Research of a Safe and Simplified Intertransverse Process Approach for the Lower Thoracic Interbody Surgery.

Objective: To assess a safe surgical approach for intertransverse process lower thoracic intervertebral body fusion (ITIF) based on measurements from enhanced three-dimensional CT reconstruction, cadaver simulated operation, and patient operation.

Methods: Enhanced three-dimensional CT image reconstruction was performed for 20 healthy volunteers on thoracic segments T8-T12. The length of the transverse process (LTP), distance between the upper and lower transverse processes (DULTP), remote distance of the transverse process (RDTP), height of the extraforaminal intervertebral space (HEIS), and oblique diameter of the intervertebral space (ODIS) were measured and recorded. The blood vessels of the intertransverse lower thoracic region were observed, and their internal diameters were measured. The rib-intervertebral space relationship for T10/11 and T11/12 was measured in 104 patients of the thoracic skeleton. Then, based on the data from the CT measurements, simulated surgery was performed on six human cadavers at the T11/12 level. An ankylosing spondylitis (AS) patient with a fracture of the T10/11 level was eventually operated on with the ITIF technique.

Results: No significant difference was found between the lengths of the left and right thoracic transverse processes. The relationship of the values of the LTP and RDTP for the measured vertebrae were found to be as follows:T8 > T9 > T10 > T11 > T12. For HEIS and DULTP, T8-9 < T9-10 < T10-11 < T11-12. The results for the ODIS were as follows: T8-T9 < T9-T10 < T10-T11 < T11-T12. The blood vessel inner diameter of T11-12 was less than that of T10-11, while there was no significant difference between the diameters for T8-9 and T11-12. Almost half of the volunteer's T10/11 intervertebral spaces were covered posteriorly by the 11th rib (45.19% on left and 41.35% on right), while for most patients, the T11/12 intervertebral space was not covered by the 12th rib (98.08%). According to the cadaver experiments, intervertebral bone grafting and ipsilateral pedicle screw fixation were performed to simulate the operation. One patient with a combined AS and T10/11 fracture was then operated on with the ITIF technique and followed up for 3 years with satisfactory results.

Conclusion: As verified by 3D CT reconstruction measurements, cadaver simulation surgery and patient operation with follow-up, the intertransverse process approach for some T10/T11 and almost all T11/T12 segments is a safe surgical pathway for operations such as ITIF, fracture bone grafting, clearance of focal lesions.