The MOVE-C Cervical Artificial Disc - Design, Materials, Mechanical Safety

The Impact of Bias and Nitrogen Pressure on TiNbN Coatings in Arc-PVD Processes—A Multifactorial Study

Titanium-based nitride physical vapour deposition (PVD) coatings, such as titanium nitride (TiN), are state-of-the-art solutions for surface modifications of CoCrMo-based implants for patients who are hypersensitive to metallic ions such as cobalt, chromium and nickel. Variations of the process parameters during the cathodic arc evaporation are known to exhibit an impact on the surface properties of coatings. The aim of this study was to characterise the effect of the substrate bias and the nitrogen pressure on the surface properties of TiNbN coatings deposited on CoCrMo alloys in a limited parameter set. Eighteen parameter sets were coated with TiNbN. The substrate bias (−100 to −200 V) and the nitrogen pressure (0.3–3.0 Pa) were selected following a randomised, multifactorial response surface test design. The coating thickness, roughness, hardness and scratch resistance were measured following standardised procedures. The structure of the coating was analysed by SEM and XRD. The substrate bias and the pressure exhibited a significant impact on the coating thickness and the surface roughness. The grain growth was predominantly impacted by the bias. The parameter variation did not show any significant impact on the XRD, hardness or scratch test results.

[Three-dimensional finite element study on combined proximal and distal knee extension rearrangement for recurrent patellar dislocation]

OBJECTIVE

To establish a three-dimensional finite element analysis model of the knee joint in fresh frozen cadavers, to verify the validity of the model and to simulate the stress distribution characteristics of the patellofemoral joint after combined proximal and distal knee extension rearrangement surgery for recurrent patellar dislocation.

METHODS

One male and one female fresh frozen cadavers (4 knees in total), using voluntary body donations, were used to measure the maximum pressure on the patellofemoral articular surface at each passive flexion angle (0°, 30°, 60°, 90°, 120°) of the normal knee joint and the model after combined proximal and distal knee extension rearrangement surgery for recurrent patellar dislocation with tibial tuberosity-trochlear groove distance (TT-TG) value >2.00 cm using pressure-sensitive paper, respectively. Then, the 2 freshly frozen cadavers were used to construct three-dimensional finite element models of normal knee joints and postoperative knee joints, and the maximum pressure on the patellofemoral articular surface was measured at various passive flexion angles. The maximum pressure was compared with the measurement results of the pressure-sensitive paper to verify the validity of the three-dimensional finite element model. In addition, the maximum pressure on the patellofemoral joint surface measured by three-dimensional finite element was compared between the normal knee joint and the postoperative knee joint at various passive flexion angles, so as to obtain an effective three-dimensional finite element model for the simulation study of the stress distribution characteristics of the patellofemoral joint after combined proximal and distal knee extension rearrangement surgery for recurrent patellar dislocation.

RESULTS

The maximum pressure on the patellofemoral joint surface measured by pressure-sensitive paper and three-dimensional finite element measurements were similar at all passive flexion angles in the normal knee joint, with a difference of -0.08-0.06 MPa; the maximum pressure on the patellofemoral joint surface measured by pressure-sensitive paper and three-dimensional finite element measurements were also similar at all passive flexion angles in the knee after combined proximal and distal knee extension rearrangement surgery, with a difference of -0.04-0.09 MPa. The maximum pressure on the patellofemoral joint surface measured by three-dimensional finite elements were also similar between the normal knee joint and the knee joint after combined proximal and distal knee extension rearrangement surgery at all passive flexion angles, with a difference of -0.50--0.03 MPa.

CONCLUSION

The three-dimensional finite element model of the normal knee joint and the knee joint after combined proximal and distal knee extension rearrangement surgery can accurately and effectively quantify the change in the maximum pressure on the patellofemoral joint surface; for recurrent patellar dislocations with TT-TG value>2.00 cm, the combined proximal and distal knee extension rearrangement surgery can achieve a maximum pressure of the patellofemoral joint surface similar to that of the normal knee joint.