Diagonal Trajectory Posterior Screw Instrumentation for Compromised Bone Quality Spine: Groove-Entry Technique/Hooking Screw Hybrid

INTRODUCTION: In an attempt to increase anchoring strength of posterior instrumentation in spine with compromised bone quality, we introduced diagonal trajectory pedicle screwing (hooking screws) that do not rely on screw thread purchase in bone but rather hook onto the strong posterior elements of vertebrae from inside the bone. METHODS: Between November 2016 and July 2017 we treated eight patients, mean age 80 years old (75-86 years old) with compromised bone quality for spinal instability. The diagnosis was osteoporotic fracture nonunion in three, ankylosed spine fracture in three, pyogenic spondylitis in two cases. All spines were percutaneously instrumented. Groove-entry technique was used for down-going thoracic screws. No additional hooks, cables, or any other augmentation was used. All patients were mobilized on post-operative day 1. RESULTS: 84 screws were inserted overall. Groove-entry technique was used for 42 screws insertion. On average, 5.3 spinal segments were fixed per case. Mean operation time was 252 min (46 min per one spinal segment). Mean intraoperative bleeding was 112 ml per case (21 ml per one fixed spinal segment). All cases achieved bony union of the fracture site or across the destroyed intervertebral disk. Mean time to union was 4 months postop (3-7 months). All patients were ambulatory at the time of discharge. No nerve injury, no skin irritation caused by implants, no screw loosening, no screw pullout, no loss of correction, and no junctional kyphosis were noted in this series. CONCLUSIONS: Diagonal screw instrumentation (our hooking screws and groove-entry technique) appears to provide sufficient anchoring strength while being minimally invasive and possibly helpful in prevention of junctional kyphosis.