title: Q-vector measurements: physical examination versus magnetic resonance imaging measurements and their relationship with tibial tubercle-trochlear groove distance.
abstract: OBJECTIVE
  An increased lateral quadriceps vector has been associated with lateral patellar dislocation. Surgical correction of this increased vector through tibial tubercle medialization is often recommended when the quadriceps vector is "excessive". This can be evaluated by physical examination measurements of Q-angle and/or tubercle sulcus angle (TSA), as well as the magnetic resonance imaging (MRI) measurement of tibial tubercle-trochlear groove (TT-TG) distance. This study examined the relationship between three objective measurements of lateral quadriceps vector (TT-TG, Q-angle, TSA). A secondary goal was to relate lateral patellar tilt to these measurements.
  
  
  METHODS
  Consecutive patients undergoing patellofemoral stabilization surgery from 9/2010 to 6/2011 were included. The Q-angle and TSA were measured on intra-operative physical examination. The TT-TG and patellar tilt were measured on MRI. TSA, Q-angle, and patellar tilt were compared to TT-TG using Pearson correlation coefficient.
  
  
  RESULTS
  The study cohort included 49 patients, ages 12-37 (mean 23.2); 62% female. The Pearson correlation coefficients showed (+) significance (p < 0.01) between the TT-TG and both TSA and Q-angle. Tilt and TT-TG were (+) non-significantly correlated. Despite positive correlations of each measurement with TT-TG, there is not uniform intra-patient correlation. In other words, if TT-TG is elevated for a patient, it does not guarantee that all other measurements, including tilt, are elevated in that individual patient.
  
  
  CONCLUSIONS
  The TT-TG distance has significant positive correlation with the measurements of TSA and Q-angle in patients undergoing surgery for patellofemoral instability. The clinical relevance is that the variability within individual patients demonstrates the need for considering both TSA and TT-TG before and during surgical intervention to avoid overcorrection with a medial tibial tubercle osteotomy.
  
  
  METHODS
  Diagnostic study, Level III.
authors.affiliation: University of Minnesota Medical School, Minneapolis, MN, USA.
authors.forename: Kristin H
authors.initials: KH
authors.lastname: Graf
authors.affiliation: Department of Orthopaedic Surgery, University of Minnesota, 2450 Riverside Avenue South, Suite R 200, Minneapolis, MN, 55454, USA.|TRIA Orthopaedic Center, Bloomington, MN, USA.
authors.forename: Marc A
authors.initials: MA
authors.lastname: Tompkins
authors.affiliation: Department of Orthopaedic Surgery, University of Minnesota, 2450 Riverside Avenue South, Suite R 200, Minneapolis, MN, 55454, USA.
authors.forename: Julie
authors.initials: J
authors.lastname: Agel
authors.affiliation: Department of Orthopaedic Surgery, University of Minnesota, 2450 Riverside Avenue South, Suite R 200, Minneapolis, MN, 55454, USA. arend001@umn.edu.
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: Arendt
mesh_terms: D000293:Adolescent; D000328:Adult; D002648:Child; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D019637:Orthopedic Procedures / Q000379:methods; D010329:Patella / Q000473:pathology* / Q000601:surgery; D031222:Patellar Dislocation / Q000175:diagnosis* / Q000601:surgery; D057071:Patellofemoral Joint / Q000000981:diagnostic imaging* / Q000601:surgery; D010808:Physical Examination / Q000379:methods*; D019651:Plastic Surgery Procedures / Q000379:methods; D013977:Tibia / Q000000981:diagnostic imaging* / Q000601:surgery; D055815:Young Adult
keywords: MRI; Magnetic resonance imaging; Patellar tilt; Q angle; Q vector; Q-angle; TSA; TT–TG distance; Tibial tubercle–trochlear groove; Tubercle sulcus angle