Posterior dislocation of the hip

Last revised by Mostafa Elfeky on 16 Feb 2021

Posterior dislocations of the hip, although uncommon, are the most common direction of dislocation for this joint, outnumbering anterior dislocations 9:1.

It most frequently occurs in the setting of significant trauma, given a large amount of force required. The most common scenario is in motor vehicle accidents (MVA) where the hip is flexed, and the knee is pushed backward by an impact on the dashboard.

Posterior dislocation may have associated fractures of the posterior lip of the acetabulum and/or injury to the acetabular labrum.

In the clinical examination, the affected lower extremity is usually shortened, adducted, and internally rotated.

AP pelvic x-rays will usually be sufficient for the diagnosis, although associated acetabular fractures will require CT to fully characterize.

Anterior and posterior dislocations may appear similar as both demonstrate loss of the normal joint congruency between the femoral head and the acetabulum. However, in a posterior dislocation, the femoral head is usually displaced posterior, superior, and slightly lateral to the acetabulum and also internally rotated hence the lesser trochanter is often obscured on the AP view. In a well centered AP film the posteriorly dislocated femoral head will appear smaller than the contralateral hip, and vice versa, on account of geometric magnification 2.

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