Background:

A successful intervertebral fusion requires biomechanical stability created by the structural support of the interbody device and loading of the bone graft material to accelerate mechanotransduction and bone remodeling. The objective of this study was to generate a quantitative map of the contact area and stress profile for 2 implant designs; a rigid monolithic polyetheretherketone (PEEK) lateral cage (MPLC), and a unique hybrid interbody design, which includes PEEK terminal supports surrounding an expandable porous mesh (P+EPM) that serves to contain bone graft.

Methods:

The construct for each test consisted of a device sandwiched between 2 flat or shaped Grade 15 foam blocks. Pressure sensitive film and thin film sensors were placed between the device and each of the foam blocks. A series of each implant type was compressed at a rate 0.1 mm/second for 2 loads (1100 N and 2000 N) with and without bone graft. Device and bone graft contact area were analyzed for each test condition and corresponding load profiles were quantified and mapped.

Results:

P+EPM demonstrated 34% greater graft volume than MPLC resulting in a 28% larger area for bone exchange when filled. The load profiles for all applied loading paradigms for P+EPM demonstrated significant direct loading on the bone graft contained within the mesh, resulting in at least 170% greater loaded area than MPLC. Furthermore, the P+EPM demonstrated load sharing with the terminal PEEK supports. MPLC for all loading conditions demonstrated negligible bone graft loading.

Conclusions:

P+EPM allows for an optimized contact area for bone exchange and graft incorporation. The load profiles confirmed that the filled mesh does not stress shield terminal PEEK supports and will load share. The expandable, compliant, porous mesh provides a greater multiplanar area for bone exchange and allows for direct contact with the viscoelastic vertebral endplates, improving the endplate and graft interface mechanics.