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Measurement of Articular Cartilage Surface Irregularity in Rat Knee Contracture
GUY TRUDEL, KO HIMORI, LOUIS GOUDREAU, and HANS K. UHTHOFF
ABSTRACT.
Methods. A total of 117 rat knees were either immobilized or sham-operated and harvested after 2, 4, 8, 16, or 32 weeks, and 11 knees were not operated. Standardized histologic sections were digitized and the contours of femoral and tibial cartilage surfaces were delineated. The rates of change in cartilage contour were calculated. Rate of change above a defined threshold constituted surface irregularity. Results. In non-operated knees, cartilage surface irregularity in femur and tibia amounted to 3.1 ± 0.5%. Immobilized knees showed significantly more irregularities than the sham-operated knees at all time points (2 weeks: 5.3 ± 0.6% vs 3.1 ± 0.4%; 4 weeks: 10.5 ± 0.9% vs 4.4 ± 0.9%; 8 weeks: 12.0 ± 1.8% vs 4.9 ± 0.2%; 16 weeks: 13.7 ± 2.0% vs 4.9 ± 0.4%; and 32 weeks: 13.8 ± 1.4% vs 3.4 ± 0.6%; all p < 0.05). No difference was observed between sham-operated and non-operated knees. Increasing duration of immobilization in weeks (t) significantly correlated with more surface irregularity, described by the logarithmic formula: % irregularity = 6.6 + 2.1 ln (t), (F = 59.3, p < 0.001). This formula showed that irregularity progressed rapidly after immobilization and plateaued after 8 weeks. Conclusion. We designed methods to quantify cartilage surface irregularity and applied them to a contracture model. Cartilage surface irregularities appeared after 2 weeks of immobilization and progressed rapidly to plateau after 8 weeks. Combined with microscopic magnetic resonance imaging, this measurement of cartilage surface irregularity may constitute a sensitive tool to detect cartilage degeneration clinically. (J Rheumatol 2003;30:2218-25) Key Indexing Terms:
CARTILAGE SURFACE
From the Bone and Joint Research Laboratory, Department of Medicine; Division of Physical Medicine and Rehabilitation; Division of Orthopaedic Surgery, University of Ottawa; and the Rehabilitation Engineering Department, The Rehabilitation Centre, Ottawa, Ontario, Canada. Supported in part by the Physicians of Ontario through the PSI Foundation and by the Canadian Institutes of Health Research. G. Trudel, MD, MSc, Bone and Joint Research Laboratory and Division of Physical Medicine and Rehabilitation; K. Himori, MD, Bone and Joint Research Laboratory; L. Goudreau, Rehabilitation Engineering Department, The Rehabilitation Centre; H.K. Uhthoff, MD, Bone and Joint Research Laboratory and Division of Orthopaedic Surgery. Address reprint requests to Dr. G. Trudel Department of Medicine, University of Ottawa, 505 Smyth Road, Ottawa, Ontario K1H 8M2, Canada. Submitted August 28, 2002; revision accepted February 28, 2003. |