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

Rohrbach M, Lüem M, Ochsner PE - J Orthop Surg Res (2008)

Bottom Line: Wear score after comparable implantation time was significantly less in the autopsy group.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).

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Affiliation: Kantonsspital Liestal, Orthopaedic Department, Rheinstrasse 26, 4410 Liestal, Switzerland. rohrbach@beachers.ch

ABSTRACT

Background: Polyethylene 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.

Methods: The 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.

Results: Wear 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 (R(2) = 0.383) and the revision group (R(2) = 0.813).

Conclusion: The 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.

No MeSH data available.


Related in: MedlinePlus

Probability curves for occurrence of fatigue-type wear. Probability curves for occurrence of fatigue-type wear with 95% confidence boundaries. Calculation was done via Kaplan-Meier survival estimates and plotted as cumulative hazard plot. Time course for autopsy and revision is not different (Log ranked test ns.) indicating that cumulative risk at a given time point was the same independently from group affiliation.
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Figure 4: Probability curves for occurrence of fatigue-type wear. Probability curves for occurrence of fatigue-type wear with 95% confidence boundaries. Calculation was done via Kaplan-Meier survival estimates and plotted as cumulative hazard plot. Time course for autopsy and revision is not different (Log ranked test ns.) indicating that cumulative risk at a given time point was the same independently from group affiliation.

Mentions: To test the assumption that inserts with higher wear scores were correlated to more distinctive use, the index of use was plotted against total medial (Fig 3b) as well as medial fatigue type wear score (Fig 3c) and linear regression was calculated. Probability curves were drawn to compare cumulative risk of fatigue type wear (delamination, pitting or cracks) and subsequently tested for difference via log ranked test. Calculation was done using the method of Kaplan-Meier and displayed as cumulative hazard plot (Fig 4).


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

Rohrbach M, Lüem M, Ochsner PE - J Orthop Surg Res (2008)

Probability curves for occurrence of fatigue-type wear. Probability curves for occurrence of fatigue-type wear with 95% confidence boundaries. Calculation was done via Kaplan-Meier survival estimates and plotted as cumulative hazard plot. Time course for autopsy and revision is not different (Log ranked test ns.) indicating that cumulative risk at a given time point was the same independently from group affiliation.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2289815&req=5

Figure 4: Probability curves for occurrence of fatigue-type wear. Probability curves for occurrence of fatigue-type wear with 95% confidence boundaries. Calculation was done via Kaplan-Meier survival estimates and plotted as cumulative hazard plot. Time course for autopsy and revision is not different (Log ranked test ns.) indicating that cumulative risk at a given time point was the same independently from group affiliation.
Mentions: To test the assumption that inserts with higher wear scores were correlated to more distinctive use, the index of use was plotted against total medial (Fig 3b) as well as medial fatigue type wear score (Fig 3c) and linear regression was calculated. Probability curves were drawn to compare cumulative risk of fatigue type wear (delamination, pitting or cracks) and subsequently tested for difference via log ranked test. Calculation was done using the method of Kaplan-Meier and displayed as cumulative hazard plot (Fig 4).

Bottom Line: Wear score after comparable implantation time was significantly less in the autopsy group.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).

View Article: PubMed Central - HTML - PubMed

Affiliation: Kantonsspital Liestal, Orthopaedic Department, Rheinstrasse 26, 4410 Liestal, Switzerland. rohrbach@beachers.ch

ABSTRACT

Background: Polyethylene 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.

Methods: The 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.

Results: Wear 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 (R(2) = 0.383) and the revision group (R(2) = 0.813).

Conclusion: The 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.

No MeSH data available.


Related in: MedlinePlus