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Shota Tamagawa, Takatoshi Okuda, Hidetoshi Nojiri, Rei Momomura, and Muneaki Ishijima

BACKGROUND

Although malpositioning of pedicle screws into the spinal canal and intervertebral foramen can cause spinal nerve root injuries, there are few reports of L5 nerve root injuries when S1 pedicle screws have been inserted anterolaterally. The authors report two cases of L5 nerve root injury caused by anterolateral malpositioning of loosened S1 pedicle screws.

OBSERVATIONS

In both patients, S1 pedicle screws were inserted toward the outside of the S1 anterior foramen, and the tip of the screws perforated the anterior sacral cortex. L5 nerve root impairment was not observed immediately after surgery. However, severe leg pain in the L5 area was observed after the S1 pedicle screws became loosened. In case 1, the symptoms could not be controlled with conservative treatment. Reoperation was performed 3 months after the initial surgery. In case 2, the symptoms gradually improved with conservative treatment because the area around the loosened S1 screw was surrounded by newly formed bone that stabilized the screws, as observed with computed tomography 1 year after surgery.

LESSONS

Surgeons should recognize that anterolateral malpositioning of S1 pedicle screws can cause L5 nerve root injury. The screws should be inserted in the correct direction without loosening.

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Hidetoshi Nojiri, Kei Miyagawa, Hiroto Yamaguchi, Masato Koike, Yoshiyuki Iwase, Takatoshi Okuda, and Kazuo Kaneko

OBJECTIVE

Lumbar surgery via a lateral approach is a minimally invasive and highly useful procedure. However, care must be taken to avoid its potentially fatal complications of intestinal and vascular injuries. The object of this study was to evaluate the usefulness of intraoperative ultrasound in improving the safety of lateral lumbar spine surgery.

METHODS

A transvaginal ultrasound probe was inserted into the operative field, and the intestinal tract, kidney, psoas muscle, and vertebral body were identified using B-mode ultrasound. The aorta, vena cava, common iliac vessels, and lumbar arteries and their associated branches were identified using the color Doppler mode.

RESULTS

The study cohort comprised 100 patients who underwent lateral lumbar spine surgery, 92 via a left-sided approach. The intestinal tract and kidney lateral to the psoas muscle on the anatomical approach pathway were visualized in 36 and 26 patients, respectively. A detachment maneuver displaced the intestinal tract and kidneys in an anteroinferior direction, enabling confirmation of the absence of organ tissues above the psoas. In all patients, the major vessels anterior to the vertebral bodies and the lumbar arteries and associated branches in the psoas on the approach path were clearly visualized in the Doppler mode, and their orientation, location, and positional relationship with regard to the vertebral bodies, intervertebral discs, and psoas were determined.

CONCLUSIONS

When approaching the lateral side of the lumbar spine in the retroperitoneal space, intraoperative ultrasound allows real-time identification of the blood vessels surrounding the lumbar spine, intestinal tract, and kidney in the approach path and improves the safety of surgery without increasing invasiveness.

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Shota Tamagawa, Takatoshi Okuda, Hidetoshi Nojiri, Tatsuya Sato, Rei Momomura, Yukoh Ohara, Takeshi Hara, and Muneaki Ishijima

OBJECTIVE

Previous reports have focused on the complications of L5 nerve root injury caused by anterolateral misplacement of the S1 pedicle screws. Anatomical knowledge of the L5 nerve root in the pelvis is essential for safe and effective placement of the sacral screw. This cadaveric study aimed to investigate the course of the L5 nerve root in the pelvis and to clarify a safe zone for inserting the sacral screw.

METHODS

Fifty-four L5 nerve roots located bilaterally in 27 formalin-fixed cadavers were studied. The ventral rami of the L5 nerve roots were dissected along their courses from the intervertebral foramina to the lesser pelvis. The running angles of the L5 nerve roots from the centerline were measured in the coronal plane. In addition, the distances from the ala of the sacrum to the L5 nerve roots were measured in the sagittal plane.

RESULTS

The authors found that the running angles of the L5 nerve roots changed at the most anterior surface of the ala of the sacrum. The angles of the bilateral L5 nerve roots from the right and left L5 intervertebral foramina to their inflection points were 13.77° ± 5.01° and 14.65° ± 4.71°, respectively. The angles of the bilateral L5 nerve roots from the right and left inflection points to the lesser pelvis were 19.66° ± 6.40° and 20.58° ± 5.78°, respectively. There were no significant differences between the angles measured in the right and left nerve roots. The majority of the L5 nerves coursed outward after changing their angles at the inflection point. The distances from the ala of the sacrum to the L5 nerve roots in the sagittal plane were less than 1 mm in all cases, which indicated that the L5 nerve roots were positioned close to the ala of the sacrum and had poor mobility.

CONCLUSIONS

All of the L5 nerve roots coursed outward after exiting the intervertebral foramina and never inward. To prevent iatrogenic L5 nerve root injury, surgeons should insert the S1 pedicle screw medially with an angle > 0° toward the inside of the S1 anterior foramina and the sacral alar screw laterally with an angle > 30°.