title: The effect of tibial tuberosity medialization and lateralization on patellofemoral joint kinematics, contact mechanics, and stability.
abstract: BACKGROUND
  Tibial tuberosity (TT) transfer is a common procedure to treat patellofemoral instability in patients with elevated TT-trochlear groove (TG) distances. However, the effects of TT lateralization or medialization on patellar stability, kinematics, and contact mechanics remain unclear.
  
  
  OBJECTIVE
  Progressive medialization and lateralization will have increasingly adverse effects on patellofemoral joint kinematics, contact mechanics, and stability.
  
  
  METHODS
  Controlled laboratory study.
  
  
  METHODS
  Eight fresh-frozen cadaveric knees were placed on a testing rig, with a fixed femur and tibia mobile through 90° of flexion. Individual quadriceps heads and the iliotibial band were separated and loaded with 205 N in anatomic directions using a weighted pulley system. Patellofemoral contact pressures and patellar tracking were measured at 0°, 10°, 20°, 30°, 60°, and 90° of flexion using pressure-sensitive film behind the patella and an optical tracking system. The intact knee was measured with and without a 10-N patellar lateral displacement load, and recordings were repeated after TT transfer of 5, 10, and 15 mm medially and laterally. Statistical analysis used repeated-measures analysis of variance, Bonferroni post hoc analysis, and Pearson correlations.
  
  
  RESULTS
  Tibial tuberosity lateralization significantly elevated lateral joint contact pressures, increased lateral patellar tracking, and reduced patellar stability (P<.048). There was a significant correlation between mean lateral contact pressure and the TT position (r=0.810, P<.001) at 10°. Tibial tuberosity medialization reduced lateral contact pressures (P<.002) and did not elevate peak medial contact pressures (P>.11).
  
  
  CONCLUSIONS
  Progressive TT lateralization elevated lateral contact pressures, increased lateral patellar tracking, and reduced patellar stability. Medial contact pressure and tracking did alter with progressive TT medialization, but the changes were smaller.
  
  
  CONCLUSIONS
  Lateral patellofemoral joint contact pressures increased with progressive lateralization of the TT; medialization of the TT reduced these effects, restoring patellar stability, and did not cause excessive peak pressures. These data provide a rationale for medial TT transfer surgery in patients with elevated TT-TG distances.
authors.affiliation: Mechanical Engineering Department, Imperial College London, London, UK.
authors.forename: Joanna M
authors.initials: JM
authors.lastname: Stephen
authors.affiliation: Mechanical Engineering Department, Imperial College London, London, UK.
authors.forename: Punyawan
authors.initials: P
authors.lastname: Lumpaopong
authors.affiliation: Mechanical Engineering Department, Imperial College London, London, UK.
authors.forename: Alexander L
authors.initials: AL
authors.lastname: Dodds
authors.affiliation: Fortius Clinic, London, UK Musculoskeletal Surgery Group, Department of Surgery and Cancer, Charing Cross Hospital, Imperial College London, London, UK.
authors.forename: Andy
authors.initials: A
authors.lastname: Williams
authors.affiliation: Mechanical Engineering Department, Imperial College London, London, UK Musculoskeletal Surgery Group, Department of Surgery and Cancer, Charing Cross Hospital, Imperial College London, London, UK a.amis@imperial.ac.uk.
authors.forename: Andrew A
authors.initials: AA
authors.lastname: Amis
mesh_terms: D000368:Aged; D001696:Biomechanical Phenomena; D002102:Cadaver; D005260:Female; D006801:Humans; D007593:Joint Instability / Q000503:physiopathology / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D010329:Patella / Q000503:physiopathology*; D057071:Patellofemoral Joint / Q000503:physiopathology / Q000601:surgery*; D011312:Pressure; D016059:Range of Motion, Articular; D013977:Tibia / Q000601:surgery*
keywords: contact pressures; patellar instability; patellofemoral tracking; surgery; tibial tuberosity–trochlear groove (TT-TG)