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Research Papers

Streaming Potential-Based Arthroscopic Device is Sensitive to Cartilage Changes Immediately Post-Impact in an Equine Cartilage Injury Model

[+] Author and Article Information
A. Changoor, J. P. Coutu

Department of Chemical Engineering,  Institute of Biomedical Engineering, École Polytechnique de Montréal, P.O. Box 6079, Station Centre-Ville Montreal, QC, H3C 3A7, Canada

M. Garon, E. Quenneville

 Biomomentum Inc., 970 Michelin St. Suite 200, Laval, QC, H7L 5C1, Canada

M. B. Hurtig

Comparative Orthopaedic Research Laboratory, Ontario Veterinary College,  University of Guelph, Guelph, ON, N1G 2W1, Canada

M. D. Buschmann1

Department of Chemical Engineering,  Institute of Biomedical Engineering, École Polytechnique de Montréal, P.O. Box 6079, Station Centre-Ville Montreal, QC, H3C 3A7, Canada

1

Corresponding author.

J Biomech Eng 133(6), 061005 (Jun 21, 2011) (9 pages) doi:10.1115/1.4004230 History: Received December 30, 2010; Revised May 06, 2011; Posted May 16, 2011; Published June 21, 2011; Online June 21, 2011

Models of post-traumatic osteoarthritis where early degenerative changes can be monitored are valuable for assessing potential therapeutic strategies. Current methods for evaluating cartilage mechanical properties may not capture the low-grade cartilage changes expected at these earlier time points following injury. In this study, an explant model of cartilage injury was used to determine whether streaming potential measurements by manual indentation could detect cartilage changes immediately following mechanical impact and to compare their sensitivity to biomechanical tests. Impacts were delivered ex vivo, at one of three stress levels, to specific positions on isolated adult equine trochlea. Cartilage properties were assessed by streaming potential measurements, made pre- and post-impact using a commercially available arthroscopic device, and by stress relaxation tests in unconfined compression geometry of isolated cartilage disks, providing the streaming potential integral (SPI), fibril modulus (Ef), matrix modulus (Em), and permeability (k). Histological sections were stained with Safranin-O and adjacent unstained sections examined in polarized light microscopy. Impacts were low, 17.3 ± 2.7 MPa (n = 15), medium, 27.8 ± 8.5 MPa (n = 13), or high, 48.7 ± 12.1 MPa (n = 16), and delivered using a custom-built spring-loaded device with a rise time of approximately 1 ms. SPI was significantly reduced after medium (p = 0.006) and high (p<0.001) impacts. Ef, representing collagen network stiffness, was significantly reduced in high impact samples only (p < 0.001 lateral trochlea, p = 0.042 medial trochlea), where permeability also increased (p = 0.003 lateral trochlea, p = 0.007 medial trochlea). Significant (p < 0.05, n = 68) moderate to strong correlations between SPI and Ef (r = 0.857), Em (r = 0.493), log(k) (r = −0.484), and cartilage thickness (r = −0.804) were detected. Effect sizes were higher for SPI than Ef, Em, and k, indicating greater sensitivity of electromechanical measurements to impact injury compared to purely biomechanical parameters. Histological changes due to impact were limited to the presence of superficial zone damage which increased with impact stress. Non-destructive streaming potential measurements were more sensitive to impact-related articular cartilage changes than biomechanical assessment of isolated samples using stress relaxation tests in unconfined compression geometry. Correlations between electromechanical and biomechanical methods further support the relationship between non-destructive electromechanical measurements and intrinsic cartilage properties.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic of a right equine trochlea with 36 positions identified as either non-impacted controls (white) or impact sites. Impact stress levels included 17 MPa (red), 28 MPa (blue), and 49 MPa (yellow). The star indicates the position that was considered an outlier from results of biomechanical tests. The same site assignments were used for the left trochlea. Impact injury was created using a custom-built impactor device with a 6.45 mm diameter tip. Not to scale.

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Figure 2

Normalized SPI values (mean ± standard deviation) for non-impacted controls (n = 24), and sites receiving low (n = 16), medium (n = 15), and high (n = 16) impacts. Normalization involved dividing average post-impact SPI by average pre-impact SPI at each site. One site that received a medium impact was excluded because SPI measurements were inconsistent for both users and had a high coefficient of variation approaching 30%. Results from paired t-tests comparing pre- and post-impact SPI are indicated with (*) for statistically significant differences (p < 0.05) and (+) for statistical trends (p < 0.10).

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Figure 3

Biomechanical parameters obtained during unconfined compression testing including (A) fibril modulus, (B) permeability, (C) matrix modulus, and (D) cartilage thickness. * indicates statistically significant differences (p < 0.05) between control and impacted cartilage. Statistical differences between low or medium impact compared to high impact are identified with (^). Cartilage thicknesses were grouped on lateral and medial surfaces for comparison, # indicates p < 0.001.

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Figure 4

Effect sizes for electromechanical and biomechanical parameters. Effect sizes for SPI were calculated as a difference in pre- versus post-impact means divided by pooled standard deviation, while effect sizes for biomechanical parameters were calculated as a difference between control and impact means divided by pooled standard deviation. Biomechanical and electromechanical parameters from medial and lateral trochlear surfaces were combined for a total of n = 24 for non-impacted controls, n = 15 for low impact, n = 15 for medium impact, and n = 14 for high impact.

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Figure 5

Scatterplots of SPI versus biomechanical parameters obtained from unconfined compression testing. Correlations between SPI and (A) fibril modulus (r = 0.857, p < 0.0001, n = 68), (B) permeability transformed to log(k) (r = −0.484, p < 0.0001, n = 68), (C) matrix modulus (r = 0.493, p < 0.0001, n = 68), and (D) cartilage thickness (r = −0.804, p < 0.0001, n = 68).

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Figure 6

PLM images of full-thickness cartilage disks from (A and B) non-impacted control and (C and D) low, (E and F) medium, and (G and H) high impact groups. Scale bars are 250 μm.

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Figure 7

Safranin-O/Fast Green/iron hematoxylin stained images of full-thickness cartilage disks from (A and B) non-impacted control and (C and D) low, (E and F) medium, and (G and H) high impact groups. Scale bars are 500 μm in A, C, E, and G and 250 μm in B, D, F, and H.

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