Computer Templating of Hip Resurfacing Arthroplasty

Abstract

The goals of conventional hip replacement surgery typically include restoration of leg length and femoral offset, and pre-operative templating has been an essential component of achieving these goals with surgery. Hip resurfacing has more limited ability to alter these variables than does conventional hip replacement [1,2]. Despite this, preoperative templating may be even more critical when planning for a hip resurfacing procedure for several reasons. First, not all patients with osteo-arthritis of the hip are appropriate for resurfacing, and templat-ing can assist in determining if a patient’s anatomy is suitable for hip resurfacing [3]. Like any hip replacement procedure, the positioning of the femoral and acetabular components is critical to the long-term success of a hip resurfacing procedure [4]. The acetabular component must be positioned with appropriate anteversion and verticality for postoperative hip stability and avoidance of impingement. Excessive vertical positioning of the acetabular component can lead to increased contact stresses and rapid wear of the metal on metal bearing. The femoral component must also be positioned properly to ensure success. Neutral or slight valgus orientation is optimal. Varus positioning or notching of the cortex of the femoral neck, particularly on the tension side, can lead to femoral neck fracture [5,6]. Furthermore, the acetabular and femoral components can only match each other within select ranges. Because of the limitations the retained femoral head presents, the acetabular component must be implanted first. However, it is important to understand the femoral component sizes that can be matched to a particular acetabular component. Typically, each acetabu-lar component can be matched with only two femoral sizes. If the femur cannot accommodate these sizes, then the acetabular component size must be altered or the plan for hip resurfacing must be abandoned in favor of a total hip replacement construct. It is more difficult to change these parameters than in conventional total hip replacement, where a wider variety of stem and neck length options are possible. In addition, it is far easier and more efficient to plan for any alteration in the operative plan before undertaking an operative procedure. Finally, it is crucial to plan for the possibility of intraoperative conversion from hip resurfacing to total hip replacement. This may become necessary for several reasons. For example, if excessive femoral head cysts become evident, such that the stability of the femoral component comes into question, or if a technical error such as creation of a significant notch or fracture in the femoral neck occurs, then conversion to a total hip construct is necessary. This possibility should be planned for and discussed with the patient beforehand. The purpose of this chapter is to discuss the use of computer templating for preoperative planning of hip resurfacing arthroplasty.