VARIATIONS IN THE MECHANICAL-PROPERTIES OF CARTILAGE FROM THE CANINE SCAPULOHUMERAL JOINT

Objective-To measure the intrinsic material properties of scapulohumer al joint cartilage in adult dogs and determine whether regional differ ences exist within or between the humeral and glenoid cartilages. Samp les-Paired shoulder joints from 7 clinically normal adult dogs. Proced ure-An automated indentation apparatus was used to obtain the intrinsi c mechanical properties of the cartilage at 7 sites on each joint surf ace. Results-Topographic variations in mechanical properties of the gl enoid and humeral cartilages were observed. The largest aggregate modu lus (H-A,) for the humerus was seen at the caudocentral site (0.92 MPa ) and for the scapula was seen at the centrocenter site (0.84 MPa). Th e mean shear modulus (mu) of humeral cartilage (0.23 MPa) was signific antly greater than that of the glenoid cartilage (0.19 MPa). The mean Poisson's ratio (nu) of humeral cartilage (0.24) was significantly sma ller than that for the glenoid cartilage (0.29). Mean humeral cartilag e aggregate modulus (0.71 MPa) was larger than the value for glenoid c artilage (0.67 MPa), but these differences were not significant. There were no significant differences in the compressive stiffness of the o pposing cartilage in the canine scapulohumeral joint. Conclusions-Diff erences in mechanical properties between opposing humeral and glenoid cartilages are not a cause of cartilage injury in the scapulohumeral j oint of adult dogs. The mechanical properties of cartilage from young dogs with open physes and incomplete subchondral bone plates may be di fferent from those of adult dogs.