The hybrid testing protocol is advocated because it better reproduces clinical observations in terms of motion following surgery, using pure moments. Using this approach, we found that the Charité artificial disc placement slightly increases motion at the implanted level, with a resultant increase in facet loading when compared to the adjacent segments, while the motions and loads decrease at the adjacent levels. However, in the load control mode that we believe is not that clinically relevant, there was a large increase in motion and a corresponding increase in facet loads, as compared to the intact.

Treatment of chronic low back pain due to degenerative lumbar spine conditions often involves fusion of the symptomatic level. A known risk of this procedure is accelerated adjacent level degeneration. Motion preservation devices have been designed to provide stabilization to the symptomatic motion segment while preserving some physiologic motion. The aim of this study was to compare the changes in relative range of motion caused as a result of application of two non-fusion, dynamic stabilization devices: the Universal Clamp (UC) and the Wallis device. Nine fresh, frozen human lumbar spines (L1-Sacrum) were tested in flexion-extension, lateral bending, and axial rotation with a custom spine simulator. Specimens were tested in four conditions: (1) intact, (2) the Universal Clamp implanted at L3-4 (UC), (3) the UC with a transverse rod added (UCTR), and (4) the Wallis device implanted at L3-4. Total range of motion at 7.5 N-m was determined for each device and compared to intact condition. The UC device (with or without a transverse rod) restricted motion in all planes more than the Wallis. The greatest restriction was observed in flexion. The neutral position of the L3-4 motion segment shifted toward extension with the UC and UCTR. Motion at the adjacent levels remained similar to that observed in the intact spine for all three constructs. These results suggest that the UC device may be an appropriate dynamic stabilization device for degenerative lumbar disorders.

Understanding spinal kinematics is essential for distinguishing between pathological conditions of spine disorders, which ultimately lead to low back pain. It’s of high importance to understand how changes in mechanical properties affect the response of the lumbar spine, specifically in an effort to differentiate those associated with disc degeneration from ligamentous changes, allowing for more precise treatment strategies. To do this the goals of this study were twofold: 1) develop and validate a finite element (FE) model of the lumbar spine and 2) systematically alter the properties of the intervertebral disc and ligaments to define respective roles in functional mechanics. A three-dimensional non-linear FE model of the lumbar spine (L3-Sacrum) was developed and validated for pure moment bending. Disc degeneration and sequential ligament failure was modeled. Intersegmental range of motion (ROM) and bending stiffness was measured. The prediction of the FE model to moment loading in all three planes of bending showed very good agreement, where global and intersegmental ROM and bending stiffness of the model fell within one standard deviation of the in vitro results. Degeneration decreased ROM for all directions. Stiffness increased for all directions except axial rotation, where it initially increased then decreased for moderate and severe degeneration, respectively. Incremental ligament failure produced increased ROM and decreased stiffness. This effect was much more pronounced for all directions except lateral bending, which is minimally impacted by ligaments. These results indicate that lateral bending may be more apt to detect the subtle changes associated with degeneration, without being masked by associated changes of surrounding stabilizing structures.

Radioscapholunate arthrodesis is a salvage procedure indicated for osteoarthritis of the radiocarpal joint involving the lunate facet of the radius. This cadaver study examines changes in wrist motion resulting from radioscapholunate arthrodesis, and the effects of surgical techniques to improve the range of motion. Simulated radioscapholunate arthrodesis, distal scaphoidectomy and triquetrectomy were carried out sequentially on six cadaver forearms and measurements (maximum flexion/extension and radial/ulnar deviation) were taken in the intact situation and after each surgical step using a magnetic tracking device. Radioscapholunate arthrodesis diminishes the amplitudes of movements of the wrist in all directions, but range of motion in the radioscapholunate fused wrist improves after scaphoidectomy and improves further after triquetrectomy (88% of original flexion/extension and 98% of original radial/ulnar deviation). Radioscapholunate arthrodesis causes a significant change in kinematics between the hamate and the triquetrum in flexion/extension.