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

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 dual-energy 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.

Compressive biomechanical properties of human nasal septal cartilage.

BACKGROUND: Nasal septal cartilage is frequently used in nasal reconstruction and is a common source of chondrocytes for cartilage tissue engineering. The biomechanical properties of septal cartilage have yet to be fully defined and this limits the ability to compare it to the various alternative tissue-implant materials or tissue-engineered neocartilage. Given the unique structure and orientation of the septum within the nose, we sought to investigate anisotropic behaviors of septal cartilage in compression and correlate this to the concentration of glycosaminoglycans (GAG) and collagen within the cartilage. METHODS: Human nasal septal cartilage specimens were tested in confined compression, with each sample analyzed in a medial orientation and also either a vertical or caudal-cephalic orientation, with the order of tests randomized. The equilibrium confined compression (aggregate) modulus, HAO, and the permeability, kp, at different offset compression levels were obtained for each compression test. After testing, the cartilage samples were solubilized, and the concentrations of GAG and collagen were obtained. RESULTS: Forty-nine compression tests (24 medial, 12 vertical, 13 caudal-cephalic) were run on cartilage specimens obtained from 21 patients. There was a significant effect of orientation on compression modulus, HAO, with the vertical (0.7 +/- 0.12 MPa) and caudal-cephalic (0.66 +/- 0.01 MPa) orientations being significantly stiffer (p = 0.05) than the medial orientation (0.44 +/- 0.04 MPa). There was a trend of an orientation effect on kp at 15% offset compression (p = 0.12) and a borderline significant effect of orientation on kp at 30% offset compression (p = 0.05), demonstrating the M orientation to be more permeable than both the vertical and caudal-cephalic orientations. Both univariate and multivariate analysis did not demonstrate a significant effect of order of compression, age, gender, thickness, dry/wet weight, GAG, or collagen on either HAO, or kp values (p > 0.05). CONCLUSION: This study provides new information on the compressive properties of septal cartilage along different axes of compression. The results demonstrate that human septal cartilage is anisotropic; the compressive stiffness is higher in the vertical and caudal-cephalic orientations than in the medial orientation. Additionally, the medial orientation tends to have the greatest permeability. The data obtained in this study provide a reference to which various craniofacial reconstruction materials and tissue-engineered neocartilage can be compared.