The menisci serve several important biomechanical functions in the knee. They distribute stresses over a broad area of articular cartilage, absorb shocks during dynamic loading, and probably assist in joint lubrication. These functions enhance the ability of articular cartilage to provide a smooth, near-frictionless articulation and to distribute loads evenly to the underlying bone of the femur and tibia. In addition, the menisci provide stability to the injured knee when the cruciate ligaments or other primary stabilizers are deficient. The ability to perform these mechanical functions is based on the intrinsic material properties of the menisci as well as their gross anatomic structure and attachments. The material properties of the menisci are determined by their biochemical composition and, perhaps more important, by the organization and interactions of the major tissue constituents: water, proteoglycan, and collagen. Interactions among the important constituents of the fibrocartilage matrix cause meniscal tissue to behave as a fiber-reinforced, porous, permeable composite material similar to articular cartilage, in which frictional drag caused by fluid flow governs its response to dynamic loading. The menisci are one-half as stiff in compression and dissipate more energy under dynamic loading than articular cartilage. Energy dissipation, or shock absorption, by the menisci is the result of high frictional drag caused by low permeability of the matrix, which is about one-sixth as permeable as articular cartilage. The dynamic shear modulus of meniscal tissue is only one-fourth to one-sixth as great as that of articular cartilage. The coarse, circumferential Type I collagen fiber bundles of the meniscus give the tissue great tensile stiffness (range, 100-300 megapascals) and strength. The highly oriented collagen ultrastructure of the menisci makes the tissue anisotropic in tension, compression, and shear and appears to dominate its behavior under all loading conditions.

Material properties and structure-function relationships in the menisci.

Importance Synovitis is common and is associated with progression of structural characteristics of knee osteoarthritis Intra-articular corticosteroids could reduce cartilage damage associated with synovitis but might have adverse effects on cartilage and periarticular bone Objective To determine the effects of intra-articular injection of 40 mg of triamcinolone acetonide every 3 months on progression of cartilage loss and knee pain Design, setting, and participants Two-year, randomized, placebo-controlled, double-blind trial of intra-articular triamcinolone vs saline for symptomatic knee osteoarthritis with ultrasonic features of synovitis in 140 patients Mixed-effects regression models with a random intercept were used to analyze the longitudinal repeated outcome measures Patients fulfilling the American College of Rheumatology criteria for symptomatic knee osteoarthritis, Kellgren-Lawrence grades 2 or 3, were enrolled at Tufts Medical Center beginning February 11, 2013; all patients completed the study by January 1, 2015 Interventions Intra-articular triamcinolone (n = 70) or saline (n = 70) every 12 weeks for 2 years Main outcomes and measures Annual knee magnetic resonance imaging for quantitative evaluation of cartilage volume (minimal clinically important difference not yet defined), and Western Ontario and McMaster Universities Osteoarthritis index collected every 3 months (Likert pain subscale range, 0 [no pain] to 20 [extreme pain]; minimal clinically important improvement, 394) Results Among 140 randomized patients (mean age, 58 [SD, 8] years, 75 women [54%]), 119 (85%) completed the study Intra-articular triamcinolone resulted in significantly greater cartilage volume loss than did saline for a mean change in index compartment cartilage thickness of -021 mm vs -010 mm (between-group difference, -011 mm; 95% CI, -020 to -003 mm); and no significant difference in pain (-12 vs -19; between-group difference, -06; 95% CI, -16 to 03) The saline group had 3 treatment-related adverse events compared with 5 in the triamcinolone group and had a small increase in hemoglobin A1c levels (between-group difference, -02%; 95% CI, -05% to -0007%) Conclusions and relevance Among patients with symptomatic knee osteoarthritis, 2 years of intra-articular triamcinolone, compared with intra-articular saline, resulted in significantly greater cartilage volume loss and no significant difference in knee pain These findings do not support this treatment for patients with symptomatic knee osteoarthritis Trial registration ClinicalTrialsgov Identifier: NCT01230424

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Effect of Intra-articular Triamcinolone vs Saline on Knee Cartilage Volume and Pain in Patients With Knee Osteoarthritis: A Randomized Clinical Trial.

Biomechanical factors play an important role in the health of diarthrodial joints. Altered joint loading - associated to obesity, malalignment, trauma or joint instability - is a critical risk factor for joint degeneration, whereas exercise and weight loss have generally been shown to promote beneficial effects for osteoarthritic joints. The mechanisms by which mechanical stress alters the physiology or pathophysiology of articular cartilage or other joint tissues likely involve complex interactions with genetic and molecular influences, particularly local or systemic inflammation secondary to injury or obesity. Chondrocytes perceive physical signals from their environment using a variety of mechanisms, including ion channels, integrin-mediated connections to the extracellular matrix that involve membrane, cytoskeletal and intracellular deformation. An improved understanding of the biophysical and molecular pathways involved in chondrocyte mechanotransduction can provide insight into the development of novel therapeutic approaches for osteoarthritis.

Biomechanical factors in osteoarthritis.

Alterations in Cartilage in Osteoarthritis The morphologic changes in joints affected by osteoarthritis were identified in writings of the Hunter brothers over 200 years ago.88 Over the intervening...

The Reaction of Articular Cartilage to Injury and Osteoarthritis

Objective. To characterize the doseresponsiveness of morphologic and biochemical chondral changes relative to mobility in mono-iodoacetate (MIA)-induced osteoarthritis (OA) in rats.

Methods. Rat mobility was assessed by biotelemetry. Articular lesions were characterized by macroscopic and histologic examinations. Cartilage proteoglycan metabolism was evaluated by the 1,9-dimethylmethylene blue dye binding assay and by radiosulfate incorporation in patellar cartilage.

Results. Spontaneous locomotor activity was rapidly, transiently, and dose-dependently decreased after MIA injection into rat knees (primary response). Thereafter, only high doses (0.3 mg and 3.0 mg) led to a secondary progressive long-term loss of spontaneous mobility on day 15, when subchondral bone was exposed. These 2 doses resulted in significant changes in cartilage proteoglycan concentration at day 15 and a strong inhibition of anabolism in the peripheral patellae by day 2, contrasting with the effects of lower doses (0.01, 0.03, and 0.1 mg).

Conclusion. When a sufficient dose of MIA is used, this model can easily and quickly reproduce OA-like lesions and functional impairment in rats, similar to that observed in human disease. These parameters, as well as proteoglycan metabolism, could serve as indicators for studying chondroprotective drugs, or for evaluating the ability of imaging techniques to detect and evaluate chondral lesions.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/art.1780400917

Mono‐iodoacetate‐induced experimental osteoarthritis. A dose‐response study of loss of mobility, morphology, and biochemistry

Degenerative lesions characterized by osteochondrophyte spur formation and cartilage degeneration were induced by partial meniscectomy in the rabbit knee. Cartilage degenerative lesions included ulceration, fissure and cyst formation, and diminished concentration of matrix proteinpolysaccharide. Proliferation of chondrocytes represented efforts at repair. Osteophytes increased in size with time. Changes resembled certain components of degenerative joint disease. The partial meniscectorny animal may be useful in studies of osteoarthritis pathogenesis, pathology and treatment.

https://www.onlinelibrary.wiley.com/doi/pdf/10.1002/art.1780160317

Experimentally induced degenerative joint lesions following partial meniscectomy in the rabbit.

Intraarticular injections of triamcinolone acetonide resulted in deleterious changes in living rabbit articular knee cartilage. These changes were characterized by an increased frequency of chondrocyte nuclear degeneration and prominent cyst formation as compared with control animals. Degenerative changes were localized to the cartilage of the medial tibial plateau. This localization may be related to the different histologic pattern seen in this cartilage surface as compared to other areas of the knee. The correlation between certain pre-existing patterns of cartilage histology and susceptibility to degenerative change may provide a clue to the localization of degenerative joint disease in humans.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/art.1780130304

James Sammarco

Papers

Experimentally induced degenerative joint lesions following partial meniscectomy in the rabbit.

Experimentally induced corticosteroid arthropathy