The Biomechanical Effects of Weave Patterns in Ligament Augmentation of Long Cervical Constructs

Introduction: Posterior cervical fusion (PCF) is a standard treatment for myeloradiculopathy and deformity. Multi-level fusion alters native biomechanics, increases motion at adjacent levels, potentially leading to distal junctional kyphosis (DJK). This study investigated the effects of semi-rigid soft-landing techniques on spinal range-of-motion (ROM) and intradiscal pressure (IDP) distal to PCF.

Methods: Seven healthy fresh-frozen human cadaveric spines (O-T7) were tested for ROM and IDP during flexion-extension using a custom-built motion simulator (±2.5Nm). Specimens were treated with PCF (C3-T2) and tested for ROM and IDP. Soft-landings were applied using tethers for ligament augmentation and consisted of hand-tied surgical tape and tensioned PET bands (100N) weaved through the spinous processes of T3-T4 and T3-T5 in U-, P-, and figure-8 configurations. ROM and IDP were normalized to intact and compared at the lowest instrumented disc (LID) with rigid or semi-rigid fixation and the first two un-instrumented distal adjacent levels (LID-1 and LID-2).

Results: Following PCF, the transition of motion was abrupt from LID-to-(LID-1) (+165% intact) and IDP decreased linearly from LID-to-(LID-2).ROM at the level below the PCF (215% intact) was reduced more with U-weave via tensioned PET bands (56% intact) than hand-tied surgical tape (132% intact). However, tensioned and hand-tied U-weave also increased IDP at this level (+203% and +91% intact) and caused a sharp jump in ROM from LID-to-(LID-1) (+168% and +117% intact). Compared to PCF, ROM at the 2nd distal level (213% intact) was reduced more with P-weave than figure-8 for hand-tied surgical tape (169% vs. 186% intact) and tensioned PET bands (83% vs.114% intact). IDP at this level was also higher with P-weave than Figure-8 for hand-tied surgical tape (154% vs. 127% intact) and tensioned PET bands (312% vs. 167% intact). The transition of motion from LID-to-(LID-1) was also more gradual with tensioned Figure-8 (+88% intact) and P-weave (+102% intact) than PCF.

Conclusion : U-weave had minimal effects on mitigating hypermobility. P-weave reduced ROM distal to the PCF more than figure-8 but caused higher IDP. Tensioned PET bands had a more gradual transition of stiffness and more motion restriction, but greater IDP than hand-tied surgical tape.