Mid-term survivorship of Mini-keel™ versus Standard keel in total knee replacements: Differences in the rate of revision for aseptic loosening

IntroductionTo reduce the size of the surgical incision, modular mini-keel tibial components have been developed with or without extensions for the Nexgen™ MIS Tibial Component. Although a smaller component could theoretically result in defective fixation, this has never been evaluated in a large comparative series. Thus, we performed the following case control study to: (1) evaluate intermediate-term survival of a modular “mini-keel” tibial component compared to a reference standard keel component from the same line of products (Nexgen LPS-Flex Tibial Component, Zimmer); (2) to identify any eventual associated factors if the frequency of loosening was increased.HypothesisThe rate of revision for aseptic tibial loosening is comparable for both components.Materials and methodsThis comparative, retrospective, single center series of 459 consecutive total knee arthroplasties (TKA) was performed between 2007 and 2010: with 212 modular “mini-keel” (MK) tibial components and 247 “standard” (S) components. Survival, rate of revision for aseptic tibial loosening and identification of a radiolucent line were analyzed at the final follow-up.ResultsAfter a median follow-up of 5 years, the rate of revision for tibial aseptic loosing was significantly higher in the MK group with 12 cases (5.7%) and 4 cases in the S group (1.6%) (P = 0.036). The use of the MK component appears to be a prognostic factor for surgical revision (hazard ratio = 3.86 (1.23–11.88), P = 0.02) but not for the development of a radiolucent line (HR = 1.75 (0.9–3.4), P = 0.097). The mean delay before revision was 38 months (8–64) in the MK group and 15.2 months (8–22) in the S group (P = 0.006). Individual factors, such as gender, body mass index (BMI) and pre- or postoperative alignment were not prognostic factors for revision or radiolucent lines.ConclusionThe modular “mini-keel” tibial component was associated with a greater risk of revision for tibial component loosening.Level of evidenceCase control study, III.