A Biomechanical and Structural Comparison of Articular Cartilage and Subchondral Bone of the Glenoid and Humeral Head.

Background: The underlying cause of glenohumeral arthritis is poorly understood. Glenohumeral arthrosis patterns have been classified and described, and differential contact stresses within the joint have been implicated as a cause of joint degeneration, but the intrinsic cause of degeneration patterns in the glenohumeral joint (GHJ) remains largely unknown.

Purpose/hypothesis: The purpose of this study was to assess morphological and mechanical differences in articular cartilage (AC) and subchondral bone (SCB) of the glenoid and humeral head in matched cadaveric specimens. We hypothesized that there would be significant zone-dependent differences between the intrinsic characteristics (AC thickness, SCB thickness, compressive forces) of the glenoid and humeral head.

Study Design: Descriptive laboratory study.

Methods: Ten human cadaveric GHJs (mean age, 60.2 years) were dissected to expose articular surfaces to facilitate biomechanical testing. A 2-mm and 6-mm osteochondral plug was harvested at 5 zones (central, anterior, posterior, inferior, superior) on the glenoid and humeral head (N = 200 plugs). Each 2-mm core was histologically sectioned and stained with hematoxylin and eosin. AC thickness measurements were taken using light microscopy. The 6-mm plugs were imaged using micro-computed tomography to measure SCB thickness. After imaging, AC specimens were removed from the SCB and tested in confined compression. The compressive aggregate modulus (H), compressive stiffening coefficient (β), and compressive modulus at 16% strain (H) and at 50% strain (H) were calculated.

Results: The overall AC thickness was significantly greater on the glenoid. The glenoid also had significantly thicker AC at the inferior, posterior, and superior zones as well as significantly higher SCB thickness overall and significantly greater SCB thickness at the anterior and central zones. The glenoid had significantly greater overall H and H values at the superior zone and had a significantly greater overall compressive stiffening coefficient (β).

Conclusion: The glenoid had thicker AC, thicker SCB, and greater compressive stiffness at high strain.

Clinical Relevance: These intrinsic differences may help better elucidate the cause of differential degeneration patterns between the glenoid and humeral head.