Impact energy during cadaveric transforaminal lumbar interbody fusion (TLIF) is replicated by a modular benchtop device

In the treatment of intervertebral disc pathologies, lumbar interbody fusion (LIF) involves the removal and replacement of the degenerative disc with an interbody fusion device (IFD). Leveraging a benchtop impaction device for repeatable replication of cadaveric IFD insertion would alleviate the challenges of relying solely on cadaveric models and accelerate the establishment of use condition parameters for refinement of IFD design and LIF procedures. Using a custom benchtop device, the objective of this work was to determine the benchtop testing conditions which mimic the impact energy absorption during cadaveric transforaminal lumbar interbody fusion (TLIF). From initial experiments with 1.0 lb (0.454 kg) drop weights of steel, zinc, and aluminum, we determined aluminum facilitated an impact duration closest to that of historical cadaveric TLIF data. Thus, subsequent testing utilized the aluminum drop weight impacting Ti-6Al-4V IFDs (12 mm height x 24 mm length). A lateral compressive load of 200 N was applied using springs with a stiffness of 63.22 lb/in (11.07 N/mm). Drop heights from which the aluminum weight was dropped ranged from 60 cm to 120 cm in increments of 10 cm. Data were collected by an impact force sensor on the IFD insertion instrument, button compression sensors on the compression platens, and a laser displacement sensor below the IFD. The impact waveform for benchtop and cadaveric data was characterized by four waveform characteristics: impact duration, area under the impulse curve, peak force, and initial impact slope of the waveform. Area under the curve represented energy absorption from the insertion instrument to the IFD. The cadaveric impact duration was replicated by all drop height groups on the benchtop device, and the peak impact force was replicated by the 90 cm, 110 cm, and 120 cm groups. The area under the impulse curve was replicated by the 110 cm and 120 cm groups. No benchtop group replicated the initial impact slope of the waveform seen in cadaveric data. In conclusion, a benchtop impaction device was validated for replication of energy absorption during insertion of IFDs in cadaveric TLIF procedures. Ultimately, this work will accelerate advancements in IFD design and failure analysis, enhancing the repeatability of TLIF surgical techniques.