Are all Cages Created Equal? Analysis of Cervical Cage Malfunctions Using FDA MAUDE Database.

STUDY DESIGN: Retrospective case series. OBJECTIVE: To characterize failure rates of cervical cages based on manufacturer and design characteristics using the nationwide database of reported malfunctions. BACKGROUND: The Food and Drug Administration (FDA) aims to ensure the safety and efficacy of cervical interbody implants postimplantation; however, intraoperative malfunctions may be overlooked. MATERIALS AND METHODS: The FDA's Manufacturer and User Facility Device Experience database was queried for reports of cervical cage device malfunctions from 2012 to 2021. Each report was categorized based on the failure type, implant design, and manufacturer. Two market analyses were performed. First, "failure-to-market share indices" were generated by dividing the number of failures per year for each implant material by its yearly US market share in cervical spine fusion. Second, "failure-to-revenue indices" were calculated by dividing the total number of failures per year for each manufacturer by their approximate yearly revenue from spinal implants in the US. Outlier analysis was performed to generate a threshold value above which failure rates were defined as greater than the normal index. RESULTS: In total, 1336 entries were identified, and 1225 met the inclusion criteria. Of these, 354 (28.9%) were cage breakages, 54 (4.4%) were cage migrations, 321 (26.2%) were instrumentation-related failures, 301 (24.6%) were assembly failures, and 195 (15.9%) were screw failures. Poly-ether-ether-ketone implants had higher failure by market share indices for both migration and breakage compared with titanium. Upon manufacturer market analysis, Seaspine, Zimmer-Biomet, K2M, and LDR exceeded the failure threshold. CONCLUSION: The most common cause of implant malfunction was breakage. Poly-ether-ether-ketone cages were more likely to break and migrate compared with titanium ones. Many of these implant failures occurred intraoperatively during instrumentation, which underscores the need for FDA evaluation of these implants and their accompanying instrumentation under the appropriate loading conditions before commercial approval.

Spinolaminar locking plates improve fixation strength compared to pedicle screws: a biomechanical analysis.

INTRODUCTION: Pedicle screw loosening is a significant complication of posterior spinal fixation, particularly among osteoporotic patients and in deformity constructs. In orthopedic trauma surgery, locking plates and screws have revolutionized the fixation of osteoporotic fractures. We have combined the traumatology principle of fixed-angle locking plate fixation with the spine principles of segmental instrumentation. METHODS: A novel spinolaminar locking plate was designed based on morphometric studies of human thoracolumbar vertebrae. The plates were fixed to cadaveric human lumbar spines and connected to form 1-level L1-L2 or L4-L5 constructs and compared to similar pedicle screw constructs. Pure moment testing was performed to assess range of motion before and after 30,000 cycles of cyclic fatigue. Post-fatigue fixture pullout strength was assessed by applying a continuous axial tensile force oriented to the principal axis of the pedicle until pullout was observed. RESULTS: Spinolaminar plate fixation resulted in superior pullout strength compared to pedicle screws (1,065 ± 400N vs. 714 ± 284N, p = 0.028). Spinolaminar plates performed equivalently to pedicle screws in range of motion reduction during flexion/extension and axial rotation. Pedicle screws outperformed the spinolaminar plates in lateral bending. Finally, no spinolaminar constructs failed during cyclic fatigue testing, whereas one pedicle screw construct did. CONCLUSIONS: The spinolaminar locking plate maintained adequate fixation post-fatigue, particularly in flexion/extension and axial rotation compared to pedicle screws. Moreover, spinolaminar plates were superior to pedicle screw fixation with respect to cyclic fatiguing and pullout strength. The spinolaminar plates offer a viable option for posterior lumbar instrumentation in the adult spine.

An Analysis of a Decade of Lumbar Interbody Cage Failures in the United States: A MAUDE Database Study.

STUDY DESIGN: A retrospective case series. OBJECTIVE: This study aims to assess the rates of lumbar interbody cage failures based on their material and manufacturer. SUMMARY OF BACKGROUND DATA: Perioperative lumbar interbody cage malfunctions are underreported events in the spine literature and may result in complications. Although the Food and Drug Administration ensures the safety of these devices under physiological conditions after implantation, these devices may experience nonphysiological conditions during implantation, which may be overlooked. MATERIALS AND METHODS: The MAUDE database was examined for reports of lumbar cage device malfunctions from 2012 to 2021. Each report was categorized based on failure type and implant design. A market analysis was performed by dividing the total number of failures per year for each manufacturer by their approximate yearly revenue from spinal implants in the United States. Outlier analysis was performed to generate a threshold value above which failure rates were defined as greater than the normal index. RESULTS: Overall, 1875 lumbar cage malfunctions were identified. Of these, 1230 (65.6%) were cage breakages, 257 (13.7%) were instrument malfunctions, 177 (9.4%) were cage migrations, 143 (7.6%) were assembly failures, 70 (4.5%) were screw-related failures, and 21 (1.1%) were cage collapses. Of the breakages, 923 (74.9%) occurred during insertion or impaction and 97 entries detailed a medical complication or a retained foreign body. Of the migrations, 155 (88.6%) were identified postoperatively, of which 73 (47.1%) detailed complications and 52 (33.5%) required a revision procedure. Market analysis demonstrated that Medtronic, Zimmer Biomet, Stryker, Seaspine, and K2M exceeded the calculated threshold. CONCLUSIONS: Lumbar cages with polyether ether ketone core material failed more frequently by breakage, whereas titanium surface cages failed more frequently by migration. Failure rates varied depending on the manufacturer. Most cage breakages identified in the present study occurred intraoperatively during implantation. These findings call for a more detailed Food and Drug Administration evaluation of these intraoperative malfunctions before commercial approval. LEVEL OF EVIDENCE: Level 4.

Pyogenic spinal infections warrant a total spine MRI.

Study design: retrospective case series. Objective: the presenting clinical symptoms of spinal infections are often nonspecific and a delay in diagnosis can lead to adverse patient outcomes. The morbidity and mortality of patients with multifocal spinal infections is significantly higher compared to unifocal infections. The purpose of the current study was to analyse the risk factors for multifocal spinal infections. Methods: we conducted a retrospective review of all pyogenic non-tuberculous spinal infections treated surgically at a single tertiary care medical center from 2006-2020. The medical records, imaging studies, and laboratory data of 43 patients during this time period were reviewed and analysed after receiving Institutional Review Board approval. Univariate and multivariate analyses were performed to identify factors associated with a multifocal spinal infection. Results: 15 patients (35 %) had multifocal infections. In univariate analysis, there was a significant association with chronic kidney disease ( p = 0.040 ), gender ( p = 0.003 ), a white blood cell count ( p = 0.011 ), and cervical ( p < 0.001 ) or thoracic ( p < 0 .001) involvement. In multivariate analysis, both cervical and thoracic involvement remained statistically significant ( p = 0.001 and p < 0.001 , respectively). Conclusions: patients with infections in the thoracic or cervical region are more likely to have a multifocal infection. Multifocal pyogenic spinal infections remain a common entity and a total spine MRI should be performed to aid in prompt diagnosis.

C1-C2 Facet Joint Penetration by C2 Pedicle Screws: Influence of Local Anatomy, Bone Mineral Density, and Screw Length.

BACKGROUND: A challenge of C2 pedicle screw placement is to avoid penetration into the C1-C2 facet joint, as this may alter normal biomechanics and accelerate joint degeneration. Our objective was to clarify how local anatomy and surgical technique may relate to C2 pedicle screw penetration into the C1-C2 facet joint. METHODS: C2 pedicle screws were inserted using a fluoroscopically assisted freehand technique. Independent fellowship-trained spine surgeons blindly reviewed intraoperative fluoroscopic and postoperative computed tomography (CT) images for evidence of facet joint penetration (FJP). C2 pedicle morphometry, the sagittal angle of the facet joint, axial and sagittal pedicle screw angles, and screw length were measured on the relevant CT images. RESULTS: A total of 34 patients fulfilled the study criteria, and a total of 68 C2 pedicle screws were placed. Eight screws (16%) penetrated the C1-C2 facet joint. The mean sagittal angle of the C1-C2 facet joint was significantly lower in the FJP group compared with the non-FJP group. The mean sagittal angle of the screws was significantly higher in the FJP group compared with the non-FJP group. The mean screw length was significantly greater for screws causing FJP compared with the non-FJP group. The mean axial screw angle was significantly lower in the FJP group compared with the non-FJP group. Pedicle width, length, height, and transverse angle were not significantly associated with FJP. Independent reviewers were able to identify FJP on intraoperative fluoroscopic imaging in 2 out of 8 cases. CONCLUSION: Lower sagittal angle of the facet joint, higher sagittal angle of the pedicle screw, and screw length >24 mm are associated with higher risk of C1-C2 FJP. When placing C2 pedicle screws under these conditions, caution should be taken to avoid FJP. CLINICAL RELEVANCE: Several anatomical and technical factors may increase the risk of C1-C2 FJP during placement of C2 pedicle screws using a fluoroscopically assisted freehand technique, underscoring the importance of preoperative planning and limiting screw length.

Fusion Mass Screws in Revision Spinal Deformity Surgery: A Simple and Safe Alternative Fixation.

BACKGROUND: Revision spinal deformity surgery has a high rate of complications. Fixation may be challenging due to altered anatomy. Screws through a fusion mass are an alternative to pedicle screw fixation. OBJECTIVE: The purpose of this retrospective study was to further elucidate the safety and efficacy of fusion mass screws (FMSs) in revision spinal deformity surgery. DESIGN: Retrospective case series. METHODS: Fifteen freehand FMSs were placed in 6 patients with adult spinal deformity between 2016 and 2018 by the senior author. FMSs were combined with pedicle screws, at times at the same level. FMSs were used to save distal levels from fusion, assist in closing a 3-column osteotomy and provide additional fixation in cases of severe instability. Computed tomography (CT) was used to assess bone mineral density (BMD) and thickness of each fusion mass preoperatively along with accuracy of FMS placement postoperatively. RESULTS: The mean BMD of the fusion mass was 397 Hounsfield units (HU; range: 156-628 HU). The mean AP thickness of the fusion mass was 15.5 ± 4.8 mm (range: 8.6-24.4 mm). The mean FMS length was 35.3 ± 5.5 mm (range: 25-40 mm). There was no evidence of FMS loosening, breakage, or pseudarthrosis at latest follow-up (mean: 2.2 years, range: 1.4-3.1 years). No neurologic deficits were observed. 1/15 screws had a low-grade breach into the canal (<2 mm). No patients required revision surgery. CONCLUSION: FMSs may be used to augment fixation in revision spinal deformity cases when pedicle screw placement may be challenging. FMSs may also provide an additional anchor at levels with pedicular fixation.

Alternatives to Traditional Pedicle Screws for Posterior Fixation of the Degenerative Lumbar Spine.

BACKGROUND: Traditional pedicle screws are currently the gold standard to achieve stable 3-column fixation of the degenerative lumbar spine. However, there are cases in which pedicle screw fixation may not be ideal. Due to their starting point lateral to the pars interarticularis, pedicle screws require a relatively wide dissection along with a medialized trajectory directed toward the centrally located neural elements and prevertebral vasculature. In addition, low bone mineral density remains a major risk factor for pedicle screw loosening, pullout, and pseudarthrosis. The purpose of this article is to review the indications, advantages, disadvantages, and complications associated with posterior fixation techniques of the degenerative lumbar spine beyond the traditional pedicle screws. METHODS: Comprehensive literature searches of the PubMed, Scopus, and Web of Science databases were performed for 5 methods of posterior spinal fixation, including (1) cortical bone trajectory (CBT) screws, (2) transfacet screws, (3) translaminar screws, (4) spinous process plates, and (5) fusion mass screws and hooks. Articles that had been published between January 1, 1990, and January 1, 2020, were considered. Non-English-language articles and studies involving fixation of the cervical or thoracic spine were excluded from our review. RESULTS: After reviewing over 1,700 articles pertaining to CBT and non-pedicular fixation techniques, a total of 284 articles met our inclusion criteria. CBT and transfacet screws require less-extensive exposure and paraspinal muscle dissection compared with traditional pedicle screws and may therefore reduce blood loss, postoperative pain, and length of hospital stay. In addition, several methods of non-pedicular fixation such as translaminar and fusion mass screws have trajectories that are directed away from or posterior to the spinal canal, potentially decreasing the risk of neurologic injury. CBT, transfacet, and fusion mass screws can also be used as salvage techniques when traditional pedicle screw constructs fail. CONCLUSIONS: CBT and non-pedicular fixation may be preferred in certain lumbar degenerative cases, particularly among patients with osteoporosis. Limitations of non-pedicular techniques include their reliance on intact posterior elements and the lack of 3-column fixation of the spine. As a result, transfacet and translaminar screws are infrequently used as the primary method of fixation. CBT, transfacet, and translaminar screws are effective in augmenting interbody fixation and have been shown to significantly improve fusion rates and clinical outcomes compared with stand-alone anterior lumbar interbody fusion. LEVEL OF EVIDENCE: Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.

Non-Pedicular Fixation Techniques for the Treatment of Spinal Deformity: A Systematic Review.

BACKGROUND: In recent years, the use of pedicle screws has become the gold standard for achieving stable, 3-column fixation of the spine. However, pedicle screw placement may not always be ideal, such as in adolescent idiopathic scoliosis, because of pedicle morphology. An understanding of the alternatives to pedicle screw fixation is therefore important in the treatment of patients with spinal deformity. The purpose of this article is to review the indications, advantages, disadvantages, and complications associated with non-pedicular fixation techniques of the thoracolumbar spine. METHODS: Comprehensive literature searches of PubMed, Scopus, and Web of Science databases were performed for 10 methods of non-pedicular fixation. Articles published between January 1, 1990, and June 1, 2019, were considered. Non-English-language articles and studies involving fixation of the cervical spine were excluded from our review. RESULTS: After reviewing >1,600 titles and abstracts pertaining to non-pedicular fixation, a total of 213 articles met our inclusion criteria. Non-pedicular fixation may be preferred in certain cases of spinal deformity and may provide stronger fixation in osteoporotic bone. The use of non-pedicular fixation techniques is often limited by the inability to place multilevel constructs on intact posterior elements. Additionally, some methods of non-pedicular fixation, such as spinous process tethering, primarily have utility for the end of constructs to minimize junctional problems. CONCLUSIONS: Pedicle screws remain the anchor of choice in spinal deformity surgery because of their ability to engage all 3 columns of the spine and provide safe correction in all 3 planes. Nevertheless, non-pedicular fixation may be useful in cases in which pedicle screw placement is extremely difficult. LEVEL OF EVIDENCE: Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.

High Prevalence of Multifocal Spine Infections Involving the Cervical and Thoracic Regions: A Case for Imaging the Entire Spine.

OBJECTIVE: Pyogenic spinal infections account for 2%-4% of orthopaedic infections. They are often difficult to diagnose, resulting in a delay in diagnosis. Risk factors for orthopaedic and spinal infection are well-documented in the literature, yet there is a paucity of studies examining risk factors specifically for multifocal spinal infections. The objective of this study was to identify predictors of multifocal spinal infections in comparison to unifocal spinal infections. METHODS: The medical records, imaging studies, and bacteriology data of 20 patients treated surgically for pyogenic spinal infection over 6 years at a tertiary referral center were reviewed and analyzed after receiving Institutional Review Board approval. Univariate and multivariate analyses were performed to identify factors associated with a multifocal spinal infection. RESULTS: Seven patients (35%) had multifocal infections. Three were bifocal, and 4 were trifocal. Patients with surgically treated cervical or thoracic spinal infections had a high rate of concomitant multifocal spinal infections (71% and 83%, respectively). Other potential predictors (e.g., patient age, body mass index, magnetic resonance image findings, etc.) did not reach statistical significance. Each of the multifocal infections involved the lumbar spine. CONCLUSION: In this study, the spinal region was the only statistically significant risk factor for multifocal infection. Patients who are diagnosed with a spinal infection that requires operative treatment should have their entire spine evaluated with magnetic resonance imaging to detect multifocal involvement promptly.