title: Tibial component alignment and risk of loosening in unicompartmental knee arthroplasty: a radiographic and radiostereometric study.
abstract: OBJECTIVE
  Unicompartmental knee arthroplasty (UKA) has shown a higher rate of revision compared with total knee arthroplasty. The success of UKA depends on prosthesis component alignment, fixation and soft tissue integrity. The tibial cut is the crucial surgical step. The hypothesis of the present study is that tibial component malalignment is correlated with its risk of loosening in UKA.
  
  
  METHODS
  This study was performed in twenty-three patients undergoing primary cemented unicompartmental knee arthroplasties. Translations and rotations of the tibial component and the maximum total point motion (MTPM) were measured using radiostereometric analysis at 3, 6, 12 and 24 months. Standard radiological evaluations were also performed immediately before and after surgery. Varus/valgus and posterior slope of the tibial component and tibial-femoral axes were correlated with radiostereometric micro-motion. A survival analysis was also performed at an average of 5.9 years by contacting patients by phone.
  
  
  RESULTS
  Varus alignment of the tibial component was significantly correlated with MTPM, anterior tibial sinking, varus rotation and anterior and medial translations from radiostereometry. The posterior slope of the tibial component was correlated with external rotation. The survival rate at an average of 5.9 years was 89%. The two patients who underwent revision presented a tibial component varus angle of 10° for both.
  
  
  CONCLUSIONS
  There is correlation between varus orientation of the tibial component and MTPM from radiostereometry in unicompartmental knee arthroplasties. Particularly, a misalignment in varus larger than 5° could lead to risk of loosening the tibial component.
  
  
  METHODS
  Prognostic studies-retrospective study, Level II.
authors: 1st Ortopaedic-Traumatologic Clinic, Istituto Ortopedico Rizzoli, University of Bologna, Via Pupilli 1, 40136, Bologna, Bo, Italy, paolobarba@hotmail.it.
authors: P
authors: P
authors: Barbadoro
authors: A
authors: A
authors: Ensini
authors: A
authors: A
authors: Leardini
authors: M
authors: M
authors: d'Amato
authors: A
authors: A
authors: Feliciangeli
authors: A
authors: A
authors: Timoncini
authors: F
authors: F
authors: Amadei
authors: C
authors: C
authors: Belvedere
authors: S
authors: S
authors: Giannini
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D019645:Arthroplasty, Replacement, Knee / Q000379:methods*; D017760:Bone Malalignment / Q000601:surgery; D005260:Female; D006801:Humans; D007592:Joint Diseases / Q000601:surgery*; D007719:Knee Joint / Q000000981:diagnostic imaging* / Q000601:surgery; D007720:Knee Prosthesis; D008297:Male; D008875:Middle Aged; D011475:Prosthesis Failure; D059869:Radiostereometric Analysis; D012189:Retrospective Studies; D012399:Rotation; D013977:Tibia / Q000000981:diagnostic imaging / Q000601:surgery*