Sacroiliac joint bridging: Demographical and anatomical aspects

Study Design. A descriptive study of the association between sacroiliac joint bridging ( SIB) and age, gender, laterality, and ethnic origin in a normal skeletal population. The effectiveness of radiographs in identifying SIB was also evaluated. Objectives. To characterize the phenomenon of SIB demographically and anatomically and to evaluate the validity of diagnosis based on roentgenograms. Summary and Background Data. Although SIB is an important diagnostic parameter in many spinal diseases, the type of association between them has never been established. Furthermore, the extent of SIB in humans and its relationship to demographic parameters await osteological research as radiograph studies hamper the results. Methods. Two thousand eight hundred and forty-five skeleton pelves were examined for SIB. Extent and laterality were recorded. Ten pelves ( 5 with SIB and 5 without) were X-rayed and the roentgenograms given to radiologists for evaluation. Results. Sacroiliac bridging was present in 12.27% of all males, contrasted with only 1.83% of females ( P < 0.001). SIB was independent of ethnic origin ( P = 0.0535) but was age-dependent ( r = 0.985; P = 0.0001). Bridging was present bilaterally in 38.6% of the individuals and in the superior region in 72.4%. Diffuse bridging ( areas 1 - 6) was present in only 2.3% of the individuals. Radiologic examination was insensitive to diagnosis of SIB. Conclusions. SIB is a common, but predominantly male phenomenon. Its occurrence is age-dependent and ethnicity independent. Bridging occurs mainly on the superior aspect of the sacroiliac joint. The irregular shape and orientation of sacroiliac joints preclude definitely distinguishing normal versus bridged joints from roentgenograms. Our findings also negate the belief that bridging/ fusion of the sacroiliac joint represents the most severe form of osteoarthritis and mandate that they be separately recorded and that their significance be determined.