Benchtop impaction device replicates cadaveric loading conditions of the transforaminal lumbar interbody fusion (TLIF) procedure

Background context

Lumbar spine disc pathologies often necessitate removal of the intervertebral disc and implantation of a lumbar interbody fusion (LIF) device. Herein, the objective was to measure use condition forces while simulating intra-operative loading conditions of transforaminal lumbar interbody fusion (TLIF) procedures.

Methods

In this work, we developed a transferable method to measure impact forces in a cadaveric intra-operative setting and designed a drop weight benchtop device equipped with force and displacement sensors to replicate cadaveric impact conditions, including number of strikes required for interbody device insertion, peak force, initial slope of the impact waveform, impact duration, and area under the force-time curve (impulse). Following cadaveric testing, a benchtop biomechanical study varying interbody device height, drop height, and drop weight was performed to evaluate the utility of the benchtop device to replicate impact loading conditions which occurred in the cadaveric model.

Results

Several benchtop test groups replicated the cadaver group in number of strikes required for device insertion. The average cadaveric peak force, 13.03 kN, was replicated by three benchtop groups: 12 mm device height, 60 cm drop height, 0.75 lb drop weight; 12 mm device height, 60 cm drop height, 1.0 lb drop weight; and 14 mm device height, 60 cm drop height, 0.50 lb drop weight. The initial slope of the impact waveform was replicated best by 12 mm devices. Both the impact duration and impulse were lower in all benchtop groups than in cadaver testing.

Conclusions

This work validated the outfitting of an impact force sensor onto an interbody device insertion instrument as a reproducible, quantifiable method for collecting impact loading data in a cadaveric model. This benchtop device and methodology will aid in testing interbody devices relative to anticipated use conditions, enhance interbody device designs, and accelerate surgical technique refinement.