Disclosed are prosthetic devices for insertion into intervertebral disc spaces after the removal of an intervertebral disc or after a corpectomy. Specifically, intervertebral devices having fixed shapes for accommodating the defined surface contours of vertebral endplates are disclosed. Also disclosed are intervertebral devices formed of osteoinductive materials, such as bone growth factors, to facilitate bone growth. A method for quantitatively determining the three-dimensional morphology of vertebral surfaces, particularly vertebral endplates, is also disclosed.

Prosthetic intervertebral devices

Treatment of delayed union, malunion, and nonunion is a challenge to the orthopaedic surgeons in veterinary and human fields. Apart from restoration of alignment and stable fixation, in many cases adjunctive measures such as bone-grafting or use of bone-graft substitutes are of paramount importance. Bone-graft materials usually have one or more components: an osteoconductive matrix, which acts as scaffold to new bone growth; osteoinductive proteins, which support mitogenesis of undifferentiated cells; and osteogenic cells, which are capable of forming bone in the appropriate environment. Autologous bone remains the "gold standard" for stimulating bone repair and regeneration, but its availability may be limited and the procedure to harvest the material is associated with complications. Bone-graft substitutes can either substitute autologous bone graft or expand an existing amount of autologous bone graft. We review the currently available bone graft and graft substitutes for the novel therapeutic approaches in clinical setting of orthopaedic surgery.

Orthopaedic applications of bone graft & graft substitutes: a review.

One hundred and fifty consecutive patients who had a burst fracture of the thoracolumbar spine and associated neurological deficits were managed with a single-stage anterior spinal decompression, strut-grafting, and Kaneda spinal instrumentation. At a mean of eight years (range, five years to twelve years and eleven months) after the operation, radiographs showed successful fusion of the injured spinal segment in 140 patients (93 per cent). Ten patients had a pseudarthrosis, and all were managed successfully with posterior spinal instrumentation and a posterolateral arthrodesis. The percentage of the canal that was obstructed, as measured on computed tomography, improved from a preoperative mean of 47 per cent (range, 24 to 92 per cent) to a postoperative mean of 2 per cent (range, 0 to 8 per cent). Despite breakage of the Kaneda device in nine patients, removal of the implant was not necessary in any patient. None of the patients had iatrogenic neurological deficits. After the anterior decompression, the neurological function of 142 (95 per cent) of the 150 patients improved by at least one grade, as measured with a modification of the grading scale of Frankel et al. Fifty-six (72 per cent) of the seventy-eight patients who had preoperative paralysis or dysfunction of the bladder recovered completely. One hundred and twenty-five (96 per cent) of the 130 patients who were employed before the injury returned to work after the operation, and 112 (86 per cent) of them returned to their previous job without restrictions. We concluded that anterior decompression, strut- grafting, and fixation with the Kaneda device in patients who had a burst fracture of the thoracolumbar spine and associated neurological deficits yielded good radiographic and functional results.

Anterior decompression and stabilization with the Kaneda device for thoracolumbar burst fractures associated with neurological deficits.

Osteoarthritis (OA) of the spine involves the facet joints, which are located in the posterior aspect of the vertebral column and, in humans, are the only true synovial joints between adjacent spinal levels. Facet joint osteoarthritis (FJ OA) is widely prevalent in older adults, and is thought to be a common cause of back and neck pain. The prevalence of facet-mediated pain in clinical populations increases with increasing age, suggesting that FJ OA might have a particularly important role in older adults with spinal pain. Nevertheless, to date FJ OA has received far less study than other important OA phenotypes such as knee OA, and other features of spine pathoanatomy such as degenerative disc disease. This Review presents the current state of knowledge of FJ OA, including relevant anatomy, biomechanics, epidemiology, and clinical manifestations. We present the view that the modern concept of FJ OA is consonant with the concept of OA as a failure of the whole joint, and not simply of facet joint cartilage.

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Osteoarthritis of the spine: the facet joints

Biodegradable Materials for Bone Repairs: A Review

Twenty-two patients with neurologic deficit due to delayed posttraumatic vertebral collapse after osteoporotic compression fractures of the thoracolumbar spine underwent anterior decompression and reconstruction with bioactive Apatite-Wollastonite containing glass ceramic vertebral prosthesis and Kaneda instrumentation. Eighteen patients previously had minor trauma that resulted in a mild vertebral compression fracture without any neurologic involvement and were either conservatively treated or not treated at all. Four had no history of back injury. The preoperative neurologic status was incomplete paralysis in all patients. The average age at surgery was 66 (53-79) years. The average follow-up was 34 (20-58) months after surgery. All patients had returned to their daily living with neurologic recovery and stable spine. This type of anterior procedure is effective in the osteoporotic patients and there was a very low incidence of instrumentation failure and very low morbidity.

The treatment of osteoporotic posttraumatic vertebral collapse using the kaneda device and a bioactive ceramic vertebral prosthesis

Cyclic axial compression-tension tests and cyclic torsional tests were performed on ten fresh human L4-5 functional spinal units to investigate the structural effects of the posterior elements on the mechanical properties of L4-5 functional spinal units. The stiffness of the functional spinal unit increased with the increase of displacement under every loading. This was same in the intact functional spinal units and the functional spinal units after removal of each posterior element, respectively. All the posterior elements contributed to the compressive, tensile, and torsional stiffness of L4-5 functional spinal units. The apophyseal joints had a significant effect on the compressive and torsional stiffness. The effect of the apophyseal joints on the torsional stiffness became greater according to the extent of displacement, whereas their effect on the compressive stiffness was constant. The posterior ligaments (supraspinous and interspinous ligaments) had a significant effect on the tensile stiffness.

The mechanical properties of the human L4-5 functional spinal unit during cyclic loading. The structural effects of the posterior elements.

Between June 1987 and December 1990, an iliac crest prosthesis made of bioactive apatite- and wollastonite-containing glass ceramic (A-W·GC) was used in 60 patients for the reconstruction of the iliac crest defect after harvesting autogenous tricortical iliac bone graft. The clinical results of this prosthesis were satisfactory. No patients felt spontaneous pain in the reconstructed area, and 93% of the patients had no tenderness there. In the radiological evaluation at the final follow-up, no apparent “radiolucent clear zone” was detected at the prosthesis-iliac bone junction in 98% of the patients. Excellent new bone formation between the prosthesis and the iliac crest was also noticed in 96% of the patients. The A-W·GC iliac crest prosthesis was beneficial for reconstruction of the iliac crest defect.

Reconstruction of an iliac crest defect with a bioactive ceramic prosthesis.

PURPOSE: To provide flexibility capable of sufficiently following the motion of a human body by respectively integrally mounting two almost plate-shaped bodies composed of a living body-active ceramic material to the upper and under surfaces of an almost plate-shaped body composed of a polymer elastic material having bio-compatibility. CONSTITUTION: Two upper and lower layers are formed from hard disc-shaped bodies 10, 11 made of ceramics such as hydroxyapatite and the intermediate layer held between two layers is formed from a disc-shaped body 12 composed of a polymer such as silicone rubber for a living body having bio-compatibility and definite elasticity to constitute a sandwich structure. Therefore, when the upper and lower ceramic disc bodies 10, 11 of this artificial intervertebral disk are bonded to the vertebral bodies of a human body, the upper and lower ceramic disc bodies 10, 11 are freely revolved in a certain degree around the polymer disc body 12 having elasticity as if the intervertebral disk is flexibly connected to the upper and lower vertebral bodies. As a result, since this artificial intervertebral disk flexibly moves in matching relation to forward and rearward movement, the whole of the spine smoothly moves and no unreasonable load is applied to the spine. COPYRIGHT: (C)1991,JPO&Japio

Artificial intervertebral disk

The human intervertebral disc is an essential element in sustaining weight and in permitting mobility of the spine, which is often subject to degeneration, injuries and disease. In this paper, a new artificial intervertebral disc is proposed to reconstruct the stability and the mobility of a human functional spinal unit. The geometry and the structure of the artificial intervertebral disc were designed by the computer simulation at 3D-FEM, as the static compressive and the torsional stiffnesses of this model agree with the stiffnesses of cadaveric lumbar discs. Consequently, the proposed model consists of two bioactive ceramic plates and intervenient substructure made from rubber-like materials. Glass-ceramics containing apatite and wollastonite was chosen as a material for the plates which come into contact with the bone, because this material is able to form a strong chemical bond with the osseous tissue. Elastic materials of medical grade in the substructure between two plates were selected, as the artificial disc has the same static stiffness properties with a cadaveric lumbar disc.

Satoshi Asano

Papers

The treatment of osteoporotic posttraumatic vertebral collapse using the kaneda device and a bioactive ceramic vertebral prosthesis

The mechanical properties of the human L4-5 functional spinal unit during cyclic loading. The structural effects of the posterior elements.

Reconstruction of an iliac crest defect with a bioactive ceramic prosthesis.

Artificial intervertebral disk

On the Structure of an Artificial Intervertebral Disc with Equivalent Static Stiffness to a Human Disc.