Implant Migration and Failure in Total Knee Arthroplasty is Related to Body Mass Index and Tibial Component Size

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Abstract

Aseptic loosening of knee implants is multifactorial. The purpose of this study was to examine the role of body mass index and tibial component size on loosening and migration of total knee arthroplasty (TKA) implants. Six thousand five hundred forty-eight primary TKAs (anatomic graduated components) were studied with aseptic loosening as the end point. A second cohort of 81 TKAs (anatomic graduated components) had radiostereometric analysis beads implanted, permitting implant migration assessment. Patient mass and tibial component surface area were used to calculate potential tibial stresses. We found that higher potential stresses were associated with increased rates of loosening in both metal-backed and all-polyethylene designs. Increased tibial implant migration, in both the varus-valgus and anterior-posterior directions, was associated with higher estimated stresses. We found an increased rate of tibial component loosening and implant migration in patients with a higher mass and smaller tibial component size.

Section snippets

Materials and Methods

This is a retrospective review of clinical and radiographic observations in 2 cohorts of primary AGC TKAs. First, we examined all primary AGC TKAs performed for osteoarthritis (OA) at our center between 1983 and 2004 with loosening and failure as the end point. Second, a cohort of 81 primary AGC TKAs, performed in Sweden, had previously had RSA beads implanted, and this data set served as a cohort with implant migration as the end point.

Statistics

Significant divisions in the stresses and tibial component alignments were determined with a regression tree analysis to determine break points in the data where failure rates were increased. These respective calculated tibial stresses and tibial component alignments and their respective failure rates were compared by Cox proportional hazards regression. A P value of .05 was considered significant.

Results

There were 22 MB and 32 AP revisions for aseptic loosening (overall failure rate, 0.8%) at a mean of 3.1 years post-TKA. The statistically significant breakdown of the effects of the stress categories and tibial component alignments is reported in Table 1. With only 524 knees in the AP cohort, tibial component alignment stratifications and stresses could not be compared independently. Therefore, all tibial component alignments were combined for the AP components and presented as estimated

Discussion

Aseptic failure of TKA implants is a multifactorial cascade of events with loosening as the final result. Polyethylene wear 3, 4, 13 with resulting debris and the ensuing inflammatory response have been a leading cause of implant loosening. Wear reductions have largely been achieved through improved sterilization techniques in oxygen-free inert environments [13], improved locking mechanisms, compression molding the polyethylene resin vs machining existing bar stock [7], and nonmodularity 8, 9.

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      These factors were included as part of the propensity-score matching criteria prior to evaluation of the revision outcome to mitigate potential indication bias and confounding. While there have been reports of higher rates of aseptic loosening of the tibial component [14,19,34] and increased stress on the proximal tibia [17,18] in patients with obesity, Crawford et al [35] found only one case of aseptic loosening in 1859 patients with a BMI ≥35 kg/m2 who underwent primary TKA with a standard tibial base plate and high viscosity cement. Similarly Parratte et al [11] randomized primary TKA patients with a BMI >30 kg/m2 to either receive a tibial stem or not and failed to observe a difference in risk of all-cause revision and revision for aseptic loosening at 2 years.

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    Unrestricted research support came from Biomet, Inc, Warsaw, Ind.

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