Vertebral shape and spinal osteoarthritis in humans: A 3D analysis

Spinal osteoarthritis (SOA) is an important contributor to back pain, but the factors that lead to its development are poorly understood. Here, we report a study designed to test the idea that vertebral shape influences the probability of developing SOA. We used geometric morphometrics to compare the 3D shape of the last thoracic (T12) and the first lumbar vertebrae (L1) of adults with and without SOA. The sample was drawn from archaeological and documented skeletons, consisting of 143 T12s and 136 L1s. Two linked hypotheses were tested. The first was that there is an association between vertebral shape and SOA. The second was that the association between in the first hypothesis exists because the risk of SOA is increased by a morphotype that includes more sagittal zygapophyseal facets and smaller interfacet distances. This hypothesis was informed by the results of two previous studies. The analyses supported the first hypothesis. MANOVAs and DFAs indicated that the vertebrae of individuals with SOA tend to have a significantly different morphotype to unaffected individuals. In contrast, the results of the analyses only partially supported the second hypothesis. PCA-derived wireframes upheld only one of the predicted differences, smaller interfacet distances. The other predicted difference more sagittal facets in affected individuals was not supported. Unexpectedly, the analyses identified several other traits that distinguish the vertebrae of individuals with SOA. All of these traits can be plausibly linked to suboptimal biomechanics for the spine. Overall, the study supports the idea that vertebral shape can increase the probability of developing SOA.