Stepwise reduction of bone mineral density increases the risk of cage subsidence in oblique lumbar interbody fusion patients biomechanically: an in-silico study

Abstract

Background Cage subsidence causes poor prognoses in patients treated by oblique lumbar interbody fusion (OLIF). Deterioration of the biomechanical environment initially triggers cage subsidence, and patients with low bone mineral density (BMD) suffer a higher risk of cage subsidence. However, whether low BMD increases the risk of cage subsidence by deteriorating the local biomechanical environment has not been clearly identified. Methods OLIF without additional fixation (stand-alone, S-A) and with different additional fixation devices (AFDs), including anterolateral single rod screws (ALSRs) and bilateral pedicle screws (BPSs) fixation, was simulated in the L4-L5 segment of a well-validated finite element model. The biomechanical effects of different BMDs were investigated by adjusting the material properties of bony structures. Biomechanical indicators related to cage subsidence were computed and recorded under different directional moments. Results Overall, low BMD triggers stress concentration in surgical segment, the highest equivalent stress can be observed in osteoporosis models under most loading conditions. Compared with the flexion-extension loading condition, this variation tendency was more pronounced under bending and rotation loading conditions. In addition, AFDs obviously reduced the stress concentration on both bony endplates and the OLIF cage, and the maximum stress on ALSRs was evidently higher than that on BPSs under almost all loading conditions. Conclusions Stepwise reduction of BMD increases the risk of a poor local biomechanical environment in OLIF patients, and regular anti-osteoporosis therapy should be considered an effective method to biomechanically optimize the prognosis of OLIF patients.

The Influence of Screw Positioning on Cage Subsidence in Patients with Oblique Lumbar Interbody Fusion Combined with Anterolateral Fixation

“…Therefore, anti-osteoporosis treatment should be considered an effective therapy to avoid subsidence risk. 29,30 Additional, previous studies confirmed that relatively flat endplates significantly diminish the incidence of subsidence. Consequently, the morphology of cage surface should be also taken into consideration when designing the next generation of cage, 23,24 which is also the future research direction of prevention of CS.…”

“…From a biomechanical perspective, low BMD triggers stress concentration in surgical segment and increases the risk of a poor local biomechanical environment in OLIF patients. Therefore, anti‐osteoporosis treatment should be considered an effective therapy to avoid subsidence risk 29,30 . Additional, previous studies confirmed that relatively flat endplates significantly diminish the incidence of subsidence.…”