Advertisement for orthosearch.org.uk
Results 1 - 3 of 3
Results per page:
Applied filters
Content I can access

Include Proceedings
Dates
Year From

Year To
Orthopaedic Proceedings
Vol. 102-B, Issue SUPP_10 | Pages 50 - 50
1 Oct 2020
Kraay MJ Bigach SD Rimnac CM Moore RD Kolevar MP Adavi P
Full Access

Introduction

The purpose of this study was to evaluate the long term changes in bone mineral density (BMD) following implantation of a low-modulus composite femoral component designed to closely match the stiffness of the proximal femur and minimize stress shielding. Specifically, we asked: 1) How does BMD in the proximal femur change with time and with Gruen zone location; 2) Does BMD in the proximal femur stabilize after two years of implantation?

Methods

We retrospectively reviewed a subgroup of sixteen patients who had preoperative and postoperative DEXA scans in an FDA multi-center prospective trial of this composite stem. Five of these sixteen patients returned for long-term DEXA scans at a mean 22.0 years post-op (range 21.2–22.6 years). BMD in the 7 Gruen zones at final follow-up was compared to immediate post-operative and 2-year follow-up values. Percentage change was calculated and change in BMD was plotted against time from immediate post-operative measurements to each subsequent follow-up.


Orthopaedic Proceedings
Vol. 100-B, Issue SUPP_13 | Pages 8 - 8
1 Oct 2018
Du JY Flanagan CD Bensusan JS Knusel KD Akkus O Rimnac CM
Full Access

Background

Structural bone allografts are an established treatment method for long-bone structural defects arising from such conditions as trauma, sarcoma, and osteolysis following total joint replacement. However, the quality of structural bone allografts is difficult to non-destructively assess prior to use. The functional lifetime of structural allografts depend on their ability to resist cyclic loading, which can lead to fracture even at stress levels well below the yield strength. Because allograft bone has limited capacity for remodeling, optimizing allograft selection for bone quality could decrease long-term fracture risk. Raman spectroscopy biomarkers can non-destructively assess the three primary components of bone (collagen, mineral, and water), and may predict the resistance of donor bone allografts to fracture from cyclic loads.

The purpose of this study was to prospectively assess the ability of Raman biomarkers to predict number of cycles to fracture (“cyclic fatigue life”) of human allograft cortical bone.

Methods

Twenty-one cortical bone specimens were from the mid-diaphysis of human donor bone tissue (bilateral femurs from 4 donors: 63M, 61M, 51F, 48F) obtained from the Musculoskeletal Transplant Foundation. Six Raman biomarkers were analyzed: collagen disorganization, type B carbonate substitution (a surrogate for mineral maturation), matrix mineralization, and 3 water compartments. Specimens underwent cyclic fatigue testing under fully reversed conditions at 35 and 45MPa (physiologically relevant stress levels for structural allografts). Specimens were tested to fracture or to 30 million cycles (“run-out”), simulating 15 years of moderate activity (i.e., 6000 steps per day). Multivariate regression analysis was performed using a tobit model (censored linear regression) for prediction of cyclic fatigue life. Specimens were right-censored at 30 million cycles.


Orthopaedic Proceedings
Vol. 92-B, Issue SUPP_I | Pages 174 - 174
1 Mar 2010
Haider H Weisenburger JN Kurtz SM Rimnac CM Freedman J Schroeder DW Garvin KL
Full Access

Concerns about reduced strength, fatigue resistance, and oxidative stability of highly crosslinked UHMWPE have limited the acceptance of these materials for TKR. It was hypothesized that a new crosslinked UHMWPE stabilized with vitamin E would substantially improve wear performance and resistance to oxidative degradation without compromising mechanical properties. The purpose of this study was to comprehensively test this hypothesis in vitro.

GUR1020 was machined from isostatic molded bar-stock, crosslinked with 100 kGy, and then doped with vitamin E. This material was compared to direct molded GUR1050 UHMWPE. Both materials were gamma irradiation sterilized as for clinical use. Small punch testing, crack growth rate fatigue testing and oxidation index measurements were performed on each material before and after accelerated aging. Knee simulator testing evaluated wear of each material for 5-million walking cycles. CR knees were tested on a 6-station AMTI knee simulator; PS knees were tested on two 4-station Instron-Stan-more knee simulators. Statistical differences in all metrics were evaluated for significance with ANOVA (p < 0.05).

After 4-week accelerated aging, the control material showed elevated oxidation, loss of small punch mechanical properties and decreased fatigue crack growth resistance. In contrast, the vitamin E stabilized material had minimal changes in these properties. Further, the vitamin E stabilized material exhibited 85% reduction in wear for both the CR and PS designs.

Highly crosslinked UHMWPE stabilized with vitamin E appears to be promising for use as a bearing surface in TKA.