Regulation of orthopaedic devices: Future implications for research and innovation.

The conception-to-market development of orthopaedic devices occurs across the total product life cycle including device design and preclinical testing, clinical investigations to support marketing applications, and monitoring of device performance after market introduction. This process involves industry, regulatory agencies, health care providers, engineers, scientists, and patients. The Food and Drug Administration (FDA) is responsible for regulating medical devices in the United States, and uses a 3-tier classification system based on the level of control necessary to provide reasonable assurance of safety and effectiveness. Classification directs the required regulatory pathway and premarket submission type. Variations in global regulations, particularly between the United States, European Economic Area (EEA), and the United Kingdom (UK), may impact industry response to orthopaedic device development. Changing device innovation and reimbursement models have led to the consolidation of market share among larger companies. Although larger companies are better able to cope with more rigorous regulatory requirements, this leads to decreased competition and increased upward price pressure. To assist with the complex regulatory processes, the FDA offers pre-submission assistance as an opportunity for early collaboration and discussion about the medical device or device-led combination product submissions. Orthopaedic organizations, such as the Orthopaedic Trauma Association (OTA), may assist in postmarket device surveillance through the coordinated development and maintenance of clinical data registries. Such registries can longitudinally follow patients with a specific orthopaedic pathology or device usage, and monitor outcomes towards improvements in next-generation device development. As technology evolves, the nexus of regulation, industry, and patient outcome monitoring will continue to support safe and effective device innovation.

Clinical and radiographic evaluation of a monoblock tibial component.

Modular tibial components are the clinical standard in total knee arthroplasty despite the lack of evidence of improved function and longevity when compared with monoblock implants. This study describes the minimum 5-year outcomes for 125 total knee arthroplasties performed with monoblock tibial components in 101 patients. No patients were lost to follow-up. Average Knee Society Score was 87.1 at a mean follow-up of 5.2 years. Clinical and radiographic follow-up showed all components to be stable, no implants at risk of loosening, no observable osteolysis, and no observed change in bone density. Survivorship free of revision for tibial component loosening was 100% at 5 years. These results show excellent midterm durability of a partially cemented porous tantalum monoblock implant with uncemented pegs.

Failure analysis of a ceramic bearing acetabular component.

BACKGROUND: Alternative bearings have been explored in an attempt to improve the longevity of total hip prostheses. A Food and Drug Administration (FDA)-approved clinical study of a nonmodular acetabular component consisting of a porous metal shell, compression-molded polyethylene, and a ceramic liner inlay was discontinued following reports of early failures. METHODS: Between October 1999 and January 2003, 429 patients were enrolled in a prospective study to evaluate a cementless ceramic-on-ceramic total hip arthroplasty design (Hedrocel ceramic bearing cup; Implex, Allendale, New Jersey). Two hundred and eighty-two patients (315 hips) were treated with the experimental acetabular implant and 147 patients (157 hips) were treated with an acetabular implant that consisted of the same porous shell but an allpolyethylene liner. Clinical data including a Harris hip score and responses to the Short Form-12 (SF-12) health survey were collected preoperatively and at twelve and twenty-four months postoperatively. Serial radiographs were made preoperatively; at six weeks, three months, six months, and twelve months postoperatively; and annually thereafter. Retrieval analysis was performed on all failed explanted components. Failure was defined as fracture or displacement of the ceramic liner out of the acetabular component. In addition, biomechanical testing was performed on unimplanted acetabular components and mechanically altered cups in an effort to recreate the mechanisms of failure. Finite element analysis was used to estimate stress and strain within the ceramic liner under extreme physiologic loading conditions. RESULTS: The ceramic liner failed in fourteen of the 315 experimental acetabular components; all of the failures were at the ceramic-polyethylene interface. Patients with a body weight of >91 kg had a 4.76 times greater odds of the ceramic liner failing than those who weighed < or =91 kg. Retrieval analysis demonstrated stripe and rim wear with evidence of adhesive wear, indicating a potentially high-friction interaction at the articulation. Finite element analysis demonstrated that the forces on the ceramic liner in cups subjected to extreme loading conditions were insufficient to cause fracture. Biomechanical testing was unable to reproduce an initial ceramic liner displacement in vitro; however, when the ceramic liner was forcibly displaced prior to biomechanical testing, complete displacement and eventual fracture of the ceramic liner resulted. CONCLUSIONS: We hypothesized that the combination of a high patient body weight, an extensive range of motion, and subluxation of the femoral head led to high friction at the articulation between the femoral head and the rim of the liner, which initiated displacement of the ceramic liner. Subsequent normal gait led to further displacement of the liner in all of the fourteen failed components and eventually to ceramic fracture in twelve of the fourteen components.

Experimental and clinical performance of porous tantalum in orthopedic surgery.

Porous tantalum, a new low modulus metal with a characteristic appearance similar to cancellous bone, is currently available for use in several orthopedic applications (hip and knee arthroplasty, spine surgery, and bone graft substitute). The open-cell structure of repeating dodecahedrons is produced via carbon vapor deposition/infiltration of commercially pure tantalum onto a vitreous carbon scaffolding. This transition metal maintains several interesting biomaterial properties, including: a high volumetric porosity (70-80%), low modulus of elasticity (3MPa), and high frictional characteristics. Tantalum has excellent biocompatibility and is safe to use in vivo as evidenced by its historical and current use in pacemaker electrodes, cranioplasty plates and as radiopaque markers. The bioactivity and biocompatibility of porous tantalum stems from its ability to form a self-passivating surface oxide layer. This surface layer leads to the formation of a bone-like apatite coating in vivo and affords excellent bone and fibrous in-growth properties allowing for rapid and substantial bone and soft tissue attachment. Tantalum-chondrocyte composites have yielded successful early results in vitro and may afford an option for joint resurfacing in the future. The development of porous tantalum is in its early stages of evolution and the following represents a review of its biomaterial properties and applications in orthopedic surgery.

Wear evaluation of cobalt-chromium alloy for use in a metal-on-metal hip prosthesis.

Wear of the polyethylene in total joint prostheses has been a source of morbidity and early device failure, which has been extensively reported in the last 20 years. Although research continues to attempt to reduce the wear of polyethylene joint-bearing surfaces by modifications in polymer processing, there is a renewed interest in the use of metal-on-metal bearing couples for hip prostheses. Wear testing of total hip replacement systems involving the couple of metal or ceramic heads on polymeric acetabular components has been performed and reported, but, until recently, there has been little data published for pin-on-disk or hip-simulator wear studies involving the combination of a metallic femoral head component with an acetabular cup composed of the same or a dissimilar metal. This study investigated the in vitro wear resistance of two cobalt/chromium/molybdenum alloys, which differed primarily in the carbon content, as potential alloys for use in a metal-on-metal hip-bearing couple. The results of pin-on-disk testing showed that the alloy with the higher (0.25%) carbon content was more wear resistant, and this alloy was therefore chosen for testing in a hip-simulator system, which modeled the loads and motions that might be exerted clinically. Comparison of the results of metal-on-polyethylene samples to metal-on-metal samples showed that the volumetric wear of the metal-on-polyethylene bearing couple after 5,000,000 cycles was 110-180 times that for the metal-bearing couple. Polyethylene and metal particles retrieved from either the lubricant for pin-on-disk testing or hip simulator testing were characterized and compared with particles retrieved from periprosthetic tissues by other researchers, and found to be similar. Based upon the results of this study, metal-on-metal hip prostheses manufactured from the high carbon cobalt/chromium alloy that was investigated hold sufficient promise to justify human clinical trials.

Radiographic evaluation of a monoblock acetabular component: a multicenter study with 2- to 5-year results.

Serial radiographs of a porous tantalum monoblock acetabular cup design were evaluated for cup stability and signs of successful osteointegration. Of 574 primary consecutive total hip replacements in 542 patients performed by 9 surgeons at 7 hospitals, 414 cases were available for minimum 2-year follow-up. Follow-up averaged 33 months and ranged from 24 to 58 months. Postoperative radiographs revealed acetabular gaps in 100 zones in 80 (19%) hips: 29 in zone I, 67 in zone II, and 4 in zone III. At last follow-up, 84 (84%) of the zones with gaps completely filled in, and all 4- and 5-mm gaps filled in. There was no progression of any postoperative gap, no evidence of continuous periacetabular interface radiolucencies, no evidence of lysis, and no revisions for loosening. Although these short-term results are encouraging, further follow-up will be required to assess whether the monoblock design and the low modulus of elasticity of porous tantalum will reduce the incidence of periacetabular stress shielding and occurrence of osteolysis.

Revision and salvage patellar arthroplasty using a porous tantalum implant.

The purpose of this study was to assess the clinical results of a new surgical technique and novel porous tantalum implant for augmentation or arthroplasty of the patella for 11 patients who underwent revision total knee arthroplasty. Preoperative average knee function and pain scores were 24 and 20, respectively, and average range of motion (ROM) was 62 degrees. The low knee scores reflect the immobility, trauma, and/or pain associated with the patients' presenting conditions. At the most recent follow-up (average, 32 months), the average knee function and pain scores were 69 and 53, respectively, and the average ROM was 103 degrees. Radiographically, all implants were stable, and patient satisfaction has been excellent. These results indicate that this surgical technique and porous tantalum prosthesis can substantially improve function and reduce pain for patients with severe patellar bone loss and other complicating factors.