Mechanism: 

• Posterior force to the flexed knee with the hip also flexed ( i.e. knee vs. dashboard).
• For prosthetic hip dislocations, trauma may be minimal or absent due to the weakened ligaments and musculature.  Therefore, patients with prosthetic hips who present with sudden pain and inability to bear weight may have dislocations, even in the absence of trauma.

Presentation:

• Patients describe pain in the hip and buttocks area. 
• The affected leg is shortened, internally rotated, slightly flexed at the hip, and adducted. 
• There may be complaints related to sciatic nerve injury, which manifests as difficulty with dorsiflexion and plantar flexion, loss of ankle deep tendon reflexes, and decreased sensation of the posterior leg and foot.