Hip fractures and dislocations are relatively rare in children accounting for less than 1% of all fractures and less than 5% of all dislocations.

Hip fractures and dislocations are usually the result of high-energy mechanisms, and 30% of patients have associated injuries to other organ systems.

The pediatric hip is unique in the interplay of its various growth plates and its susceptibility to potential avascular necrosis. The impact of both injury and treatment on the future growth of the hip must be carefully considered.

Bones

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  Ossification

  
  
  
  
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    Ossification of the femoral shaft occurs in at 7 weeks of age.

    
    
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    The femoral head begins ossification between 3 and 6 months of age.

    
    
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    The greater trochanter begins ossification at 4 years of age.

  
  
  
  
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  Growth of the proximal femur occurs at three growth plates: the proximal femoral physis, the trochanteric physis, and a physis along the lateral femoral neck ( Fig. 27-1 ).

  
  
  
  
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    The proximal femoral physis contributes to femoral neck length.

    
    
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    The trochanteric physis contributes to greater trochanteric height.

    
    
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    The lateral femoral neck physis contributes to femoral neck width and length.

    
    
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    The greater trochanter and the femoral head grow by appositional growth.

  
  

  
  

  
  

  

  
  

  
  

  The blue coloring identifies the various growth plates at the level of the proximal femur. Only three growth plates contribute to longitudinal growth: the proximal femoral physis (PFP) , trochanteric physis (TP) , and lateral femoral neck physis (LFNP) . The remaining growth plates contribute to appositional enlargement of the femoral head and the greater trochanter.

  
  
  
  
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  Fusion of the proximal femoral and trochanteric physes occurs at 14 years of age in girls and 16 years in boys.

  
  
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  The cuplike acetabulum grows through the triradiate cartilage. Growth of the acetabulum is thought to be complete near the onset of puberty, at which point the triradiate cartilage closes.

  
  
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  The continued interaction of the femoral head and the acetabulum is crucial for the normal development of both anatomic structures.

  
  
  
  
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    Deformity of the femoral head and acetabulum results from a developmentally dislocated hip.

    
    
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    Traumatic dislocations and traumatic deformity in early childhood have profound effects on this femoral head–acetabulum couple.

  
  

Vascular Supply

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  The vascular supply to the femoral head in a growing child is unique.

  
  
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  The metaphyseal blood supply present at birth essentially stops by age 4, when the proximal femoral physis becomes fully developed.

  
  
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  The intracapsular lateral epiphyseal vessels, originating from the medial circumflex artery and branching from the medial circumflex at the level of the trochanteric notch, run along the femoral neck and are the dominant blood supply to the femoral head until physeal closure ( Fig. 27-2 ).

  
  

  
  

  
  

  

  
  

  
  

  Blood supply to the femoral head. The major blood supply derives from the medial circumflex vessels and enters the intracapsular space as the lateral retinacular sheath along the superolateral aspect of the femoral neck.

  
  

  (From Herring J: Tachdjian’s pediatric orthopaedics, ed 4, Philadelphia, 2007, Saunders.)

  
  
  
  
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  The ligamentum teres contributes no clinically significant blood supply to the femoral head throughout extrauterine life.

Hip Capsule

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  The hip capsule is thick and fibrous in a child and unlikely to be disrupted by trauma.

  
  
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  The hip capsule can contain a traumatic hematoma and create significant intra-articular pressures, potentially compromising the lateral epiphyseal blood supply.

Almost all hip fractures in children are caused by high-energy trauma.

If a low-energy mechanism is offered, one should suspect a pathologic process, insufficiency fracture from metabolic disease, sickle cell disease, or a developmental condition such as slipped capital femoral epiphysis (SCFE).

Cooperative patients typically report difficulty or an inability to ambulate with severe groin or knee pain.

Hip dislocations usually involve low-energy mechanisms in patients younger than 6 years. The typical mechanism is a simple fall while at play.

Hip dislocations in older patients usually involve high-energy mechanisms, such as football and motor vehicle accidents.

Posterior dislocations occur most commonly (90%) and occur when a force is applied axially to the leg when the hip is flexed and adducted.

Rarer directions of dislocation include anterior and inferior directions.

Initial management of a child with a hip fracture or dislocation consists of board transport and immobilization of the lower extremities.

Cervical spine stabilization should also be performed because hip fractures or dislocations most often result from high-energy mechanisms and can have additional associated injuries.

An infant with a hip fracture holds the extremity flexed, abducted, and externally rotated. Pseudoparalysis of the extremity is noted.

The affected leg in an older child with a hip fracture is usually held in a shortened, externally rotated position.

Patients with acute, displaced fractures exhibit a significantly limited range of motion on examination.

Patients with subtle stress fractures around the femoral neck present with a slight limp with discomfort only at the extremes of rotation.

Patients with a dislocated hip most commonly present with the hip held adducted, flexed, and internally rotated.

In dislocations, associated injuries are frequently identified including fractures of the acetabulum or other long bone, sciatic nerve injury, femoral nerve or vessel injury, and concomitant knee pain secondary to bony bruising or internal derangement.

A complete neurologic examination is sometimes difficult in a pediatric patient. However, the initial examination should attempt to ascertain best the strength, sensation, and vascular supply of the affected extremity.

Examination of the spine and distal lower extremity should be routine in uncooperative or noncommunicative children because a pathologic process in the axial skeleton or in the lower extremity distal to the hip joint can also lead to pseudoparalysis.

Initial evaluation begins with an anteroposterior projection of the pelvis and a cross-table view of the affected hip to minimize unnecessary motion.

The hip evaluation in an infant is best done with ultrasound. Ultrasound allows visualization of the scantily ossified femoral epiphysis, the proximal femoral physis, and any associated effusions in the hip joint.

If a joint effusion is present, further diagnostic testing includes hip aspiration in the operating room with an associated arthrogram.

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  If the hip aspiration is bloody, a traumatic etiology is likely.

  
  
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  A serous aspirate makes toxic synovitis more likely.

  
  
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  A purulent aspirate confirms septic arthritis.

Subtle insufficiency or stress fractures may be delineated on computed tomography (CT) scan or bone scan.

The most sensitive additional imaging study for detecting subtle fracture is magnetic resonance imaging (MRI).

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  The fracture line appears as a black line with surrounding bony edema on T2-weighted films ( Fig. 27-3 B ).

  
  

  
  

  
  

  

  
  

  
  

  A, Anteroposterior projection of the left hip in a 14-year-old female track athlete. The lucency across the femoral neck (arrows) identifies a femoral neck stress fracture. B, Corresponding coronal plane pelvic T2-weighted MRI shows significant surrounding bony edema with a signal void at the level of the fracture.

  
  
  
  
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  MRI can detect an occult hip fracture in the first 24 hours after injury.

  
  
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  Pathologic fractures should be additionally evaluated with MRI to assess bony involvement if plain radiographs are unclear and to assess any associated soft tissue component to the lesion that may prove to be high yield on biopsy and clarify the differential diagnosis.

  
  
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  MRI can help to exclude osteomyelitis as a cause of hip pain and early avascular necrosis of various etiologies.

In patients with hip pain and without clear evidence of fracture, a complete blood count and C-reactive protein should be done to evaluate for the possibility of infection.

Hip dislocations are typically evaluated with plain radiography. Occasionally, hip dislocations in children can spontaneously reduce, and only a subtle difference in joint congruency remains ( Fig. 27-4 A ).

A, Anteroposterior projection of the pelvis after a traumatic hip dislocation with spontaneous reduction in a 9-year-old boy. Note the increased joint space in the left hip compared with the right hip (arrow) . B, Axial CT scan shows a small osteochondral fragment (arrow) . C, T2-weighted MRI shows interposed soft tissue (arrow) . During surgery, the patient was found to have a ligamentum teres avulsion with a small head fragment connected to the ligamentum.

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