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Biomechanical testing methodologies for the spine have developed over the past 50 years. During that time, there have been several paradigm shifts with respect to techniques. These techniques evolved by incorporating state-of-the-art engineering principles, in vivo measurements, anatomical structure-function relationships, and the scientific method. Multiple parametric studies have focused on the effects that the experimental technique has on outcomes. As a result, testing methodologies have evolved, but there are no standard testing protocols, which makes the comparison of findings between experiments difficult and conclusions about in vivo performance challenging. In 2019, the international spine research community was surveyed to determine the consensus on spine biomechanical testing and if the consensus opinion was consistent with the scientific evidence. More than 80 responses to the survey were received. The findings of this survey confirmed that while some methods have been commonly adopted, not all are consistent with the scientific evidence. This review summarizes the scientific literature, the current consensus, and the authors' recommendations on best practices based on the compendium of available evidence.

Background: Interbody arthrodesis is employed in the lumbar spine to eliminate painful motion and achieve stability through bony fusion. Bone grafts, metal cages, composite spacers, and growth factors are available and can be placed through traditional open techniques or minimally invasively. Whether placed anteriorly, posteriorly, or laterally, insertion of these implants necessitates compromise of the anulus--an inherently destabilizing procedure. A new axial percutaneous approach to the lumbosacral spine has been described. Using this technique, vertical access to the lumbosacral spine is achieved percutaneously via the presacral space. An implant that can be placed across a motion segment without compromise to the anulus avoids surgical destabilization and may be advantageous for interbody arthrodesis. The purpose of this study was to evaluate the in vitro biomechanical performance of the axial fixation rod, an anulus sparing, centrally placed interbody fusion implant for motion segment stabilization. Method of Approach: Twenty-four bovine lumbar motion segments were mechanically tested using an unconstrained flexibility protocol in sagittal and lateral bending, and torsion. Motion segments were also tested in axial compression. Each specimen was tested in an intact state, then drilled (simulating a transaxial approach to the lumbosacral spine), then with one of two axial fixation rods placed in the spine for stabilization. The range of motion, bending stiffness, and axial compressive stiffness were determined for each test condition. Results were compared to those previously reported for femoral ring allografts, bone dowels, BAK and BAK Proximity cages, Ray TFC, Brantigan ALIF and TL1F implants, the InFix Device, Danek TIBFD, single and double Harms cages, and Kaneda, Isola, and University plating systems. Results: While axial drilling of specimens had little effect on stiffness and range of motion, specimens implanted with the axial fixation rod exhibited significant increases in stiffness and decreases in range of motion relative to intact state. When compared to existing anterior, posterior, and interbody instrumentation, lateral and sagittal bending stiffness of the axial fixation rod exceeded that of all other interbody devices, while stiffness in extension and axial compression were comparable to plate and rod constructs. Torsional stiffness was comparable to other interbody constructs and slightly lower than plate and rod constructs. Conclusions: For stabilization of the [L.sub.5]-[S.sub.1] motion segment, axial placement of implants offers potential benefits relative to traditional exposures. The preliminary biomechanical data from this study indicate that the axial fixation rod compares favorably to other devices and may be suitable to reduce pathologic motion at [L.sub.5]-[S.sub.1], thus promoting bony fusion. [DOI: 10.1115/1.2049334] Keywords: Lumbosacral Fusion, Transaxial, Axial Fixation Device

There is a high incidence of injury during rugby tackling. Tackle biomechanics are linked to this injury risk. The effectiveness of educational methods in teaching safe rugby tackling for players of various ages and experience levels has not been elucidated. We hypothesized that watching an educational video on rugby tackling technique would alter lower extremity kinematics and reduce cervical spine and head acceleration during tackling. Kinematics and kinetics of 50 collegiate and high school-aged rugby players were recorded while tackling an opponent in a laboratory setting. Movement of the lower extremity, upper body, and head were quantified with a motion analysis system. Participants were shown video instruction on tackling technique then performed another series of tackles. Data were compared pre- and post-educational intervention. A fixed effects model was used to compare the effect of repetition versus educational intervention. Skilled collegiate players tackled with significantly greater mean knee flexion angle post-educational intervention relative to pre-instruction, indicative of better technique. The fixed effects model indicated that video instruction decreased acceleration by a mean 51.8 m/s2 in collegiate players. However, the effect of repetition was shown to increase peak acceleration by a mean 11.2 m/s2. In contrast, the educational intervention resulted in an increased acceleration of 15.4 m/s2 for high school players, but the effect of repetition was shown to decrease acceleration by a mean of 5.2 m/s2. Experienced players respond as expected to video instructional intervention. Repetition may be more important for younger rugby players to learn effective tackling. [ABSTRACT FROM AUTHOR]