2015 ISAKOS Biennial Congress ePoster #1512

Correlation of Dynamic Blunt Impact Testing, Histopathology and Visual Macroscopic Assessment in Human Osteoarthritic Cartilage

Petr Kos, MD, Prague CZECH REPUBLIC
Ferdinand Varga, DSc, Prague CZECH REPUBLIC
Milan Handl, MD, PhD, Prof., Dubai, Dubai UNITED ARAB EMIRATES
Jakub Kautzner, MD, Prague CZECH REPUBLIC
Václav Chudácek, DSc, PhD, Prague CZECH REPUBLIC
Milan Drzik, MD, Bratislava SLOVAKIA
Ctibor Povysil, Prof., Prague CZECH REPUBLIC
Tomas Trc, Prof., MD, PhD, Prague CZECH REPUBLIC
Evzen Amler, Prague Czech Republic
University Hospital Motol, Prague, CZECH REPUBLIC

FDA Status Not Applicable

Summary: Osteochondral samples were obtained during TKR, evaluated macroscopically, histologically and tested by dynamic blunt impact method. Normal stress, dissipated energy, tangent modulus, stiffness were evaluated and relation of acting force-deformation expressed by loading diagrams. Evaluation of energy dissipation appears to be a promising approach to distinguish level of cartilage degeneration.

Abstract:

Objectives
Articular cartilage has unique mechanical properties due to its composition that optimize transmission of load to subchondral bone. Degradation of cartilage resulting from osteoarthritis influences its functional properties. Improved staging of cartilage degeneration is required for prognosis and early treatment, particulary in low grades when minimal surface damage is visible. We examined correlation of dynamic mechanical properties of cartilage with histological findings and macroscopic visual score.

Materials And Methods

14 patients were included in our study (mean age 71.2 years (56-84); 5 men, 9 women; 4 right, 10 left knees). Osteochondral samples (6 mm diameter, cylindrical) were obtained during total knee joint replacement from lateral and medial condyle of femur and tibia. 2 samples were harvested from the same place for histological and biomechanical testing. Prior to mechanical testing, samples were macroscopically classified following International Cartilage Repair Society (ICRS). Dynamic blunt impact testing was used, response to a single impact evaluated. Parameters of loading resembled physiological cartilage loading. Sample deformation was read simultaneously by a sensitive piezoelectric accelerometer and laser Doppler vibrometer. Relation of acting force vs. deformation was expressed by loading diagrams. Normal stress, dissipated energy, tangent modulus and stiffness at 1 MPa stress were evaluated. Histological examination was performed on formalin-fixed parafin-embedded decalcinated samples. Slides were stained using hematoxylin-eosin, classified following ICRS visual histological scale.

Results

Regarding individual histological ICRS features, significant differences were found in dissipated energy values as well as related specific damping capacity for features 1, 2 and 3 (cartilage surface, extracellular matrix, cell distribution). No other mechanical characteristics correlated significantly with the histological score (T-test, p>0.05). Significant correlation was found between the macroscopic ICRS score, specific damping capacity and dissipated energy (ANOVA, p<0.01). Neither stiffness nor elasticity modulus values followed the macroscopic classification. Mean values of specific damping capacity increased between macroscopic grades 0-1 and 1-2 by 11.3% and 18.6% respectively. It implies that this material characteristic could serve for distinguishing between early stages of cartilage deterioration. Though no correlation between cartilage sample thickness and total histological score was proved, strong relation was found between energy dispersed in unit volume – relative dissipated energy and thickness (p<0.001, R2=0,69).

Conclusions

Among mechanical quantities characterizing cartilage, those dealing with part of compressive energy lost within the tissue were so far neglected. The current standard for staging cartilage degeneration is histology requiring invasive sample harvesting and therefore is not suitable in vivo. Clinical cartilage status examination is based on arthroscopic visual evaluation of the articular surface that gives no information about the tissue morphology. In cartilage with low grade of macroscopic degradation (ICRS 0-1) histopathologic findings varies a lot. Targeted treatment esp. of low grade arthritis demands on early diagnosis and requires improved tools for less invasive and more exact classification of cartilage status. According to our results, mechanical testing evaluating energy dissipation appears to be a promising approach.