Biomechanical effects of transthoracic microdiscectomy

The impact of bilateral facetectomy on the instantaneous helical axis of the functional thoracic spinal unit T4-5 during axial rotation

The location of the instantaneous helical axis (IHA) and the impact of the facet joints (FJ) on the kinematics in the thoracic spine remain inconclusive. This study aimed to examine the IHA in the functional spinal unit (FSU) T4-5 during axial rotation in intact conditions and after bilateral facetectomy. Four human T4-5 FSUs were examined with an established 6D measuring apparatus in intact conditions and after bilateral facetectomy. The IHA’s parameters migration, location, and direction in the horizontal plane were calculated. Defined preloads in different positions were applied. Under the intact conditions, the IHA migrated about 4 mm and from one to the contralateral side according to the applied preload. The location of the IHA was observed in the anterior part of the spinal canal. After bilateral facetectomy, the location of the IHA shifted ventrally about 10 mm compared to the intact conditions. Under intact conditions, the direction of the IHA was minimally dorsally reclined. After bilateral facetectomy, the IHA was significantly more ventrally inclined. The study determined the location of the IHA under intact conditions at the anterior part of the spinal canal. The IHA of the FSU T4-5 is substantially influenced by the guidance of the FJs.

Posterior Minimally Invasive Transpedicular Approach for Giant Calcified Thoracic Disc Herniation

STUDY DESIGN

Retrospective case series.

OBJECTIVE

Posterior surgery for thoracic disc herniation was associated with increased morbidity and mortality and new minimally invasive approaches have been recommended for soft disc herniation but not for calcified central disc. The objective of this study is to describe a posterolateral microscopic transpedicular approach for central thoracic disc herniation.

METHODS

This is a single center retrospective review of all the cases of giant thoracic calcified disc herniation as defined by Hott et al. Presence of myelopathy, percentage of canal compromise, T2 hypersignal, ASIA score, and ambulatory status were recorded. This posterolateral technique using a tubular retractor was thoroughly described.

RESULTS

Eight patients were operated upon with a mean follow-up of 16 months. Mean canal compromise was 61%. Mean operative time was 228 minutes and mean operative bleeding was 250 mL. There were no cases of dural tear or neurologic degradation.

CONCLUSION

This is the first report of posterior minimally invasive transpedicular approach for giant calcified disc herniation. There were neither cases of neurological deterioration nor increased rate of dural tears. This technique is thus safe and could be recommended for treatment of this rare disease.

Video-assisted thoracoscopic image-guided spine surgery: evolution of 19 years of experience, from endoscopy to fully integrated 3D navigation

OBJECTIVE

The purpose of this study was to describe the evolution of thoracoscopic spine surgery from basic endoscopic procedures using fluoroscopy and anatomical localization through developmental iterations to the current technology use in which endoscopy and image-guided surgery are merged with intraoperative CT scanning.

METHODS

The authors provided detailed explanations of their thoracoscopic spine surgery techniques, beginning with their early-generation endoscopy with fluoroscopic localization, which was followed with point surface matching techniques and early image guidance. The authors supplanted this with the modern era of image guidance, thoracoscopic spine surgery, and seamless integration that has reached its current level of refinement.

RESULTS

A retrospective review of single-institution thoracoscopic procedures performed by the senior author over the course of 19 years yielded a total of 160 patients, including 73 women and 87 men. The mean patient age was 55 years, and the range included patients 16-94 years of age. There were no patients with worsened neurological function. One hundred sixteen patients underwent surgery for thoracic disc herniation, 18 for underlying neoplasms with spinal cord compression, 14 for osteomyelitis and discitis, 12 for thoracic deformity with neurological changes, and 8 for traumatic etiologies.

CONCLUSIONS

More than 19 years of experience has revealed the benefits of integrating thoracoscopic spine surgery with intraoperative CT scanning and image-guided surgery, including direct decompression without manipulation of neural elements, superior 3D spatial orientation, and localization of complex spinal anatomy. With the exponential growth of machine learning, robotics, artificial intelligence, and advances in imaging techniques and endoscopic imaging, there may be further refinements of this technique on the horizon.

Finite element models can reproduce the effect of nucleotomy on the multi-axial compliance of human intervertebral discs

Finite element (FE) models can unravel the link between intervertebral disc (IVD) degeneration and its mechanical behaviour. Nucleotomy may provide the data required for model verification. Three human IVDs were scanned with MRI and tested in multiple loading scenarios, prior and post nucleotomy. The resulting data was used to generate, calibrate, and verify the FE models. Nucleotomy increased the experimental range of motion by 26%, a result reproduced by the FE simulation within a 5% error. This work demonstrates the ability of FE models to reproduce the mechanical compliance of human IVDs prior and post nucleotomy.

Challenging the Conventional Standard for Thoracic Spine Range of Motion: A Systematic Review

BACKGROUND

Segmental motion is a fundamental characteristic of the thoracic spine; however, studies of segmental ranges of motion have not been summarized or analyzed. The purpose of the present study was to present a summary of the literature on intact cadaveric thoracic spine segmental range of motion in each anatomical plane.

METHODS

A systematic MEDLINE search was performed with use of the terms "thoracic spine," "motion," and "cadaver." Reports that included data on the range of motion of intact thoracic human cadaveric spines were included. Independent variables included experimental details (e.g., specimen age), type of loading (e.g., pure moments), and applied moment. Dependent variables included the ranges of motion in flexion-extension, lateral bending, and axial rotation.

RESULTS

Thirty-three unique articles were identified and included. Twenty-three applied pure moments to thoracic spine specimens, with applied moments ranging from 1.5 to 8 Nm. Estimated segmental range of motion pooled means ranged from 1.9° to 3.8° in flexion-extension, from 2.1° to 4.4° in lateral bending, and from 2.4° to 5.2° in axial rotation. The sums of the range of motion pooled means (T1 to T12) were 28° in flexion-extension, 36° in lateral bending, and 45° in axial rotation.

CONCLUSIONS

The pooled ranges of motion were similar to reported in vivo motions but were considerably smaller in magnitude than the frequently referenced values reported prior to the widespread use of biomechanical testing standards. Improved reporting of biomechanical testing methods, as well as specimen health, may be beneficial for improving on these estimations of segmental cadaveric thoracic spine range of motion.

Surgical treatment for thoracic disc herniation: an update

STUDY DESIGN

Retrospective review of the literature.

OBJECTIVE

To update recent trends in the surgical treatment for thoracic disc herniation (TDH).

SUMMARY OF BACKGROUND DATA

TDH is rare; however, it is usually accompanied by myelopathy and is indicated for surgical treatment. A variety of surgical approaches have been described to reach these anatomically challenging lesions.

METHODS

Review of the literature.

RESULTS

Recently, minimally invasive techniques for TDH have gained popularity. These include thoracoscopic and mini-open anterolateral retropleural approaches, as well as microscopic and endoscopic surgery. In addition, this article updates important aspects of surgical treatment for TDH such as definition of surgical level, treatment of calcified and/or giant disc, multilevel lesions, and fusion requirements.

CONCLUSION

Definition of surgical level is imperative in the surgical treatment for TDH. Outcomes of minimum invasive surgery are satisfactory. Type of disc herniation and biomechanical stability are the important factors for surgical planning.

Thoracic disk herniation with paraparesis treated with transthoracic microdiskectomy in a 14-year-old girl

Herniated thoracic intervertebral disk causing spinal cord compression with paraparesis is uncommon in adults and rare in children. This article describes a case of pediatric thoracic disk herniation with paraparesis treated surgically.A 14-year-old girl presented with a 4-month history of diffuse back pain and sudden onset paraparesis. Motor strength was 4/5 in both legs, and she had lost the ability to ambulate. Magnetic resonance imaging revealed spinal cord compression due to a herniated intervertebral disk at T5-T6. Computed tomography scan after myelogram demonstrated anterior dural sac compression at T5-T6 but no intervertebral disk calcification. She underwent transthoracic microdiskectomy. The herniated disk was removed, and the thoracic spinal cord was decompressed. No fusion was performed after microdiskectomy. The postoperative course was uncomplicated, and neurologic deficit resolved within 2 weeks postoperatively. The patient was pain free with no neurologic deficit at 24-month follow-up, and computed tomography scan showed remodeling of the T5 and T6 vertebral bodies.Most cases of thoracic disk herniation are asymptomatic. If no compression of the spinal cord exists, the natural history of the disease justifies conservative management. Although the treatment of choice is conservative, surgery is required in patients who develop progressive neurologic deficit or severe radicular pain. Transthoracic microdiskectomy without fusion is considered a treatment in similar cases.

Biomechanical contribution of the rib cage to thoracic stability

STUDY DESIGN

In vitro assessment of rib cage biomechanics in the region of true ribs with the ribs intact then sequentially resected in 5 steps.

OBJECTIVE

To determine the contribution of the rib cage to thoracic spine stability and kinematics.

SUMMARY OF BACKGROUND DATA

Previous in vitro studies of rib cage biomechanics have used animal spines or human cadaveric spines with ribs left unsecured, limiting the ability of the ribs to contribute to stability.

METHODS

Eight upper thoracic specimens that included 4 ribs and sternum were tested in special fixtures that disallowed relative movement of the distal ribs and their vertebrae. While applying 7.5 Nm pure moments in 3 planes, angular motion at the middle motion segment was studied in intact specimens and then (1) after splitting the sternum, (2) after removing the sternum, (3) after removing 50% of ribs, (4) after removing 75% of ribs, and (5) after disarticulating and completely removing ribs.

RESULTS

During flexion/extension, the sternum and anterior rib cage most contributed to stability. During lateral bending, the posterior rib cage most contributed to stability. During axial rotation, stability was directly related to the proportion of ribs remaining intact. On average, intact ribs accounted for 78% of thoracic stability. An intact rib cage shifted the axis of rotation unpredictably, but its position remained consistent after partial resection of the ribs. During lateral bending, coupled axial rotation was mild and unaffected by ribs.

CONCLUSION

Because of testing methodology, the rib cage accounted for a greater percentage of thoracic stability than previously estimated. Different rib cage structures resisted motion in different loading planes.

Thoracoscopic treatment for single level symptomatic thoracic disc herniation: a prospective followed cohort study in a group of 167 consecutive cases

PROBLEM

Thoracic disc disease with radicular pain and myelopathic symptoms can have serious neurological sequelae. The authors present a relevant treatment option.

METHODS

Data of patients with single level symptomatic thoracic disc herniation treated with thoracoscopic microdiscectomy were prospectively collected over a period of 10 years. Data collection included the preoperative status and the follow-up status was 6, 12 and 24 months after surgery for every patient.

RESULTS

A total of 167 single level thorascoscopic discectomies without previous surgery on the level of the procedure were included in this study. The average preoperative duration of pain symptoms was 14.3 months, myelopathic symptoms were present for an average of 16.7 months before surgery. After the procedure pain scores measured with visual analog scale (VAS) decreased by 4.4 points and the muscle strength improved by a mean of 4.6 points (American Spinal Injury Association ASIA motor score). After 2 years, 79% of the patients reported a excellent or good outcome for pain and 80% of the patients reported a excellent or good outcome for motor function. The overall complication rate was 15.6%.

CONCLUSIONS

Thoracoscopic microdiscectomy for single level symptomatic disc herniation is a highly effective and reliable technique, it can be performed safely with low complication rate.

PREDICTION OF BIOMECHANICAL CHARACTERISTICS OF INTACT AND INJURED LOWER THORACIC SPINE SEGMENT UNDER DIFFERENT LOADS

In this study, the biomechanical roles of disc nucleus and ligaments of human lower thoracic spine (T10–T12) under different loads were investigated using finite element (FE) method. The T10–T12 FE model was developed and validated against the published results. The FE model was then modified accordingly to simulate the injured conditions of nucleus, ligaments and facets and loaded under different configurations to analyze the segmental gross responses and the stress distribution around the annulus circumference. The high first-principal stress of annulus at the posterolateral region has an important role on the disc annulus's tear and a flexion moment causes a high first-principal stress at posterolateral region, despite of the existence of ligaments. The study also shows that decompression in intervertebral discs can reduce the dilatation of annulus tears by 18% around the posterolateral regions of disc annulus. The disc nucleus and the posterior ligaments have important roles in resisting compression and flexion loads, respectively. The investigations in this paper not only supplement experimental research but are also helpful in the understandings of biomechanics of lower thoracic spine.

The effect of nucleotomy and the dependence of degeneration of human intervertebral disc strain in axial compression

STUDY DESIGN

Biomechanics of human intervertebral discs before and after nucleotomy.

OBJECTIVE

To noninvasively quantify the effect of nucleotomy on internal strains under axial compression in flexion, neutral, and extension positions, and to determine whether the change in strains depended on degeneration.

SUMMARY OF BACKGROUND DATA

Herniation and nucleotomy may accelerate the progression of disc degeneration. Removal of nucleus pulposus (NP) tissue has resulted in altered disc mechanics in vitro, including a decrease in internal pressure and an increase in the deformations at physiologically relevant strains. We recently presented a technique to quantify internal disc strains using magnetic resonance imaging (MRI).

METHODS

Degeneration was quantitatively assessed by the T1ρ relaxation time in the NP. Samples were prepared from human levels L3-L4 and/or L4-L5. A 1000-N compressive load was applied while in the magnetic resonance scanner. Nucleotomy was performed by removing 2 g of NP through the posterior-lateral annulus fibrosus (AF). The discs were rehydrated, reimaged, and retested. The analyzed parameters include axial deformation, AF radial bulge, and strains. RESULTS.: The axial deformation was more compressive after nucleotomy. In the neutral position, the axial deformation after nucleotomy correlated with degeneration (as quantified by T1ρ in the NP), with minimal alteration in nondegenerated discs. Nucleotomy altered the radial displacements and strains in the neutral position, such that the inner AF radial bulge decreased and the radial strains were more tensile in the lateral AF and less tensile in the posterior AF. In the bending loading positions the radial strains were not affected by nucleotomy.

CONCLUSION

Nucleotomy alters the internal radial and axial AF strains in the neutral position, which may leave the AF vulnerable to damage and microfractures. In bending, the effects of nucleotomy were minimal, likely due to more of the applied load being directed over the AF. Some of the nucleotomy effects are modulated by degeneration, where the mechanical effect of nucleotomy was magnified in degenerated discs and may further induce mechanical damage and degeneration.

Thoracoscopic discectomy and instrumented fusion using a minimally invasive plate system: surgical technique and early clinical outcome

OBJECT

The use of minimally invasive noninstrumented fusions has increased as thoracoscopic approaches to the spine have evolved. The addition of instrumentation is infrequent, in part because of the lack of a minimally invasive implant system. The authors describe a technique for thoracoscopic plating after discectomy and report early clinical outcomes.

METHODS

After a standard endoscopic discectomy and partial corpectomy and before exposure of the ventral thecal sac, the authors implanted a polyaxial screw and clamping element under fluoroscopic guidance. Reconstruction involves placement of autograft in the defect and subsequent placement of the remainder of the screw/plate construct with 2 screws per vertebral level.

RESULTS

Twenty-five patients underwent thoracoscopic and thoracoscopy-assisted discectomies and fusion in which the aforementioned plate system was used. Of 19 patients presenting with pain, 10 had 6-month clinical follow-up with a greater than 50% reduction in visual analog scale score, which continued to improve up to 2 years postoperatively. There were 3 cases of pneumonia, 3 CSF leaks, 1 chyle leak, and 1 death due to a massive pulmonary embolus on the 1st postoperative day.

CONCLUSIONS

The authors conclude that thoracoscopic discectomy and plate-instrumented fusion can be achieved with acceptable results and morbidity. Further studies should evaluate the role of instrumented fusions after thoracoscopic discectomy in larger groups of patients and during a longer follow-up period.

Minimally invasive extracavitary approach for thoracic discectomy and interbody fusion: 1-year clinical and radiographic outcomes in 13 patients compared with a cohort of traditional anterior transthoracic approaches

Object

Open transthoracic approaches, considered the standard in treating thoracic disc herniation (TDH), are associated with significant comorbidities. The authors describe a minimally invasive lateral extracavitary tubular approach for discectomy and fusion (MIECTDF) to treat TDH.

Methods

In 13 patients (5 men, 8 women; mean age 51.8 years) with myelopathy and 15 noncalcified TDHs, the authors achieved a far-lateral trajectory by dilating percutaneously to a 20-mm working portal docked at the transverse process–facet junction, which then provided a corridor for a near-total discectomy, bilateral laminotomies, and interbody arthrodesis requiring minimal cord retraction. A cohort of 11 demographically comparable patients treated via transthoracic approaches was used as control.

Results

Preoperative Frankel grades were B in 1 patient, C in 4, D in 5, and E in 3, whereas at mean of 10 months, 11 had Grade E function and 2 had Grade D function. Mean surgical metrics were operating room time 93.75 minutes, blood loss 33 ml, and hospital stay 3.1 days. Complications included 4 transient paresthesias, 1 CSF leak, 1 abdominal wall weakness, and 3 nonwound infections. One-year follow-up MR imaging revealed full decompression in all cases and no cage migration. Mean visual analog scales scores preoperative, at 6 weeks, 3 months, and 1 year were 5.6, 4.5, 3.2, and 1.2, respectively. No differences existed in preoperative clinical and radiographic profile of the study and control groups. Compared with controls, the MIECTDF group achieved superior scores in all metrics (p < 0.01) except for equivalent 1-year neurological outcomes.

Conclusions

Compared with transthoracic procedures, MIECTDF effectively decompressed the spinal canal, yielding identical 1-year radiographic and clinical outcomes to those seen in controls, while producing superior clinical scores in the interim. Thus, MIECTDF is the authors' treatment of choice for TDH.

Exogenous cross-linking increases the stability of spinal motion segments

STUDY DESIGN

The mechanical stability of cross-linked and control spinal motion segments was evaluated using neutral zone, range of motion (ROM), and instability score metrics.

OBJECTIVE

To determine if exogenous cross-linking could increase the stability of spinal motion segments.

SUMMARY OF BACKGROUND DATA

The microstructure of the anulus fibrosus extracellular matrix can affect the stability of the intervertebral joint. Parallel testing in our laboratory has shown that exogenous cross-linking can improve the fatigue resistance of anulus fibrosus.

METHODS

There were 3 separate experimental protocols conducted. The first study used calf lumbar intervertebral joints randomly divided into a genipin cross-linked group and phosphate buffered saline-soaked controls. After 2 days of soaking, flexion-extension ramp cycles were applied to the specimens. The second study repeated the test protocol using 22 moderately and severely degenerated human lumbar intervertebral joints. The third experiment compared the effect of cross-linking treatment on human discs with known degrees of preexisting mechanical instability. Each data set was used to assess joint instability by 3 calculations: ROM, neutral zone, and an instability score. Joint instability for each data set was evaluated using 3 calculations: ROM, neutral zone, and a novel instability score.

RESULTS

These results show that cross-link augmentation can effectively reduce instability of intervertebral discs. The stabilizing effect was observed to be higher in the more mechanically unstable discs. However, cross-linking did not appear to affect the total range of sagittal motion.

CONCLUSIONS

By reducing the neutral zone, exogenous cross-linking may help combat the progression of instability in degenerative disc disease.

Interrater Reliability of a Passive Physiological Intervertebral Motion Test in the Mid-Thoracic Spine

OBJECTIVE

To examine the interrater reliability of a passive physiological intervertebral motion (PPIM) test of a mid-thoracic spine motion segment.

METHODS

Nineteen males and 22 females with a mean age of 22.7 years (range, 19-40 years) and no known spinal pathologies were tested independently by 3 certified manual therapy instructors. Investigators performed 3-dimensional segmental mobility testing at a preselected thoracic motion segment. Interrater reliability was assessed with Cohen's kappa statistics, using 3 pairwise comparisons for determination of the direction of lateral flexion leading to the greatest amount of segmental rotation.

RESULTS

Percent agreement ranges were 63.4% to 82.5%, with kappa scores ranging from 0.27 to 0.65.

CONCLUSION

The PPIM testing demonstrated fair to substantial interrater reliability. A majority of females (91%) demonstrated greatest segmental PPIM motion in contralateral rotation with lateral flexion, whereas a majority of males (90%) demonstrated greatest segmental PPIM motion in ipsilateral rotation with lateral flexion. These findings are applicable to asymptomatic subjects of the same age category. Interrater reliability of 3-dimensional PPIM testing is fair to substantial for assessing passive segmental mobility of the mid-thoracic spine.

Endoscopic thoracic microdiscectomy

Object. The purpose of this clinical study was to evaluate prospectively surgical and neurological outcomes after endoscopic thoracic disc surgery.

Methods. The authors assessed the following quantifiable outcome data in 46 patients: operative time, blood loss, duration of chest tube insertion, narcotic use, hospital length of stay (LOS), and long-term follow-up neurological function and pain-related symptoms.

In patients who presented with myelopathy there was a postoperative improvement of two Frankel grades. Pain related to radiculopathy was improved by 75% and in one patient it worsened postoperatively. The authors also present operative data, surgical outcomes, and complications.

Conclusions. Thoracoscopic discectomy can be used to achieve acceptable results. It has several distinct advantages such as reduced postoperative pain, morbidity, and LOS compared with traditional open procedures.

Transthoracic discectomy without interbody fusion

BACKGROUND

Transthoracic discectomy is an established surgical procedure for the treatment of thoracic disk disease. Most authors advocate interbody fusion after transthoracic discectomy. The purpose of this study was to determine if there were any adverse consequences in foregoing interbody fusion after transthoracic discectomy.

METHODS

Eighteen consecutive patients underwent transthoracic discectomy without fusion between 1996 and 2002 at Mayo Clinic (Rochester, MN). There were 11 women and 7 men with the mean age of 54 years (range, 28-84 years). Surgical indications were radiculopathy in 1 patient and myelopathy in 17. Follow-up data were obtained from the clinic visits and telephone surveys. We used the available pre- and postoperative radiographs for 16 patients at the last follow-up to establish the incidence of postoperative kyphosis and/or scoliosis at the operated level. Mean duration of the radiographic follow-up was 22 +/- 24 (SD) months.

RESULTS

None of the patients reported the onset of a new axial spine pain postoperatively. No patient developed segmental kyphosis or scoliosis at the operated level during the follow-up period. Fifteen of 18 (83%) patients had significant improvement in their neurological symptoms and signs. Two patients remained unchanged. An 83-year-old patient had a slight worsening of her gait after surgery. Specifically, the only 3 nonambulatory patients regained ambulation after discectomy. There were 4 complications: 1 wound infection, 1 pleural effusion requiring pleurodesis, 1 cerebrospinal fluid leak, and 1 case of disabling intercostal neuralgia.

CONCLUSIONS

These results indicate that interbody fusion may not be necessary for selected patients undergoing transthoracic discectomy. Further long-term follow-up is needed to evaluate the development of late spinal instability and resultant deformity after this procedure.

Endoscopic thoracic microdiscectomy

Object

The purpose of this investigation was to evaluate surgical and neurological outcomes in thoracic disc surgery in a prospective fashion.

Methods

Quantifiable outcome data such as operating time, blood loss, duration of chest tube drainage, narcotic drug use, length of hospital stay (LOS), and long-term follow up of neurological function and pain-related symptoms were collected prospectively.

In patients with myelopathy there was an improvement of two Frankel grades in the thoracoscopic discectomy group and one Frankel grade in the patients treated with thoracotomy; however, patients in the thoracotomy group were significantly worse preoperatively. None of the patients experienced worsened pain, and pain related to radiculopathy was improved by 75% in the thoracoscopic group.

Conclusions

Thoracoscopic discectomy yields acceptable surgical results and has several distinct advantages, with reduced postoperative pain, morbidity, and LOS.

An in vitro human cadaveric study investigating the biomechanical properties of the thoracic spine

STUDY DESIGN

An in vitro human cadaveric study comparing the effects of anterior and posterior sequential destabilization conditions on thoracic functional unit mechanics was studied.

OBJECTIVES

To investigate the biomechanical properties of the human thoracic spine.

SUMMARY OF BACKGROUND DATA

Few studies have addressed the mechanical role of the costovertebral joints under torsion in the stability of the human thoracic spine.

METHODS

Sixteen functional spinal units with intact costovertebral joints were obtained from six human cadavers and randomized into two groups based on destabilization procedures: Group 1, anterior to posterior sequential resection; and Group 2, posterior to anterior sequential destabilization. Biomechanical testing was performed after each destabilization procedure, and the range of motion under maximum load was calculated.

RESULTS

Group 1: Under flexion-extension, lateral bending, and axial rotation loading, discectomy increased the range of motion by 193%, 74%, and 111%, respectively. Moreover, subsequent right rib head resection further increased the range of motion by 81%, 84%, and 72%, respectively. Group 2: Under all loading conditions laminectomy + medial facetectomy resulted in a 22-30% increase in range of motion. Subsequent total facetectomy led to an additional 15-28% increase in range of motion.

CONCLUSION

The rib head joints serve as stabilizing structures to the human thoracic spine in the sagittal, coronal, and transverse planes. In anterior scoliosis surgery additional rib head resection after discectomy may achieve greater curve and rib hump correction. The lateral portion of the facet joints plays an important role in providing spinal stability and should be preserved to minimize postoperative kyphotic deformity and segmental instability when performing decompressive wide laminectomy.

Thoracoscopic microdiscectomy

The thorascopic approach for the microsurgical removal of herniated thoracic discs is described, and perioperative management is also discussed. The microsurgical techniques used for decompression of the spinal canal in the thoracic spine are presented in detail. The diagnostic imaging, surgical positioning, approach, port placement, localization of the thoracic level, exposure of the surgical field, excision of the rib head, exposure with removal of the herniated disc, and postoperative management are outlined. Surgical and operative "pearls" in thoracoscopic spinal surgery for removing herniated thoracic discs when possible are described and illustrated.

Biomechanics of thoracic discectomy

The thoracic spine is a structurally unique region that renders it uniquely suceptible to thoracic disc herniation. Surgical management strategies are complicated, in part, by the regional anatomical and biomechanical nuances. Surgical approaches include posterior, posterolateral, and anterior routes. Each isassociated with specific indications and contraindications. The biomechanical principles and safe anatomical trajectories must be considered in the surgical decision-making process. These issues are discussed in the pages that follow.

Disc Related and Non-Disc Related Disorders of the Thoracic Spine

Different anatomical structures and pathophysiological functions can be responsible for lumbar pain, each producing a distinctive clinical profile. Pain can arise from the intervertebral disc, either acutely as a primary disc related disorder, or as result of the degradation associated with chronic internal disc disruption. In either case, greatest pain provocation will be associated with movements and functions in the sagittal plane. Lumbar pain can also arise from afflictions within the zygapophyseal joint mechanism, as a result of synovitis or chondropathy. Either of these conditions will produce the greatest pain provocation during three-dimensional movements, due to maximal stress to either the synovium or joint cartilage. Finally, patients can experience different symptoms associated with irritation to the dural sleeve, dorsal root ganglion, or chemically irritated lumbar nerve root. Differential diagnosis of these conditions requires a thorough examination and provides information that can assist the clinician in selecting appropriate management strategies.

Endoscopic thoracic discectomy

Object

Thoracoscopic discectomy is a minimally invasive procedure simulating a thoracotomy and is an alternative to the costotransversectomy and transpedicular approaches. In recent studies authors have concluded that thoracoscopic discectomy is the preferred procedure; however, relative historical comparisons were difficult to interpret.

The authors conducted a prospective nonrandomized study in which they compared data on 36 patients undergoing thoracoscopic discectomy with eight patients undergoing thoracotomy between 1995 and 1999.

Methods

Patients affected with one- or two-level lesions underwent a thoracoscopic discectomy, and patients with three-level lesions or more underwent thoracotomy and discectomy. Data were collected on operative time, blood loss, chest tube duration, narcotic agent use, and hospital length of stay (LOS). Longer-term follow-up study of pain-related symptoms and neurological function was conducted.

Patients who underwent thoracoscopic discectomy had shorter operative times, less blood loss, a shorter period of chest tube drainage dependence, less narcotic usage, and a shorter LOS. These findings were statistically significant (p < 0.05) for narcotic usage and shorter LOS. Pain related to radiculopathy was improved by means of 75%, and no patients exprienced worsened pain. In patients with myelopathy there was an improvement of two Frankel grades in the thoracoscopic group and one Frankel grade in the thoracotomy discectomy group, but patients in the thoracotomy group were significantly worse preoperatively. One myelopathic patient from each group suffered a worsened outcome postoperatively, although this was not attributed to the method of surgery. The incidence of complications (minor and major) was 31% in the thoracoscopic group and greater than 100% (that is, more than one complication per patient) in the thoracotomy/discectomy group.

Conclusions

One advantage to thoracoscopic discectomy is its reduced incidence of morbidity compared with thoractomy, but its steep learning curve and unfamiliar surgical techniques make this procedure less practical for surgeons not performing it frequently. The more familiar costotransversectomy, transpedicular, and thoracotomy procedures remain viable alternatives for surgeons more experienced in these procedures.

Thoracoscopic microsurgical excision of herniated thoracic discs

OBJECT

The authors began using thoracoscopy to treat pathological conditions of the spine in 1992. In this study they delineate their clinical experience in which this procedure was used to resect herniated thoracic discs.

METHODS

Fifty-five patients underwent thoracoscopy for the resection of herniated thoracic discs. Thirty-six patients presented with myelopathies and 19 with incapacitating thoracic radicular pain. Forty-three patients underwent a single-level, 11 a two-level, and one a three-level discectomy. The mean operative time for thoracoscopic microdiscectomy was 3 hours and 25 minutes (range 80-542 minutes) and the mean blood loss was 327 ml (range 124-1500 ml). Compared with thoracotomy, which was performed in 18 patients, thoracoscopy was associated with a mean of 1 hour less operative time and less than one-half of the blood loss, duration of chest tube drainage, usage of pain medication, and length of hospitalization. Compared with costotransversectomy, which was performed in 15 patients, thoracoscopy permitted more complete resection of calcified and midline thoracic discs because it provided a direct view of the entire anterior surface of the dura. Thoracotomy was associated with a significantly greater incidence of prolonged, disabling intercostal neuralgia compared with the mild transient episodes of intercostal neuralgia associated with thoracoscopy (50% compared with 16%). Thoracotomy also was associated with a significantly higher incidence of postoperative atelectasis and pulmonary dysfunction than thoracoscopy (33% compared with 7%). Clinical and neurological outcomes were excellent (mean follow-up period 15 months). Among the 36 myelopathic patients, 22 completely recovered neurologically; five improved functionally but had some residual myelopathic symptoms; and nine stabilized. Among the 19 patients with isolated thoracic radiculopathies, 15 recovered completely and four improved moderately; no patient had worsened radicular pain.

CONCLUSIONS

Thoracoscopic microdiscectomy is a reliable surgical technique that can be performed safely with excellent clinical and neurological results.