Thursday, January 24, 2013

Summary of the data behind the FDA recomendations

Summary of Data

The 1982 Orthopedic Device Classification Panel (the 1982 Panel) recommended that while general controls alone were not sufficient, sufficient information existed to establish a performance standard to provide a reasonable assurance of safety and effectiveness for metal/metal hip systems. FDA disagreed with the 1982 Panel's recommendation and classified the devices as class III stating insufficient information existed to support the conclusion that performance standards or general controls will provide reasonable assurance of the safety and effectiveness of these devices.
On August 8, 2001, the Orthopaedic and Rehabilitation Devices Panel (the Panel) recommended five to two that the hip joint metal/metal semi-constrained prostheses (cemented and uncemented) not be reclassified from class III to class II. The Panel concluded the following:
  • There was insufficient clinical and preclinical testing information to establish special controls.
  • The length and rate of long-term patient followup data were inadequate to demonstrate that special controls would provide reasonable assurance of the safety and effectiveness of these devices.
  • In terms of preclinical testing, the Panel also concluded that validation of wear simulation, non-ideal preclinical wear testing, and biological evaluation of metallic wear debris generated by the device were not established. The particle size of the metallic wear debris generated by these devices is substantially smaller than the particle size of the metallic wear debris generated by other hip joint prostheses and the short-and long-term biological effects from human retrievals or preclinical evaluation of these smaller size metallic wear particles are unknown.
FDA agreed with the Panel and believes the Panel's concerns are still relevant today. Current wear testing methods for metal/metal bearings are limited, and importantly can underestimate bearing wear by an order of magnitude compared to clinical outcomes. There are also no standardized wear methods or consensus among researchers for investigating joint micro-separation, dislocation, cup deformation, demanding gait activities and third-body abrasion. In addition, there is a lack of wear measurements from retrieved metal/metal bearings, so it is a challenge to correlate wear rates from modern devices to adverse events demonstrated clinically like pseudotumors. To complicate matters further, metal/metal bearings have shown unpredictable wear trends in simulator testing, which have not been explained. Therefore, it is a challenge to introduce sufficient special controls to mitigate the risks of modern metal/metal hip devices. The summary of information provided in response to FDA's order issued under sections 515(i) and 519 of the FD Act (21 U.S.C. 360e(i) and 360i) (refer to docket FDA-2009-M-0101) is not adequate to identify special controls sufficient to ensure safety and effectiveness and therefore not adequate to support reclassification of metal/metal hip systems.
Recent reports and evaluations further support that reclassification of metal/metal hip systems is not appropriate. The United Kingdom's (UK) Medicines and Healthcare Products Regulatory Agency (MHRA) published several alerts in 2010 outlining concerns associated with metal/metal hip systems, including soft tissue reactions (Ref. 1). The final report, published in October 2010, outlines that acetabular cup angle, femoral head size, and metal ion levels are all risk factors that will affect the outcome of metal/metal hip systems. Moreover, a recent publication in the Journal of Bone and Joint Surgery outlines case reports of arthroprosthetic cobaltism in metal/metal hip patients (Ref. 2).
The Australian Orthopaedic Association National Joint Replacement Registry's Hip and Knee Arthroplasty Annual Report of 2010 states that the “metal/metal bearing surface has the highest risk of revision compared to all other bearing surfaces.” The report found the cumulative percent revision rate at 7 years is 6.3 percent for metal/metal, compared to 4.0 percent for ceramic/ceramic, 3.7 percent for ceramic/polyethylene and 4.2 percent for metal/polyethylene (Ref. 3).Show citation box
In December 2011, the American Academy of Orthopedic Surgeons (AAOS) published “Modern Metal-on-Metal Hip Implants: A Technology Overview” (Ref. 4). The AAOS overview provides a summary of clinical outcomes in patients with metal/metal hip systems in comparison to other bearing surface combinations, addresses patient, implant, and surgical factors that may predict successful and unsuccessful outcomes of metal/metal hip systems and discusses the prevalence of adverse clinical problems from metal/metal hip systems in comparison to other bearing surface combinations. The report concludes that “analyses conducted on objective patient-oriented outcomes by two joint registries indicate that, overall, patients who receive metal-on-metal total hip arthroplasty and hip resurfacing are at greater risk for revision than patients who receive total hip arthroplasty using a different bearing surface combination.” The report references the aforementioned Australian registry.
A recent article published in a scientific journal raised serious concerns about the failure rates of metal/metal hip systems for the UK population (Ref. 5). This peer-reviewed journal article presented the following findings regarding primary metal/metal total hip replacements: (1) Increased failure rate at 5 years for metal/metal total hip replacements related to larger head sizes; (2) significantly higher risk for revision in female patients (Note: In the United States, labeling includes warnings to discourage the use of metal/metal total hip replacements in females of child bearing age); and (3) revisions for dislocation in men with metal/metal hip replacements were slightly lower, showing some benefit to larger head sizes.
These reports, as well as recent recalls of devices from the U.S. market, have indicated that preclinical testing currently used to support marketing clearance of these devices has not been sufficient to mitigate the risks associated with these devices and identify potential clinically-relevant failure modes. These reports suggest that additional study is necessary before special controls can be identified and these devices can be reclassified.

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