Hemispherical Acetabular Cup Research Articles

Optimizing acetabular component position to minimize impingement and reduce contact stress.

Component impingement due to poor positioning can limit range of motion after total hip arthroplasty. Contact stresses on ultra-high molecular weight polyethylene are also dependent on the orientation of the acetabular component. In this study, a computer kinematic model was used to determine the effects of component position and variation of head:neck ratios on prosthetic impingement and hip range of motion, and a finite element model was employed to calculate polyethylene stresses at different cup positions. ### Kinematic Analysis A three-dimensional total hip prosthesis with a hemispherical acetabular cup, femoral neck diameters ranging from 10 to 12 mm, and head sizes ranging from 22 to 32 mm was generated (Fig. 1). The maximum range of motion of the hip was measured, before impingement of the neck on the cup liner, for acetabular component abduction angles ranging from 35° to 55° and for acetabular component anteversion angles ranging from 0° to 30°. The effect, on the range of motion of the hip, of a wide chamfer that was offset 1, 2, or 3 mm above or below the center of the head was also analyzed (Fig. 2). Fig. 1: Computer model used for kinematic analysis. The head diameters ranged from 22 to 32 mm, the neck diameters ranged from 10 to 12 mm, and the liner outer diameter was 50 mm. Fig. 2: Liner with a wide chamfer that was offset 2 mm above the center of the head to increase range of motion. ### Finite Element Analysis A model of a total hip prosthesis was generated with a finite element analysis program (MARC; MSC Corporation). The acetabular liner was modeled as a hemisphere with an inner diameter of 28 mm and an outer diameter of 50 mm. The liner was composed of approximately 5000 eight-node hexahedral elements (Fig. 3). The femoral head was modeled as a spherical rigid body (28 …

Porous-coated cementless acetabular cups in revision surgery: A 6- to 11-year follow-up study

Between 1986 and 1991, 65 cementless hemispherical acetabular cups were implanted in 60 patients in revision surgery. Different designs were used, including PCA (29 cups), Duraloc (14 cups), Harris-Galante (12 cups), and Omnifit (10 cups). The mean age of patients was 54.7 years. The Paprosky types of the acetabular bone defects were type 1, 2 hips; type 2, 38 hips; type 3A, 15 hips; and type 3B, 10 hips. For unrevised hips, the mean follow-up was 8.3 years (range, 6–11 years). Bone allografts were used in 56 hips: Morcellized cancellous graft was used in 42 hips, structural graft for contained defects was used in 7 hips, and structural graft for uncontained defects was used in 7 hips. There were poor clinical results in 14 hips (22%). Re-revision was necessary in 7 hips (10.8%). There was definite radiographic loosening in 18 hips and possible loosening in 4 hips. Screw failure occured in 6 hips, and a radiolucency in 1 or more DeLee-Charnley zones was apparent in 45 hips (69.2%). Moderate or severe graft resorption were found in 4 of the 42 morcellized grafts, in 6 of the 7 structural grafts for uncontained defects, and in all 7 of the 7 structural grafts for contained defects. The best results were obtained in hips with a bone defect of less than 30%. The use of a cementless acetabular cup supplemented with screws is contraindicated in hips with a bone defect greater than 50%. Hip reconstruction using structural bone—graft to stabilize the prosthesis gives the worst results.

Roentgen stereophotogrammetric analysis of metal-backed hemispherical cups without attached markers.

A method for the detection of micromotion of a metal-backed hemispherical acetabular cup is presented and tested. Unlike in conventional roentgen stereophotogrammetric analysis, the cup does not have to be marked with tantalum markers; the micromotion is calculated from the contours of the hemispherical part and the base circle of the cup. In this way, two rotations (tilt and anteversion) and the translations along the three cardinal axes are obtained. In a phantom study, the maximum error in the position of the cup's centre was 0.04 mm. The mean error in the orientation of the cup was 0.41 degree, with a 95% confidence interval of 0.28-0.54 degree. The in vivo accuracy was tested by repeated measurement of 21 radiographs from seven patients. The upper bound of the 95% tolerance interval for the translations along the transversal, longitudinal, and sagittal axes was 0.09, 0.07, and 0.34 mm, respectively: for the rotation, this upper bound was 0.39 degree. These results show that the new method, in which the position and orientation of metal-backed hemispherical cup is calculated from its projected contours, is a simple and accurate alternative to attaching markers to the cup.

A Clinical Study of Microporous Coated Hemispherical Acetabular Cup - A comparative Study in Relation to the Size of Acetabular Reaming-

A Clinical Study of Microporous Coated Hemispherical Acetabular Cup - A comparative Study in Relation to the Size of Acetabular Reaming-

Ingrowth reduces implant-to-bone relative displacements in canine acetabular prostheses.

We examined bone-to-implant relative displacement of acetabular prostheses acutely and after ingrowth in a canine model. Uncemented hemispherical acetabular cups with titanium mesh pads comprising approximately 26% of the surface of the cup were inserted in eight adult canine hemipelves ex vivo. The acetabular prostheses were fixed with 13 mm titanium screws. Zero, one, and two-screw configurations were tested, with the order of testing randomly assigned. A load simulating 1,000 cycles of canine gait as applied to the acetabular component, and relative displacements were measured at three locations between implant and bone to determine acute fixation. A repeated measures analysis of variance showed that two screws produced only 42% of the average relative displacement of one screw and 14% that of zero screws. Eight adult mixed-breed dogs then underwent unilateral total hip arthroplasty. All acetabula were biologically fixed with two cancellous screws. The results at 4 months showed significantly less relative displacement between the implant and bone than was measured in ex vivo implantations (p = 0.014). Bone ingrowth filled 20 +/- 6% (mean +/- SD) of the available space. The relative displacements of these implants were small in all cases (12 +/- 13 microns) and did not correlate with the amount of bone ingrowth. These data suggest that acetabular fixation with two screws can lead to bone ingrowth and reduced relative motion of the prosthesis under functional loading.

Osteonecrosis of the femoral head treated with total hip arthroplasty without cement.

With use of porous-coated implants, total hip arthroplasty was performed in a consecutive series of thirty patients (thirty-five hips) who had a preoperative diagnosis of late-stage (Ficat and Arlet stage-III or IV) osteonecrosis of the femoral head. The patients were evaluated clinically and radiographically, and the data were recorded in a prospective manner. The average duration of follow-up was seven and one-half years (range, five to ten years). The average age of the patients at the time of the operation was thirty-two years (range, twenty-one to forty years). Signs of osseointegration of the femoral stem to the host bone were demonstrated in thirty-three hips (94 per cent). In the porous-coated hemispherical acetabular cups of these hips, an optimum bone-implant interface was identified and maintained, suggesting bone ingrowth. The rate of revision was 3 per cent (one hip) for the femoral side and 6 per cent (two hips) for the acetabular side, for an over-all rate of 6 per cent. All patients maintained a high level of activity postoperatively. There was moderate or severe remodeling of proximal femoral resorptive bone and stress-shielding in six hips (17 per cent) and osteolytic reactions in six hips. Complications were frequent (six hips) and included one deep infection; two dislocations; two instances of heterotopic ossification; and one fracture of the calcar femorale, which occurred intraoperatively. The thirty patients had a lower rate of revision and improved clinical outcomes compared with other reported series of young patients managed with total hip arthroplasty with cement who had the same diagnosis and similar postoperative follow-up. However, the latter series involved implants of an earlier design that had been inserted with older techniques of cementing. When arthroplasty is considered for the treatment of late-stage osteonecrosis of the femoral head in young patients, the use of total hip implants without cement that allow for bone ingrowth appears to be a viable alternative to arthroplasty with use of cement. However, longer follow-up is needed to determine the outcome of the osteolytic reactions that we observed. We therefore recommend this procedure with some caution because of the high rate of complications and the potential for failure of the arthroplasty related to the osteolytic reactions.