Variations in the individual thick lamellar properties within osteons by nanoindentation.

The nanoindentation method was used to examine variations in the individual thick lamellar properties within completed secondary osteons as a function of distance from the osteonal center (haversian canal). In general, there is a decline in both elastic modulus and hardness from the center of the osteon outward. Because some of the osteons may have a different general trend than others, an analysis of covariance was also carried out. The overall analysis was highly significant for both elastic modulus and hardness. Also, osteon number was significant as a factor, indicating that there was some difference in the overall thick lamellar properties of the different osteons. An unpaired t-test showed statistically significant differences (p = 0.0005 and 0.0004, respectively) between thick lamellar properties obtained from most of the inner two osteonal lamellae (E = 20.8 +/- 1.3 GPa and H = 0.65 +/- 0.06 GPa) and those from outermost two osteonal lamellae (E = 18.8 +/- 1.0 GPa and H = 0.55 +/- 0.05 GPa). In general, lamellar properties from near to the center of the osteon were greater than those from the outermost osteonal lamella. The mechanical properties of osteons are also significantly lower than those of the interstitial bone (p < 0.0001). The ratio (E1/E2) of the elastic moduli of the outermost osteonal lamella (E1) (considered to be the soft part of the osteons) and that of interstitial bone (E2) was approximately 0.7. These results may have important implications for the mechanical contribution of individual osteons to bone biomechanics.     

Polymorphonuclear function in Beh?et's syndrome.

Three aspects of polymorphonuclear leucocyte (PMN) function were studied in 19 patients with Behçet's syndrome (BS). By 2 different techniques directed motility was found to be increased. This increase was largely due to the subgroup of patients with ocular involvement. Counts of absolute numbers of cells migrating highlighted this finding. No difference was found in the phagocytic or adherent properties of PMN in Behçet's syndrome. Increased PMN motility in Behçet's syndrome may contribute to the expression of the syndrome. It remains to be tested whether altered PMN motility in this syndrome is genetically linked.     

Clinical judgment in rheumatoid arthritis. III. British rheumatologists'' judgments of ''change in response to therapy''.

A realistic analysis of the criteria used by rheumatologists in evaluating the progress of patients suffering from rheumatoid arthritis must be based on actual clinical judgments rather than on expressed opinions. A randomly selected 15% sample of British rheumatologists (48) recorded judgements on the progress of 50 'paper' patients, based on data taken from actual patients participating in clinical trials. The rheumatologists differed markedly in their assessments of the progress of disease, with serious disagreements even when only 'clinically important' changes were considered. Some clinicians showed little consistency in their judgments of duplicate cases. Multiple regression analysis of the patient data in relation to the disease assessments provided a model of each clinician's judgment policy. These judgment policy models showed that the differences in clinical assessment were greater than could be explained by the inconsistent application of similar assessment policies, and were a consequence also of differences in the underlying judgment policies themselves. Judgments related more closely to changes in ESR and other process measures than to changes in functional ability.     

Hardness, an indicator of the mechanical competence of cancellous bone

Hardness and calcium content in compact bone are strongly related. Variation in Young's modulus is produced mainly by variations in mineralisation. Therefore, there should be a relationship between hardness and Young's modulus. We demonstrate this. The calcium content of cancellous bone and adjacent compact bone in several species shows little difference, the cancellous bone having approximately 10% less calcium. The hardness of cancellous bone in Bos is approximately 12% less than that of adjacent compact bone, and the calcium is approximately 2% less. These lines of evidence make it unlikely that the Young modulus of cancellous bone material is much different from that of compact bone. Similar evidence suggests that the yield stress of cancellous bone is similar to that of adjacent compact bone.     

Binding of immunoglobulins and immune complexes to cartilage derived extracts

Cartilage extracts with affinity for heat aggregated immunoglobulins were prepared from human articular and bovine nasal cartilage. These extracts, containing predominantly collagen, also bound both to immune complexes (IC) prepared in vitro and to immunoglobulins from sera of many patients with rheumatoid arthritis (RA). Cryoprecipitation of rheumatoid sera removed material reacting with the extract and density gradient fractionation of a positive serum showed correlation between binding to the extract and to C1q. These results indicate that the binding materials in rheumatoid sera were likely to be IC. We suggest that some assays which apparently demonstrate anti-collagen autoantibodies in fact measure IC. These findings also have implications for models of the pathogenesis of RA.     

Are tensile and compressive Young’s moduli of compact bone different?

This study examines the question of whether the stiffness (Young’s modulus) of secondary osteonal cortical bone is different in compression and tension. Electronic speckle pattern interferometry (ESPI) is used to measure concurrently the compressive and tensile strains in cortical bone beams tested in bending. ESPI is a non-contact method of measuring surface deformations over the entire region of interest of a specimen, tested wet. The measured strain distributions across the beam, and the determination of the location of the neutral axis, demonstrate in a statistically-robust way that the tensile Young’s modulus is slightly (6%), but significantly greater than that of the compressive Young’s modulus. It is also shown that within a relatively small bone specimen there are considerable variations in the modulus, presumably caused by structural inhomogeneities.