Use of a Spine Robot to Simulate Pure Moment Testing for Spine Biomechanics

摘要

The pure moment protocol is the accepted standard for performing in-vitro biomechanical testing of spinal devices. The purpose of this study was to simulate a pure moment protocol using a programmable Spine Robot. Seven human lumbar single-level motion segment units (MSUs) at the L4-L5 level were dissected and potted. The average age of the spines was 59.7 ± 11.7 years. The Spine Robot was programmed to rotate the specimen in flexion and extension or left and right lateral bending in 0.25 degree increments, minimizing shear and axial loading after each rotation, thereby finding a quasistatic rotational path of minimal loading. The specimens were rotated to 8Nm of sagittal moment during flexion and extension and 6Nm of lateral moment during lateral bending. During lateral testing, the specimens were unconstrained axially. Throughout testing, the specimens underwent an average shear force of 0.29 ± 0.95N in the anterior direction and an average axial compressive force of 0.21 ± 1.18N. During flexion and extension tests the specimens rotated an average of 8.05 ± 2.96 degrees and 5.46 ± 1.90 degrees respectively. During left and right lateral bending tests the specimens rotated an average of 5.18 ± 2.01 degrees and 5.43 ± 1.94 degrees respectively. These values are in agreement with other published studies of lumbar spinal biomechanics. Future work for the protocol will be to allow for a user-inputted axial load to simulate the concepts of the follower load protocol used by other labs. While test methodologies differ between labs, there is currently no way to directly compare data between them. Our desire is to use the programmable Spine Robot to simulate commonly used testing methodologies to uncover how different test methods may or may not show differences in results and to develop advanced testing protocols that better simulate physiological conditions.