Polyethylene in knee arthroplasty: A review

Polyethylene (PE) has been used extensively in knee arthroplasty since the mid 20th century. Progress in material manufacturing and processing has led to newer polyethylenes over last few decades with different material properties. It has been established that PE wear in knee arthroplasty causes particle induced osteolysis which is the main reason for late failure and requires revision surgery. Although there are various causes of wear, the properties of PE have long been a matter of investigation as a contributory factor. The advent of newer highly cross linked PE has been shown to improve wear rates in hip arthroplasty but the benefits have not been shown to be of the same degree in knee arthroplasty. The laboratory and clinical studies so far are limited and slightly conflicting in their conclusions. The risks of using highly cross linked PE in knee arthroplasty include tibial post fracture, disruption of locking mechanism, liner fracture which can lead to increased wear and osteolysis. The current evidence suggests that highly cross linked polyethylenes should be used with caution and only considered in younger active patients. The results of a recently completed randomized trial to compare the conventional with high molecular weight PE in knee arthroplasty are awaited.     

Particle size and morphology of UHMWPE wear debris in failed total knee arthroplasties--a comparison between mobile bearing and fixed bearing knees.

Osteolysis induced by ultrahigh molecular weight polyethylene wear debris has been recognized as the major cause of long-term failure in total joint arthroplasties. In a previous study, the prevalence of intraoperatively identified osteolysis during primary revision surgery was much higher in mobile bearing knee replacements (47%) than in fixed bearing knee replacements (13%). We postulated that mobile bearing knee implants tend to produce smaller sized particles. In our current study, we compared the particle size and morphology of polyethylene wear debris between failed mobile bearing and fixed bearing knees. Tissue specimens from interfacial and lytic regions were extracted during revision surgery of 10 mobile bearing knees (all of the low contact stress (LCS) design) and 17 fixed bearing knees (10 of the porous-coated anatomic (PCA) and 7 of the Miller/Galante design). Polyethylene particles were isolated from the tissue specimens and examined using both scanning electron microscopy and light-scattering analyses. The LCS mobile bearing knees produced smaller particulate debris (mean equivalent spherical diameter: 0.58 microm in LCS, 1.17 microm in PCA and 5.23 microm in M/G) and more granular debris (mean value: 93% in LCS, 77% in PCA and 15% in M/G).     

N—酰化壳聚糖膜性能的研究

讨论了一系列N-酰化壳聚糖膜的抗张强度、透水性、VB_(12)的透过性、透氧性以及血液相容性。N-已酰化壳聚糖膜具有良好的血液相容性。在制膜过程中,加入分子量为1500的聚乙二醇为致孔剂,则可使N-己酰化壳聚糖膜的渗透性有较大提高。同时保持较好的血液相容性和强度。     

Polyethylene wear in primary knee arthroplasty

Abstract Polyethylene (PE) wear is a focal issue in joint replacement, so it is essential to understand how it takes place in vivo. PE wear is a multifactorial process with a complex interaction of variables related to the materials used, the mechanical conditions, operative procedures for implantation, activity of the patient and use of prosthesis. We retrieved 65 PE inserts with the respective femoral and tibial components (50 inserts of total knee prostheses and 15 monocompartmental prostheses) from first revision surgeries. The average age of the patients was 68.3 years; the average time to revision was 41.5 months. Macroscopic observation considered the grade, topography and type of wear. Degradation was also studied with scanning electron microscopy. No direct relationship was found between the level of wear and the survival of total or monocompartmental knee prostheses. The duration of 11 (22%) total prosthetic inserts with grade 2 wear was 42.6 months vs. 51.5 months of 17 (34%) total inserts with grade 1 wear. However, study of the relationship between wear grade and wear topography in total inserts suggested that there was a significant connection. In fact, the 22 (44%) prostheses with central and symmetrical wear never showed wear greater than grade 1. Instead, of the remaining 28 prostheses (56%) without central and symmetric wear, only 3 had grade 0 wear. Finally, considering the relationship between wear grade and type of wear, all 18 inserts (27.7%) with grade 2 or 3 wear had 100% delamination. In conclusion, this study suggests that the correct positioning of the prosthetic components, besides its quality, is an important cause of polyethylene wear.     

应用PEG沉淀试验测定囊虫病人血清中抗体的初步研究

用适宜浓度的PEG将囊虫病人血清浓缩,达到提高血清中特异性抗体浓度的作用,从而提高检测的敏感性。该法用于囊虫病的诊断,阳性附合率83.33%.特异性较理想。     

Celiac vagotomy attenuates the ingestive responses to epinephrine and hypertonic saline but not insulin, 2-deoxy-D-glucose, or polyethylene glycol

The ingestive responses of rats given celiac vagotomy (C), combined celiac and hepatic vagotomy (CH), or low total vagotomy (removal of all tissue from around the esophagus, stomach and duodenum; LT) were compared with sham operated controls (S) in a series of regulatory challenges. The vagotomized groups responded normally to 2-deoxy-D-glucose (2DG; 125, 250, 500 mg/kg, IP), insulin (4, 8, 12 U/kg, IP), and polyethylene glycol (10 ml/kg: 30% w/v, SC), but displayed attenuated responses to epinephrine (40, 80, 120 micrograms/kg, IP) and hypertonic saline (10 ml/kg: 0.25, 0.5, 1.0 M, IP). These results can be interpreted as evidence that the celiac vagus carries a major component of hepatic afferent innervation. Additionally, when considered with other findings they suggest that whereas the anorectic activity of epinephrine is mostly confined to the liver, 2DG hyperphagia involves stimulation of a wider population of peripheral metabolic receptors.     

Polyethylene glycol-modified ragweed pollen extract in rhinoconjunctivitis

Sixty-two ragweed-sensitive adult subjects volunteered to take part in a 2-year, placebo-controlled efficacy study of polyethylene glycol (PEG)-modified ragweed extract, in ragweed pollen-induced rhinoconjunctivitis. At the beginning of the study, subjects were stratified according to skin sensitivity to ragweed extract and PEG-modified ragweed and the severity of hay fever in the previous year. There was random allocation of half to active treatment and half to placebo treatment. Before the first ragweed pollen season the 36 most sensitive subjects received 10 weekly injections (group 1), and the remaining 26 received six injections (group 2). Before the second season all subjects received 10 injections. Doses increased by half a log concentration each week unless there were adverse reactions. The mean total dose received by group 1 in year 1 was 385 micrograms of protein (28.9 micrograms AgE) and received by group 2 was 218 micrograms of protein (16.4 micrograms AgE). In year 2 the mean total dose was 1829 micrograms (137.2 micrograms AgE). Sixty-six percent of injections elicited no reaction or a mild local reaction; the remaining injections produced local redness and swelling more than 2 inches in diameter. Four percent of injections produced systemic symptoms. PEG-modified ragweed stimulated increases in ragweed specific IgG antibody both years, but increases in ragweed specific IgE antibody were significant only in group 1 in year 1. The magnitude of the IgG antibody changes was directly related to the total dose injected. At the beginning of the second year, PEG-modified ragweed-treated subjects still had elevated IgG antibody levels.(ABSTRACT TRUNCATED AT 250 WORDS)     

聚乙二醇干扰素α-2a治疗HBeAg阳性慢性乙型肝炎的疗效和安全性

目的 探讨聚乙二醇α-2a干扰素（PEG INFα-2a）治疗HBeAg阳性慢性乙型肝炎的疗效和安全性。方法 按随机对照原则选择80例HBV DNA、HBeAg阳性的慢性乙型肝炎患者，按1：1随机分配进入PEG INFa-2a组和IFNα-2a组。结果 治疗6个月时，PEG INFα-2a组HBeAg血清转换率（45．7％）高于IFNα-2a组（35．1％），但P〉0．05。停药6个月后，持续的HBeAg血清转换率分别为48．6％和37．8％，P〉0．05。停药6个月后，持续的HBVDNA阴转率分别为62．9％和45．9％，P〉0．05。治疗后，两组的丙氨酸转氨酶（ALT）复常率差异无显著性，为62．9％和45．9％，停药后6个月，两组的联合应答率分别为57．1％和40．5％。PEG INFα-2a组有3例患者HBsAg阴转，而IFNα-2a组仅有1例患者HBsAg阴转。两组有相似的不良反应，不良反应间差异无统计学意义，两组治疗过程中均未发生重要的不良事件。结论PEG INFα-2a治疗HBeAg阳性的慢性乙型肝炎疗效优于普通干扰素IFN-2a，耐受性和安全性好。     

Expansion of human nasal chondrocytes on macroporous microcarriers enhances redifferentiation

Articular cartilage has a limited capacity for self-repair. To overcome this problem, it is expected that functional cartilage replacements can be created from expanded chondrocytes seeded in biodegradable scaffolds. Expansion of chondrocytes in two-dimensional culture systems often results in dedifferentiation. This investigation focuses on the post-expansion phenotype of human nasal chondrocytes expanded on macroporous gelatin CultiSpher G microcarriers. Redifferentiation was evaluated in vitro via pellet cultures in three different culture media. Furthermore, the chondrogenic potential of expanded cells seeded in polyethylene glycol terephthalate/ polybuthylene terephthalate (PEGT/PBT) scaffolds, cultured for 14 days in vitro, and subsequently implanted subcutaneously in nude mice, was assessed.

Chondrocytes remained viable during microcarrier culture and yielded doubling times (1.07±0.14 days) comparable to T-flask expansion (1.20±0.36 days). Safranin-O staining from pellet culture in different media demonstrated that production of GAG per cell was enhanced by microcarrier expansion. Chondrocyte–polymer constructs with cells expanded on microcarriers contained significantly more proteoglycans after subcutaneous implantation (288.5±29.2 μg) than those with T-flask-expanded cells (164.0±28.7 μg). Total collagen content was similar between the two groups.

This study suggests that macroporous gelatin microcarriers are effective matrices for nasal chondrocyte expansion, while maintaining the ability of chondrocyte differentiation. Although the exact mechanism by which chondrocyte redifferentiation is induced through microcarrier expansion has not yet been elucidated, this technique shows promise for cartilage tissue engineering approaches.