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Chapter 37: Orthopedics

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A 31-year-old man is involved in a motor vehicle crash and transported to the emergency department. On arrival, his hemodynamics are normal, but he is unable to flex or extend his left hip, and there is concern for a possible posterior hip dislocation. The anteroposterior (AP) pelvis radiograph is shown in Fig. 37-1. On clinical examination, the left lower extremity would most likely be in which of the following positions?

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Image not available.

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FIGURE 37-1. Anteroposterior pelvis radiograph. From Doherty GM (ed.). Current Diagnosis & Treatment: Surgery, 13th ed. New York, NY: McGraw-Hill; 2010: Fig. 40-13.

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(A) Flexed, adducted, internal rotation

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(B) Flexed, abducted, internal rotation

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(C) Flexed, adducted, external rotation

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(D) Flexed, adducted, external rotation

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(E) Flexed, adducted, neutral rotation

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(A) Hip dislocations are generally the result of a high-energy injury, commonly a motor vehicle crash in which the knee strikes the dashboard and forces the hip out of the acetabulum. This may often be associated with an acetabulum fracture as well, specifically a posterior wall fracture. Hip dislocations can be diagnosed based on physical examination. Posterior hip dislocation will present with a hip that is flexed, adducted, and internally rotated, whereas anterior hip dislocations will present with a hip that is flexed and abducted. In most cases, a plain pelvic radiograph, which typically shows a smaller femoral head in posterior dislocations and a larger head in anterior dislocations, is sufficient to confirm the diagnosis.

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The key structures at risk during dislocation of a hip are the circulation to the femoral head and the sciatic nerve. The posterior vascular supply to the femoral head provides the majority of the circulation. An extracapsular ring originates at the base of the neck and traverses the capsule to the head (see Fig. 37-17). Injury to this region can result in acute disruption of the vessels that are closely associated with the capsule, stretching or compression of the vessels, and venous occlusion of the vascular outflow. All of these may contribute to the risk of developing subsequent avascular necrosis.

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Image not available.

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FIGURE 37-17. Vascular ring at the base of the femoral neck. From Sherman S. Simon’s Emergency Orthopedics, 7th ed. New York, NY: McGraw-Hill; 2014: Fig. 18-2.

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The sciatic nerve is in close proximity to the posterior capsule and can be injured directly as the femoral head displaces posteriorly out of the acetabulum. A complete sciatic nerve injury can result, or more commonly the peroneal distribution is affected. A varied clinical outcome can range from isolated dorsal foot numbness to complete motor and sensory loss for ...

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