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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).

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

Zones and scores. Inlays were divided into six zones with 1–3 always representing medial and 4–6 lateral side (a). Mean total wear score for autopsy (b) and revision retrievals (c). Relative values for fatigue type wear are listed in brackets.
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Figure 1: Zones and scores. Inlays were divided into six zones with 1–3 always representing medial and 4–6 lateral side (a). Mean total wear score for autopsy (b) and revision retrievals (c). Relative values for fatigue type wear are listed in brackets.

Mentions: Retrieved polyethylene inserts were photographed and assessed for wear by visual surface examination using a modification of an established wear score from Hood et al. [7,19]. Assessment was done by the second author, who was blinded to all patient-related data. To rule out intra-observer variation, wear rating was done twice several weeks apart. Definitive scores were subsequently calculated as mean values. Each insert's joint side was divided into 6 zones (Fig 1a) in a pattern very similar to that used by Blunn et al [7]. Each zone was rated from 0 (none) to 3 (most severe) for the presence of each of the five wear modes: delamination, cracks, pitting, abrasion and polishing. Delamination was defined as sheets of polyethylene coming off the surface. Cracks were seen in some inlays presenting as white lines at the outer margins going through full thickness. They were graded as 0 (none) to 3 (most severe, with three or more cracks). Pitting was defined as irregularly shaped craters usually 2–3-mm in diameter and 1–2 mm deep. Delamination, pitting and full thickness cracks were defined as fatigue type wear modes. According to most authors they are closely related to stress exceeding material fatigue strength [24,28]. Abrasion was defined as tufted areas resulting from roughening usually when pieces of bone or cement were running over that particular inlay area. This mode was rarely seen and therefore was discarded in the calculation of the total wear score. Polishing was defined as highly polished areas most likely corresponding to adhesive loss of material. Delamination and pitting were the overwhelming majority of wear modes and usually caused substantial loss of material. Thus when calculating the total damage score for each zone, we incorporated a separate factor for loss of material ranging from 0 (none) to 3 (most severe), which was then multiplied with the number for delamination and pitting. For instance if a zone had a severely delaminated polyethylene and therefore gross loss of material the total damage score for delamination was 3 × 3 = 9. The grand total of wear score for one inlay was calculated by summation of scores for the six zones. The theoretical maximum score was 3 × 3 (delamination*material loss) plus 3 × 3 (pitting*material loss) plus 3+3+3 (cracks+pitting+polishing) multiplied by 6 zones = 162. Presence of third bodies (cement and metal particles) and erosion of central peg was noted separately.


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)

Zones and scores. Inlays were divided into six zones with 1–3 always representing medial and 4–6 lateral side (a). Mean total wear score for autopsy (b) and revision retrievals (c). Relative values for fatigue type wear are listed in brackets.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 1: Zones and scores. Inlays were divided into six zones with 1–3 always representing medial and 4–6 lateral side (a). Mean total wear score for autopsy (b) and revision retrievals (c). Relative values for fatigue type wear are listed in brackets.
Mentions: Retrieved polyethylene inserts were photographed and assessed for wear by visual surface examination using a modification of an established wear score from Hood et al. [7,19]. Assessment was done by the second author, who was blinded to all patient-related data. To rule out intra-observer variation, wear rating was done twice several weeks apart. Definitive scores were subsequently calculated as mean values. Each insert's joint side was divided into 6 zones (Fig 1a) in a pattern very similar to that used by Blunn et al [7]. Each zone was rated from 0 (none) to 3 (most severe) for the presence of each of the five wear modes: delamination, cracks, pitting, abrasion and polishing. Delamination was defined as sheets of polyethylene coming off the surface. Cracks were seen in some inlays presenting as white lines at the outer margins going through full thickness. They were graded as 0 (none) to 3 (most severe, with three or more cracks). Pitting was defined as irregularly shaped craters usually 2–3-mm in diameter and 1–2 mm deep. Delamination, pitting and full thickness cracks were defined as fatigue type wear modes. According to most authors they are closely related to stress exceeding material fatigue strength [24,28]. Abrasion was defined as tufted areas resulting from roughening usually when pieces of bone or cement were running over that particular inlay area. This mode was rarely seen and therefore was discarded in the calculation of the total wear score. Polishing was defined as highly polished areas most likely corresponding to adhesive loss of material. Delamination and pitting were the overwhelming majority of wear modes and usually caused substantial loss of material. Thus when calculating the total damage score for each zone, we incorporated a separate factor for loss of material ranging from 0 (none) to 3 (most severe), which was then multiplied with the number for delamination and pitting. For instance if a zone had a severely delaminated polyethylene and therefore gross loss of material the total damage score for delamination was 3 × 3 = 9. The grand total of wear score for one inlay was calculated by summation of scores for the six zones. The theoretical maximum score was 3 × 3 (delamination*material loss) plus 3 × 3 (pitting*material loss) plus 3+3+3 (cracks+pitting+polishing) multiplied by 6 zones = 162. Presence of third bodies (cement and metal particles) and erosion of central peg was noted separately.

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