Osteogenic protein versus autologous interbody arthrodesis in the sheep thoracic spine. A comparative endoscopic study using the Bagby and Kuslich interbody fusion device

An alternative method to evaluate lumbar interbody fusion status focusing on position change of screw-rod constructs

OBJECTIVES

The evaluation of lumbar interbody fusion status is generally subjective and may differ among raters. The authors examined whether the assessment of position change of screw-rod constructs could be an alternative method for the evaluation of fusion status.

METHODS

Sixty-three patients undergoing lumbar interbody single-level fusion were retrospectively reviewed. Three-dimensional images of screw-rod constructs were created from baseline CT examination on the day after surgery and follow-up CT examinations (3-5 months, 6-11 months, and ≥ 12 months) and superposed, with position change of screw-rod constructs being evaluated by the distance between the 3-dimensional images at baseline and follow-up. The evaluation was repeated twice to confirm the reproducibility. Fusion status on follow-up CT examinations was assessed by three raters, where inter-rater reliability was evaluated with Fleiss' kappa. The results of the fusion status were classified into fusion and incomplete fusion groups in each timing of follow-up CT examinations, where the amount of position change was compared between the two groups.

RESULTS

The evaluation of position change was completely reproducible. The Fleiss' kappa (agreements) was 0.481 (69.4%). The medians of the amount of position change in fusion and incomplete fusion groups were 0.134 mm and 0.158 mm at 3-5 months (p = 0.21), 0.160 mm and 0.190 mm at 6-11 months (p = 0.02), and 0.156 mm and 0.314 mm at ≥ 12 months (p = 0.004).

CONCLUSIONS

The assessment of position change of screw-rod constructs at 6 months or more after surgery can be an alternative method for evaluating lumbar interbody fusion status.

KEY POINTS

• Lumbar interbody fusion status (satisfactory, incomplete, or failed) is associated with the quantification of position change of screw-rod in this study. • Reference values for the evaluation of position change in identifying interbody fusion status are provided. • Position change of screw-rod could be a supportive method for evaluating interbody fusion status.

Hydroxyapatite/collagen composite graft for posterior lumbar interbody fusion: a comparison with local bone graft

Background

Autologous bone has been used for posterior lumbar intervertebral fusion (PLIF). However, harvesting autologous bone graft is associated with donor site complications. We previously developed a hydroxyapatite/collagen (HAp/Col) composite as an osteoconductive artificial bone, characterized by having a highly porous structure with sponge‐like elasticity. This study aims to investigate the effectiveness of HAp/Col composite with bone marrow aspirate (BMA) as a graft substitute in PLIF for the treatment of lumbar spinal diseases.

Methods

This study prospectively investigated patients who received one-level PLIF. For the interbody fusion, two titanium cages were inserted. On the one side of interbody space, HAp/Col composite incorporated with BMA filling the titanium cage was grafted. On the other side, local bone graft (LBG) harvested during decompressive laminotomy was grafted and then one-level instrumentation using pedicle screws was performed. The target levels were at L2/3 in 2 cases, L3/4 in 3 cases, L4/5 in 36 cases, and L5/S in 5 cases. We evaluated clinical symptoms and radiological outcomes of 46 patients and compared the fusion status of HAp/Col composite with that of LBG.

Results

The 1-year postoperative CT evaluation demonstrated that, in the HAp/Col, a complete fusion was observed in 38 patients (82.6%), whereas in the LBG, a complete fusion was observed in 35 patients (76.1%). There were no statistical differences between the HAp/Col and LBG. In the HAp/Col, incomplete fusion was observed in five patients (10.9%) and non-fusion in two patients (4.3%), and in the LBG, incomplete fusion was observed in nine patients (19.6%) and non-fusion in two patients (4.3%). At 2 years after the surgery, complete fusion increased to 44 patients (95.7%) in the HAp/Col and 41 patients (89.1%) in the LBG. There were no significant differences in the clinical scores for lumbar spine between patients with fusion and non-fusion.

Conclusions

The HAp/Col composite with BMA in the titanium cage can be effectively used as an alternative to conventional autologous LBG for intervertebral spinal fusion.

Trial registration University hospital Medical Information Network, UMIN000045010, July 30th, 2021, Retrospectively registered, https://www.umin.ac.jp/english/.

Growth Factors, Carrier Materials, and Bone Repair

This chapter provides an overview of the growth factors active in bone regeneration and healing. Both normal and impaired bone healing are discussed, with a focus on the spatiotemporal activity of the various growth factors known to be involved in the healing response. The review highlights the activities of most important growth factors impacting bone regeneration, with a particular emphasis on those being pursued for clinical translation or which have already been marketed as components of bone regenerative materials. Current approaches the use of bone grafts in clinical settings of bone repair (including bone grafts) are summarized, and carrier systems (scaffolds) for bone tissue engineering via localized growth factor delivery are reviewed. The chapter concludes with a consideration of how bone repair might be improved in the future.

New Strategies in Enhancing Spinal Fusion

The biologic steps involved in creating a bony fusion between adjacent segments of the spine are a complex and highly coordinated series of events. There have been significant advancements in bone grafts and bone graft substitutes in order to augment spinal fusion. While autologous bone grafting remains the gold standard, allograft bone grafting, synthetic bone graft substitutes, and bone graft enhancers are appropriate in certain clinical situations. This article provides an overview of the basic biology of spinal fusion and strategies for enhancing fusion through innovations in bone graft material.

The Role of Allograft Bone in Foot and Ankle Arthrodesis and High-Risk Fracture Management

Allogenic bone graft has long been accepted as a standard of care in the surgical arthrodesis of the foot and ankle and treatment of certain high-risk, comminuted fracture types that have greater potential for delayed union or nonunion. It has been shown in multiple studies to be equivalent to autograft in regard to union rates without the morbidity associated with bone graft harvest. We present a retrospective study on the efficacy of an allogenic cancellous/periosteal cellular bone matrix with mesenchymal stem cells and angiogenic growth factors. The study includes a cohort of 41 procedures and 40 patients who underwent foot and ankle arthrodesis, fracture fixation, or a simultaneous combination of both. Radiographic consolidation of the fracture/fusion site was reviewed at regular intervals (first postoperative visit at 1 week and 4, 8, and 12 weeks and at regular intervals until healing was confirmed). Age, workmen's compensation insurance, diabetes, and nicotine use were evaluated as potential risk factors. Our retrospective study indicated that allograft bone has the potential to positively affect union rates in foot and ankle arthrodesis and certain high-risk fracture types that have potential for delayed union/nonunion. Levels of Evidence: Level IV.

Biomechanical comparison between cortical screw-rod construct versus pedicle screw-rod construct in transforaminal lumbar interbody fusion

OBJECTIVE

To compare construct stiffness of cortical screw (CS)-rod transforaminal lumbar interbody fusion (TLIF) construct (G2) versus pedicle screw (PS)-rod TLIF construct (G1) in the standardized porcine lumbar spine.

METHODS

Six porcine lumbar spines (L2-L5) were separated into 12 functional spine units. Bilateral total facetectomies and interlaminar decompression were performed for all specimens. Non-destructive loading to assess stiffness in lateral bending, flexion and extension as well as axial rotation was performed using a universal material testing machine.

RESULTS

PS and CS constructs were significantly stiffer than the intact spine except in axial rotation. Using the normalized ratio to the intact spine, there is no significant difference between the stiffness of PS and CS: flexion (1.41 ± 0.27, 1.55 ± 0.32), extension (1.98 ± 0.49, 2.25 ± 0.44), right lateral flexion (1.93 ± 0.57, 1.55 ± 0.30), left lateral flexion (2.00 ± 0.73, 2.16 ± 0.20), right axial rotation (0.99 ± 0.21, 0.83 ± 0.26) and left axial rotation (0.96 ± 0.22, 0.92 ± 0.25).

CONCLUSION

The CS-rod TLIF construct provided comparable construct stiffness to a traditional PS-rod TLIF construct in a 'standardized' porcine lumbar spine model.

Bone morphogenetic protein 7 and autologous bone graft in revision surgery for non-union after lumbar interbody fusion

BACKGROUND

Potential adverse and unknown long-term effects as well as additional costs limit the use of BMPs (Bone morphogenetic proteins) in primary fusion procedures. However, the proven osteoinductive properties render BMPs attractive for the attempt to reach fusion of symptomatic non-unions. The aim of this study is to evaluate the fusion rate and potential disadvantages of eptotermin alfa (rhBMP-7) used with autologous bone graft in revision procedures for lumbar pseudoarthrosis.

MATERIALS AND METHODS

At our institution, rhBMP-7 has been used to improve fusion rates in revision surgery for symptomatic pseudoarthrosis during the past 10 years. Eighty-four fusion procedures using rhBMP-7 between 08/2003 and 07/2011 were revisions due to symptomatic lumbar pseudoarthrosis. The surgical approach was posterior in three and combined anterior-posterior in 71 patients. Of those, 74 patients had either reached fusion or had follow-up of at least 39.5 months (range 21-80 months) in the case of pseudoarthrosis. These 74 patients have been included in a retrospective follow-up study.

RESULTS

In 60 patients (81.1 %) the rhBMP-7 procedure was successful. In 14 patients, pseudoarthrosis persisted or fusion was questionable. Of those patients 12 accounted for persisting L5-S1 non-union. Persisting non-unions were found in 26.7 % of the study after four or more segment instrumentations compared to the 16.9 % after mono-, bi-, or three-segment instrumentation, and in four of 14 patients with spondylodesis of three or more levels above a pseudoarthrotic lumbosacral junction. Adverse effects related to the use of eptotermin alfa were rare in this group with symptomatic ectopic bone formation in one patient.

CONCLUSIONS

Using rhBMP-7 with autologous bone graft in revisions for lumbar pseudoarthrosis via an anterior approach is safe and can lead to fusion even under unfavorable biomechanical conditions. However, successful outcome depends on the individual constellation. Treatment of non-unions of the lumbosacral junction remains especially difficult in cases with solid fusions above those pseudoarthrotic levels.

LEVEL OF EVIDENCE

4; retrospective follow-up study.

Imaging of lumbar spine fusion

This article reviews the imaging of lumbar spinal fusion and its major indications. The most common procedures are described for the purpose of allowing understanding of postoperative imaging. Imaging options are reviewed for preoperative workup, intraoperative guidance, and postoperative purposes. Examples of hardware integrity, fusion, and loosening are provided.

Radiographic changes in patients with pseudarthrosis after posterior lumbar interbody arthrodesis using carbon interbody cages: a prospective five-year study

BACKGROUND

The aim of this study was to demonstrate longitudinal radiographic changes at up to five years in patients with pseudarthrosis after posterior lumbar interbody arthrodesis using carbon interbody cages.

METHODS

From 2003 to 2006, prospective longitudinal radiographic and CT (computed tomography) scan evaluations were made at up to five years after posterior lumbar interbody arthrodesis using carbon interbody cages at one or two levels in 153 consecutive patients. At the one-year evaluation, seventeen patients with early pseudarthrosis at nineteen levels were selected as subjects on the basis of one or more of the following characteristics: complete absence of osseous bridging between the upper and lower vertebrae, angular motion of ≥5°, and/or radiolucent zones surrounding the implant. Angular motion, continuity of osseous bridging, grafted bone quantity, and radiolucent zones around the pedicle screws and cages were observed annually until five years.

RESULTS

The mean angular motion of five levels that exhibited ≥5° of motion at one year began to decrease significantly thereafter (p = 0.046), and no level showed movement of ≥5° at five years. The mean grade of the radiolucent zones around the screws on CT showed significant improvements at two years (p = 0.039) and three years (p < 0.01). The radiolucent zones around the screws disappeared at twelve of sixteen levels by five years, and the radiolucent zones around the cages disappeared in eleven of seventeen levels by five years. Of eighteen levels with early pseudarthrosis, seven (39%) were assessed as successfully fused at three years and twelve (67%) at five years. Four (80%) of five patients with a radiolucent zone of >1 mm around the entire cage on CT at one year showed continuing pseudarthrosis at five years, whereas only two (15%) of thirteen patients without this finding did (crude relative risk = 5.2; 95% confidence interval, 1.35 to 20.02). A radiolucent zone of >1 mm around the entire cage on CT at one year could be an early predictor of permanent pseudarthrosis (odds ratio = 123; 95% confidence interval, 1.03 to 14,680).

CONCLUSIONS

The interbody arthrodesis site in patients with early pseudarthrosis may begin to change to a successful fusion one or two years after surgery, with two-thirds of such patients exhibiting successful fusion five years after surgery. Final assessment of pseudarthrosis should be performed at least three years after surgery. A radiolucent zone of >1 mm around the entire interbody cage on CT at one year may require early additional surgery.

LEVEL OF EVIDENCE

Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.

Biological performance of a polycaprolactone-based scaffold plus recombinant human morphogenetic protein-2 (rhBMP-2) in an ovine thoracic interbody fusion model

PURPOSE

We develop a sheep thoracic spine interbody fusion model to study the suitability of polycaprolactone-based scaffold and recombinant human bone morphogenetic protein-2 (rhBMP-2) as a bone graft substitute within the thoracic spine. The surgical approach is a mini-open thoracotomy with relevance to minimally invasive deformity correction surgery for adolescent idiopathic scoliosis. To date there are no studies examining the use of this biodegradable implant in combination with biologics in a sheep thoracic spine model.

METHODS

In the present study, six sheep underwent a 3-level (T6/7, T8/9 and T10/11) discectomy with randomly allocated implantation of a different graft substitute at each of the three levels: (a) calcium phosphate (CaP) coated polycaprolactone-based scaffold plus 0.54 μg rhBMP-2 (b) CaP-coated PCL-based scaffold alone or (c) autograft (mulched rib head). Fusion was assessed at 6 months post-surgery.

RESULTS

Computed Tomographic scanning demonstrated higher fusion grades in the rhBMP-2 plus PCL-based scaffold group in comparison with either PCL-based scaffold alone or autograft. These results were supported by histological evaluations of the respective groups. Biomechanical testing revealed significantly higher stiffness for the rhBMP-2 plus PCL-based scaffold group in all loading directions in comparison with the other two groups.

CONCLUSION

The results of this study demonstrate that rhBMP-2 plus PCL-based scaffold is a viable bone graft substitute, providing an optimal environment for thoracic interbody spinal fusion in a large animal model.

A comparison of radiostereometric analysis and computed tomography for the assessment of lumbar spinal fusion in a sheep model

Study Design Prospective animal study.

Objective The aim of this animal study is to evaluate the accuracy of radiostereometric analysis (RSA) compared with computed tomographic (CT) scan in the assessment of spinal fusion after anterior lumbar interbody fusion (ALIF) using histology as a gold standard.

Methods Three non-adjacent ALIFs (L1–L2, L3–L4, and L5–L6) were performed in nine sheep. The sheep were divided into three groups of three sheep. All the animals were humanely killed immediately after having the last scheduled RSA. The lumbar spine was removed and in vitro fine cut CT and histopathology were performed.

Results Using histological assessment as the gold standard for assessing fusion, RSA demonstrated better results (100% sensitivity and 66.7% specificity; positive predictive value [PPV] = 27.3%, negative predictive value [NPV] =100.0%) compared with CT (66.7% sensitivity and 60.0% specificity [PPV = 16.7%, NPV = 93.8%]).

Conclusions RSA demonstrated higher sensitivity and specificity when compared with CT. Furthermore, RSA has the advantage of much lower radiation exposure compared with fine cut CT. Further studies are required to see if RSA remains superior to CT scan for the assessment spinal fusion in the clinical setting.

Bone Regeneration Based on Tissue Engineering Conceptions - A 21st Century Perspective

The role of Bone Tissue Engineering in the field of Regenerative Medicine has been the topic of substantial research over the past two decades. Technological advances have improved orthopaedic implants and surgical techniques for bone reconstruction. However, improvements in surgical techniques to reconstruct bone have been limited by the paucity of autologous materials available and donor site morbidity. Recent advances in the development of biomaterials have provided attractive alternatives to bone grafting expanding the surgical options for restoring the form and function of injured bone. Specifically, novel bioactive (second generation) biomaterials have been developed that are characterised by controlled action and reaction to the host tissue environment, whilst exhibiting controlled chemical breakdown and resorption with an ultimate replacement by regenerating tissue. Future generations of biomaterials (third generation) are designed to be not only osteoconductive but also osteoinductive, i.e. to stimulate regeneration of host tissues by combining tissue engineering and in situ tissue regeneration methods with a focus on novel applications. These techniques will lead to novel possibilities for tissue regeneration and repair. At present, tissue engineered constructs that may find future use as bone grafts for complex skeletal defects, whether from post-traumatic, degenerative, neoplastic or congenital/developmental "origin" require osseous reconstruction to ensure structural and functional integrity. Engineering functional bone using combinations of cells, scaffolds and bioactive factors is a promising strategy and a particular feature for future development in the area of hybrid materials which are able to exhibit suitable biomimetic and mechanical properties. This review will discuss the state of the art in this field and what we can expect from future generations of bone regeneration concepts.

Establishment and characterization of an open mini-thoracotomy surgical approach to an ovine thoracic spine fusion model

A large animal model is required for the assessment of minimally invasive, tissue-engineering-based approaches to thoracic spine fusion, with relevance to deformity correction surgery for human adolescent idiopathic scoliosis. Here, we develop a novel open mini-thoracotomy approach in an ovine model of thoracic interbody fusion that allows the assessment of various fusion constructs, with a focus on novel, tissue-engineering-based interventions. The open mini-thoracotomy surgical approach was developed through a series of mock surgeries, and then applied in a live sheep study. Customized scaffolds were manufactured to conform with intervertebral disc space clearances that were required of the study. Six male Merino sheep aged 4-6 years and weighing 35-45 kg underwent the procedure mentioned earlier and were alloted a survival timeline of 6 months. Each sheep underwent a three-level discectomy (T6/7, T8/9, and T10/11) with a randomly allocated implantation of a different graft substitute at each of the following three levels: (1) polycaprolactone (PCL)-based scaffold plus 0.54 μg recombinant human bone morphogenetic protein-2 (rhBMP-2); (2) PCL-based scaffold alone; or (3) autograft. The sheep were closely monitored postoperatively for signs of pain (i.e., gait abnormalities/teeth gnawing/social isolation). Fusion assessments were conducted postsacrifice using computed tomography and hard-tissue histology. All scientific work was undertaken in accordance with the study protocol that was approved by the Institute's committee on animal research. All six sheep were successfully operated on and reached the allotted survival timeline, thereby demonstrating the feasibility of the surgical procedure and postoperative care. There were no significant complications and during the postoperative period, the animals did not exhibit marked signs of distress according to the previously described assessment criteria. Computed tomographic scanning demonstrated higher fusion grades in the rhBMP-2 plus PCL-based scaffold group in comparison to either PCL-based scaffold alone or autograft. These results were supported by a histological evaluation of the respective groups. This novel open mini-thoracotomy surgical approach to the ovine thoracic spine represents a safe surgical method that can reproducibly form the platform for research into various spine-tissue-engineered constructs and their fusion-promoting properties.

[Fusion criteria for cages as vertebral body replacement in thoracolumbar fractures]

BACKGROUND

No commonly accepted criteria to evaluate bony incorporation of cages as vertebral body replacement in thoracolumbar fractures exist. The goal of this study was a thorough radiological evaluation of the fusion process in posterior-anterior stabilized fractures.

PATIENTS AND METHODS

In this study 35 patients were evaluated radiologically including computed tomography (CT) scanning and bone mineral density measurement inside the cages. Correction loss, cage subsidence and tilting, bone growth in and around the cages as well as bone mineral density were assessed. Fusion grading was assessed with defined criteria (i.e. bridging bone, bone growth through the cage, stability in functional X-rays and no radiolucent lines).

RESULTS

After 12 months minor subsidence and tilting of the cages had caused significant correction loss of the basal plate angle of 2.4° on average. Of the patients 20 (57%) fulfilled the criteria for complete or incomplete fusion and 5 (14%) showed no signs of bony fusion. Bone mineral density measurements were unreliable due to metallic artefacts.

CONCLUSIONS

The advocated criteria allow accurate assessment of bony incorporation of cages. Bony incorporation can be detected in and around the cages over time; however, only 57% of patients showed signs of bony fusion after 1 year.

Evaluation of the efficacy of Escherichia coli-derived recombinant human bone morphogenetic protein-2 in a mini-pig spinal anterior interbody fusion model

We evaluated the efficacy of Escherichia coli-derived recombinant human bone morphogenetic protein-2 (E-BMP-2) in a mini-pig model of spinal anterior interbody fusion. A total of 14 male mini-pigs underwent three-level anterior lumbar interbody fusion using polyether etherketone (PEEK) cages containing porous hydroxyapatite (HA). Four groups of cages were prepared: 1) control (n = 10 segments); 2) 50 μg E-BMP-2 (n = 9); 3) 200 μg E-BMP-2 (n = 10); and 4) 800 μg E-BMP-2 (n = 9). At eight weeks after surgery the mini-pigs were killed and the specimens were evaluated by gross inspection and manual palpation, radiological evaluation including plain radiographs and micro-CT scans, and histological analysis. Rates of fusion within PEEK cages and overall union rates were calculated, and bone formation outside vertebrae was evaluated. One animal died post-operatively and was excluded, and one section was lost and also excluded, leaving 38 sites for assessment. This rate of fusion within cages was 30.0% (three of ten) in the control group, 44.4% (four of nine) in the 50 μg E-BMP-2 group, 60.0% (six of ten) in the 200 μg E-BMP-2 group, and 77.8% (seven of nine) in the 800 μg E-BMP-2 group. Fusion rate was significantly increased by the addition of E-BMP-2 and with increasing E-BMP-2 dose (p = 0.046). In a mini-pig spinal anterior interbody fusion model using porous HA as a carrier, the implantation of E-BMP-2-loaded PEEK cages improved the fusion rate compared with PEEK cages alone, an effect that was significantly increased with increasing E-BMP-2 dosage.

Cite this article: Bone Joint J 2013;95-B:217–23.

The maturation of grafted bone after posterior lumbar interbody fusion with an interbody carbon cage: a prospective five-year study

We evaluated the maturation of grafted bone in cases of successful fusion after a one- or two-level posterior lumbar interbody fusion (PLIF) using interbody carbon cages. We carried out a five-year prospective longitudinal radiological evaluation of patients using plain radiographs and CT scans. One year after surgery, 117 patients with an early successful fusion were selected for inclusion in the study. Radiological evaluation of interbody bone fusion was graded on a 4-point scale. The mean grades of all radiological and CT assessments increased in the five years after surgery, and differences compared to the previous time interval were statistically significant for three or four years after surgery. Because the grafted bone continues to mature for three years after surgery, the success of a fusion should not be assessed until at least three years have elapsed. There were no significant differences in the longitudinal patterns of grafted bone maturity between iliac bone and local bone. However, iliac bone grafting may remodel faster than local bone.

BMP-7 IN ORTHOPEDIC APPLICATIONS: A REVIEW

In recent years, significant progress has been made on the research of Bone Morphogenetic Protein-7, BMP-7 (OP-1). BMP-7 is a growth- and differentiating-factor and a member of the TGF-β or Transforming Growth Factor-beta Superfamily. Ever since recombinantly produced human BMP-7 (rhBMP-7) became available in the early 1990s research in this area intensified. Many publications and presentations were issued detailing the ability of rhBMP-7 to induce new bone formation and to investigate this as an option to solve a wide variety of orthopedic problems.

BMP-7's activity in bone regeneration has been established through numerous animal trials. Work has been presented on the potency of rhBMP-7 in joint revision arthroplasty, fracture healing and spinal fusion. rhBMP-7 has been investigated in a prospective controled human trial as an alternative for autograft in the treatment of tibial non-unions. In the not too distant future surgeons may have a new tool available in their daily practice for stimulating regeneration of bone and other skeletal tissue, though still many question on issues like dosing, predictability of outcomes, suitable indications and surgical techniques remain yet unanswered.

Nell-1 protein promotes bone formation in a sheep spinal fusion model

Bone morphogenetic proteins (BMPs) are widely used as bone graft substitutes in spinal fusion, but are associated with numerous adverse effects. The growth factor Nel-like molecule-1 (Nell-1) is mechanistically distinct from BMPs and can minimize complications associated with BMP therapies. This study evaluates the efficacy of Nell-1 combined with demineralized bone matrix (DBM) as a novel bone graft material for interbody spine fusion using sheep, a phylogenetically advanced animal with biomechanical similarities to human spine. Nell-1+sheep DBM or Nell-1+heat-inactivated DBM (inDBM) (to determine the osteogenic effect of residual growth factors in DBM) were implanted in surgical sites as follows: (1) DBM only (control) (n=8); (2) DBM+0.3 mg/mL Nell-1 (n=8); (3) DBM+0.6 mg/mL Nell-1 (n=8); (4) inDBM only (control) (n=4); (5) inDBM+0.3 mg/mL Nell-1 (n=4); (6) inDBM+0.6 mg/mL Nell-1 (n=4). Fusion was assessed by computed tomography, microcomputed tomography, and histology. One hundred percent fusion was achieved by 3 months in the DBM+0.6 mg/mL Nell-1 group and by 4 months in the inDBM+0.6 mg/mL Nell-1 group; bone volume and mineral density were increased by 58% and 47%, respectively. These fusion rates are comparable to published reports on BMP-2 or autograft bone efficacy in sheep. Nell-1 is an independently potent osteogenic molecule that is efficacious and easily applied when combined with DBM.

When is a spine fused?

The ability to correctly diagnose spinal non-union is vital to our ability to diagnose and treat patients with new or recurrent symptoms following spine fusion and to accurately assess the efficacy of spine fusion techniques and technologies. Surgical exploration has traditionally been the gold-standard investigation for spinal non-union. As routine surgical exploration is impractical in the majority of patients the use of non-invasive radiologic methods of spine fusion assessment is necessary. The purpose of this paper is to outline the most common radiologic methods of spine fusion assessment including the strengths and limitations associated with each imaging modality. In addition we will review the best-available evidence for the use of radiologic investigations to diagnose spine non-unions. We will then provide recommendations for what we believe to be the best methods of diagnosing successful union of cervical interbody, lumbar interbody and lumbar posterolateral fusions that can be used by spine clinicians and researchers alike.

Autologous growth factors versus autogenous graft for anterior cervical interbody fusion: an in vivo caprine model

OBJECT

Using an in vivo caprine model, authors in this study compared the efficacy of autologous growth factors (AGFs) with autogenous graft for anterior cervical interbody arthrodesis.

METHODS

Fourteen skeletally mature Nubian goats were used in this study and followed up for a period of 16 weeks postoperatively. Anterior cervical interbody arthrodesis was performed at the C3-4 and C5-6 vertebral levels. Four interbody treatment groups (7 animals in each group) were equally randomized among the 28 arthrodesis sites: Group 1, autograft alone; Group 2, autograft + cervical cage; Group 3, AGFs + cervical cage; and Group 4, autograft + anterior cervical plate. Groups 1 and 4 served as operative controls. Autologous growth factors were obtained preoperatively from venous blood and were ultra-concentrated. Following the 16-week survival period, interbody fusion success was evaluated based on radiographic, biomechanical, and histological analyses.

RESULTS

All goats survived surgery without incidence of vascular or infectious complications. Radiographic analysis by 3 independent observers indicated fusion rates ranging from 9 (43%) of 21 in the autograft-alone and autograft + cage groups to 12 (57%) of 21 in the autograft + anterior plate group. The sample size was not large enough to detect any statistical significance in these observed differences. Biomechanical testing revealed statistical differences (p < 0.05) between all treatments and the nonoperative controls under axial rotation and flexion and extension loading. Although the AGF + cage and autograft-alone treatments appeared to be statistically different from the intact spine during lateral bending, larger variances and smaller relative differences precluded a determination of statistical significance. Histomorphometric analysis of bone formation within the predefined fusion zone indicated quantities of bone within the interbody cage ranging from 21.3 +/- 14.7% for the AGF + cage group to 34.5 +/- 9.9% for the autograft-alone group.

CONCLUSIONS

The results indicated no differences in biomechanical findings among the treatment groups and comparable levels of trabecular bone formation within the fusion site between specimens treated with autogenous bone and those filled with the ultra-concentrated AGF extract. In addition, interbody cage treatments appeared to maintain disc space height better than autograft-alone treatments.

Fusion rates and subsidence of morselized local bone grafted in titanium cages in posterior lumbar interbody fusion using quantitative three-dimensional computed tomography scans

STUDY DESIGN

Prospective, controlled study.

OBJECTIVE

To determine fusion rates, cage to bone contact area ratios, and subsidences using titanium cages filled with a local bone graft for posterior lumbar interbody fusion (PLIF).

SUMMARY OF BACKGROUND DATA

PLIF using decompressed local bone inserted in titanium cages combined with pedicle screw fixation is a popular procedure for treating lumbar spine degeneration. There is no report about cage to bone contact area ratios using titanium cages filled with a local bone graft for PLIF.

METHODS

PLIF using a titanium cage filled with excised laminar and facet joint bone with pedicle screw fixation was performed in 54 (78 levels) consecutive patients. Mean age at the time of surgery was 62.5 years. Radiographic assessments of posterior and anterior disc heights were performed. Three-dimensional thin-section computed tomography assessments of cage subsidences, fused area ratios of local bone inside cages, and overall fusion rates were analyzed.

RESULTS

Mean values of anterior and posterior disc heights at 1 year after surgery were significantly greater than mean preoperative disc heights. The fusion rate of cages over both upper and lower segment endplates was 96.2%. The ratios of fused areas of local bone inside cages exposed to upper and lower segment endplates were 46.7% and 52.2% in the coronal plane and 46.4% and 49.9% in the sagittal 3-dimensional computed tomography plane, respectively. And, subsidences of titanium cages at upper and lower segment endplates were 1.26 mm and 0.72 mm in the coronal plane and 1.04 mm and 0.53 mm in the sagittal plane, respectively.

CONCLUSION

The ratio of fused area of local bone inside cages at regions exposed to endplates was <50%, which is insufficient for physiologic load transmission. The authors recommend that additional bone should be grafted into the disc space or new bone bonding interbody spacer should be considered.

Mesenchymal stem cell allograft in revision foot and ankle surgery: a clinical and radiographic analysis

A review was conducted of 23 patients who underwent implantation of mesenchymal stem cell allograft for revision foot or ankle surgery. Composed of viable mesenchymal stem cells derived from cadaveric donor tissue, the graft had osteogenic, osteoinductive, and osteoconductive properties, and was capable of direct new bone formation at the site of implantation. In all of the cases, radiographic new bone formation was observed at the area of implantation and a 91.3% union rate was observed, and no evidence of graft rejection or complications associated with implantation were recorded. Wilcoxon rank sum tests were used to determine whether gender, diabetes, chronic renal insufficiency, neuropathy, number of previous surgeries, and smoking were associated with time to healing. Spearman's rank correlation coefficient was calculated in an effort to identify the influence of continuous numeric variables on the time to bone healing. Based on the outcomes observed in this retrospective study, it appears that mesenchymal stem cell allograft is a beneficial biological adjunct to bone healing, and serves as a suitable bone autograft substitute in revision foot and ankle surgery.

LEVEL OF CLINICAL EVIDENCE

4.

Revisional hindfoot arthrodesis

Salvage of a failed hindfoot arthrodesis is an extensive undertaking for the surgeon and patient. With increased morbidity and postoperative convalescence and complications, patients must understand the risk involved in this type of revisional surgery. This article provides a systematic approach to revisional hindfoot arthrodeses, focusing on patient evaluation, surgical technique, and postoperative treatment.

Subsidence of Cylindrical Cage (AMSLUtrade mark Cage) : Postoperative 1 Year Follow-up of the Cervical Anterior Interbody Fusion

OBJECTIVE

There are numerous reports on the primary stabilizing effects of the different cervical cages for cervical radiculopathy. But, little is known about the subsidence which may be clinical problem postoperatively. The goal of this study is to evaluate subsidence of cage and investigate the correlation between radiologic subsidence and clinical outcome.

METHODS

To assess possible subsidence, the authors investigated clinical and radiological results of the one-hundred patients who underwent anterior cervical fusion by using AMSLUtrade mark cage during the period between January 2003 and June 2005. Preoperative and postoperative lateral radiographs were measured for height of intervertebral disc space where cages were placed. Intervertebral disc space was measured by dividing the sum of anterior, posterior, and midpoint interbody distance by 3. Follow-up time was 6 to 12 months. Subsidence was defined as any change in at least one of our parameters of at least 3 mm.

RESULTS

Subsidence was found in 22 patients (22%). The mean value of subsidence was 2.21 mm, and mean subsidence rate was 22%. There were no cases of the clinical status deterioration during the follow-up period. No posterior or anterior migration was observed.

CONCLUSION

The phenomenon of subsidence is seen in substantial number of patients. Nevertheless, clinical and radiological results of the surgery were favorable. An excessive subsidence may result in hardware failure. Endplate preservation may enables us to control subsidence and reduce the number of complications.

The safety and efficacy of OP-1 (rhBMP-7) as a replacement for iliac crest autograft in posterolateral lumbar arthrodesis: a long-term (>4 years) pivotal study

STUDY DESIGN

Randomized controlled trial comparing OP-1 (rhBMP-7) with iliac crest autograft in patients with symptomatic degenerative spondylolisthesis and spinal stenosis treated with decompression and uninstrumented posterolateral arthrodesis.

OBJECTIVE

To determine the safety and the clinical and radiographic efficacy of OP-1 (rhBMP-7) Putty as compared with an iliac crest bone autograft control in uninstrumented, single-level posterolateral spinal arthrodesis.

SUMMARY OF BACKGROUND DATA

Preclinical and preliminary clinical data have demonstrated successful fusion and clinical outcomes with the use of OP-1 Putty in posterolateral spinal arthrodesis. No prior randomized controlled trial with adequate study power has been performed.

METHODS

A total of 335 patients were randomized in 2:1 fashion to receive either OP-1 Putty or autograft in the setting of an uninstrumented posterolateral arthrodesis performed for degenerative spondylolisthesis and symptomatic spinal stenosis. Patients were observed serially with radiographs, clinical examinations, and appropriate clinical indicators, including ODI, Short-Form 36, and visual analog scale scores. Serum samples were examined at regular intervals to assess the presence of antibodies to OP-1. The primary end point, Overall Success, was analyzed at 24 months. The study was extended to include additional imaging data and long-term clinical follow-up at 36+ months. At the 36+ month time point, CT scans were obtained in addition to plain radiographs to evaluate the presence and location of new bone formation. Modified Overall Success, including improvements in ODI, absence of retreatment, neurologic success, absence of device-related serious adverse events, angulation and translation success, and new bone formation by CT scan (at 36+ months), was then calculated using the 24-month primary clinical endpoints, updated retreatment data, and CT imaging and radiographic end points.

RESULTS

OP-1 Putty was demonstrated to be statistically equivalent to autograft with respect to the primary end point of modified overall success. The use of OP-1 Putty when compared to autograft was associated with statistically lower intraoperative blood loss and shorter operative times. Although patients in the OP-1 Putty group demonstrated an early propensity for formation of anti-OP-1 antibodies, this resolved completely in all patients with no clinical sequelae.

CONCLUSION

OP-1 Putty is a safe and effective alternative to autograft in the setting of uninstrumented posterolateral spinal arthrodesis performed for degenerative spondylolisthesis and symptomatic spinal stenosis.

The clinical use of enriched bone marrow stem cells combined with porous beta-tricalcium phosphate in posterior spinal fusion

Cytotherapy for bone regeneration has not been widely used clinically. A new method based on enriched bone-marrow-derived mesenchymal stem cells (MSCs) combined with porous beta-tricalcium phosphate (beta-TCP) was used for posterior spinal fusion in 41 patients. The aim of the present study was to assess the clinical feasibility of peri-operative bone marrow stem cell enrichment and their combination with tricalcium phosphate. About 252 ml marrow per patient was harvested from bilateral iliac crest, the enriched MSCs were produced by a cell processor peri-operatively, then combined with porous beta-TCP granules by a negative pressure and a short-time incubation in the meantime of conventional operation, which were finally implanted back into the patient. About 45 ml enriched MSC suspension was collected, and 78+/-16% of MSCs were recovered. By enrichment technique, the number of colony-forming units which expressed alkaline phosphatase (CFUs-ALP+, to estimate the prevalence of MSCs) was increased 4.3 times; the increasing folds of bone marrow nucleated cells (NCs) and MSCs had a positive correlation. The natural log (ln) of MSC number declined with age, and also, the MSC number of younger subjects (< or =40 years) was more than that of older ones (>40 years), but none for NCs. The number of NCs and MSCs was not different significantly between men and women. However, the patients with thoracolumbar fracture (TLF) had significantly more MSCs than those with degenerative disc disease (DDD), but not for NCs. On the other hand, enriched MSCs could adhere to the wall of porous beta-TCP within 2h combination, and proliferate well during culture in vitro. After 34.5 months, 95.1% cases had good spinal fusion results. None of the samples before grafting was positive in bacterial culture. Only four patients had a little exudation or moderate swelling in their wounds, and recovered with conservative treatment.

The safety and efficacy of OP-1 (rhBMP-7) as a replacement for iliac crest autograft for posterolateral lumbar arthrodesis: minimum 4-year follow-up of a pilot study

BACKGROUND CONTEXT

Although autogenous bone is still considered to be the gold standard graft material for promoting spinal fusion, other bone graft substitutes have been developed in an attempt to improve arthrodesis rates and avoid the complications associated with the procurement of autograft. The bone morphogenetic proteins (BMPs) represent a family of osteoinductive growth factors that are known to stimulate the osteoblastic differentiation of stem cells. Osteogenic protein-1 (OP-1) Putty is a commercially available BMP preparation that is already approved for use in humans. Previous clinical studies involving patients with degenerative spondylolisthesis have reported that the efficacy and safety of OP-1 Putty is comparable to that of autograft at both 1- and 2-year follow-up.

PURPOSE

The purpose of this study was to evaluate the intermediate-term efficacy and safety of OP-1 Putty as an alternative to autogenous bone by comparing the 4-year radiographic, clinical, and safety data of these same patients who underwent decompression and uninstrumented fusion with either OP-1 Putty or iliac crest autograft.

STUDY DESIGN/SETTING

A prospective, randomized, controlled, multicenter clinical pilot study.

PATIENT SAMPLE

Thirty-six patients undergoing decompressive laminectomy and single-level uninstrumented fusion for degenerative spondylolisthesis and symptomatic spinal stenosis were randomized in a 2:1 fashion to receive either OP-1 Putty (24 patients) or autogenous iliac crest bone graft (12 patients).

OUTCOME MEASURES

Patient-reported outcome measures consisting of Oswestry Disability Index and Medical Outcomes Study 36-Item Short Form Health Survey (SF-36) scores were used to evaluate clinical efficacy. Perioperative data including operative time, estimated blood loss, and duration of hospital stay were also recorded for each surgery. Postoperatively, a neurological examination and an assessment of donor-site pain (if applicable) were performed at every follow-up visit. Radiographic fusion success was defined as the presence of continuous bridging bone formation between the transverse processes at the level of the spondylolisthesis with minimal motion evident on dynamic lateral x-ray films. The primary efficacy endpoint was the overall success rate, a composite measure derived from both radiographic and clinical parameters. The safety of OP-1 Putty was confirmed by comparing the nature and frequency of all adverse events and complications that were prospectively observed in either of the groups.

METHODS

Thirty-six patients with degenerative spondylolisthesis and symptoms of neurogenic claudication underwent decompressive laminectomy and single-level uninstrumented fusion with either OP-1 Putty or autograft. All patients were evaluated at 6 weeks and 3, 6, 9, 12, and 24 months, after which time they were instructed to return on a yearly basis. Multiple neuroradiologists blinded to the assigned treatment reviewed static and dynamic X-ray films with digital calipers to assess fusion status according to the presence of continuous bridging bone across the transverse processes as well as the amount of residual motion evident at the level of interest. Oswestry Disability Index surveys and SF-36 questionnaires were used to assess clinical outcomes.

RESULTS

At the 48-month time point, complete radiographic and clinical data were available for 22 of 36 patients (16 OP-1 Putty and 6 autograft) and 25 of 36 patients (18 OP-1 Putty and 7 autograft), respectively. Radiographic evidence of a solid arthrodesis was present in 11 of 16 OP-1 Putty patients (68.8%) and 3 of 6 autograft patients (50%). Clinically successful outcomes defined as at least a 20% improvement in preoperative Oswestry scores were experienced by 14 of 19 OP-1 Putty patients (73.7%) and 4 of 7 autograft patients (57.1%); these clinical findings were corroborated by similar increases in SF-36 scores. The respective overall success rates of the OP-1 Putty and autograft group were 62.5% and 33.3%. In this study, there were no incidents of local or systemic toxicity, ectopic bone production, or other adverse events directly related to the use of OP-1 Putty.

CONCLUSION

Despite the challenges associated with obtaining a solid uninstrumented fusion in patients with degenerative spondylolisthesis, the rates of radiographic fusion, clinical improvement, and overall success associated with the use of OP-1 Putty were at least comparable to that of the autograft controls for at least 48 months after surgery. These results appear to validate the short-term results previously reported for OP-1 Putty and suggest that this material may potentially represent a viable bone graft substitute for certain fusion applications.

CT-based classification of long spinal allograft fusion

Anterior column reconstruction of the thoracolumbar spine by structural allograft has an increased potential for biological fusion when compared to synthetic reconstructive options. Estimation of cortical union and trabecular in-growth is, however, traditionally based on plain radiography, a technique lacking in sensitivity. A new assessment method of bony union using high-speed spiral CT imaging is proposed which reflects the gradually increasing biological stability of the construct. Grade I (complete fusion) implies cortical union of the allograft and central trabecular continuity. Grade II (partial fusion) implies cortical union of the structural allograft with partial trabecular incorporation. Grade III (unipolar pseudarthrosis) denotes superior or inferior cortical non-union of the central allograft with partial trabecular discontinuity centrally and Grade IV (bipolar pseudarthrosis) suggests both superior and inferior cortical non-union with a complete lack of central trabecular continuity. Twenty-five patients underwent anterior spinal reconstruction for a single level burst fracture between T4 and L5. At a minimum of two years follow up the subjects underwent high-speed spiral CT scanning through the reconstructed region of the thoracolumbar spine. The classification showed satisfactory interobserver (kappa score = 0.91) and intraobserver (kappa score = 0.95) reliability. The use of high-speed CT imaging in the assessment of structural allograft union may allow a more accurate assessment of union. The classification system presented allows a reproducible categorization of allograft incorporation with implications for treatment.

A study of the role of nell-1 gene modified goat bone marrow stromal cells in promoting new bone formation

Nell-1 is a recently discovered secreted protein with the capacity to promote osteoblastic calvarial cell differentiation and mineralization and induce calvarial bone overgrowth and regeneration in various rodent models. However, the extent of Nell-1 osteoinductivity in large animal cells remains unknown. The objective of the study was to evaluate the feasibility of adenoviral encoding Nell-1 (AdNell-1) gene transfer into primary adult goat bone marrow stromal cells (BMSCs) in vitro and in vivo and to compare the osteoinductive effects with those produced by bone morphogenetic protein-2 (BMP-2), a well established osteoinductive molecule currently utilized for regional gene therapy. AdNell-1-transduced BMSCs expressed Nell-1 protein and underwent osteoblastic differentiation within 2 weeks in vitro, which is comparable to AdBMP-2. After intramuscular injection of nude mice, the AdNell-1- and AdBMP-2-transduced BMSCs revealed new bone formation, while untransduced or AdLacZ-transduced BMSCs showed mainly fibrotic tissue proliferation. At 4 weeks, BMP-2 induced significantly larger bone mass with a mature bone margin and central cavity filled with primarily fatty marrow tissue. Nell-1 samples had significantly less bone mass but were histologically similar to newly formed trabecular bone mixed with chondroid bone-like areas verified by type X collagen (ColX) immunohistochemistry. This distinct difference in histomorphology from the bone mass induced by BMP-2 suggests that there is a potential clinical role/advantage for Nell-1 in skeletal tissue engineering and regeneration.

Effects of direct current electrical stimulation on gene expression of osteopromotive factors in a posterolateral spinal fusion model

STUDY DESIGN

An in vivo model was used to determine levels of mRNA expression in response to direct current (DC) electrical stimulation in a rabbit posterolateral fusion model.

OBJECTIVES

This study tested the possibility that DC stimulation at the surgery site would increase expression of genes related to bone formation relative to expression in autograft alone.

SUMMARY OF BACKGROUND DATA

DC electrical stimulation as an adjunct treatment in spinal surgery has shown increased fusion rates when compared with autograft alone, yet the biology of such treatment is not fully understood.

METHODS

Thirty New Zealand White rabbits were entered into the study. A posterolateral, intertransverse process fusion was performed bilaterally at L4-L5, with autogenous bone graft. An implantable DC stimulator was placed across the decorticated transverse processes before placement of autograft. Animals were killed at 3, 7, 14, 21, and 28 days. mRNA levels of BMP-2, 4, 6, 7, VEGF, FGF-2, TGF-beta, ALK-2, and ALK-3 were evaluated with real-time RT-PCR.

RESULTS

mRNA expression was significantly higher in the DC stimulated animals versus the control animals for several of the genes studied. In particular, levels of mRNA were elevated for BMP-2, BMP-6, and BMP-7.

CONCLUSIONS

This study shows for the first time that DC stimulation results in a sustained increase of multiple osteogenic genes, suggesting that the biologic mechanism for the DC-induced increase in the rate and extent of bone formation observed clinically may be mediated by the up-regulation of these osteoinductive factors.

Lumbar body fusion with a bioresorbable cage in a goat model is delayed by the use of a carboxymethylcellulose-stabilized collagenous rhOP-1 device

The purpose of this study was to evaluate the efficacy of recombinant human osteogenic protein-1 (rhOP-1) with a carboxymethylcellulose-stabilized collagenous carrier as a bone graft substitute for instrumented lumbar spinal fusion in an established goat model. Twenty goats received a resorbable poly-L-lactic acid (PLLA) interbody cage packed with either rhOP-1 and its carrier or autologous bone graft. The carrier material was bovine collagen type-1 stabilized with carboxymethylcellulose. The fusion segments were retrieved at 3 or 6 months postimplantation and evaluated by radiographic and histologic analyses. The rhOP-1 graft substitute, used in combination with the resorbable PLLA cage, showed inferior results as compared to autologous bone graft in the goat lumbar fusion model. Whereas four out of five segments from the autograft group were fused after 6 months, none of the four segments receiving the rhOP-1 graft substitute were fused at this time point. Bone ingrowth into the cage was delayed or absent in the experimental group, whereas all autograft specimens showed advanced bone ingrowth (3 months) or fusion (6 months). We suggest that the fusion process was inhibited, because cells were unable to penetrate the rhOP-1 graft material. This led to delayed bone formation and in some cases inadequate tissue formation.

Biomechanical study on the effect of five different lumbar reconstruction techniques on adjacent-level intradiscal pressure and lamina strain

OBJECT

The objectives of this study were to compare the biomechanical effects of five lumbar reconstruction models on the adjacent segment and to analyze the effects of three factors: construct stiffness, sagittal alignment, and the number of fused segments.

METHODS

Nondestructive flexion-extension tests were performed by applying pure moments to 10 calf spinal (L3-S1) specimens. One-segment (L5-6) or two-segment (L5-S1) posterior fusion methods were simulated: 1) one-segment posterolateral fusion (PLF); 2) one-segment PLF with interbody fusion cages (one-segment PLIF/PLF); 3) two-segment PLF; 4) two-segment PLIF/PLF; and 5) two-segment PLF in kyphosis (two-segment kyphotic PLF). The range of motion (ROM) of the reconstructed segments, intradiscal pressure (IDP), and lamina strain in the upper (L4-5) adjacent segment were analyzed. The ROM was significantly decreased in the PLIF/PLF models compared with that in the PLF alone models after both the one- and two-segment fusions. If the number of fused segments was increased, the pressure and strains were also increased in specimens subjected to the PLIF/PLF procedure, more so than the PLF-alone procedure. In the one-segment PLIF/PLF model the authors observed a reduced IDP and lamina strain compared with those in the kyphotic two-segment PLF model despite the latter's higher levels of initial stiffness.

CONCLUSIONS

If the number of fused levels can be reduced by using PLIF to correct local kyphosis, then this procedure may be valuable for reducing adjacent-segment degenerative changes.

Does bioresorbable cage material influence segment stability in spinal interbody fusion?

To reduce long term complications associated with nonresorbable interbody fusion cages, bioresorbable cages are being developed. We investigated the influence of bioresorbable cage material on segment stability, intervertebral disc height and fusion in vivo using radiostereometric analysis comparing 70/30 poly(L-lactide-co-D,L-lactide) (PLDLLA) cages with titanium cages. Twenty-eight goats were randomized to receive PLDLLA (n = 21) or a titanium control (n = 7) cage at L3-L4. Range of motion for flexion and extension and change in intervertebral disc height were measured before and after surgery and at followup (3, 6, and 12 months). Fusion was graded with a validated radiographic score. Although the PLDLLA cage could not provide the optimal environment for a successful high fusion rate, the range of motion of the PLDLLA segments gradually decreased in time and was similar to the titanium control group at 12 months. In addition the decrease of intervertebral disc height was similar for both PLDLLA (1.4 +/- 0.8 mm) and titanium (1.3 +/- 1.0 mm) specimens. Both results showed a bioresorbable cage does not lead to less decrease of motion or more loss of intervertebral disc height in time compared to titanium. This study therefore supports further development of a bioresorbable cage concept.

A prospective randomized study of posterolateral lumbar fusion using osteogenic protein-1 (OP-1) versus local autograft with ceramic bone substitute: emphasis of surgical exploration and histologic assessment

STUDY DESIGN

A prospective, randomized and controlled study.

OBJECTIVES

To evaluate the osteoinductive property of Osteogenic Protein-1 (OP-1 or BMP-7) and fusion rate in human instrumented posterolateral lumbar fusion through radiographic examination, surgical exploration, and histologic assessment.

SUMMARY OF BACKGROUND DATA

The use of osteoinductive agents is a current topic in spinal fusion. Numerous preclinical investigations have demonstrated efficacy of osteoinductive proteins in spinal fusion, but few human clinical studies have been reported.

METHODS

Nineteen patients with L3-L4 or L4-L5 degenerative spondylolisthesis underwent posterolateral lumbar fusion using pedicle screw instrumentation. The patients were randomized to receive either OP-1 Putty (3.5 mg OP-1/g of collagen matrix per side) alone (n = 9), or local autograft with HA-TCP granules (n = 10). Fusion status was evaluated using plain radiography and CT scan. Radiographic fusion criteria included less than 5 degrees of angular motion, less than 2 mm of translation, and evidence of bridging bone in the posterolateral lumbar area in which the graft materials were placed following decortication. After a minimum 1-year follow-up, the patients who showed radiographic evidence of fusion underwent instrumentation removal and surgical exploration of the fusion site. Biopsy specimens were taken from the fusion mass and evaluated histologically.

RESULTS

Radiographic fusion rate was 7 of 9 OP-1 patients and 9 of 10 control patients. Based on surgical exploration of these 16 patients, new bone formation was macroscopically observed in the posterolateral lumbar region in all cases; however, solid fusion was observed in 4 of 7OP-1 and 7 of 9 HA-TCP/autograft patients. Histologic assessment demonstrated viable bone in 6 of 7 OP-1 patients. All the control (HA-TCP/autograft) specimens contained viable bone and fibrous tissue surrounding ceramic granules, suggesting slow incorporation of the graft material.

CONCLUSIONS

In a human posterolateral lumbar spine trial, OP-1 reliably induced viable amounts of new bone formation, but the fusion success rate evaluated by surgical exploration was only 4 of 7.

Application of bone morphogenetic proteins in spinal fusion

We are now entering an exciting new era in spinal surgery where the inherent osteoinductive capacity of the body has been harnessed for bone formation for therapeutic purposes. Recombinant bone morphogenetic proteins have been extensively studied in both the pre-clinical and clinical arena for spinal fusion with considerable success. The challenges facing spine surgeons now is the development of site-specific carriers and optimal doses for these growth factors. This review highlights the recent advances in this regard.

Comparison of two interbody fusion cages for posterior lumbar interbody fusion in a cadaveric model

Although the Brantigan cage and Bagby and Kuslich (BAK) cage have different geometrical characteristics, clinical observations suggest that they are equally effective in restoring disc height and stability across the involved spinal segments. This study was designed to compare their performance as posterior lumbar interbody fusion devices at two levels in fresh ligamentous cadaver lumbar spines (L2-S1). After mounting in a testing frame, the three-dimensional load-displacement behaviour of each vertebra was quantified using the Selspot II Motion Measurement System for; the intact state, posterior decompression, and stabilisation, using a pair of Brantigan or BAK cages across L4-S1, additional stabilisation using Isola spinal instrumentation across L4-S1, and cyclic loading in flexion/extension. In the "cage-only" state, the Brantigan cage did not restore the stability in right axial rotation, whereas the BAK cage not only restored stability in all six directions but also improved lateral bending. After implanting the posterior instrumentation, both groups exhibited similar stability, and cyclic loading did not alter this. Although the Brantigan cage appears less effective than the BAK cage, implantation of posterior instrumentation significantly improves stability and reduces the differences between them. This underscores the need to use posterior instrumentation to achieve a higher initial stability.

Bone reconstruction: from bioceramics to tissue engineering

Over the past 30 years, an enormous array of biomaterials proposed as ideal scaffolds for cell growth have emerged, yet few have demonstrated clinical efficacy. Biomaterials, regardless of whether they are permanent or biodegradable, naturally occurring or synthetic, need to be biocompatible, ideally osteoinductive, osteoconductive, integrative, porous and mechanically compatible with native bone to fulfill their desired role in bone tissue engineering. These materials provide cell anchorage sites, mechanical stability and structural guidance and in vivo, provide the interface to respond to physiologic and biologic changes as well as to remodel the extracellular matrix in order to integrate with the surrounding native tissue. Calcium phosphate ceramics and bioactive glasses were introduced more than 30 years ago as bone substitutes. These materials are considered bioactive as they bond to bone and enhance bone tissue formation. The bioactivity property has been attributed to the similarity between the surface composition and structure of bioactive materials, and the mineral phase of bone. The drawback in using bioactive glasses and calcium phosphate ceramics is that close proximity to the host bone is necessary to achieve osteoconduction. Even when this is achieved, new bone growth is often strictly limited because these materials are not osteoinductive in nature. Bone has a vast capacity for regeneration from cells with stem cell characteristics. Moreover, a number of different growth factors including bone morphogenetic proteins, have been demonstrated to stimulate bone growth, collagen synthesis and fracture repair both in vitro and in vivo. Attempts to develop a tissue-engineering scaffold with both osteoconductivity and osteoinductivity have included loading osteoinductive proteins and/or osteogenic cells on the traditional bioactive materials. Yet issues that must be considered for the effective application of bioceramics in the field of tissue engineering are the degree of bioresorption and the poor mechanical strength. The synthesis of a new generation of biomaterials that can specifically serve as tissue engineering scaffolds for drug and cell delivery is needed. Nanotechnology can provide an alternative way of processing porous bioceramics with high mechanical strength and enhanced bioactivity and resorbability.

Comparison of OP-1 Putty (rhBMP-7) to iliac crest autograft for posterolateral lumbar arthrodesis: a minimum 2-year follow-up pilot study

STUDY DESIGN

A prospective, randomized, controlled, multicenter clinical study.

OBJECTIVE

To compare the safety and clinical and radiographic outcomes of OP-1 (BMP-7) Putty to autogenous iliac crest bone graft in a population of patients undergoing laminectomy and posterolateral fusion for symptomatic lumbar stenosis associated with degenerative spondylolisthesis.

SUMMARY OF BACKGROUND DATA

Although the existing preclinical and clinical data suggest that OP-1 is able to achieve osteoinduction and clinical fusion in a variety of situations, the efficacy of this recombinant protein in a clinical spine fusion population has not been fully elucidated. This study directly compares the efficacy and safety of OP-1 putty to autograft bone for arthrodesis in patients with symptomatic stenosis in association with degenerative spondylolisthesis.

METHODS

Thirty-six patients with degenerative lumbar spondylolisthesis and symptoms of neurogenic claudication underwent laminectomy, bilateral medial facetectomy, and posterolateral fusion using either iliac crest autograft or OP-1 Putty. Oswestry scores and SF-36 questionnaires were used to determine the clinical response to treatment. Independent, blinded neuroradiologists reviewed both static and dynamic radiographs to determine the fusion status. Successful fusion was declared whenthe presence of continuous bridging bone between the transverse processes was observed and less than 5 degrees of angular motion and 2 mm of translational movement was measured using digital calipers.

RESULTS

Efficacy data were tabulated for 27 patients at the 24-month time point and an additional 4 patients (without evaluable 24-month results) at the 36-month time point. One patient was not evaluable for radiology, so the data reflect clinical information for 31 patients and radiology for 30 patients. Clinical success, defined as a 20% improvement in the preoperative Oswestry score, was achieved by 17 of 20 (85%) OP-1 Putty patients and 7 of 11 (64%) autograft patients. A successful posterolateral fusion was achieved in 11 of 20 (55%) OP-1 Putty patients and 4 of 10 (40%) autograft patients. SF-36 scores showed similar clinical improvement in both groups. No systemic toxicity, ectopic bone formation, recurrent stenosis, or other adverse events specifically related to the use of the OP-1 Putty implant were observed.

CONCLUSION

This study represents the first clinical trial to demonstrate the safety and similarity of OP-1 Putty as a replacement for autogenous bone graft in the posterolateral fusion environment with a minimum of 2-year follow-up. OP-1 Putty was able to achieve osteoinduction leading to a radiographically solid fusion in the absence of autogenous iliac crest bone graft in 55% of the patients at 24 and 36 months. These results compare favorably to the historical fusion rates reported for uninstrumented arthrodesis in this challenging clinical scenario.

Bioresorbable polymers: heading for a new generation of spinal cages

The use of polymer-based bioresorbable materials is now expanding to the realm of spinal interbody fusion. Bioresorbable polymers have important advantages over metals, because they are temporary, much less stiff, and radiolucent. Most promising is a group of alpha-polyesters, in particular polylactide acids (PLAs). Their biocompatibility is excellent, and they have sufficient stiffness and strength to provide initial and intermediate-term stability required for bone healing. However, polylactides have characteristics that make them vulnerable to complications if not properly controlled. Degradation rate strongly depends on polymer type, impurities, manufacturing process, sterilization, device size, and the local environment. The fact that larger implants degrade faster is contra-intuitive, and should be considered in the design process. Also optimal surgical techniques, such as careful bone bed preparation, are required for a successful application of these materials. The purpose of this paper is to highlight the specific properties of these bioresorbable polymers and to discuss their potential and limitations. This is illustrated with early preclinical and clinical data.Bioresorbable cage technology is just emerging: their time-engineered degradation characteristics allow controlled dynamization in interbody applications, facilitating spinal fusion. Their radiolucency improves image assessment of fusion healing. Acceptance and use of bioresorbable implants may increase as further research and clinical studies report on their safety, efficacy, and proper usage.

Animal models for spinal fusion

Animal models for spinal fusion are essential for preclinical testing of new fusion methods and adjuncts. They allow for control of individual variables and quantification of outcome measures. Model characteristics are considered. Preclinical experiments to evaluate proof of concept, feasibility, and efficacy are generally studied in an orderly progression from smaller to larger animal models with an evolving cascade of evidence which has become known as the "burden of proof". Methods of fusion analysis include manual palpation, radiographs, computed tomography, histology, biomechanical testing, and molecular analysis. Models which have been developed in specific species are reviewed. This sets the stage for the interpretation of studies evaluating bone graft materials such as allograft, demineralized bone matrices, bone morphogenetic proteins, ceramics, and others with consideration of the variables affecting their success. As evidence accumulates, clinical trials and applications are defined.

Interkorporelle Metallimplantate („Cages“) bei lumbalen Spondylodesen

Over the last 15 years, interbody metal implants have become commonly used worldwide for lumbar interbody fusion. The so called "cages" are made of metal or absorbable materials. By using different surgical techniques, they can be implanted either regularly or via endoscopy. The published results on surgical techniques using cages for the lumbar spine show, in most cases and with or without additional instrumentation, rates of fusion of more than 90%. It seems that the use of osteoinductive substances (especially BMP) leads to even better results. Dorsoventral fusion with internal fixation and bone show the same rate of consolidation, but the advantages of cages are primarily in the maintenance of the distraction and the possibility of a single surgical procedure without additional instrumentation (including endoscopy), and in a lower donor side morbidity.

Bone morphogenic proteins: applications in spinal surgery

The prospect of predictable and reliable oseteogenesis without the need for secondary bone grafting to treat a wide spectrum of spinal disorders is tremendously appealing. Recombinant human bone morphogenic proteins (rhBMP) have been the subject of extensive basic science, animal, and clinical research as a potential therapeutic modality to promote bony fusion. Animal studies and prospective, randomized clinical trials have demonstrated the efficacy of rhBMPs as an adjunct or substitute to autogenous bone graft in the specific treatment of certain spinal conditions. The future role of rhBMPs in spinal surgery applications remains to be determined and will be dependent upon future investigations evaluating 1) the efficacy in a variety of spinal conditions and environments, 2) the optimal dose and delivery system, 3) the long-term safety profile (immunogenicity, antibody formation), and 4) the cost effectiveness of these therapeutic growth factors.

Polyetheretherketone as a biomaterial for spinal applications

Threaded lumbar interbody spinal fusion devices (TIBFD) made from titanium have been reported to be 90% effective for single-level lumbar interbody fusion, although radiographic determination of fusion has been intensely debated in the literature. Using blinded radiographic, biomechanic, histologic, and statistical measures, we evaluated a radiolucent polyetheretherketone (PEEK)-threaded interbody fusion device packed with autograft or rhBMP-2 on an absorbable collagen sponge in 13 sheep at 6 months. Radiographic fusion, increased spinal level biomechanical stiffness, and histologic fusion were demonstrated for the PEEK cages filled with autograft or rhBMP-2 on a collagen sponge. No device degradation or wear debris was observed. Only mild chronic inflammation consisting of a few macrophages was observed in peri-implant tissues. Based on these results, the polymeric biomaterial PEEK may be a useful biomaterial for interbody fusion cages due to the polymer's increased radiolucency and decreased stiffness.

Surgical treatment of the painful motion segment: matching technology with indications

STUDY DESIGN

Literature review of current bone graft technology and bone graft substitutes used in spinal fusion applications.

OBJECTIVE

We reviewed current bone graft technologies and identified the range of bioactive properties that each possesses, such as osteoconductivity, osteoinductivity, and structural, load-bearing capabilities that can be used to either augment or replace autogenous bone graft in spinal fusions.

SUMMARY OF BACKGROUND DATA

Bioactive materials are used in spinal fusion applications to encourage bone formation across an intervertebral motion segment. To be an effective replacement for autogenous bone grafts, a bioactive material must possess the properties of osteoinduction and osteoconduction.

METHODS

Literature review.

RESULTS

Platelet gel concentrates deliver nonspecific cytokines that influence local cells at the implantation site. Demineralized bone matrix acts as a bone graft enhancer that excludes fibrous tissue of muscle interposition in a fusion mass and is a mildly osteoinductive material. Bone morphogenetic proteins are an integral part of natural bone formation response. They function as differentiation factors that act on mesenchymal stem cells to induce bone formation.

CONCLUSIONS

Patient-derived therapies such as platelet gel concentrates contain cytokines that play a role in bone formation; however, none of them is capable of inducing the entire bone formation cascade. Clinical use of these concentrates could possibly interfere with new bone formation. The use of bone marrow aspiration and concentration techniques has not been convincingly studied in spinal fusions in lower order animal or human clinical studies. Demineralized bone matrix contains small and variable amounts of naturally occurring bone morphogenetic proteins. These products can only function as bone graft extenders. Recombinant bone morphogenetic protein products contain much more highly concentrated and focused amounts of bone morphogenetic proteins, and some have been shown to be clinically effective bone graft replacements.

Strut allograft union and remodeling using rhBMP-2 in a spinal corpectomy model

STUDY DESIGN

Growth factor in a collagen sponge carrier was compared to autograft, both packed within an allograft strut following corpectomy in a bovine spinal model.

OBJECTIVE

To evaluate incorporation of cortical strut allografts after lumbar corpectomy, comparing augmentation with recombinant human bone morphogenetic protein-2 (rhBMP-2) to local autograft.

SUMMARY OF BACKGROUND DATA

Autogenous strut grafts are the gold standard for successful fusion in reconstruction following corpectomy; however, significant donor site morbidity can occur. Recent studies describing consistently successful anterior interbody fusions with BMP augmentation suggest an exciting prospect of unlimited and potent grafting material for these difficult fusions.

METHODS

Sixteen calves underwent L3 corpectomy with instrumented strut allograft reconstruction. The rhBMP-2 impregnated collagen sponges filled the empty medullary canal of the allograft in 8 animals. Eight animals had the allograft strut filled with local autogenous bone. After 4 months, the lumbar spines were harvested for radiographic, biomechanical, and histologic evaluation.

RESULTS

Computerized tomography revealed allograft fusion in 7 of 8 autograft specimens and 8 of 8 BMP specimens. The BMP treated group had denser bone at the ends of the cortical allograft, but a central void persisted. Autograft filled struts maintained a more uniform distribution of less organized bone throughout the strut canal. Histologic assessment verified remodeling and incorporation of the allografts for both groups. Biomechanical testing confirmed no significant difference in fusion strength between groups.

CONCLUSIONS

Large cortical strut allografts (after lumbar corpectomy) supplemented with rhBMP-2 had incorporation and fusion strength comparable to allografts enhanced with cancellous autograft.

A 2-year follow-up pilot study evaluating the safety and efficacy of op-1 putty (rhbmp-7) as an adjunct to iliac crest autograft in posterolateral lumbar fusions

The ability of bone morphogenetic proteins (BMPs) to induce bone formation has led to a multitude of investigations into their use as bone graft substitutes in spinal surgery. The purpose of this multi-center clinical pilot study was to evaluate the safety and efficacy of BMP-7 (osteogenic protein 1, OP-1), in the form of a putty, combined with autograft for intertransverse process fusion of the lumbar spine in patients with symptomatic spinal stenosis and degenerative spondylolisthesis following spinal decompression. Twelve patients with spinal stenosis and degenerative lumbar spondylolisthesis underwent a laminectomy and partial or complete medial facetectomy as required for decompression of the neural elements, followed by an intertransverse process fusion by placing iliac crest autograft and OP-1 putty between the decorticated transverse processes. No instrumentation was used. Patients were followed clinically using the Oswestry scale and SF-36 outcome forms, and radiographically using static and dynamic radiographs to assess their fusion status over a 2-year period. Independent and blinded radiologists assessed the films for the presence of bridging bone between the transverse processes and measured translation and angulation on dynamic films using digital calipers. Radiographic outcome was compared to a historical control (autograft alone fusion without instrumentation for the treatment of degenerative spondylolisthesis). All adverse events were recorded prospectively. The results showed eight of the nine evaluable patients (89%) obtained at least a 20% improvement in their preoperative Oswestry score, while five of ten patients (50%) with radiographic follow-up achieved a solid fusion by the criteria used in this study. Bridging bone on the anteroposterior film was observed in seven of the ten patients (70%). No systemic toxicity, ectopic bone formation, recurrent stenosis or other adverse events related to the OP-1 putty implant were observed. A successful fusion was observed in slightly over half the patients in this study, using stringent criteria without adjunctive spinal instrumentation. This study did not demonstrate the statistical superiority of OP-1 combined with autograft over an autograft alone historical control, in which the fusion rate was 45%. There were no adverse events related to the OP-1 putty implant in this study, which supports findings in other studies suggesting the safety of bone morphogenetic proteins in spinal surgery.

[Biodegradable cage. Osteointegration in spondylodesis of the sheep cervical spine]

Bioabsorbable implants are commonplace in knee and shoulder surgery. Bioabsorbable poly(l-lactide-co-D,L-lactide) (PLDLLA) cage devices have potential benefits over autologous tricortical iliac crest bone graft and metallic cages for cervical spine interbody fusion. The purpose of this study was to compare interbody fusion of an autologous tricortical iliac crest bone graft with that of a bioabsorbable cage using a sheep cervical spine interbody fusion model. This study was designed to determine differences in (1) the ability to preserve postoperative distraction, (2) biomechanical stability, and (3) histological characteristics of intervertebral bone matrix formation. Sixteen full-grown Merino sheep underwent C3/4 discectomy and fusion. After 12 weeks, there was no significant difference between the results with the bioabsorbable PLDLLA cages and tricortical bone grafts. The cage also did not show advanced interbody fusion but did, however, show large osteolysis, which allows skepticism regarding the value of this bioabsorbable implant.