Double inactivation of NF1 in tibial pseudarthrosis.

Osseous abnormalities, including long-bone dysplasia with pseudarthrosis (PA), are associated with neurofibromatosis type 1 (NF1). Prospectively acquired tissue from the PA site of two individuals with NF1 was used for immunohistochemical characterization and genotype analysis of the NF1 locus. Typical immunohistochemical features of neurofibroma were not observed. Genotype analysis of PA tissue with use of four genetic markers (D17S1863, GXALU, IN38, and 3NF1-1) spanning the NF1 locus demonstrated loss of heterozygosity. These results are the first to document double inactivation of NF1 in PA tissue and suggest that the neurofibromin-Ras signal transduction pathway is involved in this bone dysplasia in NF1.

Ambulatory activities maintain cortical bone after total hip arthroplasty.

Because periprosthetic bone loss impacts revision total hip arthroplasties and subsequent patient recovery, it is important to understand the consequences of stress shielding. We characterized bone loss attributed to stress shielding by investigating the influence of patient activity and demographics on reductions in cortical bone cross-sectional area, bone mineral density, and bone mineral content. Cortical bone shape, bone mineral content, and bone mineral density were measured in implanted and contralateral nonimplanted cadaveric femurs. Geometric measurements of transverse cross sections were measured with imaging software. Dual energy x-ray absorptiometry measured bone mineral content and bone mineral density. Patient activity was estimated by the mechanical usage score. The mechanical usage score was comprised of the ambulatory components of the Harris hip score. Regression analysis revealed a lower mechanical usage score and patient weight correlated with greater bone loss. Age, implant size, and time in situ did not correlate to bone loss. The implanted femurs were reduced in cross-sectional area and rigidity, and expanded endosteally and periosteally. Principal axis location did not change. Bone loss was more likely to occur uniformly than to change cortical bone distribution. Bone loss was minimized in patients with higher activity levels.

Oxidative degradation in highly cross-linked and conventional polyethylene after 2 years of real-time shelf aging.

Previous studies have reported oxidative degradation of conventional polyethylene (PE) components during shelf aging, following radiation. However, no studies have yet reported data concerning the effect of real-time shelf aging in the manufacturer's packaging on the oxidative degradation of commercially available highly cross-linking PE components. The null hypothesis tested was that in either highly cross-linked or conventional PE acetabular components there would be no significant difference in the amount of oxidative degradation between time zero PE liners and PE liners that had been real-time shelf aged for 2 years in their respective packaging. The results of the study indicated that after 2 years of real-time shelf aging, negligible oxidative degradation occurred with minimal changes in oxidation index, density, and percent crystallinity in commercially available highly cross-linked and conventional PE acetabular liners. These data suggested that oxidative degradation was not a clinical issue in the highly cross-linked and conventional PE components examined after 2 years of real-time shelf aging. It is likely that current manufacturing and packaging technologies have limited the previous clinical concerns related to oxidative degradation during shelf aging of highly cross-linked and conventional PE components.

Quantifying the effect of resin type and sterilization method on the degradation of ultrahigh molecular weight polyethylene after 4 years of real-time shelf aging.

Alternative sterilization methods including ethylene oxide, gas plasma, and gamma-radiation in an inert environment were implemented in the late 1990s, to limit oxidative degradation of ultrahigh molecular weight polyethylene (PE). There was also a simultaneous transition to PE resins that did not contain calcium stearate. Shelf storage duration of PE inserts following gamma-irradiation in air has been correlated to poor clinical performance and increased wear. This study aimed to determine how sterilization method and resin type influenced degradation of PE after 4 years of real-time shelf aging. It was hypothesized that gamma-irradiation and stearate containing resins would incur significantly more degradation than nonradiated, stearate-free resins. Gamma-irradiated PE samples in air and nitrogen had a significantly increased density and oxidation index, compared to nonirradiated PE after 4 years of shelf aging. Alternative sterilization methods such as ethylene oxide and gas plasma appeared to have significantly less oxidation regardless of PE resin type. A partial correlation demonstrated that density and oxidation index were not correlated (r(2) = 0.079) when examining the influence of sterilization method. The data supported that after 4 years of real-time shelf aging, the type of sterilization method had a larger influence on PE degradation than resin type.