Porous/dense composite hydroxyapatite for anterior cervical discectomy and fusion

Hydroxyapatite Use in Spine Surgery—Molecular and Clinical Aspect

Hydroxyapatite possesses desirable properties as a scaffold in tissue engineering: it is biocompatible at a site of implantation, and it is degradable to non-toxic products. Moreover, its porosity enables infiltration of cells, nutrients and waste products. The outcome of hydroxyapatite implantation highly depends on the extent of the host immune response. Authors emphasise major roles of the chemical, morphological and physical properties of the surface of biomaterial used. A number of techniques have been applied to transform the theoretical osteoconductive features of HAp into spinal fusion systems—from integration of HAp with autograft to synthetic intervertebral implants. The most popular uses of HAp in spine surgery include implants (ACDF), bone grafts in posterolateral lumbar fusion and transpedicular screws coating. In the past, autologous bone graft has been used as an intervertebral cage in ACDF. Due to the morbidity related to autograft harvesting from the iliac bone, a synthetic cage with osteoconductive material such as hydroxyapatite seems to be a good alternative. Regarding posterolateral lumbar fusion, it requires the graft to induce new bone growth and reinforce fusion between the vertebrae. Hydroxyapatite formulations have shown good results in that field. Moreover, the HAp coating has proven to be an efficient method of increasing screw fixation strength. It can decrease the risk of complications such as screw loosening after pedicle screw fixation in osteoporotic patients. The purpose of this literature review is to describe in vivo reaction to HAp implants and to summarise its current application in spine surgery.

Ceramic Biologics for Bony Fusion-a Journey from First to Third Generations

PURPOSE OF REVIEW

To provide information on characteristics and use of various ceramics in spine fusion and future directions.

RECENT FINDINGS

In most recent years, focus has been shifted to the use of ceramics in minimally invasive surgeries or implementation of nanostructured surface modification features to promote osteoinductive properties. In addition, effort has been placed on the development of bioactive synthetics. Core characteristic of bioactive synthetics is that they undergo change to simulate a beneficial response within the bone. This change is based on chemical reaction and various chemical elements present in the bioactive ceramics. Recently, a synthetic 15-amino acid polypeptide bound to an anorganic bone material which mimics the cell-binding domain of type-I collagen opened a possibility for osteogenic and osteoinductive roles of this hybrid graft material. Ceramics have been present in the spine fusion arena for several decades; however, their use has been limited. The major obstacle in published literature is small sample size resulting in low evidence and a potential for bias. In addition, different physical and chemical properties of various ceramics further contribute to the limited evidence. Although ceramics have several disadvantages, they still hold a great promise as a value-based graft material with being easily available, relatively inexpensive, and non-immunogenic.

Spinal fusion procedures in the adult and young population: a systematic review on allogenic bone and synthetic grafts when compared to autologous bone

This systematic review aims to compare clinical evidences related to autologous iliac crest bone graft (ICBG) and non-ICBG (local bone) with allografts and synthetic grafts for spinal fusion procedures in adult and young patients. A systematic search was carried out in three databases (PubMed, Scopus, Web of Science, Cochrane Central Register of Controlled Trials) to identify clinical studies in the last 10 years. The initial search retrieved 1085 studies, of which 24 were recognized eligible for the review. Twelve studies (4 RCTs, 5 prospective, 3 retrospective) were focused on lumbar spine, 9 (2 RCTs, 2 prospective, 4 retrospective, 1 case-series) on cervical spine and 3 (1 RCT, 2 retrospective) on spinal fusion procedures in young patients. Calcium phosphate ceramics, allografts, bioglasses, composites and polymers have been clinically investigated as substitutes of autologous bone in spinal fusion procedures. Of the 24 studies included in this review, only 1 RCT on cervical spine was classified with high level of evidence (Class I) and showed low risk of bias. This RCT demonstrated the safety and efficacy of the proposed treatment, a composite bone substitute, that results in similar and on some metrics superior outcomes compared with local autograft bone. Almost all other studies showed moderately or, more often, high incidence of bias (Class III), thus preventing ultimate conclusion on the hypothesized beneficial effects of allografts and synthetic grafts. This review suggests that users of allografts and synthetic grafting should carefully consider the scientific evidence concerning efficacy and safety of these bone substitutes, in order to select the best option for patient undergoing spinal fusion procedures.

Evaluation of bony fusion after anterior cervical discectomy: a systematic literature review

PURPOSE

Anterior cervical discectomy and fusion (ACDF) has proven effective in treating radicular arm pain. Post-operatively, cervical spine stability is temporarily challenged, but data on bony fusion and speed of fusion are ambiguous; optimum evaluation method and criteria are debated.

AIM

To study bony fusion accomplishment and to obtain an overview of methods to evaluate fusion.

METHODS

A literature search was performed in PubMed and Embase. Included studies had to report original data concerning 1- or 2-level ACDF with intervertebral device or bone graft, where bony fusion was assessed using CT scans or X-rays.

RESULTS

A total of 146 articles comprising 10,208 patients were included. Bony fusion was generally defined as "the presence of trabecular bridging" and/or "the absence of motion". Fusion was accomplished in 90.1% of patients at the final follow-up. No gold standard for assessment could be derived from the results. Addition of plates and/or cages with screws resulted in slightly higher accomplishment of fusion, but differences were not clinically relevant. Eighteen studies correlated clinical outcome with bony fusion, and 3 found a significant correlation between accomplishment and better clinical outcome.

CONCLUSIONS

In approximately 90% of patients, bony fusion is accomplished one year after ACDF. As there is no generally accepted definition of bony fusion, different measuring techniques cannot be compared to a gold standard and it is impossible to determine the most accurate method. Variations in study design hamper conclusions on optimising the rate of bony fusion by choice of material and/or additives. Insufficient attention is paid to correlation between bony fusion and clinical outcome. These slides can be retrieved from electronic supplementary material.

Radiological Fusion Criteria of Postoperative Anterior Cervical Discectomy and Fusion: A Systematic Review

STUDY DESIGN

Systematic review.

OBJECTIVES

Diagnosis of pseudarthrosis after anterior cervical fusion is difficult, and often depends on the surgeon's subjective assessment because recommended radiographic criteria are lacking. This review evaluated the available evidence for confirming fusion after anterior cervical surgery.

METHODS

Articles describing assessment of anterior cervical fusion were retrieved from MEDLINE and SCOPUS. The assessment methods and fusion rates at 1 and 2 years were evaluated to identify reliable radiographical criteria.

RESULTS

Ten fusion criteria were described. The 4 most common were presence of bridging trabecular bone between the endplates, absence of a radiolucent gap between the graft and endplate, absence of or minimal motion between adjacent vertebral bodies on flexion-extension radiographs, and absence of or minimal motion between the spinous processes on flexion-extension radiographs. The mean fusion rates were 90.2% at 1 year and 94.7% at 2 years. The fusion rate at 2 years had significant independence (P = .048).

CONCLUSIONS

The most common fusion criteria, bridging trabecular bone between the endplates and absence of a radiolucent gap between the graft and endplate, are subjective. We recommend using <1 mm of motion between spinous processes on extension and flexion to confirm fusion.

Clinical Application of Ceramics in Anterior Cervical Discectomy and Fusion: A Review and Update

STUDY DESIGN

Narrative review.

OBJECTIVES

Anterior cervical discectomy and fusion (ACDF) is a reliable procedure, commonly used for cervical degenerative disc disease. For interbody fusions, autograft was the gold standard for decades; however, limited availability and donor site morbidities have led to a constant search for new materials. Clinically, it has been shown that calcium phosphate ceramics, including hydroxyapatite (HA) and tricalcium phosphate (TCP), are effective as osteoconductive materials and bone grafts. In this review, we present the current findings regarding the use of ceramics in ACDF.

METHODS

A review of the relevant literature examining the clinical use of ceramics in anterior cervical discectomy and fusion procedures was conducted using PubMed, OVID and Cochrane.

RESULT

HA, coralline HA, sandwiched HA, TCP, and biphasic calcium phosphate ceramics were used in combination with osteoinductive materials such as bone marrow aspirate and various cages composed of poly-ether-ether-ketone (PEEK), fiber carbon, and titanium. Stand-alone ceramic spacers have been associated with fracture and cracks. Metallic cages such as titanium endure the risk of subsidence and migration. PEEK cages in combination with ceramics were shown to be a suitable substitute for autograft.

CONCLUSION

None of the discussed options has demonstrated clear superiority over others, although direct comparisons are often difficult due to discrepancies in data collection and study methodologies. Future randomized clinical trials are warranted before definitive conclusions can be drawn.

Anterior Cervical Corpectomy and Fusion Using a Synthetic Hydroxyapatite Graft for Ossification of the Posterior Longitudinal Ligament

The significant complication rate associated with harvesting autologous iliac bone or fibula has encouraged development of alternative graft substitutes. In this study, the authors investigated the efficacy and safety of synthetic porous hydroxyapatite (HA) combined with local vertebral bone graft for use in anterior cervical corpectomy and fusion (ACCF) for the treatment of patients with ossification of the posterior longitudinal ligament (OPLL). Since 2006, twenty-five OPLL patients underwent ACCF using HA blocks (HA group). Hydroxyapatite blocks with 40% porosity were used for the 1-level ACCFs, and HA blocks with 15% porosity were used for the 2-level ACCFs. Clinical and radiological evaluation was performed with a minimum of 2-year follow-up. Outcomes were compared with those of 25 OPLL patients who underwent ACCFs using auto-fibula grafts at the authors' institution before 2006 (FBG group). Patients' demographic data were similar in the HA and FBG groups. Both groups demonstrated significant neurological improvements postoperatively. No difference was observed in operating time, whereas the intraoperative blood loss was significantly less in the HA group. The fusion rates in the HA group were comparable to those in the FBG group. The incidences of general complications were similar in the 2 groups; however, prolonged donor-site pain was observed in 9 (36.0%) cases in the FBG group. Based on the results of this study, ACCF using HA is a safe and efficacious method for the treatment of patients with OPLL as an alternative to conventional ACCF using autologous fibula bone grafting. [Orthopedics. 2017; 40(2):e334-e339.].

The Effect of Dynamic Versus Static Plating Systems on Fusion Rates and Complications in 1-Level and/or 2-Level Anterior Cervical Discectomy and Fusion: A Systematic Review

STUDY DESIGN

A systematic review.

OBJECTIVE

To determine the effect of plate design on fusion rates in patients undergoing a 1- and 2-level anterior cervical discectomy and fusion (ACDF).

METHODS

Articles published between January 1, 2002 and January 1, 2015 were systematically reviewed to determine the fusion rate of 1- and 2-level ACDFs using either a fully constrained or semiconstrained locking plate. Additional variables that were collected included the number of levels, the type of graft/cage used, the study design, the method for determining fusion, and complications.

RESULTS

Fifty-two articles and 3053 patients were included. No significant difference in the fusion rate for 1- and 2-level ACDF using a fully constrained plate (96.1%) and a semiconstrained plate (95.29%) was identified (P=0.84). No difference (P=0.85) in the total complication rate between fully constrained plates (3.20%) and semiconstrained plates (3.66%), or the rate of complications that required a revision (2.17% vs. 2.41%, P=0.82) was identified. However, semiconstrained plates had a nonsignificant increase in total dysphagia rates (odds ratio=1.660, P=0.28) and short-term dysphagia rates (odds ratio=2.349, P=0.10).

CONCLUSIONS

In patients undergoing a 1- or 2-level ACDF, there is no significant difference in the fusion or complication rate between fully constrained plates and semiconstrained plates.

LEVEL OF EVIDENCE

Level II-systematic review.

Nanocrystalline hydroxyapatite intervertebral cages induce fusion after anterior cervical discectomy and may be a safe alternative to PEEK or carbon fiber intervertebral cages

PURPOSE

Nanocrystalline hydroxyapatite (nHA) cages have emerged as a new alternative to carbon fiber or polyether ether ketone (PEEK) devices to promote intervertebral fusion. No evidence has been published to date regarding rates of fusion for these devices after anterior cervical discectomy and fusion (ACDF).

METHODS

Eight patients underwent one- or two-level ACDF with nHA intervertebral cages (Nanoss^®-Cervical, Pioneer^® Surgical Technology, Inc., Marquette, MI). Radiographs, neck disability index (NDI) and visual analog scores (VAS) for pain were taken preoperatively and at a minimum of 19 months postoperatively.

RESULTS

At an average follow-up of 21 months, all eight patients (100%) achieved fusion as assessed by plain radiographs. Reduction in preoperative symptomology was comparable to previously published data with a mean reduction of neck VAS of 3, arm VAS of 6 and NDI reduced by 27%. Radiographs showed clear evidence of bridging bone.

CONCLUSIONS

This series provides evidence that nHA intervertebral cages can successfully promote fusion after ACDF and may provide an alternative to carbon fiber and PEEK cages.

Bone substitutes and expanders in Spine Surgery: A review of their fusion efficacies

STUDY DESIGN

A narrative review of literature.

OBJECTIVE

This manuscript intends to provide a review of clinically relevant bone substitutes and bone expanders for spinal surgery in terms of efficacy and associated clinical outcomes, as reported in contemporary spine literature.

SUMMARY OF BACKGROUND DATA

Ever since the introduction of allograft as a substitute for autologous bone in spinal surgery, a sea of literature has surfaced, evaluating both established and newly emerging fusion alternatives. An understanding of the available fusion options and an organized evidence-based approach to their use in spine surgery is essential for achieving optimal results.

METHODS

A Medline search of English language literature published through March 2016 discussing bone graft substitutes and fusion extenders was performed. All clinical studies reporting radiological and/or patient outcomes following the use of bone substitutes were reviewed under the broad categories of Allografts, Demineralized Bone Matrices (DBM), Ceramics, Bone Morphogenic proteins (BMPs), Autologous growth factors (AGFs), Stem cell products and Synthetic Peptides. These were further grouped depending on their application in lumbar and cervical spine surgeries, deformity correction or other miscellaneous procedures viz. trauma, infection or tumors; wherever data was forthcoming. Studies in animal populations and experimental in vitro studies were excluded. Primary endpoints were radiological fusion rates and successful clinical outcomes.

RESULTS

A total of 181 clinical studies were found suitable to be included in the review. More than a third of the published articles (62 studies, 34.25%) focused on BMP. Ceramics (40 studies) and Allografts (39 studies) were the other two highly published groups of bone substitutes. Highest radiographic fusion rates were observed with BMPs, followed by allograft and DBM. There were no significant differences in the reported clinical outcomes across all classes of bone substitutes.

CONCLUSIONS

There is a clear publication bias in the literature, mostly favoring BMP. Based on the available data, BMP is however associated with the highest radiographic fusion rate. Allograft is also very well corroborated in the literature. The use of DBM as a bone expander to augment autograft is supported, especially in the lumbar spine. Ceramics are also utilized as bone graft extenders and results are generally supportive, although limited. The use of autologous growth factors is not substantiated at this time. Cell matrix or stem cell-based products and the synthetic peptides have inadequate data. More comparative studies are needed to evaluate the efficacy of bone graft substitutes overall.

A Prospective Randomized Clinical Trial Comparing Bone Union Rate Following Anterior Cervical Discectomy and Fusion Using a Polyetheretherketone Cage: Hydroxyapatite/B-Tricalcium Phosphate Mixture versus Hydroxyapatite/Demineralized Bone Matrix Mixture

Study Design

Prospective randomized noninferiority trial.

Purpose

To evaluate whether the union rate of anterior cervical discectomy and fusion (ACDF) using a polyetheretherketone (PEEK) cage filled with a mixture of hydroxyapatite (HA) and demineralized bone matrix (DBM) is inferior to that of a mixture of β-tricalcium phosphate (β-TCP) and HA.

Overview of Literature

There have been no clinical trials investigating the outcomes of a mixture of HA and DBM in a PEEK cage in ACDF.

Methods

Eighty-five eligible patients were randomly assigned to group B (n=43), in which a PEEK cage with a mixture of HA and DBM was used, or group C (n=42), in which a PEEK cage with a mixture of HA and β-TCP was used. The primary study endpoint was the fusion rate, which was assessed with dynamic radiographs and computed tomography (CT) scans. Secondary endpoints included pain intensity using a visual analogue scale, functional outcome using a neck disability index score, laboratory tests of inflammatory profiles, and the infection rate.

Results

Seventy-seven patients (38 in group B and 39 in group C) were included in the final analysis. One year postoperatively, bone fusion was achieved in 87% of group B patients and 87% of group C patients on dynamic radiographs, and 87% of group B patients and 72% of group C patients on CT scans (p=1.00 and 0.16, respectively). There were also no between-groups differences with respect to the secondary endpoints.

Conclusions

A HA/DBM mixture inside a PEEK cage can provide noninferior outcomes compared to a HA/TCP mixture in ACDF.