Total Hip Arthroplasty

During the weeks of February 7 through February 17, I observed a total hip arthroplasty on a 56-year-old Caucasian female patient who suffered from a femoral neck fracture and damage to the acetabulum. The fracture was a result from a car accident where the patient’s knees collided with the dashboard, forcing the femur into the hip and breaking the femur.

For this report I will concentrate on total hip replacement, its components, main surgical technique, and complications. Sir John Charnley first developed total joint arthroplasty in the 1960s (Skinner 395). In a total hip replacement “the articular surfaces of the acetabulum and femoral head are replaced” (Lemone 1241). A prosthesis is then used to replace the entire head of the femur and a portion of the femoral neck. A prosthesis of ultrahigh-molecular-weight polyethylene (UHMWPE) is then inserted into the remodeled acetabulum (Lemone 1242 & Skinner 395). The original procedure developed by Charnley consisted of a stainless steel prosthesis for the femur and a 22-mm femoral head. Now we have different femoral head sizes (22, 25, 25.4, 28, 32, and 35mm) and different femoral lengths ranging from 110-160mm (Skinner 395). The bone attachment technique has also evolved during the years into two generic designs, the cement fixation and the porous ingrowth prostheses (Skinner 395).

Cement and uncemented are the two basic types of total hip replacement. Both types have the same bearing surfaces, either ceramic or cobalt chromium alloy that articulates with a UHMWPE bearing surface (Skinner 399). Ceramic and cobalt chromium alloy each have their own set of pros and cons. Ceramic heads will theoretically produce less debris and result in a longer life of the hip replacement, but ceramic heads cost up to three times as much as cobalt chromium heads. For this reason the cobalt chromium alloy head is most likely to be chosen (Skinner 399). The acetabular components have a “spherical outer surface with at least one hole to permit the surgeon to determine if the prosthesis is fully impacted into place” (Skinner 399). The inner surface of the acetabular component then locks the UHMWPE to limit rotation and dissociation (Skinner 399). There are two crucial factors when choosing the implants. First, if the prosthesis is too stiff then the patient may suffer from proximal osteopenia. Second, the stiffer the prosthesis is the more likely the patient will experience pain in the thigh. To avoid these two factors the surgeon should elect to use titanium ally instead of the cobalt chromium alloy.

There are several surgical techniques used for total hip replacement, including the posterolateral approach, the lateral approach, the anterolateral approach, and others. For this paper I will concentrate on the posterolateral approach since it is the most common (Skinner 396). The patient is put into the lateral decubitus position with the affected side superior after anesthesia is administered and a compression stocking is placed on the unaffected limb. The skin is covered with an adhesive drape after the incision is outlined (Skinner 396). Then the hip is flexed to 45 degrees so the “incision can be made in line with the femur from approximately 10 cm proximal to the tip of the trochanter to 10 cm distal to the tip of the trochanter” (Skinner 396). The incision will be through the fascia lata and the gluteus maximus. A Charnley retractor is used to secure the opening. In order to dislocate the hip and reveal the femoral head internal rotation is used on the flexed hip, and then the femoral head is resected with an oscillating saw (Skinner 396). Retractors are then used to reveal the acetabulum. Once in sight the acetabulum is reamed until “a good bed of bleeding subchondral bone is obtained” (Skinner 396). If a cemented cup is to be used the acetabulum must be drilled to provide a foundation for the cement, but if an uncemented cup is to be used then it is secured through impaction followed by pegging (Skinner 398). Once the acetabular surface is taken care of the femoral neck is removed using a box chisel. Once removed the prosthesis size is determined and fixed with cement into the femoral canal. After both sites have cured a prosthesis trial is used in order to assess range of motion and equal leg lengths. Range of motion is tested at 90 degrees of flexion and tested to withstand 40-45 degrees of rotation (Skinner 398). After adjusting prosthetic lengths proper cleaning of both surfaces is mandatory. The actual femoral head is then “placed on the trunion and twisted and impacted into place with several sharp blows” (Skinner 398). After the femoral head is reduced the wound is closed.

In order to prevent luxation after surgery the patient is usually placed in the supine position in bed and the affected leg is placed in slight abduction, hip flexion should be kept below 90 degrees (Nettina 994 & Lemone 1243).