Clinical study to evaluate the safety and effectiveness of the Aesculap Activ-L? artificial disc in the treatment of degenerative disc disease

Background  

The objective of this clinical study is to evaluate the safety and effectiveness of the Activ-L Artificial Disc for treatment of single-level degenerative disc disease of the lumbar spine in patients who have been unresponsive to at least six months of prior conservative care. The hypothesis of the study is that the Activ-L Disc is non-inferior to the control (the Charité^? Artificial Disc [DePuy Spine] or ProDisc-L^? Total Disc Replacement [Synthes Spine]) with respect to the rate of individual subject success at 24 months. Individual subject success is a composite of effectiveness and safety.     

Complications of artificial disc replacement: a report of 27 patients with the SB Charité disc

Disc prosthesis surgery is rapidly becoming an option in treating patients with symptomatic degenerative disc disease. Only short-term and midterm results are described in the literature. Most operated patients belong to the age group of 30-50 years. In these active patients, complications can be expected to increase with longer follow-up, similar to total joint replacements in the extremities. Reported here is a series of 27 patients from another institution, who presented with unsatisfactory results or complications after SB Charité disc replacement. The objective of this work was to describe the possible short- and long-term unsatisfactory results of disc prosthesis surgery. Twenty-seven patients were seen in a tertiary university referral center with persisting back and leg complaints after having received a Charité disc prosthesis. All patients were operated on in a neighboring hospital. Most patients were operated on at the L4-L5 and /or the L5-S1 vertebral levels. The patients were evaluated with plain radiography, some with flexion-extension x-rays, and most of them with computed tomography scans. The group consisted of 15 women and 12 men. Their mean age was 40 years (range 30-67 years) at the time of operation. The patients presented to us a mean of 53 months (range 11-127 months) following disc replacement surgery. In two patients, an early removal of a prosthesis was required and in two patients a late removal. In 11 patients, a second spinal reconstructive salvage procedure was performed. Mean follow-up for 26 patients with mid- and long-term evaluation was 91 months (range 15-157 months). Early complications were the following: In one patient, an anterior luxation of the prosthesis after 1 week necessitated removal and cage insertion, which failed to unite. In another patient with prostheses at L4-L5 and L5-S1, the prosthesis at L5-S1 dislocated anteriorly after 3 months and was removed after 12 months. Abdominal wall hematoma occurred in four cases. Retrograde ejaculation with loss of libido was seen in one case and erection weakness in another case. A temporary benefit was experienced by 12 patients, while 14 patients reported no benefit at all. Main causes of persistent complaints were degeneration at another level in 14, subsidence of the prosthesis in 16, and facet joint arthrosis in 11. A combination of pathologies was often present. Slow anterior migration was present in two cases, with compression on the iliac vessels in one case. Polyethylene wear was obvious in one patient 12 years after operation. In eight cases, posterior fusion with pedicle screws was required. In two cases, the prosthesis was removed and the segment was circumferentially fused. These procedures resulted in suboptimal long-term results. In this relatively small group of patients operated on with a Charité disc prosthesis, most problems arose from degeneration of other lumbar discs, facet joint arthrosis at the same or other levels, and subsidence of the prosthesis. It is to be expected that many more patients will be seen with late problems some years after this operation as the survivorship will decrease with time.     

Does the thickness of the vertebral subchondral bone reflect the composition of the intervertebral disc?

Degeneration of the intervertebral disc, seen radiologically as loss of disc height, is often associated with apparent remodelling in the adjacent vertebral body. In contrast, maintenance or apparent increase in disc height is a common finding in osteoporosis, suggesting the properties of the intervertebral disc may be dependent on those of the vertebral body or vice versa. We have investigated this relationship by measuring the radiological thickness of the subchondral bone and comparing it to the chemical composition of the adjacent disc. Sagittal slabs were sampled from lumbar spines obtained at autopsy and X-rayed microfocally. The thickness of the subchondral bone was measured and correlated with the composition of the adjacent intervertebral disc. Eighty-three cadaveric endplates were studied from individuals aged 17–85 years. There was regional variation in thickness of the subchondral bone, being greater adjacent to the annulus than the nucleus, and the endplates cranial to the disc were thicker than those caudal. There was a positive correlation between the thickness of the subchondral bone and the proteoglycan content of the adjacent disc, particularly in the region of the nucleus. A weaker correlation was seen here between water content and thickness, whilst there was no significant correlation at the annulus or between the bone thickness and collagen content. The positive relationship between the radiographic thickness of vertebral subchondral bone and the proteoglycan content of the adjacent disc seen in human cadaveric material could be due to the bone responding to a greater hydrostatic pressure being exerted by discs with higher proteoglycan content than by those with less proteoglycan present. It is suggested that while this is true in normal specimens, the relationship becomes altered in disease states, possibly because of changes to the nutritional pathway of the disc, with resultant endplate-bone remodelling affecting the flow of solutes to and from the intervertebral disc.     

Biomechanics of the SB Charité lumbar intervertebral disc endoprosthesis

Summary The SB Charité intervertebral disc prostheses consist of two metal end-plates and an interposed polyethylene slide core. These were subjected to static and dynamic testing in a servohydraulic test rig. When embedded in polypropylene, the prostheses were found to function adequately under a high static load, and under a lighter dynamic load for a long time. When tested in a cadaveric vertebral segment, a large end-plate surface area proved to be of critical importance in preventing collapse of the prosthesis into the vertebral body.

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Résumé La prothèse des disques intervertébraux de type SB Charité est composée de deux plaques métalliques entre lesquelles est interposé un noyau élastique de polyéthylène. Elle a été soumise à des épreuves biomécaniques comportant des expériences statiques et dynamiques de compression. Les tests faits sur des prothèses encastrées dans du polypropylène ont démontré une fonction satisfaisante après des charges statiques élevées et après des épreuves dynamiques de longue durée. L'examen de prothèses implantées sur des rachis de cadavres a montré l'importance d'une surface étendue des plaques métalliques afin d'éviter leur encastrement à l'intérieur des corps vertébraux.

     

Prospective,randomized, multicenter Food and Drug Administration investigational device exemption study of lumbar total disc replacement with the CHARITÉ artificial disc versus lumbar fusion: Five-year follow-up

Background contextThe CHARITÉ artificial disc, a lumbar spinal arthroplasty device, was approved by the United States Food and Drug Administration in 2004 based on two-year safety and effectiveness data from a multicenter, prospective, randomized investigational device exemption (IDE) study. No long-term, randomized, prospective study on the CHARITÉ disc or any other artificial disc has been published to date.PurposeThe purpose of this study was to compare the safety and effectiveness at the five-year follow-up time point of lumbar total disc replacement using the CHARITÉ artificial disc (DePuy Spine, Raynham, MA) with that of anterior lumbar interbody fusion (ALIF) with BAK cages and iliac crest autograft, for the treatment of single-level degenerative disc disease from L4 to S1, unresponsive to nonoperative treatment.Study design/settingRandomized controlled trial—five-year follow-up.Patient sampleNinety CHARITÉ patients and 43 BAK patients.Outcome measuresSelf-reported measures: visual analog scale (VAS); validated Oswestry disability index (ODI version 1.0); Short-Form 36 Questionnaire, and patient satisfaction. Physiologic measures: radiographic range of motion, disc height, and segmental translation. Functional measures: work status.MethodsOf the 375 subjects enrolled in the CHARITÉ IDE trial, 277 were eligible for the five-year study and 160 patients thereof completed the five-year follow-up. The completers included 133 randomized patients. Overall success was defined as improvement≥15 pts in ODI vs. baseline, no device failure, absence of major complications, and maintenance or improvement of neurological status. Additional clinical outcomes included an ODI questionnaire as well as VAS, SF-36, and patient satisfaction surveys. Work status was tracked for all patients. Safety assessments included occurrence and severity of adverse events and device failures. Radiographic analyses such as index- and adjacent-level range of motion, segmental translation, disc height, and longitudinal ossification were also carried out.ResultsOverall success was 57.8% in the CHARITÉ group vs. 51.2% in the BAK group (Blackwelder's test: p=0.0359, Δ=0.10). In addition, mean changes from baseline for ODI (CHARITÉ: ?24.0 pts vs. BAK: ?27.5 pts), VAS pain scores (CHARITÉ: ?38.7 vs. BAK: ?40.0), and SF-36 questionnaires (SF-36 Physical Component Scores [PCS]: CHARITÉ: 12.6 pts vs. BAK: 12.3 pts) were similar across groups. In patient satisfaction surveys, 78% of CHARITÉ patients were satisfied vs. 72% of BAK patients. A total of 65.6% patients in the CHARITÉ group vs. 46.5% patients in the BAK group were employed full-time. This difference was statistically significant (p=0.0403). Long-term disability was recorded for 8.0% of CHARITÉ patients and 20.9% of BAK patients, a difference that was also statistically significant (p=0.0441). Additional index-level surgery was performed in 7.7% of CHARITÉ patients and 16.3% of BAK patients.Radiographic findings included operative and adjacent-level range of motion (ROM), intervertebral disc height and segmental translation. At the five-year follow-up, the mean ROM at the index level was 6.0° for CHARITÉ patients and 1.0° for BAK patients. Changes in disc height were also similar for both CHARITÉ and BAK patients (0.7 mm for both groups, p=0.9827). Segmental translation was 0.4 and 0.8 mm in patients implanted with CHARITÉ at L4–L5 vs. L5–S1, respectively, and 0.1 mm in BAK patients.ConclusionsThe results of this five-year, prospective, randomized multicenter study are consistent with the two-year reports of noninferiority of CHARITÉ artificial disc vs. ALIF with BAK and iliac crest autograft. No statistical differences were found in clinical outcomes between groups. In addition, CHARITÉ patients reached a statistically greater rate of part- and full-time employment and a statistically lower rate of long-term disability, compared with BAK patients. Radiographically, the ROMs at index- and adjacent levels were not statistically different from those observed at two-years postsurgery.     

Does long-term compressive loading on the intervertebral disc cause degeneration?

STUDY DESIGN: Coil springs were stretched and attached to produce a compressive force across the lumbar intervertebral discs of dogs for up to 53 weeks. OBJECTIVE: To test the hypothesis that compressive forces applied to the intervertebral disc for a long period of time cause disc degeneration in vivo in a dog model. SUMMARY OF BACKGROUND DATA: It is a commonly held belief that high forces applied to the intervertebral disc, and to joints in general, play a role in causing degeneration. METHODS: Coil springs were stretched and attached to produce a compressive force across the lumbar intervertebral discs (L3/L4) of 12 dogs. After up to a year, the dogs were killed, and their lumbar spines were removed and radiographed. The L3/L4 disc and the controls (T13/L1 and L4/L5) were excised and examined for visible signs of degeneration. The discs then were assessed using immunohistochemical analysis and enzyme-linked immunosorbent assay. Disc chondrocytes also were assayed for apoptosis. RESULTS: No obvious signs of degeneration in the discs (L3/L4) that had been under compression for up to a year could be observed. There was no disc bulging, anular fissures, or disc space narrowing. Some changes were observed at the microscopic level, although no thickening of the endplate was apparent. The enzyme-linked immunosorbent assay analysis provided significant data for all three regions of the disc (nucleus, inner anulus, and outer anulus). When comparing the compressed disc (L3/L4) with either of the control discs (T13/L1 and L4/L5), in the compressed disc: 1) the nucleus contained less proteoglycan and more collagen I and II; 2) the inner anulus contained less proteoglycan and collagen I; and 3) the outer anulus contained more proteoglycan and less collagen I. The collagen II differences for the inner and outer anulus were not significant. CONCLUSION: Compression applied to the lumbar intervertebral discs of dogs for up to a year does not produce degeneration in any visible form. It does produce microscopic changes and numerical changes, however, in the amounts of proteoglycan and collagen in the nucleus, inner anulus, and outer anulus. The present results add no credence to the commonly held belief that high compressive forces play a causative role in disc degeneration.     

Overview of disc arthroplasty—past, present and future

Degenerative disc disease is one of the most frequent spinal disorders. The anatomy and the biomechanics of the intervertebral disc are very complex, and the pathomechanics of its degeneration are poorly understood. Despite this complexity and uncertainty, great advances have been made in the field of disc replacement technology, with promising results. Difficulties are continuously being encountered, but careful analysis of the results and intensive research and development will assist in countering these problems. There are approximately 40 clinical reports in the literature describing various aspects of randomised controlled trials involving intervertebral disc arthroplasty. However, the majority of these publications do not provide reliable information, in that they give only interim results and/or the results from just one of the many centres in multicentre studies. Such publications must be interpreted with caution, since they do not always represent the results of the whole study population and may hence be underpowered. We identified six randomised controlled trials that compared the final clinical outcomes of disc arthroplasty and spinal fusion. The present systematic review attempts to give an overview of the current status of disc arthroplasty.     

Are there differences in the symptoms, signs and outcome after lumbar disc surgery in the elderly compared with younger patients?

Age is claimed by several authors to be a predictor of bad outcome after lumbar disc surgery. The aim of this study is to evaluate the influence of the patients age on preoperative symptoms and the outcome. General data, symptoms, signs and neurological findings of 219 patients were recorded preoperatively Ninety-two per cent of the patients received a follow-up examination by an independent investigator after a mean of 298 days. All patients older than 59 years were defined as belonging to the group of elderly patients (n = 30). The other patients were defined as the younger group (n = 189). The outcome was measured by a visual analogue rating scale. Outcome was not statistically different in both groups. In our opinion, the indications for surgery for a lumbar disc herniation should be no different for older patients even though nerve root tension signs appear to be less marked in older patients.     

Gene expression of collagen types IX and X in the lumbar disc

To study gene expression of collagen typesIX and X in human lumbar intervertebral discs duringaing and degeneration and to explore the role of collagentypes IX and X in disc degeneration.     

Kyphosis one level above the cervical disc disease: is the kyphosis cause or effect?

If present, kyphotic angulation is generally at the level of the cervical disc disease (CDD) in the neck, but sometimes occurs at one level above the CDD. We name this situation as kyphosis one level above (KOLA). KOLA CDD has not been studied previously. In this study, we present 18 patients who had KOLA among 147 patients operated for CDD over a 5-year period. Seven of these 18 patients also received surgery for their KOLA. As new, surgical treatment of kyphotic level was performed with plating and without bony fusion in 5 patients. Clinical outcomes (according to Odom's criteria) and kyphotic corrections of KOLA patients receiving and not receiving surgery for their kyphosis during were compared. The 7 KOLA patients having surgery to correct the kyphosis had a mean 20.14+/-3.13 degrees correction in their kyphosis (from mean 12.85 to -7.28 degrees), whereas the 11 patients undergoing surgery only for CDD showed only a mean 3.00+/-2.52 degrees correction (from mean 7.45 to 4.45 degrees). When kyphotic corrections were compared, statistically significant difference was found between 2 groups (P<0.01). Clinical outcome scores showed a trend towards improvement in the patients operated upon for kyphosis correction. KOLA may be a factor in the development of cervical disc herniation and spondylosis, and should be treated if more than 11 degrees. In cervical region, upper adjacent level disease may be an extension of KOLA. Larger studies can further define the relationship between KOLA and CDD, and indications for surgical correction of KOLA.     

The influence of the interertebral disc on stress distribution of the thoracolumbar vertebrae under destructive load

Objectie:To compare the influence of normal and degenerative discs on stress distribution of the thoracolumbar vertebrae under destructive load,explore the biomechanical background and clinical meaning and provide theoretical basis for clinical diagnosis and treatment.Methods:A mechanical model of thoracolumbar motion segment of normal and degenerative discs was built with a three dimensional finite element method and three stresses of vertical compression,compressive flexion and distractive flexion were comparatively analyzed.Results:With vertical compression and compressive flexion loads,the thoracolumbar motion segment of the normal disc showed that the central part of the upper and lower end-plates of the vertebrae and the central part of the trabecular bone adjacent to the end-plate were lgaded with the most intensive stresses,meanwhile,the postero-lateral part of the annulus fibrosus was concentrated with stresses.Degeneratie disc showed that the stress distribution of the trabecular bone was relatively averaged,the stresses of the central part adjacent to the end-plate were low,while at the same time,the stresses of the peripheral part were elevated relatively.With distraction flexion load,the stresses of the cortex bone,trabecular bone,end-plate and annulus fibrosus of the thoracolumbar vertebrae of degenerative discs were low,neanwhile,the stresses of the posterior structure of the vertebral body were relatively elevated compared with that of normal discs.Conclusions:There is difference in influence between normal and degen erative discs on the stress distribution of the thoracolumbar vertebrae with destructive load.The transferring way of load is changed after disc degeneration.