INTRODUCTION: Interbody fusion cages are designed to restore the biomechanical integrity of the spinal column and provide anterior column support for better load sharing at the interface of bone‐implant. A novel interbody cage with a,web and truss based structure has been compared to other conventional cage designs. A finite element analysis was done to evaluate the effect of implant size and geometrical features on subsidence (bone settlement) for the 4‐WEB Spine Interbody Fusion Cage.
METHODS: The study was designed to simulate the cadaveric experiment of Kanayama et al. Aocordingly, the FE model of 4‐WEB structure was developed in different sizes and geometries (different strut thickness and footprint size) and each implant was sandwiched between the two bone blocks as per Kanayama et al. The load‐displacement behavior and stresses in Compression (500N), Flexion (5Nm), Left Bending (3Nm) and Left Rotation (50N+3Nm) were computed. The data was compared to two titanium (BAK and TITAN) and one PEEK interbody cages, which were also simulated in the FE models.
RESULTS: The predicted intra‐cage pressure of the BAK cage was within one SD of the in vitro data. The maximum pressure on the bone graft was 123.5, 304.5, 58.6 and 145.8 KPa in the WEB cage with smaller foot print (comparable to other cages) compared to 113.7, 144.1, 64.1 and 121 KPa in PEEK, 146.4, 132.6, 57.5 and 160 KPa in TITAN and 30.7, 82.7, 17.7 and 36 KPa in the BAK device. The 4‐WEB implanted segment had also lesser peak stress at the interface with bony endplates.
DISCUSSION: The more uniform stress distribution at bone‐implant interface of 4‐WEB cage, compared to the other designs, is a good predictor of lesser failure risk at the bone‐implant interface. The higher stresses in bone graft inside the WEB cage is also representative of proper load sharing on the graft which helps the fusion over the time.