title: Dynamic RSA for the evaluation of inducible micromotion of Oxford UKA during step-up and step-down motion.
abstract: Background and purpose - Implant inducible micromotions have been suggested to reflect the quality of the fixation interface. We investigated the usability of dynamic RSA for evaluation of inducible micromotions of the Oxford Unicompartmental Knee Arthroplasty (UKA) tibial component, and evaluated factors that have been suggested to compromise the fixation, such as fixation method, component alignment, and radiolucent lines (RLLs). Patients and methods - 15 patients (12 men) with a mean age of 69 (55-86) years, with an Oxford UKA (7 cemented), were studied after a mean time in situ of 4.4 (3.6-5.1) years. 4 had tibial RLLs. Each patient was recorded with dynamic RSA (10 frames/second) during a step-up/step-down motion. Inducible micromotions were calculated for the tibial component with respect to the tibia bone. Postoperative component alignment was measured with model-based RSA and RLLs were measured on screened radiographs. Results - All tibial components showed inducible micromotions as a function of the step-cycle motion with a mean subsidence of up to -0.06 mm (95% CI: -0.10 to -0.03). Tibial component inducible micromotions were similar for cemented fixation and cementless fixation. Patients with tibial RLLs had 0.5° (95% CI: 0.18-0.81) greater inducible medio-lateral tilt of the tibial component. There was a correlation between postoperative posterior slope of the tibial plateau and inducible anterior-posterior tilt. Interpretation - All patients had inducible micromotions of the tibial component during step-cycle motion. RLLs and a high posterior slope increased the magnitude of inducible micromotions. This suggests that dynamic RSA is a valuable clinical tool for the evaluation of functional implant fixation.
authors.affiliation: a Department of Orthopedics , Aarhus University Hospital , Aarhus , Denmark.
authors.forename: Kristian
authors.initials: K
authors.lastname: Horsager
authors.affiliation: b Department of Orthopedic Surgery, Biomechanics and Imaging Group , Leiden University Medical Center , Leiden , the Netherlands.
authors.forename: Bart L
authors.initials: BL
authors.lastname: Kaptein
authors.affiliation: c Department of Radiology , Aarhus University Hospital , Aarhus , Denmark.
authors.forename: Lone
authors.initials: L
authors.lastname: Rømer
authors.affiliation: a Department of Orthopedics , Aarhus University Hospital , Aarhus , Denmark.
authors.forename: Peter B
authors.initials: PB
authors.lastname: Jørgensen
authors.affiliation: a Department of Orthopedics , Aarhus University Hospital , Aarhus , Denmark.
authors.forename: Maiken
authors.initials: M
authors.lastname: Stilling
mesh_terms: D000368:Aged; D019645:Arthroplasty, Replacement, Knee / Q000009:adverse effects / Q000379:methods*; D001696:Biomechanical Phenomena; D001843:Bone Cements; D002484:Cementation; D005080:Exercise Test / Q000379:methods; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007719:Knee Joint / Q000000981:diagnostic imaging* / Q000503:physiopathology / Q000601:surgery; D007720:Knee Prosthesis / Q000009:adverse effects; D008297:Male; D008875:Middle Aged; D009038:Motion; D000071066:Patient Reported Outcome Measures; D011474:Prosthesis Design; D011475:Prosthesis Failure / Q000209:etiology*; D059869:Radiostereometric Analysis / Q000379:methods; D013977:Tibia / Q000000981:diagnostic imaging
chemical_list: D001843:Bone Cements