The effect of the orientation of the acetabular and femoral components on the range of motion of the hip at different head-neck ratios.

BACKGROUND: Prosthetic impingement due to poor positioning can limit the range of motion of the hip after total hip arthroplasty. In this study, a computer model was used to determine the effects of the positions of the acetabular and femoral components and of varying head-neck ratios on impingement and range of motion. METHODS: A three-dimensional generic hip prosthesis with a hemispherical cup, a neck diameter of 12.25 millimeters, and a head size ranging from twenty-two to thirty-two millimeters was simulated on a computer. The maximum range of motion of the hip was measured, before the neck impinged on the liner of the cup, for acetabular abduction angles ranging from 35 to 55 degrees and acetabular and femoral anteversion ranging from 0 to 30 degrees. Stability of the hip was estimated as the maximum possible flexion coupled with 10 degrees of adduction and 10 degrees of internal rotation and also as the maximum possible extension coupled with 10 degrees of external rotation. The effects of prosthetic orientation on activities of daily living were analyzed as well. RESULTS: Acetabular abduction angles of less than 45 degrees decreased flexion and abduction of the hip, whereas higher angles decreased adduction and rotation. Femoral and acetabular anteversion increased flexion but decreased extension. Acetabular abduction angles of between 45 and 55 degrees permitted a better overall range of motion and stability when combined with appropriate acetabular and femoral anteversion. Lower head-neck ratios decreased the range of motion that was possible without prosthetic impingement. The addition of a modular sleeve that increased the diameter of the femoral neck by two millimeters decreased the range of motion by 1.5 to 8.5 degrees, depending on the direction of motion that was studied. CONCLUSIONS: There is a complex interplay between the angles of orientation of the femoral and acetabular components. Acetabular abduction angles between 45 and 55 degrees, when combined with appropriate acetabular and femoral anteversion, resulted in a maximum overall range of motion and stability with respect to prosthetic impingement. CLINICAL RELEVANCE: During total hip arthroplasty, acetabular abduction is often constrained by available bone coverage, while femoral anteversion may be dictated by the geometry of the femoral shaft. For each combination of acetabular abduction and femoral anteversion, there is an optimum range of acetabular anteversion that allows the potential for a maximum range of motion without prosthetic impingement after total hip arthroplasty. These data can be used intraoperatively to determine optimum position.

Polymethylmethacrylate removal from the femur using a crescentic window technique.

This article describes a technique to aid in removal of polymethylmethacrylate during total hip arthroplasty revision. The technique is a modification of prior windowing techniques and requires no specialized instruments, offers substantial flexibility regarding cement removal and femoral prosthetic choice, and minimizes the amount and duration of stress on the femur. The technique involves making an oblong window in the anterior or anterolateral femur. Proximal and distal osteotomies are made with a crescentic oscillating saw and connected by straight beveled anterior and posterior longitudinal osteotomies using a straight oscillating saw. Once the intramedullary canal is prepared, either a nonecmented or cemented femoral prosthesis can be placed. The cortical window is replaced with a single cable used for fixation.

The press-fit condylar total knee system: 8- to 10-year results with a posterior cruciate-retaining design.

A total of 108 consecutive Press-Fit Condylar total knee arthroplasties were performed in 94 patients. All patients had implantation with a cemented posterior cruciate-retaining design, which included resurfacing of the patella. Mean age at surgery was 70 years (range, 35-87 years). Patients were followed for a mean of 9 years (range, 8-10 years) with follow-up for all surviving patients. The average postoperative functional knee score was 96 points. Nonprogressive radiolucent lines were present in 59%. One patellar component was radiographically loose. Five knees underwent revision procedures, none for aseptic loosening. Survivorship was 93.4% at 9 years with revision for any reason as the endpoint and 98.7% with aseptic loosening as the endpoint. This knee arthroplasty shows excellent results at 8 to 10 years with no patients lost to follow-up.

Late deep venous thrombosis and delayed weightbearing after total hip arthroplasty.

One hundred ninety-nine patients who underwent primary total hip arthroplasty and used in hospital pneumatic compression stockings and aspirin as thromboembolic prophylaxis were screened for deep venous thrombosis using duplex ultrasonography on the fourth postoperative day. Of the initial 98 patients, 21 underwent noncemented arthroplasty, maintained touchdown weightbearing for 6 weeks after surgery, and then began progressive partial weightbearing. Of the subsequent 101 patients, 28 underwent noncemented arthroplasty and began progressive weightbearing immediately after surgery. All other patients underwent hybrid arthroplasty and began weightbearing to tolerance immediately after surgery. After duplex screening examination, patients with proximal deep venous thrombosis were given anticoagulation therapy, and patients with negative study results were observed clinically. The relative risk of proximal deep venous thrombosis after noncemented arthroplasty using delayed weightbearing was compared with that after noncemented arthroplasty using immediate progressive weightbearing. Of patients with noncemented arthroplasty, the prevalence of proximal deep venous thrombosis was significantly lower in those using progressive weightbearing immediately after surgery (none) than in those using delayed weightbearing rehabilitation (19%). This study showed that patients undergoing noncemented total hip arthroplasty with delayed weightbearing rehabilitation risk greater potential for deep venous thrombosis after hospital discharge. This study suggests consideration for continued thromboembolic prophylaxis or routine deep venous thrombosis surveillance, or both measures, after hospital discharge, unless more rapid progression of weightbearing is allowed.