Biomechanical Comparison of 2 Veterinary Locking Plates to Monocortical Screw/Polymethylmethacrylate Fixation in Canine Cadaveric Cervical Vertebral Column

OBJECTIVE: To compare the biomechanical properties of 2 veterinary locking plates and monocortical screws/polymethylmethacrylate (PMMA) fixation in canine cadaveric cervical vertebral columns. STUDY DESIGN: Biomechanical cadaveric study. MATERIALS: Nineteen cervical vertebral columns (C2-C7) from large breed, skeletally mature, canine cadavers were used. A cortical ring was placed as a disk spacer at C4-C5 in all specimens. Seven vertebral columns were plated at C4-C5 with two 4-hole, 3.5 mm string of pearls plates (SOP) and 6 vertebral columns were plated with two 6-hole, 2.4 mm titanium locking reconstruction plates (Ti recon plate). All screws were placed monocortically. Six vertebral columns had monocortical titanium screws and PMMA (Ti screws/PMMA) placed, tested as part of a prior study. METHODS: Stiffness testing in 3 directions was performed of the unaltered C4-C5 vertebral motion unit and repeated after placement of the disk spacer and implants. Data were compared using a linear mixed model that incorporated data from previously tested spines (Ti screw/PMMA). RESULTS: The mean (95% CI) stiffness (N/m) in extension for SOP was 407 N/mm (330-503), for Ti recon plate was 284 N/mm (198-407) and for Ti screws/PMMA was 365 N/mm (314-428); in flexion for SOP was 250 N/mm (178-354), for Ti recon plate was 147 N/mm (106-204) and for Ti screws/PMMA was 311 (235-416); in lateral bending for SOP was 528 N/mm (441-633), for Ti recon plate was 633 N/mm (545-735) and for Ti screws/PMMA was 327 N/mm (257-412). There were no significant differences in stiffness between the 3 fixations for any outcome. CONCLUSION: Monocortical fixation with two 3.5 mm SOP or two 2.4 mm Ti recon plates may be an alternate fixation to monocortical screws and PMMA

Measurement of shoulder abduction angles in dogs: an ex vivo study of accuracy and repeatability

OBJECTIVE: The aim of this study was to determine the accuracy and repeatability of the shoulder abduction test and to assess the effect of transection of the medial shoulder support structures in canine cadavers. MATERIALS AND METHODS: The shoulder abduction angle was measured by three separate observers, both with the shoulder extended and at a neutral angle. Shoulder abduction was then measured, using craniocaudal fluoroscopic images. Arthroscopy was performed in all shoulder joints, with the medial support structures transected in one shoulder of each dog. The three observers again measured shoulder abduction angles in all dogs. Shoulder abduction was measured again using fluoroscopy. Accuracy and repeatability of the abduction test were assessed using linear mixed models. RESULTS: All three observers had different measured abduction angles when compared with fluoroscopy ( < 0.01); however, the experienced surgeon had an error of only 2.9°. Inter-observer repeatability was poor, with all three observers having different abduction measurements ( < 0.001). Intra-observer repeatability, however, indicated no differences on repeated measurements ( = 0.26). Placing the shoulder at a neutral standing angle, and transection of support structures caused an average increase in abduction by 8.2° ( < 0.001) and 4.4° respectively. CONCLUSION: Significant variation exists between observers performing this test, increased accuracy seen in the more experienced observer. Shoulder flexion angle can significantly affect measured abduction angles

Effect of an intervertebral disk spacer on stiffness after monocortical screw/polymethylmethacrylate fixation in simulated and cadaveric canine cervical vertebral columns.

OBJECTIVE To determine the biomechanical effect of an intervertebral spacer on construct stiffness in a PVC model and cadaveric canine cervical vertebral columns stabilized with monocortical screws/polymethylmethacrylate (PMMA). STUDY DESIGN Biomechanical study. SAMPLE POPULATION PVC pipe; cadaveric canine vertebral columns. METHODS PVC model-PVC pipe was used to create a gap model mimicking vertebral endplate orientation and disk space width of large-breed canine cervical vertebrae; 6 models had a 4-mm gap with no spacer (PVC group 1); 6 had a PVC pipe ring spacer filling the gap (PCV group 2). Animals-large breed cadaveric canine cervical vertebral columns (C2-C7) from skeletally mature dogs without (cadaveric group 1, n = 6, historical data) and with an intervertebral disk spacer (cadaveric group 2, n = 6) were used. All PVC models and cadaver specimens were instrumented with monocortical titanium screws/PMMA. Stiffness of the 2 PVC groups was compared in extension, flexion, and lateral bending using non-destructive 4-point bend testing. Stiffness testing in all 3 directions was performed of the unaltered C4-C5 vertebral motion unit in cadaveric spines and repeated after placement of an intervertebral cortical allograft ring and instrumentation. Data were compared using a linear mixed model approach that also incorporated data from previously tested spines with the same screw/PMMA construct but without disk spacer (cadaveric group 1). RESULTS Addition of a spacer increased construct stiffness in both the PVC model (P < .001) and cadaveric vertebral columns (P < .001) compared to fixation without a spacer. CONCLUSIONS Addition of an intervertebral spacer significantly increased construct stiffness of monocortical screw/PMMA fixation

Biomechanical comparison between bicortical pin and monocortical screw/polymethylmethacrylate constructs in the cadaveric canine cervical vertebral column.

OBJECTIVE To compare biomechanical stiffness of cadaveric canine cervical spine constructs stabilized with bicortical stainless steel pins and polymethylmethacrylate (PMMA), monocortical stainless steel screws with PMMA, or monocortical titanium screws with PMMA. STUDY DESIGN Biomechanical cadaver study. ANIMALS Eighteen canine cervical vertebral columns (C2-C7) were collected from skeletally mature dogs (weighing 22-32 kg). METHODS Specimens were radiographed and examined by dual energy X-ray absorptiometry. Stiffness of the unaltered C4-C5 intervertebral motion unit was measured in extension, flexion and lateral bending using non-destructive 4-point bend testing. Specimens were then stabilized by (1) bicortical stainless steel pins/PMMA, (2) monocortical stainless steel screws/PMMA, or (3) monocortical titanium screws/PMMA. Mechanical testing was repeated and stiffness data from unaltered specimens and the 3 treatment groups were compared. RESULTS All 3 surgical methods significantly increased stiffness of the C4-C5 motion unit compared with the unaltered specimen (P < .001 for all treatments), but stiffness was not significantly different among the 3 fixation groups (P = .578). CONCLUSIONS In this model, monocortical screw fixation (with stainless steel or titanium screws) was biomechanically equivalent to bicortical fixation

Evaluation of Three Human Cervical Fusion Implants for Use in the Canine Cervical Vertebral Column.

OBJECTIVE: To assess technical feasibility and mechanical properties of 3 locking plate designs (Zero-P, Zero-P VA, and Uniplate 2) for use in the canine cervical spine. STUDY DESIGN: Prospective ex vivo study. ANIMALS: Cadaver cervical spines from skeletally mature large breed dogs (n = 18). METHODS: Specimens were screened using radiography and allocated into balanced groups based on bone density. Stiffness of intact C4-C5 vertebral motion units was measured in extension, flexion, and lateral bending using nondestructive 4-point bend testing. Uniplate 2 was then implanted at C4-C5 and mechanical testing was repeated. Mechanical test data were compared against those from 6 spines implanted with monocortical screws, an allograft ring spacer, and PMMA. RESULTS: The Zero-P and Zero-P VA systems could not be surgically implanted due to anatomical constraints in the vertebral column sizes of the canine cervical spines used in this study. Fixation with Uniplate 2 or with screws/PMMA significantly increased stiffness of the C4-C5 vertebral motion units compared to unaltered specimens (P < .001) in extension. Stiffness of the titanium screw/PMMA fixation was significantly greater than the Uniplate 2 construct in extension. Flexion and lateral bending could not be evaluated in 3 of 6 specimens in the Uniplate 2 group due to failure at the bone/implant interface during extension testing. CONCLUSION: Fixation with Uniplate 2 was biomechanically inferior to screws/PMMA. Particularly concerning was the incidence of vertebral fracture after several testing cycles. Based on our results, Zero-P, Zero-P VA, and Uniplate 2 cannot be recommended for use in dogs requiring cervical fusion.College of Veterinary Medicine, The Ohio State University (intramural award)This is the author accepted manuscript. The final version is available from Wiley via http://dx.doi.org/10.1111/vsu.1253

Mapping bacterial biofilm on features of orthopedic implants in vitro

Implant-associated infection is a major complication in orthopedic surgery. One of the most common organisms identified in periprosthetic joint infections is Staphylococcus aureus, a bio-film-forming pathogen. Orthopedic implants are composed of a variety of materials such as ti-tanium, polyethylene and stainless steels which are at risk for colonization by bacterial biofilms. Little is known about how larger surface features of orthopedic hardware (such as ridges, holes, edges, etc.) influence biofilm formation and attachment. To study how biofilms might form on actual components, we submerged multiple orthopedic implants of various shapes, sizes, roughness and material type in brain heart infusion broth inoculated with Staphylococcus aureus SAP231, a bioluminescent USA300 strain. Implants were incubated for 72 hours with daily media exchanges. After incubation, implants were imaged using an in vitro imaging system (IVIS) and the metabolic signal produced by biofilms were quantified by image analysis. Scanning electron microscopy was then used to image different areas of the implants to complement the IVIS im-aging. Rough surfaces had the greatest luminescence compared to edges or smooth surfaces on a single implant and across all implants when the images were merged. Luminescence of edges were also significantly greater than smooth surfaces. These data suggest implant roughness as well as large scale surface features may be at greater risk of biofilm colonization

Influence of staphylococcus epidermidis biofilm on the mechanical strength of soft tissue allograft

We sought to determine the impact of bacterial inoculation and length of exposure on the mechanical integrity of soft tissue tendon grafts. Cultures of Staphylococcus epidermidis were inoculated on human tibialis posterior cadaveric tendon to grow biofilms. A low inoculum in 10% growth medium was incubated for 30 min to replicate conditions of clinical infection. Growth conditions assessed included inoculum concentrations of 100, 1000, 10,000 colony-forming units (CFUs). Tests using the MTS Bionix system were performed to assess the influence of bacterial biofilms on tendon strength. Load-to-failure testing was performed on the tendons, and the ultimate tensile strength was obtained from the maximal force and the cross-sectional area. Displacements of tendon origin to maximal displacement were normalized to tendon length to obtain strain values. Tendon force-displacement and stress-strain relationships were calculated, and Young's modulus was determined. Elastic modulus and ultimate tensile strength decreased with increasing bioburden. Young's modulus was greater in uninoculated controls compared to tendons inoculated at 10,000 CFU (p = 0.0011) but unaffected by bacterial concentrations of 100 and 1000 CFU (p = 0.054, p = 0.078). Increasing bioburden was associated with decreased peak load to failure (p = 0.043) but was most significant compared to the control under the 10,000 and 1000 CFU growth conditions (p = 0.0005, p = 0.049). The presence of S. epidermidis increased elasticity and decreased ultimate tensile stress of human cadaveric tendons, with increasing effect noted with increasing bioburden

Reinforced Portland cement porous scaffolds for load-bearing bone tissue engineering applications.

Modified Portland cement porous scaffolds with suitable characteristics for load-bearing bone tissue engineering applications were manufactured by combining the particulate leaching and foaming methods. Non-crosslinked polydimethylsiloxane was evaluated as a potential reinforcing material. The scaffolds presented average porosities between 70 and 80% with mean pore sizes ranging from 300 µm up to 5.0 mm. Non-reinforced scaffolds presented compressive strengths and elastic modulus values of 2.6 and 245 MPa, respectively, whereas reinforced scaffolds exhibited 4.2 and 443 MPa, respectively, an increase of ~62 and 80%. Portland cement scaffolds supported human osteoblast-like cell adhesion, spreading, and propagation (t = 1-28 days). Cell metabolism and alkaline phosphatase activity were found to be enhanced at longer culture intervals (t = 14 days). These results suggest the possibility of obtaining strong and biocompatible scaffolds for bone repair applications from inexpensive, yet technologically advanced materials such as Portland [email protected]