title: The precision and influence of rotation for measurements of bone mineral density of the distal femur following total knee arthroplasty: a methodological study using DEXA.
abstract: We evaluated the feasibility of DEXA (Norland XR-26 mark II) for quantitative measurements of bone mineral density (BMD) in the lateral plane of the distal femur after total knee arthroplasty (TKA). BMD was measured in 5-6 regions of interest (ROI) in close relation to the femoral component. In an in vitro study using 3 different distal femur phantoms, we found that the precision was affected by rotation of the distal femur. When BMD measurements were repeated within a range of motion of 40 degrees, 20 degrees, and 0 degrees, the coefficient of variation (CV) was approximately 15%, 10%, and 0.6%, respectively. We found that the use of bone cement for implant fixation had no effect on the level of BMD. Double measurements performed in 28 patients gave average CV values of 3.3%, 3.0%, and 2.6% for the uncemented Duracon, and Interax femoral components and the cemented AGC components, respectively. Our in vivo average CV measurements of BMD of the distal femur after TKA were on a level, suitable for repeated BMD measurements in prospective studies, which evaluate adaptive bone remodeling of the distal femur after cemented and uncemented TKA.
authors.affiliation: Department of Orthopedic Surgery U, Rigshospitalet, National University Hospital, Copenhagen, Denmark.
authors.forename: Matthias
authors.initials: M
authors.lastname: Therbo
authors.forename: Michael M
authors.initials: MM
authors.lastname: Petersen
authors.forename: Henrik M
authors.initials: HM
authors.lastname: Schrøder
authors.forename: Palle K
authors.initials: PK
authors.lastname: Nielsen
authors.forename: Bo
authors.initials: B
authors.lastname: Zerahn
authors.forename: Bjarne
authors.initials: B
authors.lastname: Lund
mesh_terms: D015502:Absorptiometry, Photon; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D019645:Arthroplasty, Replacement, Knee; D015519:Bone Density; D005240:Feasibility Studies; D005260:Female; D005269:Femur / Q000502:physiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D012399:Rotation