograde femoral head blood flow. Most commonly affects the median circumflex femoral artery.
Legg-Calve-Perthes disease (also called Perthes disease) causes idiopathic avascular necrosis of proximal femoral epiphysis in children.7
In the United Kingdom, the incidence of Legg-Calve-Perthes disease is 7.8 per 100,000 children aged 0-14.10
The exact cause is unknown, risk factors include:
Clinical examination findings may include:
Limp (can be painless)
Hip stiffness with loss of internal rotation and abduction
Leg length discrepancy (late finding)
A bilateral AP pelvic x-ray and ‘frog-leg’ lateral X-ray are used to diagnose Perthes disease (Figure 5).
A bone scan or MRI may be useful if the diagnosis is unclear. They can also provide information on the extent of femoral head involvement.
Key radiographic signs of Perthes disease include:11
Asymmetrical femoral epiphyseal size
Increased density of femoral head epiphysis
Coxa plana: femoral head widening and flatting (shown in Figure 4)
Coxa magna: proximal femoral neck deformity
‘Sagging rope sign’: thin sclerotic line running across the femoral neck
*Crescent’s sign is a specific finding on a radiograph in late stages of the disease and represents a subchondral fracture.
Conservative management options include:
Casting and bracing
Surgery (osteotomy) is considered, based on the patient’s age, radiographic findings and clinical features.
The following would increase the likelihood of the need for surgical intervention:9
Age over eight years old
More than 50% of the femoral head is damaged
Nonsurgical management has been unsuccessful
Complications of Legg-Calve-Perthes disease include:12
General joint stiffness and immobility
Premature physeal arrest, degenerative arthritis
Unequal, shortened limb length
Slipped capital femoral epiphysis (SCFE)
SCFE occurs when the metaphysis of the femur displaces anteriorly and superiorly, leading to the displacement of the capital femoral epiphysis.13
SCFE is the most common hip disorder in adolescents.14
The exact cause of SCFE is unknown but risk factors include:
Obesity: increases stress on physis
Puberty/endocrine disorders: hormones weaken physis, making it more prone to displacement
Clinical features of SCFE include:
Abnormal leg alignment: external rotation
Abnormal gait/limp: may have Trendelenburg gait
Decreased range of movement
Weakness and muscle atrophy
SCFE is diagnosed by obtaining bilateral AP pelvic x-rays, along with a frog-leg lateral X-ray (Figure 5).
Thyroid function tests or growth hormone may be considered in the presence of a conjunctive endocrine disorder.
Management of SCFE is usually surgical.
In situ fixation of the epiphysis with a screw
Bone graft epiphysiodesis
In situ fixation with multiple pins
Complications of SCFE include:15
SCFE in the contralateral hip
Pin associated fracture
Transient synovitis is an intermittent inflammatory disorder of the synovium of the hip, common in paediatric populations.18
Up to three percent of children have an episode of transient synovitis at some point during their life.18
The exact cause of transient synovitis is unknown. However, many children develop the disease secondary to a viral upper respiratory infection.
Clinical features of transient synovitis include:
Hip presents in flexion, abduction and external rotation
Limited range of motion: most commonly, hip abduction
Relevant laboratory investigations include:
Full blood count: raised white cell count
Inflammatory markers (CRP, ESR): will be raised
Relevant imaging investigations include:
AP, lateral or frog-leg X-ray to rule out other paediatric hip disorders
Ultrasound can be performed if there is suspicion of septic arthritis
The most important differential diagnosis to rule out is septic arthritis. Therefore, always review Kocher’s criteria and perform an ultrasound if there is clinical suspicion of this severe pathological process.19
Transient synovitis is a self-limiting disorder that typically lasts 7-10 days, therefore management is focused on relieving the patient’s symptoms:
Bed rest (short period)
Analgesia: paracetamol and NSAIDs.
There are rarely any complications of transient synovitis.
Conditions by age
The signs and symptoms of the various paediatric hip disorders often overlap. It is beneficial to think about each condition in the context of the age range most commonly affected:20
Age 0 – 4: DDH
Age 4 – 10: Perthes disease, transient synovitis
Age 10 – 16: SCFE
Table 1. Summary of common paediatric hip disorders
<4-6 months: ultrasound
4-6 months: X-ray
<6 months + reducible hip: Pavlik harness
AP pelvic X-ray
‘Frog-leg’ lateral X-ray
May be non-surgical or surgical depending on patient factors
AP pelvic X-ray
‘Frog-leg’ lateral X-ray
Usually follows upper respiratory tract infection
FBC, ESR, CRP
Ultrasound if suspicion of septic arthritis
Self-limiting: rest and analgesia
Miss Kirsty MacLeod
Dr Chris Jefferies
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