Conversion of hip arthrodesis to total hip arthroplasty.

With the predictably good outcome now found with THA, hip arthrodesis has limited indications today. The procedure still has a role in the case of the young, heavy demand male with an isolated arthritic hip condition, and developments such as the Cobra head plate have considerably improved success rates. However, a long-term hip arthrodesis can have profound effects on a patient's daily function and activities of daily living. In addition, gait pattern is considerably affected as well as other joints such as the lower back, ipsilateral knee, and contralateral hip. Many patients with a hip arthrodesis will eventually require a takedown of the fused hip and conversion to a THA. The primary indications include fusion in malposition, pseudarthrosis, or severe pain in other joints. The surgeon undertaking such a task must be familiar with the arthrodesis techniques that have been used in the past as well as the equipment that may be required to extract the fixation hardware. Clinical assessment with particular attention to leg-length discrepancy, position of the arthrodesis, and function of the abductors is of paramount importance. The surgeon must carefully review preoperative radiographs to plan the procedure. The surgeon must also be aware of the presence of pathology in other joints. After takedown of a hip arthrodesis and conversion to a THA, patients cannot expect the result to equal the success rates of primary THA. Patients generally can expect an improvement in function and mobility. Back pain and ipsilateral knee pain are usually improved postoperatively, but the effect on contralateral hip pain is less predictable. Many patients will continue to show a positive Trendelenburg sign, but further improvement in strength of the hip abductors can be expected with time. Leg-length discrepancy is generally improved substantially after THA. However, a substantial number of patients will require a walking aid postoperatively. Overall, the risk of complications and the rates of revision after converting an arthrodesed hip to a THA are quite high. The procedure can be complex. Consideration should be given to referring these patients to a specialized center under the care of an experienced arthroplasty surgeon if preoperative planning suggests that the conversion will not be straightforward.