Development of near zero-order release dosage forms using three-dimensional printing (3-DP) technology.

Three near zero-order controlled-release pseudoephedrine hydrochloride (PEH) formulations demonstrating proportional release rates were developed using 3-Dimensional Printing (3-DP) technology. Mixtures of Kollidon SR and hydroxypropylmethyl cellulose (HPMC) were used as drug carriers. The release rates were adjusted by varying the Kollidon SR-HPMC ratio while keeping fabrication parameters constant.

Tibial insert undersurface as a contributing source of polyethylene wear debris.

Sixty-seven ultrahigh molecular weight polyethylene tibial inserts from cementless total knee arthroplasties were retrieved at autopsy and revision surgery and analyzed for evidence of articular and nonarticular surface wear after a mean implantation time of 62.8 months (range, 4-131 months). Polyethylene cold flow and abrasive wear on the nonarticular insert surface (undersurface) were assigned a wear severity score (Grade 0-4).

The tradeoffs associated with modular hip prostheses.

In an effort to gain greater insight into the tradeoffs associated with modular hip prostheses, 2 approaches were taken. A questionnaire was sent to each of the orthopaedic implant manufacturing companies asking specific questions regarding modular components, and a series of retrieved prostheses, both modular and nonmodular, were examined to determine the potential sources of problems associated with modular connections. The respondents to the questionnaire generally agreed that it was more expensive to produce modular prostheses due to the required tolerances at the modular connections, and that the increased flexibility provided by the modularity was important to surgical outcome.

Loss of hydroxyapatite coating on retrieved, total hip components.

The goal of this study was to examine the early retrievals of hydroxyapatite-(HA) coated hip prostheses to assess evidence of osteoconductivity, resorption of HA, and the integrity of the HA/implant bond. Six retrieved HA-coated hip prostheses (3 femoral hip stems, 3 acetabular cups) were analyzed for the amount of bone ongrowth or ingrowth of the HA-coated surface and the extent to which the coating was still present after in vivo service. The examination of these six HA-coated prostheses indicates that HA appeared to be osteoconductive.

Failure of a well-fixed bone-ingrown titanium hip prosthesis.

A cementless titanium femoral stem was revised 5 years after implantation because of acute pain and progressive osteolysis. Substantial amounts of titanium and polyethylene wear debris were found in the surrounding tissues. Multiple sources of this debris were found as well as detachment of titanium fiber-mesh pads from the body of the femoral stem.

Interfaces between host and uncemented femoral hip prostheses.

The authors analyzed 200 uncemented hip prostheses that were retrieved. They determined the type and extent of host-implant interfaces, but found little correlation between subjective pain relief and the histology of the interfaces. Wear debris, bone resorption and looseness were related to pain, although even with these the relationship was not statistically significant.

Mechanisms of failure of modular prostheses.

The expectations of wear and longevity of total hip components are based in large part on Charnley's early work. The evolution of the total hip from the one-piece, all-polyethylene acetabular component and fixed-head femoral component to the myriad of parts that comprise many of today's total hip designs has brought with it an array of potential mechanisms for failure that were not present in the earlier design. The risk/benefit ratio of these new designs may need to be reevaluated based on the additional mechanisms for failure that they provide.

Corrosion between the components of modular femoral hip prostheses.

We studied the tapered interface between the head and the neck of 139 modular femoral components of hip prostheses which had been removed for a variety of reasons. In 91 the same alloy had been used for the head and the stem; none of them showed evidence of corrosion. In contrast, there was definite corrosion in 25 of the 48 prostheses in which the stem was of titanium alloy and the head of cobalt-chrome.

All-polyethylene patellar components are not the answer.

Recent reports of the high incidence of polyethylene failure of metal-backed patellar components have rekindled the interest in cemented, all-polyethylene designs. One hundred four retrieved patellar components of metal-backed and all-polyethylene designs were analyzed for wear. Additionally, patellofemoral contact stress as a function of flexion angle was measured for unused components using pressure-sensitive Fuji film.

The biomechanical problems of polyethylene as a bearing surface.

The metal backings of acetabular components can reduce the available polyethylene thickness, often to an alarming extent. This study indicated that the pitting and cracking of thin polyethylene surfaces have some similarities to tibial and patellar bearings and that creep-related deformation occurred more frequently in thin polyethylene components. Additionally, it appears that dimensional tolerances of the polyethylene inserts are difficult to maintain and may result in a nonuniform fit of both the femoral head into the component and the component into its own metal backing, which can lead to component separation.

Macroscopic and microscopic evidence of prosthetic fixation with porous-coated materials.

The host response to porous-coated prostheses appears favorable; there is little evidence of any adverse tissue response or significant osteoclastic activity except in grossly loose specimens. While the nature of retrieval specimens makes any statistical correlation problematic, some generalizations can be made. Femoral hip prostheses are most likely to present bone ingrowth along the lateral quadrant of their porous coating.