Dynamic plates in anterior cervical fusion surgery: graft settling and cervical alignment

Biomechanical analysis of the door-shaped titanium plate in single-level anterior cervical discectomy and fusion

BACKGROUND

Analyse and discuss the immediate stability of the cervical spine after anterior cervical discectomy and fusion using a door-shaped titanium plate and compare it with the traditional titanium plate, to provide biomechanical evidence for the rationality and effectiveness of the door-shaped titanium plate in clinical applications.

METHODS

Ten adult goat C4/5 vertebral bodies were obtained, and models were prepared using denture base resin. Biomechanical experiments were performed on the specimens before internal fixation. MTS was used to conduct non-destructive biomechanical loading tests in six directions, including flexion, extension, left-right bending, and left-right torsion, recording the range of motion (ROM) and neutral zone (NZ) of each specimen. The specimens were then randomly divided into two groups: the study group was fixed with a door-shaped titanium plate, and the control group was fixed with a traditional titanium plate. ROM and NZ in each direction were measured again. After measurements, both groups were subjected to 0.5 Hz torsion loading with a torque of 2 N m for a total of 3000 cycles, followed by measuring ROM and NZ in six directions once more.

RESULTS

Compared to before fixation, ROM and NZ in both groups significantly decreased in all six directions after fixation, with statistical significance (P < 0.05); after fixation, the study group showed slightly lower values for various mechanical reference parameters compared to the control group, with no statistical significance (P > 0.05); after 3000 torsional loads, both internal fixation groups showed increased ROM and NZ compared to after fixation but to a lower extent, and no screw or titanium plate loosening was observed. Compared to before fixation, the differences were still statistically significant (P < 0.05), with the study group having slightly lower ROM and NZ values in all directions compared to the control group, with no statistical significance (P > 0.05).

CONCLUSION

The door-shaped titanium plate exhibits mechanical properties similar to the traditional titanium plate in all directions, and its smaller size and simpler surgical operation can be used for anterior cervical endoscopic surgery, reducing surgical trauma. It is clinically feasible and deserves further research and promotion.

Follow-up of a new titanium cervical plate for fusion of the cervical spine

Cervical plates are in use since the 1990ies for anterior cervical discectomy and fusion (ACDF). The latest step in development was a dynamic plate that allows sliding of the screws facilitating the natural settling of the bone after surgery. We investigated the clinical and radiological results of such a dynamic plate in a patient cohort that underwent single or multi-level ACDF for various cervical degenerative indications, including revision cases, from 2014 to 2019. Clinical and radiological outcome were assessed in 60 eligible patients after a mean of 2.9 years. The assessed neck disability index (NDI), and the visual analogue scale (VAS) of neck and arm pain show comparable results to the literature of ACDF, and specifically other plate designs. Forty-eight Adverse and Serious Adverse Events do not show a link to the product used. Clinical and radiological outcomes of ACDF with dynamic, third generation cervical plates show comparable results to the literature. Careful reporting of all Adverse Events revealed a variety of concomitant diseases, but could not be correlated to the implant used.

Allograft Subsidence Decreases Postoperative Segmental Lordosis With Minimal Effect on Global Alignment Following ACDF

STUDY DESIGN

Retrospective cohort study.

OBJECTIVE

Studies investigating the impact of interbody subsidence in ACDF suggest a correlation between subsidence and worse radiographic and patient-reported outcomes. The purpose of this study was to assess whether allograft subsidence assessed on CT is associated with worse cervical alignment.

METHODS

We performed a retrospective review of a prospective cohort of patients undergoing 1 to 3 level ACDF. Cervical alignment was assessed on standing radiographs performed preoperatively, less than 2 months postoperatively, and greater than 6 months postoperatively. Allograft subsidence was assessed on CT scan performed at least 6 months postoperatively. Patients with at least 1 level demonstrating greater than 4mm of cage subsidence were classified as severe subsidence. Student's t-test was used to compare all means between groups.

RESULTS

We identified 66 patients for inclusion, including 56 patients with non-severe subsidence and 10 patients with severe subsidence. For the entire cohort, there was a significant increase in C2-7 Lordosis (p = 0.005) and Segmental Lordosis (p < 0.00 001) from preoperative to early postoperative. On comparison of severely and non-severely subsided levels, severely subsided levels demonstrated a significantly greater loss of segmental lordosis from early to mid-term follow-up than non-severely subsided levels (-4.89 versus -2.59 degrees, p < 0.0001), manifesting as a significantly lower segmental lordosis at >6 months postoperative (0.54 versus 3.82 degrees, p < 0.00 001). There were no significant differences in global cervical alignment parameters between patients with severe and non-severe subsidence.

CONCLUSIONS

Severe subsidence is associated with a significant increase in loss of segmental lordosis, but has minimal effect on global cervical alignment parameters.

Does Graft Position Affect Subsidence After Anterior Cervical Discectomy and Fusion?

STUDY DESIGN

Retrospective cohort study.

OBJECTIVE

Implant subsidence is an important prognostic factor after anterior cervical discectomy and fusion (ACDF). Our purpose in this study was to investigate whether graft position affects subsidence after ACDF and to determine if there is a difference in clinical results based on allograft subsidence and position.

METHODS

We reviewed 92 patients who underwent single-level ACDF with allograft and plate between January 2012 and October 2018. Treatment levels were divided based on allograft position within 2 mm of the posterior margin of the augmented plate (Anterior group) or at greater than 2 mm (Center group). Subsidence was defined as segmental vertebral body height decrease of 2 mm or more at 1 year compared to 1 week after surgery.

RESULTS

Overall subsidence prevalence was 15 (16%) cases. Subsidence was 11% in the Anterior group (8/73) and 39% in the Center group (7/19; P = .012). The subsidence group showed smaller graft footprint size (graft/endplate ratio) compared with the nonsubsidence group, and pseudarthrosis occurred frequently in the subsidence. There was no significant difference in clinical results according to graft position. These findings indicate that anterior graft position reduces risk of subsidence (95% confidence interval = 0.085-0.949).

CONCLUSION

To minimize risk of subsidence, the graft should be positioned on the anterior position of the surgical-level endplate. In addition, using a graft appropriate for endplate size will further reduce subsidence.

Pseudarthrosis of the Cervical Spine

Pseudarthrosis of the cervical spine represents a common and challenging problem for spine surgeons. Rates vary greatly from as low as 0%-20% to >60% and depend heavily on patient factors, approach, and number of levels. While some patients remain asymptomatic from pseudarthrosis, many require revision surgery due to instability, continued neck pain, or radiculopathy/myelopathy. We aimed to provide a practical, narrative review of cervical pseudarthrosis to address the following areas: (1) definitions, (2) incidence, (3) risk factors, (4) presentation and workup, (5) treatment decision-making, and (6) postoperative care. It is our hope the current review provides a concise summary for how to diagnose and treat challenging cervical nonunions.

Mid- and Long-Term Follow-Up Efficacy Analysis of 3D-Printed Interbody Fusion Cages for Anterior Cervical Discectomy and Fusion

OBJECTIVE

To evaluate the safety and stability of 3D-printed interbody fusion cages (3D-printed cages) in anterior cervical discectomy and fusion (ACDF) by investigating the mid- and long-term follow-up outcomes.

METHODS

In this prospective study, the clinical data of 30 patients with CSM admitted to the Second Hospital of Shanxi Medical University from May 2012 to May 2014 were analyzed. The cohort comprised 18 males and 12 females with an average age of 60.22 ± 3.2 years. All patients were examined by X-ray, CT and MRI before the operation. A total of 30 cases of CSM were treated by ACDF with 3D printed cage implantation. Mid- and long-term follow-ups were performed after the surgery. Clinical efficacy was evaluated by comparing the JOA score, SF-36 score, change in neurological function, cervical curvature index (CCI), vertebral intervertebral height (VIH) and fusion rate before the operation, 6 months after the operation, and at the last follow-up.

RESULTS

Two of the 30 patients were lost to follow-up. The remaining patients were followed up for 48-76 (65.23 ± 3.54) months. The patients recovered satisfactorily with a significant clinical effect. The JOA score increased meanfully and the improvement rate was 89.4% at the final follow-up. The SF-36 score increased significantly from pre- to postoperatively. The height of the intervertebral space at the last follow-up was not statistically significantly different from that at 6 months after surgery (P > 0.05), showing that the height of the intervertebral space did not change much and the severity of cage subsidence (CS) decreased. The CCI improved from pre- to postoperatively. The CCI did not change much from the 6-month follow-up to the last follow-up. and the cage rate (CR) was 100% at the 6-month and last follow-ups. No severe complications, such as spinal cord injury, esophageal fistula, cerebrospinal fluid leakage, cervical hematoma or wound infection, occurred in any of the patients.

CONCLUSION

The clinical and radiological results show that the application of 3D-printed cages in ACDF can significantly relieve symptoms. Moreover, 3D-printed cages can restore the curvature of the cervical spine, effectively maintain the intervertebral height for a long time, and prevent complications related to postoperative subsidence.

Clinical Investigation of the Association of Opening Size with Sagittal Canal Diameter Based on Single-Door Cervical Laminoplasty

Background

Many clinical studies have assessed the association of laminoplasty opening size (LOS) with sagittal canal diameter (SCD) based on single-door cervical laminoplasty (SDCL). Nevertheless, the “worn-off” lamina extracted in SDCL was neglected in these reports. We aimed to develop a simple mathematical model to analyze the relationship between the effective LOS and SCD, taking into consideration the worn-off lamina.

Material/Methods

A total of 106 patients treated by SDCL at our hospital were included in this study. Pre-operative and post-operative SCDs were assessed using a picture archiving and communication system (PACS) based on computed tomography scans. Mini-plate sizes as well as drill bit diameters were recorded in detail in order to determine the effective LOS for each vertebral lamina involved.

Results

SCD in all patients was increased significantly after SDCL (P<0.01). A linear correlation was found between effective LOS and the post-operative SCD increment from C3 to C7 (R²>0.933, P<0.001). The 12 mm mini-plate was most often used in SDCL, accounting for 64.45% of all cases, whereas 10 mm and 16 mm mini-plates were the least used, accounting for 3.85% and 3.00%, respectively.

Conclusions

There is a strong linear correlation between effective LOS and the post-operative SCD increment. The SCD was increased by about 0.5 mm per mm increase in effective LOS. Thus, post-operative SCD could be precisely calculated and predicted, enabling the selection of optimal mini-plate prior to SDCL.

Open Door Laminoplasty: Creation Of A New Vertebral Arch

BACKGROUND

We describe the carrying out of our open door laminoplasty technique by reproducing a posterior vertebral arch using a local originating autologous bony graft and titanium plates.

METHODS

We designed a prospective study and present our first 16 patients. The clinical results were evaluated with the JOA score, Nurick scale and the VAS. The functional and radiological evaluation was performed with radiographs, CT and MRI, and the measurements of the dimensions of the spinal canal were carried out with the MIPAV programme ( Johns Hopkins University). All the variables were statistically analysed by means of SPSS23.0.

RESULTS

After following up the cases for two years, the clinical evaluation showed, amongst other findings, a 75% improvement in the JOA score, while the radiological controls showed an appropriate range of motion (ROM) along with the stability of the construction. The rate of complete arthrodesis of the cervical neo-arch reached was approximately 92%.

CONCLUSIONS

Our results show that the modifications that we performed on the technique originally described have made it into a simpler, more efficacious and safer procedure, without lessening its essential objectives.

The Effect of Dynamic Versus Static Plating Systems on Fusion Rates and Complications in 1-Level and/or 2-Level Anterior Cervical Discectomy and Fusion: A Systematic Review

STUDY DESIGN

A systematic review.

OBJECTIVE

To determine the effect of plate design on fusion rates in patients undergoing a 1- and 2-level anterior cervical discectomy and fusion (ACDF).

METHODS

Articles published between January 1, 2002 and January 1, 2015 were systematically reviewed to determine the fusion rate of 1- and 2-level ACDFs using either a fully constrained or semiconstrained locking plate. Additional variables that were collected included the number of levels, the type of graft/cage used, the study design, the method for determining fusion, and complications.

RESULTS

Fifty-two articles and 3053 patients were included. No significant difference in the fusion rate for 1- and 2-level ACDF using a fully constrained plate (96.1%) and a semiconstrained plate (95.29%) was identified (P=0.84). No difference (P=0.85) in the total complication rate between fully constrained plates (3.20%) and semiconstrained plates (3.66%), or the rate of complications that required a revision (2.17% vs. 2.41%, P=0.82) was identified. However, semiconstrained plates had a nonsignificant increase in total dysphagia rates (odds ratio=1.660, P=0.28) and short-term dysphagia rates (odds ratio=2.349, P=0.10).

CONCLUSIONS

In patients undergoing a 1- or 2-level ACDF, there is no significant difference in the fusion or complication rate between fully constrained plates and semiconstrained plates.

LEVEL OF EVIDENCE

Level II-systematic review.

Do Anterior Cervical Osteophytes Prevent Dynamization of Cervical Dynamic Plates?

STUDY DESIGN

A retrospective study.

OBJECTIVE

To evaluate radiographic changes of patients with osteophytes at the anterior border of the caudal vertebral body who were treated with anterior cervical discectomy and fusion using dynamic rotational plates.

SUMMARY OF BACKGROUND DATA

Dynamic cervical plates are widely used in surgeries of the anterior cervical spine. One concern in using dynamic plates is that the subjacent anterior osteophytes might act as a bony block and prevent dynamization of the plate. To our knowledge, there are no studies that have investigated the validity of this concern.

MATERIALS AND METHODS

Twenty-eight patients were selected for the study out of patients who had undergone 1-level anterior cervical discectomy and fusion using a dynamic rotational plate. They were divided into 2 groups on the basis of the presence of osteophytes located at the anterior border of the subjacent vertebrae. Thirteen patients had osteophytes and 15 control patients did not. The mean follow-up period was 10.8±8.4 months (range, 6-36 mo). Lateral radiographs were taken preoperatively, immediately postoperatively, and at the final follow-ups to assess changes in the following radiographic parameters: Cobb angle of the adjacent segments and fused segment, horizontal distance between C2 and C7 plumb lines, height of the bone graft, vertebral heights of the operated segment, and migration distance of the plate.

RESULTS

No statistical significance was found in the Cobb angles of the adjacent segments and fused segment, distance between the C2-C7 plumb lines, height of the graft, height of vertebral bodies of the operated segment, and migration distance of the plate through the preoperative, postoperative, and final follow-ups between the 2 groups.

CONCLUSION

Osteophytes did not appear to affect the dynamization of plates in any of the measured radiographic parameters.

Anterior approaches for cervical spondylotic myelopathy: which? When? How?

Cervical spondylotic myelopathy is a degenerative disorder with an unfavorable natural history. Surgical treatment options have evolved substantially over time, with both anterior and posterior methods proving successful for certain patients with specific characteristics. Anterior decompression of the spinal canal plus fusion techniques for stabilization has several advantages and some disadvantages when compared to posterior options. Understanding the pros and cons of the approaches and techniques is critical for the surgeon to select the best operative treatment strategy for any given patient to achieve the best outcome. Multiple decision-making factors are involved, such as sagittal alignment, number of levels, shape of the pathoanatomy, age and comorbidities, instability, and pre-operative pain levels. Any or all of these factors may be relevant for a given patient, and to varying degrees of importance. Choice of operative approach will therefore be dependent on patient presentation, risks of that approach for a given patient, and to some degree surgeon experience.

Malaligned dynamic anterior cervical plate: a biomechanical analysis of effectiveness

STUDY DESIGN

Biomechanical evaluation.

OBJECTIVE

To evaluate the kinematic and load-sharing differences of dynamic anterior cervical plates when placed in-line at 0° and off-axis at 20°.

SUMMARY OF BACKGROUND DATA

The use of dynamic anterior cervical plating systems has recently gained popularity due to the theoretical benefit of improved load sharing with graft subsidence. Occasionally, due to anatomical restraints, the anterior cervical plate may be placed off-axis in the coronal plane. This may potentially decrease the dynamization capability of the plate, leading to less load sharing and potentially decreased fusion rates. The purpose of this study was to comprehensively evaluate the kinematic and load-sharing differences of a dynamic plate placed in-line versus off-axis in the coronal plane.

METHODS

Thirteen fresh-frozen human cadaveric cervical spines (C2-T1) were used. Nondestructive range-of-motion testing was performed with a pneumatically controlled spine simulator in flexion/extension, lateral bending, and axial rotation using the OptoTrak motion measurement system. A C5 corpectomy was performed, and a custom interbody spacer with an integrated load cell collected load-sharing data under axial compression at varying loads. A dynamic anterior cervical plate was placed in-line at 0° and then off-axis at 20°. Testing conditions ensued using a full-length spacer, followed by simulated subsidence by removing 10% of the height of the original spacer.

RESULTS

There were no kinematic differences noted in the in-line model versus the off-axis model. After simulated subsidence, the small decreases in stiffness and increases in motion were similar whether the plate was placed in-line or off-axis in all 3 planes of motion. There were also no significant differences in the load-sharing characteristics of the in-line plate versus the off-axis plate in either the full-length model or the subsided interbody model.

CONCLUSION

This study suggests that off-axis dynamic plate positioning does not significantly impact construct kinematics or graft load sharing. As such, we do not recommend removal or repositioning of an off-axis placed dynamic plate because the kinematic and load-sharing biomechanical properties are similar.

LEVEL OF EVIDENCE

N/A.

Impact of subsidence on clinical outcomes and radiographic fusion rates in anterior cervical discectomy and fusion: a systematic review

STUDY DESIGN

Systematic review.

OBJECTIVE

To provide a systematic review of published literature on the impact of subsidence on clinical outcomes and radiographic fusion rates after anterior cervical discectomy and fusion with plates or without plates.

BACKGROUND

Subsidence of interbody implants is common after anterior cervical spine fusions. The impact of subsidence on fusion rates and clinical outcomes is unknown.

METHODS

Systematic literature review on published articles on anterior cervical discectomy and fusion, which objectively measured graft subsidence, radiographic fusion rates, and clinical outcomes between April 1966 and December 2010.

RESULTS

A total of 35 articles that measured subsidence and provided fusion rates and/or clinical outcomes were selected for inclusion. The mean subsidence rate ranged from 19.3% to 42.5%. The rate of subsidence based on the type of implant ranged from 22.8% to 35.9%. The incidence of subsidence was not impacted by the type of implant (P=0.98). The overall fusion rate of the combined studies was 92.8% and was not impacted by subsidence irrespective of subsidence definition or the measurement technique used (P=0.19). Clinical outcomes were evaluated in 27 of 35 studies with all studies reporting an improvement in patient outcomes postoperatively.

CONCLUSIONS

Subsidence irrespective of the measurement technique or definition does not appear to have an impact on successful fusion and/or clinical outcomes. A validated definition and standard measurement technique for subsidence is needed to determine the actual incidence of subsidence and its impact on radiographic and clinical outcomes.

A unique modular implant system enhances load sharing in anterior cervical interbody fusion: a finite element study

Background

The efficacy of dynamic anterior cervical plates is somewhat controversial. Screws in static-plate designs have a smaller diameter and can cut through bone under load. While not ideal, this unintended loosening can help mitigate stress shielding. Stand-alone interbody devices with integral fixation have large endplate contact areas that may inhibit or prevent loosening of the fixation. This study investigates the load sharing ability of a novel dynamic plate design in preventing the stress shielding of the graft material compared to the non-dynamic devices.

Methods

An experimentally validated intact C5-C6 finite element model was modified to simulate discectomy and accommodate implant-graft assembly. Four implant iterations were modeled; InterPlate titanium device with dynamic surface features (springs), InterPlate titanium non-dynamic device, InterPlate titanium design having a fully enclosed graft chamber, and the InterPlate design in unfilled PEEK having a fully enclosed graft chamber. All the models were fixed at the inferior-most surface of C6 and the axial displacement required to completely embed the dynamic surface features was applied to the model.

Results

InterPlate device with dynamic surface features induced higher graft stresses compared to the other design iterations resulting in uniform load sharing. The distribution of these graft stresses were more uniform for the InterPlate dynamic design.

Conclusions

These results indicate that the dynamic design decreases the stress shielding by increasing and more uniformly distributing the graft stress. Fully enclosed graft chambers increase stress shielding. Lower implant material modulus of elasticity does not reduce stress shielding significantly.

Correlation between the clinic and the index of cervical myelopathy Torg

Objective

Cervical myelopathy is a spinal cord dysfunction related to degeneration typical of aging. Its primary pathology is related to ischemia and spinal cord compression. Patients with myelopathy present many clinical problems; more severe cases may lead to quadriplegia if not treated in a timely manner. Because the primary pathology of this disease is caused by compression, thus generating spinal cord ischemia, we believed there must be a correlation between the degree of compression and the clinical assessment of patients with cervical myelopathy, but we did not find any study in the literature that made this correlation. Because there is doubt the literature we aimed, in our study, to analyze the correlation between the degree of clinical impairment of patients with cervical myelopathy and the Torg index.

Methods

A prospective, descriptive study, evaluating 46 patients, in which radiographic measurements of the Torg index were performed, with clinical analysis through the Nurick and JOA scale.

Results

Of the 46 study patients included in the study, 100% presented a Torg score <0.8. The decrease in Torg values was directly proportional to clinical worsening on the Nurick and JOA scale.

Conclusions

The degree of clinical impairment in patients with cervical myelopathy is directly related to the degree of spinal canal stenosis. Level of Evidence I, Prognostic Studies - Investigating the effect of the characteristics of a patient on the outcome of the disease.

Cervical foraminal and discal height after dynamic rotational plating in the cervical discectomy and fusion

STUDY DESIGN

This is a retrospective study.

PURPOSE

To evaluate the effect of the dynamic rotational plate to the intervertebral foraminal and discal height after anterior cervical discectomy and fusion.

OVERVIEW OF LITERATURE

There is no report regarding the changes of foraminal and discal height following cervical dynamic rotational plating.

METHODS

We reviewed the outcomes of 30 patients (36 levels), who were followed-up for an average of 15 months (range, 12-57 months) after undergoing fusions with anterior cervical dynamic rotational plating for cervical radiculopathy, from March 2005 to February 2009. The changes of foraminal and intervertebral discal height of the operated levels were observed on oblique and lateral radiographs obtained at the preoperative, postoperative and follow-up examinations.

RESULTS

The foraminal and discal height increased sufficiently, immediately following the operation. However, follow-up results showed gradual decrease in the foraminal and discal height. After 6 months of the surgery, they showed little difference compared with the preoperative heights. However, clinically, patients showed improvements in radiating pain during the follow-up period.

CONCLUSIONS

Anterior cervical dynamic rotational plating was an effective treatment modality for cervical radiculopathy without the deterioration of the foraminal and intervertebral discal height.

Loss of lordosis and clinical outcomes after anterior cervical fusion with dynamic rotational plates

PURPOSE

The cervical dynamic rotational plating system may induce bone graft subsidence, so it may cause loss of cervical lordosis. However there were few studies for alignments of cervical spines influencing the clinical results after using dynamic rotational plates. The purpose is to evaluate the effect of graft subsidence on cervical alignments due to the dynamic rotational cervical plates and correlating it with the clinical outcomes of patients undergoing anterior cervical fusion.

MATERIALS AND METHODS

Thirty-three patients with disease or fracture underwent anterior cervical decompression and fusion using a dynamic rotational plate. The presence and extent of implant complications, graft subsidence, loss of lordosis were identified and Visual Analog Scale score (VAS score), Japanese Orthopaedic Association score (JOA score), clinical outcomes based on Odom's criteria were recorded.

RESULTS

Fusion was achieved without implant complications in all cases. The mean graft subsidence at 6 months after the surgery was 1.46 mm. The lordotic changes in local cervical angles were 5.85° which was obtained postoperatively. VAS score for radicular pain was improved by 5.19 and the JOA score was improved by 3. Clinical outcomes based on Odom's criteria showed sixteen excellent, ten good and two satisfactory results. There was no significant relationship between clinical outcomes and changes in the cervical angles.

CONCLUSION

Dynamic rotational anterior cervical plating provides comparable clinical outcomes to that of the reports of former static cervical platings. The loss of lordosis is related to the amount of graft settling but it is not related to the clinical outcomes.