INTRODUCTION. The elimination of motion and disc stress produced by spinal fusion may have potential consequences beyond the index level overloading the spinal motion segments and leading to the appearance of degenerative changes. So the “topping-off” technique is a new concept instructing dynamic fixation such as interspinous process device (IPD) for the purpose of avoiding adjacent segment disease (ASD) proximal to the fusion construct. MATERIALS AND METHODS. The study simulated spinal fusion in L4-L5, fusion combined DIAM in L3-L4. The ROM and maximum von Miss stresses were analyzed in flexion, extension, lateral bending, and torsion in response to hybrid method, compared to intact modeland fusion model. RESULTS. The investigation revealed that decreased ROM, intradiscal stress in implanted level but a considerable increase in stresses at more upper level (L2-L3) during flexion and extension in hybrid model, comparing with the fusion model. CONCLUSIONS. The raise of intradiscal pressure at the adjacent segment to a rigid fusion segment can be reduced when the rigid construct is augmented with an interspinous process device. However, the burden of stress over total spinal segments was still the same, the stress and ROM were just shift to supraadjacent levels

Anterior cervical discectomy and fusion for radiculopathy and myelopathy has the complication of the development of adjacent segment degeneration. Furthermore, reoperations may be required to treat complications of fusion, such as non-union, graft collapse, or expulsion. Cervical disc arthroplasty lays claim to preserving cervical motion and reducing the risks of adjacent segment disease in the treatment of cervical radiculopathy. We performed a prospective study in order to evaluate the radiological and clinical outcomes of cervical disc arthroplasty for single or two level disc disease with associated radiculopathy. Our study included a total of 26 patients. Each patient had cervical radiculopathy from nerve root compression due to degenerative disc disease at one or two levels. Diagnosis was made preoperatively on clinical examination and by means of MRI scanning. Each patient also had preoperative flexion and extension cervical spine x-rays in order to assess pre-operative range of neck movement. The outcomes of surgery were assessed prospectively. Range of motion at final follow-up was measured by flexion and extension view x-rays of the cervical spine. Clinical outcome was assessed by means of VAS scores for pain, SF12 for mental and physical health and the neck disability index (NDI). All complications were recorded. 14 of the patients had a follow-up for two years and the remaining 12 patients had a follow-up for one year. A Discovery disc arthoplasty by Scient'X was the implant used in all patients. A standard anterior cervical approach was used to achieve decompression and for the implantation of the prosthesis. On follow-up all patients had either maintenance or an improvement in the range of movement. There was no evidence of progression of degeneration in the segments adjacent to the arthroplasty prosthesis. Improvements in SF12, VAS, and NDI scores were seen from preoperative levels in 25 of the 26 patients. Complications included one patient with a horse voice post-operatively and one patient with minimal improvement of radicular symptoms. Post-operative MRI scanning demonstrated adequate decompression with this procedure and showed no evidence of progression of adjacent segment disease. There were no cases of implant subsidence or dislocations. We have found cervical disc arthroplasty to produce good clinical outcomes when used for single or two level cervical radiculopathy whilst maintaining neck motion with an acceptable complication rate. A longer follow-up is needed to further assess the risk of development of adjacent segment disease but we did not discover the development of adjacent segment disease in our study with a follow-up of upto 2 years

Neck pain can be caused by pressure on the spinal cord or nerve roots from bone or disc impingement. This can be treated by surgically decompressing the cervical spine, which involves excising the bone or disc that is impinging on the nerves or widening the spinal canal or neural foramen. Conventional practise is to fuse the adjacent intervertebral joint after surgery to prevent intervertebral motion and subsequent recompression of the spinal cord or nerve root. However fusion procedures cause physiological stress transfer to adjacent segments which may cause Adjacent Segment Degeneration (ASD), a rapid degeneration of the adjacent discs due to increased stress. ASD is more likely to occur in fusions of two or more levels than single level fusions and is more common where there is existing degeneration of the adjacent discs, which is not unusual in people over 30 years of age. Partial dynamic stabilisation, which generally involves a semi-rigid spinal fixation, allows a controlled amount of intervertebral motion (less than physiological, but more than fusion) to prevent increased stress on the adjacent segments (potentially preventing ASD) whilst still preventing neural recompression. Partial dynamic stabilisation is suitable for treating spinal instability after decompression as well as certain degenerative instabilities and chronic pain syndromes. Dynamic stabilisation and semi-rigid fixation systems for the spine are typically fixated posteriorly. However, choice of posterior surgical stabilisation techniques in the cervical spine is limited due to the size of the osseous material available for fixation and the close proximity of the neural structures and the vertebral artery. Posterior dynamic stabilisation systems for stabilisation of the lumbar spine often use the pedicle as an anchor point. Using the pedicle of the cervical spine as an anchor point is technically difficult because of its small size, angulation and proximity to neurovascular structures. Therefore, one of the main challenges to provide stabilisation in the cervical spine is the limitations of the anatomy. This presentation will introduce a novel spinal implant (patent pending) which is proposed for the cervical spine to provide partial dynamic stabilisation in the C3 to T1 region from a posterior approach. The implant is a single unit with a safe and technically simple insertion technique into the lateral masses. The implant uses a simple mechanism to allow limited intervertebral motion at each instrumented level. It is hoped that the simplicity of the device and removing the need to provide a bone graft anteriorly may reduce the cost of the procedure compared to traditional fusion and competing surgeries

Proximal junctional kyphosis (PJK) is defined as adjacent segment kyphosis >10° between the upper instrumented vertebrae and the vertebrae 2 levels above following scoliosis surgery. There are few studies investigating the predictors and clinical sequelae involved with this relatively common complication. Our purpose was to determine the radiographic predictors of post-op PJK and to examine the association between PJK and pain/HRQOL following surgery for AIS. The Post-Operative Recovery after Scoliosis Correction: Home Experience (PORSCHE) study was a prospective multicenter cohort of AIS patients undergoing spinal fusion surgery. Pre-op and minimum 2 year f/u scoliosis and sagittal spinopelvic parameters (thoracic kyphosis–TK, lordosis–LL, pelvic tilt-PT, sacral slope-SS, pelvic incidence-PI) were measured and compared to numeric rating scale for pain (NRS) score, SRS-30 HRQOL and to the presence or absence of PJK (proximal junctional angle >100). Continuous and categorical variables were assessed using logistic regression and binomial variables were compared to binomial outcomes using chi-square. 163 (137 females) patients from 8 Canadian centers met inclusion criteria. At final f/u, PJK was present in 27 patients (17%). Pre-op means for PJK vs No PJK: Age 14.1 vs 14.7yr; females 85 vs 86%; scoliosis 57±22 vs 62±15deg; TK 28±18 vs 19±16deg ∗, LL 62±11 vs 60±12deg, PT 8±12 vs 10±10deg, SS 39±8 vs 41±9deg, PI 47±14 vs 52±13deg, SVA −9±30 vs −7±31mm. Final f/u for PJK vs No PJK: Scoliosis 20±11 vs 18±8deg, final TK 26±12 vs 19±10deg∗, LL 60±11 vs 57±12deg, PT 9±12 vs 12±13deg, SS 39±9 vs 41±9deg, PI 48±17 vs 52±14deg, SVA −23±26 vs −9±32mm∗. Significant findings: Pre-op kyphosis >40deg has an odds ratio (OR) of 4.41 (1.50–12.92) for developing PJK∗. The presence of PJK was not associated with any significant differences in NRS or SRS-30. ∗denotes p<0.05. This prospective multicenter cohort of AIS patients demonstrated a 17% risk of developing PJK. Pre-op thoracic kyphosis >40deg was associated with the development of PJK; however, the presence of PJK was not associated with increased pain or decreased HRQOL

Cervical spinal arthrodesis is the standard of care for the treatment of spinal diseases induced neck pain. However, adjacent segment disease (ASD) is the primary postoperative complication, which draws great concerns. At present, controversy still exists for the etiology of ASD. Knowledge of cervical spinal loading pattern after cervical spinal arthrodesis is proposed to be the key to answer these questions. Musculoskeletal (MSK) multi-body dynamics (MBD) models have an opportunity to obtain spinal loading that is very difficult to directly measure in vivo. In present study, a previously validated cervical spine MSK MBD model was developed for simulating cervical spine after single-level anterior arthrodesis at C5-C6 disc level. In this cervical spine model, postoperative sagittal alignment and spine rhythms of each disc level, different from normal healthy subject, were both taken into account. Moreover, the biomechanical properties of facet joints of adjacent levels after anterior arthrodesis were modified according to the experimental results. Dynamic full range of motion (ROM) flexion/extension simulation was performed, where the motion data after arthrodesis was derived from published in-vivo kinematic observations. Meanwhile, the full ROM flexion/extension of normal subject was also simulated by the generic cervical spine model for comparative purpose. The intervertebral compressive and shear forces and loading-sharing distribution (the proportions of intervertebral compressive and shear force and facet joint force) at adjacent levels (C3-C4, C4-C5 and C6-C7 disc levels) were then predicted. By comparison, arthrodesis led to a significant increase of adjacent intervertebral compressive force during the head extension movement. Postoperative intervertebral compressive forces at adjacent levels increased by approximate 20% at the later stage of the head extension movement. However, there was no obvious alteration in adjacent intervertebral compressive force, during the head flexion movement. For the intervertebral shear forces in the anterior-posterior direction, no significant differences were found between the arthrodesis subject and normal subject, during the head flexion/extension movement. Meanwhile, cervical spinal loading-sharing distribution after anterior arthrodesis was altered compared with the normal subject's distribution, during the head extension movement. In the postoperative loading-sharing distribution, the percentage of intervertebral disc forces was further increased as the motion angle increased, compared with normal subject. In conclusion, cervical spinal loading after anterior arthrodesis was significantly increased at adjacent levels, during the head extension movement. Cervical spine musculoskeletal MBD model provides an attempt to comprehend postoperative ASD after anterior arthrodesis from a biomechanical perspective

Intervertebral disc (IVD) degeneration plays a major role in low back pain which is the leading cause of disability. Current treatments in severe cases require surgical intervention often leading to adjacent segment degeneration. Injectable hydrogels have received much attention in recent years as scaffolds for seeding cells to replenish disc cellularity and restore disc properties and function. However, they generally present poor mechanical properties. In this study, we investigated several novel thermosensitive chitosan hydrogels for their ability to mimic the mechanical properties of the nucleus pulposus (NP) while being able to sustain the viability of NP cells, and retain proteoglycans. CH hydrogels were prepared by mixing the acidic chitosan solution (2% w/v) with various combinations of three gelling agents: sodium hydrogen carbonate (SHC) and/or beta-glycerophosphate (BGP) and/or phosphate buffer (PB) (either BGP0.4M, SHC0.075M-BGP0.1M, SHC0.075M-PB0.02M or SHC0.075M-PB0.04M). The gelation speed was assessed by following rheological properties within 1h at 37°C (strain 5% and 1Hz). The mechanical properties were characterized and compared with that of human NP tissues. Elastic properties of the hydrogels were studied by evaluating the secant modulus in unconfined compression. Equilibrium modulus was also measured, using an incremental stress-relaxation test 24h after gelation in unconfined compression (5% strain at 5%/s followed by 5min relaxation, five steps). Cells from bovine IVD were encapsulated in CH-based gels and maintained in culture for 14 days. Cytocompatibility was assessed by measuring cell viability, metabolism and DNA content. Glycosaminoglycan (GAG) synthesis (retained in the gel and released) was determined using DMMB assay. Finally injectability was tested using human cadaveric discs. Unconfined compression confirmed drastically enhanced mechanical properties compared to conventional CH-BGP hydrogels (secant Young modulus of 105 kPa for SHC0.075PB0.02 versus 3–6 kPa for BGP0.04). More importantly, SHC0.075PB0.02 and SHC0.075BGP0.1 hydrogels exhibited mechanical properties very similar to NP tissue. For instance, equilibrium modulus was 5.2±0.6 KPa for SHC0.075PB0.02 and 8±0.8 KPa for SHC0.075BGP0.1 compared to 6.1±1.7 KPa for human NP tissue. Rheological properties and gelation time (G′=G″ after less than 15 s at 37°C, and rapid increase of G') of these hydrogels also appear to be adapted to this application. Cell survival was greater than 80% in SHC0.075BGP0.1 and SHC0.075PB0.02 hydrogels. Cells encapsulated in the new formulations also showed significantly higher metabolic activity and DNA content after 14 days of incubation compared to cells encapsulated in BGP0.4 hydrogel. Cells encapsulated in SHC0.075BGP0.1 and SHC0.075PB0.02 produced significantly higher amounts of glycosaminoglycans (GAG) compared to cells encapsulated in SHC0.075PB0.04 and BGP0.4 hydrogels. The total amount of GAG was higher in SHC0.075BGP0.1 hydrogel compared to SHC0.075PB0.02. Interestingly, both the SHC0.075BGP0.1 and SHC0.075PB0.02 hydrogels retained similar amounts of GAG. Injectability through a 25G syringe, filling of nuclear clefts and good retention in human degenerated discs was demonstrated for SHC0.075PB0.02 hydrogel. SHC0.075BGP0.1 appears to be a particularly promising injectable scaffold for IVD repair by providing suitable structural environment for cell survival, ECM production and mechanical properties very similar to that of NP tissue

INTRODUCTION. Lumbar total disc replacement (TDR) is an alternative treatment to avoid fusion related adverse events, specifically adjacent segment disease. New generation of elastomeric non-articulating devices have been developed to more effectively replicate the shock absorption and flexural stiffness of native disc. This study reports 5 years clinical and radiographic outcomes, range of motion and position of the center of rotation after a viscoelastic TDR. Material and methods. This prospective observational cohort study included 61 consecutive patients with monosegmental TDR. We selected patients with intermediate functional activity according to Baecke score. Hybrid constructs had been excluded. Only cases with complete clinical and radiological follow-up at 3, 6, 12, 24 and 60 months were included. Mean age at the time of surgery was 42.8 +7.7 years-old (27–60) and mean BMI was 24.2 kg/m² +3.4 (18–33). TDR level was L5-S1 in 39 cases and L4-L5 in 22 cases. The clinical evaluation was based on Visual Analog Scale (VAS) for pain, Oswestry Disability Index (ODI) score, Short Form-36 (SF36) including physical component summary (PCS) and mental component summary (MCS) and General Health Questionnaire GHQ28. The radiological outcomes were range of motion and position of the center of rotation at the index and the adjacent levels and the adjacent disc height changes. Results. There was a significant improvement in VAS (3.3±2.5 versus 6.6±1.7, p<0.001), in ODI (20±17.9 versus 51.2±14.6, p<0.001), GHQ28 (52.6±15.5 versus 64.2±15.6, p<0.001), SF 36 PCS (58.8±4.8 versus 32.4±3.4, p<0.001) and SF 36 MCS(60.7±6 versus 42.3±3.4, p<0.001). Additional surgeries were performed in 5 cases. 3 additional procedures were initially planified in the surgical program: one adjacent L3-L5 ligamentoplasty above a L5S1 TDR and two L5S1 TDR cases had additional laminectomies. Fusion at the index level was secondary performed in 2 L4L5 TDR cases but the secondary posterior fusion did not bring improvement. In the 56 remaining patients none experienced facet joint pain. One patient with sacroiliac pain needed local injections. Radiological outcomes were studied on 56 cases (exclusion of 5 cases with additional surgeries). The mean location centers of the index level and adjacent discs were comparable to those previously published in asymptomatic patients. According to the definition of Ziegler, all of our cases remained grade 0 for disc height (within 25% of normal). Discussion. The silent block design of LP-ESP provides an interesting specificity. It could be the key factor that makes the difference regarding facets problems and instability reported with other implants experimentally or clinically. Unfortunately no other comparative TDR series are available yet in the literature. Conclusion. This series reports significant improvement in mid-term follow up after TDR which is consistent with previously published studies but with a lower rate of revision surgery and no adjacent level disease pathologies. The radiographic assessment of the patients demonstrated the quality of functional reconstruction of the lumbar spine after LP ESP viscoelastic disc replacement

Cervical total disc replacement has been in practice for years now as a viable alternative to cervical fusion in suitable cases, aspiring to preserve spinal motion and prevent adjacent segment disease. Reports are rife that neck pain emerges as an annoying feature in the early postoperative period. The facet joint appears to be the most likely source of pain. 50 patients were prospectively followed up through 5 years after having received disc replacement surgery, indicated for symptomatic soft disc herniation of the cervical spine presenting with radiculopathy. • All were skeletally mature and aged between 22 to 50. • All had failed a minimum of 6 months conservative therapy. • Up to 2 disc levels were addressed. C3 till C7 levels. • Single surgeon (first author). • NDI > 30% (15/50). • Deteriorating radicular neurology. We excluded those with degenerative trophic changes of the cervical spine, focal instability, trauma, osteoporosis, previous cervical spine surgery, previous infection, ossifying axial skeletal disease and inflammatory spondyloarthritides. The device used was an unconstrained implant with stabilizing teeth. Over the 5 years, we studied their postoperative comfort level via the Neck Disability Index (NDI) and Visual Analogue Score (VAS). Pre-operative and post-operative analysis of the sagittal axis and of involved facet joints were done. 22 patients suffered postoperative neck pain as reflected by the NDI and VAS scores. Of these, 10 reported of neck pain even 24 months after surgery. However, none were neurologically worse and all patients returned to their pre-morbid functions and were relieved of pain by 28 months. All 22 patients reported of rapid dissolution of neckache after peri-facetal injections of steroids were done under image guidance. We draw attention to the facet joint as the pain generator, triggered by inappropriate implant height, eccentric stresses via hybrid constructs, eccentric loading due to unconstrained devices and unaddressed Luschka joint degeneration. Such factors require careful selection of patients for surgery, necessitate proper pre-operative templating and call for appropriate technical solutions during surgery

PEEK rods construct has been proposed to allow better load sharing among spinal components when compared to the more traditional Titanium rods constructs. However, such proposal has largely derived from single-load in-vitro testing and the biomechanical differences between the two constructs when subjected to fatigue loading remain unknown. Current study comparatively analyzed the in-vitro biomechanical performance of PEEK and Titanium rod constructs as spinal implants through a 5 hour fatigue loading test. The disc height and intradiscal pressure of the instrumented and adjacent levels pre- and post-loading were recorded for analysis. The stress levels on the rods and bone stress near the screw-bone interface were also collected to investigate the likely failure rates of the two constructs. The results showed that the Titanium rods construct demonstrated a minimum amount of loss of disc height and intradiscal pressure at the instrumented level, however, a significant loss of the disc height and intradiscal pressure at adjacent levels compared to the intact spine were identified. In contrast, the disc height and intradiscal pressure of the PEEK rods were found to be comparable to those of the intact spine for all levels. The PEEK rods group also showed significantly less bone stress near the screw-bone interface compared to the Titanium rods group. Current study has demonstrated the potential benefits of the PEEK rods construct in reducing the risks of adjacent segment disease and implant failure rates when compared to the more traditional Titanium rods construct

Introduction. Recently ventral plating implants made of carbon/PEEK composite material have been developed with apparently superior material properties in terms of implant fatigue and imaging suitability. In this study we assessed the outcome of the first clinical application of this new implant. Methods. Retrospective, single-center case series of 16 consecutive patients between 2011 and 2013 undergoing ventral stabilization surgery with a new carbon plating system (see figure 1). We collected data in terms of safety of the procedure (screw positioning, blood loss, operation time), quality and reliability of the implant (revisions, dislocations, screw loosening, fusion, adjacent segment degeneration), clinical outcome and biological tolerance (cervical pain / discomfort, dysphagia). Results. All patients were available for clinical and radiological follow up. Mean surgery time was 128 minutes, in 11 cases one in 5 cases 2 segments were treated. The clinical findings and patient's satisfaction were good in 14 and fair in two cases. All patients who completed the 6 months control had a radiographically confirmed interbody fusion; no implant loosening or failure and no infections were observed. (see figure 2). There was one implant related complication (dysphagia due to malpositioning of the plate which was removed 4 days after implant insertion) and one complication related to the approach (Horner's syndrome). Conclusion. In this retrospective study of 16 patients we found that the use of a carbon-composite plating system lead to results comparable to the “gold standard” metal plates in terms of safety / clinical outcome and reliability of the implant. There was one revision due to dysphagia. The MR imaging of the patients who have been operated with the carbon/PEEK system showed superior quality with reduced artifacts and improved diagnostical properties, especially when evaluating the neurogical structures. (see figure 3). The overall clinical outcome and patient acceptance of the implant was good. The radiologic findings on follow up of 2, 6 and 12 months have shown a high fatigue strength with no signs of implant failure in terms of dislocation, loosening or breakage. Therefore we conclude that the use of the carbon/PEEK plating system is suitable for ventral stabilization in trauma and degenerative disease

INTRODUCTION. Several clinical studies demonstrated long-term adjacent-level effects after implantation of spinal fusion devices[1]. These effects have been reported as adjacent joint degeneration and the development of new symptoms correlating with adjacent segment degeneration[2] and the trend has therefore gone to motion preservation devices; however, these effects have not been understood very well and have not been investigated thoroughly[3]. The aim of this study is to investigate the effect of varying the stiffness of spinal fusion devices on the adjacent vertebral levels. Disc forces, moments and facet joint forces were analyzed. METHODS. The AnyBody Modeling System was used to compute the in-vivo muscle and joint reaction forces of a musculoskeletal model. The full body model used in this study consists of 188 muscle fascicles in the lumbar spine and more than 1000 individual muscle branches in total. The model has been proposed by de Zee et al.[3], validated by Rasmussen et al.[4] and by Galibarov et al.[5]. The new model[5] determines the individual motions between vertebrae based on the equilibrium between forces acting on the vertebrae from muscles and joints and the passive stiffness in disks and ligaments, figure 1a. An adult of 1.75 m and 75 kg with a spinal implant in L4L5 was modeled. This model was subjected to a flexion-extension motion using different elastic moduli to analyze and compare to a non-implanted scenario. The analyzed variables were vertebral motion, the disc reaction forces and moments, as well as facet joint forces in the treated and the adjacent levels: L2L3, L3L4, L4L5 and L5-Sacrum. RESULTS. When introducing a spinal fusion device in the L4L5 joint the reaction forces and moments decreased in this joint with stiffer devices leading to lower joint loads. However, in the adjacent joints, L3L4 and L5Sacrum, an increase was observed when implanting stiffer devices. Similar trends could be found for the L2L3 joint. The loads in the facet joints showed the same trends. While introducing a spinal fusion device reduced the facet joint forces in the treated joint, the loads in the adjacent facet joints were increased according to the stiffness of the implanted device, figure 1b. DISCUSSION. While the treated disc joint showed reduced motion and loads, the adjacent levels demonstrated a significant increase. In particular, the increased facet joint forces in the adjacent levels can lead to adjacent level facet pain or accelerated facet joint degeneration. Introducing a device resulted in preventing facet contact and therefore facet joint loads, even using the device with the lowest stiffness. CONCLUSION. The presented model shows that clinical complications such as facet joint degeneration in adjacent levels after implantation of spinal fusion device are consistent with the change in the mechanical-stimulus distribution in the system

The emerging of non-fusion surgery is aimed to solve the long-term complication of fusion surgery that may bring the adjacent disc degeneration. Among several kinds of artificial discs developed in these years, the majority in the market is Prodisc-L (Synthes Inc.) which is designed with the purpose to restore the motions including anteroposterior translation, lateral bending, and axial rotation. These is also one artificial disc called Physio-L (Nexgen Spine) which were hyper-elastic material (Polycarbonate Polyurethanes) and is designed to restore the motions maintioned above plus axial loading. The concept of using hyper-elastic material as disc is to mimic the material properties of intervetebral discs so that this disc both absorb the axial loading and also restore the physiological range of motion. Few studies focused on the biomechanical behavior of hyper-elastic artificial discs have yet been reported. Therefore, the purpose of this study is to compare the biomechanical behavior between Prodisc-L and Physio-L. A validated three-dimensional finite element model of the L1-L5 lumbar intact spine was used in this study with ANSYS software [Fig.1]. Total disc replacement surgery, partial discectomy, total nuclectomy and removal of the anterior longitudinal ligament were performed at the L3/L4 segment of this intact model, and the Prodisc-L and Physio-L was implanted into L3/L4 segment, respectively. In addition, hyper-elastic materials adopted by Physio-L are usually categorized by their hardness into soft and hard [Fig.2]. Therefore, two kinds of Physio-L were studied. A 400 N follower load and a 10 N-m moment were applied to the intact model to obtain four physiological motions as comparison baseline. The implanted models were subjected to 400 N follower load and specific moments in accordance with the hybrid test method. For the Prodisc-L model in the surgical segment, the range of motion (ROM) varied by -26%, +17%, -0.01%, and -0.04% in flexion, extension, lateral bending, and axial rotation, respectively, as compared to intact model [Fig.3]. For the Physio-L (soft) model, ROM varied by +10%, +8%, +3%, and +19% in four physiological motions, respectively. For the physio-L (hard) model, ROM varied by +1%, +8%, +1%, and +11% in four physiological motions, respectively. For the Prodisc-L model in the adjacent segments, ROM varied by +4% ∼ +10%, -2% ∼ -5%, -1% ∼ -4%, and +1% ∼ -2% in four physiological motions, respectively. For the Physio-L (soft) model, ROM varied by 0% ∼ -5%, -2% ∼ -5%, -0% ∼ -5%, and -9% ∼ -11% in four physiological motions, respectively. For the physio-L (hard) model, ROM varied by +4% ∼ -2%, +8% ∼ -5%, +1 ∼ -5%, and +11% ∼ -6% in four physiological motions, respectively. As seemed in the simulation, the behavior of Physio-L (both soft and hard) is similar to that of intact model under flexion and extension, but not in axial rotation. In addition, Physio-L (hard) model is more similar to intact model as compared to Physio-L (soft) model

Introduction. The majority of spine patients present with discogenic low back pain, originating from either degenerative disc disease (DDD) or internal disc disruption (IDD). Successful treatment of this patient population relies on obtaining precision diagnosis and careful patient selection, as well as matching the pathology with reliable technology. Total disc replacement (TDR), as an alternative to spinal fusion in the treatment of DDD or IDD, has been studied and reported for several decades in long-term follow-up studies and in several randomized control trials. This prospective study presents a single surgeon experience with two-level CHARITÉ® TDR in 84 consecutive patients, with minimum follow-up of 5 years. The aims of the study were to assess the clinical outcomes of two-level TDR in patients with DDD/IDD. Based on the literature review conducted, this study is considered the largest single surgeon series experience with the two-level CHARITÉ® TDR in the treatment of lumbar DDD, with a minimum follow-up of 5 years reported to date. Materials and Methods. Between January 1997 and March 2006, n=84 consecutive patients underwent two-level TDR for the treatment of two-level DDD or IDD discogenic axial low back pain with or without radicular pain. All patients completed self-assessment outcome questionnaires pre and postoperatively (3, 6, 12 months, and yearly thereafter), including Oswestry Disability Index (ODI), Roland-Morris Disability Questionnaire (RMDQ) and Visual Analogue Score (VAS) for back and leg pain. Results. For the n=84 patients, the mean follow-up was 94.34±2.19 months (range = 62–150). The mean age was 49.6±0.94. The mean surgical time was 91±3.16 minutes and the mean blood loss was 207.5±30.62 mls. The main diagnosis was two-level DDD in 63 (76.8%) patients, followed by one-level disc herniation and one-level DDD. Seventy-three (89%) patients underwent L4-5 L5-S1 TDR and 9 (11%) patients underwent L3-4 L4-5 TDR. At all follow-up points, patients demonstrated significant improvement in ODI, RMDQ, and VAS back and leg pain scores compared to pre-operative scores (p < 0.001). The mean improvement between pre-op and last follow-up was 33.3 (66.8%) and 13.23 (74%) for ODI and RMDQ, respectively. Similarly, that was 54.8 (69 %%) and 34.8 (65%) for VAS back and VAS leg pain, respectively. At least 87.8% of the patients rated their satisfaction as good/excellent at any follow-up point. At 5 years follow-up, 54 patients (65.9%) rated their satisfaction as excellent, 19 (23.2%) as good, 7 (8.5%) as satisfactory and 2 (2.4%) as poor. Two patients (2 out of 84, 2.38%) required early revision of one of the prostheses due to failure of indication and/or failure of technique. There has been no device failure. One patient required surgery for adjacent segment disease (1.19%). Conclusion. This study has shown that statistically significant reductions in pain and functional outcomes can be obtained in patients at a minimum follow-up of 5-years following 2-level TDR for the treatment of multilevel DDD or IDD. The clinical benefits of this procedure is supported by the data, with the outcomes reflecting a precision diagnosis, stringent patient selection criteria, and a standardised surgical technique

INTRODUCTION:. As a consequence from cervical arthroplasty, spine structural stiffness, loading and kinematics are changed, resulting in issues like adjacent segment degeneration and altered range of motion. However, complex anatomical structures and lack of adequate precision to study the facet joint (FJ) segmental motion in 3D have prevented proper quantitative analyses. In the current study, we investigate the innovative use of a local coordinate system on the surface of the superior articular process of the caudal vertebral body in order to analyze FJ segmental motion using CT-based 3D vertebral models in flexion/extension. METHODS:. CT images were obtained from six patients (2F/4M, mean age: 53 y.o.) with cervical degenerative disc disease in neutral, flexion and extension positions. CT data was used to create subject-specific surface mesh models of each vertebral body. From these, mean normal vectors were calculated for all FJ surfaces and posterior walls from C3/4 down to C6/7 (Fig. 1). The global coordinate system (x, y, z) corresponds to the CT scanner. Within this system, a new local coordinate system (u, v, w) was set on the centroid of each FJ surface (Fig. 1), where the u-, v-, and w- axes correspond to the normal-to-the-FJ, right-left and cranio-caudal directions, respectively. In flexion/extension, translations in mm were calculated as differences in the FJ centroid position and rotations were calculated in degrees as angular differences of the vector of the opposing surface in flexion/extension. Results are presented as mean ± SD. Differences within vertebral levels and left/right FJs were sought using 1- or 2-way ANOVA, respectively. RESULTS:. The flexion/extension segmental motion was described in its six degrees-of-freedom. Among the three translations, the largest movement was observed in the cranio-caudal direction (u = −0.22 ± 0.47 mm, v = 0.11 ± 0.89 mm, w = −2.06 ± 1.60 mm); while the three rotations about the (u, v, w) axes showed a dominant rotation about the v-axis (u = −0.41 ± 4.42°, v = −5.12 ± 5.61°, w = −0.01 ± 2.71°). Comparing translational and rotational motions by cervical level, movements at C6/7 were shown to be smaller than those at the other levels (p < 0.05) (Figs. 2, 3). There were no significant differences in the movement of the FJ between left and right sides (p > 0.05). DISCUSSION:. A key finding of this study was that along with the expected translation in the w-axis, there was rotation about the v-axis consistent with the overall neck flexion-to-extension motion. If the rotation about the v-axes were negligible, the FJ motion could be considered as a pure translation (sliding), but the data suggests otherwise. This finding supports the hypothesis of a rolling-sliding type of facet segmental motion that might be influenced by the facet surface curvature. Future studies will focus on analyses of the changes in FJ gap with motion and characterization of the facet surfaces' curvature and congruence. SIGNIFICANCE: An innovative look into flexion/extension motion from the FJ point of view describes FJ segmental motion as a sliding-rolling motion instead of the traditional concept of sliding-only mechanism

Introduction. Anterior cervical decompression and fusion (ACDF) is considered a standard surgical treatment to degenerative discogenic diseases. Lately, the question arises whether or not ACDF significantly influences the progression of adjacent disc degeneration (ADD). The etiology of ADD is obscure and it has not been fully understood whether ADD is a consequence of fusion or it represents the aging pathway of the degenerative cervical process, thus making it a controversial topic [1-3]. There have been several discussions about the possibility of ACDF altering biomechanical conditions at adjacent segments, therefore resulting in increased load and excessive motion [3,4]. The purpose of this study was to compare the cervical segmental motion pre- and post-ACDF using novel 3D analytical techniques. Methods. Nine patients (2F/7M, mean age: 54.1 years, range 36–76 y.o.) underwent ACDF due to symptomatic cervical degenerative discogenic disease. One-level ACDF was performed in 4 patients, whereas 2-level ACDF was done in five, using cylindrical titanium porous cage implants. Pre- and post (postoperative periods ranged from 11-months, 25 days to 12-months, 22 days, mean postoperative period: 12.09 months) surgery, dynamic-CT examinations were conducted in neutral, flexion and extension positions. Subject-based 3D CT models were created for segmental motion analysis (Fig. 1). Six-degrees-of-freedom 3D segmental movements were analyzed using a validated Volume-Merge methods (accuracy: 0.1 mm in translation, 0.2°in rotation) [5]. The segmental translation was evaluated by the segmental translations of gravity centers of endplates (Fig. 2). Disc-height distribution was measured using a custom-written Visual C++ routine implementing a lease-distance calculation algorithm. The mean translation distance was calculated for the each adjacent level (Fig. 2). Differences of segmental motions and mean disc height between pre- and post-surgery at each level were compared by the Wilcoxon signed rank test. Results were presented mean±SEM. Results. Regarding the fusion level, the data shows decreases in both the flexion/extension (F/E) angular range of motion (ROM) (7.46±1.17°preoperatively vs. 3.14±0.56°post-operatively, p<0.003) and the segmental translation in the anterior/posterior direction (AP translation) after surgery (1.22±0.20 mm pre-operatively and 0.32±0.11 mm post-operatively, p<0.01). For the adjacent levels category (inferior and superior combined), the E/F angular ROM was larger after surgery (6.74±1.22°pre-operatively vs. 8.48±0.56°post-operatively, p<0.03). The lateral and axial rotational angular ranges of motion pre- and post-surgery did not show any statistically differences at the adjacent levels. The AP translation at the adjacent levels did not change after surgery (1.22±0.26 mm pre-operatively and 1.45±0.29 mm post-operatively). Translations in lateral and cranio-caudal directions also did not show change following surgery. The mean disc height in the adjacent level (2.39±0.14 mm) showed no differences with respect to the post-surgical measurements (2.40±0.19 mm). Conclusions. The use of a high-accuracy in vivo 3D kinematic analysis method enabled the detection of subtle changes in segmental movement between pre- and post-ACDF conditions. The result of the current study showed increased segmental movements in F/E angles at the adjacent level. These results are consistent with the some previous studies in the literature [4,6-11]. The magnitude of the increased movement, however, was only 1.74°from full-full-flexion to full-extension and no increase was found in AP translation. No disc height loss associated with disc degeneration was observed during a 1-year period after ACDF. Longer follow-up studies with larger patient cohorts will be required to investigate whether the increased F/E angle at the adjacent level effectively causes symptomatic ADD