Abstract
Objective: Recent reports have suggested a low incidence of neurological complications following anterior deformity surgery; however in patients with co-existing intra-spinal anomalies no quantification of this risk has been made. Also, whether SSEP monitoring and soft clamping of segmental vessels prior to their division is necessary for these anterior procedures is controversial.
The aims of this study were to determine the incidence of significant SSEP changes in patients undergoing anterior spinal deformity surgery; to ascertain whether the ‘at risk’ cord was more likely to demonstrate significant intraoperative SSEP changes and what proportion of these changes yielded post operative neurological deficit.
Design: Retrospective analysis of operative notes and somatosensory evoked potential (SSEP) traces of patients who underwent anterior spinal deformity surgery between 1990–2001.
Subjects: All patients who underwent anterior spinal deformity surgery between 1990–2001, who had complete data sets (preoperative MRI scan, patient and procedural documentation and intraoperative SSEP traces) were included in the study.
Outcome measures: All post operative neurological deficits and significant SSEP changes were noted, whether or not patients had a ‘cord at risk’.
Results: In total, 871 patients had elective anterior spinal deformity surgery. Preoperative MRI revealed 95 patients (11%) demonstrated intraspinal anomalies on MRI but of these only 27 showed abnormal pre-operative SSEP i.e. cord at risk (CAR). Seventeen (2% of total) of this group developed abnormal intraoperative SSEP responses and ten (1.3%) occurred in the normal group. The incidence of post-operative paraparesis for the whole series was 0.6% (n=5): four in the CAR group, one in the normal cord group. Sensitivity of SSEPs in detecting potential neurological deficit was 100%; specificity 98.6%, positive predictive value 29.4% and negative predictive value 100%. Significant intraoperative SSEP changes occurred more frequently in the CAR group and were more likely to have post operative paraparesis.
Conclusions: SSEP monitoring is a sensitive and specific test, which in experienced hands yields no false positive results. Spinal cord monitoring and soft clamping of segmental vessels should be performed in patients with CAR undergoing anterior spinal deformity surgery to minimise the risk of post operative paraparesis.
The abstracts were prepared by Mr Peter Millner. Correspondence should be addressed to Peter Millner, Consultant Spinal Surgeon, Orthopaedic Surgery, Chancellor Wing, Ward 28 Office Suite, St James’ University Hospital, Beckett Street, Leeds LS9 7TF.
