Comparison of transverse process and laminar resistance in thoracic spinal fixation

We measuredin vitro the maximal rupture force of lamina and transverse apophyses in the thoracic spine. Nine human thoracic spines were sampled. 67 vertebrae were tested. For each vertebra, attachments alternate on the lamina and the transverse apophyses. In every case of laminar attachment, it is the pedicles which break first. The maximal average rupture force is 628 ± 280 newtons. In transverse attachments, it is the transverse vertebrae which break most frequently. The maximal average rupture force is 479 ± 235 newtons. In a vertebra by vertebra analysis of maximal rupture force, the most fragile are T5 and T6, and the most solid is T1. We found the same maximal rupture force for laminae as appears in the literature. However, we found a higher maximal rupture force for the transverse processes (three-quarters those of the laminae). This affirms our surgical technique in fixing neuromuscular scolioses, using T1 to T8 transverse attachments. With good strength, this avoids all neurological risk, reduces bleeding and the length of operations. Similarly, the fragility of T5 and T6 and the solidity of T1 corroborate a review of the literature which demonstrates that thoracic vertebrae fractures are most frequent at T5 and T6 and rare at T1.