Object The authors report the results of a prospective randomized multicenter study in which the results of cervical disc arthroplasty were compared with anterior cervical discectomy and fusion (ACDF) in patients treated for symptomatic single-level cervical degenerative disc disease (DDD). Methods Five hundred forty-one patients with single-level cervical DDD and radiculopathy were enrolled at 32 sites and randomly assigned to one of two treatment groups: 276 patients in the investigational group underwent anterior cervical discectomy and decompression and arthroplasty with the PRESTIGE ST Cervical Disc System (Medtronic Sofamor Danek); 265 patients in the control group underwent decompressive ACDF. Eighty percent of the arthroplasty-treated patients (223 of 276) and 75% of the control patients (198 of 265) completed clinical and radiographic follow-up examinations at routine intervals for 2 years after surgery. Analysis of all currently available postoperative 12- and 24-month data indicated a two-point...

Clinical and radiographic analysis of cervical disc arthroplasty compared with allograft fusion: a randomized controlled clinical trial

This paper is a narrative review of normal cervical alignment, methods for quantifying alignment, and how alignment is associated with cervical deformity, myelopathy, and adjacent-segment disease (ASD), with discussions of health-related quality of life (HRQOL). Popular methods currently used to quantify cervical alignment are discussed including cervical lordosis, sagittal vertical axis, and horizontal gaze with the chin-brow to vertical angle. Cervical deformity is examined in detail as deformities localized to the cervical spine affect, and are affected by, other parameters of the spine in preserving global sagittal alignment. An evolving trend is defining cervical sagittal alignment. Evidence from a few recent studies suggests correlations between radiographic parameters in the cervical spine and HRQOL. Analysis of the cervical regional alignment with respect to overall spinal pelvic alignment is critical. The article details mechanisms by which cervical kyphotic deformity potentially leads to ASD and discusses previous studies that suggest how postoperative sagittal malalignment may promote ASD. Further clinical studies are needed to explore the relationship of cervical malalignment and the development of ASD. Sagittal alignment of the cervical spine may play a substantial role in the development of cervical myelopathy as cervical deformity can lead to spinal cord compression and cord tension. Surgical correction of cervical myelopathy should always take into consideration cervical sagittal alignment, as decompression alone may not decrease cord tension induced by kyphosis. Awareness of the development of postlaminectomy kyphosis is critical as it relates to cervical myelopathy. The future direction of cervical deformity correction should include a comprehensive approach in assessing global cervicalpelvic relationships. Just as understanding pelvic incidence as it relates to lumbar lordosis was crucial in building our knowledge of thoracolumbar deformities, T-1 incidence and cervical sagittal balance can further our understanding of cervical deformities. Other important parameters that account for the cervical-pelvic relationship are surveyed in detail, and it is recognized that all such parameters need to be validated in studies that correlate HRQOL outcomes following cervical deformity correction.

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Cervical spine alignment, sagittal deformity, and clinical implications: A review

Results of the prospective, randomized, controlled multicenter Food and Drug Administration investigational device exemption study of the ProDisc-C total disc replacement versus anterior discectomy and fusion for the treatment of 1-level symptomatic cervical disc disease

The aim of this work was to add to the body of data on the frequency and severity of degenerative radiographic findings at adjacent levels after anterior cervical interbody fusion and on their clinical impact and to contribute to the insights about their pathogenesis. One hundred eighty patients who were treated by anterior cervical interbody fusion and who had a follow-up of >60 months were clinically and radiologically examined by independent investigators. For all patients, the long-term Odom score was compared with the score as obtained 6 weeks after surgery. For myelopathic cases, both the late Nurick and the Odom score were compared with the initial postoperative situation. For the adjacent disc levels, a radiologic "degeneration score" was defined and assessed both initially and at long-term follow-up. At late follow-up after anterior cervical interbody fusion, additional radiologic degeneration at the adjacent disc levels was found in 92% of the cases, often reflecting a clinical deterioration. The severity of this additional degeneration correlated with the time interval since surgery. The similarity of progression to degeneration between younger trauma patients and older nontrauma patients suggests that both the biomechanical impact of the interbody fusion and the natural progression of pre-existing degenerative disease act as triggering factors for adjacent level degeneration.

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Long-term follow-up after interbody fusion of the cervical spine.

Study Design. Prospective, concurrently enrolled, multicenter trials of the Bryan Cervical Disc Prosthesis (Medtronic Sofamor Danek, Memphis, TN) were conducted for the treatment of patients with single-level and two-level (bi-level) degenerative disc disease of the cervical spine. Objectives. The studies were designed to determine whether new functional intervertebral cervical disc prosthesis can provide relief from objective neurologic symptoms and signs, improve the patient's ability to perform activities of daily living, decrease pain, and maintain stability and segmental motion. Summary of Background Data. The concept of accelerated degeneration of adjacent disc levels as a consequence of increased stress caused by interbody fusion of the cervical spine has been widely postulated. Therefore, reconstruction of a failed intervertebral disc with functional disc prosthesis should offer the same benefits as fusion while simultaneously providing motion and thereby protecting the adjacent level discs from the abnormal stresses associated with fusion. Methods. Patients with symptomatic cervical radiculopathy and/or myelopathy underwent implantation with the Bryan prosthesis after a standard anterior cervical-discectomy. At scheduled follow-up periods, the effectiveness of the device was characterized by evaluating each patient's pain, neurologic function, and radiographically measured range of motion at the implanted level. Results. Clinical success for both studies exceeded the study acceptance criteria of 85%. At 1-year follow-up, the flexion-extension range of motion per level averaged 7.9 +/- 5.3 degrees in the single-level study and 7.4 +/- 5.1 degrees in the bilevel study. No devices have been explanted. Conclusions. Discectomy and implantation of the device alleviates neurologic symptoms and signs similar to anterior cervical discectomy and fusion. Radiographic evidence supports maintenance of motion. The procedure is safe and the patients recover quickly. At least 5 years of follow-up will be needed to assess the long-term functionality of the prosthesis and protective influence on adjacent levels.

Intermediate follow-up after treatment of degenerative disc disease with the Bryan Cervical Disc Prosthesis: single-level and bi-level.

STUDY DESIGN An analysis of the change in strain distribution of intervertebral discs present after anterior cervical decompression and fusion by an original method. The analytical results were compared to occurrence of herniation of the intervertebral disc on magnetic resonance imaging. OBJECTIVES To elucidate the influence of anterior cervical decompression and fusion on the unfused segments of the spine. SUMMARY OF BACKGROUND DATA There is no consensus regarding the exact significance of the biomechanical change in the unfused segment present after surgery. METHODS Ninety-six patients subjected to anterior cervical decompression and fusion for herniation of intervertebral discs were examined. Shear strain and longitudinal strain of intervertebral discs were analyzed on pre- and postoperative lateral dynamic routine radiography of the cervical spine. Thirty of the 96 patients were examined by magnetic resonance imaging before and after surgery, and the relation between alteration in strains and postsurgical occurrence of disc herniation was examined. RESULTS In the cases of double- or triple-level fusion, shear strain of adjacent segments had increased 20% on average 1 year after surgery. Thirteen intervertebral discs that had an abnormally high degree of strain showed an increase in longitudinal strain after surgery. Eleven (85%) of the 13 discs that showed an abnormal increase in longitudinal strain had herniation in the same intervertebral discs with compression of the spinal cord during the follow-up period. Relief of symptoms was significantly poor in the patients with recent herniation. CONCLUSIONS Close attention should be paid to long-term biomechanical changes in the unfused segment.

Strain on intervertebral discs after anterior cervical decompression and fusion.

A method for evaluating the water application rate (WAR) and uniformity coefficient (Cu) of overlapping irrigation sprinklers is given for realistic field conditions which includes wind drift of the sprinkler spray. The method requires as input — the geometry of the sprinkler arrangement, trajectories of water drops from the sprinkler nozzle as calculated by the equations of motion and the WAR distribution (discharge) profile of a single sprinkler experimentally observed under windless conditions. Wind direction with respect to the main sprinkler line is shown to have a small effect on Cu and is assumed to be parallel to the main line. Results show that the effect of wind drift of sprinkler spray on Cu can be neglected for wind velocities less than 1 ms−1 (Fig. 8). Analysis of simulated discharge profiles (Table 1) shows that the maximum value of the uniformity coefficient was obtained with triangular sprinkler discharge profiles at low values of spacing, changing to trapezoidal profiles as the spacing increases (Figs. 8 and 9). The effect of nozzle pressure on WAR was evaluated for the pressure range between 294 and 490 kPa and an optimum layout of overlapping sprinklers, designed to minimize the effect of wind drift and nozzle pressure on the uniformity of WAR distribution, is presented.

Computer evaluation of sprinkler irrigation uniformity

The effects of the frictional constraint resulting from the application of palm olein oil lubricant and paraffin mineral oil lubricant on the plastic deformation of a metal work-piece were investigated by plane strain extrusion experiments and visioplasticity analyses. The experiment used an extrusion apparatus in which the plane plate tool and the tapered die with a 45-degree die half-angle were facing together, with a frictional constraint at the plane plate tool or the two tapered dies, and with zero frictional constraint (friction-free condition) at the contact plane corresponding to the plane plate tool. The billet material was annealed aluminum (JIS-A1050). The effects of the frictional constraint on the forming load, surface roughness, plastic flow characteristics, distribution of plastic flow velocity, and strain distribution in the billet were analyzed quantitatively. We confirmed that palm olein oil showed satisfactory lubrication performance, as compared to paraffin mineral oil and the friction-free condition.

Investigation of the effects of frictional constraint with application of palm olein oil lubricant and paraffin mineral oil lubricant on plastic deformation by plane strain extrusion

The performance of palm oil as a lubricant in a cold metal forming process was tested and evaluated by carrying out plane strain extrusion experiments and experimental analyses using a visioplasticity method. In the present research, two types of refined palm oil, refined, bleached, and deodorized (RBD) palm olein and RBD palm stearin, were tested as lubricants. The workpiece material was aluminum JIS-A1050. The experiments were carried out at room temperature (22°C). Paraffinic mineral oils with varying degrees of viscosity were tested for comparison. The experiment used an extrusion apparatus in which the taper dies were facing together, with zero frictional constraint at the contact plane (corresponding to the plane plate tool) conducted, and results were compared with those extruded with lubricants. Extrusion load and surface roughness of the billets were measured and compared. The distribution of the material flow velocity and effective strain in the exit zone of the billets were calculated using the...

Kenji Nakanishi

Papers

Strain on intervertebral discs after anterior cervical decompression and fusion.

Computer evaluation of sprinkler irrigation uniformity

Investigation of the effects of frictional constraint with application of palm olein oil lubricant and paraffin mineral oil lubricant on plastic deformation by plane strain extrusion

Experimental Evaluation of Refined, Bleached, and Deodorized Palm Olein and Palm Stearin in Cold Extrusion of Aluminum A1050

A backward extrusion analysis by the rigid–plastic integralless–meshless method