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Articular cartilage, a connective tissue that provides resistance to compressive forces during joint movements, has not been examined in detail by conventional Fourier transform infrared (FTIR) spectroscopy, microspectroscopy (FTIRM), or imaging (FTIRI). The current study reports FTIRM and FTIRI analyses of normal bovine cartilage and identifies the specific molecular components of cartilage that contribute to its IR spectrum. FTIRM data acquired through the superficial, middle, and deep zones of thin sections of bovine articular cartilage showed a variation in intensities of the absorbance bands that arise from the primary nonaqueous components of cartilage, collagen, and proteoglycan (primarily aggrecan) and thus reflected the differences in quantity of these specific components. The spectra of mixtures of model compounds, which had varying proportions of type II collagen and aggrecan, were analyzed to identify spectral markers that could be used to quantitatively analyze these components in cartilage. Collagen and aggrecan were then imaged by FTIRI based on markers found in the model compounds. Polarization experiments were also performed to determine the spatial distribution of the collagen orientation in the different zones of cartilage. This study provides a framework in which complex pathological changes in this heterogeneous tissue can be assessed by IR microscopic imaging. © 2000 John Wiley & Sons, Inc. Biopolymers (Biospectroscopy) 62: 1–8, 2001

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Significant evidence exists that trauma to a joint produced by a single impact load below that which causes subchondral bone fracture can result in permanent damage to the cartilage matrix, including surface fissures, loss of proteoglycan, and cell death. Limited information exists, however, on the effect of a varying impact stress on chondrocyte biophysiology and matrix integrity. Based on our previous work, we hypothesized that a stress-dependent response exists for both the chondrocyte's metabolic activity and viability and the matrix's hydration. This hypothesis was tested by impacting bovine cartilage explants with nominal stresses ranging from 0.5 to 65 MPa and measuring proteoglycan biosynthesis, cell viability, and water content immediately after impaction and 24 hours later. We found that proteoglycan biosynthesis decreased and water content increased with increasing impact stress. However, there appeared to be a critical threshold stress (15-20 MPa) that caused cell death and apparent rupture of the collagen fiber matrix at the time of impaction. We concluded that the cell death and collagen rupture are responsible for the observed alterations in the tissue's metabolism and water content, respectively, although the exact mechanism causing this damage could not be determined.

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The popliteal tendon has a significant attachment to the fibula, the popliteofibular ligament. The role of this ligament in knee stability has not been determined. In this study we used selective cutting techniques to measure the static contribution of the popliteal tendon attachments to the tibia and the popliteofibular ligament for stability of the knee. Sectioning of all the posterolateral structures except the popliteal tendon attachments to the tibia or the popliteofibular ligament resulted in increased primary posterior translation, varus rotation, external rotation, and coupled external rotation. Although statistically significant, these increases were small. Sectioning of all the posterolateral structures resulted in larger increases in primary posterior translation, varus rotation, external rotation, and coupled external rotation. Our data indicate that the popliteal tendon attachments to the tibia and the popliteofibular ligament are important in resisting posterior translation and varus and external rotation. If an isolated injury to the posterolateral structures occurs, anatomic reconstruction of the major ligaments that restrain posterior translation and varus and external rotation may provide the best functional result. Reconstruction for isolated posterolateral instability should include anatomic attachment of the popliteal tendon to the tibia and the popliteofibular ligament.