Introduction This is a prospective, consecutive series of 178 prosthetic implantations to analyse single level versus multiple level cervical arthroplasty with two years minimum follow-up

Methods Fifty-five patients underwent a total of fifty-five Porous Coated Motion (PCM) cervical arthroplasties from C3–4 to C7–T1 (Group S for single level). Fifty-four patients underwent one hundred and nine multilevel PCM cervical arthroplasties (Group M for multilevel) during the same time interval, for the same indications, performed by the same surgeons under the same clinical protocol— double level, 43 cases; three levels, 7 cases: and four levels, 4 cases. Sixteen PCM cases had been performed as complex revision procedures with prior fusions—9 in Group S and 7 in Group M. They included 1 previous Bryan Disc, 1 cage-plate, 1 patient with Klippel-Feil disease, 3 patients had failed lordotic cervical cages. One additional patient in Group M had a fracture-dislocation at C4–5 with a pseudarthrosis at C3–4 and C5–6. The demographics between Group S and Group M were very similar—mean age of patients, gender, severity of neurologic symptoms and distribution of radicular and myeloradicular symptoms.

Results There were no deaths, no infections, and no instances of iatrogenic neurologic progression in either the single level or the multiple level arthroplasty group. The mean EBL, length of surgery, and length of hospital stay were greater for the Multilevel Group. In contrast to these three operative demographic statistics, the self assessment outcomes instruments consistently showed more improvement for the multilevel cases. The mean improvement in the NDI for the single cases was 54.8 % (+/− 20.9) versus the multilevel cases mean improvement in NDI was 64.8 % (+/− 33.7). The mean improvement in the VAS showed the same relationship—single level mean improvement 62.0 % (26.9) versus the multilevel cases mean VAS improvement was 68.1% (+/− 31.4). The SF-36, Odoms, and TIGT were also more improved for the multilevel versus the single level group. The reoperation rates, adverse events, and incidence of complications were the same between the single level to the multilevel arthroplasty groups.

Discussion This prospective report of cervical arthroplasty demonstrates that each cervical vertebral level is biomechanically independent of the adjacent level, whether it contains an arthoplasty or an unoperated intervertebral disc. With the Porous Coated Motion cervical arthroplasty the incidence of reoperation did not increase proportionately higher as the number of cervical levels requiring instrumentation increased. Even in three and four level arthroplasty the true benefits of cervical disk replacement outcomes were demonstrated on functional clinical outcomes at minimum two-year follow-up

Introduction Adjacent segment disease with radiculopathy and neurologic deficit adjacent to a non-mobile spinal segment is the ideal application for cervical arthroplasty. Not only are the stresses and loads increased but unfortunately the previously fused segment is further compromised by being fixed in a kyphotic position.

Methods This is a prospective study of 40 PCM prostheses inserted in thirty patients with 50 adjacent segments previously fused or rendered immobile—ten cases were performed as bi-level implantations. The inclusion and exclusion criteria were otherwise identical to the normal FDA prospective IDE criteria with all patients presenting with radiculopathy and a corresponding neurologic deficit confirmed by an MRI compressive lesion.

Results The mean preoperative cervical lordosis was 2.65 degrees (−32 to 25), mean postoperative lordosis 12.3 degrees (−17 to 30), and the mean improvement was 9.4 degrees of cervical lordosis (range (−15 to 23). EBL = 0 to 100 cc with no patients requiring blood transfusions, Length of surgery = mean 104 minutes (60 to 150) and the length of hospital stay = mean 1.17 days (0 to 3 days). The clinical follow-up was greater than 2 years. All patients were neurologically intact at follow up with a mean improvement of NDI = 50 % and mean improvement in VAS = 58.3 %.The range of flexion and extension motion at the level of the prosthesis was a mean of 8.9 degrees (range 4 to 20 degrees).

Discussion Naturally, the adjacent segment application of a cervical disc replacement is a challenging clinical environment for cervical arthroplasty – by definition every case had prior surgery. Not only is the cervical spine position often compromised by being in excessive kyphosis, but seventeen of the 50 previously fused levels had prior cervical instrumentation. 5 patients had previous cervical cages, 2 had cage-plates, 5 patients had previous anterior cervical plates, one had a prior arthroplasty device with HO, and 4 patients had PMMA which required revision. Despite the complicated nature of the presenting pathology, the Porous Coated Motion Cervical prosthesis successfully restored some element of cervical lordosis, and restored stability to the cervical segments. An added potential bonus is the preserved 9.4 degrees of flexion – extension mobility. The PCM appeared to work well in these revision cases. This is the world’s largest study to date investigating prospectively the value of cervical arthroplasty in adjacent segment disease.

Introduction This is the largest analysis to date of any retrieved porous ingrowth disk replacement prostheses. In distinction to prior reports of retrieved implants which were conducted like “airplane crash” type pseudoanalyses, in this series the position of the components was known in vivo prior to implant removal. The digitized radiographs were used to determine if the components were in ideal, suboptimal, or poor position. There were thirty cervical disk replacements and thirty-eight lumbar disk replacements which comprised the basis of this analysis.

Methods Quantitative histomorphometry, microradiography, and histology were performed on all 68 vertebral endplates. Scanning electron microscopy was performed on ten. All 24 caprine model, 34 non-human primates, and 10 human explants with titanium calcium phosphate porous ingrowth surface were manufactured by the same vendor, D.O.T., which provides the same porous ingrowth coating for several FDA approved total hip replacements. Group I – Ideal placement, was defined as Charité or PCM Artificial Disc replacement within 3 mm of exact central axis in both the coronal planes and mid-sagittal planes (2 mm posterior to the midpoint of the vertebral body in the sagittal plane for Charité only).The endplates of the prosthesis also had to be within 5 degrees of angulation of the bony end-plate or within 5 degrees of angulation of the perpendicular axis of the vertebral body. Group II – Suboptimal placement, was defined as Charité or PCM Artificial Disc placement from 3 mm to 5 mm from exact central placement in at least one axis In addition the prosthetic endplate had to be from 5 degrees to 10 degrees of perpendicular vertebral body orientation. Group III – Poor placement, was defined as greater than 5 mm from exact central placement in at least one axis or the endplate was greater than 10 degrees off angle. Three separate observers judged the measurements of axes and made a determination of prosthesis placement after correction for magnification error.

Results The mean length of time in biologic conditions to monitor reabsorption and incorporation of the ingrowth surface was a mean of 10.5 months (range 6 to 33 months). This is the first study finding a correlation between the position of the components and amount of successful bony ingrowth. A representative group was: Ideal 50.9 +/− 13 % ingrowth, Suboptimal placement, 49.3 +/−18 % ingrowth, and Poor, 33.0 +/− 29.2 % ingrowth. There was trend but not statistically significant (F= 1.78, p = .186). The mean ingrowth of prostheses in poor and suboptimal position (defined by axis off by 3mm in either AP or Lateral plane) was 43.2 %. Whereas the mean ingrowth of prostheses inserted in “ideal position” within 3 mm of the optimal prosthesis axis in both planes was 46.4 %. The definition of successful biologic ingrowth in the extremities for total joint replacement is porous ingrowth over 30 %, which was achieved in 58 / 68 (85.3 %) of vertebral endplates.

Discussion The porous ingrowth TiCaP bioactive technology permits osseointegration despite non-ideal positioning. The surgeon’s technical shortcomings to place the prosthesis in ideal position were more than compensated for as 85.3 % of the components were successfully ingrown and biologically fixed to the vertebral trabeculae at the time of explantation. There were no cases of osteolysis or biomaterial failure encountered in this retrieval study.

Introduction This in-vitro biomechanical study was undertaken to compare the multi-directional flexibility kinematics of single versus multi-level lumbar Charité reconstructions and determine the optimal biomechanical method for surgical revision – posterior instrumentation alone or circumferential spinal arthrodesis.

Methods A total of seven human cadaveric lumbosacral spines (L1 to Sacrum) were utilized in this investigation and biomechanically evaluated under the following L4-L5 reconstruction conditions: 1) Intact Spine; 2) Diskectomy Alone, 3) Charité, 4) Charité + Pedicle Screws, 5) Two Level Charité (L4-S1), 6) Two Level Charité + Pedicle Screws (L4-S1), 7) Charité L4-L5 with Pedicle Screws and Femoral Ring Allograft (L5-S1) and 8) Pedicle Screws and Femoral Ring Allograft (L4-S1). Multi-directional flexibility testing utilized the Panjabi Hybrid Testing protocol, which includes pure moments for the intact condition with the overall spinal motion replicated under displacement control for subsequent reconstructions. Hence, changes in adjacent level kinematics can be obtained compared to pure moment testing strategies. Unconstrained intact moments of ±7Nm were used for axial rotation, flexion-extension and lateral bending testing, with quantification of the operative and adjacent level range of motion (ROM) and neutral zone (NZ). All data was normalized to the intact spine condition.

Results In axial rotation, single and two level Charité reconstructions produced significantly more motion than pedicle screw constructs combined with the Charité or femoral ring allograft (p< 0.05). There were no differences between the Charité augmented with pedicle screws or pedicle screws with femoral ring allograft (p> 0.05). Similar trends were observed under flexion-extension and lateral bending conditions with the Charité reconstructions demonstrating no significant differences compared to the intact spine (p> 0.05). However, the Charité combined with pedicle screws or pedicle screws with femoral ring allograft significantly reduced motion at the operative level compared to the Charité reconstruction (p< 0.05). The most pronounced changes in adjacent level kinematics were observed at the inferior level. The addition of pedicle screw fixation, in all cases, increased segmental motion at the inferior adjacent level (L5-S1) compared to the intact and Charité reconstruction groups (p< 0.05).

Discussion Single and two level total disc arthroplasty using the Charité device preserved segmental motion at the operative and adjacent levels compared to pedicle screw stabilization constructs. In terms of revision strategies, posterior pedicle screw reconstruction combined with an existing Charité is not statistically different from pedicle screws combined with femoral ring allograft. As we enter an era of total disc replacement and the impending necessity for surgical revision, the current study provides a biomechanical basis for posterior re-stabilization alone in lieu of combined anteroposterior revision.

Introduction The PCM cervical disc arthroplasty is an un-constrained system that stabilises the cervical spine after a discectomy and preserves the normal motion of the spine. The indications for cervical arthroplasty are the same as for anterior cervical decompression-radiculopathy or myelopathy caused by anterior cervical cord compression. The purpose of this study is to evaluate the clinical and radiological results after total anterior cervical disc replacement with PCM prosthesis.

Methods This is a prospective radiological and clinical study of patients who had undergone PCM total disc replacement with 27 months follow-up. Pain visual analog scale (VAS) and Oswestry disability index (ODI) were measured pre-operatively and at three monthly intervals out to 27 months post-operatively. Radiological images were also collected. All pain symptoms and the new neurological findings were noted.

Results Between December 2002 and February 2005 one hundred and fifteen patients underwent a total of 193 PCM arthroplasty to C3-C4 to C7-T1. Long-term clinical data on the PCM device are reported.

The neural decompression was a standard Smith-Robinson followed by a cervical arthroplasty. Eighteen PCM cases had been performed as complex revision procedures. Mean intra-operative blood loss was 113cc. Mean length of surgery was 80.7 minutes and the length of hospital stay ranged from out-patient to 3 days with 82% of patients discharged in less than 24 hours. Oswestry, VAS and Odom outcome showed significant improvements.

Discussion The PCM cervical arthroplasty appeared to be less invasive than alternative instrumented fusion procedures. The procedure allowed reconstruction of more unstable conditions than previously reported with disc replacement. Careful and appropriate patient selection is essential. Only after long-term follow-up will these early favorable results confirmed.

Introduction The current study was undertaken to investigate the biomechanical and biologic in-growth characteristics of the Porous Coated Motion™ cervical disc prosthesis following a six and twelve-month implant duration using an in-vivo caprine model.

Methods Twelve mature Nubian goats were divided into two groups based on post-operative survival periods of six (n=6) and twelve months (n=6). Using an anterior surgical approach, a complete diskectomy was performed at the C3-C4, followed by implantation of the Porous Coated Motion™ device. Functional outcomes of the disc prosthesis were based on computed tomography (CT), multi-directional flexibility testing, undecalcifed histology, histomorphometry and immunocytochemical analyses.

Results There was no evidence of prosthesis loosening, neurologic or vascular complications. CT scans demonstrated the ability to image and assess the cervical spinal canal for the presence of compressive pathology in the area of the CoCrMo prosthesis. Multi-directional flexibility testing indicated no differences in full range of intervertebral motion between the disc prosthesis and non-operative controls (n=7) under axial rotation or lateral bending conditions (p> 0.05). Flexion-extension produced significantly more motion for the intact spine compared to the cervical disc prosthesis (p< 0.05). Based on immunohistochemical and histologic analysis, there was no evidence of particulate debris, cytokines or cellular apoptosis within the local tissues overlying the operative site or systemic tissues. Moreover, review of the spinal cord at the operative levels indicated no evidence of cord lesions, inflammatory reaction, wear particles or significant pathologic changes in any treatment. Histomorphometric analysis at the metal-bone interface indicated the mean trabecular ingrowth of 40.5±24.4% at six-months and 58.65% ± 28.04 at twelve months.

Discussion All twelve goats undergoing cervical disc replacement had no evidence of implant loosening or inflammatory reactions from particulate wear debris. Segmental intervertebral motion was preserved based on multi-directional flexibility testing. The TiCaP porous ingrowth surface provided some immediate advantages for endplate osseointegration as there was no evidence of implant subluxation, despite immediate post-operative unrestricted cervical activity. Following cervical disc replacement, histological osseointegration at the implant-bone interface is possible, while preserving segmental motion.

Introduction Using a non-human primate model, the purpose of this in-vivo investigation was to evaluate the efficacy of porcine small intestine submucosa (PSIS) for anterior longitudinal ligament replacement and as an anti-adhesion barrier following total disc arthroplasty. Success criteria were based on post-mortem vascular adhesion tenacity scores, biomechanical, histological and immunohistochemical analyses.

Methods A total of ten mature male baboons (Papio cynocephalus) were included in the current study and followed for a period of six-months post-operatively. Each animal underwent an anterior transperitoneal approach followed by a total disc arthroplasty procedure at L5-L6 using one of the following treatments: (1) Charité Disc Prosthesis alone (n=5) or (2) Charité Disc Prosthesis + PSIS (n=5). Following anterior annular and anterior longitudinal ligament (ALL) resection, complete diskectomy and endplate decortication, the Charité Device (Size 1) was implanted according to the manufacturer’s specifications. The PSIS material (40mm x 30mm width) was secured across the operative site using surgical bone staples with the abluminal side oriented towards the bone. Post-mortem analysis included vascular adhesion tenacity scores (0–5), histopathology of the operative site ALL, non-destructive biomechanical testing and histomorphometry.

Results All animals survived the operative procedure and post-operative interval without significant intra- or peri-operative complication. Vascular adhesion tenacity scores were markedly lower for the PSIS treatments (14/25) versus the Charité alone (20/25) (p=0.057). Gross histopathological analysis demonstrated disorganized collagenous matrix anteriorly spanning the disc arthroplasty site in 4/5 (80%) of the PSIS specimens compared to 2/5 (40%) for the Charité alone treatments. Plain film radiographic analysis showed no lucencies or loosening of any prosthetic vertebral endplate. Multi-directional flexibility testing demonstrated increased range of motion for both treatment groups under axial rotation and decreased motion in lateral bending when compared to the intact spine condition (p< 0.05). The neutral zone values were significantly higher in axial rotation and flexion extension for the both treatments (p< 0.05), with no differences in lateral bending.

Discussion Using a non-human primate model, the current study investigated in-vivo response to PSIS following total disc arthroplasty. Surgical application of the PSIS appears to reduce great vessel adhesion and improve regeneration of collagenous tissues at the operative disc space. However, there were no differences in the operative segment range of motion or neutral zone when comparing the two treatments. The current study serves as a basic scientific basis for ongoing clinical investigations into the use and efficacy of PSIS material following total disc arthroplasty.

Introduction: A prospective randomized study of artifical disc replacement vs. lumbar fusion for one-level disc pathology with 2 year minimum follow-up was completed in compliance with a U.S. FDA protocol.

Methods: A total of 15 investigational sites enrolled 375 subjects with a randomization in a 2:1 ratio. Of the 375, 205 were randomized to receive the Charité artificial disc, and 99 were randomized to receive anterior lumbar interbody fusion with BAK cages. An additional group of 71 patients received the Charité disc as “training cases” prior to beginning randomization. Clinical outcome measures included VAS, Oswestry Disability Index, and SF-36 Healthy Surveys. A total of 6,900 radiographs were digitized throughout the 24 month treatment interval. The 276 disc replacement patients were allocated into one of three groups based on radiographic technical paramenters-- Group I – Ideal, defined as Charité disc placement within 3 mm of ideal in both planes. Coronal plane = AP radiograph = midline or within 3 mm of midline. Mid-Sagittal plane = Lateral radiograph = 2mm posterior to middle of vertebral body or within 3mm of this axis. Group II —Suboptimal (not ideal) and Group III – Poor.

Results: The Charité prosthesis was significantly more effective than BAK in restoring the height of the collapsed disk space (p < 0.001). In Charité cases, the mean initial disc space height at the L5-S1 operative level was 5.2 mm +/− 1.44 (Std Dev) and increased to a mean of 13.5 mm +/− 1.18 (Std Dev). For BAK, the initial disc space height was 5.9.mm +/− 1.74 and increased to an immediate post-operative disk space height of 11.9 mm +/− 2.07. There was less subsidence with the Charite disk replacement than the BAK control at 2 years (p < 0.001). Of the 276 subject radiographs analysed with Charité disc replacement, 83% were classified as Group I, 11% as Group II, and 6% as Group III.

The mean Oswestry Disability Index scores at 2 years correlated with technical accuracy in placement of the prosthesis: Group I – 24.1; Group II – 30.3; and Group III – 36.3 (p < .05). The Mean VAS scores at 2 years correlated with technical accuracy in placement of the prosthesis: Group I – 28.3; Group II – 35.4; and Group III – 48.4 (p = 0.016). The mean flexion/extension range of motion and prosthesis function also correlated with device placement: Group I – 7.12 +/− 4.06 degrees; Group II – 7.47 +/− 4.41 degrees; and Group III – 3.15 +/− 3.51 degrees (p = 0.003).

Discussion: The surgical technical accuracy of Charité artificial disc placement correlated with clinical outcome, range of motion, and device functionality at 2 years. The Charité Lumbar Disk replacement proved to be a successful alternative to traditional lumbar fusion in every parameter. The results from this U.S. Investigational study confirm that proper placement of the Charité artificial disc improves clinical and radiological outcomes.