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.

We could show that the distribution of cartilage thickness in the glenohumeral joint is not homogenous and that there exist several reproducible patterns. Evaluation of cartilage thickness in the glenohumeral joint is of high interest in basic and clinical research.

The objective of this study was to determine experimentally the effect of individual variations in articular surface geometry on the shoulder joint pressure distribution in functionally important arm positions. The location and size of the load-bearing areas and maximal pressures of 10 cadaver shoulder joints were examined at 30 degrees, 90 degrees, and 150 degrees of abduction (+/-90 degrees external rotation) and 120 degrees flexion with pressure-sensitive film. Only parts of the glenoid cavity were involved in the load transfer, some specimens showing central and other bicentric (superior-inferior) pressure maxima during abduction and flexion. The load-bearing areas were more central at external rotation, suggesting that the humeral head is not a perfect sphere. The maximal pressure was recorded at 90 degrees of abduction with 90 degrees external rotation, with 5.1 MPa for the elevation for single- and >10 MPa for double-arm weight. The study demonstrates that shoulder joint pressure cannot be calculated analytically but depends on subtle variations of joint incongruity.

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