Purpose: The aetiology of primary omarthrosis is still unclear. Typical radiological changes are joint space narrowing and the development of caudal osteophytes. The objective of the study is the analysis of the joint space of the shoulder in four different age groups.

Materials and Methods: Retrospective analysis of n=342 standardized X-rays (2002–2009) (true ap, axillary). Inclusion criteria: normal adulthood group I (n=60), instability group II (n=53), calcifying tendonitis of the supraspinatus tendon group III (n=109), advanced primary omarthrosis group IV (n=120). Measurement of joint space at three levels (ap: superior, central, inferior; axillary: anterior, central, posterior). Two independent measurements. Statistical analysis SPSS 17.0: U-Test acc. Mann and Whitney. Bivariate correlation analysis (Spearman), partial correlation analysis, intraclass correlation coefficient.

Results: Mean age group I 17.84±1.54, group II 31.6±11.8, group III 48.2±8.0, group IV 66.43 ±9.74 (p=0.001). Measurement joint space: interobserver reliability excellent in the ap-projection (r=0.887–0.910) and in the axillary projection (r=0.879–0.886). Joint space group I: 4.79mm±0.84 superior ap, 4.28mm±0.75 central ap, 4.57mm±0.80 inferior ap, 6.59mm±1.44 anterior axillary, 6.12mm±1.09 central axillary and 7.03mm±1.17 posterior axillary; group II: 3.78mm±0.99 superior ap, 3.12mm±0.73 central ap, 3.38mm±0.80 inferior ap, 3.92mm±1.08 anterior axillary, 3.92mm±0.77 central axillary and 4.79mm±1.18 posterior axillary; group III: 3.43mm±1.06 superior ap, 2.87mm±0.80 central ap, 3.25mm±0.79 inferior ap, 3.95mm±0.83 anterior axillary, 3.34mm±0.84 central axillary and 4.05mm±0.84 posterior axillary; group IV: 2.00mm±1.40 superior ap, 1.47mm±1.07 central ap, 1.48mm±1.93 inferior ap, 3.01mm±2.22 anterior axillary, 1.08mm±1.12 central axillary and 1.17mm±1.04 posterior axillary. The differences between the four groups for the joint space width are all statistically significant with p< 0.001 (except the difference between group I and group II for ap-central, ap-inferior and axillary anterior).

There is a significant negative correlation (r= −0,579–0,813) between the joint space width and patients age at all measured levels in both projections (p< 0.001). This negative correlation is only little smaller (r= −0,430–0,655) but still clearly significant for all measurements, if the patients with present osteoarthritis (group III) are excluded.

Conclusion: The data of the study show a decrease of joint space width in group I–IV in all measurements. This effect is negatively correlated with age. The data suggest that the decrease in joint space with loss of cartilage cover is an age-dependant process which is independent from the presence of osteoarthritis. This is in contrast to historical findings but in concordance with recent basic studies about cartilage ageing.