Thickness distribution of the subchondral mineralization zone of the trochlear notch and its correlation with the cartilage thickness: an expression of functional adaptation to mechanical stress acting on the humeroulnar joint?

Abstract

Background: The thickness of cortical bone and the density of cancellous bone have been shown to reflect local mechanical stress. However, little is known whether this also applies to the thickness of the subchondral mineralization zone (SMZ). Since the humeroulnar joint may be regarded as a model of bicentric load transmission, we examined the thickness distribution of the SMZ of the trochlear notch.

Methods: Fourteen trochlear notches were examined. Eight joint surfaces of these ulnae were completely divided, 4 incompletely subdivided, and 2 remained undivided. After embedding, sagittal sections were prepared. The thickness distributions of SMZ and cartilage were measured, graphically reconstructed, and the correlation between the two calculated for each joint.

Results: The thickness of the SMZ lies between 120 and 1,400 microns. Regular patterns were observed with ventral and dorsal maxima, with close correlations between the type of joint and the thickness distribution of the SMZ. The cartilage thickness varied between 350 and 2,000 microns. The pattern of cartilage thickness differed significantly from that of the SMZ. The mean correlation coefficient between SMZ and cartilage thickness was 0.3.

Conclusions: The SMZ thickness depends upon the type of joint and appears to be an expression of the local loading history of the SMZ. The bicentric transmission of force at the humeroulnar joint is reflected in the bicentric distribution of SMZ thickness. A possible explanation for the different distributions of SMZ and cartilage could be the differing types of local mechanical stress acting on bone and cartilage, and/or the different reactions of osteocytes and chondrocytes.