En bloc spondylectomy reconstructions in a biomechanical in-vitro study

In vitro biomechanical evaluation of a strutted intradiscal spacer for lumbar discectomy

BACKGROUND

Discectomy plus implantation of a strutted intradiscal spacer has been shown to reduce reoperations and reherniations versus discectomy alone following lumbar disc herniation. This study explored the underlying biomechanics of the intradiscal spacer.

METHODS

Six fresh-frozen cadaveric lumbar spine specimens (L2 to L5) from three donors were used. Following box annulotomy to simulate disc herniation, a discectomy was performed. One segment from each donor was randomly assigned to either an untreated control group or the test group where an intradiscal spacer was implanted. A six degree of freedom universal spine tester assessed range of motion (RoM) in flexion/extension, lateral bending and axial rotation in the native state in load controlled [±7.5 Nm] and intervals up to 60,000 cycles. Disc height was measured on fluoroscopy for multiple timepoints. The segments were also analyzed to detect possible reherniation during the cycling loading.

FINDINGS

Following 60,000 cycles, the mean percentage RoM increase versus the intact state was less for discectomy plus the intradiscal spacer versus discectomy alone for lateral bending (170.7 ± 10.0 vs. 222.5 ± 33.3 %), flexion/extension (178.5 ± 6.1 vs. 204.6 ± 44.3 %) and axial rotation (284.4 ± 127.2 vs. 362.3 % ± 240.4 %). Mean overall disc height loss versus the annulotomy state was also less with the intradiscal spacer versus discectomy alone (-19.3 ± 3.7 vs. -29.1 ± 6.1 %). There was no evidence of device subsidence or migration.

INTERPRETATION

This study helps to explain the clinical observation that insertion of a strutted intradiscal spacer following discectomy reduces reherniation rate by mechanically limiting the increase in RoM and disc height loss following lumbar discectomy.

Numerical evaluation of spinal reconstruction using a 3D printed vertebral body replacement implant: effects of material anisotropy

Background and objective

Artificial vertebral implants have been widely used for functional reconstruction of vertebral defects caused by tumors or trauma. However, the evaluation of their biomechanical properties often neglects the influence of material anisotropy derived from the host bone and implant's microstructures. Hence, this study aims to investigate the effect of material anisotropy on the safety and stability of vertebral reconstruction.

Material and methods

Two finite element models were developed to reflect the difference of material properties between linear elastic isotropy and nonlinear anisotropy. Their biomechanical evaluation was carried out under different load conditions including flexion, extension, lateral bending and axial rotation. These performances of two models with respect to safety and stability were analyzed and compared quantitatively based on the predicted von Mises stress, displacement and effective strain.

Results

The maximum von Mises stress of each component in both models was lower than the yield strength of respective material, while the predicted results of nonlinear anisotropic model were generally below to those of the linear elastic isotropic model. Furthermore, the maximum von Mises stress of natural vertebra and reconstructed system was decreased by 2-37 MPa and 20-61 MPa, respectively. The maximum reductions for the translation displacement of the artificial vertebral body implant and motion range of whole model were reached to 0.26 mm and 0.77°. The percentage of effective strain elements on the superior and inferior endplates adjacent to implant was diminished by up to 19.7% and 23.1%, respectively.

Conclusion

After comprehensive comparison, these results indicated that the finite element model with the assumption of linear elastic isotropy may underestimate the safety of the reconstruction system, while misdiagnose higher stability by overestimating the range of motion and bone growth capability.

En Bloc Surgery in the Thoracic Spine: Indications, Results, and Complications in a Series of Eighty-Five Patients Affected by Primary and Secondary Malignant Bone Tumors

BACKGROUND

En bloc resection remains the cornerstone treatment for malignant bone tumors affecting the spine. The thoracic spine poses unique challenges because of the proximity of crucial structures. This study assesses outcomes of patients who underwent en bloc spondylectomy for malignant bone tumors at the thoracic level.

METHODS

We retrospectively reviewed 85 cases of primary and secondary bone tumors in the thoracic spine, undergoing en bloc spondylectomy from 1996 to 2016. Evaluation encompassed clinical presentation, tumor characteristics, surgical outcomes, complications, survival, and recurrence.

RESULTS

Of 85 patients, 40 presented directly, whereas 45 had undergone previous intralesional surgery. Chondrosarcoma and chordoma comprised the most prevalent primary histologic types; thyroid and kidney carcinomas were the most frequent secondary tumors. Pain was reported in 75 patients at diagnosis. Margins were adequate in 54 cases and intralesional in 31. Immediate postoperative deaths amounted to 4. Major complications included substantial blood loss, neurologic deterioration, and paraplegia. The 5-year local recurrence-free survival was 58.7%, significantly influenced by the surgical margin: patients with wide margins experienced a 5-year local recurrence-free survival of 85.7%, whereas those with marginal and intralesional margins had rates of 56.7% and 45.6%, respectively; overall recurrence was 22.3%, with no notable disparities between previously treated and untreated patients. The 5-year overall survival was 63.2% and 56.2% for primary and secondary tumors, respectively. The overall survival was not significantly influenced by surgical margins.

CONCLUSIONS

Managing malignant thoracic bone tumors poses significant challenges. This study underscores the criticality of achieving adequate margins, particularly after previous intralesional approaches.

Torque forces of expandable titanium vertebral body replacement cages during expansion and subsidence in the osteoporotic lumbar spine

BACKGROUND

The application of expandable titanium-cages has gained widespread use in vertebral body replacement for indications such as burst fractures, tumors and infectious destruction. However, torque forces necessary for a satisfactory expansion of these implants and for subsidence of them into the adjacent vertebrae are unknown within the osteoporotic spine.

METHODS

Six fresh-frozen human, osteoporotic, lumbar spines were dorsally instrumented with titanium implants (L2-L4) and a partial corpectomy of L3 was performed. An expandable titanium-cage was inserted ventrally and expanded by both residents and senior surgeons until fixation was deemed sufficient, based on haptic feedback. Torque forces for expansion were measured in Nm. Expansion was then continued until cage subsidence occurred. Torque forces necessary for subsidence were recorded. Strain of the dorsal rods during expansion was measured with strain gauges.

FINDINGS

The mean torque force for fixation of cages was 1.17 Nm (0.9 Nm for residents, 1.4 Nm for senior surgeons, p = .06). The mean torque force for subsidence of cages was 3.1 Nm (p = .005). Mean peak strain of the dorsal rods was 970 μm/m during expansion and 1792 μm/m at subsidence of cages (p = .004).

INTERPRETATION

The use of expandable titanium-cages for vertebral body replacement seems to be a primarily safe procedure even within the osteoporotic spine as torque forces required for subsidence of cages are nearly three times higher than those needed for fixation. Most of the expansion load is absorbed by straining of the dorsal instrumentation. Rod materials other than titanium may alter the torque forces found in this study.

Carbon Fiber-Reinforced PolyEtherEtherKetone (CFR-PEEK) Instrumentation in Degenerative Disease of Lumbar Spine: A Pilot Study

CFR-PEEK is gaining popularity in spinal oncological applications due to its reduction of imaging artifacts and radiation scattering compared with titanium, which allows for better oncological follow-up and efficacy of radiotherapy. We evaluated the use of these materials for the treatment of lumbar degenerative diseases (DDs) and considered the biomechanical potential of the carbon fiber in relation to its modulus of elasticity being similar to that of bone. Twenty-eight patients with DDs were treated using CRF-PEEK instrumentation. The clinical and radiographic outcomes were collected at a 12-month FU. Spinal fusion was evaluated in the CT scans using Brantigan scores, while the clinical outcomes were evaluated using VAS, SF-12, and EQ-5D scores. Out of the patients evaluated at the 12-month FU, 89% showed complete or almost certain fusion (Brantigan score D and E) and presented a significant improvement in all clinical parameters; the patients also presented VAS scores ranging from 6.81 ± 2.01 to 0.85 ± 1.32, EQ-5D scores ranging from 53.4 ± 19.3 to 85.0 ± 13.7, SF-12 physical component scores (PCSs) ranging from 29.35 ± 7.04 to 51.36 ± 9.75, and SF-12 mental component scores (MCSs) ranging from 39.89 ± 11.70 to 53.24 ± 9.24. No mechanical complications related to the implant were detected, and the patients reported a better tolerance of the instrumentation compared with titanium. No other series of patients affected by DD that was stabilized using carbon fiber implants have been reported in the literature. The results of this pilot study indicate the efficacy and safety of these implants and support their use also for spinal degenerative diseases.

Long-term outcomes of the nano-hydroxyapatite/polyamide-66 cage versus the titanium mesh cage for anterior reconstruction of thoracic and lumbar corpectomy: a retrospective study with at least 7 years of follow-up

BACKGROUND

The nano-hydroxyapatite/polyamide-66 (n-HA/PA66) cage is a biomimetic cage with a lower elastic modulus than the titanium mesh cage (TMC). This study aimed to compare the long-term outcomes of the n-HA/PA66 cage and TMC in the anterior reconstruction of thoracic and lumbar fractures.

METHODS

We retrospectively studied 113 patients with acute traumatic thoracic or lumbar burst fractures, comprising 60 patients treated with the TMC and 53 treated with the n-HA/PA66 cage for anterior reconstruction following single-level corpectomy. The radiographic data (cage subsidence, fusion status, segmental sagittal alignment) and clinical data (visual analogue scale (VAS) for pain and Oswestry Disability Index (ODI) for function) were evaluated preoperatively, postoperatively, and at final follow-up after a minimum 7-year period.

RESULTS

The n-HA/PA66 and TMC groups had similar final fusion rates (96.2% vs. 95.0%). The cage subsidence at final follow-up was 2.3 ± 1.6 mm with subsidence of more than 3 mm occurring in 24.5% in the n-HA/PA66 group, which was significantly lower than the respective values of 3.9 ± 2.5 mm and 58.3% in the TMC group. The n-HA/PA66 group also had better correction of the bisegmental kyphotic angle than the TMC group (7.1° ± 7.5° vs 1.9° ± 8.6°, p < 0.01), with lower loss of correction (2.9° ± 2.5° vs 5.2° ± 4.1°, p < 0.01). The mean ODI steadily decreased after surgery in both groups. At final follow-up, the ODI and VAS were similar in the TMC and n-HA/PA66 groups.

CONCLUSIONS

The n-HA/PA66 cage is associated with excellent radiographic fusion, better maintenance of the height of the fused segment, and better correction of kyphosis than the TMC during 7 years of follow-up after one-level anterior corpectomy. With the added benefit of radiolucency, the n-HA/PA66 cage may be superior to the TMC in anterior reconstruction of thoracic or lumbar fractures.

Giant schwannoma of thoracic vertebra: A case report

BACKGROUND

It is relatively rare for schwannomas to invade bone, but it is very rare for a large mass to form concurrently in the paravertebral region. Surgical resection is the only effective treatment. Because of the extensive tumor involvement and the many important surrounding structures, the tumor needs to be fully exposed. Most of the tumors are completely removed by posterior combined open-heart surgery to relieve spinal cord compression, restore the stability of the spine and maximize the recovery of nerve and spinal cord function. The main objective of this article is to present a schwannoma that had invaded the T5 and T6 vertebral bodies and formed a large paravertebral mass with simultaneous invasion of the spinal canal and compression of the spinal cord.

CASE SUMMARY

A 40-year-old female suffered from intermittent chest and back pain for 8 years. Computed tomography and magnetic resonance imaging scans showed a paravertebral tumor of approximately 86 mm × 109 mm × 116 mm, where the adjacent T5 and T6 vertebral bodies were invaded by the tumor, the right intervertebral foramen was enlarged, and the tumor had invaded the spinal canal to compress the thoracic medulla. The preoperative puncture biopsy diagnosed a benign schwannoma. Complete resection of the tumor was achieved by a two-step operation. In the first step, the thoracic surgeon adopted a lateral approach to separate the thoracic tumor from the lung. In the second step, a spine surgeon performed a posterior midline approach to dissect the tumor from the vertebral junction through removal of the tumor from the posterior side and further resection of the entire T5 and T6 vertebral bodies. The large bone defect was reconstructed with titanium mesh, and the posterior root arch was nail-fixed. Due to the large amount of intraoperative bleeding, we performed tumor angioembolization before surgery to reduce and avoid large intraoperative bleeding. The postoperative diagnosis of benign schwannoma was confirmed by histochemical examination. There was no sign of tumor recurrence or spinal instability during the 2-year follow-up.

CONCLUSION

Giant schwannoma is uncommon. In this case, a complete surgical resection of a giant thoracic nerve sheath tumor that invaded part of the vertebral body and compressed the spinal cord was safe and effective.

Surgical nuances and construct patterns influence construct stiffness in C1-2 stabilizations: a biomechanical study of C1-2 gapping and advanced C1-2 fixation

PURPOSE

Stabilization of C1-2 using a Harms-Goel construct with 3.5 mm titanium (Ti) rods has been established as a standard of reference (SOR). A reduction in craniocervical deformities can indicate increased construct stiffness at C1-2. A reduction in C1-2 can result in C1-2 joint gapping. Therefore, the authors sought to study the biomechanical consequences of C1-2 gapping on construct stiffness using different instrumentations, including a novel 6-screw/3-rod (6S3R) construct, to compare the results to the SOR. We hypothesized that different instrument pattern will reveal significant differences in reduction in ROM among constructs tested.

METHODS

The range of motion (ROM) of instrumented C1-2 polyamide models was analyzed in a six-degree-of-freedom spine tester. The models were loaded with pure moments (2.0 Nm) in axial rotation (AR), flexion extension (FE), and lateral bending (LB). Comparisons of C1-2 construct stiffness among the constructs included variations in rod diameter (3.5 mm vs. 4.0 mm), rod material (Ti. vs. CoCr) and a cross-link (CLX). Construct stiffness was tested with C1-2 facets in contact (Contact Group) and in a 2 mm distracted position (Gapping Group). The ROM (°) was recorded and reported as a percentage of ROM (%ROM) normalized to the SOR. A difference > 30% between the SOR and the %ROM among the constructs was defined as significant.

RESULTS

Among all constructs, an increase in construct stiffness up to 50% was achieved with the addition of CLX, particularly with a 6S3R construct. These differences showed the greatest effect for the CLX in AR testing and for the 6S3R construct in FE and AR testing. Among all constructs, C1-2 gapping resulted in a significant loss of construct stiffness. A protective effect was shown for the CLX, particularly using a 6S3R construct in AR and FE testing. The selection of rod diameter (3.5 mm vs. 4.0 mm) and rod material (Ti vs. CoCr) did show a constant trend but did not yield significance.

CONCLUSION

This study is the first to show the loss of construct stiffness at C1-2 with gapping and increased restoration of stability using CLX and 6S3R constructs. In the correction of a craniocervical deformity, nuances in the surgical technique and advanced instrumentation may positively impact construct stability.

Biomechanics of artificial pedicle fixation in a 3D-printed prosthesis after total en bloc spondylectomy: a finite element analysis

Background

This study compared the biomechanics of artificial pedicle fixation in spine reconstruction with a 3-dimensional (3D)-printed prosthesis after total en bloc spondylectomy (TES) by finite element analysis.

Methods

A thoracolumbar (T10–L2) finite element model was developed and validated. Two models of T12 TES were established in combination with different fixation methods: Model A consisted of long-segment posterior fixation (T10/11, L1/2) + 3D-printed prosthesis; and Model B consisted of Model A + two artificial pedicle fixation screws. The models were evaluated with an applied of 7.5 N·m and axial force of 200 N. We recorded and analyzed the following: (1) stiffness of the two fixation systems, (2) hardware stress in the two fixation systems, and (3) stress on the endplate adjacent to the 3D-printed prosthesis.

Results

The fixation strength of Model B was enhanced by the screws in the artificial pedicle, which was mainly manifested as an improvement in rotational stability. The stress transmission of the artificial pedicle fixation screws reduced the stress on the posterior rods and endplate adjacent to the 3D-printed prosthesis in all directions of motion, especially in rotation.

Conclusions

After TES, the posterior long-segment fixation combined with the anterior 3D printed prosthesis could maintain postoperative spinal stability, but adding artificial pedicle fixation increased the stability of the fixation system and reduced the risk of prosthesis subsidence and instrumentation failure.

A finite element analysis on comparing the stability of different posterior fixation methods for thoracic total en bloc spondylectomy

Objective

To compare the spinal stability with different fixation methods after thoracic TES using finite element analysis

Methods

The spinal finite element model was established from a healthy volunteer, and the validity was verified. The models of T8 thoracic total en bloc spondylectomy (TES) with and without artificial vertebral body were established combination with different fixation methods: the first was long segment fixation with fixed segments T5–7, T9–11; the second was short segment fixation with fixed segments T6–7, T9–10; the third was modified short segment with a pair of vertebral body screws on T7 and T9 added on the basis of short segment fixation. The motions of each model in standing state were simulated in software. The range of motion (ROM) and internal fixation stress changes were analyzed.

Results

When anterior support was effective, the three fixation methods could effectively maintain the stability of the spine. However, when anterior support failed, the ROM of the long segment fixation group and the short segment fixation group in the flexion-extension directions was significantly higher than that of when the anterior support existed, while the modified short segment fixation group had no significant changes. Meanwhile, the stress of internal fixation in the long segment fixation group and the short segment fixation group were greatly increased. However, there were no significant changes in modified short segment fixation group.

Conclusion

After TES, the presence of the thoracic cage gives partial anterior stabilization. When the anterior support failed, the modified short segment fixation method can provide better stability.

In vitro comparison of personalized 3D printed versus standard expandable titanium vertebral body replacement implants in the mid-thoracic spine using entire rib cage specimens

BACKGROUND

Expandable titanium implants have proven their suitability as vertebral body replacement device in several clinical and biomechanical studies. Potential stabilizing features of personalized 3D printed titanium devices, however, have never been explored. This in vitro study aimed to prove their equivalence regarding primary stability and three-dimensional motion behavior in the mid-thoracic spine including the entire rib cage.

METHODS

Six fresh frozen human thoracic spine specimens with intact rib cages were loaded with pure moments of 5 Nm while performing optical motion tracking of all vertebrae. Following testing in intact condition (1), the specimens were tested after inserting personalized 3D printed titanium vertebral body replacement implants (2) and the two standard expandable titanium implants Obelisc™ (3) and Synex™ (4), each at T6 level combined with posterior pedicle screw-rod fixation from T4 to T8.

FINDINGS

No significant differences (P < .05) in primary and secondary T1-T12 ranges of motion were found between the three implant types. Compared to the intact condition, slight decreases of the range of motion were found, which were significant for Synex™ in primary flexion/extension (-17%), specifically at T3-T4 level (-46%), primary lateral bending (-18%), and secondary lateral bending during primary axial rotation (-53%). Range of motion solely increased at T8-T9 level, while being significant only for Obelisc™ (+35%).

INTERPRETATION

Personalized 3D printed vertebral body replacement implants provide a promising alternative to standard expandable devices regarding primary stability and three-dimensional motion behavior in the mid-thoracic spine due to the stabilizing effect of the rib cage.

Biomechanical Study of a Novel, Expandable, Non-Metallic and Radiolucent CF/PEEK Vertebral Body Replacement (VBR)

Vertebral body replacement is well-established to stabilize vertebral injuries due to trauma or cancer. Spinal implants are mainly manufactured by metallic alloys; which leads to artifacts in radiological diagnostics; as well as in radiotherapy. The purpose of this study was to evaluate the biomechanical data of a novel carbon fiber reinforced polyetheretherketone (CF/PEEK) vertebral body replacement (VBR). Six thoracolumbar specimens were tested in a six degrees of freedom spine tester. In all tested specimens CF/PEEK pedicle screws were used. Two different rods (CF/PEEK versus titanium) with/without cross connectors and two different VBRs (CF/PEEK prototype versus titanium) were tested. In lateral bending and flexion/extension; range of motion (ROM) was significantly reduced in all instrumented states. In axial rotation; the CF/PEEK combination (rods and VBR) resulted in the highest ROM; whereas titanium rods with titanium VBR resulted in the lowest ROM. Two cross connectors reduced ROM in axial rotation for all instrumentations independently of VBR or rod material. All instrumented states in all planes of motion showed a significantly reduced ROM. No significant differences were detected between the VBR materials in all planes of motion. Less rigid CF/PEEK rods in combination with the CF/PEEK VBR without cross connectors showed the smallest reduction in ROM. Independently of VBR and rod material; two cross connectors significantly reduced ROM in axial rotation. Compared to titanium rods; the use of CF/PEEK rods results in higher ROM. The stiffness of rod material has more influence on the ROM than the stiffness of VBR material.

Intraosseous Malignant Peripheral Nerve Sheath Tumor of 2 Consecutive Lumbar Vertebrae: A Case Report and Literature Review

BACKGROUND

Malignant peripheral nerve sheath tumor (MPNST), which refers to any malignant tumor that originates from peripheral nerve sheath cells, is rarely found in the spine. Primary intraosseous spinal MPNSTs are extremely uncommon; in fact, such an occurrence has been reported in a very limited number of cases hitherto. We report here one case of low-grade intraosseous MPNST in the lumbar vertebrae and review clinical research related to this rare tumor and modus operandi to its treatment.

CASE DESCRIPTION

A 51-year-old man suffering from lower back pain was initially diagnosed with lumbar tuberculosis. The intraoperative histopathologic examination, however, revealed that the occupying lesion was synovial sarcoma when surgeons intended to perform a debridement surgery of what was thought to be tuberculosis. The operation was therefore suspended. Two months later, the patient was referred to our institution. The pathologic sections were reexamined. Its results refuted the earlier thought of being synovial sarcoma, and a final diagnosis of MPNST was made. In addition, preoperative examination revealed that the tumor had advanced rapidly to the adjacent inferior vena cava and pedicle, which ruled out the possibility of performing a total en bloc spondylectomy. Therefore, a marginal resection for 2-level consecutive lumbar vertebrae was performed successfully via an anterior-posterior combined approach. No serious complications were detected at 18-month follow-up.

CONCLUSIONS

Preoperative biopsy is of great importance for the diagnosis of spinal tumors. Marginal resection of a complicated intraosseous spine MPNST via an anterior-posterior combined approach, despite being technically challenging, resulted in good survival and functional outcomes.

Design and preliminary biomechanical analysis of a novel motion preservation device for lumbar spinal disease after vertebral corpectomy

OBJECTIVE

To design a novel prosthesis, a movable artificial lumbar complex (MALC), for non-fusion reconstruction after lumbar subtotal corpectomy and to evaluate the stability, range of motion and load-bearing strength in the human cadaveric lumbar spine.

METHODS

Biomechanical tests were performed on lumbar spine specimens from 15 healthy cadavers which were divided in three groups: non-fusion, fusion and intact group. The range of motion (ROM), stability and load-bearing strength were measured.

RESULTS

The prosthesis was composed of three parts: the upper and lower artificial lumbar discs and the middle artificial vertebra. Both the MALC and titanium mesh cage re-established vertebral height, and no spinal cord compression or prosthesis dislocation was observed at the operative level. Regarding stability, there was no significant difference in all directions between the intact group and non-fusion group (P > 0.05). Segment movements of the specimens in the non-fusion group revealed significantly decreased T12-L1 ROM and significantly increased L1-2 and L2-3 ROM in flexion/extension and lateral bending compared with those in the fusion group (P < 0.05). Regarding load-bearing strength, when the lumbar vertebra was ruptured, there was no damage to the MALC and titanium mesh cage, but the maximum load in the non-fusion group was larger (P > 0.05).

CONCLUSIONS

Compared with titanium cages, the MALC prosthesis not only restored the vertebral height and effectively preserved segment movements without any abnormal gain of mobility in adjacent inter-vertebral spaces but also bore the lumbar load and reduced the local stress load of adjacent vertebral endplates.

How does a novel knitted titanium nucleus prosthesis change the kinematics of a cervical spine segment? A biomechanical cadaveric study

BACKGROUND

Total disc replacement is a possible treatment alternative for patients with degenerative disc disease, especially in the cervical spine. The aim is to restore the physiological flexibility and biomechanical behavior. A new approach based on these requirements is the novel nucleus prosthesis made of knitted titanium wires.

METHODS

The biomechanical functionalities of eight human cervical (C4-C7) spine segments were investigated. The range of motion was quantified using an ultra-sound based motion analysis system. Moreover, X-rays in full flexion and extension of the segment were taken to define the center of rotation before and after implantation of the nucleus prosthesis as well as during and after complex cyclic loading.

FINDINGS

The mean range of motion of the index segment (C5/6) in flexion/extension showed a significant reduction of range of motion from 9.7° (SD 4.33) to 6.0° (SD 3.97) after implantation (P = 0.037). Lateral bending and axial rotation were not significantly reduced after implanting and during cyclic loading in our testing. During cyclic loading the mean range of motion for flexion/extension increased to 7.2° (SD 3.67). The center of rotation remained physiological in the ap-plane and moved cranially in the cc-plane (-27% to -5% in cc height) during the testing.

INTERPRETATION

The biomechanical behavior of the nucleus implant might lower the risk for adjacent joint disorders and restore native function of the index segment. Further in vivo research is needed for other factors, like long-term effects and patient's satisfaction.

FOUR-LEVEL EN BLOC VERTEBRECTOMY: A NOVEL TECHNIQUE AND LITERATURE REVIEW

Objective:

To demonstrate a novel technique for multilevel en bloc post-vertebrectomy reconstruction.

Methods:

A novel technique for en bloc multiple post-vertebrectomy reconstruction was used in a patient presenting for curative resection of Ewing's Sarcoma at the oncology center of a public university hospital.

Results:

The procedure described was feasible for en bloc resection of the four vertebrae. The reconstruction was acceptable and satisfactory in terms of mechanical stability and was without any neurological sequelae in the patient.

Conclusion:

The use of an allograft with a locked intramedullary nail was an adequate solution for reconstructing the anterior and medial spines after multilevel vertebrectomy. In addition, the association of four intramedullary nails provided stability to the reconstruction. Immediate benefits of the technique compared to other commonly used techniques were shorter hospitalization times and reduced surgical morbidity. Level of Evidence V, Clinical study of a new surgical technique and a literature review.

Revision strategy and follow-up for implant failure in a case of combined anterior and posterior reconstruction after three-level en bloc vertebral body replacement and replacement of the aorta for chondrosarcoma of the thoracic spine

OBJECTIVE

In 2013, we reported a case of combined anterior and posterior reconstruction after three-level en bloc vertebral body replacement and replacement of the aorta for chondrosarcoma of the thoracic spine. Eight years after, we observed an implant failure and now report on revision strategy and 2-year follow-up (f/u) after revision.

METHODS

We report about the 2-year f/u of the same now 51-year-old gravedigger who needed to undergo revision surgery after implant failure. We did a combined anterior and posterior correction vertebral interbody fusion by (1) removal of broken screws in Th9 and L2, removal of broken titanium bars, correction of kyphosis, enhancement of the vertebral interbody fusion from Th8 to L4 using monoaxial titanium screws and cancellous bone transplantation and (2) removal of the broken plate and the loose cage, implantation of a novel expandable PEEK cage from Th11 to L1 and anterior stabilization from Th9/10 to L2/3, as well as autologous and allogeneic cancellous bone transplantation.

RESULTS

Two years after revision surgery, the patient presented fully reintegrated without any complains. No painkillers needed to be taken. Pain was reported with 2 out of 10 on the VAS.

CONCLUSION

Both procedures offer a good primary stabilization with excellent pain reduction and good return to life. Limited information on long-term survivors is known. Therefore, the theoretical advantage of a biological solution needs to be checked in the long-term f/u for consistency.

Risk factors of instrumentation failure after multilevel total en bloc spondylectomy

INTRODUCTION

Multilevel total en bloc spondylectomy (TES) is required to secure oncologically adequate resection margins. However, no useful information has been reported for spinal reconstruction after multilevel TES. Therefore, this study set out to assess the clinical and radiological outcomes of spinal reconstruction after multilevel TES.

METHODS

Forty-eight patients treated with multilevel TES at our institute were included in the analysis. Reconstruction was achieved with posterior pedicle screw fixation and an anterior titanium mesh cage filled with iliac autograft in all cases. Spinal shortening was performed to increase spinal stability from the reconstruction. Instrumentation failure and radiological findings were evaluated with radiography and computerized tomography (CT).

RESULTS

After excluding one patient whose general condition was deteriorating, radiological evaluations of 47 patients were performed over a period of more than a year. The follow-up time was 17 to 120 months (mean: 70.2 months). Instrumentation failure occurred in one patient (5.9%) after thoracic multilevel TES, in 4 patients (25.0%) after thoracolumbar multilevel TES, and in 3 patients (42.9%) after lumbar multilevel TES. No instrumentation failure was observed in cervicothoracic cases. Cage subsidence (>2 mm) occurred in 30 patients (63.8%). In 22 of them, subsidence appeared on the CT one month after surgery. The risk factors of instrumentation failure included a multilevel TES below the thoracolumbar level and a long span of vertebral resection. There was no instrumentation failure in any of the 11 "disc-to-disc cutting" cases.

CONCLUSIONS

This study identified the risk factors of instrumentation failure after multilevel TES. There is a high risk of instrumentation failure in cases of long vertebral resection below the thoracolumbar level. On the other hand, our reconstruction method can be successful for multilevel TES above the thoracic level.

Complete Spondylectomy Using Orthogonal Spinal Fixation and Combined Anterior and Posterior Approaches for Thoracolumbar Spinal Reconstruction: Technical Nuances and Clinical Results

STUDY DESIGN

Retrospective chart review.

OBJECTIVE

To determine the long-term efficacy of 2-stage total en bloc spondylectomy (TES).

SUMMARY OF BACKGROUND DATA

TES is a well-described technique to achieve tumor-free margins, but it is a highly destabilizing procedure that necessitates spinal reconstruction. A 2-stage anterior/posterior approach for tumor resection and instrumentation has been shown to be biomechanically superior to the single-stage approach in achieving rigid fixation, but few clinical studies with long-term outcomes exist.

METHODS

A retrospective review was performed on patients undergoing a 2-stage TES for a spinal tumor between 1999 and 2011. Results were compared with those from a literature review of case series, with a minimum of 2-year follow-up, reporting on a single-stage posterior-only approach for TES.

RESULTS

Seven patients were identified (average follow-up 52.7 mo). Tumor location ranged from T1 to L3 with the following pathologies: metastasis (n=3), hemangioma (n=1), leiomyosarcoma (n=1), giant cell tumor (n=1), and chordoma (n=1). There were no significant surgical complications. All 7 patients had intact spinal fixation. There were no failures of the orthogonal fixation (pedicle screws or anterior fixation). The average modified Rankin Scale scores improved from 2.7 preoperatively to 0.7 at last follow-up. None of the patients in our series suffered local disease recurrence at last follow-up or suffered neurological deterioration. These results were comparable with those noted in the literature review of posterior-only approach, where 12% of patients experienced instrument failure.

CONCLUSIONS

TES is a highly destabilizing procedure requiring reconstruction resistant to large multiplanar translational and torsional loads. A 2-stage approach utilizing orthogonal vertebral body screws perpendicular to pedicle screws is a safe and effective surgical treatment strategy. Orthogonal spinal fixation may lower the incidence of instrumentation failure associated with complete spondylectomy and appears to be comparable with a single-stage procedure. However, larger prospective series are necessary to assess the efficacy of this approach versus traditional means.

Fixed-Angle, Posteriorly Connected Anterior Cage Reconstruction Improves Stiffness and Decreases Cancellous Subsidence in a Spondylectomy Model

STUDY DESIGN

An idealized biomechanical model.

OBJECTIVE

The aim of this study was to evaluate the biomechanical properties of a construct designed to minimize intervertebral cage subsidence and maximize stiffness.

SUMMARY OF BACKGROUND DATA

Reconstruction after vertebral resection typically involves posterior segmental fixation and anterior interbody support. However, poor bone density, adjuvant radiation, or the oncologic need for endplate resection make interbody device subsidence and resultant instrumentation failure a significant concern.

METHODS

An idealized thoracolumbar spondylectomy reconstruction model was constructed using titanium segmental instrumentation and Delrin plastic. In vivo mechanical stress was simulated on a custom multi-axis spine simulator. Rigid body position in space was measured using an optical motion-capture system. Cancellous subsidence was modeled using a 1 cm thick wafer of number 3 closed-cell Sawbones foam at one endplate. Ten foam specimens were tested in a control state consisting of posterior segmental fixation with a free interbody cage. Ten additional foam specimens were tested in the test state, with the Delrin interbody cage "connected" to the posterior rods using two additional pedicle screws placed into the cage. Foam indentation was quantified using a precision digital surface-mapping device, and subsidence volume calculated using geometric integration.

RESULTS

The control group exhibited significantly greater foam indentation after cycling, with a mean subsidence volume of 1906 mm [95% confidence interval (95% CI) 1810-2001] than the connected cage group subsidence volume of 977 mm (95% CI 928-1026 mm; P < 0.001]. Construct stiffness was greater in the connected cage group (3.1 Nm/degree, 95% CI 3.1-3.2) than in the control group (2.3 Nm/degree, 95% CI 2.2-2.4; P < 0.001).

CONCLUSION

In an idealized spondylectomy model, connecting the anterior column cage to the posterior instrumentation using additional pedicle screws results in a construct that is nearly 40% stiffer and exhibits 50% less cancellous subsidence compared with a traditional unconnected cage.

LEVEL OF EVIDENCE

N/A.

Recurrent adamantinoma in the thoracolumbar spine successfully treated by three-level total en bloc spondylectomy by a single posterior approach

PURPOSE

Adamantinoma is a low-grade primary malignant bone tumour with slow growth and local recurrence. Its occurrence in the spine is extremely rare, particularly with multilevel involvement. This paper wants to present the first case involving a patient with recurrent thoracolumbar spinal adamantinoma, who underwent a successful three-level spondylectomy for en bloc resection.

METHODS

A 24-year-old man with osteolytic masses of T11 and T12 vertebral bodies was performed curettage by a posterior approach in 2008. The pathology report showed the excised neoplasm was a rare adamantinoma. This patient underwent a tumorectomy again because of its local recurrence nearly 3 years later. In 2012, it was unfortunately revealed that the excised tumour had relapsed and had spread to the L1 vertebral body. Due to its repeated recurrence and aggressive lesion, total en bloc spondylectomy (TES) for this malignant tumour was thought to be the best option for preventing repeated recurrence and possible cure. TES for T11-L1 thoracolumbar spine was performed and spinal reconstruction was completed with instrumentation and a titanium mesh cage through a one-stage single posterior approach.

RESULTS

After three-level TES, neurological deficits of the patient demonstrated good recovery and no evidence of adamantinoma recurrence or deformity was found at 2-year follow-up.

CONCLUSIONS

This is the first case involving multilevel thoracolumbar spinal adamantinoma with repeated recurrence to be successfully treated by three-level TES by a single posterior approach.

Clinical outcome of spinal reconstruction after total en bloc spondylectomy at 3 or more levels

STUDY DESIGN

Retrospective clinical study.

OBJECTIVE

To assess the clinical and radiological outcome of spinal reconstruction after total en bloc spondylectomy (TES) at 3 or more levels.

SUMMARY OF BACKGROUND DATA

There have been few reports of multilevel spondylectomy for spinal tumor. This is the first case series on the clinical outcome for reconstructions after 3 or more levels of TES.

METHODS

Twenty-six patients treated by 3 or more levels of TES at Kanazawa University Hospital were included in this analysis. Reconstruction was performed with pedicle screw fixation and a titanium mesh cage filled with autograft in all cases. To increase spinal stability in reconstruction, spinal shortening was performed. Instrument failure and radiological findings were evaluated using radiograph and computed tomographical scan with multiplanar reconstructions. The length of spinal shortening was also measured.

RESULTS

Excluding 4 patients with deteriorating general condition, radiological evaluation was performed for more than 1 year in 22 patients. All 22 patients had no evidence of local recurrence at the surgical site of the spine during the follow-up period. Cage subsidence was seen in 11 patients (50%). Eight of the 11 patients showed the appearance of subsidence 1 month after the surgery. There was one instrument failure that required revision surgery 8 months after TES surgery. One other patient showed bone resorption on the contact surfaces of the cage at 24 months after the surgery. The mean length of the resection vertebrae was 84.6 mm (52-124 mm), while the length of the shortening was 10.4 mm (3-22 mm).

CONCLUSION

No local recurrence was observed after TES at 3 or more levels. Cage subsidence was a common phenomenon (50%) and already observed 1 month after surgery in 8 of the 11 cases. Spinal shortening has the potential to provide good stability for multilevel TES.

LEVEL OF EVIDENCE

4.

[Multisegmental en bloc spondylectomy. Indications, staging and surgical technique]

OBJECTIVE

Description of the surgical technique including approaches and spinal reconstruction principles for patients scheduled for multilevel en bloc excision of vertebral tumors (multisegmental total en bloc spondylectomy) with the aim to attain tumor-free margins and minimize the risk of local and systemic tumor recurrence. Restoration of biomechanically sufficient spinal stability. Functional preservation and/or regaining of adequate neurological function.

INDICATIONS

Primary malignant and benign, aggressive spinal tumors. Solitary metastatic tumors of biologically and prognostically favorable primary tumor (good prognostic scores). Extracompartmental, multisegmental vertebral tumor manifestations according to Tomita type 6.

CONTRAINDICATIONS

Diffuse spinal/vertebral tumor spread according to Tomita type 7 (disseminated spinal metastatic disease). Detection of distant metastases in the staging investigation. Biologically unfavorable tumor entities or primary systemic malignant tumors/diffuse disseminated malignoma (Tomita score < 4-5 points, Tokuhashi score < 12 points).

SURGICAL TECHNIQUE

Depending on tumor growth, sequential performance of the anterior and posterior approach for local tumor release and preparation/replacement of encased large vessels. Posterior approach via dorsomedial incision and exposure of the posterior vertebral elements. Costotransversectomy, resection of the facets, resection of paravertebral rib segments. Laminectomy in the tumor-free lamina segment, resection of the ligamentum flavum and paradural ligation of affected nerve roots, bilateral ligation of the segmental arteries. Digital extrapleural palpation and dissection to the anterior vertebral body parts. Insertion of S-shaped spatulas ventral to the anterior aspect of the spine, and dissection of the disc spaces and the posterior longitudinal ligament. Instrumentation of pedicle screws and unilateral rod fixation, mobilization and careful, manual turning out/rotation of the affected vertebral segments around the longitudinal axis of the spinal cord. Interpositioning of a carbon-composite cage from posterior filled with autologous bone. Completion of the posterior stabilization, soft tissue closure, Goretex patch fixation if required in cases of chest wall resections.

POSTOPERATIVE MANAGEMENT

Intensive care monitoring with balanced volume replacement/transfusion. Postoperative adjuvant radiotherapy or chemotherapy, depending on the protocol and resection margins.

An in vitro biomechanical comparison of single-rod, dual-rod, and dual-rod with transverse connector in anterior thoracolumbar instrumentation

BACKGROUND

After thoracolumbar corpectomy, standard anterolateral instrumentation may consist of dual rods with cross-connectors. However, when the vertebral bodies are small or involved with disease, only 1 rod may be possible.

OBJECTIVE

To compare the biomechanics of an in vitro L1 corpectomy model using 1 rod, 2 rods, or 2 rods with 2 cross-connectors.

METHODS

Eight fresh frozen human cadaveric spines were potted from T9 to L3. Pure moments of 1.5, 3, and 4.5 Nm were applied, and the motion of the spine was measured using 3 infrared cameras. Loads were applied in flexion and extension, right and left lateral bending, and right and left axial rotation. Each spine was first tested in the intact state. After performing an L1 corpectomy and replacement with a carbon fiber reinforced polymer cage, 3 constructs were tested: single rod (1R), dual rod (2R), and dual rod with 2 transverse connectors (CC).

RESULTS

Analysis of variance suggests significant main effects of load (P < .0001), axis (P = .022), construct (P =.0019), and individual spine (P < .0001). Overall, the single-rod construct is significantly less rigid than the intact spine in axial rotation. There is no significant difference between the intact spine and either the dual-rod construct or the dual-rod cross-connector construct.

CONCLUSION

In our in vitro model of anterior spinal stabilization after corpectomy and grafting, a single-rod construct is significantly less rigid than the intact spine. Addition of a second rod returns the rigidity of the spine to the intact state. A dual-rod cross-connector construct is significantly more rigid than a single-rod construct.

Comparison of expandable and fixed interbody cages in a human cadaver corpectomy model, Part I: endplate force characteristics

Object

Expandable cages are becoming more popular due in large part to their versatility, but subsidence and catastrophic failure remain a concern. One of the proposed reasons of failure is edge loading of the endplate caused by a mismatch between the sagittal alignment of the motion segment and cage. This in vitro analysis investigates the endplate forces characteristic of expandable and fixed interbody cages in a single-level human cadaver corpectomy model.

Methods

Ten human thoracolumbar spines (T10–L2, L3–5) were biomechanically evaluated following a single-level corpectomy that was reconstructed with an expandable or fixed cage. Fixed cages were deployed with the best-fitting end cap combination, whereas expandable cages were deployed in normal, hypolordotic, and hyperlordotic alignment scenarios. The endplate forces and contact area were measured with a pressure measurement system, and the expansion torque applied by the surgeon was measured with a custom-made insertion device.

Results

The contact areas of the expandable cages were, in general, higher than those of the fixed cages. The endplate forces of the expandable cages were similar to those of the fixed cages in the normal alignment scenario. Higher endplate forces were observed in the hyperlordotic scenario, whereas the endplate forces in the hypolordotic and normal alignment scenarios were similar. There was no correlation with the expansion torque and the final endplate forces.

Conclusions

Expandable cages resulted in consistently higher contact area and endplate forces when compared with the fixed cages. Because the expansion torque does not correlate with the final endplate forces, surgeons should not rely solely on tactile feedback during deployment of these cages.

Two-stage multilevel en bloc spondylectomy with resection and replacement of the aorta

OBJECTIVE

We report a case of multilevel spondylectomy in which resection and replacement of the adjacent aorta were done. Although spondylectomy is nowadays an established technique, no report on a combined aortic resection and replacement has been reported so far.

METHODS

The case of a 43-year-old man with a primary chondrosarcoma of the thoracic spine is presented. The local pathology necessitated resection of the aorta. We did a two-stage procedure with resection and replacement of the aorta using a heart-lung machine followed by secondary tumor resection and spinal reconstruction.

RESULTS

The procedure was successful. A tumor-free margin was achieved. The patient is free of disease 48 months after surgery.

CONCLUSION

En bloc spondylectomy in combination with aortic resection is feasible and might expand the possibility of producing tumor-free margins in special situations.

[Biomechanical aspects of complex reconstructions following radical resection of thoracolumbar spinal tumors]

The total number of spinal tumors has increased over the past decade. However, the average survival time of tumor patients has increased due to improvements in the multidisciplinary treatment regimes. Therefore, radical tumor resection and complex reconstruction were developed in spinal surgery. Various reconstructive options for the throracolumbar spine are nowadays available and are depicted in this article. The success of complex reconstructive surgery relies on biomechanical principles and reconstruction is dependent on the size and location of the lesion, bone porosity and implant systems used. Special emphasis of this article focuses on en bloc vertebrectomy which is the most radical approach of spinal tumor surgery. The biomechanical aspects of different types of lesions and the reconstructive options are discussed in the context of the currently published literature.

Late instrumentation failure after total en bloc spondylectomy

Object

The object of this study was to investigate failures after spinal reconstruction following total en bloc spondylectomy (TES), related factors, and sequelae arising from such failures in patients with malignant spinal tumors.

Methods

Fifteen patients (12 males and 3 females, with a mean age of 46.5 years) with malignant spinal tumors who underwent TES and survived for more than 1 year were included in this analysis (mean follow-up 41.5 months). Seven patients had primary tumors, including giant cell tumors in 4 patients, chordoma in 2, and Ewing sarcoma in 1. Eight patients had metastatic tumors, including thyroid cancer in 6 and renal cell cancer and malignant fibrous histiocytoma in 1 patient each. Seven patients without prominent paravertebral extension of the tumor were treated using a posterior approach alone, and 8 patients who exhibited prominent anterior or anterolateral extension of the tumors into the thoracic or abdominal cavity were treated using a combined anterior and posterior approach. Spinal reconstruction after tumor resection was performed using a combination of anterior structural support and posterior instrumentation. The relationship between instrumentation failure and clinical and radiographic factors, including age, sex, history of previous surgery, preoperative radiotherapy, tumor histology, tumor level, surgical approach, number of resected vertebrae, rod diameter, number of instrumented vertebrae, and cage subsidence, was investigated.

Results

Six patients (40%) with spinal instrumentation failure were identified: rod breakage occurred in 3 patients, and breakage of both the rod and the cage, combined cage breakage and screw back-out, and endplate fracture arising from cage subsidence occurred in 1 patient each. All of these patients experienced acute or chronic back pain, but only 1 patient with a tumor recurrence experienced neurological deterioration upon instrumentation failure. Cage subsidence (≥ 5 mm), preoperative irradiation, and the number of instrumented vertebrae (≤ 4 vertebrae) were significantly related to late instrumentation failure.

Conclusions

Late instrumentation failure was a frequent complication after TES. Although patients with instrumentation failure experienced back pain, the neurological sequelae were not catastrophic. For prevention, meticulous preparation of the graft site and a longer posterior fixation should be considered.

Surgical management of recurrent thoracolumbar spinal sarcoma with 4-level total en bloc spondylectomy: description of technique and report of two cases

INTRODUCTION

The descriptions of total spondylectomy and further development of the technique for the treatment of vertebral sarcomas offered for the first time the opportunity to achieve oncologically sufficient resection margins, thereby improving local tumor control and overall survival. Today, single level en bloc spondylectomies are routinely performed and discussed in the literature while only few data are available for multi-level resections. However, due to the topographic vicinity of the spinal cord and large vessels, the multisegmental resections are technically demanding, represent major surgery and only few case reports are available. Surgical options are even more limited in cases of revision surgery and local recurrences when en bloc spondylectomy was considered to be not feasible due to high risk of vital complications in expanding resection margins. Deranged anatomy, implants in situ and extensive intra-/paraspinal scar tissue formation resulting from previously performed approaches and/or radiation are considered the principal complicating factors that usually hold back spine surgeons to perform revision for resection leaving the patient to palliative treatment.

METHODS

We present two patient cases with previously performed piecemeal vertebrectomy in the thoracic spine due to a solitary high-grade spinal sarcoma. After extensive re-staging, both patients underwent a multi (4)-level en bloc spondylectomy in our department (one patient with combined en bloc lung resection). Except a local wound disturbance, there was no severe intra- or postoperative complication.

RESULTS

After multilevel en bloc spondylectomy both patients showed a good functional outcome without neurological deficits, except those resulting from oncologically scheduled resection of thoracic nerve roots. After a median follow-up of 13 months, there was no local recurrence or distant metastasis. The reconstruction using a posterior screw rod system that is interconnected to an anterior vertebral body replacement with a carbon composite cage showed no implant failure or loosening. In summary, the approach of a multilevel en bloc surgery for revision and oncologically sufficient resection in cases of spinal sarcoma recurrences seems possible. However, interdisciplinary decision making in a tumor board, realistic evaluation of surgical resectability to attain tumor free margins, advanced experiences in spinal reconstructions and involvement of vascular, visceral and thoracic surgical expertise are essential preconditions for acceptable oncological and functional outcome.

Spinal instrumentation after complete resection of the last lumbar vertebra: an in vitro biomechanical study after L5 spondylectomy

STUDY DESIGN

Human cadaveric ilio-lumbosacral spines were tested in an in vitro biomechanical flexibility experiment to investigate the biomechanical stability provided by four different types of spinal reconstruction techniques after spondylectomy of the L5 vertebral body.

OBJECTIVE

To compare the biomechanical stability provided by four reconstruction methods after L5 spondylectomy.

SUMMARY OF BACKGROUND DATA

Clinical studies have shown that total spondylectomy of the L5 vertebral body presents a challenging scenario for spinal reconstruction. Biomechanical studies on spinal reconstruction after total spondylectomy have been performed at the thoracolumbar junction. However, there have been no biomechanical studies after L5 spondylectomy.

METHODS

Seven cadaveric lumbosacral spines (L2-S1) with intact ilium were used. After intact testing, spondylectomy of the L5 vertebra was performed and the spine was reconstructed using an expandable cage for anterior column support. Supplementary fixation was performed as a sequential order of: (1) bilateral pedicle screws at L4-S1 (SP), (2) anterior plate and bilateral pedicle screws at L4-S1 (ASP), (3) bilateral pedicle screws at L3-S1 and iliac screws (MP), and (4) anterior plate at L4-S1, bilateral pedicle screws at L3-S1 and iliac screws (AMP). Range of motion (ROM) for each construct was obtained by applying pure moments in flexion, extension, lateral bending, and axial rotation.

RESULTS

In flexion, extension and lateral bending all the instrumented constructs significantly decreased (P < 0.05) the range of motion (ROM) compared to intact. In axial rotation, only the circumferential support constructs (ASP, AMP) provided significantly decreased (P < 0.05) ROM, whereas posterior instrumentations alone (SP, MP) were comparable to intact spines.

CONCLUSION

After L5 spondylectomy, the L4-S1 cage with posterior short segment instrumentation provides stability in lateral bending that is not further increased by adding L3 pedicle-iliac screws and L4-S1 anterior plate. However, an anterior L4-S1 plate provides additional stability in flexion, extension, and axial rotation.

Oncosurgical results of multilevel thoracolumbar en-bloc spondylectomy and reconstruction with a carbon composite vertebral body replacement system

STUDY DESIGN

Retrospective clinical study for patients receiving multilevel en-bloc spondylectomy resection for sarcomas and solitary metastases of the thoracolumbar spine.

OBJECTIVE

Assess the clinical and radiologic outcome after multilevel en-bloc spondylectomy and reconstruction.

SUMMARY OF BACKGROUND DATA

Monolevel en-bloc spondylectomies have proven their oncosurgical effectiveness while reports on multilevel resections for extracompartmental tumor localizations are rare.

METHODS

Patients treated by multilevel en-bloc spondylectomy and restoration with a carbon composite vertebral body replacement system were investigated. Patient charts, and clinical follow-up investigations were analyzed for histopathological tumor origin, preoperative symptoms, surgical peri- and postoperative data, applied adjuvant therapies, as well as the course of disease. Solitary metastases time until occurrence and prognostic scores were evaluated (Tomita/Tokuhashi Score). CT-scans were performed and analyzed at follow up. Oncological status was evaluated including local recurrence rates, cumulative disease specific, and metastases-free survival.

RESULTS

Multilevel (2-5 segments) en-bloc spondylectomy of the thoracolumbar spine was performed in 20 patients (15 sarcomas and 5 solitary spinal metastases 9 male/11 female, mean age at surgery: 54 ± 15 years.). Wide and marginal surgical margins were achieved in 7 and 13 patients, respectively. Mean follow-up period was 25.0 (9-53) months. Thirteen patients received adjuvant therapy. No implant breakage or loosening was observed. Local recurrence occurred in one patient. Thirteen of the 18 surviving patients showed no evidence of the disease, two died of systemic disease.

CONCLUSION

Multilevel en-bloc spondylectomy offers a radical resection option for extracompartmental tumor involvement. It provides oncologically adequate resection margins with low local recurrence. However, the procedures are complex; the patient's stress is high and metastatic disease developed in one-third of patients. A judicious patient selection and a realistic feasibility evaluation must precede the decision for surgery. Reconstruction using a carbon composite cage system showed low complication rates and offers advantages for oncosurgical procedures.

Quantifying intervertebral disc mechanics: a new definition of the neutral zone

Background

The neutral zone (NZ) is the range over which a spinal motion segment (SMS) moves with minimal resistance. Clear as this may seem, the various methods to quantify NZ described in the literature depend on rather arbitrary criteria. Here we present a stricter, more objective definition.

Methods

To mathematically represent load-deflection of a SMS, the asymmetric curve was fitted by a summed sigmoid function. The first derivative of this curve represents the SMS compliance and the region with the highest compliance (minimal stiffness) is the NZ. To determine the boundaries of this region, the inflection points of compliance can be used as unique points. These are defined by the maximum and the minimum in the second derivative of the fitted curve, respectively. The merits of the model were investigated experimentally: eight porcine lumbar SMS's were bent in flexion-extension, before and after seven hours of axial compression.

Results

The summed sigmoid function provided an excellent fit to the measured data (r² > 0.976). The NZ by the new definition was on average 2.4 (range 0.82-7.4) times the NZ as determined by the more commonly used angulation difference at zero loading. Interestingly, NZ consistently and significantly decreased after seven hours of axial compression when determined by the new definition. On the other hand, NZ increased when defined as angulation difference, probably reflecting the increase of hysteresis. The methods thus address different aspects of the load-deflection curve.

Conclusions

A strict mathematical definition of the NZ is proposed, based on the compliance of the SMS. This operational definition is objective, conceptually correct, and does not depend on arbitrarily chosen criteria.

Corpectomia da coluna toracolombar com colocação de cage por acesso único via posterior: técnica cirúrgica e resultados de seis pacientes

OBJETIVO: Avaliar retrospectivamente os resultados de uma série de pacientes submetidos à corpectomia torácica e/ou lombar por via exclusivamente posterior associado à colocação de cage e à artrodese instrumentada segmentar e descrever a técnica cirúrgica. MÉTODOS: Foram avaliados retrospectivamente seis pacientes portadores de colapso vertebral, instabilidade biomecânica ou lesão neurológica por diferentes etiologias. Estes pacientes apresentavam indicação de descompressão neural e receberam indicação para a realização de corpectomia e reconstrução circunferencial com cage sendo realizado por via exclusivamente posterior. RESULTADOS: Quatro pacientes eram do sexo masculino e dois do sexo feminino. A idade média foi de 58 anos (22 a 82 anos) com tempo médio de acompanhamento de 10,5 meses (2 a 24 meses). Em três casos a ressecção foi de um corpo vertebral e em três casos de dois corpos vertebrais. Todos os pacientes apresentaram melhora do seu estado neurológico e melhora da dor lombar ou radicular. As indicações ao procedimento foram três casos por espondilodiscite, um por fratura osteoporótica, um tumor metastático e um tumor primário. Três pacientes apresentaram complicações necessitando de revisão cirúrgica evoluindo com melhora dos sintomas. As complicações foram fístula liquórica, radiculopatia lombar, infecção de ferida operatória, meningite e falha da instrumentação. CONCLUSÃO: Os pacientes submetidos à corpectomia por via exclusivamente posterior apresentaram resultados favoráveis com melhora do déficit neurológico ou dor em todos os casos. Esta técnica mostrou-se eficiente na reconstrução circunferencial da coluna evitando as complicações da abordagem tradicional por dupla via.

The biomechanical contribution of varying posterior constructs following anterior thoracolumbar corpectomy and reconstruction

OBJECT

Thoracolumbar corpectomy is a procedure commonly required for the treatment of various pathologies involving the vertebral body. Although the biomechanical stability of anterior reconstruction with plating has been studied, the biomechanical contribution of posterior instrumentation to anterior constructs remains unknown. The purpose of this study was to evaluate biomechanical stability after anterior thoracolumbar corpectomy and reconstruction with varying posterior constructs by measuring bending stiffness for the axes of flexion/extension, lateral bending, and axial rotation.

METHODS

Seven fresh human cadaveric thoracolumbar spine specimens were tested intact and after L-1 corpectomy and strut grafting with 4 different fixation techniques: anterior plating with bilateral, ipsilateral, contralateral, or no posterior pedicle screw fixation. Bending stiffness was measured under pure moments of +/- 5 Nm in flexion/extension, lateral bending, and axial rotation, while maintaining an axial preload of 100 N with a follower load. Results for each configuration were normalized to the intact condition and were compared using ANOVA.

RESULTS

Spinal constructs with anterior-posterior spinal reconstruction and bilateral posterior pedicle screws were significantly stiffer in flexion/extension than intact spines or spines with anterior plating alone. Anterior plating without pedicle screw fixation was no different from the intact spine in flexion/extension and lateral bending. All constructs had reduced stiffness in axial rotation compared with intact spines.

CONCLUSIONS

The addition of bilateral posterior instrumentation provided significantly greater stability at the thoracolumbar junction after total corpectomy than anterior plating and should be considered in cases in which anterior column reconstruction alone may be insufficient. In cases precluding bilateral posterior fixation, unilateral posterior instrumentation may provide some additional stability.

Non-fusion instrumentation of the lumbar spine with a hinged pedicle screw rod system: an in vitro experiment

In advanced stages of degenerative disease of the lumbar spine instrumented spondylodesis is still the golden standard treatment. However, in recent years dynamic stabilisation devices are being implanted to treat the segmental instability due to iatrogenic decompression or segmental degeneration. The purpose of the present study was to investigate the stabilising effect of a classical pedicle screw/rod combination, with a moveable hinge joint connection between the screw and rod allowing one degree of freedom (cosmicMIA). Six human lumbar spines (L2-5) were loaded in a spine tester with pure moments of +/-7.5 Nm in lateral bending, flexion/extension and axial rotation. The range of motion (ROM) and the neutral zone were determined for the following states: (1) intact, (2) monosegmental dynamic instrumentation (L4-5), (3) bisegmental dynamic instrumentation (L3-5), (4) bisegmental decompression (L3-5), (5) bisegmental dynamic instrumentation (L3-5) and (6) bisegmental rigid instrumentation (L3-5). Compared to the intact, with monosegmental instrumentation (2) the ROM of the treated segment was reduced to 47, 40 and 77% in lateral bending, flexion/extension and axial rotation, respectively. Bisegmental dynamic instrumentation (3) further reduced the ROM in L4-5 compared to monosegmental instrumentation to 25% (lateral bending), 28% (flexion/extension) and 57% (axial rotation). Bisegmental surgical decompression (4) caused an increase in ROM in both segments (L3-4 and L4-5) to approximately 125% and approximately 135% and 187-234% in lateral bending, flexion/extension and axial rotation, respectively. Compared to the intact state, bisegmental dynamic instrumentation after surgical decompression reduced the ROM of the two-bridged segments to 29-35% in lateral bending and 33-38% in flexion/extension. In axial rotation, the ROM was in the range of the intact specimen (87-117%). A rigid instrumentation (6) further reduced the ROM of the two-bridged segments to 20-30, 23-27 and 50-68% in lateral bending, flexion/extension and axial rotation, respectively. The results of the present study showed that compared to the intact specimen the investigated hinged dynamic stabilisation device reduced the ROM after bisegmental decompression in lateral bending and flexion/extension. Following bisegmental decompression and the thereby caused large rotational instability the device is capable of restoring the motion in axial rotation back to values in the range of the intact motion segments.

Biomechanics and materials of reconstruction after tumor resection in the spinal column

We initially review the general biomechanical principles that should be considered in surgical reconstruction of spinal tumors. This will be further clarified by more detailed descriptions for individual spinal regions in the subsequent part of the article. In the case of patients with spinal metastases, especially in patients with a median survival time less than a few months, a thorough review of the risks and benefits regarding surgical intervention must be discussed with the patient. However, once the decision for surgery has been made, a biomechanically sound reconstruction should be performed to help restore or maintain the patient's mobility.