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Anatomical patella instability risk factors on MRI show sensitivity without specificity in patients with patellofemoral instability: a systematic review
  1. Taylor J Ridley1,
  2. Betina Bremer Hinckel2,
  3. Bradley M Kruckeberg3,
  4. Julie Agel1,
  5. Elizabeth A Arendt1
  1. 1Department of Orthopaedic Surgery, University of Minnesota, Minneapolis, Minnesota, USA
  2. 2Medical School, University of Minnesota, Minneapolis, Minnesota, USA
  3. 3Institute of Orthopedics and Traumatology of the Clinical Hospital, Medical School, University of São Paulo, Minneapolis, Minnesota, USA
  1. Correspondence to Dr Elizabeth A Arendt, Department of Orthopaedic Surgery, University of Minnesota, 2450 Riverside Av. So., Ste. R200, Minneapolis 55454, MN, USA; arend001{at}


Purpose The purpose of this systematic review is to assess whether the current literature distinguishes between 9 common anatomic patellofemoral instability (PFI) imaging measurements to determine if they are consistent among the group of patients with PFI, and if a diagnostic difference exists between the control and patients with PFI in these imaging measurements.

Methods Following PRISMA guidelines, a systematic review of PubMed and CINAHL/SPORTDiscus was performed to identify all studies measuring PFI anatomic imaging factors from January 1980 to February 2015. Study inclusion criteria were: English language, MRI studies, imaging of PFI anatomic factors. References of the included articles were reviewed and those that met inclusion criteria were added to the search results. PFI group was defined as the study stating that the cohort had at least 1 objective patient episode of lateral patellar dislocation. Studies that did not report sample size, mean and SD were excluded, as well as those that used osseous (vs cartilage) landmarks, or who did not define their measurement landmarks. Meta-analysis software was used to determine weighted mean and 95% CI for PFI and control groups for each measurement. Of the 135 articles identified, 22 met the inclusion criteria.

Results Caton-Deschamps patella height index and trochlear depth measurement showed non-overlapping CIs between the control and PFI groups. Insall-Salvati ratio, lateral patella tilt, tibial tubercle-trochlear groove distance and trochlear facet asymmetry, although having statistically different means, had overlaped between the overall mean 95% CI of the 2 groups. Although few studies were available for each measurement, the number of total participants per measurement included is considerable: PFI (range 40–685); controls (range 94–671).

Conclusions A systematic search of current literature with meta-analysis reveals wide variation of PFI imaging measurements used for clinical decision-making within the controls and PFI groups. This systematic review demonstrates that appropriate abnormality thresholds of anatomic patella instability imaging factors exist for the PFI group, indicating sensitivity. The wide variation in the majority of measurements, especially in the control group, suggests poor specificity in these measurements. Trochlear depth has the best discrimination in evaluation between the control and the PFI groups.

Level of evidence Level III, systematic review.

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