S37  Parallel session
Soft Tissue Biomechanics – Cartilage

07-Jul-2015 15:20 17:00
 
 
Abstract: O 187
SITE-SPECIFIC CHANGES IN CELL BIOMECHANICS AND CARTILAGE COMPOSITION IN MATURE RABBIT KNEE JOINTS 3 DAYS AFTER A PARTIAL MENISCECTOMY

Introduction
Surgical operations that cause instabilities in the knee joint, such as partial menisectomy (PM), are commonly used in studying the progression of osteoarthritis [Colombo, 1983]. It is not known whether changes in chondrocyte biomechanics and tissue composition occur 3 days after a PM in the rabbit knee joint.

Methods
Fifteen New Zealand White rabbits (13±1 month) were divided into surgery (n=10) and control (n=5) groups. A PM of the meniscus in the lateral compartment of the rabbit knee joint was performed in a randomly chosen knee for each surgery group rabbit, and these knee joint tissues were harvested 3 days after surgery. All control group rabbit knees were harvested. Harvested sites included the patella, groove, femoral condyles and tibial plateaus. Confocal laser scanning microscopy (CLSM) with a custom-build indentation system enabled capturing optical sections from cartilages before and after indentation at steady state (2 MPa for 20 minutes) using conjugated Dextran as matrix stain. The chondrocytes were cropped, reconstructed, and their volumes were calculated [Han, 2009], and relative cell volume changes due to compression were analyzed. After CLSM, histological sections of all tissue sites were prepared, and regions of indentation were analyzed with digital densitometry [Kiviranta, 1985] and polarized light microscopy [Rieppo, 2008] for proteoglycan (PG) content and collagen fibril orientation, respectively. Profiles were acquired from the tissue surface to the bone. Profiles were interpolated to 100 points and means from the first 20 points were calculated. Group comparisons were performed with Student’s T-tests (p < 0.05).

Results
Chondrocyte biomechanics were altered in a highly site-dependent manner (figure 1A). Only in the lateral plateau, cell volume change was not affected by the surgery. The collagen orientation remained unchanged at all sites (p > 0.05), whereas the superficial PG content (up to 20 % of tissue depth) was decreased in all but one location of the knee joint, the lateral plateau (figure 1B).

Figure 1: A) Relative cell volume changes due to indentation from each site. B) Superficial PG content up to 20% of tissue depth (from surface). A clear relationship between PG loss and altered cell biomechanics is observed. Black bars denote significant differences between groups (p < 0.05)

Conclusions
These results demonstrate that biomechanical responses of chondrocytes are highly site-specific and are affected as early as 3 days following a PM. The results further suggest that the changes in cell biomechanics reflect alterations occurring in the PG content, whereas the collagen orientation remains unaltered due to the surgery. The lateral plateau was the only site where no changes were observed. Without intervention, alterations in cell biomechanics and PG loss may lead to more severe degenerative changes in cartilage and the development of osteoarthritis.

References
Colombo et al, Arthritis Rheum, 26(7):875-86, 1983. Han et al, J R Soc Inter, 7(47):895-903, 2009. Kiviranta et al, Histochem, 82(3):249-55, 1985. Rieppo et al, Microsc Res Tech, 71(4):279-87, 2008.

 
Co-authors
A. Ronkainen1, J. Fick1, A. Sawatsky2, W. Herzog2, R. Korhonen1.
1University of Eastern Finland, Department of Applied Physics, Kuopio, Finland.
2University of Calgary, Human Performance Laboratory- Faculty of Kinesiology, Calgary, Canada.

 

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