Biomechanical and Histological Assessment of a Novel Screw Retention Technology in an Ovine Lumbar Fusion Model

Publication date: Available online 31 July 2018

Source: The Spine Journal

Author(s): Jeremiah Easley, Christian M. Puttlitz, Ross Palmer, Nicole Ramo, Celeste Abjornson, Frank P. Cammisa, Kirk McGilvray

Abstract

Background Context

Screw loosening is a prevalent failure mode in orthopaedic hardware, particularly in osteoporotic bone or revision procedures where the screw-bone engagement is limited.

Purpose

The objective of this study was to evaluate the efficacy of a novel screw retention technology (SRT) in an ovine lumbar fusion model.

Study Design/Setting

This was a biomechanical, radiographic, and histology study utilizing an ovine lumbar spine model.

Methods

: Fifty-four (n = 54) sheep lumbar spines (L₂-L₃) underwent posterior lumbar fusion (PLF) via pedicle screw fixation, connecting rod, and bone graft. Three experimental variants were investigated: positive control (ideal clinical scenario), negative control (simulation of compromised screw holes), and SRT treatments (SRT). Biomechanical and histological analysis of the functional spinal unit (FSU) was determined as a function of healing time (0, 3, and 12 months post-operative).

Results

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.

Conclusions

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.

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