A modular cage may prevent endplate damage and improve spinal deformity correction.

Abstract

Anterior lumbar interbody fusion is performed to fuse pathological spinal segments, generally, with a monobloc cage inserted by impact forces. Recently developed three-part modular cages attempt to reduce the impact forces, minimize the damage to the endplates and allow more lordosis angle correction. Human lumbar motion segments (L2-3, L4-5) were used to simulate the implantation procedure of monobloc vs. modular stand-alone cages (n = 12). After preparing and embedding, a discectomy was performed followed by the two different types of cage implantation. Macroscopic images, microcomputed tomography scans and Artificial-Intelligence-based lordosis angle measurements were conducted and analyzed in the intact and implanted state and endplate damage was evaluated. The modular and monobloc group had similar impact on three defined damage classes both groups fell into the mid-damage class (29 %); the modular group fell to 13 % in the low-damage class while the monobloc one to 17 % in the high-damage class. Fragmentation appeared more in the monobloc group (71 %), while defects appeared equally. The modular implantation achieved a median lordosis of 21.3° versus 19.5° for the monobloc (P = 0.132) leading to 34 % higher increase for the modular procedure. Endplate damage occurs in both procedures but severe damage like bone fragmentation can be avoided with modular implantation. Bone fragmentation seems to affect and minimize the desired lordosis angle after cage implantation. This in vitro study underlines the need of new implantation procedures to achieve increased lordosis with anterior lumbar interbody fusion to restore the patients sagittal balance successfully.