Anterior cervical interbody fusion with a titanium box cage: early radiological assessment of fusion and subsidence

Can an Endplate-conformed Cervical Cage Provide a Better Biomechanical Environment than a Typical Non-conformed Cage?: A Finite Element Model and Cadaver Study

OBJECTIVES

To evaluate the biomechanical characteristics of endplate-conformed cervical cages by finite element method (FEM) analysis and cadaver study.

METHODS

Twelve specimens (C2 -C7 ) and a finite element model (C3 -C7 ) were subjected to biomechanical evaluations. In the cadaver study, specimens were randomly assigned to intact (I), endplate-conformed (C) and non-conformed (N) groups with C4-5 discs as the treated segments. The morphologies of the endplate-conformed cages were individualized according to CT images of group C and the cages fabricated with a 3-D printer. The non-conformed cages were wedge-shaped and similar to commercially available grafts. Axial pre-compression loads of 73.6 N and moment of 1.8 Nm were used to simulate flexion (FLE), extension (EXT), lateral bending (LB) and axial rotation (AR). Range of motion (ROM) at C4-5 of each specimen was recorded and film sensors fixed between the cages and C5 superior endplates were used to detect interface stress. A finite element model was built based on the CT data of a healthy male volunteer. The morphologies of the endplate-conformed and wedge-shaped, non-conformed cervical cages were both simulated by a reverse engineering technique and implanted at the segment of C4-5 in the finite element model for biomechanical evaluation. Force loading and grouping were similar to those applied in the cadaver study. ROM of C4-5 in group I were recorded to validate the finite element model. Additionally, maximum cage-endplate interface stresses, stress distribution contours on adjoining endplates, intra-disc stresses and facet loadings at adjacent segments were measured and compared between groups.

RESULTS

In the cadaver study, Group C showed a much lower interface stress in all directions of motion (all P < 0.05) and the ROM of C4-5 was smaller in FLE-EXT (P = 0.001) but larger in AR (P = 0.017). FEM analysis produced similar results: the model implanted with an endplate-conformed cage presented a lower interface stress with a more uniform stress distribution than that implanted with a non-conformed cage. Additionally, intra-disc stress and facet loading at the adjacent segments were obviously increased in both groups C and N, especially those at the supra-jacent segments. However, stress increase was milder in group C than in group N for all directions of motion.

CONCLUSIONS

Endplate-conformed cages can decrease cage-endplate interface stress in all directions of motion and increase cervical stability in FLE-EXT. Additionally, adjacent segments are possibly protected because intra-disc stress and facet loading are smaller after endplate-conformed cage implantation. However, axial stability was reduced in group C, indicating that endplate-conformed cage should not be used alone and an anterior plate system is still important in anterior cervical discectomy and fusion.

Titanium/Polyetheretherketone Cages for Cervical Arthrodesis with Degenerative and Traumatic Pathologies: Early Clinical Outcomes and Fusion Rates

OBJECTIVE

Anterior cervical discectomy and fusion is the most commonly employed surgical technique for treating cervical spondylosis. Although autologous bone grafts are considered the gold standard in achieving fusion, associated short- and long-term morbidities have led to a search for alternative materials. These have included carbon-fiber, titanium alloy (Ti) and ceramic and polyetheretherketone (PEEK) based implants. Recent attempts to optimize cage implants through using composite designs have combined Ti and PEEK. However, there are few published reports on the clinical and radiological outcomes of commercially available composite cages. Our study aimed to provide and evaluate initial outcomes of a composite Ti/PEEK cage.

METHODS

In this prospective single senior surgeon cohort study, 31 consecutive patients underwent a modified Smith-Robinson technique under general anesthesia and relevant data were collected. The study patients were aged between 18 and 75 years and underwent surgery from November 2013 to May 2014. Indications for surgery included traumatic and degenerative cervical disease that was unsuitable for or unresponsive to conservative management. All cages were between 5 and 8 mm and packed with super critical fluid sterilized allograft and bone marrow aspirate before insertion. Patients were followed-up for a minimum of 12 months. Fusion was assessed using fine cut CT and anteroposterior and lateral radiographs. Clinical outcomes were measured using a Visual Analogue Scale, Neck Oswestry Disability Index and Patient's Satisfaction Index.

RESULTS

Six of the original cohort were unavailable for adequate follow-up. The remaining 25 patients (17 men, 8 women; 33 operative levels) were observed for a mean of 14.6 months (range, 12-16 months). All operation levels were between C4 and C7 . Single-level operations were performed in 19 patients and additional plating in 14 patients. A fusion rate of 96% was achieved. Patients in both plated and non-plated groups experienced statistically significant improvements; good to excellent outcomes being seen in 92% of patients. There was one complication, namely recurrent laryngeal nerve palsy, which had partially resolved at 6 months follow-up.

CONCLUSION

The present study shows that enhancement of PEEK cages with Ti endplates is a safe and effective treatment with the potential for early osseointegration and early radiological evidence of fusion.

Suitability of carbon fiber–reinforced polyetheretherketone cages for use as anterior struts following corpectomy

OBJECTIVE

Fibular allograft remains a widely used strut for corpectomy surgeries. The amount of graft material that can be packed into an allograft strut has not been quantified. Cages are an alternative to fibular allograft for fusion surgeries. The authors of this study assessed the suitability of carbon fiber–reinforced polyetheretherketone (CFRP) cages for anterior corpectomy surgeries. They further explored the parameters known to affect fusion rates in clinical practice.

METHODS

Six fibular allografts were tested at standard lengths. Three sets of carbon fiber cages (Bengal, DePuy Spine), each with a different footprint size but the same lengths, were tested. The allografts and cages were wrapped in adhesive, fluid-tight transparent barriers and filled with oil. The volume and weight of the oil instilled as well as the implant footprints were measured. The fibular allografts and cages were tested at 20-, 40-, and 50-mm lengths. Two investigators independently performed all measurements 5 times. Five CFRP cubes (1 × 1 × 1 cm) were tested under pure compression, and load versus displacement curves were plotted to determine the modulus of elasticity.

RESULTS

Significantly more oil fit in the CFRP cages than in the fibular allografts (p < 0.0001). The weight and volume of oil was 4–6 times greater in the cages. Interobserver (r = 0.991) and intraobserver (r = 0.993) reliability was excellent. The modulus of elasticity for CFRP was 16.44 ± 2.07 GPa.

CONCLUSIONS

Carbon fiber–reinforced polyetheretherketone cages can accommodate much more graft material than can fibular allografts. In clinical practice, the ability to deliver greater amounts of graft material following a corpectomy may improve fusion rates.

Long-Term Follow-Up Results of Anterior Cervical Inter-Body Fusion with Stand-Alone Cages

Objective

The purpose of this study was to evaluate long-term follow-up radiologic/clinical outcomes of patients who underwent anterior cervical discectomy and inter-body fusion (ACDF) with stand-alone cages (SAC) in a single academic institution.

Methods

Total 99 patients who underwent ACDF with SAC between February 2004 and December 2012 were evaluated retrospectively. A total of 131 segments were enrolled in this study. Basic demographic information, radiographic [segmental subsidence rate, fusion rate, C2–7 global angle, and segmental angle changes)/clinical outcomes (by Odom's criteria and visual analog score (VAS)] and complications were evaluated to determine the long-term outcomes.

Results

The majority were males (55 vs. 44) with average age of 53.2. Mean follow-up period was 62.9 months. The segmental subsidence rate was 53.4% and fusion rate was 73.3%. In the subsidence group, anterior intervertebral height (AIH) had more tendency of subsiding than middle or posterior intervertebral height (p=0.01). The segmental angle led kyphotic change related to the subsidence of the AIH. Adjacent segmental disease was occurred in 18 (18.2%) patients. Total 6 (6%) reoperations were performed at the index level. There was no statistical significance between clinical and radiological outcomes. But, overall long-term clinical outcome by Odom's criteria was unsatisfactory (64.64%). The neck and arm VAS score were increased by over time.

Conclusion

Long-term outcomes of ACDF with SAC group were acceptable but not satisfactory. For optimal decision making, more additional comparative long-term outcome data is needed between ACDF with SAC and ACDF with plating.

In Vivo Study of Hydroxyapatite-coated Hat Type Cervical Intervertebral Fusion Cage Combined With IGF-I and TGF-β1 in the Goat Model

STUDY DESIGN

An in vivo animal experimental study.

OBJECTIVE

To investigate the hydroxyapatite (HA) coating in a modified fusion cage in improving the results of cervical intervertebral fusion and the role of combination of IGF-I and TGF-β1 treatment in a goat cervical spine interbody fusion model.

MATERIALS AND METHODS

Thirty-two goats were divided into 4 groups (n=8 for each) and underwent C3-4 discectomy and intervertebral fusion by the following methods: group 1, autologous tricortical iliac crest bone graft; group 2, cage only; group 3, cage coated with HA; group 4, cage coated with HA+IGF-I and TGF-β1. Radiography was performed preoperatively, postoperatively, and after 1, 2, 4, 8, and 12 weeks. At the same time points, disk space height, intervertebral angle, and lordosis angle were measured. At 12 weeks postoperatively, the goats were killed and fused segments were harvested. Biomechanical study was performed in flexion, extension, axial rotation, and lateral bending with a nondestructive stiffness method to determine the range of motion and stiffness. All cervical fusion specimens underwent histomorphologic studies.

RESULTS

All 3 cage-treated groups showed significantly higher values for disk space height, intervertebral angle, and lordosis angle compared with the autologous tricortical iliac group at 1, 2, 4, 8, and 12 weeks after surgery (P<0.05). The stiffness of hat-shaped cervical intervertebral fusion cage coated with HA+IGF-I and TGF-β1 in flexion, extension, and lateral bending was significantly greater than that of the other groups (P<0.05), and the stiffness of hat-shaped cervical intervertebral fusion cage coated with HA in extension, axial rotation, and lateral bending was significantly greater than that of fusion with the bone graft and cage-only groups (P<0.05). Histomorphologic evaluation showed better fusion in 3 cage groups than in the bone graft group. In group 4 of the cage coated with HA+IGF-I and TGF-β1, a slightly more advanced bone matrix formation was shown than in groups without coating.

CONCLUSIONS

HA coating can improve the fusion effect of the cervical intervertebral cage, and IGF-I and TGF-β1 can enhance bone fusion.

Long-term results of anterior cervical corpectomy and fusion with nano-hydroxyapatite/polyamide 66 strut for cervical spondylotic myelopathy

To assess the long-term clinical and radiographic outcomes of anterior cervical corpectomy and fusion (ACCF) with a neotype nano-hydroxyapatite/polyamide 66 (n-HA/PA66) strut in the treatment of cervical spondylotic myelopathy (CSM). Fifty patients with CSM who underwent 1- or 2-level ACCF with n-HA/PA66 struts were retrospectively investigated. With a mean follow-up of 79.6 months, the overall mean JOA score, VAS and cervical alignment were improved significantly. At last follow-up, the fusion rate was 98%, and the subsidence rate of the n-HA/PA66 strut was 8%. The "radiolucent gap" at the interface between the n-HA/PA66 strut and the vertebra was further noted to evaluate the osteoconductivity and osseointegration of the strut, and the incidence of it was 62% at the last follow-up. Three patients suffered symptomatic adjacent segment degeneration (ASD). No significant difference was detected in the outcomes between 1- and 2-level corpectomy at follow-ups. In conclusion, the satisfactory outcomes in this study indicated that the n-HA/PA66 strut was an effective graft for cervical reconstruction. Moreover, the osteoconductivity and osseointegration of the strut is still need to be optimized for future clinical application owing to the notably presence of "radiolucent gap" in present study.

Stand-Alone Cages for Anterior Cervical Fusion: Are There No Problems?

Objective

There are complications in stand-alone cage assisted anterior cervical discectomy and fusion (ACDF), such as cage subsidence and kyphosis. Here we report our clinical result on ACDF, comparing with stand-alone cages and with cervical plate system for degenerative cervical spine diseases.

Methods

Patients with degenerative cervical disease who were diagnosed and treated in Konyang University Hospital between January 2004 and December 2014 were included in this study. Patients who had operation in single level ACDF were selected. Patients scored the degree of pain using visual analog scale before and after the surgery. Subsidence was defined as ≥3-mm decrease of the segmental height, and cervical kyphosis was defined as progression of ≥5° at 12 months after postoperative follow-up compared to that measured at the immediate postoperative period.

Results

A total of 81 patients were enrolled for this study. Forty-five patients were included in a cervical plate group and the others were in stand-alone cage group. There was no statistical difference in pain score between the 2 groups. Segmental subsidence was observed in 7 patients (15.6%) in plate-assisted cervical fusion group, and 13 patients (36.1%) in stand-alone cage group. Segmental kyphosis was observed in 4 patients (8.9%) in plate-assisted cervical fusion group, and 10 patients (27.8%) in stand-alone cage group. There was statistical difference between the 2 groups.

Conclusion

There was no difference in pain between 2 groups. But stand-alone case group showed higher incidence rate than plate-assisted cervical fusion group in segmental subsidence and cervical kyphosis. When designing cervical fusion, more attention should be given selecting the surgical technique.

Analysis of clinically relevant mechanical and thermal characteristics of titanium foam spinal implants during drilling

Although high biocompatibility promotes the use of titanium (Ti) alloy in spinal implants, this material shows high stiffness, which is an issue for removal by drilling. The recently developed, porous Ti foam implants, which have shown enhanced osteoformation, may overcome this flaw. Thus, this study aimed to compare the mechanical and thermal characteristics of Ti-foam (80 % porosity) and conventional Ti alloy (0 % porosity) implants drilled in clinically relevant conditions. Mechanical properties were analyzed by measuring axial and torque forces using a pressure sensor with a drill of 2.5-mm diameter at a rotation frequency of 20 Hz. Thermography was used to evaluate the heat generated by a diamond burr attached to a high-speed (80,000 rpm) drill. The torque and axial strengths of Ti foam (13.63 ± 1.43 and 82.60 ± 7.78 N, respectively) were significantly lower (P = 0.001) than those of Ti alloy (73.58 ± 13.60 and 850.72 ± 146.99 N, respectively). Furthermore, irrigation reduced the area of local heating for Ti foam to 56-82 % of that for Ti alloy, indicating lower thermal conductivity. These data suggest that the use of Ti foam implants may be advantageous in cases with a probability of implant drilling in the future.

Cervical Stand-Alone Polyetheretherketone Cage versus Zero-Profile Anchored Spacer in Single-Level Anterior Cervical Discectomy and Fusion : Minimum 2-Year Assessment of Radiographic and Clinical Outcome

Objective

We compared the clinical and radiographic outcomes of stand-alone polyetheretherketone (PEEK) cage and Zero-Profile anchored spacer (Zero-P) for single level anterior cervical discectomy and fusion (ACDF).

Methods

We retrospectively reviewed 121 patients who underwent single level ACDF within 2 years (Jan 2011-Jan 2013) in a single institute. Total 50 patients were included for the analysis who were evaluated more than 2-year follow-up. Twenty-nine patients were allocated to the cage group (m : f=19 : 10) and 21 for Zero-P group (m : f=12 : 9). Clinical (neck disability index, visual analogue scale arm and neck) and radiographic (Cobb angle-segmental and global cervical, disc height, vertebral height) assessments were followed at pre-operative, immediate post-operative, post-3, 6, 12, and 24 month periods.

Results

Demographic features and the clinical outcome showed no difference between two groups. The change between final follow-up (24 months) and immediate post-op of Cobb-segmental angle (p=0.027), disc height (p=0.002), vertebral body height (p=0.033) showed statistically better outcome for the Zero-P group than the cage group, respectively.

Conclusion

The Zero-Profile anchored spacer has some advantage after cage for maintaining segmental lordosis and lowering subsidence rate after single level anterior cervical discectomy and fusion.

Subsidence as of 12 months after single-level anterior cervical inter-body fusion. Is it related to clinical outcomes?

BACKGROUND

Subsidence is a frequent phenomenon in the interbody fusion process in patients with anterior cervical discectomy and fusion (ACDF). There is little evidence of whether subsidence in the cervical spine has any impact on clinical outcomes.

OBJECTIVES

The purpose of this study is to investigate the correlation of subsidence and clinical outcomes after ACDF and to consider reasons subsidence might not cause unfavorable clinical outcomes.

METHODS

A total of 158 consecutive patients who underwent single-level ACDF were included. The patients were divided into a subsidence group (S-group) and a no subsidence group (N-group), with subsidence defined as a decrease by ≥3 mm in total intervertebral height (TIH). We analyzed outcomes resulting from subsidence, particularly focusing on clinical outcomes and subsequent global and segmental kyphosis using a repeated measure analysis of variance (RM-ANOVA).

RESULTS

Subsidence occurred in 74 patients (46.8%) as of a 12-month follow-up. The S-group included 58.6% with a stand-alone cage for interbody fusion (p = 0.002). Clinical outcomes improved significantly over time (neck pain, RM-ANOVA: F(1.3, 205) = 125.1, p < 0.001; arm pain, RM-ANOVA: F(1.3, 203) = 290.8, p < 0.001). There was no significant difference in interaction with subsidence and clinical outcomes between the S- and N-group (neck pain, RM-ANOVA: F(2,153) = 1.04, p = 0.356, partial η(2) = 0.229; arm pain, RM-ANOVA: F(2,153) = 0.56, p = 0.571, partial η(2) = 0.142). Segmental angle increased in both groups over time and showed a statistically significant difference between the S- and N-groups (RM-ANOVA: F(3,143) = 6.148, p = 0.001, partial η(2) = 0.959). Although, global cervical angle decreased generally and displayed no statically significant difference between the S- and N-group (RM-ANOVA: F(3,119) = 2.361, p = 0.075, partial η(2) = 0.056).

CONCLUSIONS

Radiographic subsidence after ACDF occurred in 46.8% patients as of 12 months after the single-level ACDF. The lack of correlation between bad clinical outcome and radiographic subsidence may be due to segmental kyphosis, preserved posterior height, and maintaining the global cervical angle.

Segmental kyphosis after cervical interbody fusion with stand-alone polyetheretherketone (PEEK) cages: a comparative study on 2 different PEEK cages

STUDY DESIGN

Retrospective comparative study.

OBJECTIVE

Two polyetheretherketone (PEEK) cages of different designs were compared in terms of the postoperative segmental kyphosis after anterior cervical discectomy and fusion.

SUMMARY OF BACKGROUND DATA

Segmental kyphosis occasionally occurs after the use of a stand-alone cage for anterior cervical discectomy and fusion. Although PEEK material seems to have less risk of segmental kyphosis compared with other materials, the occurrence of segmental kyphosis for PEEK cages has been reported to be from 0% to 29%. There have been a few reports that addressed the issue of PEEK cage design.

METHOD

A total of 41 consecutive patients who underwent single-level anterior discectomy and fusion with a stand-alone cage were included. Either a round tube-type (Solis; 18 patients, S-group) or a trapezoidal tube-type (MC+; 23 patients, M-group) cage was used. The contact area between the cage and the vertebral body is larger in MC+ than in Solis, and anchoring pins were present in the Solis cage. The effect of the cage type on the segmental angle (SA) (lordosis vs. kyphosis) at postoperative month 24 was analyzed.

RESULTS

Preoperatively, segmental lordosis was present in 12/18 S-group and 16/23 M-group patients (P=0.84). The SA was more lordotic than the preoperative angle in both groups just after surgery, with no difference between groups (P=0.39). At 24 months, segmental lordosis was observed in 9/18 S-group and 20/23 M-group patients (P=0.01). The patients in M-group were 7.83 times more likely than patients in S-group (P=0.04; odds ratio, 7.83; 95% confidence interval, 1.09-56.28) not to develop segmental kyphosis.

CONCLUSIONS

The design of the PEEK cage used may influence the SA, and this association needs to be considered when using stand-alone PEEK cages.

The design evolution of interbody cages in anterior cervical discectomy and fusion: a systematic review

BACKGROUND

Anterior cervical discectomy with fusion is a common surgical procedure for patients experiencing pain and/or neurological deficits due to cervical spondylosis. Although iliac crest bone graft remains the gold standard today, the associated morbidity has inspired the search for alternatives, including allograft, synthetic and factor/cell-based grafts; and has further led to a focus on cage fusion technology. Compared to their graft counterparts, cage interbody implants have enhanced biomechanical properties, with designs constantly improving to maximise biocompatibility and osseointegration. We present a systematic review examining the historical progress of implant designs and performance, as well as an update on the currently available designs, and the potential future of cervical interbody implants.

METHODS

We performed a systematic review using the keywords "cervical fusion implant design", with no limits on year of publication. Databases used were PubMed, Medline, Embase and Cochrane. In addition, the search was extended to the reference lists of selected articles.

RESULTS

180 articles were reviewed and 64 articles were eligible for inclusion. Exclusion criteria were based around study design, implant information and patient cohorts. The evolution of cage implant design has been shaped by improved understanding of ideal anatomy, progress in materials research and continuing experimentation of structural design. Originally, designs varied primarily in their choice of structure, however long-term studies have displayed the overall advantages of non-threaded, wedge shaped cages in complementing healthy anatomical profiles, and thus focus has shifted to refining material utilisation and streamlining anterior fixation.

CONCLUSIONS

Evolution of design has been dramatic over the past decades; however an ideal cage design has yet to be realised. Current research is focusing on the promotion of osseointegration through bioactiviation of surface materials, as well as streamlining anterior fixation with the introduction of integrated screws and zero profile designs. Future designs will benefit from a combination of these advances in order to achieve ideal disc heights, cervical alignments and fusions.

The Effect of the PEEK Cage on the Cervical Lordosis in Patients Undergoing Anterior Cervical Discectomy

BACKGROUND:

Loss of cervical lordosis is a significant factor in the development of degeneration of the spine with aging. This degenerative changings of the cervical spine would cause pressure effect on the cervical root and/or medulla spinalis.

AIM:

Our goal is to understand the effect of the PEEK cage on cervical lordosis in the early postoperative period. Also, to interpret the effects of one- level, two- level, three-level and four- level disc pathologies on cervical lordosis.

MATERIAL AND METHODS:

We retrospectively investigated our archive, and we selected thirty-four patients undergoing anterior cervical discectomy and fusion with PEEK cage filled with demineralized bone matrix (ACDFP).

RESULTS:

We determined that ACDFP provides improvement in the cervical lordosis angle in both groups. Also, we found statistically significant difference between group 1 and 2 regarding causes of radiculomyelopathy statistically.

CONCLUSION:

We achieved better cervical lordotic angles at the postoperative period by implanting one-level, two-level, three-level or four-level PEEK cage filled with demineralized bone matrix. Also, the causes of cervical root and or medulla spinalis impingement were different in group1 and 2. While extruded cervical disc impingement was the first pathology in group 1, osteophyte formation was the first pathology in group 2.

Comparison of two reconstructive techniques in the surgical management of four-level cervical spondylotic myelopathy

To compare the clinical efficacy and radiological outcome of treating 4-level cervical spondylotic myelopathy (CSM) with either anterior cervical discectomy and fusion (ACDF) or “skip” corpectomy and fusion, 48 patients with 4-level CSM who had undergone ACDF or SCF at our hospital were analyzed retrospectively between January 2008 and June 2011. Twenty-seven patients received ACDF (Group A) and 21 patients received SCF. Japanese Orthopaedic Association (JOA) score, Neck Disability Index (NDI) score, and Cobb's angles of the fused segments and C2-7 segments were compared in the two groups. The minimum patient follow-up was 2 years. No significant differences between the groups were found in demographic and baseline disease characteristics, duration of surgery, or follow-up time. Our study demonstrates that there was no significant difference in the clinical efficacy of ACDF and SCF, but ACDF involves less intraoperative blood loss, better cervical spine alignment, and fewer postoperative complications than SCF.

Histological, mechanical, and radiological study of osteoformation in titanium foam implants

BACKGROUND

Titanium (Ti) is widely used for implants because of its high mechanical reliability and because it aids osteoformation. However, it also produces artifacts during radiological imaging. Further, Ti implants can sometimes cause the surrounding bone to break. Owing to recent advances, Ti can be transformed into sponge-like, porous materials having a three-dimensional network of pores; such materials are called Ti foams. These foams exhibit distinct characteristics that make them more suitable than nonporous Ti. The objective of this study was to evaluate Ti foams as implant materials.

METHODS

Implants based on Ti foams having porosities of 80% and 90% were embedded in the femurs of 11 rabbits. Implants based on 0% porosity Ti were used as controls. Five rabbits were sacrificed 4 weeks after implantation, while the remaining were sacrificed after 12 weeks. The femurs containing the Ti implants were harvested and analyzed.

RESULTS

Biomechanical analyses showed that the 80% porosity implants induced greater osteoformation. There were significant differences in the average pushout strengths of the control and 80% porosity implants after 4 weeks (p = 0.048) and 12 weeks (p = 0.001). Histopathological analyses confirmed osteoformation in the case of the 80% porosity implants. Analyses of the micro-computed tomography images of the Ti foam-based implants did not suggest the presence of artifacts.

CONCLUSIONS

The 80% porosity Ti implants did not exhibit the shortcomings associated with conventional Ti implants. In addition, they induced greater osteoformation. Finally, the Ti foams did not produce radiological artifacts.

Comparison between Two Different Cervical Interbody Fusion Cages in One Level Stand-alone ACDF: Carbon Fiber Composite Frame Cage Versus Polyetheretherketone Cage

Objective

The authors conducted a retrospective study to compare the implantation of carbon fiber composite frame cages (CFCFCs) to the implantation of polyetheretherketone (PEEK) cages after anterior cervical discectomy for cervical degenerative disc disease. In addition, the predictive factors that influenced fusion or subsidence were investigated.

Methods

A total of 58 patients with single-level degenerative disc disease were treated with anterior cervical discectomy and implantation of stand-alone cages; CFCFCs were used in 35 patients, and PEEK cages were used in 23 patients. Preoperative and postoperative radiological and clinical assessments were performed.

Results

During the mean follow-up period of 41 months, fusion occurred in 43 patients (74.1%), and subsidence developed in 18 patients (31.0%). Pain decreased in all patients, and the patients' satisfaction rate was 75.9%. Neither fusion nor subsidence was related to the clinical outcome. There were no significant differences in the clinical and radiological outcomes between the CFCFC and the PEEK cage groups. Smoking history (p=0.023) was significantly associated with pseudarthrosis, and cage height (≥7mm) (p=0.037) were significantly associated with subsidence.

Conclusion

The clinical and radiological results were similar between the CFCFC and the PEEK cage groups. Fusion or subsidence did not affect the clinical outcomes. Smoking history and cage height (≥7mm) were predictive factors for pseudarthrosis or subsidence in anterior cervical discectomy and fusion with stand-alone cages.

Risk factors for subsidence in anterior cervical fusion with stand-alone polyetheretherketone (PEEK) cages: a review of 82 cases and 182 levels

INTRODUCTION

To determine risk factors for subsidence in patients treated with anterior cervical discectomy and fusion (ACDF) and stand-alone polyetheretherketone (PEEK) cages.

MATERIALS AND METHODS

Records of patients with degenerative spondylosis or traumatic disc herniation resulting in radiculopathy or myelopathy between C2 and C7 who underwent ACDF with stand-alone PEEK cages were retrospectively reviewed. Cages were filled with autogenous cancellous bone harvested from iliac crest or hydroxyapatite. Subsidence was defined as a decrease of 3 mm or more of anterior or posterior disc height from that measured on the postoperative radiograph. Eighty-two patients (32 males, 50 females; 182 treatment levels) were included in the analysis.

RESULTS

Most patients had 1-2 treatment levels (62.2 %), and 37.8 % had 3-4 treatment levels. Treatment levels were from C2-7. Of the 82 patients, cage subsidence occurred in 31 patients, and at 39 treatment levels. Multivariable analysis showed that subsidence was more likely to occur in patients with more than two treatment levels, and more likely to occur at treatment levels C5-7 than at levels C2-5. Subsidence was not associated with postoperative alignment change but associated with more disc height change (relatively oversized cage).

CONCLUSION

Subsidence is associated with a greater number of treatment levels, treatment at C5-7 and relatively oversized cage use.

Integrated intervertebral device for anterior cervical fusion: An initial experience

Objective:

To analyze the clinical and radiographic results following the use of integrated intervertebral implant in patients with cervical spine degenerative disease.

Background:

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.

Results:

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).

Conclusions:

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.

Anterior cervical discectomy and fusion using a stand-alone polyetheretherketone cage packed with local autobone : assessment of bone fusion and subsidence

Objective

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.

Methods

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.

Results

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%).

Conclusion

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.

Autologous iliac bone graft with anterior plating is advantageous over the stand-alone cage for segmental lordosis in single-level cervical disc disease

BACKGROUND

Anterior cervical discectomy and fusion (ACDF) with autologous iliac bone graft and plating has been a standard surgical method for single-level cervical disc disease. The stand-alone cage was introduced to reduce graft-related morbidity. However, problems due to focal kyphosis at the operated level have been on the rise. It has been difficult to derive a conclusive answer from previous studies for the indications of each method.

OBJECTIVE

An interim analysis of a prospective randomized study was performed to compare the sagittal alignment between a stand-alone cage (ACDF cage) and autologous iliac bone graft and plating (ACDF plate).

METHODS

Twenty-nine patients were allocated to the ACDF-cage group (M:F = 17:12) and 23 to the ACDF-plate group (M:F = 14:9). Cobb angles at the operated segment (segmental angle, SA; lordosis vs kyphosis) were compared at postoperative 12 months and the other confounding factors were explored.

RESULTS

Demographic features were not different between groups. The fusion method significantly affected segmental alignment at 12 months (P = .03; odds ratio, 5.52). Preoperatively, the SA was not different between the groups (P = .18) and was similar (P = .22) immediately following the operation. However, the SA was significantly more lordotic (P < .05) in the ACDF-plate group at postoperative 12 months in comparison with the ACDF-cage group. There was no other significant risk factor for segmental kyphosis.

CONCLUSION

The stand-alone cage and autologous bone graft with plating had similar clinical outcomes, but stand-alone cage fusion may be disadvantageous from a radiological viewpoint.

Shape optimization for the subsidence resistance of an interbody device using simulation-based genetic algorithms and experimental validation

Subsidence of interbody devices into the vertebral body might result in serious clinical problems, especially when the devices are not well designed and analyzed. Recently, some novel designs were proposed to reduce the risk of subsidence, but those designs are based on the researcher's experience. The purpose of this study was to discover the interbody device design with excellent subsidence resistance by changing the device's shape. The three-dimensional nonlinear finite element models, which consisted of the interbody device and vertebral body, were created first. Then, the simulation-based genetic algorithm, which combined the finite element model and the searching algorithm, was developed by using ANSYS® Parametric Design Language. Finally, the numerical results were carefully validated with the use of biomechanical tests. The optimum shape design obtained in this study looks like a flower with many petals and it has excellent subsidence resistance when compared with the other designs provided by the past studies. The results of the present study could help surgeons to understand the subsidence resistance of interbody devices in terms of their shapes and has directly provided the design rationales to engineers.

Sagittal geometry of the middle and lower cervical endplates

PURPOSE

Construct subsidence is a relatively common complication following anterior cervical fusion. Its occurrence has been revealed to be closely related to endplate-implant contact interface. But current literature focusing on the anatomy of cervical endplate is very scarce. The purpose of this morphometric study was to analyse the sagittal geometry, especially the concavity and slope, of vertebral endplates from C3 to C7 by employing data from CT scans.

METHODS

Reformatted CT scans of 97 individuals were analyzed and endplate concavity depth, endplate concavity apex location, as well as endplate slope were measured in midsagittal plane. Those specific parameters were compared among different age and gender groups. Meanwhile, comparison between superior and inferior endplate of each vertebra was also performed.

RESULTS

Age and gender did not influence endplate concavity depth, endplate concavity apex location, or endplate slope significantly (P > 0.05). Endplate concavity depths of superior endplates (range 0.9-1.2 mm) were significantly smaller than those of inferior endplates (range 2.1-2.7 mm). Endplate concavity apex was always located in the posterior half of the endplate, with the superior one ranged from 56 to 67% and the inferior one 52 to 57%. Average endplate slopes of superior endplates were between 4.5° and 9.0°, and average inferior endplate slopes ranged from 4.5° to 7.5°. Among all measured segments, C5 had the largest endplate slope values, while C7 the least.

CONCLUSIONS

Superior endplate is more flat than its inferior counterpart in middle and lower cervical spine, and the concavity apex is always located in the posterior half of the endplate. Endplate slope is correlated with cervical curvature, greater slope implying more significant lordosis. These sagittal endplate geometrical parameters should be taken into consideration when investigating implant subsidence following anterior cervical fusion.

Long-term results after cervical anterior fusion using an autologous bone graft (Williams-Isu method)

OBJECTIVE

Cervical anterior fusion with autologous bone grafts (Williams-Isu method) is a modified, accepted method to treat spinal degenerative disease. Here we report minimum 10-year outcomes.

METHODS

Of 101 patients we treated by cervical anterior fusion using the Williams-Isu method, 50 patients were followed up for a mean of 177 months. Among the 51 patients lost to long-term follow-up 12 were contacted by telephone; they reported their condition as good and none required reoperation. We evaluated their clinical outcomes on the Japan Orthopedic Association (JOA) score and assessed radiologic findings.

RESULTS

The average JOA score was 12.5 preoperatively, 15.9 at 2 years after surgery (recovery rate 74.9%), and 15.5 at final follow-up (recovery rate 67.0%). All 5 reoperated patients were treated on the level adjacent to the original lesion. Radiographically, cervical alignment changed from 12.5° to 9.0°, the fused segment angle changed from 5.4° to -0.6°. Although worsening of the fused segment angle did not affect the clinical results, it did affect postoperative cervical sagittal alignment. Cervical alignment and range of motion (ROM) were not different between reoperated (group I) and nonreoperated patients (group II). Fused segment angle worsening was milder than expected in group I.

CONCLUSIONS

The long-term results after the Williams-Isu method were good. The fused segment angle loss of approximately 6° did not affect long-term outcomes although it did affect sagittal cervical alignment. Postoperative worsening of the fused segment angle and hyper ROM changes in the adjacent level were not related to the need for reoperation in our study.

Significant relationship between local angle at fused segments and C2-7 angle: Average duration of longer than 20 years after anterior cervical discectomy and fusion

Background:

The authors have focused their attention to the radiological durability of cervical sagittal alignment after anterior cervical discectomy and fusion (ACDF) using autologous bone grafting.

Materials and Methods:

Among the patients who underwent ACDF with trans-unco-discal (TUD) approach between 1976 and 1997, 22 patients (16 males and 6 females) made return visits for a clinical evaluation. Patients with trauma or previously treated by anterior cervical fusion or by posterior decompression were excluded from the present study. Clinical evaluation included adjacent segment degeneration (ASD), osseous fusion, local angle at the fused segments and C2-7 angle of cervical spine.

Results:

The duration after ACDF ranged from 13 to 34 years with an average of 21.3 ± 7.0 years. A single level fusion was done on 8 patients, 2 levels on 11 patients, 3 levels on 2 patients, and 4 levels on 1 patient. Imaging studies indicated that 12 of the 22 patients (54.5%) were graded as having symptomatic ASD. Osseous bony fusion at ACDF was recognized in all cases. None of the patients demonstrated kyphotic malalignment of the cervical spine. Average degrees of local angle at the fused segments and the C2-7 angle were 7.06 and 17.6, respectively. Statistical analysis indicated a significant relationship between the local at the fused segments and C2-7 angles.

Conclusions:

Sagittal alignment of the cervical spine was durable long after ACDF when the local angle at the fused segments was well stabilized.

Anterior cervical interbody constructs: effect of a repetitive compressive force on the endplate

Graft subsidence following anterior cervical reconstruction can result in the loss of sagittal balance and recurring foraminal stenosis. This study examined the implant-endplate interface using a cyclic fatigue loading protocol in an attempt to model the subsidence seen in vivo. The superior endplate from 30 cervical vertebrae (C3 to T1) were harvested and biomechanically tested in axial compression with one of three implants: Fibular allograft; titanium mesh cage packed with cancellous chips; and trabecular metal. Each construct was cyclically loaded from 50 to 250 N for 10,000 cycles. Nondestructive cyclic loading of the cervical endplate-implant construct resulted in a stiffer construct independent of the type of the interbody implant tested. The trabecular metal construct demonstrated significantly more axial stability and significantly less subsidence in comparison to the titanium mesh construct. Although the allograft construct resulted in more subsidence than the trabecular metal construct, the difference was not significant and no difference was found when comparing axial stability. For all constructs, the majority of the subsidence during the cyclic testing occurred during the first 500 cycles and was followed by a more gradual settling in the remaining 9,500 cycles.

Comparison of Operating Time between Stand-alone Cage and a Standard Method for a Single Level Cervical Disc Disease

Objective

Autologous bone graft with anterior plating had been a standard method for anterior cervical discectomy and fusion (ACDF). Drawbacks of a standard method were donor site problem and problem associated with anterior plate. The stand-alone cage was introduced to reduce such problems. However, problems associated with subsidence and local kyphosis at the index level (segmental kyphosis) still persist with stand-alone cage and a standard method would be required in some cases. It seems that harvest of autologous bone and anterior plating procedure is time consuming, but this has not been verified. The aim of this study was to compare the operating time between patients operated on with stand-alone cage versus a standard method for single-level cervical disc disease.

Methods

Consecutive 29 patients (M:F=18:11; mean age, 58.4±12.4 years), who had undergone ACDF for single-level disc disease by a single surgeon from incision to closure during 2009-2011, were selected for this retrospective study. Seventeen patients were operated with stand-alone cage (Group I), and twelve patients were with a standard method (Group II). Operating time (from incision to closure), estimated blood loss, clinical and radiological outcomes were compared. Follow-up period was 11.4±6.3 months.

Results

Operating time was not different between groups longer; Group I (96.1±28.7 minutes) and Group II (112.4±31.7 minutes) (p=0.13). There was no surgery related complication. Excellent or good outcome was achieved in 11 and 10 patients of group I and II, respectively. Bony fusion was achieved in 15 and 10 patients of group I and II respectively, while one subsidence occurred in each group. Postoperative segmental angle at the index level and cervical curvature was not different between groups. No patient complained donor site pain at the last follow-up.

Conclusions

ACDF with a standard method for single-level cervical disc disease was not a time-consuming procedure comparing stand-alone cage.

Radiological changes in anterior cervical discectomy and fusion with cage and plate construct: the significance of the anterior spur formation sign

STUDY DESIGN

Retrospective review.

OBJECTIVE

To analyze the changes of fusion process and radiological parameters during the postoperative period after anterior cervical discectomy and fusion with cage and plate construct (ACDF-CPC).

SUMMARY OF BACKGROUND DATA

Because of its well-reported efficacy, plate augmentation has been performed to avoid the various complications associated with the cage-alone procedure. The radiological changes at the fusion site after ACDF-CPC have yet to be fully explored.

METHODS

Seventy-eight patients (122 fusion sites) who underwent ACDF-CPC were observed at 6 weeks and at 3, 6, 12, and 24 months postoperatively. Fusion status was classified into 3 categories: Type I (pseudoarthrosis), Type II (borderline), and Type III (fusion). Changes at the fusion site were described through radiological parameters at each follow-up time point. In addition, the ability of the radiological parameters to predict fusion rates was analyzed.

RESULTS

The fusion process after ACDF-CPC progresses slower when compared with the standard procedure utilizing autograft. Fusion between bone graft chips begins at 6 weeks post surgery. At 3 months, initial bone bridging between graft and host bones begins to form. Anterior spur formation occurs at 3 to 6 months, and "kissing" lesions form at 6 to 12 months. Bony incorporation is achieved at 1 to 2 years. Persistent or newly developed Type I at the 1-year follow-up exhibited significantly higher pseudoarthrosis rates in comparison with rates determined at the 3- and 6-month time points. Among 29 subsidence cases, 9 of the 16 (56.3%) cases that exhibited anterior spur formation eventually achieved fusion, whereas 2 of the 13 (15.4%) cases that did not exhibit anterior spur formation eventually achieved fusion. In cases that demonstrated anterior spur formation, the fusion rate was significantly higher than in cases without it (P = 0.016).

CONCLUSION

The fusion process after ACDF-CPC progresses slower than the standard procedure utilizing autograft. Cage subsidence of greater than 2 mm, a radiolucent defect, or a halo sign are poor prognostic signs indicating a high probability for pseudoarthrosis when detected radiographically after 1 year postoperatively. The anterior spur formation sign and "kissing" lesion, on the contrary, represent signs for eventual successful fusion.

Evaluation of bioabsorbable multiamino acid copolymer/α-tri-calcium phosphate interbody fusion cages in a goat model

STUDY DESIGN

A study of cervical interbody fusion using polyamino acid-based bioabsorbable fusion cages in a goat model.

OBJECTIVE

To compare interbody fusion of a bioabsorbable multiamino acid copolymer/α-tri-calcium phosphate (MAACP/α-TCP) fusion cage with an autologous tricortical iliac-crest bone graft and a titanium cage.

SUMMARY OF BACKGROUND DATA

Polyamino acid is widely used as a carrier for drug delivery. To our knowledge, no study investigates interbody fusion cage made of polyamino acid.

METHODS

A total of 15 sheep underwent C3/C4 discectomy and fusion. The following stabilization techniques were used: group A, autologous tricortical iliac crest bone graft (n = 5); group B, MAACP/α-TCP cage filled with autologous cancellous bone graft (n = 5); group C, titanium cage filled with autologous cancellous bone graft (n = 5). Radiographic scans to determine disc space height were performed before and after surgery and after 4, 8, and 12 weeks, respectively. After 12 weeks, the C3/C4 motion segment was isolated and sectioned to create a 5-mm thick parasagittal section from which lateral radiographs were obtained. All the radiographs were encoded and reviewed in a blinded fashion to evaluate interbody fusion within the cage devices according to a three-point radiographic score. Biomechanical testing was performed in flexion, extension, axial rotation, and lateral bending to determine range of motion (ROM). Histomorphological and histomorphometrical analyses were performed to evaluate fusion and foreign-body reactions associated with the bioabsorbable cages.

RESULTS

Radiographic results showed that the disc space height (DSH) in MAACP/α-TCP cage group was better than that of bone graft group and the best radiographic score was found in MAACP/α-TCP cage group. Biomechanical test showed that no significant difference was found in ROM between MAACP/α-TCP cage group and titanium cage group whereas the value of ROM in bone graft group was the largest. Histologic evaluation showed a higher intervertebral bone volume/total volume ratio and a better interbody fusion in the MAACP/α-TCP cage group than in the other two groups. Two MAACP/α-TCP cages showed microcracks and the other three cages had maintained their original geometry. All MAACP/α-TCP cages showed excellent biocompatibility.

CONCLUSION

After 12 weeks, there was no significant difference between the MAACP/α-TCP cage and the titanium cage in distractive properties and biomechanical properties. Compared with titanium cages, MAACP/α-TCP cages showed an advanced interbody fusion. Although MAACP/α-TCP cages developed cracks after only 12 weeks, they showed significantly better distractive properties, biomechanical properties, and an advanced interbody fusion than the tricortical iliac crest bone graft. Improvement should be made to insure the strength of MAACP/α-TCP cage last at least 6 month after implantion.

β-Tricalcium phosphate promotes bony fusion after anterior cervical discectomy and fusion using titanium cages

STUDY DESIGN

Retrospective consecutive cohort study.

OBJECTIVE

To study the effectiveness of β-tricalcium phosphate (β-TCP) granules as a packing material in the titanium cages for anterior cervical discectomy and fusion (ACDF), compared with the conventional hydroxyapatite (HA) granules.

SUMMARY OF BACKGROUND DATA

ACDF using titanium cages is a standard procedure for the treatment of cervical spinal degenerative diseases. Synthetic bone substitutes are widely used to pack the titanium cage to augment intervertebral bony fusion, but the efficacy has not been confirmed.

METHODS

Fusion condition was evaluated on lateral radiographs and computed tomography. Complete fusion of the treated segments was defined by three criteria: movement of the spinous process at flexion and extension positions of less than 3 mm, bony bridging between vertebral bodies, and absence of the halo around the titanium cage. The evaluation was performed at 6 months, 1 year, and 2 years after surgery.

RESULTS

Intervertebral fusion was studied in patients who underwent ACDF using β-TCP (93 segments of 57 patients) or HA (72 segments of 48 patients) packing of cylindrical titanium cages. Complete fusion rate at 6 months and 1 year was significantly better in the β-TCP group (46% at 6 months and 69% at 1 year) than in the HA group (24% at 6 months and 49% at 1 year), but the rate was similar at 2 years in the β-TCP group (94%) and the HA group (90%). There were no material-related adverse effects.

CONCLUSION

Satisfactory final fusion rates were obtained after ACDF using both β-TCP- and HA-packed titanium cages. β-TCP showed higher fusion rate in the early stage after surgery and can be recommended as a bone substitute for ACDF with titanium cages.

Comparative study of clinical outcomes of anterior cervical discectomy and fusion using autobone graft or cage with bone substitute

Study Design

A retrospective study.

Purpose

To compare the clinical and radiological outcomes of autogenous bone graft and cage with bone substitute for anterior cervical discectomy and fusion.

Overview of Literature

The clinical outcomes of cage with bone substitute for anterior cervical discectomy and fusion is satisfactory.

Methods

Eighty four patients who underwent cervical spine surgery between February 2004 and April 2009 were included. Fifty-nine patients were approached anteriorly and underwent anterior cervical discectomy and fusion by the Smith-Robinson method (Group A), and 25 patients underwent fusion by decompression of the cervical spine and cage with bone substitute (Group B). We measured and evaluated the postoperative period until patients were able to ambulate, for pre- and postoperative symptomatic improvement, postoperative complications, pre- and postoperative change of lordosis, degree of endplate collapse or subsidence, and fusion rate and period of union.

Results

By Robinson's criteria, respectively 45, 10 and 4 patients in Group A experienced excellent, good and fair symptomatic improvement, and respectively 19, 5 and 1 patients in Group B experienced excellent, good and fair symptomatic improvement. The postoperative period in which patients became ambulant and the period of hospital stay was significantly shorter in Group B. Increase of lordosis at final follow up after surgery was significantly larger in Group A, as was the fusion period. Significantly more endplate collapse occurred in Group B.

Conclusions

Of patients who had anterior cervical discectomy and fusion, results of both groups were both satisfactory.

Detailed study of graft sinking and worsening of the fused segment angle in patients with cervical disease treated with the Williams-Isu method

Detailed changes involved in the worsening of the fused segment angle were assessed after application of the Williams-Isu method using autologous bone grafts from cervical vertebral bodies in 30 patients with cervical disease treated by single-level anterior fusion. The mean follow-up duration was 25.4 months. The fused segment angle was measured on serial radiographs. Whole cervical spine alignment changed from 12.8° to 9.9°. The alignment of the fused segment worsened by mean 3.3°. To elucidate the characteristics of worsening of the fused segment, the 30 patients were divided into 2 groups: Group I (n = 20) without and Group II (n = 10) with postoperative worsening of the fused segment. The loss in the fused segment angle was significantly greater in Group II (8.0°) than Group I (0.9°). Preoperative range of motion and disc height were significantly greater in Group II than Group I. Worsening of the fused segment angle occurred within 1 month in Group I, whereas stabilization was observed after 3 months in Group II. Graft subsidence was primarily posterior and inferior. Our results indicate that the preoperative range of motion and disc height of the fused segment must be considered to prevent worsening in that segment after anterior fusion. Such detailed information is useful for the selection and postoperative monitoring of patients eligible for treatment by the Williams-Isu method.

Subsidence and nonunion after anterior cervical interbody fusion using a stand-alone polyetheretherketone (PEEK) cage

Background

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.

Methods

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.

Results

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).

Conclusions

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.

Efficacy of PEEK cages and plate augmentation in three-level anterior cervical fusion of elderly patients

Background

To evaluate the clinical efficacy of three-level anterior cervical arthrodesis with polyethyletherketone (PEEK) cages and plate fixation for aged and osteoporotic patients with degenerative cervical spinal disorders.

Methods

Twenty one patients, who had undergone three-level anterior cervical arthrodesis with a cage and plate construct for degenerative cervical spinal disorder from November 2001 to April 2007 and were followed up for at least two years, were enrolled in this study. The mean age was 71.7 years and the mean T-score using the bone mineral density was -2.8 SD. The fusion rate, change in cervical lordosis, adjacent segment degeneration were analyzed by plain radiographs and computed tomography, and the complications were assessed by the medical records. The clinical outcomes were analyzed using the SF-36 physical composite score (PCS) and neck disability index (NDI).

Results

Radiological fusion was observed at a mean of 12.3 weeks (range, 10 to 15 weeks) after surgery. The average angle of cervical lordosis was 5° preoperatively, 17.6° postoperatively and 16.5° at the last follow-up. Degenerative changes in the adjacent segments occurred in 3 patients (14.3%), but revision surgery was unnecessary. In terms of instrument-related complications, there was cage subsidence in 5 patients (23.8%) with an average of 2.8 mm, and loosening of the plate and screw occurred in 3 patients (14.3%) but there were no clinical problems. The SF-36 PCS before surgery, second postoperative week and at the last follow-up was 29.5, 43.1, and 66.2, respectively. The respective NDI was 55.3, 24.6, and 15.9.

Conclusions

For aged and osteoporotic patients with degenerative cervical spinal disorders, three-level anterior cervical arthrodesis with PEEK cages and plate fixation reduced the pseudarthrosis and adjacent segment degeneration and improved the clinical outcomes. This method is considered to be a relatively safe and effective treatment modality.

Avaliação do tratamento da discopatia degenerativa cervical pela artrodese via anterior utilizando placas associadas a cages ou cages em peek isoladamente

OBJETIVOS: Avaliar comparativamente o tratamento da discopatia degenerativa cervical por discectomia e artrodese cervical via anterior utilizando placas associadas a cages ou cages em PEEK isoladamente. MÉTODOS: Foi realizado um estudo retrospectivo comparativo entre dois grupos de pacientes operados pela técnica de discectomia e artrodese cervical via anterior. Foram selecionados aleatoriamente 70 pacientes, 35 operados com o método de fixação com placas associadas a cages - denominado Grupo I - e 35 com o cage em PEEK isoladamente - Grupo II. Realizou-se anamnese, exame físico, escores de dor (escala visual e analógica da dor) e função (critérios de Odom's, SF-36, Indice de incapacidade do pescoço) o pré e pós-operatório e exames de imagem. RESULTADOS: Houve predominância de pacientes do sexo feminino em ambos os grupos, com média de idade de 55 anos no Grupo I e 47 no Grupo II. Ambos os grupos apresentaram distribuição semelhante quanto ao número de níveis operados, assim como nas complicações encontradas e escores de dor, cervicalgia e SF36 no pré e pós-operatório. Houve 97.1% de fusão com 94.3% de bons resultados no Grupo I e 100% de fusão, com 97 % de bons resultados no Grupo II. CONCLUSÕES: O estudo comparativo da utilização de placas com cages e cages em PEEK isoladamente apresentou resultados semelhantes e satisfatórios para os grupos estudados, não se constatando superioridade ou inferioridade de um método com relação ao outro.

A unique device, the disc space-fitted distraction device, for anterior cervical discectomy and fusion: early clinical and radiological evaluation

OBJECT

To perform interbody distraction and to obtain spinal curvature correction during anterior cervical discectomy and fusion (ACDF), the authors recently adopted a new stand-alone device, a disc space-fitted distraction device (DFDD). In this preliminary report the authors introduce this unique device and discuss some advantages in terms of short-term clinical and radiological evaluations.

METHODS

The most unique aspect of the DFDD is the function of gentle distraction at anterior disc space with maximum lordotic correction of up to 8 degrees while rotating a screw at the front of the device. Additional advantages are related to its configuration such as disc space-matched shape in all dimensions, tapering contour for easy insertion into the disc space, multiple spikes to avoid dislodgment, wider contact area to the vertebral endplate for diminishing sinking process, and sufficient space for accommodation of bone-conductive materials. Twenty-four patients who have been observed more than 12 months after ACDF were involved in this evaluation.

RESULTS

The objective clinical outcome, measured by the Neurological Cervical Spine Scale, was significantly improved. In radiological evaluation, statistically significant improvement compared with preoperative values was noted on the curvature index, C2-7 curvature, and disc angle (p < 0.01) throughout the entire postoperative period, up to 12 months. A high fusion rate and remodeling process around the implants were also observed.

CONCLUSIONS

The DFDD may have some advantages over other devices-its distraction action, diminished sinking, and early solid bone union resulted in maintaining sufficient correction of the spinal curvature. This corrected spinal curvature may play an important role in preventing progressive adjacent-disc degeneration subsequent to ACDF in the long term.

Plate augmentation in anterior cervical discectomy and fusion with cage for degenerative cervical spinal disorders

Anterior cervical discectomy and fusion (ACDF) with cage alone (ACDF-C) is associated with a significant incidence of subsidence, local kyphosis, and migration. The use of concurrent plate augmentation may decrease the incidence of these complications while improving the fusion rate. The purpose of the study is to present our results with ACDF with cage and plate augmentation (ACDF-CPA) and to compare these results to previous reports of outcomes following ACDF-C. We evaluated the radiologic and clinical parameters of 83 patients (266 fusion sites) who had an ACDF-CPA between March 2002 and May 2006. Radiologic parameters included fusion rate, fusion time, fusion type, site of pseudoarthrosis and rate and degree of subsidence. Clinical parameters included complications and overall outcomes assessed with Robinson's criteria; 79 of 83 patients showed bony fusion (95.1%) at last follow-up postoperatively, and there was no significant difference in fusion rate between the number of fusion levels. Type I (pseudoarthrosis) was noticed in 9 patients (12 fusion sites), type II in 14 (19 fusion sites), and type III in 60 (235 fusion sites). Five type I and all type II fusions converged into type III by the last follow-up; 76 of 83 patients (91.6%) experienced good clinical outcomes. Pseudoarthrosis occurred more commonly in more proximal locations, and the subsidence rate was significantly greater in two-level fusions when compared with single-level fusions (P = 0.046). There were four metal-related complications. Plate augmentation in one- or two-level anterior cervical fusions for degenerative cervical spine disorders may improve fusion rates and reduce subsidence and complication rates, resulting in improved clinical outcomes.

Comparing anterior cervical fusion using titanium cage with hydroxyapatite and with autograft

Background: Anterior cervical discectomy and fusion using autogenous iliac bone graft may lead to donor site pain. This has led some surgeons to use hydroxyapatite but it has greater rates of complications. Objective: Analyze results of the treatment of cervical spine spondylosis by anterior cervical discectomy, and to compare fusion using titanium cage with hydroxyapatite and with autograft. Methods: We evaluated eighty patients (at 146 cervical levels) that had been treated by anterior cervical discectomy and fusion with hydroxyapatite or autograft. In a prospective study, patients were divided into two groups: 1) 77 levels of anterior cervical fusion from in 40 patients who were treated with cage and hydroxyapatite, and 2) 69 levels of anterior cervical fusions in 40 patients who were treated with cage and autograft. Results were evaluated using the Japanese Orthopedic Association (JOA) scoring system before and after surgery, subsidence, non-union and complication. Results: According to JOA score, the first group (hydroxyapatite) had improved from 9.8 preoperation to 14.5 postoperation. The subsidence rate was 26.0%, the non-union rate was 10.4%, and there was no intra and post-operative complication. In the other group (autograft), the preoperative JOA score had improved from 9.3 to 14.1. The subsidence rate was 11.6%, and there were no non-union and complications. Statistical significance was found in non-union and subsidence aspect between groups, but the clinical outcome of JOA score was not significantly different. Conclusion: Anterior cervical discectomy and fusion in cervical spondylosis patients, titanium cage implantation with hydroxyapatite is a highly useful alternative to autograft.

Metallic Scaffolds for Bone Regeneration

Bone tissue engineering is an emerging interdisciplinary field in Science, combining expertise in medicine, material science and biomechanics. Hard tissue engineering research is focused mainly in two areas, osteo and dental clinical applications. There is a lot of exciting research being performed worldwide in developing novel scaffolds for tissue engineering. Although, nowadays the majority of the research effort is in the development of scaffolds for non-load bearing applications, primarily using soft natural or synthetic polymers or natural scaffolds for soft tissue engineering; metallic scaffolds aimed for hard tissue engineering have been also the subject of in vitro and in vivo research and industrial development. In this article, descriptions of the different manufacturing technologies available to fabricate metallic scaffolds and a compilation of the reported biocompatibility of the currently developed metallic scaffolds have been performed. Finally, we highlight the positive aspects and the remaining problems that will drive future research in metallic constructs aimed for the reconstruction and repair of bone.

Artrodese cervical anterior em três e quatro níveis com dispositivo intersomático não associado à placa cervical

OBJETIVO: avaliar a taxa de consolidação em pacientes submetidos à artrodese cervical anterior de três e quatro níveis utilizando dispositivo intersomático não associado à placa cervical no sexto mês de pós-operatório. MÉTODOS: no período de Novembro de 2005 a Julho de 2008, 20 pacientes foram submetidos ao tratamento cirúrgico proposto. Os critérios de inclusão foram: diagnóstico clínico e por imagem de doença discal degenerativa cervical em três ou quatro níveis; dor axial e/ou irradiada com, no mínimo, seis meses de pós-operatório. O critério de exclusão foi a presença de instabilidade cervical traumática. Foram avaliadas as taxas de consolidação, a presença de sintomas, a taxa de complicações e a posição dos dispositivos intersomáticos (subsidence) após seis meses. RESULTADOS: todos os pacientes obtiveram consolidação em três meses, porém, dois pacientes apresentaram fenômeno de subsidence, ou seja, migração com consolidação em cifose, sem alterar os resultados clínicos e a consolidação da artrodese após seis meses de pós-operatório. Os pacientes tiveram melhora da dor pré-operatória e apenas três (15%) apresentaram dor residual. Não houve complicações maiores. O tempo de hospitalização foi de dois dias. Não foi utilizada imobilização rígida no pós-operatório. CONCLUSÃO: obteve-se consolidação com esta técnica em todos os casos. A técnica se mostrou segura e promoveu bons resultados radiológicos e clínicos.

Long term outcome and adjacent disc degeneration after anterior cervical discectomy and fusion with titanium cylindrical cages

BACKGROUND

Anterior cervical discectomy and fusion (ACDF) is widely performed for the treatment of cervical spinal degenerative disease. Autogenic or allogenic bone grafts are used for interbody fusion with satisfactory long term outcomes. However, harvest of the autograft causes donor site complications and allograft is associated with low fusion rate. Threaded titanium cages (TC) have recently been introduced to cope with these disadvantages, but there is little evidence of long term results.

METHODS

The long term outcome was studied after ACDF using TC. Clinical and imaging follow up was performed in 41 patients for at least 5 years (range 5-8.3 years). New computer-assisted measurement methods for radiographs are proposed.

FINDINGS

ACDF with TC achieved 80% excellent or good outcome by Odom's criteria, 95% fusion rate, and few minor complications. Asymptomatic adjacent disc degeneration was detected in 50% of the patients by our measurement methods. However, symptomatic adjacent disc degeneration occurred in 5% of the patients and only 2% required additional surgery.

CONCLUSIONS

These results are comparable or better than those after ACDF with autograft or allograft. ACDF with TC can achieve rigid fixation and provide good long term results.

Long-term follow-up results in patients with cervical disk disease treated by cervical anterior fusion using titanium cage implants

This study is a retrospective analysis of 146 patients, 85 males and 61 females aged 21-80 years (mean 52 years), with cervical disk disease who underwent anterior fusion and titanium cage implantation with follow-up periods of no less than 72 months after surgery. All patients underwent the conventional anterior cervical approach. After removing the protruded disk and osteophyte, cylindrical titanium cages were placed. Single, two, and three level fusion was performed in 76 (52%), 64 (44%), and 6 (4%) patients, respectively. Functional assessment used the Neurosurgical Cervical Spine Scale (NCSS). The curvature index and range of motion were evaluated pre- and postoperatively. The clinical outcomes were satisfactory and there were no significant complications. The mean NCSS was 9.7 before and 12.7 at 1 year after the operation, and 12.1 at final examination. No postoperative cage extrusion or pseudoarthrosis occurred, but the cages descended in 10 patients (7%) although alignment was satisfactory. At 5 years after the operation, 140 of the 146 patients (96%) had solid fusion. The long-term results of anterior fusion with titanium cage implantation in patients with cervical disk disease were satisfactory. Titanium cage placement is a highly useful alternative to the conventional treatment method in these patients.

Radiologic Assessment of Subsidence in Stand-Alone Cervical Polyetheretherketone (PEEK) Cage

OBJECTIVE

Aim of study was to find a proper method for assessing subsidence using a radiologic measurement following anterior cervical discectomy and fusion (ACDF) with stand-alone polyetheretherketone (PEEK), Solistrade mark cage.

METHODS

Forty-two patients who underwent ACDF with Solistrade mark cage were selected. With a minimum follow-up of 6 months, the retrospective investigation was conducted for 37 levels in 32 patients. Mean follow-up period was 18.9 months. Total intervertebral height (TIH) of two fused vertebral bodies was measured on digital radiographs with built-in software. Degree of subsidence (DeltaTIH) was reflected by the difference between the immediate postoperative and follow-up TIH. Change of postoperative disc space height (CT-MRDeltaTIH) was reflected by the difference between TIH of the preoperative mid-sagittal 2D CT and that of the preoperative mid-sagittal T1-weighted MRI.

RESULTS

Compared to preoperative findings, postoperative disc height was increased in all cases and subsidence was observed only in 3 cases. For comparison of subsidence and non-subsidence group, TIH and CT-MRDeltaTIH of each group were analyzed. There was no statistically significant difference in TIH and CT-MRDeltaTIH between each group at 4 and 8 weeks, but a difference was observed at the last follow-up TIH (p=0.0497).

CONCLUSION

ACDF with Solistrade mark cage was associated with relatively good radiologic long-term results. Fusion was achieved in 94.5% and subsidence occurred in 8.1% by the radiologic assessment. Statistical analysis reveals that the subsidence seen later than 8 weeks after surgery and the development of subsidence does not correlate statistically with the change of the postoperative disc space height.