Intraoperative Neurophysiological Changes Induced by Thoracic Pedicle Screws Intentionally Placed Within the Spinal Canal: An Experimental Study in Pigs

Which Malpositioned Pedicle Screws Should Be Revised?

BACKGROUND

Up to 10% of free-hand pedicle screws are malpositioned, and 1 in 300 patients may undergo return to surgery for revision of malpositioned screws. The indications for revision of asymptomatic malpositioned screws have not been carefully examined in the literature. We sought to evaluate the threshold among spinal deformity surgeons for revision of malpositioned screws.

METHODS

Twelve experienced spine surgeons reviewed x-ray and computed tomographic images of 32 malpositioned pedicle screws with variable degrees of anterior, medial, and lateral breeches. The surgeons were asked whether based on the image they would revise the screw: (1) intraoperatively before rod placement; (2) intraoperatively after rod placement; (3) in clinic with an asymptomatic patient. For each scenario, we assumed stable neuromonitoring and no neurological changes. Agreement and multirater κ was calculated.

RESULTS

There was good agreement as to which screws were malpositioned (80% agreement, κ=0.703). After the rod was placed or postoperatively (scenarios 2 and 3), surgeons less frequently recommended screw revision, and there was greater variability among the surgeons' recommendations. For return to surgery from clinic for asymptomatic screw revision, % agreement was only 65% (κ=0.477). The majority recommended revision surgery for screws which approached the dura (10/12) or the aorta (7/12 surgeons). Half of the surgeons recommended revision surgery for an asymptomatic screw if the entire screw diameter was in the canal. Revision surgery was not recommended for asymptomatic patients with screws partially violating the canal (<½ the screw diameter), malpositioned laterally in the rib head, or with small anterior cortical violations remote from a vascular structure.

CONCLUSIONS

There is significant variability of opinion among surgeons regarding which malpositioned screws can be safely observed in an asymptomatic patient. Given the frequency of malpositioned screws and morbidity of surgical return to surgery, more long-term data are needed to develop practice guidelines for determining which screws require revision surgery.

LEVEL OF EVIDENCE

Level III-retrospective comparative study.

Delayed Dural Leak Following Posterior Spinal Fusion for Idiopathic Scoliosis Using All Posterior Pedicle Screw Technique

BACKGROUND

In pediatric patients, pedicle screws are malpositioned 5% to 15% of the time. Complications associated with malpositioned screws are infrequently reported in the literature. We present a series of adolescent idiopathic scoliosis (AIS) patients who presented in a delayed manner with positional headache and chronic dural leak adjacent to the pedicle screw tract.

METHODS

Scoliosis databases at 2 centers were reviewed, and cases of delayed positional headaches following posterior spinal fusion for AIS were identified. Demographic and clinical data were collected.

RESULTS

Of 322 patients, 4 patients presented with positional headaches at a mean of 12.8 weeks following posterior spinal fusion surgery for AIS, with an interval time to diagnosis of 5 months. Computed tomographic myelogram demonstrated severe pedicle screw malposition in 1 patient, and minimal malposition in 3 patients (<2 mm violation). The patients had delayed presentation with positional headaches secondary to dural leak. All patients successfully underwent revision surgery with repair of the dural leak. At the time of latest follow-up, all patients are asymptomatic.

CONCLUSIONS

Pedicle screw malposition can result in dural leaks. Patients may present in a delayed manner with positional headaches and an acquired Chiari malformation. Clinical suspicion should prompt imaging of the brain or cervical spine followed by computed tomographic myelogram to determine site of leak. This is a rare complication from pedicle screw malposition.

LEVELS OF EVIDENCE

Level IV-case series.