The NJR Implant Scrutiny Committee reports Level 1 outlier implants to the MHRA. There are currently 10 hip stems, 11 hip acetabular (cup) components and 31 hip stem / cup combinations reported. A total of 15 knee brands are currently reported. Knee implants with and without patella resurfacing are now included in implant outlier analysis.
An implant is considered to be a Level 1 outlier when its Prosthesis Time Incident Rate (PTIR) is more than twice the PTIR of the group, allowing for confidence intervals. These are shown as the number of revisions per 100 prosthesis-years. As of March 2015, we have started to identify the best performing implants, these would have a PTIR less than half that of their group, allowing for confidence intervals. To date no implants have reached that level.
Components and constructs previously reported to MHRA, but no longer at Level 1 using the PTIR method are identified.
Hip implant performance
Best performing hip implants
There are no hip implants or combinations performing statistically less than half their expected PTIR.
Knee implant performance
Implants may be subjected to closer scrutiny under certain conditions, such as when reports are received from surgeons concerned about the performance of certain variants, or when a device seems to have a very specific mode of failure. Kaplan-Meier analysis of revision rate is performed, using the average for all knees recorded in the NJR as the “expected” value, and if necessary followed up with other statistical tests.
If a variant is found to be significantly (p<0.001) outside the expected range, then this is also reported to the company and the MHRA. As a consequence of this the committee has reported two specific variants in the NexGen total knee replacement brand. These are combinations of the Option cemented (non-precoat) tibial implant, specifically when used in conjunction with the posterior stabilised Flex femoral components (Flex and Flex GSF). These combinations have been used in approximately 6% of all cases (approximately 13% of all posterior stabilised variants) of the NexGen implantations within the areas that the NJR covers.
All other NexGen constructs were similarly examined in detail and not found to be significantly outside of the expected performance, indeed some were found to perform better than expected, especially among the cruciate retaining variants.
The NJR is currently undertaking similar investigations of other devices and will report any adverse findings to the clinical community should any be identified. Any surgeons who have specific concerns about the performance of joint replacement implants and/ or specific variants that would benefit from closer examination, can contact the NJR Implant Scrutiny Committee at njr@njr.org.uk.
Best performing knee implants
There are no knee implants performing statistically less than half their expected PTIR.