title: Assessment of demographic and pathoanatomic risk factors in recurrent patellofemoral instability.
abstract: OBJECTIVE
  The WARPS/STAID classification employs clinical assessment of presenting features and anatomic characteristics to identify two distinct subsets of patients within the patellofemoral instability population. The purpose of this study was to further define the specific demographics and the prevalence of risky pathoanatomies in patients classified as either WARPS or STAID presenting with recurrent patellofemoral instability. A secondary purpose was to further validate the WARPS/STAID classification with the Banff Patella Instability Instrument (BPII), the Marx activity scale and the Patellar Instability Severity Score (ISS).
  
  
  METHODS
  A convenience sample of 50 patients with recurrent patellofemoral instability, including 25 WARPS and 25 STAID subtype patients, were assessed. Clinical data were collected including assessment of demographic risk factors (sex, BMI, bilaterality of symptoms, affected limb side and age at first dislocation) and pathoanatomic risk factors (TT-TG distance, patella height, patellar tilt, grade of trochlear dysplasia, Beighton score and rotational abnormalities of the tibia or femur). Patients completed the BPII and the Marx activity scale. The ISS was calculated from the clinical assessment data. Patients were stratified into the WARPS or STAID subtypes for comparative analysis. An independent t test was used to compare demographics, the pathoanatomic risk factors and subjective measures between the groups. Convergent validity was tested with a Pearson r correlation coefficient between the WARPS/STAID and ISS scores.
  
  
  RESULTS
  Demographic risk factors statistically associated with a WARPS subtype included female sex, age at first dislocation and bilaterality. Pathoanatomic risk factors statistically associated with a WARPS subtype included trochlear dysplasia, TT-TG distance, generalized ligamentous laxity, patellar tilt and rotational abnormalities. The independent t test revealed a significant difference between the ISS scores: WARPS subtype (M = 4.4, SD = 1.1) and STAID subtype (M = 2.5, SD = 1.5); t(48) = 5.2, p < 0.001. The relationship between the WARPS/STAID and the ISS scores, measured using a Pearson r correlation coefficient, demonstrated a strong relationship: r = -0.61, n = 50, p < 0.001.
  
  
  CONCLUSIONS
  This study has demonstrated statistically significant evidence that certain demographics and pathoanatomies are more prevalent in each of the WARPS and STAID patellofemoral instability subtypes. There was no difference in quality-of-life or activity level between the subtypes. The WARPS/STAID score demonstrated convergent validity to the ISS and divergent validity to the BPII score and the Marx activity scale. This study has further validated both the WARPS/STAID classification and the ISS of patients that present with recurrent patellofemoral instability.
  
  
  METHODS
  III.
authors.affiliation: Banff Sport Medicine, PO Box 1300, Banff, AB, T1L 1B3, Canada. hiemstra@banffsportmed.ca.|Department of Surgery, University of Calgary, Calgary, Canada. hiemstra@banffsportmed.ca.
authors.forename: Laurie Anne
authors.initials: LA
authors.lastname: Hiemstra
authors.affiliation: Banff Sport Medicine, PO Box 1300, Banff, AB, T1L 1B3, Canada.|Department of Physical Therapy, University of Alberta, Edmonton, Canada.
authors.forename: Sarah
authors.initials: S
authors.lastname: Kerslake
authors.affiliation: Department of Health and Physical Education, Mount Royal University, Calgary, Canada.
authors.forename: Mark
authors.initials: M
authors.lastname: Lafave
mesh_terms: D000328:Adult; D005260:Female; D005269:Femur; D006801:Humans; D007593:Joint Instability / Q000209:etiology; D008297:Male; D008875:Middle Aged; D010329:Patella / Q000601:surgery; D031222:Patellar Dislocation / Q000453:epidemiology / Q000209:etiology* / Q000601:surgery; D057071:Patellofemoral Joint / Q000601:surgery*; D015995:Prevalence; D011788:Quality of Life; D012008:Recurrence; D012307:Risk Factors; D013977:Tibia / Q000601:surgery; D055815:Young Adult
keywords: Patellar Instability Severity Score; Patellar instability; Patellar tilt; Patellofemoral instability; Trochlear dysplasia; WARPS/STAID classification