Discectomies of the lower cervical spine using interbody biopolymer (B.O.P.) implants. Advantages in the treatment of complicated cervical arthrosis. A review of 150 cases

Extrusion of Biocompatible Osteoconductive Polymer (BOP) Causing Cervical Myelopathy

BACKGROUND

As the prevalence of spinal fusion surgery has increased, reliable and safe bone graft substitutes have been developed in response. Biocompatible osteoconductive polymer (BOP) has been used as a bone graft alternative for spine surgery. We present a case of cervical myelopathy due to extrusion of BOP 23 years after surgery and discuss the pathophysiology in terms of spinal fusion.

CASE DESCRIPTION

A 65-year-old man presented with a 3-month history of cervical myelopathic symptoms. Twenty-three years earlier, the patient had undergone cervical surgery for a C6-7 herniated disc with the use of BOP. Imaging studies of the cervical spine showed cord compression due to extruded BOP at C6-7. He underwent corpectomy of the C7 vertebral body and removal of the BOP for the neural decompression, combined with interbody fusion by use of an iliac bone graft and plate fixation. During the operation, crumbly fibers of the BOP were easily removed. His myelopathic symptoms improved immediately after surgery. Postoperative magnetic resonance imaging also showed successful decompression of the spinal cord. Histologically, a foreign body reaction and bony degeneration were found around the synthetic fibers of the BOP.

CONCLUSIONS

Spine surgeons should recognize the pathophysiology of the BOP used for spine fusion surgery. Although BOP is not currently used for spinal surgery, patients undergoing previous surgery with the BOP can present with related complications. Revision surgery is recommended to remove the unincorporated BOP and achieve solid spine fusion.

Implantation of the anterior atlantoaxial lateral mass intervertebral cage using the transoral approach

BACKGROUND

The purpose of this study was to evaluate the possibility of implanting the anterior atlantoaxial lateral mass intervertebral cage, a new type of fixation, by the transoral approach.

METHOD

This study examined the possibility of implantation in vivo by the quantitative measurement on the dry atlantoaxial bone and implantation of the anterior atlantoaxial lateral mass intervertebral cage in specimens. Anterior atlantoaxial lateral mass intervertebral cages were implanted in 10 atlantoaxial joint specimens using the transoral approach. Eight anatomical parameters (width, the thickness, ordinates, abscissas, and declination angles of the mass) from each of the 30 dry atlas and axis bone specimens were measured. These parameters determined the size and the design of the cage and the way of implantation.

RESULTS

The course of the vertebral artery forms the safe boundary for transoral surgery. The shape of the area of work exposure was an inverted trapezoid. In specimens, the anterior atlantoaxial lateral mass intervertebral cages could be successfully implanted using the transoral approach. The parameters of the human atlantoaxial lateral masses exposed anteriorly showed that there was enough space, for the safe anterior implantation of the cage. The surgery using the transoral atlantoaxial reduction and plate makes possible the implantation of the anterior cage.

CONCLUSION

The implantation of anterior atlantoaxial lateral mass intervertebral cage through transoral approach is possible.

Bone graft substitutes in anterior cervical discectomy and fusion

Anterior cervical discectomy with fusion is a common surgical procedure for patients suffering pain and/or neurological deficits and unresponsive to conservative management. For decades, autologous bone grafted from the iliac crest has been used as a substrate for cervical arthrodesis. However patient dissatisfaction with donor site morbidity has led to the search for alternative techniques. We present a literature review examining the progress of available grafting options as assessed in human clinical trials, considering allograft-based, synthetic, factor- and cell-based technologies.

[Posterior extrusion of Biocompatible Orthopaedic Polymer (BOP) graft mimicking a calcified lumbar disc herniation: case report]

OBJECTIVE AND IMPORTANCE

We present a case of intracanalar extrusion of a L5S1 Biocompatible Orthopaedic Polymer (BOP) graft associated with a L4L5 disc herniation 19 years after a lumbar intersomatic fusion for a L5S1 disc herniation. Radiological aspect of this complication should be recognized by neurosurgeons.

CLINICAL PRESENTATION

A 55-year old man presented with a right L5 sciatic pain. Neurological examination found a severe weakness in dorsal flexion of the foot. A lumbar CT scanner disclosed aspects consistent with right L4L5 and huge calcified L5S1 lumbar disc herniation.

INTERVENTION

The patient was operated via a bilateral paravertebral approach and a L5 laminectomy. A dense and extensive epidural scarring was seen. The right L4L5 herniated disc was excised. At the left L5S1 level, fibres from a BOP graft had separated into large fragments extruded into the vertebral canal through the dura. The fibres could only be removed partially because of nerve roots adherence. The patient developed postoperative cerebrospinal fluid (CSF) leakage that required a second operation for dural closure. The postoperative course was uneventful and the patient recovered the right L5 root deficit.

CONCLUSION

Neurosurgeons should be aware of the radiological aspect of this complication. If it is recognized on CT scan and asymptomatic, conservative management should be proposed because of the risk of nerve roots injury or postoperative CSF leakage.

High rate of fusion in sheep cervical spines following anterior interbody surgery with absorbable and nonabsorbable implant devices

STUDY DESIGN

Fourteen sheep were fused using anterior interbody implants at C2-C3 and C4-C5 and followed for 6 months.

OBJECTIVE

To evaluate the effect of absorbable and nonabsorbable implants on fusion rate, cage migration, and implant integrity.

SUMMARY OF BACKGROUND DATA

Despite the high clinical success rate with metallic plates and interbody grafting, complications such as dysphagia, imaging artifacts, and revision difficulties exist. Less permanent and lower profile implants could minimize these problems.

METHODS

Four treatments were studied: 1) carbon fiber-reinforced polymer (CFRP) cage alone, 2) CFRP cage with an absorbable tension band, 3) absorbable cage with an absorbable tension band, and 4) absorbable cage with a titanium plate. Fusion was assessed using radiographs, biomechanical testing, and micro-CT analysis.

RESULTS

Treatments with the CFRP cage alone had the lowest fusion rate at 3 months (2/6) and 6 months (4/6). The CFRP cage with the absorbable strap treatments had 5/6 fusions at 6 months. The absorbable cage with absorbable strap also had 5/6 fusions, but two of the cages fractured. The absorbable cage with titanium plate had 5/6 fusions, but the one partial fusion was attributed to poor screw and plate placement.

CONCLUSION

Using both absorbable and nonabsorbable implants, high fusion rates were achieved in the challenging sheep cervical spine model. However, the absorbable cages were not able to withstand the mechanical forces during the 6-month survival period.

Maintenance of interbody space in one- and two-level anterior cervical interbody fusion: comparison of the effectiveness of autograft, allograft, and cage

The use of allografts, autologous iliac crest grafts, and cages for anterior cervical fusion is well documented, however there is no comparison regarding the effectiveness of maintaining the interbody space with the three approaches. We retrospectively measured the rate and amount of interspace collapse, segmental sagittal angulations, clinical results, and radiographic fusion success rates to determine which is the best fusion material. We assessed 73 patients who had one- and two-level cervical discectomies and interbody fusions without instrumentation. The three groups had similar clinical results and fusion rates. However, in the autograft group union occurred in 4 months. In the allograft group, union did not occur until 5.54 months. Moreover, the loss of cervical lordosis (2.75 degrees) was less in the cage group than in the allograft group (9.23 degrees). Additionally, the anterior interspace collapse (1.73 mm) in the cage group was less than the collapse recorded in the autograft group (2.82 mm) and in the allograft group (4 mm). An interspace collapse of 3 mm or greater was observed in 56.1% of the patients in the allograft group, compared with only 19% of the patients in the cage group. We showed that the cage is superior to the allograft and autograft in maintaining cervical interspace height and cervical lordosis after one-level and two-level anterior cervical decompression procedures.

LEVEL OF EVIDENCE

Therapeutic study, Level III-2 (retrospective cohort study).

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.

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.

Effects of neck movements on stability and subsidence in cervical interbody fusion: an in vitro study

OBJECT

The aim of this in vitro study was to determine the influence of simulated postoperative neck movements on the stabilizing effect and subsidence of four different anterior cervical interbody fusion devices. Emphasis was placed on the relation between subsidence and spinal stability.

METHODS

The flexibility of 24 human cervical spine specimens was tested before and directly after being stabilized with a WING, BAK/C, AcroMed I/F cage, or with bone cement in standard flexibility tests under 50 N axial preload. Thereafter, 700 pure moment loading cycles (+/- 2 Nm) were applied in randomized directions to simulate physiological neck movements. Additional flexibility tests in combination with measurements of the subsidence depth were conducted after 50, 100, 200, 300, 500, and 700 loading cycles. In all four groups, simulated postoperative neck movements caused an increase of the range of motion (ROM) ranging from 0.4 to 3.1 degrees and of the neutral zone from 0.1 to 4.2 degrees. This increase in flexibility was most distinct in extension followed by flexion, lateral bending, and axial rotation. After cyclic loading, ROM tended to be lower in the group fitted with AcroMed cages (3.3 degrees in right lateral bending, 3.5 degrees in left axial rotation, 7.8 degrees in flexion, 8.3 degrees in extension) and in the group in which bone cement was applied (5.4 degrees, 2.5 degrees, 7.4 degrees, and 8.8 degrees, respectively) than in those fixed with the WING (6.3 degrees, 5.4 degrees, 9.7 degrees, and 6.9 degrees, respectively) and BAK cages (6.2 degrees, 4.5 degrees, 10.2 degrees, and 11.6 degrees, respectively).

CONCLUSIONS

Simulated repeated neck movements not only caused an increase of the flexibility but also subsidence of the implants into the adjacent vertebrae. The relation between flexibility increase and subsidence seemed to depend on the implant design: subsiding BAK/C cages partially supported stability whereas subsiding WING cages and AcroMed cages did not.

Subsidence resulting from simulated postoperative neck movements: an in vitro investigation with a new cervical fusion cage

STUDY DESIGN

A biomechanical in vitro subsidence test of different cervical interbody fusion devices was performed using a new testing protocol that simulates physiologic conditions.

OBJECTIVES

To investigate the effect of simulated postoperative neck movements on the subsidence of the new WING cervical interbody fusion cage in comparison with two other cages and bone cement.

SUMMARY OF BACKGROUND DATA

Cervical interbody fusion cages sometimes cause complications because of subsidence into the adjacent vertebrae with collapse of the intervertebral space. Complications such as cage dislocation or nonunion with instability also have been reported. To prevent such complications, the new WING cervical interbody fusion cage (Medinorm AG, Quierschied, Germany) has been developed. Its area of contact with the adjacent vertebrae is supposed to be large enough to resist excessive subsidence and small enough to prevent stress protection of the tissue growing in the cage.

METHODS

In this study, 24 human cervical spine specimens were tested after stabilization with either a WING, BAK/C, AcroMed I/F cage or bone cement. Then, in a new testing protocol, 700 pure-moment loading cycles (+/-2 Nm) were applied in randomized directions (lateral bending, flexion-extension, and axial rotation alone or in combination with each other) to simulate the patient's neck movements during the first few postoperative days. Measurements of the subsidence depth (total height loss) in combination with flexibility tests (+/-2.5 Nm) were performed before cyclic loading and after 50, 100, 200, 300, 500, and 700 loading cycles.

RESULTS

Cyclic loading caused subsidence in all four device groups, most distinct with BAK/C-cages (1.63 mm after 700 loading cycles) followed by the new WING (0.90 mm) and the AcroMed (0.82 mm) cages. No statistically significant difference could be found among the three cage designs. However, all three cage types showed a significantly higher subsidence depth than bone cement (0.48 mm;P = 0.023 between each of the three cage-types and bone cement). A moderate correlation between bone mineral density and subsidence depth could be found only in the BAK/C group (r2 = 0.495). A large subsidence depth after 700 loading cycles was associated with a large flexibility increase in the WING (r2 = 0.786) and AcroMed groups (r2 = 0.21), but with a small flexibility increase in the BAK/C group (r2 = 0.58).

CONCLUSIONS

Postoperative neck movements caused subsidence in all cervical interbody implant types. The new WING cage and the AcroMed cage seemed to have a better resistance against subsidence than the BAK/C cage. However, all three cage types had a significantly higher subsidence tendency than bone cement.

Combined use of titanium mesh and biocompatible osteoconductive polymer in the treatment of full thickness calvarial defects

Restoration of bony defects is a common problem in craniofacial surgery. This article describes a versatile approach using a combination of titanium micromesh or midimesh and biocompatible osteoconductive polymer to restore calvarial bone loss.

Biocompatible osteoconductive polymer versus iliac graft. A prospective comparative study for the evaluation of fusion pattern after anterior cervical discectomy

STUDY DESIGN

One hundred fifteen patients having symptomatic cervical disc disease were recruited prospectively for this study. They were allocated randomly for either autologous iliac bone graft or biocompatible osteoconductive polymer implants. Both groups were compared clinically and radiologically.

OBJECTIVES

Complications, long-term clinical and radiologic outcome, and hospital stay were compared to determine if biocompatible osteoconductive polymer was an improvement on iliac bone graft in terms of reduced donor site pain and shortened hospital stay.

SUMMARY OF BACKGROUND DATA

Donor site morbidity is a significant problem in anterior cervical fusion. Hospital stay is another factor in the recent era of cost consciousness. Biocompatible osteoconductive polymer has been used in many centers as a biodegradable implant to circumvent these problems.

METHODS

Smith-Robinson technique was used in 74 patients, and Cloward technique was used in 41 patients. Sixty-five patients had biocompatible osteoconductive polymer implants, and 50 patients had iliac bone graft. Patients were followed-up routinely in the outpatient clinic where pain visual analogue scale and Odom's criteria were used for outcome evaluation. Plain radiography, computed tomography scan, and magnetic resonance imaging were used for radiologic evaluation.

RESULTS

The mean hospital stay was 4.8 days for those with iliac bone graft and 4.7 days for those with biocompatible osteoconductive polymer. Clinical outcome was identical in both groups. The incidence of partial graft protrusion and postoperative intersegmental kyphosis was statistically higher with iliac bone graft (P = 0.018 and P = 0.02, respectively). "Sclerosis" started to form around biocompatible osteoconductive polymer like a "halo" at 2 months. It increased with time, and sometimes was associated with new osteophyte formation; however, there was no biocompatible osteoconductive polymer incorporation or biodegradation

CONCLUSIONS

Biocompatible osteoconductive polymer acts as a good "spacer" that reduces graft collapse and intersegmental kyphosis. However, it did not show any radiologic evidence of biodegradation or incorporation during the follow-up period of 24 months.

Anterior cervical discectomy with or without fusion with acrylate. A randomized trial

STUDY DESIGN

A prospective randomized trial with assessment of treatment results by an independent observer and by patient questionnaire.

OBJECTIVES

This study evaluated whether implantation of polymethylmethacrylate after anterior cervical discectomy improved clinical results and whether polymethylmethacrylate provided a solid bony union with preservation of anatomical relations of the cervical spine.

SUMMARY OF BACKGROUND DATA

Discectomy without fusion disturbs anatomical relations of the cervical spine. Use of an autologous bone graft frequently causes donor-site complications. Therefore, synthetic materials such as polymethylmethacrylate have been used instead of bone to obtain spinal fusion. Whether these implants improve the clinical results of anterior discectomy is unknown. In addition, the radiological follow-up of discectomy with polymethylmethacrylate has hardly been investigated.

METHODS

Between April, 1986, and April, 1990, all patients with radiologically proven cervical disc pathology and a radicular syndrome were eligible for this study. The primary endpoint of the study was the clinical result after 2 years. Assessment of the result was rated both by an independent observer using Odom's criteria and by the patient using a written questionnaire. Before surgery and during follow-up, radiographs were obtained.

RESULTS

Two patients died during follow up. A good result was obtained in 28 of 42 patients (70%) treated with polymethylmethacrylate and in 30 of 39 patients (77%) of patients treated with discectomy only. Pre-operative neck pain subsided earlier if polymethylmethacrylate was used, but the difference was temporary and clinically insignificant. The use of polymethylmethacrylate resulted in a significant lower bony union rate. Polymethylmethacrylate frequently migrated into adjacent vertebrae.

CONCLUSIONS

No relevant clinical differences between treatments were found. The radiological results of anterior discectomy with polymethylmethacrylate were inferior to those of discectomy only. Based on these results, the use of polymethylmethacrylate to obtain fusion after anterior discectomy is not recommended.

Management of cervical spondylotic myelopathy and radiculopathy

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BOP: biocompatible osteoconductive polymer: an experimental approach

BOP (biocompatible osteoconductive polymer) is a material proposed for osteosyntheses and for filling of bone defects in orthopaedics, neurosurgery and stomatology. It is a composite made of a copolymer of N-vinylpyrrolidone and methylmethacrylate, of polyamide-6 fibers and of calcium gluconate. The histological investigation includes the study of 30 intact rabbit femurs instrumented with a BOP rod, as well as the study of organs of the reticuloendothelial system. The currently available results show the absence of toxicity on hematopoietic tissue. Zones of osteoblastic activity surround the rods, coupled with an osteoclastic reaction which may result in the partial fragmentation of the polyamide fibers and its incorporation in the newly formed bone. We also observed the encapsulation of the material. The biomechanical approach investigated the mechanical properties of the material in bending and in shear. The radiological aspects of the investigation consisted of computerized axial tomography of the implanted femurs to measure density at the bone-implant interface.

Anterior cervical discectomy and vertebral interbody fusion with hydroxy-apatite ceramic. Preliminary results

Intervertebral plates of hydroxy apatite ceramic (HAC) have been used in three patients for cervical vertebral interbody fusion after anterior discectomy. In one case a pure HAC "Disc" was used, which proved to be too friable. Specially designed intervertebral plates, which were composed of an HAC-coated core of alumina ceramic, were used in the other two cases. Clinically and radiologically optimal results after 1-year- and 2-year-follow-up suggest that HAC-ceramic might be a very promising material for vertebral interbody fusion. Possible complications and pain due to bone removal from the iliac crest are avoided, and the operative procedure is simplified.

Percutaneous interbody osteosynthesis in the treatment of thoracolumbar traumatic or tumoural lesions. A review of 51 cases

The authors describe a technique of percutaneous interbody osteosynthesis applicable to the dorsal and lumbar spine. 51 patients were so treated for different aetiologies: traumatic conditions (35 cases) and tumoural lesions (16 cases). The material used consisted of special instruments that are positioned in double obliquity by a percutaneous posterolateral approach. A posterior approach limited to the pathological focus was used jointly whenever a graft or a decompression was necessary (19 cases). Several types of anaesthesia were used (local, local-regional, general, neuroleptanalgesia). The patients benefited by the advantages that usually accompany percutaneous techniques. The advantages and limitations of the method are discussed.