Measuring compressive loads on a 'smart' lumbar interbody fusion cage: Proof of concept.

Vivek A S Ramakrishna, Uphar Chamoli, Subhas C Mukhopadhyay, Ashish D Diwan, B Gangadhara Prusty

Journal: Journal of biomechanics 2023;147():111440

PMID: 36640615

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Abstract

There are several complications associated with lumbar interbody fusion surgery however, pseudarthrosis (non-union) presents a multifaceted challenge in the postoperative management of the patient. Rates of pseudarthrosis range from 3 to 20 % in patients with healthy bone and 20 to 30 % in patients with osteoporosis. The current methods in post-operative follow-up - radiographs and CT, have high false positive rates and poor agreement between them. The aim of this study was to develop and test a proof-of-concept load-sensing interbody cage that may be used to monitor fusion progression. Piezoresistive pressure sensors were calibrated and embedded within a polyether ether ketone (PEEK) interbody cage. Silicone and poly (methyl methacrylate) (PMMA) were inserted in the graft regions to simulate early and solid fusion. The load-sensing cage was subjected to distributed and eccentric compressive loads up to 900 N between synthetic lumbar vertebral bodies. Under maximum load, the anterior sensors recorded a 56-58 % reduction in pressure in the full fusion state compared to early fusion. Lateral regions measured a 36-37 % stress reduction while the central location reduced by 45 %. The two graft states were distinguishable by sensor-recorded pressure at lower loads. The sensors more effectively detected left and right eccentric loads compared to anterior and posterior. Further, the load-sensing cage was able to detect changes in endplate stiffness. The proof-of-concept 'smart' cage could detect differences in fusion state, endplate stiffness, and loading conditions in this in vitro experimental setup.

Address: School of Mechanical and Manufacturing Engineering, University of New South Wales, Sydney, Kensington, New South Wales, Australia; Spine Labs, St. George & Sutherland Clinical School, University of New South Wales, Sydney, New South Wales, Australia; School of Engineering, Faculty of Science and Engineering, Macquarie University, Sydney, New South Wales, Australia. Electronic address: [email protected].; Spine Labs, St. George & Sutherland Clinical School, University of New South Wales, Sydney, New South Wales, Australia; School of Biomedical Engineering, Faculty of Engineering and Information Technology, University of Technology Sydney, Ultimo, New South Wales, Australia.; School of Engineering, Faculty of Science and Engineering, Macquarie University, Sydney, New South Wales, Australia.; Spine Labs, St. George & Sutherland Clinical School, University of New South Wales, Sydney, New South Wales, Australia; Spine Service, Department of Orthopaedic Surgery St. George Hospital Campus, Kogarah, New South Wales, Australia.; School of Mechanical and Manufacturing Engineering, University of New South Wales, Sydney, Kensington, New South Wales, Australia.

DOI: 10.1016/j.jbiomech.2023.111440

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MeSH Terms: Humans, Pseudarthrosis, Spinal Fusion, Cadaver, Lumbar Vertebrae, Polyethylene Glycols