Distance to the spinal canal and vertebral body from the insertion point of percutaneous pedicle screws in the lumbar spine: radiographic anatomy on computed tomography images for a safe and efficient procedure.

PURPOSE: This study aimed to evaluate the distance for the safe and efficient insertion of percutaneous pedicle screws (PPSs) in lumbar fixation surgery.

METHODS: On lumbar computed tomography thin-slice images parallel to the cranial vertebral endplate, two different insertion points of the PPS were defined: (1) the lateral wall of the pedicle (defined as the LP) and (2) the angle between the transverse process and superior articular process (TS). From these points, we measured the distance to the inner wall of the pedicle (A) and the posterior wall of the vertebral body (B). The distance was measured bilaterally from L1 to L5 of consecutive 60 patients.

RESULTS: The results of PL-A (the mean distance ± standard deviation) from the L1 level to the L5 were 17.9 ± 3.0, 18.1 ± 2.9, 18.9 ± 3.1, 18.7 ± 3.4, and 19.9 ± 3.3 mm, respectively. Those of PL-B were 24.1 ± 3.5, 23.2 ± 3.4, 23.0 ± 3.8, 22.1 ± 4.1, and 21.9 ± 3.8 mm. The results of TS-A were 17.9 ± 2.6 mm, 17.6 ± 2.2, 18.0 ± 2.3, 16.3 ± 2.2, and 17.1 ± 2.3, whereas those of TS-B were 22.8 ± 2.6 mm, 21.6 ± 2.3, 21.2 ± 2.1, 18.6 ± 2.1, and 18.3 ± 2.2, respectively. Moreover, the PL-A, PL-B, TS-A, and TS-B of all L1-L5 were 18.7 ± 3.2, 22.9 ± 3.8, 17.4 ± 2.4, and 20.5 ± 2.9 mm.

CONCLUSION: This study can contribute to the safe and efficient insertion of the lumbar PPS.