title: Comparison of fixation methods after anteromedialization osteotomy of the tibial tubercle for patellar instability.
abstract: OBJECTIVE
  The aim of this study was to evaluate the biomechanical strength of two 4.5-mm screws and three 3.5-mm screws for fixation of the tibial tubercle after anteromedialization osteotomy.
  
  
  METHODS
  Anteromedialization of the tibial tubercle was performed on 5 pairs of fresh-frozen cadaveric lower extremities. One leg from each pair was randomized to fixation with two 4.5-mm screws and the contralateral leg to fixation with three 3.5-mm screws. Each specimen was loaded cyclically to simulate an active straight-leg raise and then to failure while displacement of the tubercle fragment was recorded.
  
  
  RESULTS
  There was no difference in mean tubercle fragment displacement under cyclic loading at any cycle number (P > .352). Maximum failure load for osteotomies secured with two 4.5-mm screws was 1,459 ± 540 N, and for three 3.5-mm screws it was 1,360 ± 707 N. This was not a statistically significant difference (P = .723). Tubercle migration of 7 mm was chosen as clinical failure. At this amount of displacement, mean load was 1,085 ± 398 N and 764 ± 313 N in the 4.5-mm and 3.5-mm groups, respectively, which was also not significantly different (P = .146).
  
  
  CONCLUSIONS
  Both 2 × 4.5-mm and 3 × 3.5-mm screw constructs after tibial tubercle anteromedialization are equally capable of withstanding physiologic forces like those encountered during an active straight-leg raise and have similar failure strength.
  
  
  CONCLUSIONS
  Although both configurations are comparable, the use of the smaller 3.5-mm screws may reduce the need for hardware removal related to prominence and soft tissue irritation.
authors.affiliation: Departments of Orthopaedics and Biomedical Engineering, (P.S.W.), University of North Carolina School of Medicine, Chapel Hill, North Carolina, U.S.A.. Electronic address: bwarner@unch.unc.edu.
authors.forename: Brent T
authors.initials: BT
authors.lastname: Warner
authors.forename: Ganesh V
authors.initials: GV
authors.lastname: Kamath
authors.forename: Jeffrey T
authors.initials: JT
authors.lastname: Spang
authors.forename: Paul S
authors.initials: PS
authors.lastname: Weinhold
authors.forename: R Alexander
authors.initials: RA
authors.lastname: Creighton
mesh_terms: D000368:Aged; D001696:Biomechanical Phenomena; D001863:Bone Screws / Q000592:standards; D002102:Cadaver; D006801:Humans; D007593:Joint Instability / Q000209:etiology / Q000503:physiopathology / Q000601:surgery*; D007719:Knee Joint / Q000503:physiopathology / Q000601:surgery*; D008875:Middle Aged; D010027:Osteotomy / Q000379:methods*; D010329:Patella / Q000293:injuries / Q000601:surgery*; D031222:Patellar Dislocation / Q000150:complications / Q000601:surgery; D013977:Tibia / Q000601:surgery*