Recent studies have indicated that there may be a correlation between acute chondrocyte damage and joint degeneration reminiscent of early-stage osteoarthritis (OA). P188 surfactant has been shown to acutely restore the integrity of damaged chondrocytes; however, its long-term efficacy is unknown. The hypothesis of this study was that a single injection of P188 into a traumatized joint would acutely repair damaged cell membranes and maintain their viability in the long term. Twelve rabbits were divided into two groups, with and without P188, and sacrificed 4 days after tibiofemoral (TF) impact. Another six rabbits were sacrificed after 6 weeks and divided into two groups, with and without P188 treatment immediately posttrauma. Treatment with P188 increased the viable cell density 4 days posttrauma. A higher density of viable cells was also documented 6 weeks posttrauma in the treated versus untreated limb. The results of the current study confirm the acute efficacy of P188 treatment, and may suggest long-term efficacy of treatment, but additional studies are still needed to investigate the chronic implications of the acute repair of cells in the traumatized joint. ß

Mechanical loading of articular cartilage can influence chondrocyte metabolism and lead to alterations in cartilage matrix composition. Most previous studies have focused on the effect of cyclic loading on cartilage mechanical properties and proteoglycan synthesis. However, the role of proteoglycans synthesized from cyclically loaded cartilage in response to an acute overload has not been elucidated. Therefore, we conducted studies where low intensity, intermittent cyclic loading was applied to chondral explants prior to an acute unconfined compression on the tissue. The chondral explants were randomly assigned to three groups: 7, 14, and 21 days of 10 cycles of 0.2 Hz sinusoidal loading at 0.5 MPa followed by an unloaded interval of 3,600 s. All explants were then taken to 25 MPa of unconfined compression. Biochemical assays were conducted to determine the tissue proteoglycan and hydroxyproline contents. The results showed cyclic preloading increased the proteoglycan content and mechanically stiffened the explants, making them more resistant to matrix damage and cell death under 25 MPa of unconfined compression up to 14 days. After 21 days of cyclic loading, however, the explants lost compressive stiffness and suffered more extensive damage in the unconfined compression test. This study investigated the role of cyclic loading in response of chondral explants to a potentially damaging, acute overload. In the long term, these types of studies may help understand the role of preconditioning of articular cartilage for in vitro or even in vivo studies of blunt force trauma to a joint. ß

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The rabbit model is often used for the study of the mechanical properties of articular cartilage. In numerous cases the authors are investigating the initiation and progression of osteoarthritis. The studies have shown that the mechanical properties of articular cartilage vary across the medial and lateral compartments of the tibial plateau. A review of these data indicates numerous inconsistencies in the location dependent mechanical properties and correlations with the macroscopic and microscopic characteristics of the tissue. For example, Hoch et al. [1] and Rasanen et al. [2] document a higher equilibrium tissue modulus in the medial than the lateral compartments of the tibial plateau, using a linear elastic model of the cartilage due to Hayes et al. [3]. In contrast, a recent study by Roemhildt el al. [4] documents a lower aggregate modulus in the medial versus the lateral compartments of the plateau, based on a linear biphasic model analysis. The study also documents a lower Poisson’s ratio in the medial than lateral facets, while more surface fissuring is noted in the medial compartment. While this surface morphology explains a higher permeability of the tissue in the medial than lateral compartments, the data are inconsistent with a notion set forth by Kiviranta et al. [5]. Using a fibril reinforced biphasic model analysis, this study would suggest a less structurally intact collagen network in the cartilage would yield a higher Poisson’s ratio in the medial than lateral compartments. These various inconsistencies in mechanical properties across the tibial plateau may be, in part, due to limitations of each computational model. The hypothesis of the current study is that a more structurally-based fibril-reinforced, biphasic model analysis of the rabbit cartilage will correlate better with the macroscopic and microscopic aspects of the tissue across the tibial plateau.