Biomechanical and histologic assessment of a novel screw retention technology in an ovine lumbar fusion model

• Published in: The spine journal 2018-12, Vol.18 (12), p.2302-2315
• Main Authors: Easley, Jeremiah, Puttlitz, Christian M., Seim, Howard, Ramo, Nicole, Abjornson, Celeste, Cammisa, Frank P., McGilvray, Kirk C.
• Format: Article
• Language: English
• Subjects: Animals; Biomechanical Phenomena; Biomechanics; Bone screw enhancement; Bone Transplantation - methods; Histology; Humans; Lumbar fusion; Lumbar Vertebrae - surgery; Lumbosacral Region - surgery; Models, Animal; Ovine; Pedicle Screws; Screw loosening; Screw purchase; Sheep; Spinal Fusion - instrumentation; Spinal Fusion - methods; Spine fusion
• ISSN: 1529-9430; 1878-1632
• DOI: 10.1016/j.spinee.2018.07.021

Screw loosening is a prevalent failure mode in orthopedic hardware, particularly in osteoporotic bone or revision procedures where the screw-bone engagement is limited. The objective of this study was to evaluate the efficacy of a novel screw retention technology (SRT) in an ovine lumbar fusion model. This was a biomechanical, radiographic, and histologic study utilizing an ovine lumbar spine model. : In total, 54 (n=54) sheep lumbar spines (L2–L3) underwent posterior lumbar fusion (PLF) via pedicle screw fixation, connecting rod, and bone graft. Following three experimental variants were investigated: positive control (ideal clinical scenario), negative control (simulation of compromised screw holes), and SRT treatments. Biomechanical and histologic analyses of the functional spinal unit (FSU) were determined as a function of healing time (0, 3, and 12 months postoperative). Screw pull-out, screw break-out, and FSU stability of the SRT treatments were generally equivalent to the positive control group and considerably better than the negative control group. Histomorphology of the SRT treatment screw region of interest (ROI) observed an increase in bone percentage and decrease in void space during healing, consistent with ingrowth at the implant interface. The PLF ROI observed similar bone percentage throughout healing between the SRT treatment and positive control. Less bone formation was observed for the negative control. The results of this study demonstrate that the SRT improved screw retention and afforded effective FSU stabilization to achieve solid fusion in an otherwise compromised fixation scenario in a large animal model.