ABSTRACT:In clinical outcome studies, small component sizes, female gender, femoral shape, focal bone defects, bad bone quality, and biomechanics have been associated with failures of resurfacing arthroplasties. We used a well-established experimental setup and human bone specimens to analyze the effects of bone density on cement fixation of femoral hip resurfacing components. Thirty-one fresh frozen femora were prepared for resurfacing using the original instruments. ASR TM resurfacing prostheses were implanted after dual-energy X-ray densitometer scans. Real-time measurements of pressure and temperature during implantation, analyses of cement penetration, and measurements of micro motions under torque application were performed. The associations of bone density and measurement data were examined calculating regression lines and multiple correlation coefficients; acceptability was tested with ANOVA. We found significant relations between bone density and micro motion, cement penetration, cement mantle thickness, cement pressure, and interface temperature. Mean bone density of the femora was 0.82 AE 0.13 g/cm 2 , t-score was À0.7 AE 1.0, and mean micro motion between bone and femoral resurfacing component was 17.5 AE 9.1 mm/Nm. The regression line between bone density and micro motion was equal to À56.7 Â bone density þ 63.8, R ¼ 0.815 (p < 0.001). Bone density scans are most helpful for patient selection in hip resurfacing, and a better bone quality leads to higher initial component stability. A sophisticated cementing technique is recommended to avoid vigorous impaction and incomplete seating, since increasing bone density also results in higher cement pressures, lower cement penetration, lower interface temperatures, and thicker cement mantles. Clinical studies of hip resurfacing arthroplasties identified risk factors for failure, including presence of femoral head cysts, small fixation area, small component size, female sex, and varus positioning of the femoral component. [1][2][3][4] Initial fixation and stability is critical to minimize membrane formation and prevent micro motions of more than 100-150 mm, which can lead to loosening. [5][6][7] The young patients that usually receive hip resurfacing arthroplasties need the best bone preparation and circumferential cement fixation. They should avoid impact activities to minimize the risk for loosening and femoral neck fractures. 8 Surgical technique modifications like increased numbers of femoral head drill holes and the area in which these holes are drilled or cementation of the metaphyseal stem (initially designed for component alignment purposes) were introduced to increase the area of bone-cement interface and enhance initial component stability. 9 Patient selection to avoid low bone density, focal defects, suboptimal shape, and poor hip biomechanics has been emphasized. 4 Our aim was to assess the usefulness of dual-energy X-ray densitometer (DEXA) bone density data for patient selection and prognosis of a sufficient initial stability. We used a well-es...

Purpose In clinical and retrieval analyses, over-penetration of cement, incomplete seating of the prosthesis with a resultant polar cement mass, or both, have been associated with early femoral failures of resurfacing arthroplasties. We used human bone specimens to experimentally compare the initial stability of different cementing techniques. Methods Twenty-six pairs of fresh frozen femora were prepared for resurfacing using original instruments (DePuy ASR). ASR femoral resurfacing prostheses were implanted using two different cementing techniques: (1) component filling and (2) cement applicator. Real-time measurements of pressure and temperature during implantation, analyses of cement penetration and micro motions under torque application were performed. Results Applicator use reduced significantly the cement penetration depth (9.2 mm vs 5.3 mm with the applicator, p=0.001), polar mantle (8.1 mm vs 2.6 mm, p=0.008), cement defects (3.7 mm vs 0.1 mm, p = 0.008) and interface temperatures (40.3°C vs 33.1°C, p<0.001 ). Initial rotational stability showed statistically significant less extreme values with the cement applicator technique (range 3.4-51.7 m°/Nm, 11.0-29.7 m°/Nm, p=0.024). Conclusions The cement applicator technique significantly reduces cement defects, incomplete seating, overpenetration and interface temperatures with a more consistent initial stability of the ASR femoral resurfacing prostheses.