Dislocation, Hip, Posterior

Ovid: 5-Minute Sports Medicine Consult, The

Dislocation, Hip, Posterior
Greg Nakamoto
  • Hip dislocations can be classified into congenital and traumatic (1):
    • Congenital hip dislocations occur in 2–4 cases per 1,000 live births.
    • ∼80–85% of congenital dislocations occur in girls.
    • Congenital hip dislocations are commonly the result of femoral head or acetabular dysplasia.
  • The remainder of this topic is dedicated to the evaluation and management of traumatic (posterior) hip dislocations:
    • Posterior hip dislocation is an orthopedic emergency in which the femoral head is displaced posteriorly relative to the acetabulum.
    • Of primary concern when evaluating the patient with a posterior hip dislocation is the attainment of early reduction (within 6 hr) to prevent long-term sequelae and the search for additional injuries (often life- or limb-threatening due to the excessive forces necessary to create this injury).
    • In the case of posterior dislocation without fracture, the experienced physician may perform 1 attempt at closed reduction. If reduction is not accomplished with ease, or if there is an associated fracture of the hip, then emergent orthopedic consultation is warranted.
  • Because of the forces required for this injury, it is relatively uncommon in contact sports. Seen more often in high-energy trauma, such as with motor sports, equestrian events, and high-speed mountain sports.
  • Posterior dislocations account for ∼90% of all hip dislocations.
  • More common in young males because these injuries are associated with risk-taking behavior (1)
  • Age (1):
    • Trauma (such as motor vehicle accident) is a more common cause in patients younger than 35 yrs than in older patients.
    • Falls are a more common cause in those older than 65 yrs than in younger patients.
Risk Factors
  • High-energy trauma
  • Mechanism is forced adduction, internal rotation, and some degree of flexion of the hip (2).
  • Most common cause is knee striking the dashboard in a head-on motor vehicle accident:
    • Depending on the position of the hip, this can result in either anterior or posterior dislocation.
    • This mechanism of injury is associated with an incidence of simultaneous severe knee injury in 26% of patients (including patellar fracture in 4%) (2).
  • In athletic competition, low-energy mechanisms of injury include a forward fall onto the knee with a flexed hip or a blow from behind while down on all 4 limbs (3).
Commonly Associated Conditions
  • Life-threatening internal organ damage, bleeding, and shock
  • Ipsilateral sciatic nerve injured in 10–14% of cases; changes a posterior hip dislocation from an orthopedic urgency to a true surgical emergency
  • Irreducible dislocations occur in up to 16% of simple posterior dislocations.
  • Fractures of the pelvis, acetabulum, femoral head, neck, and shaft:
    • 81% of adult posterior hip dislocations have an associated posterior acetabular fracture (2).
  • Ligamentous injury to the ipsilateral knee is not uncommon when the mechanism of injury involves a blow to the anterior knee.
  • Delayed reduction increases risk of avascular necrosis (AVN).
  • Other chronic complications include recurrent posterior dislocation, post-traumatic arthritis, and heterotopic bone formation (myositis ossificans) of the thigh or buttocks.
  • Mechanism? Can help guide the search for associated visceral and orthopedic injuries.
  • Position at time of injury? Simple posterior dislocation most commonly occurs with force on a flexed knee with the hip in varying degrees of flexion and adduction. Addition of hip abduction increases the risk of associated acetabular fracture or anterior dislocation.
Physical Exam
  • Immediate, severe pain and disability
  • Limb shortening with hip flexion, internal rotation, and adduction
  • Classic position may be absent if there is an associated femoral shaft fracture.
  • Vital signs and complete trauma evaluation essential because of the high association with life-threatening injuries
  • Look for classic presenting position as described above. Femoral head may be palpable in the buttocks.
  • Pelvic rocking and pubic compression tests to examine for associated pelvic rim fractures
  • Distal neurovascular examination to assess for sciatic nerve or vascular injures, which merit more urgent reduction
Diagnostic Tests & Interpretation
  • Laboratories are ordered as needed on the basis of the trauma assessment and for preoperative planning.
  • Type and cross of blood products may be necessary.
  • Initial x-rays: Anteroposterior (AP) and lateral views of the pelvis (4)[A]. AP often reveals the dislocation, but a true lateral may be needed to confirm the direction.
  • P.127

  • Search for associated pelvic rim, acetabular, femoral head, neck, and shaft fractures generally merits additional x-rays, including 3/4 internal and external obliques of the pelvis as well as femur films.
  • Of particular importance is the ruling out of femoral neck fractures before reduction procedures are performed (3).
Differential Diagnosis
  • Anterior dislocation of the hip
  • Combined fracture-dislocation
  • Fracture of the pelvis, acetabulum, or femur
  • Traumatic hip subluxation
  • Hip pointer
  • GI or genitoureteral visceral injury
  • 835.01 Closed posterior dislocation of hip
  • 835.11 Open posterior dislocation of hip

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