Swiss National Science Foundation, Hospital of Aarau, University of Basel, Gottfried und Julia Bangerter-Rhyner Foundation, Hippocrate Foundation, and Nora van Meeuwen-Häfliger Foundation.

No abstract

BackgroundRadial mismatch, glenohumeral conformity ratios and differences between cartilaginous and osseous radii highly depend on the measured plane. The comparison of cartilaginous radii between humeral head and glenoid in different planes provides new information to understand the degree of conformity during abduction of the upper limb.MethodsTo investigate the radii, CT-images in soft-tissue kernel of 9 specimen were analysed using an image visualization software. Statistical analysis of the obtained data was performed using the t-test.ResultsMeasurements of the radii in the glenoid revealed a significantly larger radius for bone than cartilage, whereas for the humeral head the opposite was the case. Highest ratios for cartilage in the transverse plane were found in the inferior and central areas of the joint surface, whereas the smallest ratios were found in the superior area. The radial mismatch varied between 0.1 mm and 13.6 mm, depending on the measured plane.ConclusionsThe results suggest that in abduction, the cartilaginous guidance of the humeral head decreases. This might permit the humeral head an anterior-posterior shifting as well as superior-inferior translation. Surgical reconstruction of the normal glenohumeral relationships necessitates precise information about the glenohumeral morphology to ensure proper sizing and correct placement of prosthetic components and osteochondral allografts.

Subchondral mineralization represents the loading history of a joint and can be measured in vivo using computed tomography osteoabsorptiometry. Different mineralization patterns in the glenohumeral joint have been explained by the principle of physiologic incongruence. We sought to support this explanation by measurement of mineralization, radii, and cartilage thickness in 18 fresh shoulder specimens. We found three mineralization patterns: bicentric, monocentric anterior, and monocentric central. Mean radii of the glenoids were 27.4 mm for bicentric glenoids, 27.3 mm for monocentric anterior, and 24.8 mm for monocentric central glenoids. Cartilage thickness measurement revealed the highest values in anterior parts; the thinnest cartilage was found centrally. Our findings support the principle of a physiologic incongruence in the glenohumeral joint. Bicentric mineralization patterns exist in joints consisting of more flat glenoids compared to the corresponding humeral head. Monocentric distribution with a central maximum was found in specimens with glenoids being more curved, indicating higher degrees of congruence, which might represent an early stage of degenerative disease. The obtained information might also be important for implant fixation in resurfacing procedures or to achieve the best possible fit of an osteochondral allograft in the repair of cartilage defects. ß