Evaluation of subchondral bone mineral density associated with articular cartilage structure and integrity in healthy equine joints with different functional demands

Chad W. Lewis Department of Mechanical Engineering, College of Engineering, Colorado State University, Fort Collins, CO 80523.
Present address is Department of Bioengineering, Jacobs School of Engineering, University of California-San Diego, La Jolla, CA 92093.

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Amanda K. Williamson Department of Bioengineering, Jacobs School of Engineering, University of California-San Diego, La Jolla, CA 92093.

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Albert C. Chen Department of Bioengineering, Jacobs School of Engineering, University of California-San Diego, La Jolla, CA 92093.

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Won C. Bae Department of Bioengineering, Jacobs School of Engineering, University of California-San Diego, La Jolla, CA 92093.

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Michele M. Temple Department of Bioengineering, Jacobs School of Engineering, University of California-San Diego, La Jolla, CA 92093.

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Van W. Wong Department of Bioengineering, Jacobs School of Engineering, University of California-San Diego, La Jolla, CA 92093.

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Gayle E. Nugent Department of Bioengineering, Jacobs School of Engineering, University of California-San Diego, La Jolla, CA 92093.

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Susan P. James Department of Mechanical Engineering, College of Engineering, Colorado State University, Fort Collins, CO 80523.

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Donna L. Wheeler Department of Mechanical Engineering, College of Engineering, Colorado State University, Fort Collins, CO 80523.

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Robert L. Sah Department of Bioengineering and Whitaker Institute of Biomedical Engineering, Jacobs School of Engineering, University of California-San Diego, La Jolla, CA 92093.

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Chris E. Kawcak Department of Clinical Sciences, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, CO 80523

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Abstract

Objective—To determine and correlate subchondral bone mineral density and overlying cartilage structure and tensile integrity in mature healthy equine stifle (low magnitude loading) and metacarpophalangeal (high magnitude loading) joints.

Animals—8 healthy horses, 2 to 3 years of age.

Procedure—Osteochondral samples were acquired from the medial femoral condyle (FC) and medial trochlear ridge (TR) of the stifle joint and from the dorsal (MC3D) and palmar (MC3P) aspects of the distal medial third metacarpal condyles of the metacarpophalangeal joint. Articular cartilage surface fibrillation (evaluated via India ink staining) and tensile biomechanical properties were determined. The volumetric bone mineral density (vBMD) of the underlying subchondral plate was assessed via dualenergy x-ray absorptiometry.

Results—Cartilage staining (fibrillation), tensile moduli, tensile strength, and vBMD were greater in the MC3D and MC3P locations, compared with the FC and TR locations, whereas tensile strain at failure was less in MC3D and MC3P locations than FC and TR locations. Cartilage tensile moduli correlated positively with vBMD, whereas cartilage staining and tensile strain at failure correlated negatively with vBMD.

Conclusions and Clinical Relevance—In areas of high joint loading, the subchondral bone had high vBMD and the articular cartilage surface layer had high tensile stiffness but signs of structural wear (fibrillation and low failure strain). The site-dependent variations and relationships in this study support the concept that articular cartilage and subchondral bone normally adapt to physiologic loading in a coordinated way. (Am J Vet Res 2005;66:1823–1829)

Abstract

Objective—To determine and correlate subchondral bone mineral density and overlying cartilage structure and tensile integrity in mature healthy equine stifle (low magnitude loading) and metacarpophalangeal (high magnitude loading) joints.

Animals—8 healthy horses, 2 to 3 years of age.

Procedure—Osteochondral samples were acquired from the medial femoral condyle (FC) and medial trochlear ridge (TR) of the stifle joint and from the dorsal (MC3D) and palmar (MC3P) aspects of the distal medial third metacarpal condyles of the metacarpophalangeal joint. Articular cartilage surface fibrillation (evaluated via India ink staining) and tensile biomechanical properties were determined. The volumetric bone mineral density (vBMD) of the underlying subchondral plate was assessed via dualenergy x-ray absorptiometry.

Results—Cartilage staining (fibrillation), tensile moduli, tensile strength, and vBMD were greater in the MC3D and MC3P locations, compared with the FC and TR locations, whereas tensile strain at failure was less in MC3D and MC3P locations than FC and TR locations. Cartilage tensile moduli correlated positively with vBMD, whereas cartilage staining and tensile strain at failure correlated negatively with vBMD.

Conclusions and Clinical Relevance—In areas of high joint loading, the subchondral bone had high vBMD and the articular cartilage surface layer had high tensile stiffness but signs of structural wear (fibrillation and low failure strain). The site-dependent variations and relationships in this study support the concept that articular cartilage and subchondral bone normally adapt to physiologic loading in a coordinated way. (Am J Vet Res 2005;66:1823–1829)

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