[Development and clinical application of a thoracoscopy implantable plate frame for treatment of thoracolumbar fractures and instabilities]

[Current status of thoracoscopic surgery for thoracic and lumbar spine. Part 1: general aspects and treatment of fractures]

INTRODUCTION

Thoracoscopic surgery or video-assisted thoracic surgery (VATS) of the thoracic and lumbar spine has greatly evolved since it appeared less than 20 years ago. Nowadays, it is indicated in a large number of processes and injuries. The aim of this article, in its 2 parts, is to review the current status of VATS in treatment of the thoracic and lumbar spine in its entire spectrum.

DEVELOPMENT

After reviewing the current literature, we develop each of the large groups of indications where VATS is used, one by one. This first part contains a description of general thoracoscopic surgical technique including the necessary prerequisites, transdiaphragmatic approach, techniques and instrumentation used in spine reconstruction, as well as a review of treatment and specific techniques in the management of spinal fractures.

CONCLUSIONS

Thoracoscopic surgery is in many cases an alternative to conventional open surgery. The transdiaphragmatic approach has made endoscopic treatment of many thoracolumbar junction processes possible, thus widening the spectrum of therapeutic indications. These include the treatment of fractures and deformities, as well as the reconstruction of injured spinal segments and decompression of the spinal canal in any etiological processes if the lesion placement is favourable to antero-lateral approach. Good clinical results of thoracoscopic surgery are supported by the growing experience reflected in a large number of articles. The degree of complications in thoracoscopic surgery is comparable to open surgery, with benefits in morbidity of the approach and subsequent patient recovery.

Six-year outcome of thoracoscopic ventral spondylodesis after unstable incomplete cranial burst fractures of the thoracolumbar junction: ventral versus dorso-ventral strategy

PURPOSE

The purpose of this study is to determine the long term-results after thoracoscopic spondylodesis particularly with respect to a ventral versus dorso-ventral treatment strategy.

METHODS

In this prospective cohort study, a follow-up examination was performed in 19 patients (seven men, 12 women, average age: 37.7 years, follow-up rate: 79 %), six years after ventral thoracoscopic spondylodesis of unstable, incomplete burst fractures. Nine patients received a ventral monosegmental spondylodesis with iliac crest bone graft. The other ten cases were treated dorso-ventrally, five undergoing a ventral monosegmental treatment with iliac crest bone graft; the other five a ventral bisegmental treatment with expandable titanium cage.

RESULTS

The complication rate was 15.7 %, the rate of revision of 10.5 %. No complication was related to the ventral thoracoscopic approach, whereas all of them were related to the iliac crest bone graft. The operative bisegmental kyphotic reduction was higher in the dorso-ventrally treated group. Afterwards, the loss of reduction was similar in both study groups. The mean VAS spine score summed up to more than 80 in both groups. The mean PCS scores were comparable to a normal healthy collective of the same age.

CONCLUSIONS

The ventral thoracoscopic approach to the spine seems to be a safe therapeutic strategy. A dorso-ventral treatment concept goes along with a higher operative reduction potential.

6-Year follow-up of ventral monosegmental spondylodesis of incomplete burst fractures of the thoracolumbar spine using three cortical iliac crest bone grafts

INTRODUCTION

Autologous bone graft is the gold standard for vertebral body replacement. Currently, after modern implants for vertebral body replacement are available, controversies exist regarding the optimal implant strategy.

PATIENTS AND METHODS

Between 2002 and 2003, 17 patients were included in this study, all suffering from incomplete burst fractures of the thoracolumbar spine. All of them were treated by ventral monosegmental spondylodesis using iliac crest bone graft. The individual treatment strategy depended on the fracture situation and patient's condition. After an average of 74 months (range 66-84) a clinical and computer tomographic follow-up examination was performed in 14 patients (average age, 35.2 years) including VAS spine score and SF 36 score. Nine patients were treated ventral only five patients dorsoventrally.

RESULTS

Complete osseous consolidation was visible in nine, partial consolidation (>30 %) in four, and lysis in one patient, without any significant differences between ventral only or dorsoventral approach. After removal of the fixateur interne the level of consolidation improved in all patients, treated dorsoventrally. There was no significant correlation between percentage of osseous consolidation and the clinical follow-up parameters. After 6 years, 71 % of the patients suffered from persistent pain associated with the approach to the iliac crest. Two revision surgeries have been necessary.

CONCLUSION

High rates of osseous consolidation are visible 6 years after ventral spondylodesis by iliac crest bone grafts. A further improvement of consolidation can be expected after dorsal implant removal. But the surgical approach to the iliac crest is accompanied with a relevant complication rate.

Adipose lesions of nerve: the need for a modified classification

OBJECT

Adipose lesions of nerve are rare and poorly understood. Their current classification, although not universally accepted, generally includes lipomatosis of nerve with or without localized macrodactyly, and intra- as well as extraneural lipoma. The authors believe that the spectrum of these lesions and their interrelationships are not currently appreciated. They propose an adaptation to the existing framework to illustrate the expanding spectrum of adipose lesions of nerve by considering lipomatosis and lipoma singly or in combination.

METHODS

Fourteen representative cases are presented to demonstrate not only the intraneural and extraneural examples of lipomatosis and lipoma, but also their anatomical combinations.

RESULTS

Based on the cases presented and a careful literature review, a conceptual approach to the classification of adipose lesions of nerve is generated. This approach incorporates the 2 essential lesions, lipomatosis of nerve and lipoma, in both their intra- and extraneural forms. This permits expansion to encompass combinations.

CONCLUSIONS

To press the concept that adipose tumors of nerve are a broad but interrelated spectrum of lesions, the authors propose modification of the present classification system. This approach provides an orderly platform for progress, reflects understanding of these interrelated lesions, and facilitates optimal treatment by distinguishing resectable from nonresectable components.

A new distractable implant for vertebral body replacement: biomechanical testing of four implants for the thoracolumbar spine

INTRODUCTION

Expandable titanium implants for vertebral body replacement in the thoracolumbar spine have been well established in the reconstruction of the anterior spinal column. Load transfer at the bone-implant interface remains a point of concern. The purpose of the study was to compare the performance in axial load transfer from the implant to the vertebral body in four different implants, all of them in clinical use to date.

MATERIALS AND METHODS

We tested a second generation implant (Synex II) in comparison to three different expandable titanium cages: Synex I, Obelisc and X-Tenz. Twenty-four intact fresh frozen human lumbar vertebrae (L1-L4) were distributed into four identical groups according to bone mineral density (BMD). The BMD was determined by quantitative computed tomography (qCT). Specimens were loaded in craniocaudal direction with a material testing machine (Mini Bionix II) at a constant speed of 5 mm/min. Load displacement curves were continuously recorded for each specimen until failure (diminishment of compressive force (F) and/or obvious implant migration through the vertebral body end plate). One-way analysis of variance (ANOVA) and post-hoc tests (Bonferroni) were applied to detect differences at 1, 2, 3, and 4 mm displacement (F (1-4 mm)) between implant groups.

RESULT

No significant differences were observed with regard to maximum compression force (F (max)) and displacement (d (max)) until failure: Synex II (1,782.3 N/4.67 mm); Synex I (1,645.3 N/4.72 mm); Obelisc (1,314.0 N/4.24 mm); X-Tenz (1470.3 N/6.92 mm). However, the mean compression force at 1-4 mm displacement (F (1-4 mm): 300-1,600 N) was highest for Synex II. The difference at 2 mm displacement was significant (p = 0.028) between Synex II (F (2 mm) = 879 N) and X-Tenz (F (2 mm) = 339 N).

CONCLUSION

The modified end plate design of Synex II was found to perform comparably at least with regard to the compressive performance at the implant-bone interface. The risk of the new implant for collapse into the vertebral body might be reduced when compared to the competitors.

Video-assisted treatment of thoracolumbar junction fractures using a specific distractor for reduction: prospective study of 50 cases

Posterior instrumentation allows good osteosynthesis for thoracolumbar junction fractures. However, in approximately 20% of cases, anterior bone defects may persist, leading to pseudoarthrosis and loss of reduction. Anterior approaches can circumvent this drawback, but they are considered aggressive with a high rate of complications. The advent of the endoscopic mini-invasive techniques has led to a reduction in the number of complications while maintaining the same consolidation rate. Nevertheless, poor restitution of anatomic curves is a reproach for this technique. This prospective study reports clinical and radiological result of 50 patients (19 women and 31 men) operated between April 2000 and March 2006 with a video-assisted anterior approach using an endodistractor for reduction and consequent insertion of the implant. There were A3 (n = 44), A2 (n = 2), A1 (n = 3) and C1 (n = 1) fractures (Magerl classification). The specific system for fracture reduction was used in the last 39 cases of this series. A Pyramesh cage (Medtronic, Memphis, USA) was used in 15 patients, a peek cage (Creaspine, Bordeaux, France) in 30 patients and a tricortical graft in 5 patients. Standard X-rays and CT scan were performed pre-operatively. Kyphosis, and angulations were measured pre-, per- and post-operatively. Mean immediate postoperative gain in localized kyphosis was 12.18 degrees and mean gain at last follow-up was 11.71 degrees. Mean immediate postoperative gain in RA was 13.24 degrees and remained identical at last follow-up. Five patients had a transient pulmonary atelectasia and there was one pulmonary infection. No neurological complication occurred. Fracture reduction is comparable to the best thoracotomy series while limiting approach-related complications.

[Spinal column injuries in sport: treatment strategies and clinical results]

BACKGROUND

The management of patients with sport-related injuries of the spine is a challenging issue with regard to the ability to resume former sport activities. The current study analyses the rate of resumption of sports participation after conservative and operative treatment.

METHODS

In a 2-year period, 96 patients with sport-related injuries of the thoracic and lumbar spine were included in this prospective study. Conservative (19%) or operative treatment (81%) was performed depending on the extent, severity and instability of the trauma. The reduction, the loss of reduction over time and the VAS and Odom scores were assessed. A questionnaire was included to estimate the rate of resumption of sports participation.

RESULTS

Of the patients 91% resumed sports participation and 9% had to abandon all sport activities mostly due to neurological deficits. Minor loss of correction was found in patients with 360 degrees short segment fusions and major loss was found after conservative treatment.

CONCLUSION

The current management of injuries of the spine effectuates a high rate of resumption of sports activity following conservative or operative treatment.

[An improved vertebral body replacement for the thoracolumbar spine. A biomechanical in vitro test on human lumbar vertebral bodies]

BACKGROUND

In recent years, the use of expandable titanium cages for vertebral body replacement in the thoracolumbar spine has been well established for the treatment of tumors, unstable traumatic lesions, or posttraumatic deformity. Collapse of the implant into the vertebral body remains a point of concern. A biomechanical compression test was designed to assess implant subsidence for a newly developed prototype for vertebral body replacement in the thoracolumbar spine using human cadaveric lumbar vertebrae. The objective of this study was to compare the compressive performance of a new expandable cage with modified end-plate design with three commonly available expandable cages for vertebral body replacement.

MATERIALS AND METHODS

The compressive strengths at the implant-vertebral body interface were measured via axial loading of the new prototype (Synex II) in comparison with three different expandable titanium cages: Synex I (Synthes), Obelisc (Ulrich Medical) and X-Tenz (DePuy Spine). Twenty-four intact, fresh frozen human lumbar vertebrae (L1-L4) were distributed into four identical groups according to BMD (determined by quantitative computed tomography) and the vertebral level. Specimens were loaded in the craniocaudal direction with a material testing machine at a constant speed of 5 mm/min. Load displacement curves were continuously recorded for each specimen until failure (diminishment of compressive force (F)/obvious implant migration through the vertebral body endplate). One-way analysis of variance and post-hoc tests (Bonferroni) were applied to detect differences at 1, 2, 3, 4 mm displacement (F1-4 mm), and Fmax between implant groups.

RESULTS

The four expandable cages did not show statistically significant biomechanical differences in terms of maximum compression force (Fmax) until failure: Synex II (1,782 N/4.7 mm); Synex I (1,645 N/4.7 mm); Obelisc (1,314 N/4.2 mm); X-Tenz (1,470 N/6.9 mm). However, the mean compression force until 4 mm displacement (F1-4 mm: 300-1,600 N) was highest for Synex II. The difference at 2 mm displacement was significant (p=0.028) between Synex II (F2 mm=879 N) and X-Tenz (F2 mm=339 N).

CONCLUSION

The modified endplate design of the new prototype was found to improve its compressive performance under constrained uniaxial loading conditions at the implant-bone interface. The improved compressive behaviour of the new implant might help to reduce the risk of implant subsidence and collapse into the vertebral body in vivo.

Endoscopic treatment of spinal trauma at the thoracolumbar junction

Attempts of treating unstable fractures of the thoracolumbar junction by posterior reduction and fixation alone often result in a significant loss of correction, especially in lesions where a severe destruction of the vertebral body and the intervertebral disc is present. The conventional open approaches like classic thoraco-phreno-lumbotomy produces additional iatrogenic trauma at the lateral chest and abdominal wall which not rarely leads to intercostal neuralgia, as well as post-thoracotomy syndromes. The endoscopic trans-diaphragmatic approach described below opens up the whole thoracolumbar junction to a minimally invasive procedure allowing one to perform all the procedures needed for a full reconstruction of the anterior column of the spine like corpectomy, decompression, vertebral body replacement and anterior plating. The key to address also the subdiaphragmal and retroperitoneal section of the thoracolumbar junction is a partial detachment of the diaphragm which runs along the attachment at the spine and the ribs. The technique was published first in 1998 and has been used now in 650 endoscopic procedures at the thoracolumbar junction out of a total of more than 1300 thoracoscopic operations of the spine in the BG Unfallklinik Murnau, Germany since 1996.

Minimally Invasive Transmuscular Pedicle Screw Fixation of the Thoracic and Lumbar Spine

OBJECTIVE:

This study assessed the feasibility and safety of percutaneous posterior pedicle screw fixation for instabilities of the thoracic and lumbar spine, using standard instruments designed for the open approach and fluoroscopy.

METHODS:

All patients who underwent percutaneous posterior pedicle screw fixation of the thoracic and lumbar spine were studied retrospectively. Charts and operative notes were analyzed for epidemiological data, underlying spinal pathological features, and indications for stabilization, stabilized segments, number of implanted pedicle screws, surgical time, and complications. Postoperative computed tomographic scans were analyzed for screw position.

RESULTS:

From May 2002 through May 2005, 115 internal fixators were implanted percutaneously in 104 patients. A total of 488 pedicle screws were implanted, stabilizing 1 to 5 spinal motion segments. Median surgical time was 93 minutes. On postoperative computed tomographic scans, 87% of screw positions were rated good, 10% were rated acceptable, and 3% were rated unacceptable. A total of 11 revisions were necessary, 9 for misplaced screws and 2 for loosening of anchor bolts. Only two of the patients experienced new clinical symptoms (i.e., radicular pain) because of screw misplacement. No patients experienced new neurological deficits or other surgery-related morbidity. @@@@CONCLUSION:@@ This study shows that percutaneous internal pedicle screw fixation using standard instruments is feasible and safe for posterior stabilization of the thoracic and lumbar spine. It is a straightforward alternative for open approaches or minimally invasive ones using navigation in conjunction with customized instruments. Accuracy of screw placement is similar to that reported for other techniques.

Two column lesions in the thoracolumbar junction: anterior, posterior or combined approach? A comparative biomechanical in vitro investigation

There are various surgical techniques for the treatment of spinal fractures in the thoracolumbar region. Several implants have been developed for anterior or posterior instrumentation. Optimal treatment of unstable thoracolumbar osseous and ligamentous injuries remains controversial. To compare the stabilizing effects of an antero-lateral, thoracoscopically implantable plate system (macsTL, Aesculap, Germany) with the stability provided by a fixateur interne (SOCON, Aesculap, Germany), this in vitro investigation examined six human bisegmental (T12-L2) spinal units. Specimens were tested intact, and with simulation of osseous lesions in the anterior and ligamentous lesions in the posterior column (combined A/B-fracture). While loaded in the main anatomical planes such as flexion/extension, left and right lateral bending and left and right axial rotation with a bending moment of 7.5 Nm in a special testing jigs, motion analysis was performed. Quantitative interpretation of the stabilizing effect was achieved using a contactless three-dimensional motion analysis system. Each specimen was tested in four different scenarios: the first step measured movements of intact spinal segments. For the second step, specimens underwent simulation of combined A/B-fracture provided with bisegmental (T12/L2) antero-lateral fixation and bone strut graft from the iliac crest. For the third step, segments were additionally stabilized by the fixateur interne. The last measurement (fourth step) was performed after removing the anterior instrumentation. Range of motion (ROM) values were compared and statistically evaluated. Compared to the intact specimens the anterior instrumentation of the combined lesion, simulated A/B-fracture, leads to a stabilizing effect in flexion/extension and lateral bending. In contrast to these findings the torsional instability increased for the upper segment and bisegmentally. A maximum rigidity, beyond intact values, was registered for each anatomical plane with the combined instrumentation: antero-lateral and fixateur interne. After removing the anterior screw plate system maximum movements, in all segments for flexion/extension and lateral bending, bisegmentally and for the upper segment in axial rotation, were less than ROM values measured with the anterior system only. With respect to these findings a combined ventro-dorsal stabilization procedure should be considered for ligamentous disruptions of the posterior column in combination with A-fractures in the thoracolumbar junction.

Improved anchorage in osteoporotic vertebrae with new implant designs

The goal of our study was to evaluate two newly developed implant designs and their behavior in terms of subsidence in lumbar vertebral bodies under cyclic loading. The new implants were evaluated in two different configurations (two small prototypes vs. one large prototype with similar load-bearing area) in comparison to a conventional screw-based implant (MACS TL). A pool of 13 spines with a total of 65 vertebrae was used to establish five testing groups of similar bone mineral density (BMD) distribution with eight lumbar vertebrae each. In additional to BMD assessment via dual-energy X-ray absorptiometry, cancellous BMD and structural parameters were determined using a new generation in vivo 3D-pQCT. The specimens were loaded sinusoidally in force control at 1 Hz for 1000 cycles at three load levels (100, 200, and 400 N). A survival analysis using the number of cycles until failure (Cox regression with covariates) was applied to reveal differences between implant groups. All new prototype configurations except the large cylinder survived significantly longer than the control group. The number of cycles until failure was significantly correlated with the structural parameter Tb.Sp. and similarly with the cancellous BMD for three of five implants. In both large prototypes the cycle number until failure significantly correlated with the preoperative distance to the upper endplates. Although the direct relationship between bone structure or density and mechanical breakage behavior cannot be conclusively proven, all the prototypes adapted for poor bone structure performed better than the comparable conventional implant.

[Video-assisted mini-thoracotomy for surgical treatment of thoracolumbar junction fractures]

PURPOSE OF THE STUDY

There are several solutions for the treatment of fractures of the thoracolumbar junction (classical anterior, posterior, combined approaches). The advent of video-assisted minimally invasive techniques has helped minimize complications. The aim of this work was to analyze the clinical and radiological outcome in a prospective series of 20 patients who underwent video-assisted mini-thoracotomy for the treatment of thoracolumbar junction fractures.

MATERIAL AND METHODS

This prospective study included 20 patients, mean age 43.3 years, with at least one year follow-up. All patients presented a normal neurological examination (Frankel E). Fractures were classified Magerl A (n = 19) and B (n = 1). Corporectomy/correction (aided with an endodistractor in the last nine cases) was performed with grafting and osteosynthesis. Perioperative and postoperative complications were noted. Focal kyphosis and regional angulation were noted before and after the operation and at last follow-up using the Stagnara system.

RESULTS

The arthrodesis had fused at last follow-up in all patients. There were three cases of alelectasia which regressed in two months. Overall outcome showed satisfactory angular correction which was maintained at last follow-up. The gain in focal kyphosis was 13.71 degrees on average in the immediate postoperative period and persisted at last follow-up (13.31degrees). The gain in corrected regional angulation was 14 degrees in the immediate postoperative period and 14 degrees at last follow-up. The gain in focal kyphosis and regional angulation was two-fold greater with the endodistractor than with external maneuvers.

DISCUSSION

The complication rate was very low. Corrections obtained were comparable with those reported in the literature and persisted over time.

CONCLUSION

Bearing in mind the learning curve, there are fewer complications with the video-assisted minimally invasive approach than with classical thoracotomy or anterior surgery. This is true for perioperative and early and late postoperative complications. The correction achieved is satisfactory and lasting. A specific ancillary is essential for the reduction and for fitting the anterior graft without lost of correction. This technique combines the best results achieved with thoracotomy (Onimus) with a limited rate of complications.

Influence of screw positioning in a new anterior spine fixator on implant loosening in osteoporotic vertebrae

STUDY DESIGN

A biomechanical study was designed to assess implant cut-out of three different angular stable anterior spinal implants. Subsidence of the implant relative to the vertebral body was measured during an in vitro cyclic loading test.

OBJECTIVES

The objective of the study was to evaluate two prototypes (Synthes) of a new anterior spine fixator with different screw angulations in comparison to the established MACSTL(R) Twin Screw Concept (Aesculap). The influence of factors like load-bearing cross-sectional area, screw angulation and bone mineral density upon implant stability should be investigated.

SUMMARY OF BACKGROUND DATA

Epidemiologic data predict a growing demand for appropriate anterior spinal fixation devices especially in patients with inferior structural and mechanical bone properties. Although different concepts for anterior spinal instrumentation systems have been tried out, implant stability is still a problem.

METHODS

Three angular stable, anterior spinal implants were tested using 24 human lumbar osteoporotic vertebrae (L1-L5; age 84 (73-92)): MASC TL system (Aesculap); prototype 1 (MP1) with 18 degrees and prototype 2 (MP2) with 40 degrees screw angulation (both Synthes). All implants consisted of two screws with different outer screw diameters: 7-mm polyaxial screw with 6.5-mm stabilization screw (MASC TL), two 5-mm locking-head screws each (MP1 and MP2). Bone mineral density (BMD) and vertebral body width of the three specimen groups were evenly distributed. The specimens were loaded in craniocaudal direction (1Hz) for 1000 cycles each at three consecutive load steps; 10-100 N, 10-200 N and 10-400 N. During cyclic loading subsidence of the implant relative to the vertebral body was measured in the unloaded condition. Cycle number at failure (defined as a subsidence of 2 mm) was determined for each specimen. A survival analysis (Cox Regression) was performed to detect differences between implant groups at a probability level of 95%.

RESULTS

High correlations were found between BMD and number of cycles until failure (MP1; r = 0.905, P = 0.013; MP2: r = 0.640, P = 0.121; MACS TL: r = 0.904, P = 0.013) and between load bearing cross sectional area and number of cycles until failure (MP1: r = 0.849, P = 0.032;MP2: r = 0.692, P = 0.085; MACS TL: r = 0.902, P = 0.014). Both Prototypes survived significantly longer than the MACS TL implant (MP1: P = 0.012, MP2: P = 0.014). The survival behaviour of MP1 and MP2 was not significantly different (P = 0.354).

CONCLUSIONS

Implant stability within each implant group was influenced by BMD and load bearing cross-sectional area. The angulation of the two screws did not have a significant influence on cut-out. As conclusion from this study, promising approaches for further implant development are: 1) increase of load-bearing cross-sectional area (e.g., larger outer diameter of the anchorage device), 2) screw positioning in areas of higher BMD (e.g., opposite cortex, proximity to pedicles or the endplates).

Primary stability of anterior lumbar stabilization: interdependence of implant type and endplate retention or removal

This is a comparative in vitro biomechanical study of the primary stability of an anterior lumbar interbody stabilization. The objective was to compare the stability of a interbody stabilizing titanium cage with and without the retention of the bordering vertebral endplates, as well as to compare the titanium cage with a tricalcium phosphate block when the endplates are removed. An adequate blood supply is critical for interbody fusion, which suggests surgical treatment of the bordering endplates. On the other hand, primary stability is improved by the retention of the endplates. Furthermore, bone substitute materials are finding more frequent use due to complications associated with autologous bone grafts. Ten bovine lumbar spine motion segments (average age 6 months) were investigated. Pure bending loadings as well as eccentric axial compression loadings were applied. A titanium cage and tricalcium phosphate block, were tested in conjunction with an anterior augmentation (MACS). Range of motion, neutral zone (NZ) and bending stiffness were measured under pure bending to 10 Nm, and bending stiffness under axial loads of up to 1,500 N. Range of motion of both implants in flexion-extension was significantly smaller than physiologic (cage without endplates 4.3 degrees , cage with 2.8 degrees , block without 3.4 degrees , and physiologic 6.6 degrees , all p<0.001). The cage with endplates and the block without endplates were both significantly stiffer than physiologic in all directions except left lateral bending. The block without endplates and the cage with endplates were both stiffer than the cage without endplates. The results suggest that the use of the bone substitute block provides better stability than the cage when the endplates are removed.

Comparison of the biomechanical effects of posterior and anterior spine-stabilizing implants

Posteriorly and anteriorly fixed implants for stabilizing unstable spines are available on the market. Differences in the biomechanical behavior of these implant types are not yet fully clear. They were investigated using three-dimensional nonlinear finite element models of the lumbar spine in an intact state, with an anteriorly fixed MACS-TL implant and with posteriorly fixed internal fixators. The bisegmental implants spanned the L3 vertebra, and bone grafts were used with both implant types to replace parts of the two bridged discs. The computer models were loaded with partial body weight and muscle forces simulating standing, flexion, extension and axial rotation. Both implant types have reduced intersegmental rotation for flexion, extension, and axial rotation in the bridged region. The reduction is more pronounced for the MACS-TL implant. The implant type has only a minor effect on intradiscal pressure. Maximum von Mises stresses in the vertebrae are lower for flexion and extension with the MACS-TL implant than with the internal fixator. Very high stresses are predicted for flexion after insertion of internal fixators. For standing and torsion, maximum stresses differ only negligibly between the two implant types. In the period immediately after surgery, patients with osteoporotic vertebrae and who are treated with an internal spinal fixation device should therefore avoid excessive flexion. This study adds new information about the mechanical behavior of the lumbar spine after insertion of posterior and anterior spine-stabilizing implants. This information improves our biomechanical understanding of the spine.

Surgical technique and results of endoscopic anterior spinal canal decompression

OBJECT

Decompression of the spinal canal in the management of thoracolumbar trauma is controversial, but many authors have advocated decompression in patients with severe canal compromise and neurological deficits. Anterior decompression, corpectomy, and fusion have been shown to be more reliable for spinal canal reconstruction than posterior procedures; however, traditional anterior-access procedures, thoracotomy, and thoracoabdominal approaches are associated with significant complications. Endoscopy-guided spinal access avoids causing these morbidities, but it has not been shown to yield equivalent results in spinal canal clearance. This study was conducted to demonstrate the effectiveness of endoscopic spinal canal decompression and reconstruction quantitatively by using pre- and postoperative computerized tomography (CT) scanning.

METHODS

Thirty patients with thoracolumbar canal compromise underwent endoscopic anterior spinal canal decompression, interbody reconstruction, and stabilization for fractures (27 cases), and tumor, infection, and severe degenerative disc disease (one case each). The mean follow-up period was 42 months (range 24 months-6 years). Neurological examinations, Frankel grades, radiological studies, and intraoperative findings were prospectively collected. Spinal canal clearance quantified on pre- and postoperative CT scans improved from 55 to 110%. A total of 25% of patients with complete paraplegia and 65% of those with incomplete neurological deficit improved neurologically. The complication rate was 16.7% and included one reintubation, two pleural effusions, one intercostal neuralgia, and one persistent lesion of the sympathetic chain.

CONCLUSIONS

The authors describe the endoscopic technique of anterior spinal canal decompression in the thoracolumbar spine. The morbidities associated with an open procedure were avoided, and excellent spinal canal clearance was accomplished as was associated neurological improvement.

Is a single anterolateral screw-plate fixation sufficient for the treatment of spinal fractures in the thoracolumbar junction? A biomechanical in vitro investigation

Controversy exists about the indications, advantages and disadvantages of various surgical techniques used for anterior interbody fusion of spinal fractures in the thoracolumbar junction. The purpose of this study was to evaluate the stabilizing effect of an anterolateral and thoracoscopically implantable screw-plate system. Six human bisegmental spinal units (T12-L2) were used for the biomechanical in vitro testing procedure. Each specimen was tested in three different scenarios: (1) intact spinal segments vs (2) monosegmental (T12/L1) anterolateral fixation (macsTL, Aesculap, Germany) with an interbody bone strut graft from the iliac crest after both partial corpectomy (L1) and discectomy (T12/L1) vs (3) bisegmental anterolateral instrumentation after extended partial corpectomy (L1), and bisegmental discectomy (T12/L1 and L1/L2). Specimens were loaded with an alternating, nondestructive maximum bending moment of +/-7.5 Nm in six directions: flexion/extension, right and left lateral bending, and right and left axial rotation. Motion analysis was performed by a contact-less three-dimensional optical measuring system. Segmental stiffness of the three different scenarios was evaluated by the relative alteration of the intervertebral angles in the three main anatomical planes. With each stabilization technique, the specimens were more rigid, compared with the intact spine, for flexion/extension (sagittal plane) as well as in left and right lateral bending (frontal plane). In these planes the bisegmental instrumentation compared to the monosegmental case had an even larger stiffening effect on the specimens. In contrast to these findings, axial rotation showed a modest increase of motion after bisegmental instrumentation. To conclude, the immobilization of monosegmental fractures in the thoracolumbar junction can be secured by means of bone grafting and the implant used in this study for all three anatomical planes. After bisegmental anterolateral stabilization a sufficient reduction of the movements was registered for flexion/extension and lateral bending. However, the observed slight increase of the range of motion in the transversal plane may lead to loosening of the implant before union. Therefore, the use of an additional dorsal fixation device should be considered.

Thoracoscopic-assisted Treatment of Thoracic and Lumbar Fractures: A Series of 371 Consecutive Cases

OBJECTIVE

Conventional approaches for the treatment of thoracic and thoracolumbar fractures require extensive surgical exposure, often leading to significant postoperative pain and morbidity. Thoracoscopic spinal surgery was performed to reduce the morbidity of these approaches while still achieving the primary goals of spinal decompression, reconstruction, and stabilization.

METHODS

Between May 1996 and May 2001, 371 patients with fractures of the thoracic and thoracolumbar spine (T3–L3) were treated with a thoracoscopically assisted procedure. In the first 197 patients, a conventional open anterior plating system was used. The last 174 patients were treated with the MACS-TL system (Aesculap, Tuttlingen, Germany), which was designed specifically for endoscopic placement, thereby significantly reducing operative times.

RESULTS

Seventy-three percent of the fractures were located at the thoracolumbar junction. In 49% of patients, mobilization of the diaphragm was performed to expose the fracture, with later repair. Both x-ray canal compromise and neural deficit were present in 15% of patients. In 35% of patients, a stand-alone anterior thoracoscopic reconstruction was performed. In 65% of patients, a supplemental posterior pedicle-screw construct was also placed either before or after the anterior construct. A steep learning curve was present, with an average operating time of 300 minutes in the first 50% of cases and an average of 180 minutes with the MACS-TL system. The severe complication rate was low (1.3%), with one case each of aortic injury, splenic contusion, neurological deterioration, cerebrospinal fluid leak, and severe wound infection. Compared with a group of 30 patients treated with open thoracotomy, thoracoscopically treated patients required 42% less narcotics for pain treatment after the operation.

CONCLUSION

A complete anterior thoracoscopically assisted reconstruction of thoracic and thoracolumbar fractures can be safely and effectively accomplished, thereby reducing the pain and morbidity associated with conventional thoracotomy and thoracolumbar approaches. Although the learning curve is steep, the functional and cosmetic benefits to the patient warrant the difficult training process.