Integration of native bone into orthopedic devices is a key factor in long-term implant success. The material-tissue interface is generally accepted to consist of a hydroxyapatite layer so bioactive materials that can spontaneously generate this hydroxyapatite layer after implantation may improve patient outcomes. Per the ISO 22317:2014 standard, "Implants for surgery - In vitro evaluation for apatite-forming ability of implant materials," bioactivity performance statements can be assessed by soaking the material in simulated body fluid (SBF) and evaluating the surface for the formation of a hydroxyapatite layer; however, variations in test methods may alter hydroxyapatite formation and result in false-positive assessments. The goal of this study was to identify the effect of SBF formulation on bioactivity assessment. Bioglass® (45S5 and S53P4) and non-bioactive Ti-6Al-4V were exposed to SBF formulations varying in calcium ion and phosphate concentrations as well as supporting ion concentrations. Scanning electron microscopy and X-ray powder diffraction evaluation of the resulting hydroxyapatite layers revealed that SBF enriched with double or quadruple the calcium and phosphate ion concentrations increased hydroxyapatite crystal size and quantity compared to the standard formulation and can induce hydroxyapatite crystallization on surfaces traditionally considered non-bioactive. Altering concentrations of other ions, for example, bicarbonate, changed hydroxyapatite induction time, quantity, and morphology. For studies evaluating the apatite-forming ability of a material to support bioactivity performance statements, test method parameters must be adequately described and controlled. It is unclear if apatite formation after exposure to any of the SBF formulations is representative of an in vivo biological response. The ISO 23317 standard test method should be further developed to provide additional guidance on apatite characterization and interpretation of the results.

Before medical products can be marketed in the United States, it is necessary for the manufacturer to submit detailed information to the Food and Drug Administration (FDA) and to receive marketing permission. In the past, products intended to diagnose or treat various medical conditions consisted of single-entity products – drugs, devices, and biological products. More recently, manufacturers have been pursuing combination products, diagnostic tools, or treatments that combine more than one type of medical product into a single product – drug/device, biological product/device, drug/biological product, or drug/device/biological product. Because of the unique characteristics of the individual components and differences in the legal framework governing each of these entities, the regulation of combination products presents a challenge to the regulated industry and the FDA. Interactions between staff in the Center for Biologics Evaluation and Research, the Center for Drug Evaluation and Research, and the Center for Devices and Radiological Health within the FDA, as well as the coordinating activities of the FDA's Office of Combination Products, are resulting in a more streamlined review process and a clearer outline of the regulatory framework that governs these unique medical products. This article explores the regulatory environment associated with combination products compared to single-entity medical products.

Wear characteristics of metal-backed, polyethylene patellar components were tested using cobalt-chromium, titanium alloy (Ti), and ion-implanted titanium alloy (IITi) articular surfaces. Patellar components were cycled in a bovine serum bath at 3 Hz for 1 million cycles, under a compressive load that varied from 343 N at 0 degree flexion to 2255 N at 120 degrees flexion. After testing, the polyethylene articular surfaces of the patellar components were evaluated for wear and graded using a subjective numbering system. Overall wear damage to the polyethylene surface was much worse with both Ti and IITi than with cobalt-chromium. Differences in mean wear scores were statistically significant when cobalt-chromium was compared with either Ti or IITi, but there were no statistically significant differences between Ti and IITi. Polyethylene surfaces that articulated against Ti femoral surfaces had more severe scratching. The IITi test group had areas of delamination not observed in the other test groups. Subjective evaluation of the metal surfaces showed evidence of wear damage as well. The metal articular surface of IITi resisted scratching as long as the treated surface was intact. In the high-stress areas, however, such as the edges of the intercondylar notch, the ion-implanted surface quickly wore away, exposing the untreated titanium alloy. The cobalt-chromium femoral articular surface had the least amount of scratching and no evidence of loss of metal.

Four fresh-frozen anatomic knee specimens were tested for knee stability, patellar tracking, and patellofemoral contact points with the femoral component positioned in 5 degrees internal, 5 degrees external, or neutral axial rotational alignment of the femoral component referenced on the posterior femoral condyles. The externally rotated specimens had varus-valgus stability of the knee that was closest to the normal control. The internally rotated specimens shifted into valgus alignment with flexion. Patellar tracking also was closest to normal in the externally rotated specimens. Patellofemoral contact was more evenly distributed between the medial and lateral contact areas in the externally rotated specimens than in the internally rotated or in the neutral specimens. Internal rotation of the femoral component in the knee with perpendicular resection of the tibia causes undesirable changes in knee stability, patellar tracking, and patellofemoral contact points. Neutral positioning produces similar but less negative effects on knee stability and patellar kinematics. External rotation improves both patellar tracking and knee stability characteristics.

Two uncemented unicompartmental tibial components were examined for initial fixation stability. A conventional design that employed a single posteriorly angled peg was compared with a new design that was held in place by cancellous bone screws. The components were implanted into the medial condyles of 12 preserved human tibiae, and a cyclic load was first applied anteromedially and then posteromedially. The screwed implants failed at significantly higher loads (1634.8 +/- 121.6 N, mean +/- standard error of the mean) than the pegged implants (1103.3 +/- 152.0 N). On application of a 19.6-N preload, the screwed implants moved significantly less than the pegged implants. Although the differences in micromotion and subsidence were not always significant, there were definite trends. The screwed implants had much lower levels of temporary and permanent displacement compared with the pegged implants for all load levels from the initial load of 245.2 N up to and including the failure load. When the motion that resulted from moving the load from the anterior position to the posterior position was examined, the screwed implant's average total motion was less than 10 microns compared with almost 135 microns for the pegged implant after the 245.2-N load cycle. For the cycle before failure, the screwed implant's average motion increased to less than 29 microns, whereas the pegged implant's average total motion was almost 354 microns. From this information it appears clear that screws provide better initial fixation stability than angled pegs for uncemented unicondylar tibial components.

Rotational loosening has recently emerged as an important cause of failure of the femoral component of total hip arthroplasties. This study was designed to investigate the role played by torsional loads in loosening of cementless femoral components and to evaluate three cementing techniques involving a combination of canal irrigation, manual insertion, and vacuum mixing combined with pressure injection of the cement for their ability to improve rotational fixation. Rotational micromotion and subsidence were measured in 24 preserved human anatomic specimen femora. Acoustic emission (AE) technique was applied as a non-destructive method for evaluating material failure during loading. From the micromovement data, torque to 50 mu subsidence and torque to failure were surprisingly low with cementless fixation and with poor cement technique but were markedly improved with pulsed irrigation. Further improvement was achieved by pressure injection and vacuum mixing of the cement. However, AE was detected even in the most carefully performed cement specimens under torsional-loading conditions commonly occurring in daily activities. These signs of microfailure of the cement mantle at relatively low torsional loads suggest that the mode of failure of deeply penetrated cement is by microfracture of the cement mantle. The poor performance suggests that cementless fixation of intramedullary stems provides unsatisfactory fixation against torsional loading. There is need for major improvements in fixation mechanisms and techniques. The signs of failure of the cement mantle at normally occurring torsional loads suggest that even the best cement technique is prone to failure in torsion when exposed to normal daily use.