Causes / typical injury mechanism: Traumatic hip dislocations (THDs) in the pediatric population are rare but severe injuries that should be addressed expeditiously due to the high possibility of complications such as avascular necrosis (AVN) of the femoral head.

Classic history and presentation: The patient typically presents with an inability to bear weight on the affected lower extremity along with severe groin and/or buttock pain. If the dislocation is posteriorly directed (90%-95% of cases), the affected extremity will appear shortened, slightly flexed, adducted, and internally rotated. If the dislocation is anteriorly directed, the affected extremity will appear extended, abducted, and externally rotated. If the dislocation is inferiorly directed, the affected extremity will appear hyperflexed or abducted. An associated traumatic event with the affected lower extremity is almost always present.

Prevalence: THDs in the pediatric population are rare and make up approximately 5% of all pediatric dislocations. 90%-95% of these dislocations are directed posteriorly.

• Sex / gender – This condition can occur in either sex but is more common 4:1 in males.

Risk factors:

• In patients aged older than 10 years, high-energy trauma such as a motor vehicle accident (MVA).
• In patients aged younger than 10 years, low-energy trauma such as a sports injury or fall.

Pathophysiology: The condition occurs when the head of the femur is forced out of the acetabulum. The force required to dislocate a pediatric hip increases with age due to increased skeletal maturity coupled with capsular and ligamentous increase in strength. In children older than 10 years, THD is usually the result of a high-energy trauma (eg, MVA). Typically, a large force against a flexed knee, such as hitting the knee against the car dashboard, forces the femoral head to dissociate from the acetabulum. However, in children younger than 10 years, the condition usually results from low-energy trauma (eg, a sports injury or fall) due to the particularly flexible joint structure of the immature hip. As a result of this trauma, the femoral head can be pushed posteriorly (most common), anteriorly, or inferiorly. When this dislocation occurs, the surrounding structures, such as the capsular ligaments, labrum, and osteochondral portion of the posterior wall of the acetabulum are typically torn or damaged. A fracture of the ipsilateral femoral neck or proximal femoral physis, as well as injury to the surrounding muscles, sciatic nerves, or gluteal nerves, can also occur.

Classification system: Hip dislocations can be classified by their direction and further described by the head-acetabulum relationship and presence or absence of associated fractures. These classifications are traditionally used for adult THDs but may be referenced in the pediatric and adolescent populations.

Posterior hip dislocations (Thompson and Epstein classification)

• Type 1 – Simple dislocation with no or minor fracture
• Type 2 – Dislocation with a single large fracture of posterior acetabular rim
• Type 3 – Dislocation with a comminuted acetabular rim
• Type 4 – Dislocation with a fracture of the acetabular floor
• Type 5 – Dislocation with a fracture of the femoral head

Anterior hip dislocations (Epstein classification)

• Type 1 – Superior dislocations (pubic and subspinous)
  • Type 1A – No associated fractures
  • Type 1B – Associated fracture or impaction of femoral head
  • Type 1C – Associated fracture of acetabulum
• Type 2 – Inferior dislocations (obturator and perineal)
  • Type 2A – No associated fractures
  • Type 2B – Associated fracture or impaction of femoral head
  • Type 2C – Associated fracture of acetabulum