Dislocation of the hip is a serious condition that may have significant complications. Pure hip dislocation with or without fracture of the acetabulum or femoral head can cause complications. The worse complication associated with dislocation of the hip is avascular necrosis, due to damage to the blood supply. AVN is death of a segment of the bone in the femoral head. Avascular necrosis may occur if the dislocation is not reduced in a reasonable period of time. Emergency reduction of dislocations is needed in less than 8 hours of injury. Although x-ray is helpful, a CT scan clearly outlines the bony injury. Other complications associated with dislocation of the hip is injury to the sciatic nerve and arthritis of the hip joint. Injury to the sciatic nerve occurs in about 10-20% of the cases involving posterior dislocation. The sciatic nerve starts in the lower back and runs through the buttock and lower limb. In the lower thigh, just above the back of the knee, the sciatic nerve divides into two nerves, the tibial and peroneal nerves, which innervate different parts of the lower leg. The common peroneal nerve then travels anterior, around the fibular neck, dividing into superficial and deep peroneal nerves. The deep peroneal nerve dives innervation to the tibialis anterior muscle of the lower leg which is responsible for dorsiflexion of the ankle.
When injury occurs to the sciatic nerve due to posterior hip dislocation, the common peroneal nerve is usually affected, causing weakness in dorsiflexion of the ankle and loss of toe extension can also occur. Injury to the sciatic nerve usually involves the common peroneal nerve. Injury can occur in carrying degrees of severity and can be missed. Movement of the toes may appear as dorsiflexion; however, this really is the result of plantarflexion. Documenting the injury is important to avoid medical legal problems. Injury to the sciatic nerve typically occurs from the dislocation and not from the reduction. The longer the wait for reduction of the dislocation, the more the patient is predisposed to sciatic nerve injury. The length of time a hip remains dislocated influences the incidence and severity of major sciatic nerve injury. The patient may require an anti-foot drop splint.
Peroneal nerve injury/foot drop is treated with physical therapy and waiting. EMG and other nerve studies may be used to assess the condition of the muscles. This condition may take a long time for recovery, usually a partial recovery of the nerve is achieved in a majority of cases. If no recovery is achieved, a surgeon should explore the nerve for repair, graft, or tendon transfer. Sciatic nerve palsy could occur from surgery due to retractors or from traction, usually in posterior hip surgery. Preoperative partial injury of the nerve could deteriorate after surgery. Preoperative documentation of the nerve injury is important.