Biomechanical effects of disc cement for lumbar locking interbody cementation: Finite-element mobility analysis and debris-removing reamer design

Abstract

Background: Before locking interbody cementation, debris from the reamed disc should be thoroughly cleared to increase the cement volume and decrease its flow resistance to the vertebrae.

Methods: A finite element lumbosacral model was used to assess the biomechanical effects of five different disc cement sizes on disc mobility. A new reamer featuring staggered, barbed, and multilayered cutting edges, along with spiral and conical profiles, was designed and 3D-printed to enhance debris removal. Biomechanical and clinical tests were performed using synthetic and patient discs to compare the debris weights removed by the standard drill bit and the 3D-printed reamer.

Findings: Cement size significantly affected disc mobility beyond the impact of torsional factors alone. Larger cement volumes produced a more stable cage-cement foundation and reduced sagittal and coronal motions by approximately 23.8 % compared to the standard 5 mm-thick cement coverage. The average weight of synthetic disc debris removed was 926.28 ± 49.71 mg with the 3D-printed reamer versus only 63.04 ± 4.86 mg with the standard drill bit (p < 0.01). When the drill bit was withdrawn, debris easily slipped from the spiral cutting edge. In contrast, drill bits failed to retain debris effectively, whereas the reamer's staggered and barbed features consistently hooked and removed disc material.

Interpretation: Implanting a 5 mm cage requires removing approximately 6 ml of disc material. A larger cement fill provides a more stable cage-cement interface. The 3D-printed reamer's staggered barbs removed debris more efficiently than traditional drill bits.

Keywords: Cement discoplasty; Degenerative lumbar; Finite element analysis; Interbody cementation; Reamer.