Subchondral marrow changes after laser diskectomy in the lumbar spine: MR imaging findings and clinical correlation.

OBJECTIVE: We examined MR imaging findings and determined the clinical significance of subchondral bone marrow changes in the lumbar spine of holdium:yttrium aluminum garnet laser diskectomy patients. MATERIALS AND METHODS: We retrospectively reviewed the pre- and postoperative MR images of 109 patients with recurrent radiculopathy, lower back pain, or both 1 year after laser diskectomy of 178 disks. From this group of patients, MR images were also obtained in 11 patients with subchondral marrow changes 5-7 years after surgery. These patients were interviewed regarding residual lower back pain. Thirteen asymptomatic laser diskectomy patients also underwent follow-up MR imaging within 1 year of surgery. RESULTS: After surgery, subchondral marrow abnormalities were identified in 41 of 109 laser diskectomy patients. The remaining 68 patients had no postoperative subchondral bone marrow changes. Postoperative subchondral marrow changes were not associated with inflammation of the adjacent disk space and did not affect surgical outcome. Bone marrow changes decreased in size in the 11 patients examined 5-7 years after laser diskectomy, and eight of these patients described their lower back pain as improved. In 13 asymptomatic laser diskectomy patients, one new subchondral marrow abnormality was identified. CONCLUSION: Subchondral marrow abnormalities may occur in the vertebral end plates after holmium:yttrium aluminum garnet laser diskectomy. However, these changes probably do not affect surgical outcomes and appear to resolve over time.

Reversing the inhibitory effect of nicotine on spinal fusion using an osteoinductive protein extract.

STUDY DESIGN: The effect on spinal fusion of an osteoinductive bone protein extract in the presence of a known inhibitor of spinal fusion (systemic nicotine) was studied prospectively in an animal model of posterolateral lumbar fusion. OBJECTIVES: To evaluate the ability of a bovine-derived osteoinductive bone protein extract to overcome the inhibitory effect of nicotine in a rabbit spine fusion model. SUMMARY OF BACKGROUND DATA: Multiple studies have demonstrated the ability of a variety of osteoinductive growth factors to serve as a bone graft substitute for lumbar spinal fusion under "normal" healing conditions. METHODS: Forty-eight adult female New Zealand white rabbits underwent spine arthrodesis at L5-L6 while receiving systemic nicotine through a subcutaneous miniosmotic pump. Arthrodesis was performed using one of the following three graft materials: 1) autogenous iliac crest, 2) osteoinductive bone protein delivered in an allogeneic demineralized bone matrix/ collagen carrier, or 3) osteoinductive bone protein delivered with autogenous iliac crest. Fusions were assessed by blinded manual palpation, radiography, and biomechanical testing. RESULTS: Of the 44 rabbits manually tested by blinded observers, all 14 in the osteoinductive bone protein plus autogenous iliac crest bone group had solid fusions (14 of 14), whereas the fusion rate was less in the osteoinductive bone protein plus demineralized bone matrix group (nine of 14, 64%; P = 0.02), and there were no fusions in the autogenous iliac crest only group (0 of 16, 0%; P = 0.000001). The use of osteoinductive bone protein with autogenous bone produced stronger and stiffer fusions compared with those using autogenous bone alone or osteoinductive bone protein with allograft bone. CONCLUSIONS: Cigarette smoking and nicotine are inhibitory factors in the healing of fractures and spine fusions. This study shows that the inhibitory effect of nicotine can be overcome with an osteoinductive bone growth factor in an animal model.

In vivo evaluation of a resorbable osteoinductive composite as a graft substitute for lumbar spinal fusion.

The purpose of this prospective animal study was to evaluate the efficacy of a resorbable coral particulate to serve as a carrier with several doses of a bovine-derived osteoinductive bone protein mixture. A previously validated rabbit model for posterolateral intertransverse process lumbar spinal fusion was used. Posterolateral intertransverse process arthrodeses were performed at L5-L6 in 64 adult New Zealand white rabbits. The bone graft substitute evaluated consisted of a Biocoral/collagen composite with one of four doses (0, 100, 300, or 1,000 micrograms) of a bovine-derived osteoinductive bone protein extract (BP). Fusions were assessed at 5 weeks by manual palpation, radiography, histology, and biomechanical testing. Use of the Biocoral/collagen carrier without BP resulted in no solid fusions. Biocoral/collagen with 100 micrograms BP resulted in solid fusions in 31% (4 of 13) of the rabbits. Biocoral with 300 micrograms or 1,000 micrograms BP resulted in solid spinal fusion in all rabbits (27 of 27). There were no neurologic complications related to the growth factor or carrier. Small subcutaneous collections of serous fluids were noted in 26% of the animals in the 1st postoperative week, but resolved without problems by the 5th week. Such seromas may limit the clinical utility of this growth factor-carrier combination. Biocoral/collagen combined with the appropriate dose of bovine-derived osteoinductive bone protein was efficacious as a bone graft substitute for achieving posterolateral lumbar spinal fusion in the rabbit model. A dose of 300 micrograms BP was determined as the threshold to reliability produce solid spinal fusions.

Operative treatment of degenerative cervical disk disease.

The surgical treatment of degenerative cervical disk disease should be considered only after an adequate trial of conservative management has failed. When surgery is contemplated, the decision must be based on sound indications and the operative strategy and approach must address the specific abnormality responsible for the patient's symptom complex.

Nonoperative treatment of degenerative cervical disk disease.

The therapeutic goal in treating patients with degenerative neck pain is prompt return to normal activity with the least diagnostic and therapeutic expense. Although many noninvasive treatment modalities exist, most are based on empiricism and tradition and lack scientific validation. With few exceptions, degenerative cervical pain syndromes require an initial period of conservative therapy, since their natural course favors spontaneous resolution. Patients with a clinical history suggestive of either progressive myelopathy, infection, or malignancy warrant more aggressive initial assessment and treatment.

A rabbit model for nonunion of lumbar intertransverse process spine arthrodesis.

STUDY DESIGN: A rabbit model for lumbar intertransverse process spine arthrodesis was utilized, with blind evaluation of the control and experimental animals. OBJECTIVES: To establish an animal model for motion-induced nonunion of lumbar intertransverse process spine arthrodesis and to determine if there was an early time period during which excessive motion at the arthrodesis site was deleterious to fusion. SUMMARY OF BACKGROUND DATA: Most previously reported animal models for nonunion of lumbar spine arthrodesis do not use intertransverse process fusion and do not allow variable control of the nonunion-inducing factor. METHODS: Forty-two adult New Zealand white rabbits underwent posterolateral intertransverse process spine arthrodesis with autogenous iliac crest graft. Rabbits in the experimental group (n = 23) underwent a lifting protocol to produce motion at the arthrodesis site; those in the control group (n = 12) remained undisturbed in their cages. Arthrodeses were assessed radiographically and manually to determine if fusion had occurred. RESULTS: Lifted rabbits exhibited a 13% fusion rate compared to a 50% fusion rate in controls. Rabbits lifted during only the first 2 postoperative weeks exhibited a fusion rate that was significantly less (P = 0.03) than that of controls. CONCLUSIONS: A small animal model for motion-induced nonunion of lumbar intertransverse process spine arthrodesis has been established. With respect to excessive motion as a promoter of nonunion in spine arthrodeses, the early postoperative time period appears critical.

1995 Volvo Award in basic sciences. The use of an osteoinductive growth factor for lumbar spinal fusion. Part I: Biology of spinal fusion.

STUDY DESIGN: The histology of lumbar intertransverse process spinal fusion was studied in an experimental model in rabbits. OBJECTIVES: To qualitatively and quantitatively analyze the sequential histology of spinal fusion using a previously validated animal model. SUMMARY OF BACKGROUND DATA: Few previous studies have described the sequential histology during the posterolateral spinal fusion healing process using autogenous bone, and a basic understanding of the biology of this repair process is lacking. METHODS: Fourteen adult New Zealand white rabbits underwent single-level posterolateral lumbar intertransverse process arthrodesis with autogenous iliac bone graft. Animals were killed 1-10 weeks after surgery, and the fusion masses were analyzed histologically and quantitated using a semiautomated image analysis system. RESULTS: Three distinct phases of healing were identified (inflammatory, reparative, and remodeling) and occurred in sequence but in a delayed fashion in the central zone of the fusion mass compared with the outer transverse process zones. Membraneous bone formation, evident first at the ends of the fusion eminating from the decorticated transverse processes, was the predominant mechanism of healing. The central zone was somewhat different in that there was a period of endochondral bone formation during weeks 3 and 4 in this zone where cartilage formed and was converted to bone. Remodeling in the central zone had equilibrated with the transverse process zones by 10 weeks. CONCLUSIONS: Lumbar intertransverse process spinal fusion is a complex process from a spatial and temporal standpoint. When autogenous bone is used as the graft material, this process critically depends on a variety of factors from the decorticated host bone and exposed marrow. The persistence of a central cartilage zone may be related to some types of nonunions and deserves future investigation. This enhanced understanding of the biology of spinal fusion with autogenous bone graft will provide a foundation for optimizing the use of osteoinductive bone growth factors in this healing process.

1995 Volvo Award in basic sciences. The use of an osteoinductive growth factor for lumbar spinal fusion. Part II: Study of dose, carrier, and species.

STUDY DESIGN: Efficacy of a bovine-derived osteoinductive growth factor was studied in a rabbit model and in a nonhuman primate model of posterolateral lumbar spinal fusion. OBJECTIVES: To determine the minimum effective dose of growth factor and the influence of different carrier material on the outcome of intertransverse process lumbar fusion. SUMMARY OF BACKGROUND DATA: Bone morphogenetic proteins and related growth factors are becoming increasingly available in purified extract or genetically engineered forms and are capable of inducing new bone formation in vivo. Osteoinductive growth factors to enhance lumbar spinal infusion have not been well studied in models of posterolateral intertransverse process fusion. Because of the diminished potential of bone regeneration in primates (including humans) compared with phylogenetically lower animals, extrapolations regarding dose and efficacy cannot be made directly from results obtained in experiments performed on phylogenetically lower animals. Experiments on non-human primates are a critical step before attempting to use these growth factors on humans. METHODS. One hundred fifteen adult New Zealand white rabbits and 10 adult rhesus macaques underwent single level posterolateral intertransverse process lumbar spinal arthrodesis to evaluate different doses and carrier materials for a bovine-derived osteoinductive bone protein extract. Rabbit fusion masses were evaluated 5 weeks after arthrodesis by manual palpation, radiography, biomechanical testing, and light microscopy. Monkey fusion masses were evaluated 12 weeks after arthrodesis by radiography and light microscopy. RESULTS: Successful posterolateral intertransverse process spinal fusions were achieved in the rabbit models using an osteoinductive growth factor with three different carriers (autogenous iliac bone, demineralized allogeneic bone matrix, and natural coral). There was a dose-dependent response to the osteoinductive growth factor in the rabbit model, indicating that a threshold must be overcome before bone formation is induced. The methodology for biologic enhancement of spinal fusion developed in the rabbit model transferred successfully to the rhesus monkey, where the use of the osteoinductive growth factor with a demineralized bone matrix carrier resulted in spinal fusion in 12 weeks. CONCLUSION: These experiments provide an essential building block in the understanding of the biology of spinal fusion and the use of osteoinductive growth factors to enhance a posterolateral intertransverse process spinal fusion. The achievement of posterolateral spinal fusion in the rhesus monkey using an osteoinductive growth factor is a significant step toward the biologic enhancement of spinal fusion in humans.

Biologic enhancement of spinal fusion.

STUDY DESIGN: Literature review. OBJECTIVES: To review the available animal and clinical data on biologic enhancements of spinal fusion. SUMMARY OF BACKGROUND DATA: Lumbar spinal arthrodesis may result in pseudarthrosis in 5% to 35% of patients. Although much research has focused on the mechanical factors affecting spinal fusion, the use of internal fixation has not eliminated the problem of spinal nonunions. Accordingly, biologic enhancement of spinal fusion has become an important focus of spinal research. METHODS: Medline and hand searches. RESULTS: Electric stimulation, bone graft substitutes, and bone growth factors have been researched most extensively. Electric stimulation and early attempts at bone graft substitutes (allograft, xenograft) have yielded variable results. The feasibility of biologic enhancement of spinal fusion with osteoinductive growth factors has been shown in animals. CONCLUSION: The efficacy of bone growth factors for lumbar fusion remains to be definitively established in humans.

Lumbar intertransverse-process spinal arthrodesis with use of a bovine bone-derived osteoinductive protein. A preliminary report.

The use of a bovine bone-derived osteoinductive protein extract as a bone-graft substitute was evaluated in a rabbit model of intertransverse process arthrodesis of the lumbar spine. Forty-five adult New Zealand White rabbits had arthrodesis between the fifth and sixth lumbar vertebrae with use of one of three graft materials: autogenous iliac-crest bone, osteoinductive protein delivered in an allogeneic demineralized bone matrix/collagen carrier, or demineralized bone matrix/collagen carrier or demineralized bone matrix/collagen carrier without osteoinductive protein. Fusion was assessed by manual palpation, radiography, biomechanical testing, and light microscopy at two and five weeks after the operation. At two weeks, light microscopic analysis of the arthrodesis site in which osteoinductive protein had been used showed that most of the demineralized bone matrix was still present, with small amounts of membranous and endochondral bone formation at the peripheral margins of the implant. Light microscopic analysis of the five-week specimens showed increased new-bone formation and a more homogeneous and mature fusion mass with the osteoinductive bone protein than with the autogenous bone graft. At five weeks, the fusions with the osteoinductive protein extract were characterized by more secondary spongiosa, with formation of bone marrow centrally and a cortical rim peripherally. Of the thirty-five rabbits that were examined at five weeks, all ten in the group that had received osteoinductive bone protein had a solid fusion, but the rate of fusion was significantly less in the other two groups: eight of thirteen rabbits (p = 0.05) in the group that had received autogenous bone graft and two of twelve rabbits (p = 0.0001) in the group that had received demineralized bone matrix/collagen carrier without osteoinductive bone protein. The use of osteoinductive bone protein resulted in stronger (p = 0.02) and stiffer (p = 0.005) fusions compared with those obtained with the use of autogenous iliac-crest graft.

The effect of nicotine on spinal fusion.

STUDY DESIGN: An animal model of posterior lateral intertransverse process fusion healing in the face of systemic nicotine. OBJECTIVES: To evaluate the effect of systemic nicotine on the success of spinal fusion and its effect on the biomechanic properties of a healing spinal fusion in an animal model. SUMMARY OF BACKGROUND DATA: Clinical observations suggested that cigarette smoking interferes with the healing of bony fusion. No direct link has been made to implicate nicotine as a cause for impaired healing of spinal fusions or fractures. METHODS: Twenty-eight adult female New Zealand white rabbits underwent single level lumbar posterior lateral intertransverse process fusion using autologous iliac bone graft. Animals were randomly assigned to either receive systemic nicotine or receive no nicotine. Animals were killed 35 days after surgery. Manual testing of the fusion mass was performed to determine the fusion status. Each fusion mass underwent biomechanic testing. RESULTS: Fifty-six percent of the control animals were judged to have solidly fused lumbar spines, and there were no solid fusions in the nicotine group (P = 0.02). The mean relative fusion strength in the control group was greater (P = 0.09) than in the nicotine group. For the comparable stiffness figures, the control group was greater than the nicotine group (P = 0.08). CONCLUSIONS: This animal model established a direct relationship between the development of a nonunion in the presence of systemic nicotine. The results suggested that bone formed in the face of systemic nicotine may have inferior biomechanic properties.

Experimental spinal fusion with recombinant human bone morphogenetic protein-2.

STUDY DESIGN: Lumbar intertransverse process arthrodesis using recombinant human bone morphogenetic protein-2 was performed in a previously established rabbit model for posterolateral spinal fusion and compared with fusions achieved using autogenous bone graft. OBJECTIVES: To qualitatively compare different recombinant human bone morphogenetic protein-2 dosages and carriers and to determine the efficacy of recombinant human bone morphogenetic protein-2 as a bone graft substitute to produce lumbar intertransverse process fusion in a validated rabbit model for posterolateral spinal fusion. SUMMARY OF BACKGROUND DATA: Autogenous bone was considered the most successful bone graft material used for spinal arthrodesis. Problems with its use may occur in 25-30% of patients and prompted the search for and investigation of bone graft substitutes and osteoinductive growth factors, such as bone morphogenetic proteins. Recombinant human bone morphogenetic protein-2 was used successfully in orthotopic sites to generate bone in animal mandibular and long bone defect models. METHODS: Posterolateral intertransverse process arthrodeses were performed at L5-L6 in 56 rabbits using recombinant human bone morphogenetic protein-2 or autogenous bone graft. Rabbits were killed either 5 weeks later to qualitatively compare fusions achieved using different recombinant human bone morphogenetic protein-2 dosages and carriers or 4 weeks later to compare the efficacy of recombinant human bone morphogenetic protein-2 in achieving spinal fusion compared with using autogenous bone graft. Inspection, manual palpation, radiography, histology, and biomechanic testing were used to assess the fusion. RESULTS: All rabbits implanted with recombinant human bone morphogenetic protein-2 achieved solid spinal fusion by manual palpation and were fused radiographically, whereas only 42% of the autograft control fusions were solid. More mature fusions with greater trabecular bone formation were shown radiographically and histologically in rabbits implanted with the high-dose recombinant human bone morphogenetic protein-2 than with the low-dose recombinant human bone morphogenetic protein-2. Fusions achieved using recombinant human bone morphogenetic protein-2 delivered in the collagen carrier were more remodeled and homogeneous compared with using recombinant human bone morphogenetic protein-2 delivered in autograft +/- collagen carrier. Fusions achieved with recombinant human bone morphogenetic protein-2 were biomechanically stronger and stiffer than fusions achieved using autogenous bone graft. CONCLUSIONS: Recombinant human bone morphogenetic protein-2 successfully and reliably achieved lumbar intertransverse process fusion in a validated rabbit model for posterolateral spinal fusion. Radiographically and histologically, greater and more rapid bone formation, consolidation, and remodeling were shown with recombinant human bone morphogenetic protein-2 compared with autogenous bone graft. Fusions achieved with recombinant human bone morphogenetic protein-2 were biomechanically stronger and stiffer than autograft fusions.

An experimental lumbar intertransverse process spinal fusion model. Radiographic, histologic, and biomechanical healing characteristics.

OBJECTIVE: The purpose of this investigation was to develop, characterize, and validate an animal model for lumbar intertransverse process fusion. STUDY DESIGN: This study used a rabbit model to characterize the radiographic, histologic, and biomechanical properties of the intertransverse process spinal fusion healing process. METHODS: Sixty adult New Zealand white rabbits underwent bilateral posterolateral spinal fusion at L5-L6 using autogenous iliac bone graft. Four of the rabbits were used as negative controls: two received bone graft without decortication of the transverse process, and two underwent decortication without bone grafting. Rabbits were killed at 2, 3, 4, 5, 6, or 10 weeks and the spinal fusions were analyzed by radiography, manual palpation, and uniaxial tensile mechanical testing or light microscopy. RESULTS: Overall the nonunion rate was 33% in animals 4 or more weeks from surgery. Biomechanical strength and stiffness of the fusions became statistically different from the adjacent unfused control levels after the third week (P < 0.05). Tensile strength of the nonunions (1.4 times unfused control levels) was statistically less (P < 0.05) than that of the solidly fused levels (1.8 times unfused controls) in weeks 4, 5, 6, and 10. Fusion was not achieved in any of the control animals with omission of decortication or bone grafting. Light microscopic analysis showed three distinct and reproducible phases of spinal fusion healing. CONCLUSIONS: This animal model overcomes the limitations of previous models by more closely replicating the human procedure in surgical technique, graft healing environment, and outcome (i.e., a nonunion rate similar to that seen in humans). This model provides an opportunity to explore questions relevant to the biology of intertransverse process fusion and to investigate the coupling of the membranous and endochondral mechanisms of bone formation during spinal fusion.

Spine update. Animal use in spinal research.

Progress in biomedical research often has depended on the use of animals as a testing ground for both experimental and clinical hypotheses. Animal models have been widely used in all specialties of medicine and have been crucial for acquiring basic science and clinical knowledge pertaining to spinal surgery. In addition to overcoming the many ethical and societal restrictions normally encountered in human studies, the use of animal models permits certain methodologic approaches inapplicable in humans. The purpose of this article is to: 1) review the general concepts of models, 2) discuss recommendations and regulations regarding the use of animals in biomedical research, and 3) present guidelines for the selection of the most suitable model for a particular study. Animal data are only as applicable as the model from which it is derived. Thus, future animal models must be carefully chosen using rational guidelines and should overcome the deficiencies and limitations of previous models.

Spine update. The use of animal models to study spinal fusion.

The outcome of a spinal fusion depends upon a multifactorial process. Therefore, it is difficult and impractical to study individual variables clinically. Animal models have been useful in studying the parameters that influence the spinal fusion process. Despite the knowledge gained from previous animal studies, there exists a large void in our basic understanding of this complex process. The purpose of this update is to review the concept of animal models of spine fusion by summarizing previous models, identifying strengths and deficiencies, reviewing the strategy for selecting a model, and highlighting knowledge gaps suitable for future research. With recent advances in the knowledge regarding gene-specific therapies and the availability of osteoinductive proteins, we have entered a new era of biologic manipulation of bone formation. Animal data, however, are only as applicable as the model from which it is derived, and future animal models must overcome the deficiencies highlighted in this review. A valid animal model will prove essential in studying the use of growth factors for spinal fusion. The ultimate goal is that fusion nonunions will no longer be of clinical concern.

Chronic donor site pain complicating bone graft harvesting from the posterior iliac crest for spinal fusion.

To explore the relationship between surgical approach and chronic posterior iliac crest donor site pain, 151 bone graft harvests with follow-up periods longer than 1 year were evaluated using a detailed questionnaire and follow-up clinical visits. There was no difference in the incidence of chronic donor site pain between harvests performed through the primary midline incision versus a separate lateral oblique incision (28 vs 31%). Twice as many donor sites harvested for reconstructive spinal procedures were reported as having chronic pain as compared with those harvested for spinal trauma, regardless of approach used (39 vs 18%). The association of chronic donor site pain with residual back pain was also greater in the spinal reconstructive group. Thus, it appears that incidence of chronic donor site pain is more dependent on diagnosis than on surgical approach.

An isolated nonosseous metastasis to the epidural space from an osteogenic sarcoma.

Metastatic disease from osteosarcoma most commonly occurs in the lung and bony sites. Both primary spinal osteosarcomas and spinal metastatic lesions are rare. A case is reported of a nonosseous epidural metastatic lesion from osteosarcoma. It was visualized best by metrizamide-enhanced computed tomographic scanning. The patient symptomatically improved with excision of the lesion although there was massive recurrence despite combined therapy.