Does Spanning a Lateral Lumbar Interbody Cage Across the Vertebral Ring Apophysis Increase Loads Required for Failure and Mitigate Endplate Violation

Study Design. Randomized Biomechanical Cadaveric StudyLevel II. Objective. We aimed to elucidate that placing lateral lumbar interbody cages that span the stronger ring apophysis will require increasing loads for failure, decreasing rates of subsidence, regardless of bone density or endplate integrity. Summary of Background Data. There are several reports regarding the rates and grades of cage subsidence when utilizing the lateral lumbar interbody fusion technique. However, there is limited data on how spanning the lateral cage across the ring apophysis can prevent it. Methods. Eight fresh-frozen human spines (L1-L5) were utilized. Each vertebra was placed with their endplates horizontal in an MTS actuator. A total of 40 specimens were randomized into Groups: G1-intact endplate with short cage. G2-intact endplate with long cage spanning the ring apophysis. G3-endplate decortication with short cage. G4-endplate decortication with long cage spanning the ring apophysis. Load displacement data was collected at 5Hz until failure. Results. Longer cages spanning the ring apophysis provided more strength in compression with less subsidence relative to shorter cages, regardless of endplate integrity. Longer cages, spanning the ring apophysis, resting on intact endplates (G2) had a significant (P< 0.05) increase in strength and less subsidence when compared with the smaller cage group resting on intact endplates (G1) (P = 0.003). Longer cages spanning the ring apophysis of intact endplates (G2) showed a significant (P< 0.05) increase in strength and resistance to subsidence when compared with similar length cages resting on decorticated endplates (G4) (P = 0.028). Conclusion. Spanning the ring apophysis increased the load to failure by 40% with intact endplates and by 30% with decorticated endplates in this osteoporotic cadaveric model. Larger cages that span the endplate ring apophysis could improve the compressive strength and decrease subsidence at the operative level despite endplate violation or osteoporosis.