Patient and surgery related factors associated with fatigue type polyethylene wear on 49 PCA and DURACON retrievals at autopsy and revision

Abstract

BackgroundPolyethylene wear is an important factor for longevity of total knee arthroplasty. Proven and suspicious factors causing wear can be grouped as material, patient and surgery related. There are more studies correlating design and/or biomaterial factors to in vivo wear than those to patient and surgery related factors. Many retrieval studies just include revision implants and therefore may not be representative. This study is aimed to correlate patient- and surgery- related factors to visual wear score by minimizing design influence and include both autopsy and revision implants. Comparison between the groups was expected to unmask patient and surgery-related factors responsible for wear.MethodsThe amount of joint side wear on polyethylene retrievals was measured using a modification of an established visual wear score. Fatigue type wear was defined as summation of the most severe wear modes of delamination, pitting and cracks. Analysis of patient and surgery related variables suspicious to cause wear included prospectively sampled patient activity which was measured by self reported walking capacity. Statistical analysis was done by univariate analysis of variance. Activity level and implantation time were merged to an index of use and correlated to the wear score.ResultsWear score after comparable implantation time was significantly less in the autopsy group. Even so, fatigue type wear accounted for 84 and 93 % of total wear score on autopsy and revision implants respectively. A highly significant influence on wear score was found in time of implantation (p = 0.002), level of activity (p = 0.025) and inserts belonging to revision group (p = 0.006). No influence was found for the kind of patella replacement (p = 0.483). Body mass index and accuracy of component alignment had no significant influence on visual wear score. Fatigue-type wear in the medial compartment was closely correlated to the index of use in the autopsy (R2 = 0.383) and the revision group (R2 = 0.813).ConclusionThe present study's finding of substantial fatigue type wear in both autopsy and revision retrievals supports the theory that polyethylene fatigue strength is generally exceeded in this type of prosthesis. Furthermore, this study correlated fatigue-type polyethylene wear to an index of use as calculated by activity over time. Future retrieval studies may use activity over time as an important patient related factor correlated to the visual wear score. When evaluating total knee arthroplasty routine follow up, the surgeon must think of substantial wear present even without major clinical signs.

Wear Damage in Mobile-bearing TKA is as Severe as That in Fixed-bearing TKA

“…This limitation cannot be avoided due to the difficulty in obtaining implants at the time of autopsy. A study that compared 24 implants removed at autopsy to 25 implants retrieved at reoperation using a similar damage-grading methodology did find lower wear scores in the autopsy group [14]. Therefore, the implants from our study are likely a worst-case example of wear damage.…”

“…Assessments were made for each of seven wear damage modes: burnishing, scratching, pitting, delamination, surface deformation, abrasion, and third-body embedded debris. A scale of 0 to 3 was used to reflect the extent and severity of the damage; the scale of Hood et al [9] has been used to identify damage by our group [19,20] and others [5,7,10,11,14] since 1983. It is a subjective score that does not assess wear directly, but instead qualitatively identifies damage.…”

Orthopedic Implant Retrieval and Failure Analysis

“…However, like Engh et al [174], Harman et al detected no difference between the revision specimens and autopsy specimens [175]. Rohrbach et al also studied both revision and autopsy specimens, and used an elaborate scoring scheme to measure wear and damage [176]. Both retrieved groups showed fatigue and wear damage.…”

“…Time in situ did not change first generation ingrowth [179]. However, time in situ directly correlated with increased wear especially for fatigue failure in PCA and Duracon prostheses [176]. Kinematics showed wear predominantly in those areas of highest contact femoral tibial articulation on motion fluoroscopics, stair climbing, and gait.…”

“…High stress load in low conforming designs can lead to polyethylene overload. This may be accelerated clinically with poor undercorrection of varus/ valgus, which correlated to sliding distance on the bearing surface [176]. Implants are designed to maximize the conformity while permitting the natural motions of the knee.…”