Comparison of thoracoscopic and open thoracic discectomy in a live ovine model for anterior spinal fusion

Biologic Annulus Fibrosus Repair: A Review of Preclinical In Vivo Investigations

Lower back pain, the leading cause of workplace absences and disability, is often attributed to intervertebral disc degeneration, in which nucleus pulposus (NP) herniates through lesions in the annulus fibrosus (AF) and impinges on the spinal cord and surrounding nerves. Surgeons remove extruded NP via discectomy when indicated by local/radicular pain supported by radiographic evidence; however, current interventions do not alter the underlying disease or seal the AF. The reported rates of recurrent herniation or pain following discectomy cases range from 5% to 25%, which has pushed spine research in recent years toward annular repair and closure strategies. Synthetic implants designed to mechanically seal the AF have been subject to large animal and clinical trials, with limited success in preventing recurrent herniation. Like gold standard interventions, purely mechanical devices fail to promote tissue integration, long-term healing, or restore native biomechanical function to the spine. Biological repair strategies utilizing principles of tissue engineering have demonstrated success in overcoming the inadequacies of current interventions and mechanical implants, yet, none has reached clinical or proof-of-concept trials in humans. In this review, we will discuss annular repair strategies promoting biological healing that have been implemented in small and large animal models in vivo, and ways to enhance the efficacy of these treatments.

A computational model to describe the regional interlamellar shear of the annulus fibrosus

Interlamellar shear may play an important role in the homeostasis and degeneration of the intervertebral disk. Accurately modeling the shear behavior of the interlamellar compartment would enhance the study of its mechanobiology. In this study, physical experiments were utilized to describe interlamellar shear and define a constitutive model, which was implemented into a finite element analysis. Ovine annulus fibrosus (AF) specimens from three locations within the intervertebral disk (lateral, outer anterior, and inner anterior) were subjected to in vitro mechanical shear testing. The local shear stress-stretch relationship was described for the lamellae and across the interlamellar layer of the AF. A hyperelastic constitutive model was defined for interlamellar and lamellar materials at each location tested. The constitutive models were incorporated into a finite element model of a block of AF, which modeled the interlamellar and lamellar layers using a continuum description. The global shear behavior of the AF was compared between the finite element model and physical experiments. The shear moduli at the initial and final regions of the stress-strain curve were greater within the lamellae than across the interlamellar layer. The difference between interlamellar and lamellar shear was greater at the outer anterior AF than at the inner anterior region. The finite element model was shown to accurately predict the global shear behavior or the AF. Future studies incorporating finite element analysis of the interlamellar compartment may be useful for predicting its physiological mechanical behavior to inform the study of its mechanobiology.

Thoracoscopy for minimally invasive thoracic spine surgery

Thoracoscopy has been used worldwide for many years by thoracic surgeons. Despite a long learning curve and technical demands of the procedure, thoracoscopy has several advantages, including better cosmesis, adequate exposure to all levels of the thoracic spine from T2 to L 1, better illumination and magnification at the site of surgery, less damage to the tissue adjacent to the surgical field, less morbidity when compared with standard thoracotomy in terms of respiratory problems, pain, blood loss, muscle and chest wall damages, consequent shorter recovery time, less postoperative pulmonary function impairment, and shorter hospitalization. Good results at short- and medium-term follow-up need to be confirmed at long-term follow-up.

Prone thoracoscopic release does not adversely affect pulmonary function when added to a posterior spinal fusion for severe spine deformity

STUDY DESIGN

Prospective clinical study.

OBJECTIVE

To analyze the effect of adding a thoracoscopic release and fusion performed in the prone position with double lung ventilation to a posterior spinal fusion and instrumentation (PSFI) for severe idiopathic scoliosis.

SUMMARY OF BACKGROUND DATA

A prone thoracoscopic anterior release (TAR) offers the advantages of a minimally invasive approach, without requiring repositioning for the PSFI, and has significantly less acute pulmonary complications since single lung ventilation is avoided. It is unclear whether prone thoracoscopy adversely affects pulmonary function tests (PFT) when added to a PSFI for severe deformity.

METHODS

A prospective consecutive series of patients from a single institution undergoing spinal deformity surgery were reviewed. Those patients who underwent prone TAR followed by PSFI were compared to patients who had PSFI alone. In addition, those patients who had a thoracoplasty and PSF (PSFI-T) were compared to those who had a TAR and PSFI with T. (PFTs were measured before surgery and 1, 3, 6 weeks, 3 and 6 months, and 1 year after surgery. Forced vital capacity (FVC) and FE-1 parameters were compared to baseline levels for each patient. RESULTS.: There were 13 patients in the TAR + PSFI groups and 83 in the PSFI groups. The patients in the TAR + PSFI group had larger thoracic curves (83.2 degrees vs. 59.7 degrees ), greater correction (59.4% vs. 50.1%) (P = 0.07), and greater increase in thoracic height (16.4% vs. 6.8%) following surgery. (P < 0.05) PFTs declined more rapidly for the TAR + PSFI patients in the first 3 weeks, however, improved rapidly until 1 year when they were significantly better than the PSFI group for predicted FVC % (29.7% vs. 7.5% above baseline) and forced expiratory volume (FEV) 1% (28.5% and 8.9% above baseline). (P < 0.05) When a thoracoplasty was added to the procedure, the differences in PFTs between those who had a TAR and those who did not was not significant. The TAR + PSFI-T group had FVC % predicted of 5.3% above baseline compared to 4.3% above baseline for the PSFI-T group. The percent predicted FEV 1% was 10.4% above baseline for the TAR + PSFI-T group compared to 4.5% for the PSF-T group (P > 0.05).

CONCLUSION

When performing a prone thoracoscopic release for severe thoracic deformity, excellent coronal plane correction is achieved. There does not appear to be any detrimental effect on pulmonary function when a prone thoracoscopic release using double lung ventilation is added to a PSFI. This technique can be efficacious in achieving excellent deformity correction without adversely affecting pulmonary function and is recommended when treating severe spinal deformity. Adding a thoracoplasty provided a negative effect on pulmonary function and limited the benefits of performing a thoracoscopic release to the PSFI patients.

Anterior and thoracoscopic scoliosis surgery for idiopathic scoliosis

Surgical management of idiopathic scoliosis is based on the natural history of this spinal disorder and on the likelihood of developing a worsening deformity. Anterior surgical treatments continue to evolve and provide advantages over posterior procedures in specific instances. Open and thoracoscopic anterior approaches allow direct access to the anterior stabilizing structures of the spine, enable mobilization of a rigid deformity, and provide a large surface area for arthrodesis. Thoracoscopic procedures provide a more cosmetically appealing alternative to a large midline posterior or anterolateral thoracotomy scar. Although the indications and contraindications for anterior versus posterior surgical intervention (for thoracic and thoracolumbar curve patterns) have been defined to some degree, there remains appropriate flexibility in the decision-making process, allowing the surgeon to make an optimal recommendation for each patient based on surgeon experience and patient needs.

Histomorphometric assessment of thoracoscopically assisted anterior release in a porcine model: safety and completeness of disc discectomy with surgeon learning curve

STUDY DESIGN

A retrospective study using histomorphometric analysis to quantify the percentage of discectomy following thoracoscopic anterior release and fusion in a porcine model.

OBJECTIVE

To investigate the safety and completeness of disc and endplate removal with respect to the learning curve of the surgeon in a porcine thoracoscopic anterior fusion model.

SUMMARY OF BACKGROUND DATA

The thoracoscopic approach has been used to perform an anterior release and fusion before an open posterior instrumentation, however, there is concern that the technique may not provide sufficient visualization or exposure to perform safely and completely.

METHODS

A total of 32 pigs (160 discs) were assigned to 2 groups (early experience, n = 16; late experience, n = 16), and underwent 5 level thoracoscopic anterior release followed by anterior instrumentation and fusion from T5 to T10. At 4 months after surgery, the spines were harvested, and each discectomy disc was histomorphometrically analyzed to determine the percentage of disc excision and amount of endplate removal.

RESULTS

There were no significant differences in the percent disc excision between the early (67% +/- 11%) and late groups (69% +/- 10%). Greater than 50% of the disc was excised in 151 of 160 discectomies (94%). Both superior and inferior endplates were resected in 92 of 160 disc levels (57%). The amount of endplate removal had improved over time in both early and late groups (P < 0.0001). The histologic examination revealed no evidence for posterior longitudinal ligament disruption or spinal canal encroachment in any disc.

CONCLUSIONS

Video-assisted thoracoscopic discectomy is safe and allows for a significant amount of disc material excision. This study did not demonstrate a learning curve with respect to the amount of disc material excised, but a learning curve was seen for endplate excision.

Osseointegration of hollow cylinder based spinal implants in normal and osteoporotic vertebrae: a sheep study

INTRODUCTION

Osteoporosis is not only responsible for an increased number of metaphyseal and spinal fractures but it also complicates their treatment. To prevent the initial loosening, we developed a new implant with an enlarged implant/bone interface based on the concept of perforated, hollow cylinders. We evaluated whether osseointegration of a hollow cylinder based implant takes place in normal or osteoporotic bone of sheep under functional loading conditions during anterior stabilization of the lumbar spine.

MATERIALS AND METHODS

Osseointegration of the cylinders and status of the fused segments (ventral corpectomy, replacement with iliac strut, and fixation with testing implant) were investigated in six osteoporotic (age 6.9 +/- 0.8 years, mean body weight 61.1 +/- 5.2 kg) and seven control sheep (age 6.1 +/- 0.2 years, mean body weight 64.9 +/- 5.7 kg). Osteoporosis was introduced using a combination protocol of ovariectomy, high-dose prednisone, calcium and phosphor reduced diet and movement restriction. Osseointegration was quantified using fluorescence and conventional histology; fusion status was determined using biomechanical testing of the stabilized segment in a six-degree-of-freedom loading device as well as with radiological and histological staging.

RESULTS

Intact bone trabeculae were found in 70% of all perforations without differences between the two groups (P = 0.26). Inside the cylinders, bone volume/total volume was significantly higher than in the control vertebra (50 +/- 16 vs. 28 +/- 13%) of the same animal (P<0.01), but significantly less (P<0.01) than in the near surrounding (60 +/- 21%). After biomechanical testing as described in Sect. "Materials and methods", seven spines (three healthy and four osteoporotic) were classified as completely fused and six (four healthy and two osteoporotic) as not fused after a 4-month observation time. All endplates were bridged with intact trabeculae in the histological slices.

CONCLUSIONS

The high number of perforations, filled with intact trabeculae, indicates an adequate fixation; bridging trabeculae between adjacent endplates and tricortical iliac struts in all vertebrae indicates that the anchorage is adequate to promote fusion in this animal model, even in the osteoporotic sheep.

Minimally Invasive Fusion and Fixation Techniques

Instrumented fusion plays an important role in treating a variety of degenerative and traumatic diseases of the spine. Traditional open techniques have been associated with a high degree of approach-related morbidity because of muscle retraction and blood loss. A variety of minimally invasive techniques have been developed for instrumentation of the entire spine. Advances in our understanding of the cellular and molecular mechanisms for stable bony fusion should promote the use of even less invasive techniques in the future.

Neuroendoscopy for spinal disorders: a brief review

Neuroendoscopy has grown rapidly in the last 20 years as a therapeutic modality for treating a variety of spinal disorders. Spinal endoscopy has been widely used to treat patients with cervical, thoracic, and lumbosacral disorders safely and effectively. Although it is most commonly used with minimally invasive lumbar spine surgery, endoscopy has gained widespread acceptance for the treatment of thoracic disc herniations and for anterior release and rod implantation in the correction of thoracic spinal deformity. The authors review the use of endoscopy in spine surgery and in the treatment of spinal disorders as well as in the treatment of intrathoracic nonspinal lesions. Endoscopy has some significant advantages over open or other minimally invasive techniques in that it can allow for better visualization of the lesion, smaller incision sizes with reduced morbidity and mortality, reduced hospital stays, and ultimately lower cost. In addition, spinal endoscopy allows observers and operating room staff to be more involved in each case and fosters education. Spinal endoscopy, like any novel modality, carries with it additional risks and the surgeon must always be prepared to convert to an open procedure. The learning curve for spinal endoscopy is steep and the procedure should not be attempted alone by a novice surgeon. Nevertheless, with training and experience, the spine surgeon can achieve better outcomes, reduced morbidity, and better cosmesis with spinal endoscopy, and the operating times are comparable to open procedures. As technology evolves and more experience is obtained, neuroendoscopy will likely achieve further roles as a mainstay in spine surgery.

Mini-open thoracoscopically assisted thoracotomy versus video-assisted thoracoscopic surgery for anterior release in thoracic scoliosis and kyphosis: a comparison of operative and radiographic results

BACKGROUND CONTEXT

Combining anterior release and interbody fusion with posterior instrumented fusion is an accepted treatment for severe rigid spinal deformity. Video-assisted thoracoscopic surgery (VATS) and mini-open thoracoscopically assisted thoracotomy (MOTA) are two minimally invasive approaches to the thoracic spine. Both reduce surgical trauma, improve cosmesis and provide effective exposure for release and fusion. Published data and the authors' surgical experience have demonstrated that both techniques are equivalent in degree of release to traditional open thoracotomy, but no comparison between these two minimally invasive alternatives has been published to our knowledge.

PURPOSE

This study compared MOTA and VATS under the hypothesis that both result in similar corrections and comparable operative parameters when used in conjunction with posterior instrumented fusion.

STUDY DESIGN/SETTING

Retrospective chart review of consecutive case series by two surgeons.

PATIENT SAMPLE

Twenty-one (13 female, 8 male) patients underwent MOTA and 24 patients (17 female, 7 male) underwent VATS for anterior release, discectomy and fusion prior to posterior instrumented fusion.

OUTCOME MEASURES

Outcomes were measured at a minimum of 1-year follow-up and included radiographic Cobb measurements and operative parameters.

METHODS

The indications for surgery included rigid and severe scoliosis or thoracic kyphosis. Data collection included preoperative demographics, number of levels released, primary curve correction, operative time and blood loss. Data were normalized per number of levels released anteriorly. Statistical analysis of results was done using a two-sample t test assuming equal variances with two-tail p values less than .05.

RESULTS

More anterior levels were operated on average in the VATS group (6.33 vs. 4.38 levels). Curve correction per anterior level released was similar in both groups (8.7 and 8.8 degrees/level for MOTA and VATS, respectively). There was a significant difference in operative time with MOTA averaging 131.7 minutes and VATS averaging 162.8 minutes. However, a comparison of the operative time per anterior level operated, approached statistical significance in favor of VATS (33.0 vs. 28.4 minutes, p=.08). There was no significant difference in estimated blood loss during the anterior portion of the surgeries. There was a trend toward decreased blood loss per operated level favoring VATS (68.4 vs. 38.9 cc, p=.09).

CONCLUSIONS

Both approaches resulted in corrections that compare favorably with open thoracotomy. We suggest that a factor in choosing between these two minimally invasive techniques is the number of thoracic levels requiring release. For four levels or less, MOTA provides an excellent alternative to standard thoracotomy. For five or more levels, VATS provides for excellent exposure of additional levels with the advantages of less operative time and blood loss per operated level.

Animal models for spinal fusion

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

Accurate Preoperative Rod Length Measurement for Thoracoscopic Anterior Instrumentation and Fusion for Idiopathic Scoliosis

OBJECTIVE

Anterior thoracoscopic instrumentation/fusion for adolescent idiopathic scoliosis has long operative times and does not allow surgeons to adjust rod length within the chest. Intraoperative rod length measurement requires placing measurement devices into the chest, adding operative time, and results in overestimation of rod length. The study purpose was to develop a method to preoperatively determine accurate rod length.

METHODS

Two groups of patients were analyzed depending on when the rod length was determined: group 1: intraoperatively using intraoperative rod-measuring device (n = 12); group 2: preoperatively using the new technique (n = 12). For group 2, the preoperative convex length was measured between planned instrumented levels on the preoperative posteroanterior (PA) film, and ideal rod length was measured on the postoperative PA radiograph. The conversion ratio was determined by dividing the preoperative convex length by the ideal rod length and was 1.29 +/- 0.08.

RESULTS

For group 1, the actual rod length was 3.8 cm longer than the ideal length compared with 0.8 cm for group 2 (P < 0.05). Operative times improved (51.4 vs 46.2 min/disc level) after adopting this technique.

CONCLUSIONS

A simple and accurate preoperative method to determine appropriate rod length for thoracoscopically assisted anterior instrumentation/fusion was developed, which saves operative time and is more accurate when compared with the intraoperative method. This technique can be applied when using an open anterior approach.

Thoracolumbar fracture stabilization: comparative biomechanical evaluation of a new video-assisted implantable system

Minimally invasive techniques for spinal surgery are becoming more widespread as improved technologies are developed. Stabilization plays an important role in fracture treatment, but appropriate instrumentation systems for endoscopic circumstances are lacking. Therefore a new thoracoscopically implantable stabilization system for thoracolumbar fracture treatment was developed and its biomechanical in vitro properties were compared. In a biomechanical in vitro study, burst fracture stabilization was simulated and anterior short fixation devices were tested under load with pure moments to evaluate the biomechanical stabilizing characteristics of the new system in comparison with a currently available system. With interbody graft and fixation the new system demonstrated higher stabilizing effects in flexion/extension and lateral bending and restored axial stability beyond the intact spine, as well as having comparable or improved effects compared with the current system. Because of this biomechanical characterization a clinical trial is warranted; the usefulness of the new system has already been demonstrated in 45 patients in our department and more than 300 cases in a multicenter study which is currently under way.

Endoscopic Instrumented Posterolateral Lumbar Fusion with Healos and Recombinant Human Growth/Differentiation Factor-5

OBJECTIVE

The goal of this study was to use a minimally invasive endoscopic surgical technique in a sheep model to evaluate the efficacy of an osteoinductive growth factor, recombinant human growth/differentiation factor-5 (also designated MP52), and an osteoconductive matrix formulation (Healos; DePuy AcroMed, Inc., Mountain View, CA) for inducing and facilitating bone formation.

METHODS

Twelve mature sheep underwent bilateral posterolateral lumbar fusion and pedicle screw fixation via a posterior endoscopic approach. Each sheep received two different types of graft material, autogenous iliac crest bone, or a bone graft substitute (MP52 with Healos), inserted into the right and left sides of the spine in an alternating fashion. Groups of four sheep were killed at 2, 4, and 6 months postoperatively for manual, radiographic, and histological evaluation.

RESULTS

No neurological impairments, infections, or other complications were observed. After 2 months, partial fusion on both sides was observed, but radiographic evaluation showed greater bone growth on the side that received the bone graft substitute. Solid posterolateral fusion was observed in both autograft and bone graft substitute sites at 4 and 6 months, and autograft and Healos MP52 fusion sites were essentially the same at histological examination. There was no abnormal overgrowth of new bone from either of these two materials.

CONCLUSION

Endoscopic posterolateral lumbar arthrodesis and instrumentation is feasible, safe, and effective in a sheep model. Healos is a useful bonding agent that mimics natural bone in posterolateral intertransverse fusion sites. Combined with MP52, it produced fusion comparable to that of autogenous bone graft. Minimally invasive techniques and bone graft substitutes could eliminate morbidity and increase the likelihood of successful fusion.

A comparison between the prone and lateral position for performing a thoracoscopic anterior release and fusion for pediatric spinal deformity

STUDY DESIGN

Retrospective review of all patients who had a single stage thoracoscopic anterior release and spine fusion followed by a posterior spinal fusion with posterior instrumentation.

OBJECTIVE

To analyze the results and complications of patients undergoing a thoracoscopic anterior release and fusion comparing those performed prone with those in the lateral position.

SUMMARY OF BACKGROUND DATA

The lateral position has traditionally been used when performing a thoracoscopic anterior spinal release and fusion during a single-stage anterior spinal release and fusion/posterior spinal fusion with instrumentation. Although some have reported the thoracoscopic technique in the prone position, there are no direct comparison studies between the prone and lateral position.

METHODS

A retrospective review was performed of all patients who had a single stage thoracoscopic anterior spinal release and fusion and posterior spinal fusion with instrumentation from a single institution. The medical record was reviewed to determine demographic data, positioning of the patient, levels fused, anesthesia time, operative time, chest tube drainage, and complications. Radiographs were reviewed to determine preoperative curve magnitude and postoperative curve correction. The Student t test was used to compare groups and statistical significance was defined as P < 0.05.

RESULTS

There were 16 patients in the prone group and 27 in the lateral group. Adolescent idiopathic scoliosis was the most common diagnosis in both groups. All patients had a single-stage thoracoscopic anterior spinal release and fusion/posterior spinal fusion with instrumentation. In the prone group, the patient was positioned prone on a Hall-Relton frame or roll (small patients) for both the anterior spinal release and fusion and posterior spinal fusion with instrumentation. There were no significant differences between the prone and lateral groups with respect to age, gender, height, weight, and curve magnitude (73.8 degrees vs. 71.5 degrees ). There were fewer fused anterior levels in the prone group (5.3 vs. 6.2) (P = 0.05). When analyzing parameters that reflect potential difficulties imposed by the prone position, there were no statistically significant differences noted between groups, although there was a trend toward less anterior operative time per disc (24.3 vs. 25.9 minutes/disc), greater blood loss/anterior disc level (33.5 vs. 26.8 cc/disc), greater total chest tube drainage (445 vs. 419 cc), and less days with the chest tube in place (2.2 vs. 2.3 days) for the prone group when compared to the lateral group. There were statistically significant differences between the prone and lateral groups with respect to anesthesia preparation time (42.8 vs. 64.8 minutes), delay between the completion of the anterior procedure and the start of the posterior procedure (11.8 vs. 69.5 minutes), and the incidence of complications related to the use of single-lung ventilation (0 vs. 14.8%)(P < 0.05). Patients in the prone group required less time on oxygen after surgery (34.8 vs. 51.6 hours) and were discharged home earlier (4.6 vs. 5.5 days) (P < 0.05).

CONCLUSIONS

A thoracoscopic anterior spinal release and fusion in the prone position appears to achieve the same results as when performed in the lateral position for pediatric spinal deformity. The prone position saves time in the operating room due to decreasing the time needed by the anesthesiologists and the transition time between the anterior and posterior procedures. Potentially serious complications related to single-lung ventilation are avoided with bilateral-lung ventilation in the prone position.

Anterior endoscopic discectomy and fusion for adolescent idiopathic scoliosis

STUDY DESIGN

A review of adolescent patients with idiopathic scoliosis undergoing endoscopic release and spinal fusion.

OBJECTIVE

To describe the indications, techniques, results, and complications of thoracic anterior endoscopic scoliosis surgery.

SUMMARY OF BACKGROUND DATA

Anterior endoscopic treatment of thoracic adolescent idiopathic scoliosis has become an alternative method of surgical treatment.

METHODS

Twenty-one patients with adolescent idiopathic scoliosis have undergone a thoracic anterior endoscopic release and fusion followed by posterior instrumentation and fusion. Indications for the endoscopic fusion were large curve magnitude, skeletal immaturity, and/or thoracic hyperkyphosis. Eleven patients have undergone anterior endoscopic instrumentation and fusion for thoracic scoliosis curves between 45 degrees and 70 degrees, using a single screw/single rod construct and autogenous rib bone graft.

RESULTS

Results from the anterior endoscopic release and fusion procedures followed by a posterior instrumentation and fusion had an average preoperative curve of 82 degrees (range, 41 degrees -125 degrees ), with postoperative correction to 28 degrees (range, 5 degrees -60 degrees ) showing 70% correction. For patients undergoing an anterior endoscopic instrumentation and fusion, the average preoperative Cobb measurement of 53 degrees (range, 44 degrees -62 degrees ) was corrected to an average 26 degrees (range, 18 degrees -38 degrees ) for an average correction rate of 51%. One patient undergoing an anterior endoscopic release was converted to an open procedure for end plate bony bleeding without sequelae. One patient with an anterior endoscopic instrumentation and fusion had revision anterior surgery for a distal set screw dislodgment and subsequent posterior instrumentation and fusion for pseudarthrosis.

CONCLUSIONS

The use of both anterior endoscopic release and fusion combined with either anterior instrumentation or separate posterior instrumentation and fusion continues to evolve. Surgeons treating patients with these techniques must understand that there are specific indications for them and many technique options available to optimize surgical results.

Thoracoscopic anterior instrumentation and fusion for idiopathic scoliosis

Thoracoscopically assisted surgery is a new approach to access the anterior spine to perform biopsies, anterior releases, diskectomies, and anterior instrumentation and fusion for idiopathic thoracic scoliosis. This approach compromises the chest wall less than an open thoracotomy does because it uses several small portal incisions. It has been suggested that this approach allows fusion of fewer motion segments and better correction of curvature than does posterior spinal fusion and instrumentation. The technique, which is still evolving, is technically demanding, requiring advanced training and special instrumentation and anesthesia techniques.

Enhanced primary stability through additional cementable cannulated rescue screw for anterior thoracolumbar plate application

OBJECT

The authors conducted a study to investigate the biomechanical in vitro influence of a new anchorage system for fixation of anterior stabilization devices and the possibility of using additional cement after screw insertion to compensate for poor bone quality. The incidence of osteoporosis-related fractures has increased nearly twofold in the last decade. Because of problems associated with anterior screw fixation such as loosening, mechanical failure, and the weakness of osteoporotic bone, current surgical treatments of vertebral body (VB) fractures are problematic. This is due to poor fixation strength of anterior screws in the adjacent segments. The aim of this study was to determine whether a new cemented and uncemented VB screw provides improved primary stability following placement of anterior instrumentation in cases of fracture.

METHODS

The primary stability-related parameters of a new uncemented/cemented screw were compared with those of conventional monocortical screw fixation in a burst fracture model in which strut graft and anterior overbridging instrumentation were used. The use of the new uncemented screw improved the range of motion (ROM) of the stabilized spine in flexion-extension by approximately 22%, in rotation by 20%, and in lateral bending by 15%. Additional cementation improved the ROM by approximately 41% in flexion-extension, 32% in rotation, and 30% in lateral bending compared with conventional monocortical screw fixation.

CONCLUSIONS

The new cannulated screw improves fixation strength and primary stability parameters. It is useful in the initial treatment of fractures in cases of poor bone quality and as a rescue device if previously inserted screws do not remain securely in place.

Thoracoscopic discectomy and fusion in an animal model: safe and effective when segmental blood vessels are spared

STUDY DESIGN

Disc-endplate excision and spine fusion were compared in animals randomly assigned to segmental vessel-spared and segmental vessel-ligated groups in an in vivo goat model of anterior spine discectomy and fusion using thoracoscopic techniques.

OBJECTIVES

To compare safety and completeness of disc and endplate excision, and to perform a histologic and biomechanical comparison between fusion masses when the segmental vessels are spared and when they are ligated using thoracoscopic techniques. SUMMARY OFF BACKGROUND DATA: Because thoracoscopy is relatively new and technically demanding, many surgeons ligate the segmental blood vessels to enhance spine exposure and limit the risk of injury during discectomy and fusion. Although rare, spinal cord compromise secondary to segmental vessel ligation has been reported.

METHODS

This study was divided into two phases. In Phase 1, 10 mature goats were randomly assigned to either the segmental vessel-ligated or the segmental vessel-spared group. Disc and endplate excision was performed at six consecutive thoracic levels in each animal (30 levels per group). The animals were killed, and the depth of disc excision was measured in the transverse and sagittal planes. The vertebral bodies then were separated through the disc space; photographic images of the endplates were digitized, and the area of endplate excision was calculated. In Phase 2, 12 mature goats were randomly assigned to the segmental vessel-ligated or vessel-spared group, and five noncontiguous thoracic segments were fused using autologous iliac crest graft. At 4 months the animals were killed, and the spines were harvested. At each disc level, the three-dimensional rotational and translational motions were analyzed and histomorphometric analysis was performed.

RESULTS

Phase 1: Each animal survived the operative procedure, and no surgical complications occurred. No difference was found between vessel-ligated and vessel-spared groups in operative time (21.8 vs 22.7 minutes per disc), blood loss (97 vs 159 mL), or transverse (81% vs 74%) or sagittal (85% vs 85%) disc excision. The total area of endplate excision was 70% in the vessel-ligated group and 67% in the vessel-spared group (P > 0.1). Phase 2: Biomechanical testing demonstrated no difference in stiffness of the fused segments between the two groups in flexion-extension or axial rotation. However, greater flexibility in lateral bending was found in the specimens whose vessels were ligated (P < 0.05). The percentage of trabecular bone volume was similar between the two groups.

CONCLUSIONS

The segmental vessels in the thoracic spine can be effectively spared without injury during disc excision and fusion. Although slightly more disc area was excised with ligation of the vessels, this was not statistically significant, and the fusion mass was similar between the two groups. Sparing the segmental vessels may provide blood supply that aids fusion mass, and the result may be greater spine stiffness in the coronal plane. Sparing the segmental vessels during thoracoscopic anterior disc excision and fusion can be safe. It should be considered in patients with a high risk for neurologic injury because of decreased spinal cord perfusion in revision surgery, severe kyphosis, congenital anomalies. Because the neurologic risk of vessel ligation has not been clearly established for idiopathic scoliosis, the surgeon will have to consider the risk-benefit ratio of adopting these methods when deciding not to ligate vessels in these patients.

Postoperative Clostridium perfringens lumbar discitis with septicemia: report of a case with survival

This case report describes the successful treatment of a case of Clostridium perfringens postoperative discitis and suggests a management protocol for this condition. The medical literature to date reports only one similar case, treated without success. The patient has been well but the affected space later collapsed with mechanical pain and has required fusion. C. perfringens discitis can be treated successfully.

[Endoscopic surgery for thoracic spine. Critical review]

After the development of video-assisted technology, endoscopic techniques have assumed an important therapeutic role into thoracic cavity. This is a literature review article to show the current state of the endoscopy for thoracic spine. Disc herniations, deformities, infections, tumors, congenital disorders and traumatic events have been treated by endoscopic techniques. On reviewing the literature, the advantages over open approaches are: enhanced visualization, shorter recovery time and decreased blood loss, costs, infection rate and post operative morbidity. Some disadvantages are: one lung anesthesia, significant learning curve, and technical problems in operating on small children, repairing the dura and performing instrumentation. Overall benefits are apparently clear. However, despite the high degree of enthusiasm, authors are cautious to state that endoscopic techniques to the spine already represent a definitive alternative to standard techniques. Comparison between endoscopic and open approaches are still difficult because of the lack of appropriate comparative studies. Authors, although optimistic recommend more prospective, multicentric and randomized studies in order to stand a definitive conclusion.