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Techniques have changed significantly with the advent of less invasive surgical techniques for disc excision and spinal fusion; these include the development of rigid internal fixation devices using multiple points of fixation and the better knowledge of the biology of spinal fusion. Despite these improvements in technology, room exists for alternative forms of surgical treatment because of significant failures particularly related to spinal fusions.
OBJECTIVE: To compare the efficacy of calcium sulfate pellets plus bone obtained from decompression with fresh autologous iliac crest bone in lumbar and lumbosacral spinal fusion with decompression. DESIGN: A prospective randomized clinical trial. SETTING: Four tertiary care centres in Halifax, NS. PATIENTS: All were consenting, skeletally mature and suffering from degenerative disc disease or spondylolisthesis. The first 40 patients from a single test centre are reported; 32 of these had completed 1-year follow-up. INTERVENTIONS: Posterolateral lumbar or lumbosacral spinal fusion with spinal canal decompression and randomized placement of test material (decompression bone plus an equal volume of calcium sulfate pellets) on one side and control material (autologous posterior iliac crest bone of equal volume to the test material) on the contralateral side, which allowed subjects to act as their own control. OUTCOME MEASURES: Assessment of bone formation by radiographic evaluation at 6 and 12 months after fusion by an independent musculoskeletal radiologist blinded to the placement of test material. RESULTS: At 6 and 12 months after fusion, 78% and 88% of patients, respectively, showed bone formation at the test site that was 75% to 100% of, equal to or more than that at the control site. Increases in bone formation at 6 and 12 months were almost identical at both sites. Smoking status, patient gender or age, instrumentation used and volume of graft used were not predictive of outcome. CONCLUSIONS: Calcium sulfate pellets plus decompression bone provided bone formation equivalent to autologous iliac crest bone in a majority of patients. Calcium sulfate pellets plus decompression bone may provide a viable alternative to autologous iliac crest as a graft material for spinal fusion.
STUDY DESIGN: Study of posterolateral fusions in a rabbit model. OBJECTIVES: To characterize the contribution of paraspinal musculature to the healing of posterolateral spinal fusions in a rabbit model. SUMMARY OF BACKGROUND DATA: Previous studies have demonstrated that successful spinal arthrodesis requires vascular ingrowth from adjacent decorticated bone. In other areas of the body, such as the tibia, vascular ingrowth from the surrounding musculature has also been shown to be important. The role of the surrounding paraspinal musculature in spinal fusions has yet to be assessed. METHODS: Twenty-five New Zealand white rabbits underwent posterolateral spinal fusion. One side of the animals was treated with autograft alone and served as the control group. On the contralateral side, the autograft was contained within porous or nonporous barrier sheets. Following euthanization, high-resolution radiographs, CT scans, and histologic analyses were performed to assess fusion and characterize vascular ingrowth. RESULTS: Using histologic evaluation, the fusion rate in the porous group was 90%, in the nonporous group 40%, and in the control group 55%. Vascular ingrowth was evident from the muscle through the porous sheet into the fusion mass. CONCLUSIONS: These results support our hypothesis that the paraspinal musculature provides important vascular ingrowth into the fusion site. Use of a porous barrier sheet appears to improve fusion by preventing muscle interposition while allowing vascular ingrowth from surrounding muscle.
STUDY DESIGN: A retrospective matched cohort study. OBJECTIVE: To comprehensively compare the 2-year postoperative results of posterior correction and fusion with segmental pedicle screw instrumentation versus those with hook constructs in adolescent idiopathic scoliosis (AIS) treated at a single institution. SUMMARY OF BACKGROUND DATA: Despite the reports of satisfactory correction and maintenance of scoliotic curves by pedicle screw instrumentation compared to hook constructs, few reports on the comprehensive comparison of segmental pedicle screw instrumentation versus hook instrumentation exist. MATERIALS AND METHODS: A total of 52 patients with AIS at a single institution who underwent a posterior spinal fusion with segmental pedicle screw (26) or hook (26) instrumentation were sorted and matched according to four criteria: similar age at surgery (14.8 years in pedicle screw group and 14.2 years in hook group), identical Lenke curve types, same number of fused vertebrae (11.7 in each group), and identical operative methods (18 posterior spinal fusions with thoracoplasty, 4 posterior spinal fusions with iliac crest bone graft, and 4 anterior and posterior spinal fusions in each group). Patients were evaluated before surgery, immediate after surgery, and at the 2-year follow-up according to radiographic changes in curve correction, pulmonary function tests, operative time, intraoperative blood loss, implant costs, and SRS-24 scores. RESULTS: After surgery, the average major curve correction was 76% in the screw group and 50% in the hook group (P < 0.001). At the 2-year follow-up, loss of the major curve correction was less in the screw group (5.4%) compared with the hook group (8.0%) (P = 0.35). Postoperative global coronal and sagittal balance was similar in both groups. An average of 0.8 levels from the distal end vertebra was saved using pedicle screws compared with hook constructs (P = 0.002). Postoperative 2-year proximal junctional change in the sagittal plane (angle between uppermost instrumented vertebra and two vertebral bodies above the uppermost-instrumented vertebra) was 9 degrees in the screw group and 6 degrees in the hook group (P = 0.19). Postoperative 2-year distal junctional change in the sagittal plane was similar in both groups. Operative time averaged 341 minutes in the screw group and 338 minutes in the hook group (P = 0.86), and intraoperative blood loss was similar in both groups (879 mL in screw group vs. 896 mL in hook group) (P = 0.12). Average implant cost in the hook group (11.8 fixation points; 5,816 U.S. dollars) was significantly lower than that of the screw group (17.1 fixation points; 11,508 U.S. dollars) (P < 0.001). Two years following surgery, the screw group demonstrated improved percent predicted pulmonary function values compared with that of the hook group (FVC, 80%--> 79% in screw group vs. 82%--> 74% in hook group, P = 0.0056; FEV-1, 73%--> 76% in screw group vs. 80%--> 79% in hook group, P = 0.017). Postoperative 2-year SRS-24 scores were similar in both groups (screw group [97] vs. hook group [101]) (P = 0.15). There were no neurologic or visceral complications related to hook or pedicle screw instrumentation. CONCLUSION: Pedicle screw instrumentation, although more expensive, offers a significantly better major and minor curve correction without neurologic problems and improved pulmonary function values in the operative treatment of AIS and enables a slightly shorter fusion length than segmental hook instrumentation.
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.
STUDY DESIGN: A prospective review of upper extremity function in 25 patients after anterior thoracotomy for instrumentation and fusion of thoracic adolescent idiopathic scoliosis was conducted. OBJECTIVE: To assess the effects of anterior spinal fusion with open thoracotomy on upper extremity function. SUMMARY OF BACKGROUND DATA: The treatment of idiopathic scoliosis through anterior thoracotomy and spinal fusion using instrumentation is a new method for correcting and stabilizing patients with major thoracic and thoracolumbar curves. No studies have assessed the functional outcome for the upper extremities after anterior open thoracotomy that involves splitting through the latissimus dorsi and serratus anterior muscles. METHODS: For this study, 25 adolescent patients with idiopathic scoliosis treated surgically were examined over a 3-year period. The average patient age was 15 years and 3 months, with a range of 11 years and 11 months to 20 years and 9 months. Preoperative activities of daily living, active range of motion, and strength were recorded by an independent occupational therapist (L.P.) for both upper extremities. Postoperative measurements were assessed at 1, 3, 6, 12, and 24 months. All the patients underwent a right thoracotomy with ribs used for autograft. The left upper extremity served as the control limb. No patients had associated anomalies or previous upper extremity surgery. All the patients underwent an upper extremity postoperative stretching and strengthening protocol. RESULTS: At 1 month, 35% of the patients had some difficulty with activities of daily living, primarily in tying their shoes and cutting meat with a knife during meals (P = 0.03). However, by 3 months, all the patients could equivocally and independently perform activities of daily living: dressing, bathing, grooming, attending to hygiene, and feeding (P = 1). Full active range of motion in their upper extremities and shoulder was achieved in all the patients by 1 month (P = 1). All 25 patients had regained normal, bilaterally symmetric strength by 3 months (P = 0.25). No postoperative complications occurred. CONCLUSIONS: Patients undergoing anterior spinal fusion with instrumentation after open thoracotomy can expect to regain full function of the ipsilateral upper extremity in terms of strength, active range of motion, and activities of daily living within 3 months. Compliance with a structured postoperative flexibility and strengthening protocol is recommended to optimize functional outcomes. A novel rehabilitation protocol for the upper extremities is presented.
The literature reports on the safety and efficacy of titanium cages (TCs) with additional posterior fixation for anterior lumbar interbody fusion. However, these papers are limited to prospective cohort studies. The introduction of TCs for spinal fusion has resulted in increased costs, without evidence of superiority over the established practice. There are currently no prospective controlled trials comparing TCs to femoral ring allografts (FRAs) for circumferential fusion in the literature. In this prospective, randomised controlled trial, our objective was to compare the clinical outcome following the use of FRA (current practice) to the use of TC in circumferential lumbar spinal fusion. Full ethical committee approval and institutional research and development departmental approval were obtained. Power calculations estimated a total of 80 patients (40 in each arm) would be required to detect clinically relevant differences in functional outcome. Eighty-three patients were recruited for the study fulfilling strict entry requirements (>6 months chronic discogenic low back pain, failure of conservative treatment, one- or two-level discographically proven discogenic low back pain). The patients completed the Oswestry Disability Index (ODI), Visual Analogue Score (VAS) for back and leg pain and the Short-Form 36 (SF-36) preoperatively and also postoperatively at 6, 12 and 24 months, respectively. The results were available for all the 83 patients with a mean follow-up of 28 months (range 24-75 months). Five patients were excluded on the basis of technical infringements (unable to insert TC in four patients and FRA in one patient due to the narrowing of the disc space). From the remaining 78 patients randomised, 37 received the FRA and 41 received the TC. Posterior stabilisation was achieved with translaminar or pedicle screws. Baseline demographic data (age, sex, smoking history, number of operated levels and preoperative outcome measures) showed no statistical difference between groups (p<0.05) other than for the vitality domain of the SF-36. For patients who received the FRA, mean VAS (back pain) improved by 2.0 points (p<0.01), mean ODI improved by 15 points (p=<0.01) and mean SF-36 scores improved by >11 points in all domains (p<0.03) except that of general health and emotional role. For patients who received the TC, mean VAS improved by 1.1 points (p=0.004), mean ODI improved by 6 points (p=0.01) and SF-36 improved significantly in only two of the eight domains (bodily pain and physical function). Revision procedures and complications were similar in both groups. In conclusion, this prospective, randomised controlled clinical trial shows the use of FRA in circumferential lumbar fusion to be associated with superior clinical outcomes when compared to those observed following the use of TCs. The use of TCs for circumferential lumbar spinal fusion is not justified on the basis of inferior clinical outcome and the tenfold increase in cost.
STUDY DESIGN: Fifteen patients meeting rigid study entrance criteria for undergoing a combined anteroposterior L4-S1 spinal fusion as a first time operation were included in the study. Bone mineral density changes at adjacent segments (L3 and L2) were assessed by scanning patients in the anteroposterior and lateral projections before surgery and 3 and 6 months after surgery. OBJECTIVES: To prospectively evaluate changes in bone mineral density at adjacent segments after lumbar spinal fusion and postoperative bracing. SUMMARY OF BACKGROUND DATA: The majority of studies investigating changes in bone mineral density after spinal fusion have been performed in canines. Although such work has provided valuable insight, its application to humans is questionable because the loading mechanics are so different. METHODS: Bone mineral density was assessed noninvasively by dual energy x-ray absorptiometry in the lateral and anteroposterior projections. Data were analyzed with special edge detection software. RESULTS: In the lateral projection at L3, one level above the fusion, the preoperative bone mineral density was 0.91 +/- 0.24 (mean +/- standard deviation in g/cm2). This decreased significantly at 3 months to 0.82 +/- 0.24 and remained reduced at 6 months (0.80 +/- 0.21). This reflected a loss of primarily trabecular bone. In the anteroposterior projection at L2, there was a significant loss at 3- and 6-month follow-up (1.24 +/- 0.15 to 1.19 +/- 0.15 and 1.19 +/- 0.14). This may reflect changes at either or both of the anterior and posterior columns. CONCLUSION: Significant decreases in bone mineral density were noted above fused lumbar segments. This may have been related to immobilization or altered mechanics associated with arthrodesis. Trabecular bone of the axial skeleton is most responsive to change, compared with cortical bone, because of the higher metabolic activity. This may explain the reduction of bone mineral density at L3. Changes at L2 may have been related to altered loads at the anterior or posterior columns and should be further investigated.
STUDY DESIGN: Prospective study. OBJECTIVES: To prospectively evaluate sequential pulmonary function tests (PFTs) at a minimum 2-year follow-up after an open anterior spinal fusion (ASF) with instrumentation for thoracic AIS. SUMMARY OF BACKGROUND DATA: Anterior spinal fusion with instrumentation is currently undergoing evaluation as an alternative to posterior spinal fusion (PSF) for thoracic adolescent idiopathic scoliosis (AIS). However, the effect of an open thoracotomy on pulmonary function in these patients is unknown. METHODS: Fifty-one patients with thoracic AIS with an average age of 15+0 (range 11+2 to 20+5) had PFTs consisting of volume (FVC), flow (FEV-1), and total lung capacity (TLC). Parameters were obtained preoperatively, and at 3 months, 1 year, and a minimum 2-year follow-up. All patients had a single or double open thoracotomy with the diaphragm kept intact. Fusion levels ranged from T4 (most proximal) to L1 (most distal). The average preoperative thoracic coronal Cobb measurement was 53 degrees (range 38 degrees to 80 degrees ), and the average postoperative coronal measurement was 24 degrees (range 7 degrees to 49 degrees ). The average preoperative thoracic sagittal kyphosis (T5-T12) averaged 22 degrees (range 10 degrees to 58 degrees ), and the average postoperative sagittal kyphosis measured 29 degrees (range 7 degrees to 67 degrees ). RESULTS: There was a significant decline (P< or =0.05) in PFT absolute values (L) of 19%-FVC, 15%-FEV-1, and 11%-TLC at 3 months postoperatively with subsequent improvement and no statistical difference between preoperative and 2-year postoperative values. When evaluating percent predicted values, there was a statistical decline (P< or =0.05) at 3 months postoperatively averaging 19% FVC, 14% FEV-1, and 12% TLC. These values returned to within 94% to 96% of baseline by the 2-year follow-up visit, but were still statistically less than the preoperative values (P</=0.05). CONCLUSIONS: Pulmonary function following thoracotomy with ASF with instrumentation demonstrated a significant decline of 3-month postoperative PFT values, but returned to preoperative baseline absolute values (L) by the 2-year follow-up visit. The percent predicted values returned to within 95% of baseline 2 years postoperatively. Scoliosis surgeons should be aware of these findings when deciding upon the approach (anterior versus posterior) utilized for thoracic AIS.
STUDY DESIGN: A retrospective evaluation of screw position after double-rod anterior spinal fusion in idiopathic scoliosis using computerized tomography (CT). OBJECTIVE: To evaluate screw position and complications related to screw position after double-rod anterior instrumentation in idiopathic scoliosis. SUMMARY OF BACKGROUND DATA: Anterior instrumentation and fusion in idiopathic scoliosis is gaining widespread use. However, no studies have been published regarding the accuracy of screw placement and screw-related complications in double-rod and double-screw anterior spinal fusion and instrumentation in idiopathic thoracolumbar scoliosis surgery. METHODS: CT examinations were performed after surgery in 17 patients with idiopathic scoliosis. At each instrumented level, the position of the screw and the plate relative to the spinal canal, relative to the neural foramen, and relative to the aorta was measured. Complications related to screw position were registered. RESULTS: A total of 189 screws in 17 patients were evaluated. Malposition occurred in 23% (16 patients) of the total number of screws. Three screws (2 patients) were partially in the spinal canal (1%). This resulted in pain in the right leg in 2 patients. However, electromyography showed no abnormalities. At three levels (3 patients), there was contact between the instrumentation and the aorta. However, no vascular complications occurred. A total of 113 screws (10 patients) were placed under fluoroscopic control and 76 screws (7 patients) were placed without use of fluoroscopy. Less screw malposition was observed in the group in which fluoroscopic control was used (19% vs. 30%, not significant). CONCLUSIONS: Screw placement in double-rod anterior spinal fusion in idiopathic scoliosis seems to be technically demanding, and the use of fluoroscopic control results in less frequent malposition. The risk of neurologic and vascular complications is low.
Persistent thoracolumbar kyphosis in patients with achondroplasia is typically prevented with sitting modifications and bracing. When the kyphosis persists and progresses despite bracing, spinal fusion is indicated to prevent further progression and neurologic complications. Previous reports have suggested that instrumentation in such patients carries a high risk of neurologic injury. The purpose of this study was to evaluate the safety and efficacy of a two-stage procedure to control progressive kyphosis in the patient with achondroplasia. The authors treated four such patients (4-8 years old) surgically. The first stage involved an anterior spinal fusion with instrumentation and a posterior spinal fusion, and the second stage involved an additional posterior fusion. There were no neurologic complications. Correction ranged from 23.0% to 31.25%. All patients achieved a solid fusion. These results suggest that when nonoperative treatments fail, this procedure for thoracolumbar kyphosis in the achondroplastic patient can be done safely and effectively.
The risk of accelerating the degeneration of adjacent disc levels after lumbar spinal fusion is a controversial issue. A finite element model consisting of L1 to L5 lumbar spines was used to assess the effect on adjacent disc level after lumbar spinal fusion. We compared intact, L4/5 posterior interbody fusion (PLF), and L4/5 posterior lumbar interbody fusion (PLIF) models. The loading conditions applied were compressive force, compressive force plus flexion moment, and compressive force plus extension moment. Evaluations were made for von Mises stress on each vertebral end-plate, Tresca stress of all the annulus fibrosus, and Tresca stress of the annulus fibrosus from the posterior surface of the disc to the neural foramen. As the result, the von Mises stress adjacent to the fusion level was higher than the other nonfusion levels; it was higher under conditions of flexion moment loading plus compression loading [112% (2.59 PMa) in the PLF model and 117% (2.72 Mpa) in the PLIF model] than in the intact model. The Tresca stress of all the annulus fibrosus adjacent to the fusion level was higher than that on other nonfusion intervertebral levels; it was higher under conditions of flexion moment loading plus compression loading [127% (0.57 PMa) in the PLF model and 209% (0.89 Mpa) in the PLIF model] than in the intact model. The Tresca stress of the annulus fibrosus from the posterior surface of the disc to the neural foramen adjacent to the fusion level was higher than that on other nonfusion intervertebral levels; and it was higher under conditions of flexion moment loading plus compression loading [107% (1.48 PMa) in the PLF model and 112% (1.54 Mpa) in the PLIF model] than in the intact model. These findings demonstrate that with lumbar fusion, stresses on the vertebral end-plate and the annulus fibrosus were high adjacent to the fusion level; furthermore, stresses were higher in the PLIF model than in the PLF model. These results suggested that lumbar spinal fusion might bring with it a risk of damage to the annulus fibrosus and the vertebral end-plate adjacent to the fusion level.
The effect of autogeneic bone marrow (BM) cells and allogeneic demineralized bone matrix (DBM), alone or combined, as transplantation materials was studied in an experimental posterior thoracic spinal fusion model in rabbits. Transplantation of composite grafts composed of BM and DBM showed the first signs of fusion between two spinal segments after four weeks, reaching 86% after 20 weeks. Late fusion results achieved with DBM alone were similar. The capacity of BM per se to build up a spinal fusion was insignificant. Calcified tissue, documented roentgenographically, was shown to develop locally with time, and the earliest bridging of an interspace was noted after four weeks. Histologically, formation of new bone and cartilage was observed after two weeks, showing mature lamellar bone formation between thoracic segments after 20 weeks. Furthermore, increased 45Ca activity was still observed in the fused tissues after 20 weeks. Although, with grafting materials used, this model for experimental spinal fusion gave promising results, further investigations with other fusion techniques could give still better effects.
Despite the fact that pseudarthrosis is the most common complication after posterior spinal fusion, no reproducible diagnostic method has been established. This study analyzes the accuracy of the anteroposterior trispiral tomography in evaluating the posterior spinal fusion mass. Tomography was shown to be both sensitive and specific in its ability to detect the presence or absence of a pseudarthrosis. Radiation exposure is not increased when tomography is performed in lieu of less accurate diagnostic studies. Anteroposterior trispiral tomography is a useful adjunct in the routine postoperative evaluation of the patient who has undergone a posterior spinal arthrodesis.
Twenty-four patients requiring spinal fusion with Harrington rod instrumentation were studied prospectively to determine the effects of moderate hypotension on blood loss, operating conditions, operating time and spinal cord function. Hypotension reduced blood loss and improved operating conditions but did not shorten operating time. Five patients had alterations in somatosensory cortical evoked potentials after straightening of the spine that prompted us to reverse hypotension (when present) and haemodilution, and then to do wake-up tests. All wake-up tests were normal and all evoked potential alterations resolved during operation. Hypotension seems unlikely to increase the risk of neurological damage if spinal cord function is monitored. Our findings suggest that patients subjected to spinal fusion need not be awakened during operation for testing of cord function provided somatosensory evoked potentials are monitored and remain stable.
STUDY DESIGN: Nineteen dogs underwent L4-L5 intertransverse process fusions with either 58 micrograms, 115 micrograms, 230 micrograms, 460 micrograms, or 920 micrograms of recombinant human bone morphogenetic protein-2 carried by a polylactic acid polymer. A previous study (12 dogs) compared 2300 micrograms of recombinant human bone morphogenetic protein-2, autogenous iliac bone, and carrier alone in this model. All fusions subsequently were compared. OBJECTIVES: To characterize the dose-response relationship of recombinant human bone morphogenetic protein-2 in a spinal fusion model. SUMMARY OF BACKGROUND DATA: Recombinant osteoinductive morphogens, such as recombinant human bone morphogenetic protein-2, are effective in vertebrate diaphyseal defect and spinal fusion models. It is hypothesized that the quality of spinal fusion produced with recombinant human bone morphogenetic protein-2, above a threshold dose, does not change with increasing amounts of inductive protein. METHODS: After decortication of the posterior elements, the designated implants were placed along the intertransverse process space bilaterally. The fusion sites were evaluated after 3 months by computed tomography imaging, high-resolution radiography, manual testing, mechanical testing, and histologic analysis. RESULTS: As in the study using 2300 micrograms of recombinant human bone morphogenetic protein-2, implantation of 58-920 micrograms of recombinant human bone morphogenetic protein-2 successfully resulted in intertransverse process fusion in the dog by 3 months. This had not occurred in animals containing autograft or carrier alone. The cross-sectional area of the fusion mass and mechanical stiffness of the L4-L5 intersegment were not dose-dependent. Histologic findings varied but were not related to rhBMP-2 dose. Inflammatory reaction to the composite implant was proportional inversely to the volume of the fusion mass. CONCLUSIONS: No mechanical, radiographic, or histologic differences in the quality of intertransverse process fusion resulted from a 40-fold variation in dose of recombinant human bone morphogenetic protein-2.
Postoperative wound infections following spinal fusion with instrumentation often present diagnostic and therapeutic difficulties. This article reviews 34 such infections. An infection rate of 3.7% was noted. Depending on various clinical indicators, treatment strategies included short-course antibiotics, prolonged intravenous antibiotics, or intravenous antibiotics followed by suppressive antibiotics and eventual hardware removal. To eradicate these infections, removal of instrumentation is often required; this option, however, may result in an unstable spine. Treatment algorithms were developed for treatment of postoperative spinal surgical site infections and to minimize the possibility of spine instability. All patients were cured of their infections.
The purpose of this study was to achieve spinal fusion in the absence of bone graft material using a new, injectable, and semi-liquid synthetic polymer (polylactic acid polyethylene glycol [PLA-PEG] block copolymer) containing recombinant human bone morphogenetic protein-2 (rhBMP-2). Twenty-seven skeletally mature beagles underwent anterior thoracic spinal fusion at T9-T10. Group I (n = 9) was injected with 1 mL of PLA-PEG block copolymer carrier alone into space under the vertebral pleura and the anterior longitudinal ligament. Group II (n = 9) was injected with 1 mL of PLA-PEG carrier containing 500 microgram of rhBMP-2. Group III (n = 9) was injected with 1 mL of PLA-PEG carrier containing 1000 microgram of rhBMP-2. In the Group I animals, no evidence of new bone formation was noted at the implanted sites both radiographically and histologically. In contrast, all of the nine animals in Group III showed new bone formation in 12 weeks, and four of the nine animals in Group II showed bony mass at the injected sites. However, vertebral bony fusion was incomplete despite the significant amount of new bone formation in both groups that showed new bone formation. In addition to resulting in improvements in the surgical procedure, injection of rhBMP-2 and a synthetic polymer is useful for bone formation for spinal fusion.