title: Measuring polyethylene wear in total knee arthroplasty by RSA: differences between weight-bearing and non-weight-bearing positioning.
abstract: Measuring the minimum-joint-space-width (mJSW) in total knee arthroplasty (TKA) in Roentgen stereophotogrammetric analysis (RSA) provides valuable information on polyethylene wear, a leading cause for TKA failure. Most existing studies use non-weight-bearing (NWB) patient positioning. The latter may compromise mJSW measurements due to knee laxity with subsequent non-contact between the TKA components. We investigated the difference in mJSW between weight-bearing (WB) and NWB images and the association with mediolateral (ML) knee stability. At one-year follow-up, 23 TKAs were included from an ongoing RSA study, and ML stability was evaluated. For each examination, the mJSW and femoral-tibial contact locations were measured. A linear regression model was used to analyze the association between the mJSW difference (NWB-WB) with the ML stability and contact locations. The mean mJSW difference was 0.28 mm medially and 0.20 mm laterally. Four TKAs had medium (5-9°) and 19 TKAs had high (<5°) ML stability. A higher mJSW difference was found for TKAs with medium stability (0.36 mm, P = 0.01). In conclusion, mJSW measurements in existing (NWB) RSA studies are influenced by knee laxity, but may still provide information on wear progression based on TKA with high ML stability. A direct comparison of mJSW measurements from WB and NWB data is not possible.
authors.affiliation: Biomechanics and Imaging Group, Department of Orthopaedics, Leiden University Medical Center, Leiden, The Netherlands.
authors.forename: Emiel A
authors.initials: EA
authors.lastname: van Ijsseldijk
authors.forename: Edward R
authors.initials: ER
authors.lastname: Valstar
authors.forename: Berend C
authors.initials: BC
authors.lastname: Stoel
authors.forename: Ruud
authors.initials: R
authors.lastname: de Ridder
authors.forename: Rob G H H
authors.initials: RG
authors.lastname: Nelissen
authors.forename: Bart L
authors.initials: BL
authors.lastname: Kaptein
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D019645:Arthroplasty, Replacement, Knee; D005260:Female; D006801:Humans; D007593:Joint Instability / Q000000981:diagnostic imaging; D007595:Joint Prosthesis; D007719:Knee Joint / Q000000981:diagnostic imaging* / Q000502:physiology; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D020959:Polyethylene; D011446:Prospective Studies; D059869:Radiostereometric Analysis; D016474:Weight-Bearing
chemical_list: D020959:Polyethylene
keywords: polyethylene wear; roentgen stereophotogrammetric analysis; total knee arthroplasty