A Literary Analysis and Cadaveric Evaluation of the Medtronic Intellis™ AdaptiveStim Spinal Cord Stimulator: Anatomical Correlates and Clinical Implications

Moultrie, GA

Background/Objectives:

The clinical efficacy of spinal cord stimulation (SCS) for chronic neuropathic pain depends on precise epidural lead placement to appropriately target the dorsal columns specific to patient cases. However, anatomical variability within the thoracic spinal canal, such as discrepancies between vertebral levels and spinal cord segments, differences in epidural fat distribution, ligamentum flavum thickness, and spinal cord dimension, may alter the spatial relationship between implanted leads and neural targets. These variations may contribute to inconsistent stimulation coverage and clinical outcomes due to alterations that can be avoided for better patient satisfaction.

Methods:

A focused anatomical and literature-based evaluation, along with a cadaver analysis, was conducted to identify thoracic spinal canal features that may influence SCS lead placement and neuromodulation effectiveness. Key parameters examined included the relationship between vertebral levels and underlying spinal cord segments, epidural fat distribution within the posterior epidural space, ligamentum flavum thickness, and variation in spinal cord dimensions and positioning within the vertebral canal. These anatomical factors were examined in the context of published literature and clinical trials evaluating spinal cord stimulation outcomes, stimulation thresholds, and variability in paresthesia coverage among patients.

Results:

Clinical studies of SCS have demonstrated variability in stimulation thresholds and paresthesia coverage among patients despite similar procedural techniques. Anatomical factors showed distinct relationships in vertebral levels and underlying spinal cord segments, epidural fat thickness, ligamentum flavum thickness, and the spatial relationship between the epidural space and the dorsal columns that could have caused the placed lead to work more efficiently. Epidural fat present in the location where the lead was placed showed that the more fat present in the area, the wider the distance between the lead and the dorsal cord fibers, along with more electrical impedance in the space. The ligamentum flavum, if it had distinct abnormalities such as hypertrophy, could cause the paddle to not articulate as it should, along with causing the lead to send signals through the LF, causing stimulation-evoked discomfort. Spinal cord orientation changes, such as slightly non-central position within the vertebral canal, can create an asymmetry in the distance between the posterior epidural space and the dorsal surface of the cord. This anatomical orientation could indicate that minor deviations in lead positioning due to asymmetry can lead to misplaced signal transmission. These observations highlight anatomical features that may influence stimulation coverage and thresholds during SCS therapy.

Conclusion:

Variability in thoracic spinal canal anatomy may represent an underrecognized contributor to differences in spinal cord stimulation preference and patient outcomes reported in clinical trials. Greater consideration of patient-specific anatomical factors, including epidural fat distribution, vertebral spinal cord segment alignment, and spinal cord positioning, may improve procedural lead planning and targeting strategies. Incorporating a broader perspective and additional variables could optimize patient interaction with SCS neuromodulation and open opportunities for patients who were not able to achieve therapeutic outcomes in SCS trials.