Anterior Lumbar Interbody Fusion Implant Positioning in Relation to the Epiphyseal Rim: An Experimental Study on Bone Surrogates Reconstructed From Computer Tomography.

STUDY

DESIGN

Biomechanical study on bone surrogates reconstructed from cadaveric vertebrae.

OBJECTIVE

The goal of this study was to evaluate the influence of cage positioning on construct strength and to determine the relationship between the depth of the epiphyseal rim and subsidence load in anterior lumbar interbody fusion (ALIF).

SUMMARY OF BACKGROUND DATA: Cage subsidence is a significant complication affecting fusion success with an incidence range of 6%-23%. Cage subsidence can result in chronic pain due to altered spine alignment, loss of intervertebral height, and inflammatory response. Reoperation rates can range from 5% to 20%. Understanding the impact of cage positioning and endplate characteristics on subsidence is crucial for optimizing surgical outcomes.

MATERIALS AND

METHODS

Sixteen cadaveric (L3-L5) lumbar segments were utilized. Bone surrogates were prepared to represent the heterogeneous structure of lumbar vertebrae. Compression testing was performed using a cage, similar to the cages used in ALIF procedures, shaped indenter with 3 cage positioning configurations: maximized, partial, and null overlap with the epiphyseal rim. Construct stiffness and subsidence load were measured.

RESULTS

Cage positioning significantly influenced subsidence load ( P <0.01) and construct stiffness ( P =0.02). More specifically, cages with maximized epiphyseal contact demonstrated significantly higher subsidence loads than the others ( P =0.01). The thickness of the cortical bone was highly correlated with subsidence load when maximized epiphyseal rim contact was achieved ( R2 = 0.83, P < 0.01).

CONCLUSION

Placement of ALIF cages along the anterior epiphyseal rim increases construct strength. A correlation exists between the thickness of the epiphyseal rim and cage subsidence, suggesting potential preoperative estimation of subsidence load based on epiphyseal rim thickness.