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Current failure mechanisms after knee arthroplasty have changed: polyethylene wear is less common in revision surgery (JBJS 2015)

Screenshot-2015-05-20-00.12.34-e1432095302195-73x98 Current failure mechanisms after knee arthroplasty have changed: polyethylene wear is less common in revision surgery (JBJS 2015) Joint Reconstruction | JC Journal Club


Background/Purpose
-Previous studies from 1986-2000 showed polyethylene wear reason for revision in 25%
-This study to clarify more up-to-date reasons for failure/revision of TKA correlated with time and to see if polyethylene wear still major reason for revision

Methods
-Retrospective including 1st revisions b/w 2005-2010 @ 2 high volume joint centers (university academic + nonuniversity academic)
-Failure times from index arthroplasty: early (<1 yr), intermediate (1-3 yrs), late (>3 yrs)

Results:
-358 patients, mean age 69.3 yrs, 65% F, mean BMI 28.7
-highest failure within 6yrs (77.9%)
-19.8% in 1st year, 45.5% b/w 1-3 yrs, 34.6% >3 yrs
-of pts requiring revision 91% had index arthroplasty within past 10 yrs (important b/c of different techniques/material quality)
-median interval b/w primary and revision was 4yrs (0-20); mean 1.5 yrs in early/intermediate group and 7.9 yrs in late group
-although considered any component replaced “revision” nearly all pts had complete component exchange
-overall most common indications for revision were aseptic loosening (21.8%), instability (21.8%), malalignment (20.7%), and periprosthetic infection (14.5%)
-Early group (<1 yr): periprosthetic infection (26.8%), instability (23.3.%) and malalignment (18.3%)
-Intermediate group (1-3yrs): malalignment (29.4%), ligament instability (23.3%), and aseptic loosening (16%)
-Late (>3yrs): aseptic loosening (34.7%), ligament instability (18.5%), and polyethylene wear (18.5%), only 8.9% infection
-arthrofibrosis rare in total cohort

Limitations:
-80% were referrals for revision from outside orthopaedists
-wide range of time from index to revision
-although almost consistent use of implants, can’t exclude systematic impact of multiple prosthetic designs and development of surgical techniques
-no long-term analysis (>20yrs) and may impact results in future studies

Conclusions:
-previous studies showed polyethylene wear as leading etiology for failure (25%); only 7% in this study with most >3yrs (18.5% of late failures); likely lower rates 2/2 improvements in poly manufacturing and material properties
-surprisingly high early deep infection in 1st year (26.8%)
-increased rate of inadequate component alignment (20.7%) as predicted (likely b/c higher detection with use of CT)
-femoral component: >10 deg ER or >5 deg IR considered pathologic
-tibial component: <18 deg IR normal
-ligament instability a leading cause of failure illustrating importance of soft-tissue balancing and use of appropriate implant design
-infection 4th most common cause of failure overall (14.5% of all failures with 26.8% in first year); “early” infections likely result of OR environment, intraop contamination, or immediate postop wound complications and can probably be reduced by addressing patient and surgeon-related risk factors
-this study identified aseptic loosening, instability, infection, and malalignment as leading failure mechanisms, irrespective of time interval considered and are surgeon-related factors

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