Clinical applications of bone graft substitutes in spine surgery: consideration of mineralized and demineralized preparations and growth factor supplementation.

Bone graft substitutes may be broadly classified as mineralized and demineralized preparations. This article reviews the basic science and biology underlying each preparation. A review of the clinical and experimental applications of each preparation follows. The text concludes with a review of growth factors as biological supplements.

Acute biomechanical and histological effects of intradiscal electrothermal therapy on human lumbar discs.

STUDY DESIGN: Human cadaver lumbar spines were used to assess the acute effects of intradiscal electrothermal therapy in vitro. OBJECTIVE: To determine whether intradiscal electrothermal therapy produces acute changes in disc histology and motion segment stability. SUMMARY OF BACKGROUND DATA: Intradiscal electrothermal therapy has been introduced as an alternative for the treatment of discogenic low back pain. Several hypothesized mechanisms for the effect of intradiscal electrothermal therapy have been suggested including shrinkage of the nucleus or sealing of the anulus fibrosus by contraction of collagen fibers, and thermal ablation of sensitive nerve fibers in the outer anulus. METHODS: Intradiscal electrothermal therapy was performed with the Spinecath by Oratec on 19 fresh, frozen human lumbar cadaver specimens. In a separate study, eight specimens were tested biomechanically and instrumented to map the thermal distribution, whereas five specimens were tested only biomechanically, both before and after intradiscal electrothermal therapy. Six additional specimens were heated with intradiscal electrothermal therapy, and the resulting canal was backfilled with a silicone rubber compound to allow colocalization of the catheter and anular architecture. RESULTS: A consistent pattern of increased motion and decreased stiffness was observed. For the specimens in which only biomechanical measurements were taken, a 10% increase in the motion, on the average, at 5 Nm torque was observed after intradiscal electrothermal therapy. No apparent alteration of the anular architecture was observed around the catheter site in the intradiscal electrothermal therapy-treated discs. CONCLUSION: The data from this study suggest that the temperatures developed during intradiscal electrothermal therapy are insufficient to alter collagen architecture or stiffen the treated motion segment acutely.

Clinical outcome of trans-sacral interbody fusion after partial reduction for high-grade l5-s1 spondylolisthesis.

STUDY DESIGN: A clinical retrospective study was conducted. OBJECTIVE: To evaluate the clinical and radiographic outcome of reduction followed by trans-sacral interbody fusion for high-grade spondylolisthesis. SUMMARY OF BACKGROUND DATA: In situ posterior interbody fusion with fibula allograft has improved the fusion rates for patients with high-grade spondylolisthesis. The use of this technique in conjunction with partial reduction has not been reported. METHODS: Nine consecutive patients underwent treatment of high-grade (Grade 3 or 4) spondylolisthesis with partial reduction followed by posterior interbody fusion using cortical allograft. The average age at the time of surgery was 27 years (range, 8-51 years), and the average follow-up period was 43 months (range, 24-72 months). Before surgery, eight patients had low back pain, seven patients had radiating leg pain, and five patients had hamstring tightness. The average grade of spondylolisthesis by Meyerding grading was 3.9 (range, 3-5). Charts and radiographs were evaluated, and outcomes were collected by use of the modified SRS outcomes instrument. RESULTS: Radiographic indexes demonstrated significant improvement with partial reduction and fusion. The slip angle, as measured from the inferior endplate of L5, improved from 41.2 degrees (range, 24-82 degrees ) before surgery to 21 degrees (range, 5-40 degrees ) after surgery. All the patients were extremely or somewhat satisfied with surgery. The two patients who underwent this operation without initial instrumentation experienced fractures of their interbody grafts. Both of these patients underwent repair of the pseudarthrosis with placement of trans-sacral pedicle screw instrumentation and subsequent fusion. CONCLUSIONS: Partial reduction followed by posterior interbody fusion is an effective technique for the management of high-grade spondylolisthesis in pediatric and adult patient populations, as assessed by radiographic and clinical criteria. Pedicle screw instrumentation with the sacral screws capturing L5 is recommended when this technique is used for the treatment of high-grade spondylolisthesis. According to the clinical and radiographic results from this study, partial reduction and posterior fibula interbody fusion supplemented with pedicle screw instrumentation is an effective technique for select patients with high-grade spondylolisthesis at L5-S1.

Management of fixed sagittal plane deformity: results of the transpedicular wedge resection osteotomy.

STUDY DESIGN: Retrospective review of a consecutive clinical series. OBJECTIVES: To evaluate the efficacy of the transpedicular wedge resection osteotomy as a technique for correction of sagittal and coronal deformity and to assess the clinical value of the procedure as assessed by patient satisfaction. SUMMARY OF BACKGROUND DATA: The transpedicular wedge resection osteotomy is a well-established procedure for management of fixed sagittal deformity in ankylosing spondylitis. The utility of the procedure for applications in fixed deformity other than ankylosing spondylitis has not been demonstrated, and the efficacy of the procedure in the correction of coronal deformity has not been reported. METHODS: A total of 13 consecutive cases undergoing transpedicular wedge resection osteotomy for the management of sagittal deformity of any etiology were reviewed. Radiographic studies, complications, and satisfaction assessment using the modified Scoliosis Research Society instrument were the outcome parameters measured. RESULTS: Etiologies of deformity included postsurgical, ankylosing spondylitis, idiopathic, and infectious. Measurement of C7 sagittal plumb line to sacrum improved 63% at the most recent follow-up. Lumbar lordosis increased from -15.5 degrees to -45.4 degrees. Coronal balance was improved in all patients who had preoperative imbalance, with an average improvement of 60% maintained at follow-up. Patient satisfaction was high in all patients and not dependent on the etiology of deformity. CONCLUSIONS: The transpedicular wedge resection osteotomy is an effective procedure for the management of fixed sagittal deformity and is generalizable for multiple etiologies. Simultaneous correction of coronal deformity is possible. The clinical value of the procedure is demonstrated in high rates of patient satisfaction.

Excision of hemivertebrae in the management of congenital scoliosis involving the thoracic and thoracolumbar spine.

We present a study of ten consecutive patients who underwent excision of thoracic or thoracolumbar hemivertebrae for either angular deformity in the coronal plane, or both coronal and sagittal deformity. Vertebral excision was carried out anteriorly alone in two patients. Seven patients had undergone previous posterior spinal fusion. Their mean age at surgery was 13.4 years (6 to 19). The mean follow-up was 78.5 months (20 to 180). The results were evaluated by radiological review of the preoperative, postoperative and most recent follow-up films. The mean preoperative coronal curve was 78.2 degrees (30 to 115) and was corrected to 33.9 degrees (7 to 58) postoperatively, a mean correction of 59%. Preoperative coronal decompensation of 35 mm was improved to 11 mm postoperatively. Seven patients had significant coronal decompensation preoperatively, which was corrected to a physiological range postoperatively. There were no major complications and no neurological damage. We have shown that resection of thoracic and thoracolumbar hemivertebrae can be performed safely, without undue risk of neurological compromise, in experienced hands.

Anterior and posterior allografts in symptomatic thoracolumbar deformity.

The radiographic and clinical results of 105 patients with symptomatic spinal deformities were categorized retrospectively based on surgical approach and type of bone autograft or allograft used for each patient's fusion surgery into seven different groups and compared with one another. The three bone autograft control groups were posterior autograft only (n = 20), anterior autograft only (n = 6), and combined anterior and posterior autograft (n = 12). The allograft groups were posterior morcellized allograft (n = 7), posterior morcellized allograft and anterior autograft (n = 11), anterior structural interbody allografts and posterior mixture of allograft and autograft (n = 37), and anterior strut allograft with posterior mixture of allograft and autograft (n = 12). Radiographs revealed high pseudoarthrosis rates for adults with a posterior-only allograft and with anterior strut allografts spanning four or more levels. Results of the self-assessment outcomes questionnaire, at a mean follow-up period of 52 months, revealed less pain and improved cosmesis for all groups, and improved function in patients who had undergone combined anteroposterior fusion. The authors conclude that posterior cancellous allograft is a poor substitute for autograft bone and that strut allografts spanning more than four levels require technique modifications to enhance their effectiveness. In general, anterior structural allografts are effective in maintaining correction, result in fusion rates comparable to those of autografts, and correlate to improved outcomes.

The effect of static in vivo bending on the murine intervertebral disc.

BACKGROUND CONTEXT: Intervertebral disc cell function in vitro has been linked to features of the local environment that can be related to deformation of the extracellular matrix. Epidemiologic data suggest that certain regimens of spinal loading accelerate disc degeneration in vivo. Yet, the direct association between disc cell function, spinal loading and ultimately tissue degeneration is poorly characterized. PURPOSE: To examine the relationships between tensile and compressive matrix strains, cell activity and annular degradation. STUDY DESIGN/SETTING: An in vivo study of the biologic, morphologic and biomechanical consequences of static bending applied to the murine intervertebral disc. SUBJECT SAMPLE: Twenty-five skeletally mature Swiss Webster mice (12-week-old males) were used in this study. OUTCOME MEASURES: Bending neutral zone, bending stiffness, yield point in bending, number of apoptotic cells, annular matrix organization, cell shape, aggrecan gene expression, and collagen II gene expression. METHODS: Mouse tail discs were loaded for 1 week in vivo with an external device that applied bending stresses. Mid-sagittal sections of the discs were analyzed for cell death, collagen II and aggrecan gene expression, and tissue organization. Biomechanical testing was also performed to measure the bending stiffness and strength. RESULTS: Forceful disc bending induced increased cell death, decreased aggrecan gene expression and decreased tissue organization preferentially on the concave side. By contrast, collagen II gene expression was symmetrically reduced. Asymmetric loading did not alter bending mechanical behavior of the discs. CONCLUSIONS: In this model, annular cell death was related to excessive matrix compression (as opposed to tension). Collagen II gene expression was most negatively influenced by the static nature of the loading (immobilization), rather than the specific state of stress (tension or compression).

Loss of sagittal plane correction after removal of spinal implants.

STUDY DESIGN: A retrospective review of a clinical series was performed. OBJECTIVES: To evaluate the incidence of adult patients who experienced spinal collapse after spinal implant removal after a long spinal arthrodesis, and to assess the various factors that may influence the likelihood of collapse after implant removal. SUMMARY OF BACKGROUND DATA: Published reports describing the benefits or complications of spinal implant removal do not exist. Spinal implant removal, often considered a benign procedure, is even required by the Food and Drug Administration (FDA) for certain implants. METHODS: The medical records and radiographs of 116 consecutive adult patients with long posterior instrumented fusions (>5 segments) were reviewed. The information obtained included original diagnosis, patient age, number of previous surgeries before implant removal, levels of anterior and posterior fusion, time from fusion to implant removal, time from implant removal to failure, and reason for hardware removal. Radiographs also were assessed including scoliosis, lordosis, and kyphosis measurements before implant removal, after hardware removal, after failure, and after revision surgery. RESULTS: Of 116 patients, 14 underwent spinal implant removal. Most of these patients reported prominent implants either proximally in the thoracic spine or distally in the ilium (Galveston technique). Of these 14 patients, 4 experienced increased pain and collapse after implant removal despite thorough intraoperative explorations demonstrating solid fusion. CONCLUSIONS: Spinal implant removal after long posterior fusion in adults may lead to spinal collapse and further surgery. Removal of instrumentation should be avoided or should involve partial removal of the prominent implant.

Cellular contribution of bone graft to fusion.

Although a number of studies have examined the fate of graft-derived cells during the process of fusion, there remains no consensus regarding their exact contribution to bone formation within the fusion mass. We developed two chimeric mouse isograft fusion models that allowed us to track the fate of graft cells within the host fusion bed. Cortical/cancellous bone graft (1:1 ratio of pelvic to vertebral body bone) from male mice was placed between (a) the tibia and fibula or (b) the coccygeal spine transverse processes of syngeneic female hosts. Both models were characterized histologically and histochemically. Graft-derived cells were then identified by fluorescent in situ hybridization for Y-chromosome sequences present in only the graft (male) cells. When the fusion mass was healing but not yet fused (at 1 and 2 weeks), numerous graft-derived cells were observed throughout the fusion site. The predominant graft-derived cell types included chondrocytes, osteoblasts, and fibroblasts. Chondrocytes arose from precursor cells in the graft de novo. as cartilage was not transplanted during the surgical procedure. By the time a mature fusion mass had formed (at 6 weeks), graft-derived cells persisted as osteocytes within the cortical rim surrounding the fusion mass. These osteocytes likely differentiated from graft-derived precursors that had directly formed bone, because transplanted osteocytes within cortical bone graft fragments were noted to rarely survive even at 1 and 2 weeks. Collectively, our results demonstrate for the first time that bone graft contributes cells that, in conjunction with host cells, directly form bone within the fusion mass during all phases of fusion rather than just the early phases.

Calcium sulfate- and calcium phosphate-based bone substitutes. Mimicry of the mineral phase of bone.

Calcium sulfate and calcium phosphate have provided the orthopedic surgeon a viable alternative to autogenous bone grafting as either an osteoconductive bone void filler or a bone graft extender. These materials mimic the mineral phase of bone and are resorbed at a rate similar to the rate of bone formation. Thus, they are able to provide some structural support and prevent ingrowth of fibrous tissue while facilitating creeping substitution by the host bone.

Thromboembolic complications after major thoracolumbar spine surgery.

STUDY DESIGN: Adult spinal surgery patients were studied prospectively to determine the incidence of subclinical deep venous thrombosis. An overlapping group of patients was reviewed retrospectively for symptomatic thromboembolism. OBJECTIVES: To determine the incidence of symptomatic and asymptomatic thromboembolism in spinal surgery patients. SUMMARY OF BACKGROUND DATA: Although thromboembolic complications are known to occur after spinal operations, there are limited published data on the incidence of pulmonary embolus or deep venous thrombosis after major spinal surgery. METHODS: One hundred sixteen adult spinal surgery patients were examined with duplex ultrasound to determine the incidence of deep venous thrombosis. Seventy-three of these patients also underwent lung perfusion scans to look for subclinical pulmonary embolism. A retrospective review was conducted of symptomatic thromboembolic complications occurring in a 2-year period at the authors' center. Three hundred and eighteen major spinal reconstructive procedures were performed during the period reviewed, which included the period of the prospective study and therefore the patients of the prospective group. Thigh-length compression stockings and pneumatic compression leggings were used for prophylaxis in all patients. RESULTS: One patient had an asymptomatic iliac vein thrombosis, and seven patients had symptomatic pulmonary embolism (2.2%). Six of the symptomatic pulmonary emboli occurred after combined anterior/posterior spinal fusions (6%), whereas only one occurred after posterior decompression and fusion (0.5%). CONCLUSIONS: Duplex ultrasound appeared insensitive for diagnosing clots before embolization in this patient group. Simple mechanical prophylaxis for thromboembolism, which may be adequate for patients undergoing posterior procedures, may not be as protective for patients undergoing combined anterior/posterior spine surgery.

Patient outcomes after decompression and instrumented posterior spinal fusion for degenerative spondylolisthesis.

STUDY DESIGN: A retrospective study of patient outcomes after decompression and fusion for degenerative spondylolisthesis, using the SF-36 survey and a functional questionnaire. SUMMARY OF BACKGROUND DATA: In recent studies, patient outcomes have been examined more specifically; however, detailed functional outcomes are not available nor have widely used outcomes instruments been administered. METHODS: Thirty patients aged more than 40 years (average, 60.1 years) who had degenerative spondylolisthesis were evaluated after decompression and instrumented posterior fusion. Charts and radiographs were also reviewed. Questionnaires were administered by telephone, and consisted of the Medical Outcomes Study short form (SF-36) and 27 questions designed to evaluate function, quality of life, medication usage, and satisfaction with surgical results. RESULTS: Ninety-three percent of patient's were satisfied with their outcomes. Patients improved significantly in their ability to perform heavy and light activities, participate in social activities, sit, and sleep (P < 0.001) and also improved in pain, depression, and medication usage (P < 0.0001). SF-36 data showed significantly better overall assessment of health in all categories than that in a published cohort of patients with low back pain. The current study group also showed no difference in seven of eight categories when compared with the general population. Fusion rate was 93% at an average of 128 days. Three patients required reoperation: two for pseudarthrosis and one for a deep infection. A poorer outcome, scored by the SF-36, was associated with greater preoperative stenosis (P < 0.05) or occurrence of a complication (P < 0.05). CONCLUSIONS: Patients treated with decompression and fusion for degenerative spondylolisthesis had improved functional outcomes, when measured by a disease-specific questionnaire and by widely used instruments.

Use of a collagen-hydroxyapatite matrix in spinal fusion. A rabbit model.

STUDY DESIGN: The efficacy of a specially designed mineralized bovine collagen matrix as a carrier for bone marrow stem cells was studied in a rabbit posterolateral spinal fusion model. OBJECTIVES: To determine if bone marrow cells added to Healos matrix will lead to fusion rates, biomechanical properties, and histologic properties comparable with those of fusions using autologous iliac crest bone graft; and to determine if the addition of preservative-free heparin to anticoagulate the bone marrow during harvest will adversely affect the fusion rate. SUMMARY OF BACKGROUND DATA: Although the development of new preparations of osteoinductive agents has advanced rapidly in recent years, the carrier systems that have been used in their application have received less attention. The composition and structure of the matrix used are key components affecting the ability of the matrix to function as a scaffold on which cells can migrate, adhere, proliferate, and form bone. The composition and design of matrix components also determine the ability of osteoinductive agents to influence local and hematogenously derived osteogenic precursor cells, which migrate to or are brought into the fusion site. Thus, the properties of the carrier can affect the behavior and efficacy of the osteoinductive agent that is used. The authors studied the properties of a new mineralized collagen matrix called Healos, which has been engineered specifically for spinal fusion application. METHODS: Forty-four adult female New Zealand white rabbits were divided into five groups. Groups 1-4 underwent bilateral intertransverse fusion between L5 and L6. The fusions were augmented with either autologous iliac crest bone graft, Healos matrix alone, Healos matrix mixed with autologous bone marrow, or Healos matrix combined with heparinized autologous bone marrow. At 8 weeks after surgery, the fusions were characterized radiographically, histologically, and biomechanically. The rate of fusion was determined by radiographic analysis. The fifth group consisted of two animals whose bone marrow was aspirated from their tibias and femurs and then sent for determination of total nucleated cell count. RESULTS: At 8 weeks, the radiographically determined fusion rate for autologous bone graft was 75% (9/12 animals), compared with 100% (10/10 and 9/9 animals) for groups in which fusions were done by using Healos matrix augmented with bone marrow (P < or = 0.1). Matrix used alone yielded a fusion rate of 18% (2/11 animals, P < or = 0.006). Histologically, the most mature bone was seen in the group augmented with autologous iliac crest graft, followed in decreasing order by the groups augmented with Healos with heparinized bone marrow, Healos with unheparinized bone marrow, and Healos alone. Biomechanically, the group augmented with autologous graft had the highest mean stiffness, followed by the groups augmented with Healos with heparinized bone marrow, Healos with untreated bone marrow, and finally Healos matrix alone. However, the differences in stiffness between groups were not statistically significant with the number of spines tested. CONCLUSIONS: These results show that Healos is an osteoconductive matrix that can be a useful carrier in the biologic and mechanical environment of a posterolateral intertransverse fusion site. In combination with bone marrow, it produces fusion rates that are comparable with those of autologous bone graft. However, it must be combined with an osteoinductive or osteogenic agent to ensure reliable fusion rates and alone cannot produce reliable osteogenesis. The Healos matrix was not compared with other commercially available matrices currently in use. Therefore, the efficacy of Healos relative to these other materials could not be determined.

Nutritional depletion in staged spinal reconstructive surgery. The effect of total parenteral nutrition.

STUDY DESIGN: A prospective randomized study evaluating nutritional depletion in spine surgery patients. OBJECTIVE: To determine whether use of total parenteral nutrition (TPN) in patients undergoing staged spinal reconstructive procedures could affect their nutritional parameters or decrease their complication rates. SUMMARY OF BACKGROUND DATA: Several studies have shown that nutritional depletion occurs after major spinal surgery and that patients undergoing staged spinal surgery may be at particular risk of nutritional loss and its complications. METHODS: Forty adult patients undergoing staged spinal reconstructive surgery were randomized as to whether they received TPN postoperatively. Nutritional parameters, including skin fold measurement and albumin, pre-albumin, transferrin, and total lymphocyte counts, were obtained pre-operatively and at regular intervals. RESULTS: Five patients did not complete the study, leaving 35 patients for analysis. There was a significant decrease in incidence of albumin and pre-albumin depletion for the patients who did not receive TPN compared with those who did receive TPN (P < 0.025, P < 0.006, respectively). Patients with depleted albumin or pre-albumin counts were more likely to develop other postoperative infectious complications such as pneumonia or urinary tract infections (P < 0.035). There were no statistically significant differences in wound complications in this small patient study. There were no complications secondary to use of the TPN. CONCLUSIONS: For complex patients requiring staged anterior/posterior surgery, TPN appears to significantly lessen the decrease in nutritional parameters. Because depletion of nutritional parameters appears to correlate with an increased likelihood of perioperative infectious complications, use of TPN may result in a decrease of such complications in these patients.

Use of ultrasound in spinal arthrodesis. A rabbit model.

STUDY DESIGN: The biomechanical and histologic characteristics of posterolateral spinal fusion in a rabbit model with and without the application of low-intensity ultrasound were analyzed. OBJECTIVES: To evaluate the use of ultrasound to improve the spinal fusion rate and biomechanical characteristics of the fusion mass in a rabbit model. SUMMARY OF BACKGROUND DATA: This is the first study in which the benefits of ultrasound in spinal fusion have been assessed. Posterolateral intertransverse process fusion in the rabbit has a pseudarthrosis rate similar to that recorded in humans (5-40%). METHODS: Fourteen New Zealand White rabbits were randomly assigned to each of two groups to undergo spinal fusion using autologous bone with ultrasound or autologous bone without ultrasound. A specially designed plastic constraint was used to focus the ultrasound over the rabbits' lumbar spine 20 minutes per day. Animals were killed at 6 weeks for biomechanical and histologic testing. RESULTS: The rate of pseudarthrosis, evaluated radiographically and manually in a blinded fashion, decreased at a statistically significant rate (from 35% to 7%) with ultrasound. Biomechanical analysis of the fusion mass showed that ultrasound resulted in statistically significant increases in stiffness (33%; P = 0.03), area under the load displacement curve (25%; P = 0.05), and load to failure of the fusion mass (24%; P = 0.04). Qualitative histologic assessment showed increased bone formation in those fusions exposed to ultrasound. CONCLUSIONS: Lumbar spinal fusion is a complex biologic process. The results of the current study demonstrate the reproducibility of a rabbit fusion model and the ability of ultrasound to induce a statistically significant increase in fusion rate, stiffness, area under the load displacement curve, and load to failure of the fusion mass. These results provide a basis for continued evaluation of biologic improvement of spinal arthrodesis with the use of ultrasound.

Lumbar fusion results related to diagnosis.

STUDY DESIGN: Pain outcome and functional outcome after primary lumbar fusion surgery were determined by a self-assessment questionnaire. The responses were correlated with various clinical parameters. OBJECTIVES: To determine the result of fusion surgery among patients in various diagnostic groups using semiquantitative outcome scales. SUMMARY OF BACKGROUND DATA: Most previous studies on the results of primary lumbar fusion have reported the presence of pain, but few have addressed function outcomes. Results of a literature review were inconclusive as to whether a patient's diagnosis is a predictor of improved results. METHODS: During the 3-year period from 1988 to 1990, 165 patients underwent a primary lumbar fusion procedure. They had a chart and radiograph review and were categorized into five major diagnostic groups: 1) pediatric, 2) grade I-II spondylolisthesis (low-slip), 3) grade III-IV spondylolisthesis (high-slip), 4) degenerative disc disease, and 5) postdiscectomy. At a follow-up period of 5 years (mean) after the fusion, patients were mailed a questionnaire in which they described their pain and functional status before and after their lumbar fusion surgery. Questionnaires were returned by 92% of the patients. The questionnaire scores, complications, and revision procedures were grouped by patient diagnosis and analyzed. RESULTS: Patient satisfaction with the results of primary lumbar fusion ranged from 69% (for the postdiscectomy group) to 100% (for the pediatric and high-slip groups). For all diagnostic groups, lumbar fusion resulted in a significant decrease in back pain and leg pain (visual analog scale), which was maintained throughout the follow-up period. For back pain, the pediatric and high-slip groups showed significantly more improvement than the degenerative disc disease or postdiscectomy groups. Leg pain among patients in the pediatric and high-slip groups was significantly more improved than leg pain among patients in the low-slip, degenerative disc disease, or postdiscectomy groups. There was no deterioration of pain scores during the follow-up period. After fusion, all groups had a significant decrease in Oswestry disability scores; patients in the pediatric and high-slip group had significantly more improvement than patients in the degenerative disc disease or postdiscectomy groups. High- and low-slip groups had a significant improvement in their pain drawing score. Medication use was substantially reduced in all groups. After fusion, a lack of improvement in back pain score or disability score was significantly correlated with pseudarthrosis. CONCLUSIONS: The outcome of primary lumbar fusion surgery was decreased pain and increased function for the majority of patients in all five diagnostic categories. The amount of improvement varied by diagnostic group. Patients with developmental conditions showed greater improvement than patients with degenerative conditions.

Use of electromagnetic fields in a spinal fusion. A rabbit model.

STUDY DESIGN: The biomechanical and histologic characteristics of posterolateral spinal fusion in a rabbit model with and without the application of a pulsed electromagnetic field were analyzed in a prospective, randomized trial. In addition, fusion rate with and without a pulsed electromagnetic field in this model was assessed by biomechanical testing, radiographs, and manual palpation. OBJECTIVES: To evaluate the influence of a pulsed electromagnetic field on the spinal fusion rate and biomechanical characteristics in a rabbit model. SUMMARY OF BACKGROUND DATA: Previous studies performed to assess the benefits of a pulsed electromagnetic field in spinal fusion have been complicated by the use of instrumentation, and the animal models used do not have a pseudarthrosis rate comparable to that seen in humans. In contrast, the posterolateral intertransverse process fusion in the rabbit is uncomplicated by the use of instrumentation and has been shown to have a pseudarthrosis rate similar to that found in humans (5-35%). METHODS: Ten New Zealand white rabbits each were randomly assigned to undergo spinal fusion using either 1) autologous bone with electromagnetic fields, or 2) autologous bone without electromagnetic fields. A specially designed plastic constraint was used to focus the pulsed electromagnetic field over the rabbits' lumbar spine 4 hours per day. Animals were killed at 6 weeks for biomechanical and histologic testing. RESULTS: The rate of pseudarthrosis, as evaluated radiographically and manually in a blinded fashion, decreased from 40% to 20% with the pulsed electromagnetic field, but this decrease in the nonunion rate was not statistically significant given the number of animals per group. Biomechanical analysis of the fusion mass showed that a pulsed electromagnetic field resulted in statistically significant increases in stiffness (35%), area under the load-displacement curve (37%), and load to failure of the fusion mass (42%). Qualitative histologic assessment showed increased bone formation in those fusions exposed to a pulsed electromagnetic field. CONCLUSIONS: This study demonstrates the reproducibility of a rabbit fusion model, and the ability of a pulsed electromagnetic field to induce a statistically significant increase in stiffness, area under the load-displacement curve, and load to failure of the fusion mass. This investigation provides a basis for continued evaluation of biologic enhancement of spinal arthrodesis with the use of a pulsed electromagnetic field.

Vertebral column resection for the treatment of rigid coronal decompensation.

STUDY DESIGN: A retrospective study of patients with rigid coronal decompensation. OBJECTIVES: To determine if patients with rigid coronal decompensation can be safely and successfully treated by anterior-posterior vertebral column resection, spinal shortening, posterior instrumentation, and fusion to correct their deformities. SUMMARY OF BACKGROUND DATA: Previous investigators have described reconstructive techniques used to treat patients with sagittal and coronal spine deformities. These techniques include osteotomy and anterior or posterior fusion. Although a number of these studies consider the problems associated with failed back syndrome (flatback, coronal and axial imbalance, pseudarthrosis), they have not satisfactorily addressed the management of rigid coronal decompensation. The patient population of the current study, on average, presented with more severe, fixed deformities than those detailed in the literature, and required more extensive surgery than previously described. METHODS: Twenty-four patients (average age, 27 years) with rigid coronal decompensation underwent anterior-posterior vertebral column resection, spinal shortening, posterior instrumentation, and fusion. Degree of curvature was measured in the coronal and sagittal planes, and decompensation was assessed. Follow-up was from 2 to 10 years. RESULTS: Coronal and sagittal decompensation were corrected an average of 82% and 87%, respectively; T1 tilt and pelvic obliquity were improved by 65% and 53%, respectively; and scoliosis was improved by 52%. Complications occurred in 14 patients, but at follow-up all patients rated their results as either good or excellent. CONCLUSIONS: Patients with fixed, decompensated spinal deformity may be safely corrected by vertebrectomy, decancellation, spinal shortening, instrumentation, and fusion. Complications are transient, and the benefits in this select group of patients outweigh the risks.