Cadaveric study for ideal dorsal pedicle screw entry point.

OBJECTIVE: To determine the entry for the dorsal pedicular screw in relation to the notch present at the junction of base of the lateral margin of superior articular process with superior border of transverse process in dorsal spine. The advantage of this technique is a constant and easily identifiable entry point which does not involve partial resection of the inferior facet, thus maintaining stability and maintaining the well defined transverse and sagittal screw angles and decreasing the incidence of medial and inferior pedicle violation.

MATERIALS AND METHODS: The study was carried out using ten cadavers (four male and six female). Spinal column was dissected completely from cadavers. Before the experiment, normal anatomy was confirmed on all cadavers excluding cases of spinal deformity. Dissection was done by the spine surgeons taking care to preserve all the bony landmarks near the entry point. This study was carried out bilaterally on pedicles between the first and twelfth thoracic (T) vertebrae.

RESULTS: The relation of the superior articular notch and transverse process to the thoracic spine pedicles was studied. It was found that superior third of the pedicle was related to the superior articular notch and the transverse process in the first five thoracic vertebrae. The relation of these structures to the pedicle of the sixth thoracic vertebra was somewhat equally distributed between the superior and middle third of the pedicle. From the 7th to 12th thoracic vertebrae the superior articular process and transverse process were related to the middle third of the pedicle in almost all the cases. It is important to note that the inferior 1/3rd of the pedicle was not related to these landmarks at any of the levels.

CONCLUSION: We conclude that the ideal pedicle entry point described here should be considered by surgeons during thoracic pedicle screw instrumentation. The notch at the base of the superior articular process will always remain constant and therefore an important anatomical landmark in guiding the screw toward the entry of the pedicle.