Most hip dislocations are posterior and result from severe posteriorly directed force to the knee while the knee and hip are flexed (eg, against a car dashboard).
(See Overview of Dislocations.)
Complications may include
Sciatic nerve injury
Delayed osteonecrosis of the femoral head
Associated injuries include
Patella fractures
Posterior cruciate ligament injuries
Acetabular and femoral head fractures
In patients with posterior dislocations, the leg is shortened, adducted, and internally rotated. Anterior dislocations are rare and result in the leg being abducted and externally rotated.