Aims

This study aimed to explore whether serum combined with synovial interleukin-6 (IL-6) measurement can improve the accuracy of prosthetic joint infection (PJI) diagnosis, and to establish the cut-off values of IL-6 in serum and synovial fluid in detecting chronic PJI.

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 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.