Bone ingrowth in retrieved Bryan Cervical Disc prostheses

Ceramics in total disc replacements: A scoping review

BACKGROUND

Ceramics are used in Total Disc Replacements (1) in articulating surfaces for their wear resistance and biocompatibility and (2) on endplates to promote osseointegration. They furthermore exhibit MRI and CT compatibility. These properties address main challenges associated with non-ceramic Total Disc Replacements i.e. wear, migration and postoperative imaging. While brittleness of ceramics caused fear of fracture in the past, improvements of ceramic materials were made and considerable clinical experience with ceramic Total Disc Replacements was gained. This review aims to assess the evidence on the use of ceramics in Total Disc Replacements and compare safety and effectiveness of ceramic Total Disc Replacements to spinal fusion and Total Disc Replacements in general.

METHODS

We conducted a scoping review on the use of ceramics in Total Disc Replacements using Scopus, Web of Science and PubMed. The review includes 36 clinical, ex vivo and nonhuman in vivo, tribological and mechanical studies and case reports.

FINDINGS

Ceramics are used in cervical Total Disc Replacements, with safety and efficacy confirmed in clinical studies, with up to 10 and 3.3 years follow-up, for articulation and osseointegration applications, respectively. Clinical evidence shows that ceramic Total Disc Replacements (alike non-ceramic ones) restore segmental motion and result in non-inferior and possibly superior outcomes to spinal fusion. In vivo studies show osseointegration comparable to non-ceramic devices. Tribological studies suggest appropriate wear properties.

INTERPRETATION

We found no indications of systematic problems with the use of ceramics in Total Disc Replacements. Ceramics are suitable materials for Total Disc Replacements.

Comparison of adverse events between cervical disc arthroplasty and anterior cervical discectomy and fusion: a 10-year follow-up

BACKGROUND CONTEXT

Cervical disc arthroplasty (CDA) has been advocated as an alternative to anterior cervical discectomy and fusion (ACDF) with the added potential to reduce the risk of adjacent level disc degeneration and segmental instability. However, the long-term adverse events of arthroplasty have yet to be fully reported.

PURPOSE

To investigate the 10-year follow-up adverse events rates between CDA and ACDF.

STUDY DESIGN/SETTING

The study was a randomized, prospective, multicenter Investigational Device Exemption (IDE) trial and its continued follow-up as a postapproval study (PAS). Single level surgeries were performed for cervical disc pathologies between May 2002 and October 2004.

PATIENT SAMPLE

n=463 patients.

OUTCOME MEASURES

Adverse events comparison of CDA and ACDF from self-reported and physiologic measures.

METHODS

At each evaluation time point, subjects were queried for adverse events since their last visit; and all adverse events were documented, regardless of whether or not they appeared related to the surgery or device. Adverse events were recorded, categorized, and assessed for severity and relationship to the study device and/or surgical procedure. The 10-year cumulative rates for each type of adverse events were summarized using a life-table method for the time-to-event analysis. A log-rank test was used to compare the two treatment groups.

RESULTS

A total of 242 patients received CDA and 221 patients received ACDF. At 10-year follow-up, 54% (130/242) of CDA patients and 47% (104/221) of the ACDF subjects were evaluated. At up to 10-year follow-up, 231 patients in the CDA group (cumulative rate 98.4%) and 199 patients in the ACDF group (cumulative rate 98.7%) had at least one adverse event. Overall, the difference in the cumulative rate of all adverse events over 10 years was not statistically different (p=0.166). The cumulative rates of the following adverse events were not different between the two groups for cancer, cardiovascular, death, dysphonia/dysphagia, gastrointestinal, infection, urogenital, respiratory, implant displacement/loosening, implant malposition, neck and arm pain, neurological, other pain, spinal events, and intraoperative vascular injury. However, there were more adverse events in the CDA group resulting from trauma (p=.012) and more spinal events at the index level (p=.006). The ACDF group had significantly more nonunion events (p=.019), and nonunion outcome pending (p=.034), adjacent level spinal events (p=.033), and events that fell into the "other" category (p=.015).

CONCLUSIONS

The cumulative rates of patients who had any adverse events were not different between the artificial cervical disc and the anterior cervical arthrodesis groups. In addition, the cumulative rates were not different between the two groups for the majority of categories as well.

Effect of porous orthopaedic implant material and structure on load sharing with simulated bone ingrowth: A finite element analysis comparing titanium and PEEK

Osseointegration of load-bearing orthopaedic implants, including interbody fusion devices, is critical to long-term biomechanical functionality. Mechanical loads are a key regulator of bone tissue remodeling and maintenance, and stress-shielding due to metal orthopaedic implants being much stiffer than bone has been implicated in clinical observations of long-term bone loss in tissue adjacent to implants. Porous features that accommodate bone ingrowth have improved implant fixation in the short term, but long-term retrieval studies have sometimes demonstrated limited, superficial ingrowth into the pore layer of metal implants and aseptic loosening remains a problem for a subset of patients. Polyether-ether-ketone (PEEK) is a widely used orthopaedic material with an elastic modulus more similar to bone than metals, and a manufacturing process to form porous PEEK was recently developed to allow bone ingrowth while preserving strength for load-bearing applications. To investigate the biomechanical implications of porous PEEK compared to porous metals, we analyzed finite element (FE) models of the pore structure-bone interface using two clinically available implants with high (> 60%) porosity, one being constructed from PEEK and the other from electron beam 3D-printed titanium (Ti). The objective of this study was to investigate how porous PEEK and porous Ti mechanical properties affect load sharing with bone within the porous architectures over time. Porous PEEK substantially increased the load share transferred to ingrown bone compared to porous Ti under compression (i.e. at 4 weeks: PEEK = 66%; Ti = 13%), tension (PEEK = 71%; Ti = 12%), and shear (PEEK = 68%; Ti = 9%) at all time points of simulated bone ingrowth. Applying PEEK mechanical properties to the Ti implant geometry and vice versa demonstrated that the observed increases in load sharing with PEEK were primarily due to differences in intrinsic elastic modulus and not pore architecture (i.e. 4 weeks, compression: PEEK material/Ti geometry = 53%; Ti material/PEEK geometry = 12%). Additionally, local tissue energy effective strains on bone tissue adjacent to the implant under spinal load magnitudes were over two-fold higher with porous PEEK than porous Ti (i.e. 4 weeks, compression: PEEK = 784 ± 351 microstrain; Ti = 180 ± 300 microstrain; and 12 weeks, compression: PEEK = 298 ± 88 microstrain; Ti = 121 ± 49 microstrain). The higher local strains on bone tissue in the PEEK pore structure were below previously established thresholds for bone damage but in the range necessary for physiological bone maintenance and adaptation. Placing these strain magnitudes in the context of literature on bone adaptation to mechanical loads, this study suggests that porous PEEK structures may provide a more favorable mechanical environment for bone formation and maintenance under spinal load magnitudes than currently available porous 3D-printed Ti, regardless of the level of bone ingrowth.

Ten-year Outcomes of Cervical Disc Replacement With the BRYAN Cervical Disc: Results From a Prospective, Randomized, Controlled Clinical Trial

STUDY DESIGN

A prospective, randomized multicenter IDE trial between May 2002 and October 2004.

OBJECTIVE

The aim of this study was to report on the 10-year safety and efficacy of BRYAN cervical disc arthroplasty (CDA).

SUMMARY OF BACKGROUND DATA

Cervical disc arthroplasty (CDA) is a potential alternative for anterior cervical decompression and fusion (ACDF) with the hope that maintenance of motion may decrease the likelihood of adjacent segment disease.

METHODS

This is an analysis of a US Food and Drug Administration (FDA) investigation comparing CDA with ACDF for single-level patients. Eligible patients were ≥ 21 years of age with symptomatic cervical disc disease who had failed conservative care. Patients were followed at regular intervals with the current data set at > 10 years. Protocol for overall success: ≥ 15-point improvement in NDI scores, maintenance or improvement in neurologic status, no serious adverse events related to implant or implant/surgical procedure, and no subsequent surgery or intervention classified as "failure."

RESULTS

At 10-year follow-up, 128 (CDA) and 104 (ACDF) patients were available for evaluation. Overall success rate was significantly higher for CDA group (81.3% vs. 66.3%; P = 0.005). The rate of second surgeries at adjacent levels was lower for CDA group (9.7% vs. 15.8%; P = 0.146). NDI scores improved significantly in CDA group (Δ38.3 vs. Δ31.1; P = 0.010). Visual Analog Scale (VAS) neck and arm improved in the CDA group (Δ54.3 vs. Δ49.2; P = 0.119), (Δ58.1 vs. Δ51.6; P = 0.0.60) respectively. About 4.1% of CDA patients and 4.9% of ACDF patients had serious adverse events related to study device. Mean angular motions at index level for BRYAN disc and ACDF were 8.69° and 0.60°, respectively.

CONCLUSION

CDA can preserve and maintain motion in the long term compared with ACDF. There was a trend toward fewer adjacent segment surgeries for BRYAN disc that did not reach significance. Significant improvement in CDA NDI scores may suggest better long-term success for CDA as compared to fusion.

LEVEL OF EVIDENCE

2.

A systematic review of cervical artificial disc replacement wear characteristics and durability

Study design: Systematic review.

Clinical questions: (1) What evidence is available from studies of cervical total disc arthroplasty (C-ADR) failure and retrieval regarding durability, wear, and reasons for failure of C-ADR? (2) What evidence is available from experimental models regarding the durability of C-ADR beyond 5 years?

Methods: We searched electronic databases to identify published reports of explanted cervical artificial discs and biomechanical simulations of disc wear.

Results: Nine articles were identified describing 17 devices explanted from human patients and four articles describing 23 devices explanted from non-human subjects. Wear properties were not consistently reported across studies, so summaries for specific variables are based on few cases. No device had been implanted longer than 4 years. In both human and non-human subjects, devices showed evidence of metallic and polymeric (for discs with polymer components) debris. Inflammatory cells were frequently present in surrounding soft tissues. Signs of infection were uncommon.

Four patients had reactions interpreted as hypersensitivity to metal. We identified three articles on biomechanical wear simulations. Devices were tested between 10 and 20 million cycles in axial loading, flexion/extension, and lateral bending. No device failures were reported. One study suggests such simulations may represent 50 or more years of wear in actual patients.

Conclusion: Cervical disc implants consistently produced polymeric and metallic debris, which was typically accompanied by inflammation. Hypersensitivity to metal may increase risk for device failure. Biomechanical simulations indicate that cervical disc implants may be durable beyond the currently reported length of clinical follow-up.

Implant failure of Bryan cervical disc due to broken polyurethane sheath: a case report

STUDY DESIGN

A case report.

OBJECTIVE

A rare case of Bryan disc implantation failure due to broken polyurethane sheath was reported. The bone ingrowth at implant-bone interface and wear debris leaking from broken Bryan disc were also observed.

SUMMARY OF BACKGROUND DATA

The Bryan disc is one of the most commonly used cervical prostheses and has shown satisfactory results compared with anterior cervical discectomy and fusion in short- and long-term follow-up. The complications, including neurological worsening, heterotopic ossification, kyphosis, and so forth, still occur, although infrequently. The broken polyurethane sheath is an extremely rare complication that has seldom been reported before.

METHODS

A 55-year-old female patient experienced progressive neck pain after 8 years of Bryan disc implantation because of cervical spondylotic myelopathy at C5-C6 level. The subsequent magnetic resonance imaging scan demonstrated a cystic mass in front of Bryan disc, with high-signal intensity on T2-weighted images. The Bryan disc was removed and segment (C5-C6) was fused with cage and plate. The bone ingrowth and wear debris of retrieved Bryan disc were studied. RESULTS.: In revision surgery, a cyst with thick pseudocapsule connecting the anterior part of Bryan disc was excised. A transverse crack (5 mm) was identified in the anterior part of polyurethane sheath. The bacteria test of fluid from the cyst showed a negative result. Micro-computed tomography and histological study both indicated abundant bone ingrowth at implant-bone interface. The metal wear debris could be observed around titanium alloy shells.

CONCLUSION

This case demonstrates the unique incident of broken Bryan disc after 8 years of implantation. Follow-up imaging shortly after the procedure should be mandatory to monitor such potential complication.

Complications of Bryan cervical disc replacement

The primary goals of cervical disc replacement are to avoid fusion in the affected segment, maintain the mobility and function of the involved cervical segments, allow patients to quickly return to routine activities and reduce or eliminate adjacent-segment disease. A large number of patients have already undergone, and more and more patients will in the future undergo, cervical disc replacement. The cervical device which best preserves movement, and has therefore been the device of choice, has been the Bryan cervical disc. Although a safe surgical technique has been demonstrated and favorable results of using the Bryan disc reported, some complications have also accompanied this arthroplasty. Complications of Bryan cervical disc replacement include those related to the operative approach and decompression process, loosening and failure of the device, postoperative kyphosis, heterotopic ossification, and loss of movement due to spontaneous fusion. In order to avoid these complications, strict patient selection criteria and a meticulous knowledge of anatomy are necessary.

Retrieval analysis of motion preserving spinal devices and periprosthetic tissues

This article reviews certain practical aspects of retrieval analysis for motion preserving spinal implants and periprosthetic tissues as an essential component of the overall revision strategy for these implants. At our institution, we established an international repository for motion-preserving spine implants in 2004. Our repository is currently open to all spine surgeons, and is intended to be inclusive of all cervical and lumbar implant designs such as artificial discs and posterior dynamic stabilization devices. Although a wide range of alternative materials is being investigated for nonfusion spine implants, many of the examples in this review are drawn from our existing repository of metal-on-polyethylene, metal-on-metal lumbar total disc replacements (TDRs), and polyurethane-based dynamic motion preservation devices. These devices are already approved or nearing approval for use in the United States, and hence are the most clinically relevant at the present time. This article summarizes the current literature on the retrieval analysis of these implants and concludes with recommendations for the development of new test methods that are based on the current state of knowledge of in vivo wear and damage mechanisms. Furthermore, the relevance and need to evaluate the surrounding tissue to obtain a complete understanding of the biological reaction to implant component corrosion and wear is reviewed.

Cervical spinal disc replacement

Cervical spinal disc replacement is used in the management of degenerative cervical disc disease in an attempt to preserve cervical spinal movement and to prevent adjacent disc overload and subsequent degeneration. A large number of patients have undergone cervical spinal disc replacement, but the effectiveness of these implants is still uncertain. In most instances, degenerative change at adjacent levels represents the physiological progression of the natural history of the arthritic disc, and is unrelated to the surgeon. Complications of cervical disc replacement include loss of movement from periprosthetic ankylosis and ossification, neurological deficit, loosening and failure of the device, and worsening of any cervical kyphosis. Strict selection criteria and adherence to scientific evidence are necessary. Only prospective, randomised clinical trials with long-term follow-up will establish any real advantage of cervical spinal disc replacement over fusion.

Comparison of BRYAN cervical disc arthroplasty with anterior cervical decompression and fusion: clinical and radiographic results of a randomized, controlled, clinical trial

STUDY DESIGN

A prospective, randomized, multicenter study of surgical treatment of cervical disc disease.

OBJECTIVE

To assess the safety and efficacy of cervical disc arthroplasty using a new arthroplasty device at 24-months follow-up.

SUMMARY OF BACKGROUND DATA

Cervical disc arthroplasty preserves motion in the cervical spine. It is an alternative to fusion after neurologic decompression, whereas anterior decompression and fusion provides a rigorous comparative benchmark of success.

METHODS

We conducted a randomized controlled multicenter clinical trial enrolling patients with cervical disc disease. Ultimately 242 received the investigational device (Bryan Cervical Disc), and 221 patients underwent a single-level anterior cervical discectomy and decompression and fusion as a control group. Patients completed clinical and radiographic follow-up examinations at regular intervals for 2 years after surgery.

RESULTS

Analysis of 12- and 24-month postoperative data showed improvement in all clinical outcome measures for both groups; however, 24 months after surgery, the investigational group patients treated with the artificial disc had a statistically greater improvement in the primary outcome variables: Neck disability index score (P = 0.025) and overall success (P = 0.010). With regard to implant- or implant/surgical-procedure-associated serious adverse events, the investigational group had a rate of 1.7% and the control group, 3.2%. There was no statistical difference between the 2 groups with regard to the rate of secondary surgical procedures performed subsequent to the index procedure. Patients who received the artificial cervical disc returned to work nearly 2 weeks earlier than the fusion patients (P = 0.015).

CONCLUSION

Two-year follow-up results indicate that cervical disc arthroplasty is a viable alternative to anterior cervical discectomy and fusion in patients with persistently symptomatic, single-level cervical disc disease.

Biomechanical studies on cervical total disc arthroplasty: a literature review

BACKGROUND

Many models of cervical disc prostheses are currently commercially available or under clinical trial, and are based on several design concepts and built employing different materials. This paper is targeted to the understanding of the possible relationships between the geometrical, mechanical and material properties of the various cervical disc prostheses and the restoration of a correct biomechanics of the implanted spine.

METHODS

Papers about cervical disc arthroplasty, based on ex vivo testing, mathematical models, and radiographic measurements, were included in the present review.

FINDINGS

Although disc arthroplasty was found to be generally able to preserve a nearly physiological motion in the cervical spine, several alterations in the spine biomechanics due to disc arthroplasty were reported in the literature. An increase of the range of motion at the implanted level was observed in some ex vivo studies. Loss of mobility and heterotopic ossification were reported in radiographic investigations. Loss of lordosis at the implanted level was detected as well. Wear debris was usually found very limited and device stability seemed not to be an actual problem.

INTERPRETATION

The possible relationships between the observed alterations in the spine biomechanics after disc arthroplasty and the properties of the various cervical disc prostheses have been reviewed. Clinical studies are needed to assess the validity of the considerations inferred from the biomechanical papers.

A radiostereometric analysis of the Bryan Cervical Disc prosthesis

STUDY DESIGN

Prospective, radiostereometric study of the Bryan Cervical Disc prosthesis (Medtronic Sofamor Danek, Memphis, TN) for the treatment of a single-level disc disease of the cervical spine.

OBJECTIVE

To study the stability of the titanium endplates of the disc prosthesis at the interface between the bone and prosthesis.

SUMMARY OF BACKGROUND DATA

Cervical disc prosthesis is a motion-sparing technology in which the longevity is dependent on initial fixation as well as secondary fixation with bone ingrowth into the surface of the device. Little is known regarding the stability of this fixation with the currently studied prosthesis.

METHODS

Eleven patients with symptomatic cervical radiculopathy underwent implantation of a radiostereometry modified Bryan prosthesis after a standard anterior cervical discectomy. The adjacent vertebrae were perioperatively marked with tantalum markers. The patients were then frequently studied with radiostereometric radiographs and evaluated for pain, and neurologic and physical function for 2 years.

RESULTS

Both titanium endplates of the device were immediately stable in 5 patients. Small but measurable changes (micromotions) were recorded in 4 patients until the 3-month examination and in 2 patients at the 3-6-month time period. All prostheses continued to be stable after 6 months until the final assessment at 2 years after surgery. The recorded micromotions did not influence the clinical results.

CONCLUSIONS

The Bryan prosthesis is immediately stable in many patients and is securely fixed to the bone within 3-6 months in all patients. The result of this study suggests that there is sufficient bone ingrowth on the coated surface of the Bryan prosthesis endplates to stabilize securely the prosthesis.

Cervical spine disc prosthesis: radiographic, biomechanical and morphological post mortal findings 12 weeks after implantation. A retrieval example

There is a gap between in vitro and clinical studies concerning performance of spinal disc prosthesis. Retrieval studies may help to bridge this gap by providing more detailed information about motion characteristics, wear properties and osseous integration. Here, we report on the radiographic, mechanical, histological properties of a cervical spine segment treated with a cervical spine disc prosthesis (Prodisc C, Synthes Spine, Paoli, USA) for 3 months. A 48-year-old male received the device due to symptomatic degenerative disc disease within C5-C6. The patient recovered completely from his symptoms. Twelve weeks later, he died from a subarachnoid hemorrhage. During routine autopsy, C3-T1 was removed with all attached muscles and ligaments and subjected to plain X-rays and computed tomography, three dimensional flexibility tests, shear test as well as histological and electronic microscopic investigations. We detected radiolucencies mainly at the cranial interface between bone and implant. The flexibility of the segment under pure bending moments of +/-2.5 Nm applied in flexion/extension, axial rotation and lateral bending was preserved, with, however, reduced lateral bending and enlarged neutral zone compared to the adjacent segments C4-C5, and C6-C7. Stepwise increase of loading in flexion/extension up to +/-9.5 Nm did not result in segmental destruction. A postero-anterior force of 146 N was necessary to detach the lower half of the prosthesis from the vertebra. At the polyethylene (PE) core, signs of wear were observed compared to an unused core using electronic microscopy. Metal and PE debris without signs of severe inflammatory reaction was found within the surrounding soft tissue shell of the segment. A thin layer of soft connective tissue covered the major part of the implant endplate. Despite the limits of such a case report, the results show: that such implants are able to preserve at least a certain degree of segmental flexibility, that direct bone implant contact is probably rare, and that debris may be found after 12 weeks.

Lumbar hemivertebra resection

BACKGROUND

A single lumbar hemivertebra can be expected to cause progressive scoliosis. The aim of this study was to evaluate the results of a lumbar hemivertebra resection and short-segment fusion through a combined posterior and anterior approach.

METHODS

From 1987 to 2002, a consecutive series of twenty-one patients with congenital scoliosis or kyphoscoliosis due to a lumbar hemivertebra were managed by resection of the hemivertebra through a combined posterior and anterior approach and with the use of a short anterior and posterior convex-side fusion.

RESULTS

The mean age at the time of surgery was 3.3 years (range, twelve months to 10.2 years). The mean followup period was 8.6 years. There was a mean improvement of 71.4% in the segmental scoliosis curve from a mean angle of 32.9 degrees before surgery to 9.4 degrees at the time of the latest follow-up assessment, and a mean improvement of 63.9% in the global scoliosis curve from 34.1 degrees to 12.3 degrees. The mean final lordosis was within normal values.

CONCLUSIONS

Excision of a lumbar hemivertebra is safe and provides stable correction when combined with a short-segment fusion. Surgery should be performed as early as possible to avert the development of severe local deformities and prevent secondary structural deformities that would require a more extensive fusion later.