Measurement of articular cartilage surface irregularity in rat knee contracture.
OBJECTIVE
To design novel quantitative methods to evaluate the irregularity of articular cartilage surface; and to apply these methods for assessment of surface irregularity in a rat knee contracture model.


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.


CONCLUSIONS
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.
Trudel
Guy
G
Bone and Joint Research Laboratory, Department of Medicine, University of Ottawa, 505 Smyth Road, Ottawa, Ontario K1H 8M2, Canada.
Himori
Ko
K
Goudreau
Louis
L
Uhthoff
Hans K
HK
D000818:Animals; D002358:Cartilage, Articular / Q000473:pathology*; D003286:Contracture / Q000209:etiology / Q000473:pathology*; D019417:Hindlimb Suspension / Q000009:adverse effects; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging; D008297:Male; D012372:ROC Curve; D051381:Rats; D017207:Rats, Sprague-Dawley; D013264:Stifle / Q000473:pathology*; D013499:Surface Properties