L5 nerve root injury caused by anterolateral malpositioning of loosened S1 pedicle screws: illustrative cases

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

doi:10.3171/case21207

Cited by 2 publications

(4 citation statements)

References 32 publications

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“…Some reports have also focused on the complications of L5 nerve root injury caused by anterolateral misplacement of the S1 pedicle screws. [22][23][24] Sacral screw fixation is the gold standard for sacral bone purchase. The two most commonly used methods of screw insertion are into the promontory through the S1 pedicle with an anteromedial orientation and into the ala of the sacrum with an anterolateral orientation.…”

Section: Discussionmentioning

confidence: 99%

“…Therefore, inserting the S1 pedicle screws medially with an angle > 0° toward the inside of the S1 anterior foramina can help avoid injury of the L5 nerve root. Previously, Tamagawa et al 24 reported 2 cases of L5 nerve root injury due to anterolateral misplacement of the S1 pedicle screws. In those cases, as the S1 pedicle screws were inserted outside of the S1 anterior foramina over bicortical fixation, the L5 nerve roots were stimulated by the screw tips.…”

Section: Discussionmentioning

confidence: 99%

“…[19][20][21] Moreover, previous reports have highlighted the complications of L5 nerve root injury when S1 pedicle screws were inserted anterolaterally. [22][23][24] Although some cadaveric studies have demonstrated the anatomical relationship between the lumbar pedicle and adjacent dural sac and nerve roots, [25][26][27] few reports have detailed the anatomy of the L5 nerve root in the pelvis. Previous reports have measured the distance from the sacroiliac joint to the L5 nerve root, 28,29 which is not practical for use as a reference to prevent iatrogenic L5 nerve root injury when inserting the sacral screws under intraoperative fluoroscopy due to differences in patients' body sizes.…”

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confidence: 99%

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Anatomy of the L5 nerve root in the pelvis for safe sacral screw placement: a cadaveric study

Tamagawa

Okuda

Nojiri

et al. 2022

Journal of Neurosurgery: Spine

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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°.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

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Anatomy of the L5 nerve root in the pelvis for safe sacral screw placement: a cadaveric study

Tamagawa

Okuda

Nojiri

et al. 2022

Journal of Neurosurgery: Spine

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“…Outlet views of the S1 and S2 segments can be obtained with the beam parallel to the "tunnels" of each pair of neural foramina and help the surgeon avoid iatrogenic violation of the foramina by clearly defining these structures. [13][14][15] "Optimal" outlet views perfectly aligned by these definitions may be difficult to achieve in patients with large body habitus or anteverted pelves with increased pelvic incidence because the necessary caudal tilt of the C-arm gantry is not possible due to collision of the C-arm radiation source and detector with the undersurface of the radiolucent operating table and the thighs of the patient, respectively. Suboptimal fluoroscopic views of the upper sacral neural foramen can lead to the misinterpretation of the position of instruments and implants relative to osseous and neurovascular structures and subsequently increase the risk of iatrogenic complications.…”

Section: Introductionmentioning

confidence: 99%

Incidence of Suboptimal Fluoroscopic Outlet Imaging of the Sacrum and Pelvic Retroversion Necessary for Optimal Views

Patterson,

Brown,

Hasegawa

et al. 2024

Journal of Orthopaedic Trauma

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OBJECTIVES: To estimate the prevalence of suboptimal fluoroscopy of sacral outlet images due to anatomic and equipment dimensions. Pelvic retroversion is hypothesized to mitigate this issue. Design: In silico simulations using retrospectively collected computed tomography (CT) data from human patients. Setting: Level I trauma center. Patient Selection Criteria: Adults with AO/OTA 61 pelvic ring disruptions treated with posterior pelvic fixation between July and December 2021. Outcome Measures and Comparisons : C-arm tilt angles required to obtain three optimal fluoroscopic sacral outlet images, defined as vectors from pubic symphysis to S2 and parallel to the first and second sacral neural foramina, were calculated from sagittal CT images. A suboptimal view was defined as collision of the C-arm radiation source or image intensifier with the patient/operating table at the required tilt angle simulated using the dimensions of five commercial C-arm models and trigonometric calculations. Incidence of suboptimal outlet views and pelvic retroversion necessary to obtain optimal views without collision, which may be obtained by placement of a sacral bump, was determined for each view for all patients and C-arm models. RESULTS: CT data from 72 adults were used. Collision between patient and C-arm would occur at the optimal tilt angle for 17% of simulations and at least one view in 68% of patients. Greater BMI was associated with greater odds of suboptimal imaging (standard outlet: OR 0.84, CI 0.79-0.89, p<0.001; S1: OR 0.91, CI 0.87-0.97, p=0.002; S2: OR 0.85, CI 0.80-0.91, p<0.001). S1 anterior sacral slope was associated with suboptimal S1 outlet views (OR 1.12, Cl 1.07-1.17, p<0.001). S2 anterior sacral slope was associated with suboptimal standard outlet (OR 1.07, Cl 1.02-1.13, p=0.004) and S2 outlet (OR 1.16, Cl 1.09-1.23, p<0.001) views. Retroversion of the pelvis 15-20° made optimal outlet views possible without collision in 95%-99% of all simulations, respectively. CONCLUSIONS: Suboptimal outlet imaging of the sacrum is associated with greater BMI and sacral slope at S1 and S2. Retroversion of the pelvis by 15-20° with a bump under the distal sacrum may offer a low-tech solution to ensure optimal fluoroscopic imaging for percutaneous fixation of the posterior pelvic ring. Level of Evidence: Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.

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L5 nerve root injury caused by anterolateral malpositioning of loosened S1 pedicle screws: illustrative cases

Cited by 2 publications

References 32 publications

Anatomy of the L5 nerve root in the pelvis for safe sacral screw placement: a cadaveric study

Anatomy of the L5 nerve root in the pelvis for safe sacral screw placement: a cadaveric study

Incidence of Suboptimal Fluoroscopic Outlet Imaging of the Sacrum and Pelvic Retroversion Necessary for Optimal Views

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