Contribution of collagen fibers to the compressive stiffness of cartilaginous tissues

Cartilaginous tissues such as the intervertebral disk are predominantly loaded under compression. Yet, they contain abundant collagen fibers, which are generally assumed to contribute to tensile loading only. Fiber tension is thought to originate from swelling of the proteoglycan-rich nucleus. However, in aged or degenerate disk, proteoglycans are depleted, whereas collagen content changes little. The question then rises to which extend the collagen may contribute to the compressive stiffness of the tissue. We hypothesized that this contribution is significant at high strain magnitudes and that the effect depends on fiber orientation. In addition, we aimed to determine the compression of the matrix. Bovine inner and outer annulus fibrosus specimens were subjected to incremental confined compression tests up to 60 % strain in radial and circumferential direction. The compressive aggregate modulus was determined per 10 % strain increment. The biochemical composition of the compressed specimens and uncompressed adjacent tissue was determined to compute solid matrix compression. The stiffness of all specimens increased nonlinearly with strain. The collagen-rich outer annulus was significantly stiffer than the inner annulus above 20 % compressive strain. Orientation influenced the modulus in the collagen-rich outer annulus. Finally, it was shown that the solid matrix was significantly compressed above 30 % strain. Therefore, we concluded that collagen fibers significantly contribute to the compressive stiffness of the intervertebral disk at high strains. This is valuable for understanding the compressive behavior of collagen-reinforced tissues in general, and may be particularly relevant for aging or degenerate disks, which become more fibrous and less hydrated.     

Innervation pattern of different cartilaginous tissues in the rat

BACKGROUND: The innervation of skeletal tissues by sensory nerves is poorly understood - especially of nerve fibres which reach into the bony and cartilaginous tissue. METHODS: Samples of rat cartilaginous tissues from different locations (knee joint, vertebral column, temporomandibular joint) were fixed by perfusion and decalcified. The distribution of protein gene product (PGP) 9.5-, calcitonin gene-related peptide (CGRP)- and tachykinin (TK)-immunoreactive axons was analysed using fluorescence immunohistochemistry. RESULTS: Nerve fibres were detected in the outer regions of the hyaline cartilage of the knee joint, in the hyaline cartilage of the vertebral body, in the fibrocartilage of the intervertebral disc and menisci, and in the articular disc of the temporomandibular joint. Predominantly, they were found to be CGRP-immunoreactive. CONCLUSION: The neuropeptidergic innervation of the hyaline cartilage in different locations and the presence of nerve fibres in the fibrocartilage might indicate that in addition to the classical neuronal afferent and efferent pathway these fibres may also mediate trophic actions like tissue adaptation and repair.     

Microtensile measurements of single trabeculae stiffness in human femur

In this paper, the authors perform microtensile tests of single trabeculae excised from a human femur head. One of the main issues of this work is to establish some experimental procedures for preparing and testing the specimens. The use of a well-characterized microtensile apparatus allows for a low intraspecimen dispersion of the measured stiffness. Tensile/compressive tests were chosen because they appear less sensitive to errors in the cross-sectional area measurements with respect to bending tests. By these considerations, some tensile/compressive tests of plate-like trabecular specimens have been carried out. Typical stiffness values are 74.2+/-0.7Nmm(-1) for tensile tests, and 58.9+/-0.6Nmm(-1) for compressive test. Another compressive test performed on a shorter specimen yielded a stiffness value of 148.3+/-5.3Nmm(-1). The maximum applied load was about 0.5N. Rough measurements of specimens sizes yielded a Young's modulus value ranging from 1.41 to 1.89GPa.     

Single-molecule measurement of the stiffness of the rigor myosin head

The force-extension curve of single myosin subfragment-1 molecules, interacting in the rigor state with an actin filament, has been investigated at low [ATP] by applying a slow triangle-wave movement to the optical traps holding a bead-actin-bead dumbbell. In combination with a measurement of the overall stiffness of the dumbbell, this allowed characterization of the three extensible elements, the actin-bead links and the myosin. Simultaneously, another method, based on an analysis of bead position covariance, gave satisfactory agreement. The mean covariance-based estimate for the myosin stiffness was 1.79 pN/nm (SD = 0.7 pN/nm; SE = 0.06 pN/nm (n = 166 myosin molecules)), consistent with a recent report (1.7 pN/nm) from rabbit muscle fibers. In the triangle-wave protocol, the motion of the trapped beads during interactions was linear within experimental error over the physiological range of force applied to myosin (±10 pN), consistent with a Hookean model; any nonlinear terms could not be characterized. Bound states subjected to forces that resisted the working stroke (i.e., positive forces) detached at a significantly lower force than when subjected to negative forces, which is indicative of a strain-dependent dissociation rate.     

Ultrastructure of the substantia spongiosa of the femur head and talus

The results of the SEM examination of the zone between the cartilage and the spongeous substances are described precisely. For the first time, W. Lierse examined the 'tensulae' of calcium-collagen lamellae by light microscopy. The examination of this zone was initiated by the fact that the hydrodynamic flow can take place in the calcified zone of the cartilage which is filled with synovial fluid and that the calcified zone adheres to the subchondral substantia corticalis. The subchondral corticalis is characterized by funnel-like indentations with a high number of calcium-collagen and chondrocyte 'tensulae' which are up to now uncounted. The special aim was to locate the separation of the space of adipose and arterial supplies.     

Ligament of the head of the femur in the orangutan and Indian elephant

A literature search revealed that for over 100 years there has been a consensus that the ligament of the head of the femur (LHF) is absent in the orangutan and elephant. A dissection of the hip joints of an adult orangutan and an adult Indian elephant exposed, in each joint, a robust LHF that is functionally important. These LHFs are easily overlooked during a cursory examination of the hip joints because of the way they differ from the human LHF.     

Histologic studies of cartilaginous structures in the anterior region of the head of the sperm whale Physeter macrocephalus

Recently discovered cartilaginous structures in the forehead of the sperm whale (Behrmann and Klima 1985) were investigated histologically. The largest and most important of these structures is the nasal roof cartilage which can be derived from the tectum nasi, a part of the embryonic nasal capsule (Klima et al. 1986). In the investigated sperm whale fetuses, this structure consists of embryonic hyaline cartilage which is well suited for morphogenetic processes and fast growth. In the investigated adult sperm whale, the originally hyaline cartilage has been transformed into a special kind of elastic cartilage. The arrangement of cells, territories, and extracellular substance resembles hyaline cartilage. This component represents an adaptation to pressure load. The appearance and arrangement of elastic fibres resembles elastic cartilage. This component is an adaptation to distortion forces. Obviously, pressure and distortion are the strongest mechanical strains that the nasal roof cartilage is exposed. We see the function of this cartilage structure therein that, being a pressure-elastic skeletal support and following the left nasal meatus along its whole extension through the massive and soft forehead, it secures the only direct respiratory passage. Additionally, fibre bundles of transversely striated muscles are anchored in the perichondrium of the nasal roof cartilage. The function of this delicately interwoven muscle system is seen by us in the fine tuning of contraction and dilatation of the respiratory passage. Moreover, a possible function as a sound conducting cartilaginous structure serving the echolocation system is considered (c.f. Pilleri et al. 1983).     

The mechanical behaviour of intracondylar cancellous bone of the femur at different loading rates

The compressive properties of human cancellous bone of the distal intracondylar femur in its wet condition were determined. Specimens were obtained from six cadaveric femora and were tested at a strain rate of 0.002, 0.10 and 9.16 sec⁻¹. It was found that the compressive strength decreases with an increasing vertical distance from the joint. The highest compressive strength level was recorded in the posterior medial condyle. Correlations among the mechanical properties, the bulk specimen density and the bone mineral content yield (i) highly significant correlations between the compressive strength and the elastic modulus (ii) highly significant correlations between the compressive strength or the modulus of elasticity and the bulk specimen density (iii) a doubtful correlation between the compressive strength and the bone mineral content. All recorded graphs of the impact loaded specimens displayed several well defined stress peaks, unlike the graphs recorded at low loading rates. It can be concluded that upon impact loading the localized trabecular failure which is associated with each peak, does not affect the spongy bone's stress capacity in a detrimental way.     

gamma-Glutamyltransferase activity of different sections of the vertebrate brain

The activity of gamma-glutamyl transferase (GGTF; EC 2.3.2.2) has been measured in the cerebral hemispheres, cerebellum, hippocamp and brain stem of mature wild and laboratory rodents (Oryctolagus cuniculus, Cavia porcellus, Rattus norvegicus, var. alb., Ochotona pusilla, Mesocricetus auratus, Clethrionimus glareolis, Mus musculus. var. alb.), as well as in homogenates of the whole brain of the tortoise Testudo horsfieldi, frog Rana temporaria and loach Misgurnus fossilis. In wild rodents the activity of GGTF was found to be higher than in laboratory ones. GGTF activity in the brain of warm-blooded animals is higher than that in the brain of the tortoise, frog and loach.     

Arsenic content in the femur head of the residents of southern and central Poland

Arsenic content was assayed in the samples of the femur head of the people living in southern and central Poland (Kraków, n=13; Silesian region, n=13; Łódź, n=12). The average age being 68.7±8.7 yr. Arsenic content in the femur head was determined applying the hydride generation atomic absorption spectrometry (HG-AAS) method after microwave mineralization. The average arsenic contents in the femur head of the residents of the Łódź, Kraków, and Silesian regions were 0.41 μg/g, 0.37 μg/g, and 0.18 μg/g, respectively. No correlation has been found between arsenic content in the femur head and the content of other metals. Neither the age nor sex of the people tested affected the arsenic content in the femur head.     

Changes of heavy metal concentrations in cross-sections of human femur head

The concentrations of 12 elements (Ni, Ma, Cr, Cd, Pb, Cu, Fe, Zn, Mg, K, Na, Ca) were determined in cross-sections of human femur heads. The highest concentrations of these elements was found in the cortical bone, and the lowest concentrations occurred in the trabecular bone, with exception of the E cross-section, in which the lowest values were found in articular cartilage. The average concentrations of Na, Ca, K, and Mg were highest in cortical bone and lowest in articular cartilage. Pb was found in higher concentrations in articular cartilage and lowest in trabecular bone, with exception of cross-sections A and E. The Fe contents in the cortical parts were highest in cross-sections A, B, and D. Cu was highest in cross-sections B, C, and D of articular cartilage. These results show that the contents of the selected metals in the femur head varied considerably. As expected, the largest concentrations were found in the outmost part of cross-section E and the lowest in its innermost one, possibly related to mechanical stress.     

Correlations between stiffness and the chemical constituents of cartilage on the human femoral head

A method is described, in outline, for measuring the compressive stiffness of articular cartilage on the human femoral head, in vitro. Indentations were measured normal to the articular surface, and from these measurements creep moduli were calculated at 2 sec after application of the load. Correlations between the stiffness and the following quantities were determined: (1) Total glycosaminoglycan content, (2) chondroitin sulphate content, (3) ‘keratin sulphate’ content, and (4) collagen content. These quantities were determined from chemical analyses of the indented areas of cartilage and expressed as a percentage of the dry weight.The following observations were made: there was a statistically significant correlation between the stiffness, expressed as the creep modulus, and the total glycosaminoglycan content. Approximately equal correlation coefficients were recorded between the stiffness and chondroitin sulphate and ‘keratan sulphate’ content respectively; however, at a given concentration, the influence of ‘keratin sulphate’, on the stiffness, was greater than that of chondroitin sulphate. In contrast, the correlation between stiffness and collagen content was considerably less significant.