In vivo analysis of cervical kinematics after implantation of a minimally constrained cervical artificial disc replacement

Changes in the centre of rotation and the anterior bone loss of the vertebral body in Mobi-C artificial disc replacement segments after cervical hybrid surgery: a retrospective study

OBJECTIVE

To examine the short-term efficacy and imaging results of using the Mobi-C in cervical hybrid surgery on 2-level cervical spondylolisthesis. To observe post-operative changes in the flexion-extension centre of rotation (FE-COR) and anterior bone loss (ABL) of the anterior cervical disc replacement (ACDR) segment.

METHODS

Forty-two patients (20 males and 22 females, aged 42‒67 years) who underwent cervical hybrid surgery were retrospectively analysed. Their ACDR segment used Mobi-C, and the fusion segment used ROI-C, with a follow-up of 25‒42 months (31.1 ± 4.8 months). The modified Japanese Orthopaedic Association (mJOA) score, Neck Disability Index (NDI), and visual analogue scale (VAS) were used to assess clinical outcomes. Pre-operative, 6-month post-operative, and final follow-up radiographs were collected to compare total cervical spine curvature (C2-C7), curvature of the operated segments, range of motion (ROM) in the total cervical spine, operated segmental ROM, ACDR segmental ROM, and operated adjacent segmental ROM. The height of the superior articular process (HSAP), the orientation of zygapophyseal joint spaces (OZJS), and the length of the superior articular surface (LSAS) were measured. The FE-COR of the ACDR segment was measured using the mid-plumb line method. The translation distance of the Mobi-C was measured. The degree of disc degeneration in the adjacent segment, bony fusion of the ACDF segment, and ABL of the upper and lower vertebra of the ACDR segment were observed.

RESULTS

In our group, all patients have shown improvements in their postoperative mJOA, NDI, and VAS scores. Overall cervical ROM and surgical segmental ROM decreased (P < 0.05). However, there was no significant decrease in ACDR segmental ROM and upper or lower adjacent segmental ROM compared with pre-operatively (P > 0.05). For FE-COR-X, only the last follow-up compared with pre-surgery showed statistical significance (46.74 ± 7.71% vs. 50.74 ± 6.92%, P < 0.05). For FE-COR-Y, the change was statistically significant at both 6 months post-operation and the final follow-up compared to pre-operation (45.37% ± 21.11% vs. 33.82% ± 10.87%, 45. 37% ± 21.11% vs. 27.48% ± 13.58%, P < 0.05). No significant difference in the Mobi-C translation distance was observed (P > 0.05). Moreover, the difference in HSAP was not statistically significant at each node (P > 0.05). The OZJS and LSAS were significantly different at the final follow-up compared to the pre-operative period (P < 0.05). All the ACDF segments were observed in a stable condition at the final follow-up. Furthermore, 9 of the adjacent segments showed imaging ASD (9/82, 10.98%), and all were present at the last follow-up, of which 6 were mild, and 3 were moderate. Twenty of the 42 Mobi-C segments had no significant ABL (grade 0) 6 months post-operatively (47.62%). Sixteen cases (38.10%) showed mild ABL (grade 1), and 6 cases (14.28%) showed moderate ABL (grade 2). No severe ABL occurred.

CONCLUSION

The cervical hybrid surgery using Mobi-C artificial cervical discs can achieve satisfactory results. The Mobi-C segmental FE-COR-X shows a slow forward shift trend, and FE-COR-Y drops noticeably within 6 months post-surgery before stabilizing. It's common to see mild to moderate ABL after cervical hybrid surgery using Mobi-C, and significant progression is unlikely in the short term. Furthermore, changes in the FE-COR after hybrid surgery in the Mobi-C segment might not affect clinical outcomes.

Range of motion after 1, 2, and 3 level cervical disc arthroplasty

Background

Motion of a solid body involves translation and rotation. Few investigations examine the isolated translational and rotational components associated with disc arthroplasty devices. This study investigates single- and multi-level cervical disc arthroplasty with respect to index and adjacent level range of motion. The investigators hypothesized that single- and multilevel cervical disc replacement will lead to comparable or improved motion at implanted and adjacent levels.

Methods

Seven human cervical spines from C2 to C7 were subjected to displacement-controlled loading in flexion, extension, and lateral bending under intact, 1-Level (C5-C6), 2-Level (C5-C6, C6-C7) and 3-Level (C5-C6, C6-C7, C4-C5) conditions. 3D motions sensors were mounted at C4, C5, and C6. Motion data for translations and rotations at each level for each surgical condition and loading mode were compared to intact conditions.

Results

1-Level: The index surgery resulted in statistically increased translations in extension and lateral bending at all levels with statistically increased translation observed in flexion in the superior and inferior levels. In rotation, the index surgeries decreased rotation under flexion, with remaining levels not statistically different to intact conditions.

2-Level

A device placed inferiorly resulted in statistically increased translations at all levels in extension with statistically increased translations superior and inferior to the index level in flexion. Lateral bending resulted in increased nonsignificant translations. Rotations were elevated or comparable to the intact level for all loading.

3-Level

Translations were statistically increased for all levels in all loading modes while rotations were elevated or were comparable to the intact level for all loading modes and levels.

Conclusions

Micromotion sensors permitted monitoring and recording of small magnitude angulations and translations using a loading mechanism that did not over constrain cervical segmental motion. Multilevel cervical disc arthroplasty yielded comparable or increased overall motion at the index and adjacent levels compared to intact conditions.

Influence of the deviated center of rotation on the range of motion after cervical disc arthroplasty -an in vivo study with a minimum of 10-year follow-up

BACKGROUND

Short-term researches have studied the change of the center of rotation (COR) after the Bryan Cervical disc arthroplasty (CDA). But there is a lack of long-term studies focusing on the location of COR and its influence after surgery.

METHODS

Clinical and radiographic materials of patients who received CDA were retrospectively reviewed. Written informed consents were obtained. Clinical outcome was accessed by Japanese Orthopaedic Association (JOA), Neck Disability Index (NDI), and Odom's scale. Radiographic evaluation underwent before surgery, at early (3 months) follow-up and final (minimal 10 years) follow-up. The ROM of the global cervical spine and index level, the functional spine unit (FSU) angle and C2-C7 angle were measured. COR was identified and its coordinates were calculated. The absolute change of COR-x and COR-y were compared in subgroup analysis.

RESULTS

Sixty patients were included, with an average age of 55.9 ± 8.1 years old. The mean duration of follow up was 135.1 ± 16.1 (120-155) months. JOA, NDI and Odom's scale showed significant improvements at 10 years after surgery. The COR of index level was located in the posterior superior half of the caudal vertebral body. Following the implant of Bryan Disc, the COR shifted forward and downward. During the 10-year follow-up, the location of COR remained stable. ROM at the index level decreased from 10.6 ± 4.0° preoperatively to 9.3 ± 4.0° at the early follow-up (p = 0.03). The ROM at the index level remained unchanged from early follow-up to the final follow-up (9.3 ± 4.0° vs 9.5 ± 5.2°, p = 0.80). In subgroup analysis, larger changes of both COR-x and COR-y were related with decreased ROM.

CONCLUSIONS

Our study illustrated that Bryan CDA could achieved favorable clinical and radiographic outcome over a minimal 10-year follow-up. The reduction of the flexion-extension ROM may be correlated with a more deviated postoperative COR. More attention should be paid to preoperative design and intraoperative technique to obtain a more native COR.

Clinical and radiological outcome 1-year after cervical total disc replacement using the Signus ROTAIO - Prosthesis

INTRODUCTION

The instantaneous center of rotation (iCOR) of a motion segment has been shown to correlate with its total range of motion (ROM). Importantly, a correlation of the correct placement of cervical total disc replacement (cTDR) to preserve a physiological iCOR has been previously identified. However, changes of these parameters and the corresponding clinical relevance have hardly been analyzed. This study assesses the radiological and clinical correlation of iCOR and ROM following cTDR.

MATERIALS/METHODS

A retrospective multi-center observational study was conducted and radiological as well as clinical parameters were evaluated preoperatively and 1 year after cTDR with an unconstrained device. Radiographic parameters including flexion/extension X-rays (flex/ex), ROM, iCOR and the implant position in anterior-posterior direction (IP ap), as well as corresponding clinical parameters [(Neck Disability Index (NDI) and the visual analogue scale (VAS)] were assessed.

RESULTS

57 index segments of 53 patients treated with cTDR were analyzed. Pre- and post-operative ROM showed no significant changes (8.0° vs. 10.9°; p > 0.05). Significant correlations between iCOR and IP (Pearson's R: 0.6; p < 0.01) as well as between ROM and IP ap (Pearson's R: - 0.3; p = 0.04) were identified. NDI and VAS improved significantly (p < 0.01). A significant correlation between NDI and IP ap after 12 months (Pearson's R: - 0.39; p < 0.01) was found.

CONCLUSION

Implantation of the tested prosthesis maintains the ROM and results in a physiological iCOR. The exact position of the device correlates with the clinical outcome and emphasize the importance of implant design and precise implant positioning.

Effect of Facet Tropism on Postoperative Cervical Range of Motion After Single-Level Cervical Disc Arthroplasty

STUDY DESIGN

Retrospective analysis.

OBJECTIVES

Cervical disc arthroplasty (CDA) was designed to replace the degenerated disc with the prosthesis to preserve cervical motion. The commonly used artificial discs are designed symmetric, whereas the facet joints were reported to be asymmetric in many people. This study aimed to evaluate the effect of facet tropism on the cervical range of motion (ROM) after single-level CDA using Prestige LP.

METHODS

A total of 90 patients who underwent single-level CDA using Prestige LP from 2012 to 2017 were retrospectively reviewed. Radiographs were taken at each time point to measure the C2-C7 ROM and the ROM at the surgical segment. The pre-operation CT scans were utilized to reconstruct and calculate the angular direction of facet joints with respect to transverse, coronal, and sagittal reference planes. Facet tropism above 7° was defined as facet joint asymmetry.

RESULTS

No significant difference was found in flexion-extension C2-C7 ROM or ROM at the surgical segment between patients with symmetric and asymmetric fact joints regarding the sagittal plane. Patients with coronal asymmetric facet joints had lower flexion-extension ROM at the surgical level. Patients with transverse asymmetric facet joints had both lower flexion-extension C2-C7 ROM and ROM at the surgical level. After CDA surgery, patients obtained good clinical outcomes including increased Japanese Orthopedic Association (JOA) and decreased Neck Disability Index (NDI) as well as Visual Analogue Scale (VAS).

CONCLUSION

The coronal and transverse tropism seemed to be correlated with decreased flexion-extension ROM after CDA using Prestige LP.

Mid-long-term follow-up of operated level kinematics after single-level artificial cervical disc replacement with Bryan disc

OBJECTIVE

Evaluation of the mid-long-term kinematics of single-level Bryan artificial cervical disc replacement (ACDR) in vivo by analyzing the center of rotation (COR) at the operated level.

METHODS

A retrospective analysis was conducted using data collected from 38 patients who underwent single-level Bryan ACDR from January 2010 to March 2013. Radiological parameters including range of motion (ROM), lordosis angle, translation, and COR were obtained. Clinical outcomes were assessed based on Odom Criteria, modified Japanese Orthopedic Association (mJOA), Neck Disability Index (NDI), and Visual Analogue Scale (VAS) scores. Correlations between COR and other follow-up data were discussed at the last follow-up.

RESULTS

Compared with preoperative values, the last follow-up data showed that 86.84% of cases achieved good-or-excellent outcomes based on Odom criteria; Significant improvements were observed across all scales assessed for clinical outcomes (P < 0.05); Lordosis angle was significantly increased in both the overall cervical spine and the operated level (P < 0.05); ROM of the overall cervical spine, operated level, and adjacent levels was preserved (P > 0.05); There was no significant change in COR at the operated level (P > 0.05). At the last follow-up and at the operated level, COR (Y) showed negative correlations with ROM and translation (P < 0.05), but no follow-up data correlated with COR (X) were found (P > 0.05).

CONCLUSIONS

Satisfactory clinical and radiological outcomes were achieved 7 years or more after single-level Bryan ACDR. At the operated level, preoperative COR was maintained, probably due to replicating the physiological interrelations of COR (Y), translation, and ROM.

Cervical disc prostheses need a variable center of rotation for flexion / extension below disc level, plus a separate COR for lateral bending above disc level to more closely replicate in-vivo motion: MRI-based biomechanical in-vivo study

Background

Cervical disc prostheses are used to preserve motion after discectomy, but they should also provide a near-physiological qualitative motion pattern. Nevertheless, they come in many completely different biomechanical concepts. This caused us to perform an in-vivo MR-based biomechanical study to further investigate cervical spine motion with the aim to gain new information for improving the design of future cervical arthroplasty devices.

Methods

Fifteen healthy volunteers underwent MRI-investigation (in order to avoid radiation exposure) of their cervical spines from C3 to C7; for each segment centers of rotation (COR) for flexion / extension were determined from 5 different positions, and CORs for lateral bending from 3 different positions. The motion path of the COR is then described and illustrated in relation to the respective COR for maximum flexion / extension or lateral bending, respectively, and the findings are translated into implications for a better biomechanical prosthesis-design.

Results

The COR for flexion / extension does not remain constant during motion. The CORs for the respective motion intervals were always found at different positions than the COR for maximum flexion /extension showing that the COR moves both along the x- and the y-axis throughout flexion / extension. For lateral bending a completely independent COR was found above disc-level.

Conclusion

Flexion / extension is not a simple circular motion. Disc prostheses need a variable COR for flexion / extension below disc level with the capability to move both along the x- and the y-axis during motion, plus a second completely independent COR for lateral bending above disc level to closely replicate in-vivo motion. These findings are important for improving the biomechanical design of such devices in the future.

Viscoelastic cervical total disc replacement devices: Design concepts

Cervical disc replacement (CDR) is a motion-preserving surgical procedure for treating patients with degenerative disorders. Numerous reports of first generation CDR "ball-and-socket" articulating devices have shown satisfactory clinical results. As a result, CDR devices have been safely implemented in the surgeon's armamentarium on a global scale. However, only minor design improvements have been made over the last few years, as first generation CDRs devices were based on traditional synovial joint arthroplasty designs. As a consequence, these articulating designs have limited resemblance to the complex kinematic behavior of a natural disc. This has driven the development of deformable viscoelastic CDR devices to better mimic the biomechanical behavior of a natural disc. As a result, several viscoelastic CDR devices have been developed in recent years that vary in terms of materials, design and clinical outcomes. Since these viscoelastic CDR devices are fairly new, their weaknesses and strengths, which are related to their design characteristics, have not been well described. Therefore, this literature review discusses design related advantages and disadvantages of deformable viscoelastic CDR devices. As such, this paper can provide insight for surgeons and engineers on specific design characteristics of several viscoelastic devices and could potentially help to develop and design future implants. Eleven viscoelastic CDR devices were identified. An extensive database search on the devices' tradenames in Medline and PubMed was performed next. The devices were categorized based on common design characteristics to give an overview of both category and device specific complications and advantages. Overall, literature shows that most of these viscoelastic CDR devices can provide motion in all six degrees-of-freedom and have a variable center of rotation. Nevertheless, the viscoelastic materials used do not have an extensive history in orthopedics, so the long-term material behavior in vivo is still unknown. Although the viscoelastic devices have common benefits and risks, each specific design and category also has its own design related advantages and drawbacks that are described in this review. Altogether, viscoelastic total disc replacements seem to be a promising option for the future of cervical arthroplasty, but long-term clinical outcome is needed to confirm the advantages of mimicking the viscoelasticity of a natural disc.

In cervical arthroplasty, only prosthesis with flexible biomechanical properties should be used for achieving a near-physiological motion pattern

Background

In cervical arthroplasty, qualitative motion analysis generally investigates the position of the center of rotation (COR) before and after surgery. But is the pre-op COR suitable as reference? We believe that only a comparison against healthy individuals can answer whether a physiological motion pattern has been achieved. The aim of our study was to examine how the COR for flexion/extension after insertion of 3 biomechanically completely different types of disc prostheses compares to healthy volunteers, and whether and how prosthesis design contributes to a more natural or maybe even worse motion pattern.

Methods

In 15 healthy volunteers, MRI in flexion and in extension was taken, and the coordinates for the CORs (COR-HV) from C3 to C7 were determined. Then pre- and post-op flexion/extension x-rays from 30 patients with a one-level disc prosthesis underwent analysis for determination of COR from C3 to C7; 10 patients who received a Bryan, a Prestige STLP, or a Discover prosthesis were chosen, respectively. Change of post-op COR position was investigated in relation to the COR-HV.

Results

The pre-operative COR is not congruent with the COR found in healthy subjects and therefore cannot be used as reference for investigation whether a disc prosthesis resembles natural motion. However, the comparison with healthy individuals shows that prosthesis insertion can change the coordinates of the COR to any direction in all levels from C3/4 to C6/7 regardless of the operated segment. Prostheses with flexible biomechanical properties can contribute to shift the COR toward normal, but devices with unphysiological biomechanical design, like fixed ball socket designs, for instance, can make the motion pattern even worse.

Conclusions

Even if the small cohorts in our study do not allow strong conclusions, it seems that in cervical arthroplasty, the biomechanical concept of the prosthesis has a significant impact whether a near-physiological motion pattern can be achieved or not. As it is a rumor but not scientifically proven that prosthesis design has no influence on clinical outcome, surgeons should only choose devices with flexible biomechanical properties for disc replacement.

Anterior bone loss after cervical Bryan disc arthroplasty: insight into the biomechanics following total disc replacement

BACKGROUND CONTEXT

Cervical disc arthroplasty (CDA) is an innovative procedure launched in the early 2000s. Compared with anterior cervical discectomy and fusion, many studies show that CDA offers equivalent clinical outcomes while reducing secondary procedures and total cost.

PURPOSE

We sought to determine the incidence of anterior bone loss after CDA and the related biomechanical effects.

STUDY DESIGN/ SETTING

Retrospective chart review.

PATIENT SAMPLE

Patients who underwent CDA with one level Bryan Disc (Medtronic SofamorDanek, Memphis, TN, USA) at one institution.

OUTCOME MEASURES

Radiological measurements, including the extent of anterior bone loss, global alignment angle, shell angle, lordotic angle, mean degree of angle of the endplate with the horizontal line, global range of motion (ROM) and ROM of the index level were recorded. The grading of anterior bone loss of the index level was defined as Grade 0, no remodeling; Grade 1, spur disappearance or mild change in body contour; Grade 2, obvious bone regression with Bryan Disc exposure.

METHODS

Anatomical measures and ROM were compared by grade of bone loss.

RESULTS

Of the 121 patients included in the study, anterior bone loss was found in 53 (43.8%) on the upper adjacent level and 54 (44.6%) on the lower adjacent level. Twenty-nine patients (23.9%) had anterior bone loss in both levels. The majority of cases had Grade 1 anterior bone loss. Grade 2 bone loss was noted in the upper adjacent vertebra in only 5 patients and in 4 patients in the lower adjacent vertebra. Age, sex, operative level, and hybrid surgery had no effect on anterior bone loss. Most radiological assessments, including global alignment angle, lordotic angle, mean degree of angle of the endplate with the horizontal line, global ROM, and ROM of the index level, showed no correlation to anterior bone loss. Shell angle was found to be different in groups with or without remodeling in the upper adjacent level: 5.0 degreesin the Grade 0 group and 7.0 degrees in the Grade 1-2 group, p<.05.

CONCLUSIONS

Many more patients than predicted had anterior bone loss. Increasing the shell angle of the artificial disc may increase the incidence of anterior bone loss after CDA. Further study of the biomechanics following CDA should help clarify the mechanisms at work.

Iatrogenic biological fracture of the cervical spine during gradual halo traction for kyphotic deformity correction: case report

Background

Severe kyphotic deformities carry high risk for neurological injuries as osteotomies are often required for correction. Surgeons often utilize a staged approach for dealing with these conditions starting with a period of halo traction to stretch tight soft tissues and partially correct the deformity, followed by surgery. Halo traction is a relatively safe procedure and complications are uncommon. We report a unique case of iatrogenic fracture of the cervical spine during gradual halo traction for deformity correction of a severe cervical kyphosis.

Case presentation

An 80-year-old female with previous cervical spine tuberculosis infection and C5-C6 anterior spinal fusion developed severe cervical kyphosis of 64° from C2-C6 and neck pain requiring deformity correction surgery. Gradual increase in traction weight was applied, aiming for a maximum traction weight of 45 pounds or half body weight. During the 1st stage halo-gravity traction, sudden neck pain and a loud cracking sound was witnessed during increase of the traction weight to 14 pounds. Imaging revealed a fracture through the C4 and reduction in kyphosis deformity to 11° from C2-C6. There was no neurological deficit. No further traction was applied and the patient underwent an in-situ occipital to T3 fusion without osteotomies. At 3-year follow-up, the patient was symptom-free and radiographs showed solid fusion and maintenance of alignment.

Conclusions

Iatrogenic fracture may occur with halo traction. Elderly patients with osteoporotic and diseased bone should be closely monitored during the treatment. A fracture without complications was a fortunate complication as the patient was able to avoid any high-risk osteotomies for deformity correction.

Level of evidence

IV

Clinical Relevance of Cervical Kinematic Quality Parameters in Planar Movement

Comprehending cervical spinal motion underlies the understanding of the mechanisms of cervical disorders. We aimed to better define the clinical relevance of cervical spine kinematics, focusing on quality parameters describing cervical spine planar motion. The most common study focuses were kinematic quality parameters after cervical arthroplasty and in normal subjects, patients with cervical degeneration, and patients with cervical deformities. Kinematic quality parameters are important for cervical degeneration prevention, being detected sooner than differences on imaging examinations and being significantly related to the degree of cervical degeneration. Kinematic quality parameters are effective for evaluating the changes of cervical motion pattern after cervical fusion and non‐fusion, assessing operative and adjacent segments in the early stages, and predicting adjacent segment degeneration. However, owing to current research limitations, and controversy about the changes of kinematic quality parameters after different surgical procedures, current assessments are limited to cervical spine flexion and extension. Different osteotomy methods of cervical deformity have different effects on cervical motion patterns and quality parameters. Choosing the most effective surgical method remains a challenge and kinematic quality parameters in cervical deformity are important future research topics. This review highlights the instantaneous center of rotation, the center of rotation, and the instantaneous axis of rotation as being important kinematic quality parameters of cervical spinal motion. These can be used to detect abnormal cervical mobility, to diagnose cervical degeneration, to design disc protheses, and to evaluate surgical effects earlier than other methods. Owing to limitations of research methods there is variation in the way parameters are defined by various researchers. No uniform standard exists for defining degenerative motion quality parameters in normal asymptomatic, degenerative, and postoperative patients. Therefore, further study is required. New study techniques and defining kinematic quality parameters in normal subjects will clarify the definitions of these parameters, enhancing their future clinical usefulness.

Characteristics of deformity surgery in patients with severe and rigid cervical kyphosis (CK): results of the CSRS-Europe multi-centre study project

INTRODUCTION AND PURPOSE

Little information exists on surgical characteristics, complications and outcomes with corrective surgery for rigid cervical kyphosis (CK). To collate the experience of international experts, the CSRS-Europe initiated an international multi-centre retrospective study.

METHODS

Included were patients at all ages with rigid CK. Surgical and patient specific characteristics, complications and outcomes were studied. Radiographic assessment included global and regional sagittal parameters. Cervical sagittal balance was stratified according to the CSRS-Europe classification of sagittal cervical balance (types A-D).

RESULTS

Eighty-eight patients with average age of 58 years were included. CK etiology was ankylosing spondlitis (n = 34), iatrogenic (n = 25), degenerative (n = 9), syndromatic (n = 6), neuromuscular (n = 4), traumatic (n = 5), and RA (n = 5). Blood loss averaged 957 ml and the osteotomy grade 4.CK-correction and blood loss increased with osteotomy grade (r = 0.4/0.6, p < .01). Patients with different preop sagittal balance types had different approaches, preop deformity parameters and postop alignment changes (e.g. C7-slope, C2-7 SVA, translation). Correction of the regional kyphosis angle (RKA) was average 34° (p < .01). CK-correction was increased in patients with osteoporosis and osteoporotic vertebrae (POV, p = .006). 22% of patients experienced a major long-term complication and 14% needed revision surgery. Patients with complications had larger preop RKA (p = .01), RKA-change (p = .005), and postop increase in distal junctional kyphosis angle (p = .02). The POV-Group more often experienced postop complications (p < .0001) and revision surgery (p = .02). Patients with revision surgery had a larger RKA-change (p = .003) and postop translation (p = .04). 21% of patients had a postop segmental motor deficit and the risk was elevated in the POV-Group (p = .001).

CONCLUSIONS

Preop patient specific, radiographic and surgical variables had a significant bearing on alignment changes, outcomes and complication occurrence in the treatment of rigid CK.

[Fixed cervical high-grade kyphosis : Chin-on-chest deformity-Treatment plan]

BACKGROUND

Surgical correction of severe and rigid cervical kyphosis with chin-on-chest deformity poses significant challenges to both the patient and surgeon once surgery is considered as the treatment of choice.

OBJECTIVES

This article presents the current concepts of corrective surgery for patients with severe and rigid cervical kyphosis.

MATERIAL AND METHODS

Narrative review and report of clinical experience.

RESULTS

The treatment of severe cervical kyphosis indicates a dedicated deformity assessment, the analysis of regional and global imbalance, the identification of spinal sagittal plane compensation mechanisms, detailed radiographic and clinical planning of corrective surgery, and the meticulous performance of surgical correction. Most recent large-scale studies serve as evidence for the benefit of surgical correction and outline the complications that need to be targeted during and after surgery.

CONCLUSION

Surgical correction of severe cervical kyphosis can be a pleasant and life-changing event for the disabled patient.

Osteotomies in ankylosing spondylitis: where, how many, and how much?

INTRODUCTION

This article presents the current concepts of correction of spinal deformity in ankylosing spondylitis (AS) patients. Untreated AS can be a debilitating disease. In a few patients, disease progression results in severe spinal deformity affecting not only the thoracolumbar, but also the cervical spine. Surgery for correction in AS patients has a long history. With the advent of modern instrumentation, standardization of surgical and anesthesiologic techniques, surgical safety and corrective results could be improved and experiences from lumbar osteotomies could be transferred to the cervical spine.

METHODS

This article presents the current concepts of correction of spinal deformity in AS patients. In particular, questions regarding the localization and number of osteotomies, the optimal surgical target angle as well as planning and prediction of postoperative alignment are discussed.

RESULTS

Insight into recent technical developments, current challenges with correction and geometric analysis of center of rotation (COR) in cervical 3-column osteotomies (3CO) will be presented.

CONCLUSION

The article should encourage readers to improve surgical correction efficacy and provide a better understanding of correction geometry in 3CO for thoracolumbar and cervical spinal deformities.

Correlation between cervical lordosis and adjacent segment pathology after anterior cervical spinal surgery

PURPOSE

To evaluate the incidence and risk factors for adjacent segment pathology (ASP) after anterior cervical spinal surgery.

METHODS

Fourteen patients (12 male, mean age 47.1 years) who underwent single-level cervical disk arthroplasty (CDA group) and 28 case-matched patients (24 male, mean age 53.6 years) who underwent single-level anterior cervical discectomy and fusion (ACDF group) were included. Presence of radiologic ASP (RASP) was based on observed changes in anterior osteophytes, disks, and calcification of the anterior longitudinal ligament on lateral radiographs.

RESULTS

The mean follow-up period was 43.4 months in the CDA group and 44.6 months in the ACDF group. At final follow-up, ASP was observed in 5 (35.7%) CDA patients and 16 (57.1%) ACDF patients (p = 0.272). The interval between surgery and ASP development was 33.8 months in the CDA group and 16.3 months in the ACDF group (p = 0.046). The ASP risk factor analysis indicated postoperative cervical angle at C3-7 being more lordotic in non-ASP patients in both groups. Restoration of lordosis occurred in the CDA group regardless of the presence of ASP, but heterotopic ossification development was associated with the presence of ASP in the CDA group. And the CDA group had significantly greater clinical improvements than those in the ACDF group when ASP was present.

CONCLUSION

In both CDA and ACDF patients, RASP developed, but CDA was associated with a delay in ASP development. A good clinical outcome was expected in CDA group, even when ASP developed. Restoration of cervical lordosis was an important factor in anterior cervical spine surgery.

Does sagittal position of the CTDR-related centre of rotation influence functional outcome? Prospective 2-year follow-up analysis

PURPOSE

Recent studies describe significant rates of heterotopic ossification (HO) after cervical total disc replacement (CTDR). Little is known about the reasons, and one aspect that requires further in vivo investigation is the biomechanical alteration after CTDR and the role of the implant-related centre of rotation (CORi) in particular. The role of the sagittal position of the CORi on functional outcome in two versions of a semi-constrained disc prosthesis with sagittally different CORi is the topic of this study.

METHODS

Patients were candidates for single-level CTDR between C3 and C7 who suffered from CDDD and received a standard or flat version of activ C™ (Aesculap AG, Tuttlingen). Clinical and radiographic assessments were determined preoperatively, intraoperatively, at discharge and again at 6 weeks, 6 months, 1 and 2 years. Radiographic examinations were performed independently using specialized quantitative motion analysis software.

RESULTS

Clinical outcome improved significantly regarding NDI as well as VAS on neck and arm pain with no differences in mean improvement by study group. Segmental angle measures show a significantly better lordotic alignment for both groups after surgery, but the degree of correction achieved is higher in the flat group. Correlation analysis proves that the more anterior the CORi is positioned, the higher the lordotic correction is achieved (Pearson rho -0.385). Segmental ROM decreased in the standard group but was maintained for flat implants. At present, our data do not demonstrate a correlation between CORi and ROM at 2 years. Two years after surgery, severe HO grade III-IV was present in 31.6 % standard and 13.1 % flat cases with significant differences. Grouping according to HO severity showed comparable sagittal positions of CORi for flat implants but a more posterior position in the severe HO group for standard implants.

CONCLUSIONS

Our results confirm the influence of CORi location on segmental alignment, kinematics and HO for a semi-constrained CTDR, but it also indicates a multifactorial process.