Polarized light microscopy is a traditional method for visualizing the collagen network architecture of articular cartilage. Articular cartilage repair and tissue engineering studies have raised new demands for techniques capable of quantitative characterization of the scar and repair tissues, including properties of the collagen network. Modern polarized light microscopy can be used to measure collagen fibril orientation, parallelism, and birefringence. New commercial instruments are computer controlled and the measurements are easy to perform. However, often the interpretation of results causes difficulties, even errors, because the theoretical aspects of the technique are demanding. The aim of this study was to describe the instrumentation and properties of a modern polarized light microscope, to point out some sources of error in the interpretation of the results, and to recall the theoretical background of the polarized light microscopy.

A new microspectrophotometric method was developed for quantitation of glycosaminoglycans with Safranin O dye in articular cartilage matrix. From histological sections molar extinction coefficient of Safranin O was determined and used to measure the dye content of the sections. The amount of glycosaminoglycans was determined with depth of bovine articular cartilage by both gas chromatography and thin layer chromatography to calculate the fixed negative charge content. Comparison between the results revealed that binding of Safranin O to glycosaminoglycan polyanions was stoichiometric and showed minimal nonspecific staining. The method provides an accurate technique for quantitation and localization of fixed negative charge content of glycosaminoglycans in the articular cartilage matrix. Specific enzyme digestions enable detection of separate glycosaminoglycans.

The local influences of physical exercise on thickness and glycosaminoglycan (GAG) content of canine articular cartilage were measured by microspectrophotometry of Safranin O- and periodic acid-Schiff (PAS)-stained tissue sections. Female Beagle dogs were housed in individual cages (bottom 0.9 x 1.2 m) and divided into runner (n = 6) and control (n = 8) groups. The training program started at the age of 15 weeks. During the subsequent 10 weeks, the dogs were accustomed to running on a treadmill inclined 15 degrees uphill. Thereafter, the dogs ran 1 h daily, 5 days a week, at a speed of 4 km/h for 15 weeks. At the age of 40 weeks, the dogs were killed, and the samples for histology were taken from 11 different anatomical locations of the right knee (stifle) joint. The thickness of the uncalcified cartilage increased 19-23% on the lateral condyle and patellar surface of the femur, whereas the enhancement was smaller in other parts of the trained cartilage. The calcified cartilage did not show thickness alterations. Total GAGs were augmented by 28% in the summits on the femoral condyles, more on the medial than lateral side. The increased GAGs appeared to be predominantly chondroitin sulphates and were localized in the intermediate, deep, and even in the calcified zones, whereas the superficial zone did not show changes. There was a concomitant increase of non-GAG oligosaccharides in the intermediate and deep zones, but not in the calcified cartilage.(ABSTRACT TRUNCATED AT 250 WORDS)

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The macromolecular structure and mechanical properties of articular cartilage are interrelated and known to vary topographically in the human knee joint. To investigate the potential of delayed gadolinium-enhanced MRI of cartilage (dGEMRIC), T 1 , and T 2 mapping to elucidate these differences, full-thickness cartilage disks were prepared from six anatomical locations in nonarthritic human knee joints (N ‫؍‬ 13). Young's modulus and the dynamic modulus at 1 Hz were determined with the use of unconfined compression tests, followed by quantitative MRI measurements at 9.4 Tesla. Mechanical tests revealed reproducible, statistically significant differences in moduli between the patella and the medial/ lateral femoral condyles. Typically, femoral cartilage showed higher Young's (>1.0 MPa) and dynamic (>8 MPa) moduli than tibial or patellar cartilage (Young's modulus <0.9 MPa, dynamic modulus <8 MPa). dGEMRIC moderately reproduced the topographical variation in moduli. Additionally, T 1 , T 2 , and dGEMRIC revealed topographical differences that were not registered me-

The present study revealed dynamic changes of the collagen network during growth and maturation of the pigs. The structure of the collagen network of young pigs gradually approached a network with the classical Benninghoff architecture. The probable explanation for the alterations is growth of the bone epiphysis with simultaneous adaptation of the cartilage to increased joint loading. The maturation of articular cartilage advances gradually with age and offers, in principle, the possibility to influence the quality of the tissue, especially by habitual joint loading. These observations in porcine cartilage may be of significance with respect to the maturation of human articular cartilage.

According to the present results, T(2) mapping is capable of detecting histological differences in cartilage collagen architecture among species, likely to be strongly related to the differences in maturation of the tissue. This diversity in the MRI appearance of healthy articular cartilage should also be recognized when using juvenile animal tissue as a model for mature human cartilage in experimental studies.