It remains debatable whether cervical spine fusion cages should be filled with any kind of bone or bone substitute. Cortical and subcortical bone from the anterior and posterior osteophytes of the segment could be used to fill the cage. The purposes of the present study are to evaluate the clinical outcomes and radiological outcomes including bone fusion and subsidence that occurred after anterior cervical discectomy and fusion using a stand-alone cage packed with local autobone graft.
Thirty-one patients who underwent anterior cervical fusion using a stand-alone polyetheretherketone (PEEK) cage packed with local autobone graft from July 2009 to december 2011 were enrolled in this study. Bone fusion was assessed by cervical plain radiographs and computed tomographic scan. Nonunion was evaluated according to the absence of bony bridge on computed tomographic scan. Subsidence was defined as a ≥2 mm decrease of the interbody height at the final follow-up compared to that measured at the immediate postoperative period.
Subsidence was observed in 7 patients (22.6%). Of 7 patients with subsidence greater 2 mm, nonunion was developed in 3. Three patients with subsidence greater 2 mm were related with endplate damage during intraoperative endplate preparation. Solid bone fusion was achieved in 28 out of 31 patients (90.3%).
With proper patient selection and careful endplate preparation, anterior cervical discectomy and fusion (ACDF) using a stand-alone PEEK cage packed with local autobone graft could be a good alternative to the standard ACDF techniques with plating.
Cage; Cervical spine; Discectomy; Local bone
Fusion of cervical spine in kyphotic alignment has been proven to produce an acceleration of degenerative changes at adjacent levels. Stand-alone cages are reported to have a relatively high incidence of implant subsidence with secondary kyphotic deformity. This malalignment may theoretically lead to adjacent segment disease in the long term. The prospective study analysed possible risk factors leading to cage subsidence with resulting sagittal malalignment of cervical spine. Radiographic data of 100 consecutive patients with compressive radiculo-/myelopathy due to degenerative disc prolapse or osteophyte formation were prospectively collected in those who were treated by anterior cervical discectomy and implantation of single type interbody fusion cage. One hundred and forty four implants were inserted altogether at one or two levels as stand-alone cervical spacers without any bone graft or graft substitute. All patients underwent standard anterior cervical discectomy and the interbody implants were placed under fluoroscopy guidance. Plain radiographs were obtained on postoperative days one and three to verify position of the implant. Clinical and radiographic follow-up data were obtained at 6 weeks, 3 and 6 months and than annually in outpatient clinic. Radiographs were evaluated with respect to existing subsidence of implants. Subsidence was defined as more than 2 mm reduction in segmental height due to implant migration into the adjacent end-plates. Groups of subsided and non-subsided implants were statistically compared with respect to spacer distance to the anterior rim of vertebral body, spacer versus end-plate surface ratio, amount of bone removed from adjacent vertebral bodies during decompression and pre- versus immediate postoperative intervertebral space height ratio. There were 18 (18%) patients with 19 (13.2%) subsided cages in total. No patients experienced any symptoms. At 2 years, there was no radiographic evidence of accelerated adjacent segment degeneration. All cases of subsidence occurred at the anterior portion of the implant: 17 cases into the inferior vertebra, 1 into the superior and 1 into both vertebral bodies. In most cases, the process of implant settling started during the perioperative period and its progression did not exceed three postoperative months. There was an 8.7° average loss of segmental lordosis (measured by Cobb angle). Average distance of subsided intervertebral implants from anterior vertebral rim was found to be 2.59 mm, while that of non-subsided was only 0.82 mm (P < 0.001). Spacer versus end-plate surface ratio was significantly smaller in subsided implants (P < 0.001). Ratio of pre- and immediate postoperative height of the intervertebral space did not show significant difference between the two groups (i.e. subsided cages were not in overdistracted segments). Similarly, comparison of pre- and postoperative amount of bone mass in both adjacent vertebral bodies did not show a significant difference. Appropriate implant selection and placement appear to be the key factors influencing cage subsidence and secondary kyphotisation of box-shaped, stand-alone cages in anterior cervical discectomy and fusion. Mechanical support of the implant by cortical bone of the anterior osteophyte and maximal cage to end-plate surface ratio seem to be crucial in the prevention of postoperative loss of lordosis. Our results were not able to reflect the importance of end-plate integrity maintenance; the authors would, however, caution against mechanical end-plate damage. Intraoperative overdistraction was not shown to be a significant risk factor in this study. The significance of implant subsidence in acceleration of degenerative changes in adjacent segments remains to be evaluated during a longer follow-up.
Cervical vertebrae surgery; Spinal fusion; Equipment failure analysis; Postoperative complications; Subsidence
Interbody cages are widely used instruments for cervical fusion operations. Long-term follow-up studies are needed to clarify if these devices are dependable. In this prospective study, 79 patients (42 women and 37 men) with a mean age of 51 years operated between January 2000 and December 2005 for treatment of degenerative cervical disc disease and spondylosis associated with radiculopathy or myelopathy were evaluated. Patients underwent two-level contiguous anterior cervical discectomy and fusion operations with standard anterior Smith–Robinson approach. To achieve fusion PEEK cages packed with demineralized bone matrix mixed with autologous blood were used. Clinical outcome was evaluated with Odom’s criteria and results were evaluated as ‘excellent’, ‘good’, ‘fair’ and ‘poor’. Spinal curves, mobility and fusion status were assessed with anterior–posterior and lateral (neutral, flexion and extension) radiographs obtained before surgery and at 3, 12, 24 and 36 months postoperatively. The Ishihara curvature index (ICI) was used for spinal curve evaluation. Lateral dynamic (flexion and extension) radiographs at postoperative 12th month revealed the fusion status classified as 1A, 1B, 2A and 2B. The radiological outcomes were classified as ‘non-fusion’ when 2B healing was observed, and as ‘fusion’ when 1A, 1B or 2A healing was observed at the levels subjected to surgery. According to Odom’s criteria, clinical outcomes were classified as ‘excellent’ or ‘good’ in 69 patients (success rate: 87.3%). Eight patients were graded as ‘fair’ and two as ‘poor’. Preoperative mean ICI was 10.4 ± 3.72 and postoperative mean ICI was 10.1 ± 3.14. The difference was statistically insignificant (P > 0.05); therefore, preoperative lordosis was said to be preserved at final follow-up. Final fusion rate (Types 1A, 1B, and 2A) was 91.7% (145/158 levels). Radiological imaging showed no cage failure or dislodgement and reoperation due to non-fusion was not needed.
ACDF; Two-level cervical disc disease; Demineralized bone matrix; Long-term follow-up; PEEK cage
Clinical outcomes of the stand-alone cage have been encouraging when used in anterior cervical discectomy and fusion (ACDF), but concerns remain regarding its complications, especially cage subsidence. This retrospective study was undertaken to investigate the long-term radiological and clinical outcomes of the stand-alone titanium cage and to evaluate the incidence of cage subsidence in relation to the clinical outcome in the surgical treatment of degenerative cervical disc disease.
A total of 57 consecutive patients (68 levels) who underwent ACDF using a titanium box cage for the treatment of cervical radiculopathy and/or myelopathy were reviewed for the radiological and clinical outcomes. They were followed for at least 5 years. Radiographs were obtained before and after surgery, 3 months postoperatively, and at the final follow-up to determine the presence of fusion and cage subsidence. The Cobb angle of C2–C7 and the vertebral bodies adjacent to the treated disc were measured to evaluate the cervical sagittal alignment and local lordosis. The disc height was measured as well. The clinical outcomes were evaluated using the Japanese Orthopaedic Association (JOA) score for cervical myelopathy, before and after surgery, and at the final follow-up. The recovery rate of JOA score was also calculated. The Visual Analogue Scale (VAS) score of neck and radicular pain were evaluated as well. The fusion rate was 95.6% (65/68) 3 months after surgery.
Successful bone fusion was achieved in all patients at the final follow-up. Cage subsidence occurred in 13 cages (19.1%) at 3-month follow-up; however, there was no relation between fusion and cage subsidence. Cervical and local lordosis improved after surgery, with the improvement preserved at the final follow-up. The preoperative disc height of both subsidence and non-subsidence patients was similar; however, postoperative posterior disc height (PDH) of subsidence group was significantly greater than of non-subsidence group. Significant improvement of the JOA score was noted immediately after surgery and at the final follow-up. There was no significant difference of the recovery rate of JOA score between subsidence and non-subsidence groups. The recovery rate of JOA score was significantly related to the improvement of the C2–C7 Cobb angle. The VAS score regarding neck and radicular pain was significantly improved after surgery and at the final follow-up. There was no significant difference of the neck and radicular pain between both subsidence and non-subsidence groups.
The results suggest that the clinical and radiological outcomes of the stand-alone titanium box cage for the surgical treatment of one- or two-level degenerative cervical disc disease are satisfactory. Cage subsidence does not exert significant impact upon the long-term clinical outcome although it is common for the stand-alone cages. The cervical lordosis may be more important for the long-term clinical outcome than cage subsidence
Anterior cervical discectomy and fusion; Stand-alone cage; Cervical spine; Complication; Subsidence; Cervical alignment
Cages have been widely used for the anterior reconstruction and fusion of cervical spine. Nonmetal cages have become popular due to prominent stress shielding and high rate of subsidence of metallic cages. This study aims to assess fusion with n-HA/PA66 cage following one level anterior cervical discectomy.
Materials and Methods:
Forty seven consecutive patients with radiculopathy or myelopathy underwent single level ACDF using n-HA/PA66 cage. We measured the segmental lordosis and intervertebral disc height on preoperative radiographs and then calculated the loss of segmental lordosis correction and cage subsidence over followup. Fusion status was evaluated on CT scans. Odom criteria, Japanese Orthopedic Association (JOA) and Visual Analog Pain Scales (VAS) scores were used to assess the clinical results. Statistically quantitative data were analyzed while Categorical data by χ2 test.
Mean correction of segmental lordosis from surgery was 6.9 ± 3.0° with a mean loss of correction of 1.7 ± 1.9°. Mean cage subsidence was 1.2 ± 0.6 mm and the rate of cage subsidence (>2 mm) was 2%. The rate of fusion success was 100%. No significant difference was found on clinical or radiographic outcomes between the patients (n=27) who were fused by n-HA/PA66 cage with pure local bone and the ones (n=20) with hybrid bone (local bone associating with bone from iliac crest).
The n-HA/PA66 cage is a satisfactory reconstructing implant after anterior cervical discectomy, which can effectively promote bone graft fusion and prevent cage subsidence.
Cervical spine; anterior fusion; discectomy; nano-hydroxyapatite/polyamide-66 cage
Retrospective comparative study of 80 consecutive patients treated with either anterior cervical discectomy fusion (ACDF) or anterior cervical corpectomy fusion (ACCF) for multi-level cervical spondylosis. To compare clinical outcome, fusion rates, and complications of anterior cervical reconstruction of multi-level ACDF and single-/multi-level ACCF performed using titanium mesh cages (TMCs) filled with autograft and anterior cervical plates (ACPs). Reconstruction of the cervical spine after discectomy or corpectomy with titanium cages filled with autograft has become an acceptable alternative to both allograft and autograft; however, there is no data comparing the outcome of multi-level ACDF and single-/multi-level ACCF using this reconstruction. We evaluated 80 consecutive patients who underwent surgery for the treatment of multi-level cervical spondylosis at our institution from 1998 to 2001. In this series, 42 patients underwent multi-level ACDF (Group 1) and 38 patients underwent ACCF (Group 2). Interbody TMCs and local autograft bone with ACPs were used in both procedures. Medical records were reviewed to assess outcome. Clinical outcome was measured by Odom’s criteria. Operative time and blood loss were noted. Radiographs were obtained at 6 and 12 weeks, 6 months, 1 year, and 2 years (if necessary). Early hardware failures and pseudarthroses were noted. Cervical sagittal curvature was measured by Ishihara’s index at 1 year. Group 1 had a mean age 46.2 years (range 35–60 years). Group 2 had a mean age 50.1 years (range 35–70 years).The operative time was significantly lower (P < 0.001) and blood loss significantly higher (P < 0.001) in Group 2 than in Group 1. At a minimum of 1 year follow up, patients in both groups had equivalent improvement in their clinical symptoms. The fusion rates for Group 1 were 97.6 and 92.1% for Group 2. The rates of early hardware failure were higher in Group 2 (2.6%) than in Group 1 (0%). The fusion rates for Group 1 were not significantly higher than Group 2 (P > 0.28). There was one patient in Group 1 and 2 patients in Group 2 with pseudarthroses. Complication rates in Group 2 were not significantly higher (P > 0.341). Cervical lordosis was well-maintained (80%) in both groups. Both multi-level ACDF and ACCF with anterior cervical reconstruction using TMC filled with autograft and ACP for treatment of multi-level cervical spondylosis have high fusion rates and good clinical outcome. However, there is a higher rate of early hardware failure and pseudarthroses after ACCF than ACDF. Hence, in the absence of specific pathology requiring removal of vertebral body, multi-level ACDF using interbody cages and autologous bone graft could result in lower morbidity.
Cervical fusion; Cervical spondylosis; Anterior cervical discectomy and fusion; Anterior cervical corpectomy
With minimally invasive technique becoming more popular, endoscopic operations such as arthroscopy or laparoscopy have become the standard of care in several other areas. In this study, we evaluated the 5-year follow-up outcomes of anterior cervical (Ahn et al. in Photomed Laser Surg 23:362–368, 2005) discectomy and interbody fusion (ACDF) performed via endoscopic approach. Sixty-seven patients who underwent anterior cervical discectomy and cage fusion performed using endoscopic technique were followed for at least 5 years. We reviewed the clinical and radiographic records of these patients. The postoperative radiographic measures accessed were the anterior intervertebral height (AIH) and the lordosis angle (LDA). Clinical outcomes were determined using the previously validated Japanese Orthopaedic Association (JOA) and the pain visual analog scale (VAS). Patients included had a minimal follow-up period of 5 years and based on the outcomes criteria (JOA, VAS), 86.6% of patients reported excellent or good results. The AIH increased on average 18.7% of the original height (p < 0.01), and the LDA were more physiologic at final follow-up. Of the 67 cases, there was no segmental instability, and the bone fusion rate was 100%. One patient required revision open ACDF due to adjacent segment disc herniation 6 years postoperatively. There were no intraoperative complications, dysphasia or esophageal injury in this study group. It indicated endoscopic technique for ACDF can obtain satisfactory results in patients with cervical disc herniation, cervical myelopathy, or radiculopathy. Compared with a traditional approach, this technique may be associated with less morbidity while improving cosmesis and postoperative recovery. Prospective randomized control trials are needed to directly compare these two procedures.
Cervical spine; Interbody fusion; Discectomy; Endoscopic microsurgery; Cage
In an effort to avoid the morbidity associated with autogenous bone graft harvesting, cervical cages in combination with allograft bone are used to achieve fusion. The goal of the current study was to assess the reliability and efficacy of anterior cervical discectomy and interbody fusion (ACDF) using a PEEK anatomical cervical cage in the treatment of patients affected by single-level cervical degenerative disease.
Methods and materials
Twenty-five patients affected by single-level cervical degenerative pathology between C4 and C7 were enrolled in this study. The clinical findings were assessed using the Neck Disability Index and the Visual Analog Scale. Surgical outcomes were rated according to Odom’s criteria at last follow-up. Fusion was graded as poor, average, good or excellent by assessing the radiographs. Cervical spine alignment was evaluated by sagittal segmental alignment and sagittal alignment of the whole cervical spine preoperatively, 6 months postoperatively and at the last follow-up.
Twenty-five patients underwent ACDF using a PEEK anatomical cervical cage. All patients had a minimum 2 years of follow-up. The operative levels were C4–C5 in 5 patients, C5–C6 in 12 patients and C6–C7 in 8 patients. Preoperatively, average NDI was 34, 13 at 6 months, and 10 at latest follow-up. The mean preoperative VAS was 7; the mean postoperative VAS at latest follow-up was 3. Good or excellent fusion was achieved in all patients within 10 months (mean 5 months). Preoperatively, average sagittal segmental alignment (SSA) was 0.2° and average sagittal alignment of the cervical spine (SACS) 15.8°. Six months after surgery, average SSA was 1.8° and average SACS 20.9°, and at last follow-up, average SSA was 1.6° and average SACS 18.5°.
Anterior cervical discectomy and interbody fusion using PEEK anatomical cervical cages can be considered a safe and effective technique to cure cervical disc herniation with intractable pain or neural deficit in cases where conservative treatment failed.
ACDF; PEEK cage; Allograft bone
The purpose of this study was to compare the characteristics of interbody fusion achieved using the hat type cervical intervertebral fusion cage (HCIFC) with those of an autologous tricortical iliac crest graft, Harms cage and the carbon cage in a goat cervical spine model. Thirty-two goats underwent C3-4 discectomy and fusion. They were subdivided into four groups of eight goats each: group 1, autologous tricortical iliac crest bone graft; group 2, Harms cage filled with autologous iliac crest graft; group 3, carbon cage filled with autologous iliac bone; and group 4, HCIFC filled with autologous iliac graft. Radiography was performed pre- and postoperatively and after one, two, four, eight and 12 weeks. At the same time points, disc space height, intervertebral angle, and lordosis angle were measured. After 12 weeks, the goats were killed and fusion sites were harvested. Biomechanical testing was performed in flexion, extension, axial rotation, and lateral bending to determine the stiffness and range of motion. All cervical fusion specimens underwent histomorphological analyses. One week after operation, the disc space height (DSH), intervertebral angle (IVA) and lordosis angle (LA) of HCIFC and carbon cage were statistically greater than those of autologous iliac bone graft and Harms cage. Significantly higher values for DSH, IVA and LA were shown in cage-treated goats than in those that received bone graft over a 12-week period. The stiffness of Harms cage in axial rotation and lateral bending were statistically greater than that of other groups. Radiographic and histomorphological evaluation showed better fusion results in the cage groups than in the autologous bone group. HCIFC can provide a good intervertebral distractability and sufficient biomechanical stability for cervical fusion.
A variety of bone graft substitutes, interbody cages, and anterior plates have been used in cervical interbody fusion, but no controlled study was conducted on the clinical performance of β-tricalcium phosphate (β-TCP) and the effect of supplemented anterior plate fixation. The objective of this prospective, randomized clinical study was to evaluate the effectiveness of implanting interbody fusion cage containing β-TCP for the treatment of cervical radiculopathy and/or myelopathy, and the fusion rates and outcomes in patients with or without randomly assigned plate fixation. Sixty-two patients with cervical radiculopathy and/or myelopathy due to soft disc herniation or spondylosis were treated with one- or two-level discectomy and fusion with interbody cages containing β-TCP. They were randomly assigned to receive supplemented anterior plate (n = 33) or not (n = 29). The patients were followed up for 2 years postoperatively. The radiological and clinical outcomes were assessed during a 2-year follow-up. The results showed that the fusion rate (75.0%) 3 months after surgery in patients treated without anterior cervical plating was significantly lower than that (97.9%) with plate fixation (P < 0.05), but successful bone fusion was achieved in all patients of both groups at 6-month follow-up assessment. Patients treated without anterior plate fixation had 11 of 52 (19.2%) cage subsidence at last follow-up. No difference (P > 0.05) was found regarding improvement in spinal curvature as well as neck and arm pain, and recovery rate of JOA score at all time intervals between the two groups. Based on the findings of this study, interbody fusion cage containing β-TCP following one- or two-level discectomy proved to be an effective treatment for cervical spondylotic radiculopathy and/or myelopathy. Supplemented anterior plate fixation can promote interbody fusion and prevent cage subsidence but do not improve the 2-year outcome when compared with those treated without anterior plate fixation.
β-TCP; Bone graft substitutes; Cervical spine; Interbody fusion; Anterior cervical plating
The object of this study is to compare radiographic outcomes of anterior cervical decompression and fusion (ACDF) versus cervical disc replacement using the Bryan Cervical Disc Prosthesis (Medtronic Sofamor Danek, Memphis, TN) in terms of range of motion (ROM), Functional spinal unit (FSU), overall sagittal alignment (C2–C7), anterior intervertebral height (AIH), posterior intervertebral height (PIH) and radiographic changes at the implanted and adjacent levels. The study consisted of 105 patients. A total of 63 Bryan disc were placed in 51 patients. A single level procedure was performed in 39 patients and a two-level procedure in the other 12. Fifty-four patients underwent ACDF, 26 single level cases and 28 double level cases. The Bryan group had a mean follow-up 19 months (12–38). Mean follow-up for the ACDF group was 20 months (12–40 months). All patients were evaluated using static and dynamic cervical spine radiographs as well as MR imaging. All patients underwent anterior cervical discectomy followed by autogenous bone graft with plate (or implantation of a cage) or the Bryan artificial disc prosthesis. Clinical evaluation included the visual analogue scale (VAS), and neck disability index (NDI). Radiographic evaluation included static and dynamic flexion-extension radiographs using the computer software (Infinitt PiviewSTAR 5051) program. ROM, disc space angle, intervertebral height were measured at the operative site and adjacent levels. FSU and overall sagittal alignment (C2–C7) were also measured pre-operatively, postoperatively and at final follow-up. Radiological change was analyzed using χ2 test (95% confidence interval). Other data were analyzed using the mixed model (SAS enterprises guide 4.1 versions). There was clinical improvement within each group in terms of VAS and NDI scores from pre-op to final follow-up but not significantly between the two groups for both single (VAS p = 0.8371, NDI p = 0.2872) and double (VAS p = 0.2938, NDI p = 0.6753) level surgeries. Overall, ROM and intervertebral height was relatively well maintained during the follow-up in the Bryan group compared to ACDF. Regardless of the number of levels operated on, significant differences were noted for overall ROM of the cervical spine (p < 0.0001) and all other levels except at the upper adjacent level for single level surgeries (p = 0.2872). Statistically significant (p < 0.0001 and p = 0.0172) differences in the trend of intervertebral height measurements between the two groups were noted at all levels except for the AIH of single level surgeries at the upper (p = 0.1264) and lower (p = 0.7598) adjacent levels as well as PIH for double level surgeries at the upper (p = 0.8363) adjacent level. Radiological change was 3.5 times more observed for the ACDF group. Clinical status of both groups, regardless of the number of levels, showed improvement. Although clinical outcomes between the two groups were not significantly different at final follow-up, radiographic parameters, namely ROM and intervertebral heights at the operated site, some adjacent levels as well as FSU and overall sagittal alignment of the cervical spine were relatively well maintained in Bryan group compared to ACDF group. We surmise that to a certain degree, the maintenance of these parameters could contribute to reduce development of adjacent level change. Noteworthy is that radiographic change was 3.5 times more observed for ACDF surgeries. A longer period of evaluation is needed, to see if all these radiographic changes will translate to symptomatic adjacent level disease.
Bryan; Arthroplasty; Arthrodesis; Radiologic degenerative change; Adjacent level
To evaluate the effectiveness of anterior cervical discectomy with fusion for degenerative cervical disc disease.
Overview of Literature
Anterior spinal surgery originated in the mid-1950s and graft for fusion was also employed. Currently anterior cervical microdiscectomy and fusion with an intervertebral cage is a widely accepted procedure for treatment of cervical disc hernia. Artificial grafts and cages for fusion are preferred because of their lower morbidity, reduced operating time and acceptable fusion rate.
The study involved retrospective analysis and investigation of long-term results for 41 consecutive patients who had undergone anterior cervical discectomy and fusion with an intervertebral cage for cervical disc hernia. The angle of lordosis, segmental height and range of motion were evaluated preoperatively and postoperatively at 1 month and 2 years. The clinical outcome was assessed by the visual analog scale and Odom's criteria.
The angle of lordosis increased by 2.62° and the range of motion angle increased by 5.14° after the operation. The segmental height did not change. The visual analog scale and Odom's criteria scores decreased significantly after the operation.
Using a cage in anterior cervical discectomy prevents segmental collapse, so the segmental height and the angle of lordosis are preserved and newly-developed pain does not occur.
Cervical vertebral fusion; Cervical lordosis; Outcome assesment; Range of motion; Polyetheretherketone cage
Introduction: Intervertebral carbon fiber cages may reduce graft collapse and promote bony fusion. Their safety and efficacy in the cervical spine have been investigated; however, no study has compared the outcomes of anterior cervical decompression and placement of a carbon fiber cage with placement of allograft and plate. Methods: Forty consecutive patients who met inclusion criteria were enrolled and randomized to anterior cervical discectomy with carbon fiber cage alone (n=20) or with allograft with plating (n=20). Clinical and radiographic evaluations were performed at baseline and at 6 weeks, 3, 6, 12 and 24 months. Neck and arm pain as well as neck disability index (NDI) were assessed at every visit. The Short Form (SF)-36 was completed prior to operation and at 12-month intervals. Cervical radiographs were evaluated pre-op and at every follow-up for evidence of fusion and instability. Results: No significant difference was found between the two randomized groups with respect to pre-operative age (mean 50 years), sex, employment status, duration of pain or cervical levels affected. The mean follow-up period was 14 months (range, 6–26 months). The clinical pain and disability improvements were similar for both treatments. Post-operative donor site pain was only present in the cage group, but not of significant long-term disability. At up to 24 months, NDI scores were significantly improved in both groups when compared with baseline. At 12 and 24 months, all SF-36 questionnaire responses were also improved in both the treatment groups. However, there was no statistically significant difference in outcomes between the two groups at any time. The fusion rate was 100% in both groups by 12 and 24 months, without evidence of instability. There were no differences in complications between both groups. Conclusions: The outcomes after cervical decompression and placement of a carbon fiber cage appear to be similar to cervical decompression with allograft and plating by the Smith–Robinson technique.
Anterior cervical plating; Arthrodesis; Carbon fiber cage; Interbody fusion
Although there are several accepted methods of surgical treatment for single-level cervical radiculopathy, the choice depend on the surgeon’s preference. The techniques may vary in peri-operative morbidity, short- and long-term outcome, but no study so far has analyzed their cost-effectiveness. This study might give some insight in balancing cost and effectiveness and deciding the right technique. Sixty consecutive patients (15 each group), mean age 36 (range 24–76 years) with single-level cervical disc disease underwent surgical treatment with four different techniques in two centers over the period of 1999–2005. The four groups were—(1) plate and tricortical autograft, (2) plate, cage, and bone substitute, (3) cage only, and (4) disc arthroplasty. The data was collected prospectively according to our protocol and subsequently analyzed. The clinical outcome was assessed comparing visual analog scale (VAS) of neck pain and, short form 12 (SF12) questionnaire both pre- and postoperatively. The radiological assessment was done for fusion rate and postoperative related possible complications at 3 months, 6 months, 1 year, and final follow-up. The cost analysis was done calculating the operative time, hospital stay, implant cost together. The mean follow-up period was 31 months (range 28–43 months). The clinical outcome in terms of VAS of neck and arm pain and SF12 physical and mental score improvement (P = 0.001) were comparable with all four techniques. The radiological fusion rate was comparable to current available data. As the hospital stay was longer (average 5 days) with plate and autograft group, the total cost was maximum (average £2,920) with this group. There was satisfactory clinical and radiological outcome with all four techniques. Using the cage alone was the most cost-effective technique, but the disc arthroplasty was comparable to the use of cage and plate. Anterior cervical discectomy and fusion is an established surgical treatment for cervical radiculopathy. Single-level cervical radiculopathy was treated with four different techniques. The clinical outcome and cost-effectiveness were compared in this study.
Cervical radiculopathy; ACDF; Disc arthroplasty; Clinical outcome; Cost-effectiveness
From July 2004 to June 2005, 19 patients with 25 discs underwent anterior cervical discectomy and interbody fusion (ACDF) in which polyetheretherketone (PEEK) cages were filled with freeze-dried cancellous allograft bone. This kind of bone graft was made from femoral condyle that was harvested during total knee arthroplasty. Patient age at surgery was 52.9 (28–68) years. All patients were followed up at least 1 year. We measured the height of the disc and segmental sagittal angulation by pre-operative and post-operative radiographs. CT scan of the cervical spine at 1 year was used to evaluate fusion rates. Odom's criteria were used to assess the clinical outcome. All interbody disc spaces achieved successful union at 1-year follow-up. The use of a PEEK cage was found to increase the height of the disc immediately after surgery (5.0 mm pre-operatively, 7.3 mm immediately post-operatively). The final disc height was 6.2 mm, and the collapse of the disc height was 1.1 mm. The segmental lordosis also increased after surgery (2.0° pre-operatively, 6.6° immediately post-operatively), but the mean loss of lordosis correction was 3.3° at final follow-up. Seventy-four percent of patients (14/19) exhibited excellent/good clinical outcomes. Analysis of the results indicated the cancellous allograft bone-filled PEEK cage used in ACDF is a good choice for patients with cervical disc disease, and avoids the complications of harvesting iliac autograft.
Treatment of multilevel cervical spondylotic myelopathy/radiculopathy is a matter of debate, more so in elderly patients due to compromised physiology. We evaluated the clinical and radiological results of cervical fusion, using wedge-shaped tricortical autologous iliac graft and Orion plate for three-level anterior cervical discectomy in elderly patients.
Materials and Methods:
Twelve elderly patients with mean age of 69.7 years (65–76 years) were treated between April 2000 and March 2005, for three-level anterior cervical discectomy and fusion, using wedge-shaped tricortical autologous iliac graft and Orion plate. Outcome was recorded clinically according to Odom's criteria and radiologically in terms of correction of lordosis angle and intervertebral disc height span at the time of bony union. The mean follow-up was 29.8 months (12–58 months).
All the patients had a complete recovery of clinical symptoms after surgery. Postoperative score according to Odom's criteria was excellent in six patients and good in remaining six. Bony union was achieved in all the patients with average union time of 12 weeks (8–20 weeks). The mean of sum of three segment graft height collapse was 2.50 mm (SD = 2.47). The average angle of lordosis was corrected from 18.2° (SD = 2.59°) preoperatively to 24.9° (SD = 4.54°) at the final follow-up. This improvement in the radiological findings is statistically significant (P < 0.05).
Cervical fusion with wedge-shaped tricortical autologous iliac graft and Orion plate for three-level anterior cervical discectomy is an acceptable technique in elderly patients. It gives satisfactory results in terms of clinical outcome, predictable early solid bony union, and maintenance of disc space height along with restoration of cervical lordosis.
Anterior discectomy; elderly patients; plating; three-level cervical spine disease; wedge-shaped autograft
A prospective, randomized, controlled study was carried out to compare the radiological and clinical outcomes after anterior cervical decompression and fusion (ACDF) with Trabecular Metal™ (TM) to the traditional Smith–Robinson (SR) procedure with autograft. The clinical results of cervical fusion with autograft from the iliac crest are typically satisfactory, but implications from the donor site are frequently reported. Alternative materials for cervical body interfusion have shown lower fusion rates. Trabecular Metal is a porous tantalum biomaterial with structure and mechanical properties similar to that of trabecular bone and with proven osteoconductivity. As much as 80 consecutive patients planned for ACDF were randomized for fusion with either TM or tricortical autograft from the iliac crest (SR) after discectomy and decompression. Digitized plain radiographic images of 78 (98%) patients were obtained preoperatively and at 2-year follow-up and were subsequently evaluated by two senior radiologists. Fusion/non-fusion was classified by visual evaluation of the A–P and lateral views in forced flexion/extension of the cervical spine and by measuring the mobility between the fused vertebrae. MRI of 20 TM cases at 2 years was successfully used to assess the decompression of the neural structures, but was not helpful in determining fusion/non-fusion. Pain intensity in the neck, arms and pelvis/hip were rated by patients on a visual analog scale (VAS) and neck function was rated using the Neck Disability Index (NDI) the day before surgery and 4, 12 and 24 months postoperatively. Follow-ups at 12 and 24 months were performed by an unbiased observer, when patients also assessed their global outcome. Fusion rate in the SR group was 92%, and in the TM group 69% (P < 0.05). The accuracy of the measurements was calculated to be 2.4°. Operating time was shorter for fusion with TM compared with autograft; mean times were 100 min (SD 18) and 123 min (SD 23), respectively (P = 0.001). The patients’ global assessments of their neck and arm symptoms 2 years postoperatively for the TM group were rated as 79% much better or better after fusion with TM and 75% using autograft. Pain scores and NDI scores were significantly improved in both groups when compared with baseline at all follow-ups, except for neck pain at 1 year for the TM group. There was no statistically significant difference in clinical outcomes between fusion techniques or between patients who appeared radiologically fused or non-fused. There was no difference in pelvic/hip pain between patients operated on with or without autograft. In our study, Trabecular Metal showed a lower fusion rate than the Smith–Robinson technique with autograft after single-level anterior cervical fusion without plating. There was no difference in clinical outcomes between the groups. The operative time was shorter with Trabecular Metal implants.
Spinal fusion; Cervical vertebrae; Tantalum; Trabecular Metal; Randomized controlled trial
This retrospective study evaluated a single surgeon's series of patients treated by multilevel cervical disc excision (two or three levels), allograft tricortical iliac crest arthrodesis, and anterior instrumentation. The objective of this retrospective study was to compare fusion success and clinical outcome between multilevel Smith-Robinson interbody grafting and tricortical iliac strut graft reconstruction, both supplemented with anterior instrumentation in the cervical spine. The incidence of nonunion for cervical discectomy and fusion varies widely depending on the number of disc levels involved, type of bone graft used, and whether the anterior grafting is supplemented with instrumentation. An alternative to multilevel interbody fusion is corpectomy and strut grafting, in which the incidence of nonunion has been reported to be 27% with autograft and 41% with allograft. Sixty-four consecutive patients who underwent allograft tricortical iliac crest reconstruction and anterior cervical plating were studied. The average follow-up was 39 months. There were 38 patients in the discectomy and interbody grafting group and 26 patients in the corpectomy and strut graft reconstruction group. Pseudoarthrosis occurred in 42% of the anterior cervical interbody fusion patients and 31% of the corpectomy patients. Nonunion in two-level interbody fusions occurred in 36% of the patients as compared to 10% for patients with one-level corpectomies; while 54% of patients with three-level interbody fusions and 44% of patients with two-level corpectomies were noted to have pseudoarthrosis. Higher percentages of nonunion were noted in multilevel interbody grafting than in corpectomy with strut grafting and when more vertebral levels were involved. These radiographic and clinical findings underscore the shortcomings of multilevel anterior cervical allograft reconstruction with plating. Corpectomy may be the preferred method when multiple disc levels are fused. In addition, anterior corpectomy affords decompression of significant osteophytes in a safer and quicker manner. In retrospective studies, there is a need for long-term follow-up before accurate statements can be made about the study population.
Allograft fusions; Multilevel anterior cervical interbody fusion; Strut graft Anterior cervical plating
The purposes of the present study are to evaluate the subsidence and nonunion that occurred after anterior cervical discectomy and fusion using a stand-alone intervertebral cage and to analyze the risk factors for the complications.
Thirty-eight patients (47 segments) who underwent anterior cervical fusion using a stand-alone polyetheretherketone (PEEK) cage and an autologous cancellous iliac bone graft from June 2003 to August 2008 were enrolled in this study. The anterior and posterior segmental heights and the distance from the anterior edge of the upper vertebra to the anterior margin of the cage were measured on the plain radiographs. Subsidence was defined as ≥ a 2 mm (minor) or 3 mm (major) decrease of the segmental height at the final follow-up compared to that measured at the immediate postoperative period. Nonunion was evaluated according to the instability being ≥ 2 mm in the interspinous distance on the flexion-extension lateral radiographs.
The anterior and posterior segmental heights decreased from the immediate postoperative period to the final follow-up at 1.33 ± 1.46 mm and 0.81 ± 1.27 mm, respectively. Subsidence ≥ 2 mm and 3 mm were observed in 12 segments (25.5%) and 7 segments (14.9%), respectively. Among the expected risk factors for subsidence, a smaller anteroposterior (AP) diameter (14 mm vs. 12 mm) of cages (p = 0.034; odds ratio [OR], 0.017) and larger intraoperative distraction (p = 0.041; OR, 3.988) had a significantly higher risk of subsidence. Intervertebral nonunion was observed in 7 segments (7/47, 14.9%). Compared with the union group, the nonunion group had a significantly higher ratio of two-level fusion to one-level fusions (p = 0.001).
Anterior cervical fusion using a stand-alone cage with a large AP diameter while preventing anterior intraoperative over-distraction will be helpful to prevent the subsidence of cages. Two-level cervical fusion might require more careful attention for avoiding nonunion.
Anterior cervical fusion; PEEK cage; Subsidence; Nonunion
Growth factors have proven to promote spine fusion. However, no comparative evaluation of growth factors in spinal fusion has yet been performed. The purpose of this study was to compare the efficacy and safety of combined IGF-I and TGF-ß1 application with BMP-2 application and autologous cancellous bone graft at an early time point in a sheep cervical spine fusion model. Thirty-two sheep underwent C3/4 discectomy and fusion. They were divided into four groups, according to their treatment: group 1, titanium cage (n=8); group 2, titanium cage filled with autologous cancellous iliac crest bone grafts (n=8); group 3, titanium cage coated with a poly-(D,L-lactide) (PDLLA) carrier including BMP-2 (5% w/w) (n=8); group 4, titanium cage coated with a PDLLA carrier including IGF-I (5% w/w) and TGF-ß1 (1% w/w) (n=8). Blood samples, body weight and temperature were analysed. Radiographic scans were performed pre- and postoperatively and after 1, 2, 4, 8 and 12 weeks. At the same time points, disc space height and intervertebral angle were measured. After 12 weeks, the animals were killed and fusion sites were evaluated using functional radiographic views in flexion and extension. Quantitative computed tomographic scans were performed to assess bone mineral density, bone mineral content and bony callus volume. Biomechanical testing was carried out and the values for range of motion, and neutral and elastic zone were determined. Histomorphological and histomorphometrical analysis were performed and polychrome sequential labelling was used to determine the time frame of new bone formation. The results showed that, in comparison to the group treated with the cage alone (group 1), the cage plus BMP-2 group (group 3) and the cage plus IGF-I and TGF-ß1 group (group 4) demonstrated a significantly higher fusion rate in radiographic findings, a higher biomechanical stability, a more advanced interbody fusion in histomorphometrical analysis, and an accelerated interbody fusion on fluorochrome sequence labelling. In comparison to the bone graft group (group 2), the BMP-2 (group 3) and IGF-I/TGF-ß1 group (group 4) showed significantly less residual motion on functional radiographic evaluation, higher bone mineral density of the callus and higher biomechanical stability in extension, rotation and bending. The BMP-2 group showed significantly less residual motion on functional radiographic evaluation and higher intervertebral bone matrix formation on fluorochrome sequence labelling at 9 weeks in comparison to the IGF-I/TGF-ß1 group. In contrast, the IGF-I/TGF-ß1 group showed a significantly higher bone mineral density of the callus than the BMP-2 group. In comparison to the autologous cancellous bone graft group, both growth factors (BMP-2 and combined IGF-I and TGF-ß1) significantly improved the biomechanical results of interbody fusion. No systemic side effects were observed for either growth factor. On the basis of these preliminary results, it would appear that combined IGF-I/TGF-ß1 application yields equivalent results to BMP-2 application at an early time point in anterior sheep cervical spine fusion.
Cervical spine Sheep Animal model Interbody fusion BMP-2 IGF-I TGF-ß1 Growth factor
To analyze the clinical and radiographic results following the use of integrated intervertebral implant in patients with cervical spine degenerative disease.
Though excellent results have been reported following anterior cervical discectomy and fusion using iliac crest autograft/allograft with plating, the morbidity associated with autograft harvest and small chances of complications with plating always exists. Recently, there has been development of a cervical stand-alone cage with integrated fixation for cervical fusion and stabilization with a possible low morbidity and optimal clinical outcome.
Materials and Methods:
A retrospective study of 16 patients who underwent anterior cervical discectomy and fusion using the integrated intervertebral device was performed. Intra-operative parameters, clinical features [Neck Disability Index (NDI), visual analog scale (VAS) score for neck/arm pain], and presence or absence of dysphagia was recorded. Radiographs were evaluated for assessment of implant failure and fusion.
Mean age of patients was 54 years (range: 38-84 years) with male: female ratio of 1:3. Follow-up ranged from 6 to 12 months (mean: 10 months). In the early postoperative period, 2 of the 15 patients (13%) patients had mild dysphagia that resolved during follow-up with no patient having complaints of dysphagia at 3-month follow-up. One of the patients with diffuse idiopathic skeletal hyperostosis (DISH) and severe preoperative dysphagia had significant improvement in swallowing function at 3-month follow-up that was stable at 1-year follow-up. There was no evidence of implant failure, with fusion occurring in 95% (19/20) of operated levels. Analysis of follow-up VAS and NDI scores showed significant reduction in VAS score for neck pain (P < 0.019), radicular arm pain (P < 0.003), and NDI score (P < 0.007) in 77, 92, and 77% of patients, respectively, at a mean follow-up of 10 months (6-12 months).
Our preliminary results with the use of this cervical stand-alone anterior fusion device with integrated screw fixation show its efficacy in anterior cervical decompression and fusion with stabilization with optimal clinical and radiographic outcome. Lower chances of dysphagia with no device-related complications are appealing, which needs to be verified in larger studies.
Cervical; degenerative; integrated; interbody cage; stand-alone; zero profile
Anterior cervical discectomy and fusion (ACDF) is currently treatment of choice for managing medical therapy refractory cervical degenerative disc disease. Numerous studies have demonstrated the effectiveness of ACDF; patients generally experience rapid recoveries, and dramatic improvement in their pain and quality of life. However, as several studies reported symptomatic adjacent segment disease attributed to fusions’ altered kinematics, cervical disc arthroplasty emerged as a new motion-sparing alternative to fusion. Fusion at one level increases motion at adjacent levels along with increased intradiscal pressures. This phenomenon can result in symptomatic adjacent level degeneration, which can necessitate reoperation at these levels. The era of cervical arthroplasty began in Europe in the late 1990s. In recent years, artificial cervical disc arthroplasty (ACDA) has been increasingly used by spine surgeons for degenerative cervical disc disease. There have been several reports of safety, efficacy and indications of ACDA.
Cervical arthroplasty offers several theoretical advantages over anterior cervical discectomy and fusion (ACDF) in the treatment of selected patients with medically refractory cervical radiculopathy. Preserving motion at the operated level, cervical TDR has the potential to decrease the occurrence of adjacent segment degeneration.
There are a few studies on the efficacy and effectiveness of ACDA compared to cervical fusion. However, the true scenery of cervical arthroplasty yet to be identified.
This study is intended to define patients' characteristics and outcomes of ACDA by a single surgeon in Iran.
This retrospective study was performed in two general Hospitals in Tehran, Iran from 2005 To 2010. All patients were operated by one senior neurospine surgeon. One hundred fifty three patients were operated in this period. All patients signed the informed consent form prior to surgery. All patients presented with cervical discopathy who had myelopathy or radiculopathy and failed conservative management, undergoing cervical disc arthroplasty by ACDA were included, consecutively. Patients were followed for at least 2 years.
Exclusion criteria was age greater than 60 years, non compliance with the study protocol, osteoporosis, infection, congenital or post traumatic deformity, malignancy metabolic bone disease, and narrow cervical canal (less than 12 mm). Heterotopic ossification and adjacent segment degenerative changes were assessed at 2 years follow up by means of neutral and dynamic xrays and CT/MRI if clinically indicated. Neck and upper extremity pain were assessed before the procedure and in the first post-operative visit and 3 months later by means of visual analogue scale.
A standard approach was performed to the anterior cervical spine. Patients were positioned supine while holding neck in neutral position. A combination of sharp and blunt dissection was performed to expose longus coli musculature and anterior cervical vertebrae. Trachea and esophagus were retracted medially and carotid artery and jugular vein laterally. After a thorough discectomy, the intersomatic space is distracted in a parallel way by a vertebral distracter. Followed by Caspar distractor is applied to provide a working channel into posterior disc space. In this stage, any remnant disc materials as well as osteophytes are removed and foraminal decompression is done. Posterior longitudinal ligament (PLL) opening and removal, although discouraged by some, is done next. In order to define the size of the prosthesis, multiple trials are tested. It is important not to exceed the height of the healthy adjacent disc to avoid facet joint overdistraction. An specific insertor is applied to plant the prosthesis in disc space. Control X-rays are advised to check the precise positioning of the implant.
one hundred-fifty three patients including 87 females and 66 males were included. The mean age was 41 for females and 42 for males. Affected level was C5-C6 in 81 cases, C6-C7 in 72 cases and C4-C5 in 10 cases. The most common applied ACDA was DiscoCerv which was inserted in 127 cases followed by prodisc-c in three patients and Baguera in thirty three psatients.Ten cases had two levels involvement. Both neck and upper extremity pain improved significantly in early and late post op assessments compared to pre-op. There was only one operative complication of quadriparesis which might be attributed to the iatrogenic cervical spinal trauma.
Cervical disc arthroplasty has been advocated to address drawbacks of fusion including loss of motion segment and adjacent level degeneration; our study along with several other reports provide considerable evidence in this regard. Cervical disc arthroplasty is a safe and effective alternative for fusion in cervical degenerative disc disease.
Cervical degenerative disc disease, Artificial cervical disc arthroplasty, Safety, Efficacy
The objective of this study is to compare the clinical, functional, and radiological outcomes of using bone-filled Polymethylmethacrylate (PMMA) implant as an inexpensive alternative to Polyetheretherketone (PEEK) cage and Autologous bone graft (ABG) fusion after anterior cervical discectomy (ACD) for the treatment of single level cervical disc disease.
60 patients were prospectively randomized according to the material used for fusion after ACD into: 1) PMMA implant; 2) ABG; and 3) PEEK implant. The clinical outcomes were evaluated using Visual Analogue Scale (VAS), whereas the functional outcomes were evaluated using Odom's criteria. Radiological evaluations were also conducted using radiography and Computerized tomography (CT) scans and considered the following factors; bony fusion, cervical stability and disc space height (DSH) changes. The post- operative outcomes were evaluated at the following intervals; 2 weeks, 3 and 6 months.
The clinical outcomes demonstrated insignificant difference among the three treated groups throughout their follow up period. ABG group showed significant lower satisfactory functional outcomes (68.1%) compared to PMMA and PEEK groups (85% and 88.9%, respectively) at the 2-week post operative evaluation, but the ABG group showed closer functional outcomes to the PMMA and PEEK groups at the 3 and 6-month post operative evaluations. Despite the inferior bony fusion rates of the PMMA group (30%) compared to ABG group (86.3%) and PEEK group (77.7%) at the 6-month post operative evaluation, the clinical and functional outcomes were comparable.
Bone-filled PMMA implant is a reliable treatment option; despite its inferior fusion rate at the 6-month postoperative evaluation, it still provides acceptable segmental stability, satisfactory clinical and functional outcomes that are comparable to ABG and PEEK grafting procedures.
Cervical; Fusion; Polymethylmethacrylate; Polyetheretherketone; Autograft
A primary object with a fusion cage is avoidance of graft collapse with subsequent subsidence and malalignment of the cervical spine that is observed after bone grafting alone. No randomized studies exist that demonstrate the difference between these two methods in terms of graft subsidence and angulation of the fused segment. The size of the study population was calculated to be 24 patients to reach a significant difference at the 95% CI level. Patients with one-level cervical radiculopathy scheduled for surgery were randomized to anterior discectomy and fusion (ACDF) with autograft or to fusion cage, both without plate fixation. Tantalum markers were inserted in the two adjacent vertebrae at the end of surgery. Radiostereometry was performed immediately postoperatively and at regular intervals for 2 years. Questionnaires were used to evaluate the clinical outcome and an unbiased observer graded the outcome after 2 years. No significant differences were found between the two methods after 2 years in regard of narrowing of the disc space (mean 1.7 and 1.4 mm, respectively) or deformation of the fused segment into flexion (mean 7.7° and 4.6°, respectively). Patients in the cage group had a significantly better clinical outcome. The findings of subsidence and flexion deformation of the fused segment after 2 years seem to be of no clinical importance after one-level cervical disc surgery. However, in multi-level surgery using the same methods, an additive effect of the deformations of the fused segments may affect the clinical outcome.
Cervical discectomy; Fusion; Cage; Randomization; Radiostereometry
Study design: Randomized controlled trial.
Objective: To compare fusion rates, time to fusion, complication rates and subsidence between 1) a static, 2) a dynamic angulation, and 3) a dynamic translation plate in anterior cervical discectomy and fusion for symptomatic degenerative cervical disease.
Methods: Thirty-six patients with two level, symptomatic cervical degenerative changes requiring surgery were randomized in a blinded fashion to receive a statically locked plate, Cervical Spine Locking Plate (CSLP) (Synthes, Paoli, PN, USA), an Atlantis Vision® Anterior Cervical Plate System (Medtronic, Memphis, TN, USA) which allows angular dynamization, or a Premier® Anterior Cervical Plate System (Medtronic) which allows translational dynamization. Structured data collection and measurement protocols were used. Intervertebral composite allograft cages were used in all groups. Identical external immobilization and antiinflammatory medication protocols were followed. X-rays were obtained at preset time points postoperatively. Assessment of the primary outcomes was blinded. Rate of and time to fusion, graft/instrumentation complications, subsidence, and reoperation for adjacent level disease were measured. Paired t-test and three-way Analysis of Variance test (ANOVA) were used to assess statistical differences between groups.
Results: The three groups were similar demographically. Fusion rates in the CSLP, Atlantis and Premier plate groups were 100%, 91%, and 92% respectively. Mean time to fusion was 6.1, 8.3 and 6.3 months respectively but differences were not statistically significant. Mean subsidence in the groups was 1.9, 1.6, and 2.6 mm respectively. Subsidence was found even for the static (CSLP) plate, but no statistically significant differences were found.
Conclusions: We found no clinical advantage of dynamic plates over static plates with regards to fusion rates, time to fusion, subsidence, complications, or adjacent-level surgery. Static plating allows for subsidence at similar levels to dynamic plating.
The definiton of the different classes of evidence is available on page 83.