Anterior interbody fusion of the cervical spine with coralline hydroxyapatite

Anterior cervical discectomy and fusion with implantable titanium cage: initial impressions, patient outcomes and comparison to fusion with allograft

BACKGROUND CONTEXT

The use of metal cage prosthetic devices in anterior cervical discectomy with fusion (ACDF) has increased rapidly. One of these devices is the titanium Rabea cage (Signus, Alzenau, Germany) [correction]. There are no peer-reviewed objective reports on the use of these cages in cervical discectomy.

PURPOSE

The authors present preliminary outcomes data on the Rabea cage. This study is intended to provide adjunct data for surgeons who are using or are considering the use of these devices.

STUDY DESIGN/SETTING

Patients in a private practice were studied prospectively as part of a long-term assessment of outcomes using several surgical procedures. Data were collated and analyzed by an independent researcher.

PATIENT SAMPLE

Rabea cages were used in consecutive candidates (n=37) for ACDF. The results using Rabea cages were compared with two prospectively studied control groups, one historical (n=66) and one concurrent (n=28), both groups using ACDF with bone allograft and no instrumentation.

OUTCOME MEASURES

Success at 6 months after surgery was determined using six major patient-reported outcome measures, including visual analog scales (VAS) for arm and neck pain, the Oswestry pain and disability scale, four-part (excellent-through-poor) scales for measurement of return to activities of daily living or to work and satisfaction with the results of surgery. Perioperative complications, number of vertebral levels fused, and worker's compensation and smoking status were also compared among the study groups. Fusion and subsidence were evaluated for the Rabea cage group.

METHODS

Criteria for inclusion consisted of consecutive patients who presented with unremitting radicular arm pain, with or without neck pain, and/or a neurological deficit that correlated with appropriate level and side neural compression on magnetic resonance imaging or computed tomography. Questionnaire follow-up was at 6 months after surgery with 100% compliance.

RESULTS

A total of 50 cages were implanted in the 37 patients. At 6-month follow-up, 78% of patients reported successful arm pain relief (VAS scores below 5). Patient satisfaction was successful in 78% of the cases. Other success rates included neck pain relief in 73% and Oswestry pain and disability scale in 70%. There was a median improvement in the Oswestry scores of 28 points (61% change). Worker's compensation patients fared dramatically worse than did the noncompensation patients in all outcome measurements. Combining all three study groups resulted in significantly worse outcomes for multilevel than for single-level procedures and for smokers compared with nonsmokers, but low case numbers precluded conclusive analysis for the Rabea group alone. In the Rabea group there were two complications, neither cage related, whereas none were reported for the ACDF controls. Rabea group fusion rates were 84% at 3 months and 95% at 6 months, but the clinical relevance of this radiological evidence when metal prostheses are used is questionable. The outcomes results were clinically and statistically indistinguishable from those of our control groups and were similar to published studies using other titanium cages.

CONCLUSIONS

This is the first prospective, independently conducted report on Rabea cages. Results of the short-term (6 months) follow-up did not differ from outcomes results in our patients who have undergone ACDF with bone allograft. Although this is a preliminary assessment, the Rabea cage may represent an alternative to bone dowels and hip graft. As is the case for other allografts, artificial or bone, the main advantage is elimination of donor site complications, and the disadvantages include difficulty in radiographic assessment of fusion and potential for cage subsidence.

Pitfalls of Anterior Cervical Fusion Using Titanium Mesh and Local Autograft

Cervical fusion cages have been developed to provide an anterior structural support without harvesting tricortical iliac bone. Limited numbers of investigations have focused on pitfalls of anterior cervical fusion using cage implants. The objective of this study is to report clinical results and implant-related complications in anterior cervical fusion using titanium mesh and anterior plating. Twenty-four cases with anterior cervical fusion using a titanium mesh with local autograft and anterior plating were reviewed. One-level fusion was performed in 7 cases, and 17 patients underwent two-level fusion with corpectomy. The mean follow-up period was 27 months. Radiographic assessment included sagittal alignment, fusion status, and complications related to cage implants. Iliac bone graft harvesting was obviated in all the patients, whereas 15 patients required concomitant use of ceramic bone substitute. Sagittal alignment of the operative level was lordotic in 19 cases (79%) and neutral in 5 cases (21%) at the final follow-up. No late kyphotic collapse was observed. Twenty-three cases (96%) achieved a solid fusion, whereas the time to fusion was averaged 6.2 months. Cage subsidence frequently occurred in 42% of upper vertebrae and 50% of lower vertebrae. The use of titanium mesh and local autograft for anterior cervical fusion obviated the need for harvesting iliac bone block and provided structural anterior column support. However, it required a longer period to achieve a solid fusion when compared with tricortical iliac autograft. Cage subsidence was frequently observed in the early postoperative period.

Anterior decompression for cervical spondylotic myelopathy

Cervical spondylotic myelopathy is a clinical entity that manifests itself due to compression and ischemia of the spinal cord. The goal of treatment is to decompress the spinal cord and stabilize the spine in neutral, anatomical position. Since the obstruction and compression of the cord are localized in front of the cord, it is obvious that an anterior surgical approach is the preferred one. The different surgical procedures, complications, and outcome are discussed here.

Lumbar spinal fusion with a mineralized collagen matrix and rhBMP-2 in a rabbit model

STUDY DESIGN

A new mineralized collagen matrix combined with or without growth factor was used for the posterolateral spinal fusion in the rabbit lumbar spine.

OBJECTIVES

The availability of a new osteoconductive matrix with or without recombinant osteoinductive growth factors offers a possible alternative to the use of autogenous bone for grafting indications. This study evaluated the bone-forming activity of the biomimetic matrix: nano-hydroxyapatite/collagen/polylactic acid (nHAC/PLA) combined without or with recombinant human bone morphogenetic protein-2 (rhBMP-2) in a rabbit posterolateral spinal fusion.

SUMMARY OF BACKGROUND DATA

Many bone grafting materials such as titanium alloy, ceramics, and polymers were used to repair bony defects. However, each has specific disadvantaged. The permanent implantation still has possibility to be eroded in vivo, which is caused by late breakdown and abscess formation. The acidic outcome of polymer biodegradation was also negatively affected in the later-stage results of bone repair. It needed a promising material for an alternative to the use of autogenous bone for grafting indications.

MATERIALS AND METHODS

Sixty-four rabbits were randomly divided into four groups: autologous iliac crest bone group (ACB), nHAC/PLA composite group (nHAC/PLA), autologous iliac crest bone mixed with nHAC/PLA composite group (ACB + nHAC/PLA), nHAC/PLA composite with recombinant human BMP-2 group (nHAC/PLA + rhBMP-2). The lumbar intertransverse process fusions were assessed by manual palpation, radiographic, histologic, and mechanical strength, and scanning electronic microscopy (SEM) in a 10-week observation.

RESULTS

Optimal formulations of the ACB + nHAC/PLA and nHAC/PLA + rhBMP-2 groups were shown to perform similar to ACB in both the fusion ratio and mechanical strength in the 6 and 10 weeks after surgery. From the microstructure analysis of the samples, there was no negative effect when the compound implanted this composite with autogenous iliac crest, and there was also new bone-like tissue formation implanted this composite without combined rhBMP-2 early at the second week after surgery.

CONCLUSIONS

This study shows the effective results of nHAC/PLA in rabbit posterolateral spinal fusion combined with rhBMP-2. It is an alternative method to autograft by compounding this osteoconductive matrix with growth factors.

Anterior lumbar intervertebral fusion with artificial bone in place of autologous bone

The feasibility of anterior lumbar intervertebral fusion with artificial bone in place of autogenous bone was investigated. Porous hydroxyapatite (HA)/ZrO2 ceramics loading bone morphogenetic protein (BMP) were implanted after removal of lumbar vertebral disc in rabbits. The adjacent intervertebral discs were also removed by the same way and autogenous illic bone was implanted. SEM observation and biomechanical test were carried out. Compound bone had a bit lower osteoinductive activity than autogenous bone by SEM (Osteoinductive activity of artificial bone in 12 weeks was the same as that of autogenous bone in 9 weeks). Biomechanical test revealed that compound bone had lower anti-pull strength than autogenous bone (P < 0.001), but there was no significant difference in anti-pull strength between compound bone at 12th week and autogenous bone at 9th week (P > 0.05). It was concluded that compound bone could be applied for anterior spinal fusion, especially for those patients who can't use autogenous bone.

In vivo evaluation of bone marrow stromal-derived osteoblasts-porous calcium phosphate ceramic composites as bone graft substitute for lumbar intervertebral spinal fusion

STUDY DESIGN

Autogenous bone marrow stromal-derived osteoblasts-porous calcium phosphate ceramic composites were constructed in vitro under cell culture for 48 hours and implanted as a bone graft substitute for lumbar intervertebral spinal fusion in rabbits.

OBJECTIVES

To evaluate the efficacy of autogenous bone marrow stromal-derived osteoblasts-porous calcium phosphate ceramic composites as an alternative to autogenous graft materials in a lumbar interbody spinal fusion model.

SUMMARY OF BACKGROUND DATA

Bone marrow contains a population of rare progenitor cells capable of differentiating into bone, cartilage, muscle, tendon, and other connective tissues. These cells can be induced and differentiated into osteogenic osteoblasts with addition of osteogenic supplements. Combining bone marrow stromal-derived osteoblasts with porous ceramics gave rise to bone tissue in subcutaneous sites and repaired critical size segmental femoral defects. Little work has been done in the spine to assess fusion rates and associated biomechanical characteristics.

METHODS

Five experimental groups were evaluated: sham operation (Group I); porous calcium phosphate ceramics alone (Group II); autogenous tricortical iliac crest (Group III); bone marrow stromal-derived osteoblasts-calcium phosphate ceramic composites (Group IV); bone marrow stromal-derived osteoblasts-calcium phosphate ceramic composites with rhBMP-2 (Group V). All rabbits were killed 12 weeks after surgery, and the spinal fusion segments underwent the evaluation of gross inspection, manual palpation, radiography, computed tomography, nondestructive biomechanical testing, and histologic analysis.

RESULTS

Successful spinal fusion was achieved by manual palpation in 100% (6/6) of animals in Group IV and Group V, 66.7% (4/6) in Group III, 50% (3/6) in Group II, and 0% (0/6) in Group I. Radiographic studies showed that minimal disc height loss was observed with ceramic blocks than with autograft. Biomechanical testingconfirmed that spines from Group IV and Group V were statistically significantly stiffer in flexion, extension, left and right bending, and left and right torsion than Group III and Group II. Histologic analysis demonstrated a qualitative increase of bone formation in fusion mass in Group IV and Group V versus all other groups. The size of fusion mass and the stiffness of fusion segments were greatest in Group V.

CONCLUSION

The results indicate that bone marrow stromal-derived osteoblasts-calcium phosphate ceramic composites may provide an alternative to autogenous graft materials for lumbar interbody spinal fusion. Adding recombinant human bone morphogenetic protein-2 into the composites may reinforce the biomechanical stiffness for spinal fusion segments. Porous calcium phosphate ceramics alone were not suitable as a bone graft substitute for lumbar interbody spinal fusion.

Implantation of an empty carbon fiber composite frame cage after single-level anterior cervical discectomy in the treatment of cervical disc herniation: preliminary results

OBJECT

The authors sought to evaluate retrospectively the radiological and clinical outcome of anterior cervical discectomy followed by implantation of an empty carbon fiber composite frame cage (CFCF) in the treatment of patients with cervical disc herniation and monoradiculopathy.

METHODS

Twenty-five consecutive patients (12 men, 13 women, mean age 45 years) with monoradiculopathy due to cervical disc herniation were treated by anterior cervical discectomy followed by implantation of an empty CFCF cage. On lateral flexion-extension radiographs segmental stability at a mean follow up of 14 months (range 5-31 months) was demonstrated in all 25 patients, and bone fusion was documented in 24 of 25 patients. The mean anterior intervertebral body height was 3.4 mm preoperatively and 3.8 mm at follow up in 20 patients. In these patients the mean segmental angle (angle between lower endplate of lower and upper vertebra) was 0.9 degrees preoperatively and 3.1 degrees at follow up. In the remaining five patients preoperative images were not retrievable. Self-scored neck pain based on a visual analog scale (1, minimum; 10, maximum) changed from a preoperative average of 5.6 to an average of 2 at follow up; radicular pain was reduced from 7.7 to 2.1 postoperatively. Analysis of the SF12 questionnaires showed a significant improvement in both the physical capacity score (preoperative mean 32.4 points; follow up 46 points) and the mental capacity score (preoperative mean 45.8 points; follow up 57.5 points).

CONCLUSIONS

Implantation of an empty CFCF cage in the treatment of cervical disc herniation and monoradiculopathy avoids donor site morbidity associated with autologous bone grafting as well as the use of any supplementary material inside the cage. Restoration or maintenance of intervertebral height and thus segmental lordosis and a very high rate of segmental stability and fusion are achieved using this technique.

A prospective randomized comparison of coralline hydroxyapatite with autograft in cervical interbody fusion

STUDY DESIGN

A prospective randomized trial with independent clinical and radiographic outcome review of patients receiving either hydroxyapatite or tricortical iliac crest graft for cervical interbody fusion was conducted.

OBJECTIVE

To determine whether coralline-derived hydroxyapatite is a suitable bone graft substitute in cervical interbody fusion.

SUMMARY OF BACKGROUND DATA

Tricortical iliac crest bone is the "gold standard" graft material for cervical interbody fusion. Various bone substitutes have been used for this procedure to avoid potential donor site morbidity. ProOsteon 200 is a coralline-derived hydroxyapatite product, the use of which remains unclear for cervical interbody fusion.

METHODS

In this study, 29 patients undergoing anterior cervical fusion and plating were randomized to receive either ProOsteon 200 or iliac crest grafts. The SF-36 and Oswestry Disability Index were used to measure clinical outcome. Postoperative radiographs were analyzed for graft fragmentation, loss of height, angular alignment, and hardware failure to assess structural integrity of the graft material. Plain radiographs and computed tomography scans were used to evaluate fusion.

RESULTS

Both the ProOsteon 200 and iliac crest groups demonstrated significant improvement in clinical outcome scores. There was no significant difference in clinical outcome or fusion rates between the two groups. Graft fragmentation occurred in 89% of the hydroxyapatite grafts and 11% of the autografts (P = 0.001). Significant graft settling occurred in 50% of the hydroxyapatite grafts, as compared with 11% of the autografts (P = 0. 009). One patient in the ProOsteon 200 group required revision surgery for graft failure.

CONCLUSIONS

ProOsteon 200 does not possess adequate structural integrity to resist axial loading and maintain disc height or segmental lordosis during cervical interbody fusion.

Anterior lumbar interbody fusion with processed sea coral (coralline hydroxyapatite) as part of a circumferential fusion

STUDY DESIGN

A retrospective review of 20 patients undergoing circumferential lumbar fusion with coralline hydroxyapatite blocks anteriorly and autograft with transpedicular or translaminar facet screw fixation posteriorly.

OBJECTIVES

To examine the efficacy of coralline hydroxyapatite as a bone graft substitute for anterior lumbar interbody fusion.

SUMMARY OF BACKGROUND DATA

Autograft is the gold standard for bone grafting in the anterior lumbar spine. Harvesting bone from the iliac crest leads to significant postoperative pain and morbidity. Femoral ring allograft is a widely used alternative to autograft but has some inherent problems. Coralline hydroxyapatite was shown to be 100% successful for anterior cervical fusion when combined with rigid plating.

METHODS

A retrospective review of 20 patients with low back pain and indicated for surgical intervention. A circumferential instrumented fusion was performed with coralline hydroxyapatite blocks anteriorly and transpedicular or translaminar facet fixation and autograft posteriorly. All patients reached a minimum 3-year clinical and radiologic follow-up.

RESULTS

Radiographic follow-up yielded a solid arthrodesis rate of 93.8% by level (30 of 32 disc spaces) and 90% by patient (18 of 20). Clinical follow-up generated a mean pain reduction of 61.8% with clinical success demonstrated in 80% (16 of 20) of all patients who reported good or excellent pain relief. Eight of 12 (66.7%) patients employed before surgery returned to work in some capacity.

CONCLUSIONS

Coralline hydroxyapatite is a practicable anterior lumbar interbody fusion alternative to autograft and allograft as part of a circumferential fusion with rigid posterior fixation. It is not recommended for stand-alone anterior lumbar interbody fusion without further study.

Development of an artificial vertebral body using a novel biomaterial, hydroxyapatite/collagen composite

Hydroxyapatite/collagen (HAp/Col) composites having a bone-like nanostructure were synthesized and shaped into implants. This study was designed to develop an artificial vertebra system using this novel implant for anterior fusion of the cervical spine. Anterior fusion was carried out on 6 beagle dogs with the implants adsorbing rhBMP-2 (400 microg/ml). and 9 dogs with the implants without rhBMP-2. In 3 dogs of the rhBMP-treated group, as well as 6 dogs of the non-rhBMP-treated group, the implant was fixed with a poly-L-lactide plate and 2 titanium screws. Implants were taken out after 13 weeks from each 3 dogs in the rhBMP(-):plate(-). rhBMP(-):plate(+) and rhBMP(+):plate(+) groups. Also, the implants were removed from each 3 dogs in the rhBMP(-):plate(+) and rhBMP(+):plate(+) groups after 24 weeks. Histological and radiographical analysis suggested that since the larger part of the composite material was absorbed within 13 weeks, reduction of the intervertebral distance was caused, and that enhancement of callus formation and bone bridging by rhBMP-treatment was effective to prevent collapse of the implant, even though an effect of anterior plate-fixation was not obvious. The HAp/Col implant adsorbing rhBMP-2 may be a suitable replacement for the existing ceramics in anterior interbody fusion of the cervical spine.

A modified technique for anterior multilevel cervical fusion

Anterior cervical fusion with interbody bone graft and anterior plating is commonly performed. Unfortunately, the plate has been reported to shield the graft from loading, thus reducing fusion rates. Interbody fusion cages have been effective in the lumbar spine and have gained acceptance in the cervical spine. Twenty-five patients underwent anterior cervical fusion with this modified technique. All patients received anterior diskectomy and corpectomy, placement of an interbody fusion cage packed with corpectomy bone, and application of an anterior cervical plate. Fusion was defined by radiographic evidence of trabecular bone bridging through the cage. No external bracing was used except soft collars as needed. Pre- and postoperative pain scales were completed and statistically analyzed using paired t tests. There were no cases of pseudoarthrosis or major neurological, vascular, or wound complications. There was one case of mild dysphagia that remained unresolved. Mean operative time was comparable to standard instrumented multilevel cervical fusion surgeries. Visual analogue pain scales were significantly improved following surgery. The advantages of using interbody cages with anterior plating include immediate stability and support, elimination of donor site pain from iliac crest bone autograft, and a decrease in pseudoarthrosis by halving the number of fusion surfaces.

Hydroxyapatite block for use in posterolateral lumbar fusion: a report of four cases

Autologous bone grafts for posterolateral lumbar fusion are harvested from the iliac crests. Recently, several alternatives to autologous bone have been evaluated (such as graft substitutes, graft extenders, or both) with variable results. However, no clinical long-term studies have validated the efficacy of these techniques in posterolateral lumbar fusion. This study evaluated radiographic and histologic findings in four patients (mean age, 66 years) during the first 5 years after posterolateral fusion with an hydroxyapatite block. The mean followup was 7 years 1 month. Radiologic evaluation was by plain radiographs and computed tomography scans. Histologic evaluation was done in one patient. Capillaries extended into the porous structure of the hydroxyapatite substrate, and some of the pores were replaced by newly formed bone tissue. The long-term results of graft substitutes were stable and hydroxyapatite appeared to have some potential to achieve union in posterolateral lumbar fusion. However, hydroxyapatite block alone has not functioned effectively as a complete graft substitute in posterolateral lumbar fusion. Thus, a suitable osteogenic material is required to induce the formation of new bone and achieve a solid union.

Bone grafting alternatives in spinal surgery

BACKGROUND CONTEXT

Bone grafting is used to augment bone healing and provide stability after spinal surgery. Autologous bone graft is limited in quantity and unfortunately associated with increased surgical time and donor-site morbidity. Alternatives to bone grafting in spinal surgery include the use of allografts, osteoinductive growth factors such as bone morphogenetic proteins and various synthetic osteoconductive carriers.

PURPOSE

Recent research has provided insight into methods that may modulate the bone healing process at the cellular level in addition to reversing the effects of symptomatic disc degeneration, which is a potentially disabling condition, managed frequently with various fusion procedures. With many adjuncts and alternatives available for use in spinal surgery, a concise review of the current bone grafting alternatives in spinal surgery is necessary.

STUDY DESIGN/SETTING

A systematic review of the contemporary English literature on bone grafting in spinal surgery, including abstract information presented at national meetings.

METHODS

Bone grafting alternatives were reviewed as to their efficacy in extending or replacing autologous bone graft sources in spinal applications.

RESULTS

Alternatives to autologous bone graft include allograft bone, demineralized bone matrix, recombinant growth factors and synthetic implants. Each of these alternatives could possibly be combined with autologous bone marrow or various growth factors. Although none of the presently available substitutes provides all three of the fundamental properties of autograft bone (osteogenicity, osteoconductivity and osteoinductivity), there are a number of situations in which they have proven clinically useful.

CONCLUSIONS

Alternatives to autogenous bone grafting find their greatest appeal when autograft bone is limited in supply or when acceptable rates of fusion may be achieved with these substitutes (or extenders) despite the absence of one or more of the properties of autologous bone graft. In these clinical situations, the morbidity of autograft harvest is reasonably avoided. Future research may discover that combinations of materials may cumulatively result in the expression of osteogenesis, osteoinductivity and osteoconductivity found in autogenous sources.

Bone grafting, implants, and plating options for anterior cervical fusions

The basic principles of cervical spine surgery continue to include adequate decompression, provision of a structurally competent, biologically functional bone graft, and creation of a stable construct to allow for solid fusion. In recent years, the options to achieve these goals have expanded significantly. Bone banking and bone graft substitutes yield increasingly viable alternatives to autogenous bone graft. New prosthetic implants and cages are currently under investigation. The science of bone growth factors seems to be promising and is expected to revolutionize the approach to spinal arthrodesis. Various plating systems are available to provide internal stability to cervical spine constructs. It is important to understand the biomechanics of plating systems so that the optimal system may be used in a given situation. Long constructs place significant loads on SGs and anterior plates. It is important to consider the use of additional fixation, such as posterior segmental fixation in long constructs, which may be prone to failure using only anterior plate fixation. Anterior cervical plating for single-level ACDF remains controversial, whereas plating has been shown to improve the results of multilevel ACDF. Plating may provide a useful salvage option for a cervical nonunion, especially if deformity or neurologic compression dictates an anterior approach. Hardware failures may occur with anterior cervical plating, but most remain asymptomatic and do not require operative intervention.

Anterior cervical fusion with carbon fiber cage containing coralline hydroxyapatite: preliminary observations in 45 consecutive cases of soft-disc herniation

OBJECT

The purposes of bone substitutes for anterior cervical fusion (ACF) are immediate biomechanical support and osteointegration of the graft. The authors report their preliminary results in performing ACF in which carbon fiber cages (CFCs) containing coralline hydroxyapatite (HA) are used as bone substitute.

METHODS

During a 24-month period, anterior microsurgical discectomy was performed in 45 consecutive patients for soft-disc cervical herniation. In all cases ACF was performed using a CFC containing a core of granulated coralline HA. Fifty-seven CFCs were implanted in 33 single-level and 12 two-level procedures. The mean operative time was 83 minutes for one-level and 97 minutes for two-level procedures. The mean hospital stay was 1.51 days, and there were no permanent complications. At a mean follow up of 22.3 months, the pain had decreased or disappeared in all patients, and the patients' satisfaction rate was very high. Good results were also obtained in patients who smoked cigarettes. Patients underwent radiographic evaluation at Day 1, and 1, 3, 6, and 12 months postoperatively. Implant-related complications were not observed and revision surgeries were not performed. Twelve-month cervical x-ray films demonstrated complete fusion in all cases, without evidence of breakage, collapse, pseudarthrosis, subsidence, angular deformity, or protrusion. Signs of pathological absorption and necrosis were not found in contiguous vertebral bodies, and inflammatory reactions were never seen around cages.

CONCLUSIONS

These preliminary results suggest that implants composed of CFC containing granulated coralline HA are promising bone substitutes to be used in ACF, with a good rate of incorporation and no significant complications.

Complications related to hydroxyapatite vertebral spacer in anterior cervical spine surgery

STUDY DESIGN

This is a report of complications related to the hydroxyapatite vertebral spacer used for anterior cervical reconstructive surgery. Compression of the spinal cord by broken fragments of hydroxyapatite spacer as well as its surrounding radiolucent clear zone were observed in seven patients.

OBJECTIVES

To report complications related to the use of hydroxyapatite vertebral spacer for anterior cervical reconstructive surgery and to discuss how to prevent these complications.

SUMMARY OF BACKGROUND DATA

Despite previous articles reporting the clinical applications of hydroxyapatite vertebral spacer for the cervical spine, clinical reports regarding the long-term results of hydroxyapatite spacer for anterior cervical surgery and its complications have been limited.

METHODS

The authors reviewed patients who underwent anterior reconstructive surgery using the hydroxyapatite spacer at other hospitals and had postoperative complications related to hydroxyapatite spacer.

RESULTS

Seven patients previously treated by anterior cervical spine surgery using the hydroxyapatite vertebral spacer were referred to the authors because of unsatisfactory surgical outcomes. All the patients had a radiolucent clear zone around the spacer and experienced severe neck pain. Four had fracture of the hydroxyapatite spacer, and two had compression of the spinal cord by retropulsed fragments of broken hydroxyapatite spacers.

CONCLUSIONS

Although hydroxyapatite has been used in many medical fields because of its bioactive characteristics, its mechanical properties should be improved to lessen the risks of breakage and subsequent spinal cord compression. Gentle insertion maneuvers are also important to avoid the production of cracks inside the spacer.

Nonallograft osteoconductive bone graft substitutes

An estimated 500,000 to 600,000 bone grafting procedures are done annually in the United States. Approximately (1/2) of these surgeries involve spinal arthrodesis whereas 35% to 40% are used for general orthopaedic applications. Synthetic bone graft substitutes currently represent only 10% of the bone graft market, but their share is increasing as experience and confidence in their use are accrued. Despite 15 to 20 years of clinical experience with various synthetic substitutes, there have been few welldesigned, controlled clinical trials of these implants. Synthetic bone graft substitutes consist of hydroxyapatite, tricalcium phosphate, calcium sulfate, or a combination of these minerals. Their fabrication technique, crystallinity, pore dimensions, mechanical properties, and resorption rate vary. All synthetic porous substitutes share numerous advantages over autografts and allografts including their unlimited supply, easy sterilization, and storage. However, the degree to which the substitute provides an osteoconductive structural framework or matrix for new bone ingrowth differs among implants. Disadvantages of ceramic implants include brittle handling properties, variable rates of resorption, poor performance in diaphyseal defects, and potentially adverse effects on normal bone remodeling. These inherent weaknesses have refocused their primary use to bone graft extenders and carriers for pharmaceuticals. The composition, histologic features, indications, and clinical experience of several of the synthetic bone graft substitutes approved for orthopaedic use in the United States are reviewed.

Comparative evaluation of microdiscectomy only, autograft fusion, polymethylmethacrylate interposition, and threaded titanium cage fusion for treatment of single-level cervical disc disease: a prospective randomized study in 125 patients

OBJECT

The need for interbody fusion or stabilization after anterior cervical microdiscectomy is still debated. The objectives of this prospective randomized study were 1) to examine whether combined interbody fusion and stabilization is more beneficial than microdiscectomy only (MDO) and 2) if fusion is found to be more beneficial than MDO, to determine which is the best method of fusion by comparing the results achieved using autologous bone graft (ABG), polymethylmethacrylate (PMMA) interposition, and threaded titanium cage (TTC).

METHODS

A total of 125 patients with a single-level cervical disc disease were included in this prospective study. All patients were randomized and assigned to one of the four following groups: Group 1 (33 patients), MDO; Group 2 (30 patients), microdiscectomy followed by ABG; Group 3 (26 patients), microdiscectomy followed by injection of PMMA; and Group 4 (36 patients), microdiscectomy followed by placement of a TTC. Clinical outcome according to Odom criteria was summarized as 1) excellent and good or 2) satisfactory and poor. One-year follow-up examination was performed in 123 patients. Patients in the TTC group experienced a significantly better outcome 6 months after surgery (92% excellent and good results) compared with those in the MDO and ABG groups (72.7 and 66.6% excellent and good results, respectively). Twelve months after surgery there was still a significant difference in outcomes between the TTC group (94.4% excellent and good results) and the MDO group (75.5% excellent and good results). Outcome in patients treated with PMMA was comparable with that in those treated with TCC after 6 (91.6%) and 12 months (87.5%), but no segmental fusion was achieved. Differences compared with MDO and ABG were, however, not significant, which may be related to the smaller number of patients in the PMMA group.

CONCLUSIONS

Interbody cage-assisted fusion yields a significantly better short- and intermediate-term outcome than MDO in terms of return to work, radicular pain, Odom criteria, and earlier fusion. In addition, the advantages of interbody cages over ABG fusion included better results in terms of return to work, Odom criteria, and earlier fusion after 6 months. These results suggest that interbody cage-assisted fusion is a promising therapeutic option in patients with single-level disc disease. Polymethylmethacrylate seems to be a good alternative to interbody cage fusion but is hindered by the absence of immediate fusion.

Threaded cages for degenerative cervical disease

Multiple techniques are used to accomplish anterior interbody fusion in the cervical spine. These various options reflect the lack of any one approach to obtain superior results. Extrapolating from the lumbar spine experience, a cervical cage was proposed as an alternative to the status quo. A device evaluation study was done to determine the safety and efficacy of the cage with a comparison with current allograft or autograft fusion techniques. The study resulted in two publications. One study is a multicenter trial whereas the other is a one-author study with long-term results. A review of the data from both studies follows. Comparable outcomes were seen with the allograft and autograft control group and the experimental group in the multicenter trial. However, that study reported significantly better fusion rates for the patients with cervical cages compared with the control group. Both studies reported a high percentage of donor site morbidity in the patients in the control group who had autograft fusion. A trend toward better outcomes for patients who received a cervical cage was seen in the long-term followup study. The data presented suggest interbody fusion cages are a safe and effective treatment of degenerative cervical disc disorders and avoid iliac crest donor site morbidity.

Anterior lumbar interbody fusion with titanium mesh cages, coralline hydroxyapatite, and demineralized bone matrix as part of a circumferential fusion

BACKGROUND CONTEXT

Anterior lumbar interbody fusion (ALIF) has become one of the primary choices for eliminating motion between vertebral segments in patients with severe discogenic pain and other lumbar pathologies. Autograft is the gold standard for spinal fusion. However, multiple authors have reported complication and morbidity rates associated with iliac crest harvesting to be as high as 25%. Drawbacks to the use of allograft in the anterior column include slower incorporation rates, the possibility for disease transmission, increasing cost resulting from stringent processing and unavailability on a worldwide basis resulting from religious and economic concerns.

PURPOSE

To determine the clinical and arthrodesis efficacy of coralline hydroxyapatite as an osteoconductive bone graft substitute in the anterior lumbar spine using a titanium mesh cage.

STUDY DESIGN

A series of 50 patients returning for long-term prospective follow-up, implanted with titanium mesh cages filled with coralline hydroxyapatite and demineralized bone matrix for ALIF as part of a circumferential fusion.

PATIENT SAMPLE

Long-term clinical and radiographic follow-up were examined for the first 50 patients undergoing this technique by one surgeon.

OUTCOME MEASURES

Pain was measured with a visual analog scale and function was measured with the Oswestry Disability Index.

METHODS

All 50 patients underwent successful ALIF with titanium mesh cages, coralline hydroxyapatite and demineralized bone matrix, as well as an autologous posterolateral fusion with rigid posterior instrumentation. Patients filled out follow-up questionnaires and appropriate radiographs were taken.

RESULTS

A solid fusion rate of 96% was achieved. Mean pain decrease was 60% overall. A total of 70% of all patients either returned to work or to full home activities at a mean of 8 months after surgery. Ninety percent felt the surgery was successful.

CONCLUSIONS

The combination of titanium mesh cages, coralline hydroxyapatite and demineralized bone matrix is effective for anterior interbody fusion of the lumbar spine when used as part of a rigidly instrumented circumferential fusion.

Two-level anterior cervical discectomy and cage-assisted fusion without plates

Object

Anterior cervical discectomy (ACD) is an effective and safe treatment for nerve root or spinal cord compression caused by disc herniation or spondylosis. Cervical interbody fusion allows preservation of the physiological lordosis and stability of the cervical spine. Based on data reported in the literature, fusion rates decrease significantly when more than one level undergoes surgery, and some authors recommend the addition of a plate system to improve results. At the authors' institution cervical carbon fiber cages (CFCs) are routinely used after ACD. They describe their experience in the treatment of 24 patients with two-level disease treated with CFCs alone.

Methods

Twenty-one patients with cervical radiculopathy and three with radiculomyelopathy underwent ACD. Surgery was performed at C5–6 and C6–7 in 18, at C4–5 and C5–6 in four, and at C3–4 and C5–6 in two patients. All the patients underwent magnetic resonance imaging and 15 also underwent computerized tomography (CT) to assess the results of surgery.

Radiculopathy improved after surgery in all the cases, whereas myelopathy resolved in only one patient. At 1 year fusion was achieved in 96% of the surgically treated discs; this was verified on cervical spine x-ray films in all patients and on CT scans in three patients. Cervical lordosis was restored in eight of the nine patients in whom it was lost preoperatively. No complications related to cage extrusion and no cases of symptomatic pseudarthrosis were observed.

Conclusions

Interbody fusion cages have a load-sharing function and stabilize the spine to increase segmental stiffness, thus achieving fusion rates similar to those associated with bone grafts, even in multilevel disease.

Prospective controlled study of rectangular titanium cage fusion compared with iliac crest autograft fusion in anterior cervical discectomy

Object

The complications of autogenous bone grafting compel spine surgeons to seek alternative methods for cervical spinal fusion. This prospective study was conducted to evaluate the safety and efficacy of using rectangular titanium cage fusion compared with the widely performed iliac crest autograft fusion.

Methods

A total of 36 patients with cervical disc disease in whom an anterior approach was indicated for discectomy were included in this prospective controlled study. The first 18 consecutive patients received iliac crest autograft; the next 18 consecutive patients received rectangular titanium cages. The intergroup demographic and clinical data were comparable. All patients attended follow up for 1 year. According to Odom criteria, 15 (83%) of 18 patients in both groups experienced good to excellent functional recovery. According to the Patient Satisfaction Index, 17 (94%) of 18 patients in both groups were satisfied. The evaluation of neck pain and arm pain did not indicate statistically significant differences between either group. Fusion was present after 1 year in 16 (89%) of 18 patients who received iliac crest autografts and in 15 (83%) of 18 patients who received rectangular titanium cages. In the autograft group, a pseudarthrosis was present in one patient and marked hip pain was observed in three patients. In the cage group, there was one case of temporary vocal cord paresis but no implant-related complications.

Conclusions

The authors conclude that the use of titanium cages in anterior cervical discectomy constitutes a safe and efficient alternative to iliac crest bone autograft.

Outcome analysis of anterior decompressive surgery and fusion for cervical ossification of the posterior longitudinal ligament: report of 107 cases and review of the literature

Object

This study was designed to determine the surgical technique and surgery-related outcome, fusion rate, and complication of anterior decompression and fusion (with various graft materials) performed in patients with ossification of the posterior longitudinal ligament (OPLL) of the cervical spine.

Methods

Between 1980 and 1998, 107 patients with radiologically proven OPLL underwent surgery via the anterior approach for direct removal of the ossified mass. Graft materials included iliac crest in 45 cases, vertebral body (VB) in 37 cases; and interbody fusion cages in 25 cases. In four patients with three-level VB grafts and one with a two-level VB graft, anterior plates were placed. Surgery-related outcome was excellent or good in 89% and fair in 11%. This clinical improvement correlated well with the severity of preoperative myelopathy. Only one patient with severe myelopathy due to extensive mixed-type OPLL developed a segmental weakness of the bilateral upper extremities. The overall fusion rate was 97%. Three patients with obvious spinal instability due to pseudarthrosis required reoperation. Of the graft materials used in this series, VB grafts were the most fragile.

Conclusions

The anterior approach is an effective route for decompressing the cervical cord with OPLL. Slight asymptomatic kyphotic deformity may be encountered. Of the graft materials used in our series, VB graft was considered most fragile, and thus least optimal.

Nonautologous interbody fusion materials in cervical spine surgery: how strong is the evidence to justify their use?

STUDY DESIGN

A review of the literature concerning the use of interbody fusion devices and materials in anterior cervical surgery.

OBJECTIVES

To examine the evidence supporting the use of interbody fusion devices as an alternative to autologous bone after anterior cervical discectomy.

SUMMARY OF BACKGROUND DATA

Concerns over the morbidity associated with harvesting autologous bone and the risk of transmissible infectious from allografts and xenografts have prompted the search for alternative methods of achieving interbody fusion. Several of these methods have been associated with an unacceptable rate of complications. The clinical and health economic implications of the widespread introduction of interbody fusion devices in the absence of sound evidence cannot be ignored.

METHODS

A systematic review of the literature relating to cervical interbody fusion was undertaken. Studies were assessed critically with respect to their methodology, results, and conclusions.

RESULTS

Thirty-two clinical studies and 10 laboratory studies were analyzed. Methodologic weaknesses were identified in the majority. Only four clinical reports were either randomized or blinded or involved independent assessment of their outcomes. Fewer than half of the studies included a valid statistical analysis. Radiologic evidence of fusion was limited in many cases. There was little evidence that nonautologous fusion devices offered a reduction in the length of hospital stay. Autologous bone was as effective as, or superior to, many other fusion devices. The early results of some new fusion techniques used alone or in combination showed promise.

CONCLUSIONS

There is limited evidence supporting the use of a cervical interbody fusion device in place of autologous bone. There is a need to standardize the testing of implants with good quality laboratory work preceding clinical use. Certain devices including cages, some forms of hydroxyapatite, and bone morphogenic proteins merit further study.

A prospective randomized multicenter clinical evaluation of an anterior cervical fusion cage

STUDY DESIGN

A prospective, concurrently controlled, randomized, multicenter trial of an anterior Bagby and Kuslich cervical fusion cage (BAK/C; Sulzer Spine-Tech, Minneapolis, MN) for treatment of degenerative disc disease of the cervical spine.

OBJECTIVES

To report clinical results with maximum 24-month follow-up of fusions performed with the BAK/C fusion cage.

SUMMARY OF BACKGROUND DATA

Threaded lumbar cages have been used during the past decade as a safe and effective surgical solution for chronic disabling low back pain. Threaded cages have now been developed for use in anterior cervical interbody fusions to obviate the need for allografts or autogenous bone grafting procedures while providing initial stability during the fusion process.

METHODS

Patients with symptomatic cervical discogenic radiculopathy were treated with either anterior cervical discectomy with uninstrumented bone-only fusion (ACDF) or BAK/C fusion cage(s). Independent radiographic assessment of fusion was made and patient-based outcome was assessed by visual analog pain scale and a Short Form (SF)-36 Health Status Questionnaire.

RESULTS

Data analysis included 344 patients at 1 year and 180 at 2 years. When the two cage groups (hydroxya, patite-coated or noncoated) were compared with the ACDF group, similar outcomes were noted for duration of surgery, hospital stay, improvements in neck pain and radicular pain in the affected limb, improvements in the SF-36 Physical Component subscale and Mental Component subscale, and the patients' perception of overall surgical outcome. Symptom improvements were maintained at 2 years. A greater percentage of patients with ACDF needed an iliac crest bone harvest than did BAK/C patients (67% vs.- 3%). Successful fusion for one-level procedures at 12 months was 97.9% for the BAK/C groups and 89.7% for the ACDF group (P < 0.05). The complication rate for the ACDF group was 20.4% compared with an overall complication rate of 11.8% with BAK/C. There was no difference in complications that necessitated a second operative procedure.

CONCLUSIONS

These results demonstrate that outcomes after a cervical fusion procedure with a threaded cage are the same as those of a conventional uninstrumented bone-only anterior discectomy and fusion with a low risk of complications and rare need for autogenous bone graft harvest.

A randomized prospective study of an anterior cervical interbody fusion device with a minimum of 2 years of follow-up results

OBJECT

Despite variations in technique, inherent problems persist with current approaches to anterior cervical fusion. This study was performed to determine whether anterior cervical fusion performed using an investigational device was safe and effective in the treatment of degenerative cervical disc disorders and whether this device offered advantages over current techniques.

METHODS

Fifty-four patients with radiculopathy with or without mild myelopathy due to one- or two-level cervical degenerative disc disease were randomized as part of a Food and Drug Administration device study. Following microsurgical discectomy, the control group was treated with iliac crest graft fusion; the experimental study group underwent insertion of an interspace cage and placement of a local autograft. All patients received postoperative follow-up care for at least 2 years. Good or excellent results were found in approximately 97% of the experimental group and 88% of the control group. A solid fusion was achieved in all patients who underwent one-level cage placement, and a solid fusion at one or both levels was achieved in over 90% of both groups. Chronic donor site pain was reported by 31% of the control group.

CONCLUSIONS

In this study, the use of an interbody fusion cage avoided donor site morbidity and placement of autograft achieved a high rate of good or excellent results. Interbody fusion cages appear safe and effective, and their use helps to avoid some of the inherent problems in performing current anterior cervical fusion techniques.