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.

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.