B. Nelson (Fort Collins, US)
Colorado State University Clinical SciencesPresenter Of 2 Presentations
18.3.8 - Ovine knee cartilage differs in structural and functional properties across articular surfaces
Abstract
Purpose
Articular cartilage is a critical joint tissue. Once damaged, it has limited repair potential and large efforts have gone towards investigating emerging repair strategies. Sheep are commonly used because of their ability to translate results to human orthopedic conditions, although it is not known if variation in structural and functional properties exist across the surface. Therefore, the purpose of this study is to characterize cartilage heterogeneity as a function of location in adult ovine stifles by measuring mechanical performance (creep behavior), biochemical properties (GAG content), and thickness across the femoral condylar and trochlear surfaces.
Methods and Materials
In ten stifle (knee) joints, cartilage regions of interest (ROIs) were generated within each femoral trochlea (8 ROIs) and condyle (6 medial, 6 lateral). Each cartilage ROI was evaluated with macroindentation testing, dimethylmethylene blue assay and µCT scan to determine percent creep, GAG content and cartilage thickness, respectively. Results of each variable were mapped based upon anatomical locations and compared using a mixed model ANOVA. Significance was defined as P<0.05.
Results
For percent creep (Figure 1), ROIs within each knee location were significantly different (lateral condyle: P<0.0001; medial condyle: P<0.0001; trochlea: P=0.0004). Percent creep on the medial femoral condyle was significantly lower than the femoral trochlea and lateral condyle (both P<0.0001). For GAG content (Figure 2), there were significant differences between ROIs within the following knee locations: lateral condyle (P<0.0001), medial condyle (P=0.01) and trochlea (P<0.0001). When evaluated collectively, differences in GAG content between knee locations were not detected. Medial femoral condyle cartilage was significantly thicker than the femoral trochlea and lateral condyle (P<0.0001).
Conclusion
Cartilage mechanical properties, biochemical composition and thickness vary across distal femoral joint surfaces. Clinicians and researchers working with ovine cartilage should recognize this potential variability and standardize cartilage sites accordingly to obtain accurate results based on study goals.
23.2.7 - Cationic contrast enhanced computed tomography characterizes articular cartilage in an equine impact model
Abstract
Purpose
Current imaging methods are unable to detect subtle articular cartilage injury. Loss of glycosaminoglycans (GAGs) is a hallmark of early osteoarthritis. Cationic contrast enhanced computed tomography (CCECT) is a new diagnostic method capable of predicting GAG content and the compressive strength of normal cartilage, but its capacity to distinguish normal from early degenerative cartilage is unknown. The objectives of this study are to induce subtle articular cartilage injury in vivo and use CCECT to distinguish normal from degenerative cartilage. We hypothesize that CCECT attenuation of articular cartilage will correlate with its biochemical, mechanical and histological properties.
Methods and Materials
Mechanical impact injury (41 MPa, 32.7 mm2) was applied to the equine femoral trochlear surface in vivo to establish subtle cartilage degeneration using horse-matched and site-matched controls. CCECT was performed in vivo (clinical) and postmortem (microCT). Articular cartilage was characterized by glycosaminoglycan (GAG) content, biochemical moduli and histological scores. Subchondral bone beneath each cartilage site was characterized by volume density (BV/TV) and trabecular number (Tb.N.), thickness (Tb.Th.) and spacing (Tb.Sp.).
Results
CCECT attenuation (microCT) of cartilage correlated with GAG (r=0.74, P<0.0001), equilibrium compressive modulus (Eeq)(r=0.79, P<0.0001) and safranin-O histological score (r=-0.66, P<0.0001) of cartilage (Figure 1), and correlated with BV/TV (r=0.37, P=0.0005), Tb.N. (r=0.39, P=0.0003), Tb.Th. (r=0.28, P=0.0095) and Tb.Sp. (r=-0.44, P<0.0001) of bone. Mean [95% CI] CCECT attenuation at the impact site (2215 [1987, 2443] Hounsfield Units [HUs]) was lower than site-matched controls (2836 [2490, 3182] HUs, P=0.036) and corresponded with safranin-O stain distribution (Figure 2). Clinical cationic CECT attenuation correlated with GAG (r=0.23, P=0.049), Eeq (r=0.26, P=0.025) and safranin-O histology score (r=-0.32, P=0.0046).
Conclusion
Cationic CECT (microCT) reflects biochemical, mechanical and histological articular cartilage properties enabling segregation of subtly degenerated from healthy tissue. CCECT also reflects bone morphometric properties on CT. Cationic CECT is capable of characterizing articular cartilage properties in clinical scanners.