Prevalence of Fusion Between Adjacent Thoracic Spinous Processes in Adult Cadavers

INTRODUCTION: Thoracic vertebrae play a crucial role in spinal stability and the protection of the spinal cord. Thoracic spinous process fusion, whether congenital or acquired, can affect spinal biomechanics and complicate surgical procedures. Thoracic spinous process fusion is an anatomical variation with potential clinical significance; however, its prevalence and distribution remain underreported. This study aimed to determine the prevalence and vertebral-level distribution of thoracic spinous process fusion in adult cadavers. METHODS: A cross-sectional observational cadaveric study was conducted on 30 formalin-fixed adult cadavers (15 males, 15 females) aged 60-95 years. After dissection and removal of soft tissues, the thoracic spinous processes from T1 to T12 were examined for osseous fusion between the adjacent vertebrae. Fusion was defined as complete bony continuity without interspinous gaps or fibrous tissues. The presence of fusion and vertebral levels was documented. Descriptive statistics and Fisher's exact tests were used for the analyses. RESULTS: Thoracic spinous process fusion was observed in five of 30 thoracic spine specimens (360 thoracic vertebrae) (16.7%), with two men (6.7%) and three women (10.0%) affected. Fusion occurred at the T3-T4, T6-T7, T9-T12, and T11-T12 levels, with T11-T12 showing the highest frequency (6.7%). No statistically significant sex differences were found (p=1). All fused spinous processes demonstrated complete bony continuity without the presence of fibrous tissue. CONCLUSION: Thoracic spinous process fusion is a notable anatomical variation, with a prevalence of 16.7% in the adult cadaveric sample. Awareness of its prevalence and localization can assist surgeons in preoperative planning and intraoperative level identification, thereby reducing surgical errors and improving patient outcomes.