INTRODUCTION: To examine the destruction and changes to the interspinous and supraspinous ligament complex after interspinous process device (IPD) implantation.
METHODS: Biomechanical and anatomic assessments were performed on fresh human cadavers. The biomechanical examination assayed the force necessary to disrupt the interspinous‐supraspinous ligament complex without and after implantation of an IPD. For the anatomic examination, the lumbar spine was plastinated. Serial 4mm thick sections were cut in sagittal and horizontal planes. The macro anatomical positioning of the implants was then analysed.
RESULTS: Biomechanical: The average age of the cadavers was 80.6±10.2 years. The minimum average disrupting forces measured 313.74±113.44 N without and 239.47±63.64 N after IPD implantation, a significant (p<0.018) decrease of an average 23.7%. Anatomical: After posterolateral percutaneous IPD implantation, the posterior third of the interspinous ligament, the supraspinous ligament, the thoracolumbar fascia and paraspinous muscles bordering the inter‐/supraspinous ligament complex remained undamaged.
DISCUSSION: The spinous ligament complex has an important stabilising function, supported extensively by the trunk and back musculature. Thus, the interaction between spinous ligaments and musculature, occurring through intricate collagenous cross‐linking and neurogenic innervation that has not yet been completely clarified, should be kept as intact as possible. The implantation of an interspinous "stand alone" spacer significantly minimises the force necessary to disrupt the ISL/SSL complex. Because the dorsal portion of the ISL and the entire SSL are preserved, on average 23.7% less force is necessary to sever the ISL/SSL complex. After posterolateral percutaneous implantation, the thoracolumbar fascia and associated musculature, which act in synergy with the ISL/SSL complex to stabilise the vertebral column, remain intact.