The biomechanics of iatrogenic spinal destabilization and implant failure

Myth or fact: 3D-printed off-the-shelf prosthesis is superior to titanium mesh cage in anterior cervical corpectomy and fusion?

BACKGROUND

To find out if three-dimensional printing (3DP) off-the-shelf (OTS) prosthesis is superior to titanium mesh cages in anterior cervical corpectomy and fusion (ACCF) when treating single-segment degenerative cervical spondylotic myelopathy (DCSM).

METHODS

DCSM patients underwent ACCF from January 2016 to January 2019 in a single center were included. Patients were divided into the 3DP group (28) and the TMC group (23). The hospital stays, operation time, intraoperative blood loss, and the cost of hospitalization were compared. The Japanese Orthopedic Association (JOA) scores and Neck Disability Index (NDI) were recorded pre-operatively, 1 day, 3, 6, 12, and 24 months post-operatively. Radiological data was measured to evaluate fusion, subsidence, and cervical lordosis. Patients were sent with SF-36 to assess their health-related quality of life (HRQoL).

RESULTS

The differences in operative time, intraoperative blood loss, and hospital stay were not statistically significant between groups (p > 0.05). Postoperative dysphagia occurred in 2 cases in the 3DP group and 3 cases in the TMC group, which all relieved one week later. The difference in improvement of JOA and NDI between the two groups was not statistically significant (p > 0.05). No hardware failure was found and bony fusion was achieved in all cases except one in the 3DP group. The difference in cervical lordosis (CL), fused segmental angle (FSA), mean vertebral height (MVH), and subsidence rates between groups at each follow-up time point was not statistically significant and the results of the SF-36 were similar (p > 0.05). The total cost was higher in the 3DP group with its higher graft cost (p < 0.05).

CONCLUSION

In treating single-segment DCSM with ACCF, both 3DP OTS prosthesis and TMC achieved satisfactory outcomes. However, the more costly 3DP OTS prosthesis was not able to reduce subsidence as it claimed.

Early Clinical Results of Intervertebral Joint Stabilization by Injectable Load-Sharing Polymers

Background

Genipin is a polymer-forming collagen bonding substance that can be dissolved in a buffered carrier and injected into disc annulus tissues. Therapeutic benefit is derived from the mechanical support provided by a large number of genipin polymers attached to collagen fibers in a degraded disc.

Study Design/Setting

IRB-approved prospective, multi-site, single-arm, 12-month feasibility studies were undertaken in two countries to evaluate the safety and efficacy of the genipin-based implant for treating discogenic chronic low back pain (CLBP).

Patient Sample

Twenty CLBP patients with symptomatic discs at one or two levels were enrolled in the study.

Outcome Measures

The primary safety endpoint was serious adverse events at 1 month, and the primary efficacy endpoint was reduction of pain and disability at 3 months. Secondary efficacy endpoints included reduction of pain and disability at 2 weeks, 1 month, 6 months, and 12 months; reduction of flexion-extension instability; increase in segmental lordosis and rotation; and patient satisfaction.

Methods

Fluoroscopic image-guidance was used to deliver two posterolateral injections of buffered genipin to each symptomatic disc. Flexion-extension radiographs were used to quantify joint kinematics at three time-points.

Results

Clinically meaningful improvements in pain and disability scores were reported in 80% or more of patients from 2 weeks to 1 year post-treatment. For the more severely unstable joints, treatment significantly reduced the instability score from a pre-treatment level of 2.4 standard deviations above the mean for an asymptomatic population to the asymptomatic mean at the 3-month follow-up.

Conclusion

These initial clinical data demonstrate the safety and efficacy of a genipin-based collagen tethering device capable of improving spinal joint stability while successfully addressing CLBP. This work merits additional randomized clinical studies.

Risk Factors and Radiologic Changes in Subsidence after Single-Level Anterior Cervical Corpectomy: A Minimum Follow-Up of 2 Years

Objective

Anterior cervical corpectomy using a titanium mesh cage may result in delayed nonunion and thus a change in cervical alignment, and patients may require revision surgery. We investigated the radiologic and clinical outcomes of cervical corpectomy and the risk factors for subsidence.

Methods

We studied 74 patients who underwent single-level anterior cervical corpectomy for cervical spondylotic myelopathy with or without ossification of the posterior longitudinal ligament between 2007 and 2014. Graft subsidence was considered present when there was a reduction in the anterior and posterior heights by an average of 4 mm or more 2 years after the operation. We measured cervical parameters before surgery, immediately after surgery, and 6, 12, and 24 months after surgery. The clinical outcomes were the neck and arm visual analog scale scores and reoperation rate.

Results

In the subsidence group, these values gradually decreased over the 24 months. The radiologic parameters did not differ between the 2 groups for 24 months after the onset of subsidence. There were no differences in clinical outcome or reoperation rate. In the analysis of the risk factors, subsidence occurred with a large T1 slope and a large change in the C27 Cobb angle (p=0.020 and p=0.026, respectively).

Conclusion

Subsidence gradually occurred after single-level anterior cervical corpectomy for up to 24 months. However, the presence of subsidence did not affect the radiologic and clinical outcomes. When the T1 slope was large and the C27 Cobb angle change was severe, more subsidence occurred.

Factors Related to Instrumentation Failure in Titanium Mesh Reconstruction for Thoracic and Lumbar Tumors: Retrospective Analysis of 178 Patients

Purpose

To investigate risk factors for instrumentation failure (IF) in titanium (Ti) mesh reconstruction for thoracic and lumbar tumors.

Patients and Methods

The clinical data of patients with thoracic or lumbar tumors who received Ti mesh reconstruction via the posterior approach in our hospital from 2013 to 2018 were analyzed retrospectively. The observation indexes included sex, age, BMI, the vertebra resection mode, the number of resected vertebral segments, application of bone cement, radiotherapy, chemotherapy, revision or primary surgery, and primary tumor metastasis. Correlations between these factors and IF were analyzed by Kaplan–Meier survival and logistics regression analyses.

Results

The 178 patients included 108 males and 70 females with a mean age of 48.09±16.21 (6–78) years and a mean follow-up period of 51.18 (24–90) months. The data showed that 17 patients (9.55%) were inflicted with IF, involving the thoracic vertebra in 11 cases, thoracolumbar vertebrae (T12–L1) in 2 cases, and lumbar vertebrae in 4 cases. The mean interval between surgery to IF was 35.18±14.17 (14–59) months. Univariate analysis showed that total vertebral body resection, the number of resected vertebral segments, radiotherapy and multiple tumor resection were potential factors for IF, while multivariate analysis showed that only total vertebral body resection, the number of resected vertebral segments and radiotherapy were independent factors.

Conclusion

Total vertebra resection, the number of resected vertebral segments (≥2) and radiotherapy before and after operation were significant risk factors related to IF.

Oblique lateral interbody fusion combined percutaneous pedicle screw fixation in the surgical treatment of single-segment lumbar tuberculosis: A single-center retrospective comparative study

OBJECTIVE

To evaluate the clinical efficacy of oblique lateral interbody fusion combined posterior percutaneous pedicle screw fixation in the treatment of single segment lumbar tuberculosis.

METHODS

Patients who underwent surgical treatment for single segment lumbar tuberculosis from 2015 to 2018 in our department were retrospectively included in this study. The included patients were divided into two groups, namely oblique lateral interbody fusion combined percutaneous pedicle screw fixation (OLIF) group and traditional posterior transforaminal or transpedicular approach debridement and pedicle screws fixation (PTA) group, according to the surgical methods. Outcomes including operative time, operative blood loss, hospital stay, visual analogue scale (VAS) score, Oswestry disability index (ODI), erythrocyte sedimentation rate (ESR), C reactive protein (CRP), Cobb angle correction and loss, bone fusion time, ASIA grade and complications were all recorded and compared.

RESULTS

A total of 60 patients were included in this study, involving 23 patients in the OLIF group and 37 patients in the PTA group. The OLIF group had less operative time, blood loss and shorter hospital stay compared with the PTA group (P < 0.05). Both the two groups achieved significant improvements in ESR, CRP and ASIA grade at the last follow-up (P < 0.05), but no significant differences were found between them (P>0.05). There were no significant differences in Cobb angle correction and loss between the two groups (P > 0.05), but the bone graft fusion time of the OLIF group was significantly shorter than the PTA group (P < 0.05). The two groups achieved similar improvement in VAS score and ODI at 12 months postoperative and the last follow-up, however, OLIF group had a lower VAS score and ODI at 1 month, 3 months and 6 months postoperative (P < 0.05). No significant difference was found in complications between the two groups (P > 0.05) and all patients were cured after active treatment.

CONCLUSIONS

Both OLIF and PTA can achieve satisfactory clinical efficacy in the surgical treatment of single segment lumbar TB, but OLIF has the advantages of less surgical trauma, faster postoperative recovery and shorter bone fusion time.

Reduction and Open Fixation of a Cervical Teardrop Fracture: A Technical Note

BACKGROUND

Cervical teardrop fractures are hyperflexion and axial loading injuries associated with significant ligamentous disruption. Patients sustaining these types of injury are classically treated with a cervical corpectomy and anterior fusion. However, there are notable disadvantages of this approach, namely, disruption of the patient's true anatomic alignment and a reduction in the number of fixation points available for cervical fusion. Here we present a novel method of open reduction and internal fixation in a neurologically intact patient with cervical teardrop fracture.

CASE DESCRIPTION

A 34-year-old man presented to Ryder Trauma Center after a helmeted motorcycle accident. The patient was found to be neurologically intact on arrival, and imaging demonstrated a C5 teardrop fracture without bony retropulsion. The patient was taken to the operating room for an open reduction and internal fixation of the fracture using a novel technique. This technique used traditional diskectomies at the C4-5 and C5-6 levels, along with a temporary, unicortical screw into the C5 body to capture the anteriorly displaced fragment. A bicortical screw was then placed into the contralateral side, and now, having fully reduced the fracture, the first (temporary) screw was replaced with a bicortical screw. The patient was neurologically intact postoperatively, with 2-month follow-up computed tomography scan demonstrating stable reduction of the fracture.

CONCLUSIONS

Here we present a novel technique for open reduction and internal fixation of a cervical teardrop fracture that does not require cervical corpectomy. This technique is particularly useful in patients with an anteriorly displaced fragment and without neurologic deficit or compromise.

Stopping at Sacrum Versus Nonsacral Vertebra in Long Fusion Surgery for Adult Spinal Deformity: Meta-Analysis of Revision with Minimum 2-Year Follow-Up

OBJECTIVE

A pooled comparison was conducted on a revision to the sacrum (S) versus a nonsacral (NS) surgical strategy in adult spinal deformity (ASD).

METHODS

Strictly following the PRISMA 2009 guidelines, the MEDLINE, EMBASE, and Cochrane Library databases were used to search for studies published in English up to March 2018 that addressed the S versus NS surgical approach for a long fusion to treat ASD. Data on total revisions and revision reasons were extracted from the included studies and were pooled analyzed.

RESULTS

Eight retrospective studies with a total of 1846 ASD patients (528 S and 1318 NS) were included. The total revision rate was 11.38% (S: 17.80% and NS: 8.80%), and implant failure, pseudarthrosis, adjacent segment degeneration, and proximal junctional kyphosis (PJK) were common reasons for revision. The pooled results indicated that the NS group had decreased incident rates of total revision (95% confidence interval [CI] 1.20-2.32, P = 0.002; I2 = 0%) and pseudarthrosis (95% CI 2.16-15.44, P = 0.0005; I2 = 0%) compared with the S group. No significant differences were observed in implant failure (95% CI 0.86-3.90, P = 0.12; I2 = 0%), adjacent segment degeneration (95% CI 0.08-1.25, P = 0.10; I2 = 0%), and PJK (95% CI 0.54-6.88, P = 0.35; I2 = 0%) between the 2 groups.

CONCLUSIONS

Revision in ASD patients is a serious problem with a total rate of 11.38%, and implant failure, pseudarthrosis, adjacent segment degeneration, and PJK are common reasons for revision. Stopping at the sacrum vertebra in long fusion surgery on ASD patients seems to increase the incidence rates of total revision and pseudarthrosis.

Placement of Titanium Mesh in Hybrid Decompression Surgery to Avoid Graft Subsidence in Treatment of Three-Level Cervical Spondylotic Myelopathy: Cephalad or Caudal?

Background

Hybrid decompression has been used to treat patients with cervical spondylotic myelopathy (CSM). However, no published study has investigated the effect of titanium mesh (TM) located cephalad or caudal in hybrid decompression surgery on the graft subsidence in treatment of three-level CSM.

Material/Methods

Forty-eight cases with three-level CSM who underwent the procedure of hybrid decompression from Jan 2014 to Jan 2017 were retrospectively reviewed. Radiological outcomes immediately postoperatively and at the final follow-up were compared between cases from group A (TM located cephalad, n=21) and group B (TM located caudal, n=27).

Results

No differences were observed in the 2 groups in terms of number, sex, or duration of follow-up. The average follow-up was 4.38±0.439 months in group A and 4.81±0.509 months in group B (p>0.05). The index loss of anterior (AIBH), middle (MIBH), and posterior interbody height (PIBH) in group A were 0.857±0.448/1.00±0.525/1.33±0.608, respectively, which were all lower than that in group B (P<0.05), as was the occurrence of TM subsidence. However, there was no significance difference in height loss of adjacent intervertebral space between groups. All angles were decreased at the final follow-up in both groups (p<0.05). More decrease of C2–C7 angle occurred in group B (p>0.05), and segmental angle in group A decreased more than in group B (p>0.05).

Conclusions

TM inferior to intervertebral cage (IC) in hybrid decompression has a higher risk for developing subsidence, and when the choice of the position of TM is available in hybrid decompression surgery, TM located cephalad was recommend to alleviate TM subsidence.

Spinal Deformity Surgery : It Becomes an Essential Part of Neurosurgery

Among the spinal disorders, the treatment approach for spinal deformities has been discussed least among department of neurosurgery. But nowadays, more and more neurosurgeons are interested in spinal deformities as well as complex spinal disorders and are doing not a few surgeries for these kinds of disease. Nevertheless, it is mandatory to understand the course of spinal deformity, principles of treatment, and surgical outcomes and complications. Understanding of the biology, biomechanics and metallurgy of the spine and instrumentation are also required for successful spinal deformity surgery. We need senior mentors and good surgical and neurophysiologic monitoring team. Knowledge of spinal deformity may be augmented with spine fellowships and surgical experience. Step by step training such as basic knowledge, orthopedic as well as neurosurgical disciplines and surgical skills would be mandatory. Neurosurgeons can have several advantages for spinal deformity surgeries. By high-level technical ability of the spinal cord handling to preserve neurological function and familiarity with microscopic surgery, better synergistic effect could be expected. A fundamental understanding of pediatric spinal deformity and growing spine should be needed for spinal deformity surgery.

Anterior transcorporeal tunnel approach for cervical myelopathy guided by CT-based intraoperative spinal navigation: Technical note

Cervical spondylotic myelopathy (CSM) is the most common degenerative disease of the spine in elderly patients. Although there are several surgical options for the treatment of this disease, minimally invasive techniques for localized decompression of the true clinical generator of the patient's disease has revolutionized spinal surgery recently. This article presents an alternate application of the anterior transcorporeal tunnel approach in combination with computed tomography (CT)-based intraoperative navigation in the treatment of patients with cervical myelopathy secondary to spondylosis. Three clinical cases are used as examples to demonstrate how this procedure can be used to decompress a localized target in cervical spondylotic myelopathy. Clinical images of each case are shown. Cervical decompression was successfully achieved in all three patients, with the improvement of preoperative symptoms. The anterior transcorporeal tunnel approach combined with the use of CT-based intraoperative spinal navigation may be a feasible minimally invasive procedure for the treatment of cervical spondylotic myelopathy in selected cases.

Global and segmental kinematic changes following sequential resection of posterior osteoligamentous structures in the lumbar spine: An in vitro biomechanical investigation using pure moment testing protocols

Lumbar spinal surgeries may compromise the integrity of posterior osteoligamentous structures implicating mechanical stability. Circumstances necessitating a concomitant surgery to achieve restabilisation are not well understood. The main objective of this in vitro study was to quantify global and segmental (index and adjacent levels) kinematic changes in the lumbar spine following sequential resection of the posterior osteoligamentous structures using pure moment testing protocols. Six fresh frozen cadaveric kangaroo lumbar spines (T12-S1) were tested under a bending moment in flexion-extension, bilateral bending, and axial torsion in a 6-degree-of-freedom Kinematic Spine Simulator. Specimens were tested in the following order: intact state (D0), after interspinous and supraspinous ligaments transection between L4 and L5 (D1), further after a total bilateral facetectomy between L4 and L5 (D2). Segmental motions at the cephalad, damaged, and caudal levels were recorded using an infrared-based motion tracking device. Following D1, no significant change in the global range of motion was observed in any of the bending planes. Following D2, a significant increase in the global range of motion from the baseline (D0) was observed in axial torsion (median normalised change +20%). At the damaged level, D2 resulted in a significant increase in the segmental range of motion in flexion-extension (+77%) and axial torsion (+492%). Additionally, a significant decrease in the segmental range of motion in axial torsion (-35%) was observed at the caudal level following D2. These results suggest that a multi-segment lumbar spine acts as a mechanism for transmitting motions, and that a compromised joint may significantly alter motion transfer to adjacent segments. We conclude that the interspinous and supraspinous ligaments play a modest role in restricting global spinal motions within physiologic limits. Following interspinous and supraspinous ligaments transection, a total bilateral facetectomy resulted in a significant increase in axial torsion motion, both at global and damaged levels, accompanied with a compensatory decrease in motion at the caudal level.

Lumbar transpedicular implant failure: a clinical and surgical challenge and its radiological assessment

Study Design

It is a multicenter, controlled case study review of a big scale of pedicle-screw procedures from January 2000 to June 2010. The outcomes were compared to those with no implant failure.

Purpose

The purpose of this study was to review retrospectively the outcome of 100 patients with implant failure in comparison to 100 control-patients, and to study the causes of failure and its prevention.

Overview of Literature

Transpedicular fixation is associated with risks of hardware failure, such as screw/rod breakage and/or loosening at the screw-rod interface and difficulties in the system assembly, which remain a significant clinical problem. Removal or revision of the spinal hardware is often required.

Methods

Two hundred patients (88 women, 112 men) were divided into 2 major groups, with 100 patients in group I (implant failure group G1) and 100 patients in group II (successful fusion, control group G2). We subdivided the study groups into two subgroups: subgroup a (single-level instrumented group) and subgroup b (multilevel instrumented group). The implant status was assessed based on intraoperative and follow-up radiographs.

Results

Implant failure in general was present in 36% in G1a, and in 64% in G1b, and types of implant failure included screw fracture (34%), rod fracture (24%), rod loosening (22%), screw loosening (16%), and failure of both rod and screw (4%). Most of the failures (90%) occurred within 6 months after surgery, with no reported cases 1 year postoperatively.

Conclusions

We tried to address the problem and study the causes of failure, and proposed solutions for its prevention.

Segmental anterior decompression and fusion for multilevel ossification of the posterior longitudinal ligament

The purpose of this study was to evaluate the outcome of segmental anterior decompression and fusion for multilevel ossification of the posterior longitudinal ligament. Data were collected from 23 patients with multilevel ossification of the posterior longitudinal ligament. Average operative time and blood loss were 121 minutes and 201.6 mL, respectively. The Nurick score significantly decreased from 2.7±0.9 preoperatively to 1.8±0.9 at last follow-up (P<.01). The preoperative Japanese Orthopaedic Association score was 8.2, which significantly increased to 13.8 points at last follow-up (P<.01), with an improvement rate of 64.5%. The operation also significantly increased cervical lordosis (P<.01) from 7.7° preoperatively to 13.3° postoperatively. The fusion rate was 95.7% at 6 months postoperatively, and 100% at 12 months postoperatively. The loss of cervical lordosis and height of fusion segments were 1.2° and 0.9 mm at last follow-up, respectively. No hardware complications occurred. Cerebrospinal fluid leakage occurred in 2 patients, and hematoma occurred in 1 patient who needed an emergency operation. Segmental anterior decompression and fusion was generally effective and safe in the treatment of multilevel ossification of the posterior longitudinal ligament if indications were well controlled.

Biomechanical analysis of pedicle screw thread differential design in an osteoporotic cadaver model

BACKGROUND

Pedicle screw fixation, the standard surgical care for posterior stabilization in the thoraco-lumbar spine has a high rate of failure in osteoporotic individuals. Screw design factors and insertion techniques have been shown to influence the biomechanical performance of pedicle screws. Our objective was to investigate the biomechanical characteristics of pedicle screw fixation in osteoporotic bone by comparing standard screws with newly designed differential crest thickness dual lead screws.

METHODS

An in-vitro spinal-level paired factorial study design was used to examine thoraco-lumbar spine biomechanical outcomes for differential pedicle screw thread designs. Six cadaveric human spines (T8-L5) were tested for six groups (n=20) consisting of 2 different crest thickness and 3 different insertion techniques. Bone mineral density was assessed and peak insertion torque measured while placing one screw of new design and control on the contralateral side. Screw pullout properties were measured from classical American Society for Testing and Materials protocols.

FINDINGS

The screws designed specifically for osteoporotic bone showed significantly larger insertion torque compared with the standard screw design irrespective of insertion technique. Much of the variability in pullout failure and stiffness was explained by bone mineral density. The osteoporotic screws of different crest thickness were statistically similar to each other in all outcome measures.

INTERPRETATION

Compared with standard pedicle screws, the dual lead osteoporotic-specific pedicle screws demonstrated significantly larger insertion torques and similar pullout properties. Non-significant increased biomechanical strength was observed for thin crest compared to thick crest dual lead pedicle screws indicating their enhanced purchase in osteoporotic bone.

The stabilizing potential of anterior, posterior and combined techniques for the reconstruction of a 2-level cervical corpectomy model: biomechanical study and first results of ATPS prototyping

Clinical studies reported frequent failure with anterior instrumented multilevel cervical corpectomies. Hence, posterior augmentation was recommended but necessitates a second approach. Thus, an author group evaluated the feasibility, pull-out characteristics, and accuracy of anterior transpedicular screw (ATPS) fixation. Although first success with clinical application of ATPS has already been reported, no data exist on biomechanical characteristics of an ATPS-plate system enabling transpedicular end-level fixation in advanced instabilities. Therefore, we evaluated biomechanical qualities of an ATPS prototype C4-C7 for reduction of range of motion (ROM) and primary stability in a non-destructive setup among five constructs: anterior plate, posterior all-lateral mass screw construct, posterior construct with lateral mass screws C5 + C6 and end-level fixation using pedicle screws unilaterally or bilaterally, and a 360° construct. 12 human spines C3-T1 were divided into two groups. Four constructs were tested in group 1 and three in group 2; the ATPS prototypes were tested in both groups. Specimens were subjected to flexibility test in a spine motion tester at intact state and after 2-level corpectomy C5-C6 with subsequent reconstruction using a distractable cage and one of the osteosynthesis mentioned above. ROM in flexion-extension, axial rotation, and lateral bending was reported as normalized values. All instrumentations but the anterior plate showed significant reduction of ROM for all directions compared to the intact state. The 360° construct outperformed all others in terms of reducing ROM. While there were no significant differences between the 360° and posterior constructs in flexion-extension and lateral bending, the 360° constructs were significantly more stable in axial rotation. Concerning primary stability of ATPS prototypes, there were no significant differences compared to posterior-only constructs in flexion-extension and axial rotation. The 360° construct showed significant differences to the ATPS prototypes in flexion-extension, while no significant differences existed in axial rotation. But in lateral bending, the ATPS prototype and the anterior plate performed significantly worse than the posterior constructs. ATPS was shown to confer increased primary stability compared to the anterior plate in flexion-extension and axial rotation with the latter yielding significance. We showed that primary stability after 2-level corpectomy reconstruction using ATPS prototypes compared favorably to posterior systems and superior to anterior plates. From the biomechanical point, the 360° instrumentation was shown the most efficient for reconstruction of 2-level corpectomies. Further studies will elucidate whether fatigue testing will enhance the benefit of transpedicular anchorage with posterior constructs and ATPS.

Iatrogenic spinal deformity

Patients with postoperative spinal deformities are being identified with increasing frequency as the number of instrumented spinal operations increases. Thus, it is important for the neurosurgeon to understand ways to minimize postoperative deformity and to understand its operative and nonoperative management. A variety of intra- and postoperative risk factors have been associated with postoperative deformity, including patient age, operative positioning, preoperative medical condition, and the use of prior radiation therapy. The evaluation of all patients who have been suspected of iatrogenic deformity should include a detailed physical examination, plain x-rays, and computed tomographic or magnetic resonance imaging, depending on the condition. Conservative therapy includes physical therapy and pain control, which may be effective in some patients. However, patients with flat-back syndrome typically require reoperation. A wide variety of reoperative procedures may be performed, depending on the area of the pathological deformity, extent of disease, and patient condition.

Comparative biomechanical study of cervical spine stabilisation by cage alone, cage with plate, or plate-cage: a porcine model

PURPOSE

To compare stability and subsidence associated with 3 types of cervical spine stabilisation.

METHODS

The C3 to C4 vertebrae of 28 Polish pigs were used. Pigs with intact vertebrae (group 1) underwent standard anterior cervical discectomy (group 2), followed by stabilisation using a cage alone (group 3), a cage with plate (group 4), or a plate-cage (group 5). Cervical spine stability and subsidence were compared in all 5 groups.

RESULTS

Stability was significantly increased after stabilisation by a cage with plate or a plate-cage, but not by a cage alone. The difference between stabilisation by a cage with plate and a plate-cage was not significant. Subsidence was maximal after the cage-alone stabilisation (3.1 mm), being 1.6 mm after the cage-with-plate and plate-cage stabilisations.

CONCLUSION

Additional plating as a supplement to anterior interbody cervical cage stabilisation significantly improves segmental stability and subsidence.

Cervical anterior transpedicular screw fixation. Part I: Study on morphological feasibility, indications, and technical prerequisites

Multilevel cervical spine procedures can challenge the stability of current anterior cervical screw-and-plate systems, particularly in cases of severe three-column subaxial cervical spine injuries and multilevel plated reconstructions in osteoporotic bone. Supplemental posterior instrumentation is therefore recommended to increase primary construct rigidity and diminish early failure rates. The increasing number of successfully performed posterior cervical pedicle screw fixations have enabled more stable fixations, however most cervical pathologies are located anteriorly and preferably addressed by an anterior approach. To combine the advantages of the anterior approach with the superior biomechanical characteristics of cervical pedicle screw fixation, the authors developed a new concept of a cervical anterior transpedicular screw-and-plate system. An in vivo anatomical study was performed to explore the feasibility of anterior transpedicular screw fixation (ATPS) in the cervical spine. The morphological study was conducted based on 29 cervical spine CT scans from healthy patients and measurements were performed on the pedicle sizes, angulations, vertebral body depth, height and width at C2 to T1. Significant morphologic parameters for the new technique are discussed. These parameters include the sagittal and transverse intersection points of the pedicle axis with the anterior vertebral body wall, as well as the distances between sagittal intersection points from C2 to T1. On the basis of these results, standard spine models were reconstructed and used for the conceptual development of a preclinical release prototype of an anterior transpedicular screw-and-plate system. The morphological feasibility of the new technique is demonstrated, and its indications, biomechanical considerations, as well as surgical prerequisites are thoroughly discussed. In the future, the technique of cervical anterior transpedicular screw fixation might diminish the number of failures in the reconstruction of multilevel and three-column cervical spine instabilities, and avoid the need for supplemental posterior instrumentation.

Cervical anterior transpedicular screw fixation (ATPS)--Part II. Accuracy of manual insertion and pull-out strength of ATPS

Reconstruction after multilevel decompression of the cervical spine, especially in the weakened osteoporotic, neoplastic or infectious spine often requires circumferential stabilization and fusion. To avoid the additional posterior surgery in these cases while increasing rigidity of anterior-only screw-plate constructs, the authors introduce the concept of anterior transpedicular screw (ATPS) fixation. We demonstrated its morphological feasibility as well as its indications in a previous study in Part I of our project. Consequently, the objectives of the current study were to assess the ex vivo accuracy of placing ATPS into the cervical vertebra as well as the biomechanical performance of ATPS in comparison to traditional vertebral body screws (VBS) in terms of pull-out strength (POS). Twenty-three ATPS were inserted alternately to two screws into the pedicles and vertebral bodies, respectively, of six cadaveric specimens from C3-T1. For insertion of ATPS, a manual fluoroscopically assisted technique was used. Pre- and post insertional CT-scans were used to assess accuracy of ATPS insertion in the axial and sagittal planes. A newly designed grading system and accuracy score were used to delineate accuracy of ATPS insertion. Following insertion of screws, 23 ATPS and 22 VBS were subjected to pull-out testing (POT). The bone mineral density (BMD) of each specimen was assessed prior to POT. Statistical analysis showed that the incidence of correctly placed screws and non-critical pedicles breaches in axial plane was 78.3%, and 95.7% in sagittal plane. Hence, according to our definition of "critical" pedicle breach that exposes neurovascular structures at risk, 21.7% (n = 5) of all ATPS inserted showed a critical pedicle breach in axial plane. Notably, no critical pedicle perforation occurred at the C6 to T1 levels. Pull-out testing of ATPS and VBS revealed that pull-out resistance of ATPS was 2.5-fold that of VBS. Mean POS of 23 ATPS with a mean BMD of 0.566 g/cm(2) and a mean osseus screw purchase of 27.2 mm was 467.8 N. In comparison, POS of 22 VBS screws with a mean BMD of 0.533 g/cm(2) and a mean osseus screw purchase of 16.0 mm was 181.6 N. The difference in ultimate pull-out strength between the ATPS and VBS group was significant (p < 0.000001). Also, accuracy of ATPS placement in axial plane was shown to be significantly correlated with POS. In contrast, there was no correlation between screw-length, BMD, or level of insertion and the POS of ATPS or VBS. The study demonstrated that the use of ATPS might be a new technique worthy of further investigation. The use of ATPS shows the potential to increase construct rigidity in terms of screw-plate pull-out resistance. It might diminish construct failures during anterior-only reconstructions of the highly unstable decompressed cervical spine.

4- and 5-level anterior fusions of the cervical spine: review of literature and clinical results

In the future, there will be an increased number of cervical revision surgeries, including 4- and more-levels. But, there is a paucity of literature concerning the geometrical and clinical outcome in these challenging reconstructions. To contribute to current knowledge, we want to share our experience with 4- and 5-level anterior cervical fusions in 26 cases in sight of a critical review of literature. At index procedure, almost 50% of our patients had previous cervical surgeries performed. Besides failed prior surgeries, indications included degenerative multilevel instability and spondylotic myelopathy with cervical kyphosis. An average of 4.1 levels was instrumented and fused using constrained (26.9%) and non-constrained (73.1%) screw-plate systems. At all, four patients had 3-level corpectomies, and three had additional posterior stabilization and fusion. Mean age of patients at index procedure was 54 years with a mean follow-up intervall of 30.9 months. Preoperative lordosis C2-7 was 6.5 degrees in average, which measured a mean of 15.6 degrees at last follow-up. Postoperative lordosis at fusion block was 14.4 degrees in average, and 13.6 degrees at last follow-up. In 34.6% of patients some kind of postoperative change in construct geometry was observed, but without any catastrophic construct failure. There were two delayed unions, but finally union rate was 100% without any need for the Halo device. Eleven patients (42.3%) showed an excellent outcome, twelve good (46.2%), one fair (3.8%), and two poor (7.7%). The study demonstrated that anterior-only instrumentations following segmental decompressions or use of the hybrid technique with discontinuous corpectomies can avoid the need for posterior supplemental surgery in 4- and 5-level surgeries. However, also the review of literature shows that decreased construct rigidity following more than 2-level corpectomies can demand 360 degrees instrumentation and fusion. Concerning construct rigidity and radiolographic course, constrained plates did better than non-constrained ones. The discussion of our results are accompanied by a detailed review of literature, shedding light on the biomechanical challenges in multilevel cervical procedures and suggests conclusions.

Pediatric iatrogenic spinal deformity

This article reviews current published literature regarding pediatric iatrogenic spinal deformity, with particular emphasis on the cervical spine. The results of published series reporting the incidence, etiology, age, risk factors, surgical techniques, and treatment options are summarized. Iatrogenic deformity resulting from radiation therapy and a variety of surgical procedures are addressed.

Surgical management of cervical myelopathy: indications and techniques for laminectomy and fusion

BACKGROUND

Cervical spondylotic myelopathy (CSM) is a commonly encountered surgical disease that may be approached through a variety of operative techniques. Operative goals in the treatment of CSM include effective neural element decompression and maintaining spinal stability to avoid delayed deformity progression and neurologic compromise. Determining the most appropriate operative approach requires careful consideration of the patient's clinical presentation and radiographic imaging.

PURPOSE

To review the indications and techniques for multilevel laminectomy and fusion in the treatment of CSM.

CONCLUSIONS

When indications permit, a multilevel laminectomy is an effective and safe method of neural element decompression. Recognizing the potential for spinal instability is essential to prevent neurologic compromise and intractable axial neck pain caused by deformity progression. A variety of techniques have been described to supplement the posterior tension band after laminectomy; however, lateral mass fixation has evolved into the preferred stabilization technique. Although clinical success is well documented, a successful outcome is dependent on a comprehensive, individualized evaluation of each patient presenting with CSM.

Anterior correction of cervical spine lordosis using an adjustable depth tap: technical note

OBJECTIVE

In cases of multilevel anterior cervical spine decompression where intervening vertebral bodies need to be incorporated into the anterior plate construct, it may be difficult to apply the plate flush against the entire anterior cortical surface of the spine segment. Some have suggested using the levering property of bicortical screws to "pull" the body against the plate. Others have recommended contouring the anterior cervical plate with a plate bender. The objective of this work was to describe a novel technique using the adjustable depth tap provided in the Atlantis plating system for achieving cervical spine alignment against the lordotic plate after multilevel anterior decompression.

METHODS

We describe an illustrative case of a 14-year-old girl with complex cervical spine fractures after trauma. We used the 4.0-mm adjustable depth tap in the Atlantis plating system to lever the C4 body against the premachined lordotic plate.

RESULTS

Cervical lordosis and anterior cervical plate placement were accomplished after multilevel anterior cervical decompression with the use of an adjustable depth tap.

CONCLUSIONS

Bicortical screw placement and plate bending have drawbacks in trying to apply the anterior cervical plate firmly to the anterior surface of the cervical spine. We describe a new and safe technique of using an adjustable depth tap for achieving that same goal without any obvious drawbacks.