Threaded lumbar interbody spinal fusion devices (TIBFD) made from titanium have been reported to be 90% effective for single-level lumbar interbody fusion, although radiographic determination of fusion has been intensely debated in the literature. Using blinded radiographic, biomechanic, histologic, and statistical measures, we evaluated a radiolucent polyetheretherketone (PEEK)-threaded interbody fusion device packed with autograft or rhBMP-2 on an absorbable collagen sponge in 13 sheep at 6 months. Radiographic fusion, increased spinal level biomechanical stiffness, and histologic fusion were demonstrated for the PEEK cages filled with autograft or rhBMP-2 on a collagen sponge. No device degradation or wear debris was observed. Only mild chronic inflammation consisting of a few macrophages was observed in peri-implant tissues. Based on these results, the polymeric biomaterial PEEK may be a useful biomaterial for interbody fusion cages due to the polymer's increased radiolucency and decreased stiffness.

Summary: A fully three-dimensional finite element model of a C 5 X 6 motion segment of the human spine was developed and validated for the purpose of investigating the biomechanical significance of uncinate processes and Luschka joints. The original intact cervical model was modified to create two additional models. The first simulated the absence of Luschka joints by replacing the fissures with continuous annulus fibrosus and leaving the uncinate processes intact. The second model simulated a surgical resection of the uncinate processes, while leaving the Luschka joints intact. The results of these two models were compared with the intact model, which served as a baseline; thus, the relative contributions of these two structures to cervical motion were established. With use of our model, it was possible, for the first time, to provide quantitative data concerning the source of coupled motions in the lower cervical spine. In principle, the results from this model support the hypothesis of Penning and Wilmink. Our results indicate that the facet joints and Luschka joints are the major contributors to coupled motion in the lower cervical spine and that the uncinate processes effectively reduce motion coupling and primary cervical motion (motion in the same direction as load application), especially in response to axial rotation and lateral bending loads. Luschka joints appear to increase primary cervical motion, showing an effect on cervical motion opposite to that of the uncinate processes. Surgeons should be aware of the increase in motion accompanied by resection of the uncinate processes.The function of uncinate processes and Luschka joints in passive control of lower cervical motion has not been definitively clarified. Frykholm (9) suggested that the uncinate processes provide a means for the cervical spine to protect the brachial plexus, whereas Hall (13) theorized that they allow for rotational movement. Penning and Wilmink (20) hypothesized that the coupling motion observed in the cervical spine is not determined solely by the orientation of the facets. Rather, they suggested that the location and orientation of the uncinate processes are such that coupled motions in the lower cervical spine could be explained by their presence.The uncinate processes are bony protuberances that extend cranially from the lateral margins of the superior endplates in the lower cervical spine (Fig. 1). A unique feature of the cervical intervertebral disc is the presence of a fissure or cleft that runs along the uncinate process toward the nucleus pulposus. This fissure, called a Luschka or uncovertebral joint, appears in the Received October 28,1996; accepted March 15,1997. Address correspondence and reprint requests to V. K. Goel at Department of Biomedical Engineering, EB 1208, University of Iowa, Iowa City, 1A 52242, U.S.A. E-mail: Vijay-Goel@uiowa.edu annular lamellae, and the adjacent collagenous fibers reorient and run parallel with the fissure (9,13,14). Luschka joints appear in the latter part of the first decade of li...

To the best of the authors' knowledge, this is the first report of a validated, three-dimensional model of the C0-C1-C2 complex with application to rheumatoid arthritis. The data indicate that there may be a mechanical component (in addition to enzymatic degradation) associated with the osseous resorption observed during rheumatoid arthritis. Specifically, erosion of the odontoid base may involve Wolff's law of unloading considerations. Changes through the lateral aspects of the atlas suggest that this same mechanism may be partially responsible for the erosive changes seen during progressive rheumatoid arthritis. Anterior and posterior atlantodental interval values indicate that complete destruction of the transverse ligament coupled with alar and/or capsular ligament compromise is requisite if advanced levels of atlantoaxial subluxation are present.

Object. Titanium lumbar interbody spinal fusion devices are reported to be 90% effective in cases requiring single-level lumbar interbody arthrodesis, although radiographic determination of fusion has been debated. Methods. Using blinded radiographic, biomechanical, histological, and statistical measures, researchers in the present study evaluated a radiolucent 70/30 poly(l-lactide-co-d,l-lactide) interbody fusion device packed with autograft or recombinant human bone morphogenetic protein—2 on a collagen sponge in 25 sheep at 3, 6, 12, 18, and 24 months. A trend of increased fusion stiffness, radiographic fusion, and histologically confirmed fusion was demonstrated at 3 months to 24 months postimplantation. Device degradation was associated with a mild to moderate chronic inflammatory response at all postoperative sacrifice times. Conclusions. Use of this material in interbody fusion may be a viable alternative to metals.

The weakest link in immature baboon lumbar functional spinal units (FSUs) with lysis during an A-P shear load was the growth plate, between the cartilaginous and osseous end plates. Surgeons may assess this lesion on MRI views, thereby predicting the possible development and preventing progression of olisthesis. Finite element model results predict that more sagittally orientated facets and/or a pars fracture are prerequisites for olisthesis to occur.