Summary
Mini-Keel tibial implants are associated with a higher risk of early revision and failure when compared to standard tibial implants.
Abstract
Background
Implant design plays an important role in total knee arthroplasty (TKA) durability, as it influences polyethylene wear, implant fixation and bone ingrows. Tibial mini-keel implants have been developed in order to minimize incision length and allow mini-invasive surgeries. The purpose of this case control study was to compare Standard and Mini-Keel of the same NexGen LPS Flex Implant (Zimmer) at mid-term follow-up with a special attention to survivorship, clinical and radiographical outcomes. The hypothesis was that the revision rates were similar in both groups.
Methods
Clinical and radiographic data were reviewed retrospectively to determine the five-year Kaplan-Meier survival rate following 459 primary total knee arthroplasties performed in 439 patients from 2007 to 2010. Two groups were defined based on NexGen tibial tray implanted : Mini–Keel® group (MK: 212 knees) and standard keel group (S: 247 knees). Both groups were comparable in terms of age, gender, BMI, pre and post op coronal alignment, surgical approach, follow up.
Results
At mid-term follow-up (mean 5 years (+/-1,6)), fifteen (7%) of the 233 implants in the MK group had been revised for any reason, compared with seven (2,8%) of the 266 implants in S group (p = 0.057).Twelve (5,7%) patients in the MK group were revised for aseptic tibial implant loosening versus four (1.6%) in the S groups (p=0.036). Mini-Keel implants were associated to revision (HR=3.86 (CI-95% 1.23-11.88), p=0.02) but not to radiologic aseptic loosening (HR=1,75 (CI-95% 0,9-3,4), p=0,097). Regarding to the survical curve, an important decrease was reported after 40 months, only in the MK group. Individual factors such as gender, BMI, pre or post-operative axis were not prognosis factors for revision or aseptic loosening in both groups.
Conclusion
Mini-Keel tibial implants are associated with a higher risk of early revision and failure when compared to standard tibial implants.