The anterior dislocation of the native hip is the least prevalent type of dislocation and accounts for approximately 8–15% of total hip dislocations.(6) Bilateral anterior dislocations comprise less than 1% of all hip dislocations. Anterior dislocations are more uncommon than posterior dislocations because the anterior capsule of the hip joint is thicker than the posterior capsule, and the insertion of the iliofemoral ligament reinforces the anterior capsule.(7)
Most hip dislocations occur due to high-impact injury, particularly in unrestrained passengers. The patient was riding a bike in the rear seat in our scenario. The direction of applying forces and the local anatomy of the femur and acetabulum dictate the type of dislocation. If the applied force drives the hip into abduction and flexion, anterior femoral head dislocation occurs.(2, 8) These forces may act from the knee up or along the inner thigh. The location of the hip dictates the femoral head's eventual position outside the pelvis. Before the application of deforming stress, the hip in its resting flexion and extension postures results in obturator and pubic anterior dislocations, respectively.
The anterior dislocations have been classified into antero-inferior and antero-superior. These have further been classified as follows under the Epstein system:
Type I - Superior dislocations
• IA: no associated fractures • IB: associated fracture or impaction of the femoral head • IC: associated fracture of the acetabulum.
Type II - Inferior dislocations
• IIA: no associated fractures • IIB: associated fracture or impaction of the femoral head • IIC: associated fracture of the acetabular.(8, 9)
Our patient sustained a dislocation of type 2A. The timing of the reduction is critical. Delay in reduction causes an increased risk of avascular necrosis of the femur head. Our patient arrived six hours after the accident.
The patient's initial visit to a primary health care centre and subsequent referral to us caused the delay. We promptly took the patient to be reduced under propofol anaesthesia. Avn risk is significantly increased in patients with dislocated hip and concomitant fractures. Numerous factors have a role in the development of AVN in the aftermath of anterior dislocation.(9)
The primary explanation is that the femur head's blood supply is compromised due to mechanical injury to the vasculature caused by the head itself. Another cause is spasms of the major blood vessels in the absence of pathology.(9)
Complications following anterior dislocation have been divided as either early or late. Acetabular fractures, femoral head fractures, femoral nerve or artery damage, sciatic nerve damage, and ipsilateral knee injuries such as meniscal tears are early sequelae. Late-term complications include AVN (2–10% of cases), post-traumatic osteoarthritis (20% of cases), and heterotopic ossification (10% of cases) (2.8 to 9 per cent).(1)