L5 spinal nerve injury caused by misplacement of outwardly-inserted S1 pedicle screws

Abstract

Purpose: To evaluate L5 nerve root injuries caused by outwardly misplaced S1 pedicle screws. Pedicle screws remain the criterion standard for fixation of L5-S1 to correct lumbosacral instability. When inserting S1 pedicle screws, it is possible to injure the L5 nerve root if screws are inserted outwardly and the tip of the screw perforates the anterior cortex of the sacrum. Despite this risk, to our knowledge this type of injury has never been reported as a case series.

Methods: We experienced 2 cases of L5 nerve root injury caused by outwardly-inserted S1 pedicle screws. In both cases, bilateral S1 pedicle screws were inserted outwardly using a free-hand technique, and on one side, screws induced severe pain by impinging on an L5 root. Computed tomography after the selective rootgraphy of the injured nerve showed the nerve compressed laterally by screw threads in Case 1 and crushed between the screw threads and the sacral body in Case 2.

Results: In both cases, leg pain disappeared immediately after the infiltration of the nerve with lidocaine, but symptoms recurred within a few days in Case 1 and within an hour in Case 2. Conservative treatment of three spinal nerve infiltrations was effective in Case 1, but reinsertion of the rogue screw was necessary in Case 2.

Conclusions: Surgeons should recognize that lateral inclination of S1 pedicle screws can cause L5 nerve root injury, which may require reinsertion of the screw, especially in cases where insertion is difficult because of overlapping surrounding muscle or bony tissue.

Fig. 1

Right L5 selective rootgraphy. The outwardly-inserted pedicle screw laterally compresses the L5 nerve root

Fig. 2

Computed tomography (CT) after the right L5 rootgraphy. a In the axial section, the right L5 nerve root is compressed laterally by the perforating S1 screw (white arrow heads). The right s1 pedicle screw passes diagonally against the pedicle medullary canal toward the far lateral side, at an outward angle of 15° and penetrates 9.0 mm distant from the anterior cortex of the sacrum. b In the coronal section, the L5 nerve root is compressed laterally by the perforating S1 screw (white arrow heads)

Fig. 3

Right L5 selective rootgraphy using 1.0 ml of iotorolan shows that the nerve root is pushed inward by a misplaced S1 screw

Fig. 4

a CT after the right L5 rootgraphy shows that bilateral screws were not inserted through the pedicle and abutted the outer cortex of the vertebral body. The right S1 screw was inserted 17° outwardly and penetrated 8.6 mm distant from the anterior cortex of the sacrum. The right L5 nerve root is crushed between the pedicle screw and the lateral side of the S1 endplate, without any space to move. b CT after reinsertion indicates that the right screw was reinserted with 4° medial inclination and anchored in the vertebral body