Incidence of Misplaced Pedicle Screws Causing Neurological Deficits in X-ray Guided TLIF Surgery
The incidence of misplaced pedicle screws causing neurological deficits in X-ray guided Transforaminal Lumbar Interbody Fusion (TLIF) surgery is approximately 1-3% of patients. 1, 2
Pedicle Screw Malposition Rates and Neurological Complications
- Overall misplacement rates for pedicle screws in lumbar spine surgery range from 5-41% of screws, with most studies reporting rates around 5-20% when using conventional X-ray guided techniques 1, 2
- Frank pedicle screw misplacement (screws completely outside pedicular boundaries) occurs in approximately 5% of cases using conventional fluoroscopy techniques 1
- Neurological deficits resulting from misplaced screws occur in approximately 1-2% of patients undergoing lumbar pedicle screw fixation 1, 2
- In a study of 102 patients with 424 inserted screws, only 2% of patients experienced radicular pain and neurological deficits due to misplaced screws 1
Severity and Types of Screw Malposition
Misplaced screws are typically classified based on the direction and extent of cortical breach:
- Minor penetration: up to 2mm outside pedicle cortex
- Moderate penetration: 2.1-4mm outside pedicle cortex
- Severe penetration: >4mm outside pedicle cortex 1
Medial breaches (toward the spinal canal) pose the highest risk for neurological complications, with 32.4% of misplaced screws having medial direction 1, 2
Lateral breaches (8.6% of misplaced screws) rarely cause neurological symptoms 1
Risk Factors for Screw Malposition and Neurological Deficits
- Preoperative cervical spinal instability is a significant risk factor for screw misplacement (RR 2.12, p = 0.03) 3
- Degenerative changes in vertebrae complicate screw insertion and increase the risk of misplacement 3
- Patients with cerebral palsy have higher risk of implant failure (HR 10.91, p = 0.03) 3
Role of Intraoperative Monitoring in Reducing Neurological Deficits
- Electromyography (EMG) monitoring during pedicle screw placement significantly reduces the risk of neurological complications 4
- Using a stimulation threshold of 20V for EMG monitoring provides 64% sensitivity and 83% specificity for detecting screw malposition 4
- In studies using continuous EMG monitoring during minimally invasive TLIF, surgeons altered pedicle access needle trajectory in 76.2% of cases based on EMG feedback, resulting in 0% incidence of clinically relevant malpositioned hardware 5
Recovery from Neurological Deficits
- Most patients with neurological deficits from misplaced screws recover completely with appropriate management 1
- In a study of 102 patients, all patients with neurological deficits from misplaced screws had completely recovered their neurological function at follow-up 1
- Radicular pain resulting from screw malposition typically resolves with screw repositioning or removal 1, 2
When to Revise Misplaced Screws
- There is significant variability among surgeons regarding which malpositioned screws require revision in asymptomatic patients (65% agreement, κ=0.477) 6
- Most surgeons recommend revision for screws that:
- Approach the dura (83% of surgeons)
- Approach major vascular structures like the aorta (58% of surgeons)
- Have the entire screw diameter in the spinal canal (50% of surgeons) 6
- Screws with partial canal violation (<½ screw diameter), lateral malposition in the rib head, or small anterior cortical violations remote from vascular structures generally do not require revision in asymptomatic patients 6
Strategies to Reduce Neurological Complications
- Intraoperative EMG monitoring is highly recommended during pedicle screw placement in TLIF procedures 4
- Using a continuous stimulation pedicle access needle alerts the surgeon to incorrect medial trajectories and may lead to safer pedicle cannulation 5
- Screws with stimulation thresholds less than 20V should be subject to corrective action 4
- Careful preoperative surgical planning, accurate knowledge of spinal anatomy, and surgical experience can reduce the risk of screw malposition 1