Misdirection- What The Eyes See and The Ears Hear, The Mind Believes- A Retrospective Study of Misdirected Pedicle Screw Fixations in Thoracolumbar Spine

Abstract

Transpedicular stabilization has become an established method for instrumentation of the thoracic and lumbar spine because of its immediate rigidity, better coronal and sagittal correction and shorter fusion length when compared to the other instrumentation techniques. Pedicle screw insertion resulting in neurologic deficit is rare, but may be due to faulty placement of the screw, with perforation of the cortex and impingement on adjacent neural structures. Despite improvements in the design of the instruments and attention to insertion techniques, cortical perforation does occur. Because many transgressions are asymptomatic, the true incidence is not known. Roy-Camille et al report in their experience 10% of screws were not completely in the pedicle. A retrospective study was done to determine the incidence of screw misplacement and complications in 120 transpedicular screws (30 patients) in the thoracolumbar spine with conventional open technique and intraoperative fluoroscopy. Outcome measures were: Accuracy of screw placement was evaluated by postoperative CT scan. Screw position was classified as 1.correct when the screw was completely surrounded by the pedicle cortex, 2. cortical breach and as 3. frank penetration when the screw was outside the pedicular boundaries. Frank penetration was further subdivided as grade A (up to 2.0 mm), grade B(2.1-4 mm), and grade C(> 4 mm).Results- In our study we found out that only 56 screws were in the category of correct, while a total of 40 pedicle screws had Frank penetration, mostly medially(followed by laterally and anteriorly) with a grade B penetration (followed by grade A and grade C) with 8 complications attributable to this misdirections, of which, 4 each had medial and lateral breech, all of which thankfully completely resolved with time at subsequent follow up. The use of pedicle screw instrumentation was described by Boucher in 1950s and was popularized by Roy-Camille et al in 1960s. The initial use of pedicle screws began in the lumbar spine and as surgeons became more comfortable with the complex anatomy required for accurate screw placement, they evolved the use of pedicle instrumentation in thoracolumbar and thoracic spine.Transpedicular screw fixation has many advantages over other spinal instrumentations such as Harrington rod fixation, Luque's instrumentation, etc., in various pathologies. Pedicle screws also prevent the need to place instrumentation within the spinal canal like sublaminar wiring, which creates the risk of neurological injury. Transpedicular stabilization has become an established method for instrumentation of the thoracic and lumbar spine because of its immediate rigidity, better coronal and sagittal correction and shorter fusion length when compared to the other instrumentation techniques. Comparing pedicle screws, wires, and hooks, the highest incidence of symptomatic impingement occurs with pedicle screws, with nerve root injury or irritation occurring in a reported 3.2% of cases. Pedicle screw insertion resulting in neurologic deficit is rare, but may be due to faulty placement of the screw, with perforation of the cortex and impingement on adjacent neural structures. Despite improvements in the design of the instruments and attention to insertion techniques, cortical perforation does occur. Because many transgressions are asymptomatic, the true incidence is not known. Roy- Camille et al report in their experience 10% of screws were not completely in the pedicle. Ideally, the pedicle screw is completely contained within the pedicle, and the spinal canal is not violated. Pedicle screws that violate the pedicle cortex increase the risk of neurologic injury; however, minor violations of the cortex are not uncommon and may be asymptomatic. In these cases, the screw position may be acceptable. Ultimately, patient symptomatology is probably the most important factor in determining acceptable positioning of the screw.