Eeric Truumees

Bone grafting alternatives in spinal surgery

BACKGROUND CONTEXT Bone grafting is used to augment bone healing and provide stability after spinal surgery. Autologous bone graft is limited in quantity and unfortunately associated with increased surgical time and donor-site morbidity. Alternatives to bone grafting in spinal surgery include the use of allografts, osteoinductive growth factors such as bone morphogenetic proteins and various synthetic osteoconductive carriers. PURPOSE Recent research has provided insight into methods that may modulate the bone healing process at the cellular level in addition to reversing the effects of symptomatic disc degeneration, which is a potentially disabling condition, managed frequently with various fusion procedures. With many adjuncts and alternatives available for use in spinal surgery, a concise review of the current bone grafting alternatives in spinal surgery is necessary. STUDY DESIGN/SETTING A systematic review of the contemporary English literature on bone grafting in spinal surgery, including abstract information presented at national meetings. METHODS Bone grafting alternatives were reviewed as to their efficacy in extending or replacing autologous bone graft sources in spinal applications. RESULTS Alternatives to autologous bone graft include allograft bone, demineralized bone matrix, recombinant growth factors and synthetic implants. Each of these alternatives could possibly be combined with autologous bone marrow or various growth factors. Although none of the presently available substitutes provides all three of the fundamental properties of autograft bone (osteogenicity, osteoconductivity and osteoinductivity), there are a number of situations in which they have proven clinically useful. CONCLUSIONS Alternatives to autogenous bone grafting find their greatest appeal when autograft bone is limited in supply or when acceptable rates of fusion may be achieved with these substitutes (or extenders) despite the absence of one or more of the properties of autologous bone graft. In these clinical situations, the morbidity of autograft harvest is reasonably avoided. Future research may discover that combinations of materials may cumulatively result in the expression of osteogenesis, osteoinductivity and osteoconductivity found in autogenous sources.

A Pilot Study Evaluating the Safety and Efficacy of OP-1 Putty (rhBMP-7) as a Replacement for Iliac Crest Autograft in Posterolateral Lumbar Arthrodesis for Degenerative Spondylolisthesis

Study Design. A prospective, randomized, controlled, multicenter clinical study was conducted. Objective. To compare the clinical and radiographic outcomes of patients treated with OP-1 (BMP-7) Putty to autogenous iliac crest bone graft for one-level uninstrumented posterolateral fusion of the lumbar spine following decompressive laminectomy for the treatment of symptomatic degenerative spondylolisthesis with spinal stenosis. Background. Preclinical studies have demonstrated that osteoinductive recombinant human osteogenic protein1 in the form of OP-1 Putty is successful at achieving a posterolateral fusion in rabbits and dogs without any significant safety concerns. Methods. Thirty-six patients with degenerative lumbar spondylolisthesis and symptoms of neurogenic claudication were randomized (2:1) to either OP-1 Putty (3.5 mg of OP-1 per side) or autogenous iliac crest bone graft for one-level uninstrumented posterolateral fusion following a decompressive laminectomy. Enrollment in the study was complete when 24 OP-1 Putty patients and 12 autograft patients had been randomized and treated. A patient administered Oswestry scale and SF-36 scale were used to determine clinical outcomes. Independent, blinded neuroradiologists reviewed both static and dynamic radiographs to determine fusion status. Results. At the 1-year follow-up, 32 patients were available for clinical analysis and 29 patients were available for radiographic review. Clinical success as measured on the Oswestry scale was achieved by 18 of 21 (86%) OP-1 Putty patients and 8 of 11 (73%) autograftpatients. SF-36 pain index scores showed similar results. Fourteen of 19 (74%) OP-1 Putty patients and 6 of 10 (60%) autograft patients achieved a successful posterolateral fusion fulfilling all fusion criteria. Of the 29 evaluable patients, 15 were both clinical and radiographic successes, 5 were radiographic successes but were clinicalfailures, 1 patient was both a radiographic and clinical failure, and 8 patients were radiographic failures but were clinical successes. No systemic toxicity, ectopic bone formation, recurrent stenosis, or other adverse events related to the OP-1 Putty implant were observed. Conclusion. Although the posterolateral spine is a challenging fusion environment in patients with degenerative spondylolisthesis, successful radiographic fusion was obtained using OP-1 Putty at a rate that was similar to autograft given the number of patients in this study. Importantly, there were no apparent adverse consequences related to the use of the OP-1 Putty implant in this patient population.

Comparison of OP-1 Putty (rhBMP-7) to Iliac Crest Autograft for Posterolateral Lumbar Arthrodesis : A Minimum 2-Year Follow-up Pilot Study

Study Design. A prospective, randomized, controlled, multicenter clinical study. Objective. To compare the safety and clinical and radiographic outcomes of OP-1 (BMP-7) Putty to autogenous iliac crest bone graft in a population of patients undergoing laminectomy and posterolateral fusion for symptomatic lumbar stenosis associated with degenerative spondylolisthesis. Summary of Background Data. Although the existing preclinical and clinical data suggest that OP-1 is able to achieve osteoinduction and clinical fusion in a variety of situations, the efficacy of this recombinant protein in a clinical spine fusion population has not been fully elucidated. This study directly compares the efficacy and safety of OP-1 putty to autograft bone for arthrodesis in patients with symptomatic stenosis in association with degenerative spondylolisthesis. Methods. Thirty-six patients with degenerative lumbar spondylolisthesis and symptoms of neurogenic claudication underwent laminectomy, bilateral medial facetectomy, and posterolateral fusion using either iliac crest autograft or OP-1 Putty. Oswestry scores and SF-36 questionnaires were used to determine the clinical response to treatment. Independent, blinded neuroradiologists reviewed both static and dynamic radiographs to determine the fusion status. Successful fusion was declared whenthe presence of continuous bridging bone between the transverse processes was observed and less than 5° of angular motion and 2 mm of translational movement was measured using digital calipers. Results. Efficacy data were tabulated for 27 patients at the 24-month time point and an additional 4 patients (without evaluable 24-month results) at the 36-month time point. One patient was not evaluable for radiology, so the data reflect clinical information for 31 patients and radiology for 30 patients. Clinical success, defined as a 20% improvement in the preoperative Oswestry score, was achieved by 17 of 20 (85%) OP-1 Putty patients and 7 of 11 (64%) autograft patients. A successful posterolateral fusion was achieved in 11 of 20 (55%) OP-1 Putty patients and 4 of 10 (40%) autograft patients. SF-36 scores showed similar clinical improvement in both groups. No systemic toxicity, ectopic bone formation, recurrent stenosis, or other adverse events specifically related to the use of the OP-1 Putty implant were observed. Conclusion. This study represents the first clinical trial to demonstrate the safety and similarity of OP-1 Putty as a replacement for autogenous bone graft in the posterolateral fusion environment with a minimum of 2-year follow-up. OP-1 Putty was able to achieve osteoinduction leading to a radiographically solid fusion in the absence of autogenous iliac crest bone graft in 55% of the patients at 24 and 36 months. These results compare favorably to the historical fusion rates reported for uninstrumented arthrodesis in this challenging clinical scenario.

Outcome of Local Bone Versus Autogenous Iliac Crest Bone Graft in the Instrumented Posterolateral Fusion of the Lumbar Spine

Study Design. Retrospective, comparative study of clinical and radiologic outcome with independent, blinded observer. Objectives. To compare the clinical and radiologic outcome of instrumented posterolateral lumbar fusion using local bone versus autogenous iliac crest bone graft (ICBG). Summary of Background Data. There is no published report of outcome of posterolateral spinal fusion using local bone alone for degenerative disorders of the lumbar spine. Materials and Methods. Seventy-six cases (male 26, female 50) of spinal stenosis, operated during 1996 and 1997 by the senior author, were reviewed. All the cases had decompression and posterior spinal fusion with pedicle screw instrumentation. Forty cases had only local bone graft obtained from decompression, morselized in a bone mill, and 36 cases had autogenous ICBG. Mean age was 60 years (range, 27–83 years). Fusion was performed at one level in 51 (67%), two levels in 16 (21%), three levels in 5 (7%), and four or more levels in 4 cases (5%). Minimum follow-up was 2-years (mean, 28 years; range, 24–72 months). An independent, blinded radiologist rated plain radiographs as fused, indeterminate, or nonunion. Results. There was no difference in age, sex, and diagnosis between the two groups. Overall fusion rate was higher in the ICBG group (75%, 27 of 36) compared with the local bone group (65%, 26 of 40) but not significantly different (P = 0.391). Analyzed separately according to the number of fusion levels, the local bone group achieved similar fusion rate (∼80%) in single-level fusion but a much smaller fusion rate in multilevel fusion (20% vs. 66%, P = 0.029) compared with the ICBG group. Mean improvement in the Oswestry Disability Inventory was 36% in the local bone group and 32% in the ICBG group. There was no significant difference in overall clinical outcome between the two groups. There was no correlation between fusion status and clinical outcome. Blood loss and hospital stay were significantly less in the local bone group; however, blood losswas more significantly related to the sum total number of segments undergoing decompression and fusion. Conclusions. Use of local bone graft alone achieved a similar fusion rate in single-level fusion but a much smaller fusion rate in multilevel fusion compared with the ICBG group. Local bone graft alone achieved a similar clinical outcome but less morbidity irrespective of number of fusion level.

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

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

Epidural Hematoma and Intraoperative Hemorrhage in a Spine Trauma Patient on Pradaxa (dabigatran)

Study Design. The authors present a case report of a 72-year-old man who presented with back pain and lower extremity weakness after a fall from his roof. Objective. Use of dabigatran (Pradaxa), a new oral anticoagulant, is rapidly increasing. Spine specialists should aware of this medications place for the management of patients with spine pathology. In particular, we intend to report on the emergent treatment of a patient with spinal trauma and epidural hematoma with cord compression. Summary of Background Data. Dabigatran (Pradaxa) is approved by the Food and Drug Administration to decrease stroke risk in patients with atrial fibrillation. Unlike warfarin, dabigatran does not require international normalized ratio monitoring. On the contrary, it is difficult to reverse in patients requiring emergent surgical intervention. Methods. This is a retrospective review of a patient treated at our institution. Results. The patient presented with burst fractures at the T7 and T12 levels. Cord compression was noted at both levels, and was worse at T12. Canal stenosis resulted from both retropulsed bone and epidural hematoma. The patient exhibited bilateral lower extremity numbness and weakness, ASIA C. The patient was taken urgently to the operating room for cord decompression and planned operative stabilization. The treating team used a number of recommended “reversal” agents with little effect on the severe intraoperative hemorrhage. Failure to control the bleeding required interruption of the procedure after the canal decompression. The patient was taken back to the operating room 7 days later for an instrumented posterior spinal fusion. Conclusion. As dabigatran (Pradaxa) has recently been approved by the Food and Drug Administration, many spine specialists are not familiar with this agent. Many of the reversal agents (e.g., vitamin K and protamine), useful for other classes of anticoagulants, have no impact on Pradaxa. Similarly, prothrombin time and partial thromboplastin times have limited utility in estimating the patients true clotting status. The purpose of this case report is to alert spine specialists to this drug and its implications on spine care. The drugs pharmacokinetics, clinical assessment of clotting status, and reversal options are discussed.

Failure of human cervical endplates: a cadaveric experimental model.

Study Design. An in vitro biomechanical study using a servohydraulic testing machine on cadaveric endplates. Objectives. To characterize the effects of bone mineral density, endplate geometry, and preparation technique on endplate failure load. Summary of Background Data. The effects of endplate preparation methods on failure loads are only partly characterized in the literature. Endplate burring has been recommended to increase fusion rates. However, graft subsidence may complicate anterior reconstruction procedures. Methods. After radiographic screening, 21 cadaveric cervical spines underwent dual-energy x-ray absorptiometry scanning to quantify mineral content. Endplate geometry was calculated in 55 randomly selected endplates from the inferior C2 to the superior T1 levels. These vertebrae were embedded in polyester resin and randomly left intact, perforated, or burred. The cervical endplates were loaded at a rate of 0.2 mm/s on an Instron materials tester with an attached 9 mm diameter polycarbonate rod (an area of 64 mm2). A stepwise, univariate linear regression was used to compare the point of endplate failure with the vertebral level, endplate area, gender, age, bone mineral density, and preparation technique. Results. Mean bone mineral density, as measured by dual-energy x-ray absorptiometry, was 0.713 g/cm2 (± 0.173 g/cm2). Mean endplate area was calculated at 323 mm2. A mean compressive force of 754 N (± 445 N) was required before endplate failure. Trends toward increasing compressive loads were noted with decreasing endplate area and increasing bone mineral density. Increasing age (P = 0.0203), caudal vertebral level (P < 0.0001), endplate burring (P = 0.0068), and female gender (P = 0.0452) were associated with significantly lower endplate fracture loads in compression. Conclusions. Bone quality was predictive of endplate compressive failure loads. Intact endplates failed at significantly higher loads than their perforated or burred counterparts.

Effects of Disc Height and Distractive Forces on Graft Compression in an Anterior Cervical Corpectomy Model

Study Design. An in vitro biomechanical study using a calibrated distractor and a subminiature load cell in a cadaveric cervical corpectomy construct. Objective. To study the inter-relationships of defect height, graft height, and compressive and distractive forces in an anterior cervical corpectomy model. Summary of Background Data. The effects of graft size on compressive and distractive forces in cervical corpectomy remain unknown. Larger grafts afford neural decompression through anterior column distraction, but may subject the graft and vertebral bodies to excessive loads, increasing graft fracture, and subsidence risk. Methods. The intended corpectomy defect was measured radiographically in 17 specimens. A C6 corpectomy was performed and the specimens embedded in polyester resin. A distractive force was applied through a strain gauge fitted distractor to allow introduction of allograft struts fixed to a subminiature load cell. After distraction was removed, immediate compressive force was measured. The specimen was then placed in a loading frame to simulate head weight. Results. Distractive forces of 36.65, 70.90, and 118.10 N were required to insert 23, 25, and 27 mm grafts, respectively. On removal of this distraction, immediate compressive loads of 2.87, 4.74, and 8.95 N were noted. No statistically significant relationship between the intended corpectomy height and graft distraction forces was found. A statistically significant relationship was observed between distractive force required for graft insertion and immediate graft compressive force. Distractive force was also significantly related to the compressive force borne by the loaded strut graft. Conclusion. Significantly higher distractive and compressive forces were recorded with larger grafts. Intended corpectomy height was not an accurate predictor of graft loads.

Biomechanical evaluation of the kinematics of the cadaver lumbar spine following disc replacement with the ProDisc-L prosthesis.

Study Design. Biomechanical study of the ProDisc-L in a cadaveric model under pure moment loading. Objective. To determine the kinematic properties of a lumbar spine motion segment and the adjacent level following ProDisc-L disc replacement in the cadaveric spine. Summary of Background Data. Total disc replacement is intended to preserve native motion, in an attempt to prevent accelerated adjacent segment degeneration. The quality and quantity of the motion following TDR may have important consequences on the facet joints of the same motion segment, as well as the motion at the prosthetic component interface. Methods. Ten cadaveric lumbar spines were radiographed (L3–L5) and tested under pure moments (+10 Nm to −10 Nm) with an applied follower load (200 N). Load-deformation was tested in flexion/extension, lateral bending (LB), and axial rotation (AR). Range of Motion (ROM) data were recorded. Superior adjacent disc pressure (L3–L4) was measured using subminiature pressure transducers. The L4–L5 disc was subsequently instrumented with a ProDisc-L. Radiographs and biomechanical tests were repeated. Results. Disc replacement significantly reduced extension (ROM 2.2° ± 0.5° before and 1.2° ± 0.7° after instrumentation) (P = 0.001), but not flexion (ROM 5.6° ± 3.1° before and 6.2° ± 1.2° after) (P = 0.34). Combined flexion/extension motion was marginally reduced (P = 0.517). LB ROM (7.4° ± 2.0°) was marginally reduced (P = 0.072) following instrumentation (6.2° ± 2.5°), while ROM in AR (3.4° ± 1.1°) was significantly increased (4.4° ± 1.2°) (P = 0.001). Superior adjacent segment ROM was preserved. No significant differences in disc pressure were observed at the adjacent motion segment before (199 kPa at maximum flexion and 171 kPa at maximum extension) or after disc replacement (252 kPa and 208 kPa, respectively). Conclusion. In cadaveric spines, ROM of operated and adjacent motion segments was preserved following ProDisc-L insertion. Excision of the anterior anulus may increase laxity, which is taken up by the restoration of disc height and lordosis, at the cost of a moderate loss of flexion/extension motion. Adjacent segment kinematics were unaffected following TDR.

Preoperative Embolization in the Treatment of Spinal Metastasis

Because of advances in the treatment of cancer, the average rate of patient survival is increasing. As patients with cancer live longer, the incidence of spinal metastasis also likely will increase. To help control pain and maintain function, some of these metastases will require surgical intervention. Because >60% of spinal metastases are hypervascular, preoperative embolization may be considered in order to decrease hemorrhage risk and improve outcomes. Embolization for spinal metastasis can be performed through the angiogram catheter. When such embolization is performed carefully, the complication rate is low.