A new device for patellofemoral instrumented stress-testing provides good reliability and validity

Ana Leal, Renato Andrade, Betina B. Hinckel, Marc Tompkins, Paulo Flores, Filipe Silva, João Espregueira-Mendes, Elizabeth Arendt

Research output: Contribution to journalArticlepeer-review

7 Scopus citations


Purpose: To evaluate the reliability of an instrumented patellofemoral (PF) stress-testing—the Porto Patellofemoral Testing Device (PPTD)—and validate the instrumented assessment method comparing to manual physical examination. Methods: Eight asymptomatic volunteers underwent bilateral PF-instrumented examination with the PPTD and magnetic resonance imaging (MRI) to assess intra-rater reliability of the instrumented assessment methodology. Six patients with unilateral PF instability underwent physical examination and PPTD concomitantly with MRI. Manual examination was performed by two blinded surgeons and compared with PPTD test. Ligament stiffness was calculated and compared between injured and non-injured lower limbs. Results: PPTD showed a pre-determined and reproducible stress-force application with excellent intra-rater agreement (intra-class correlation coefficient 0.83–0.98). The manual exam was imprecise with variable examiner-dependent stress-force application. The PPTD resulted in greater lateral patellar translation (converted in quadrants) than manual exam for patients that have reached maximum translation force. Measurement of patellar position and displacement using PPTD was more accurate and precise than the visual estimation of translated quadrants by manual exam. Ligament stiffness curves showed no relevant changes in patellar displacement after 62 N. Conclusion: The PPTD instrumented stress-testing is a valid device to quantify PF position and displacement with high intra-rater reliability, showing more accuracy, more precision and less variability than physical examination. This device provides an accurate and objective measure to quantify the patellar movement which can augment the physical examination procedures and assist clinicians in the management of decision-making and in the assessment of post-treatment outcomes of PF pathological conditions.

Original languageEnglish (US)
Pages (from-to)389-397
Number of pages9
JournalKnee Surgery, Sports Traumatology, Arthroscopy
Issue number2
StatePublished - Feb 1 2020

Bibliographical note

Funding Information:
The authors would like to sincerely acknowledge: the Clinical Director of SMIC Drag?o (Dr. Rui Aguiar) and the Head of the CMRR (Juta Ellerman) and their teams for the technical support in the imaging study; the University of Minnesota Professors Joan Bechtold and Jack Lewis for their valuable discussions on the validity study approach and the Department of Orthopedics Research Fund from University of Minnesota for the financial support for the validity study.

Publisher Copyright:
© 2019, European Society of Sports Traumatology, Knee Surgery, Arthroscopy (ESSKA).


  • Arthrometer
  • Laxity
  • Magnetic resonance imaging
  • Patellofemoral
  • Patellofemoral instability

PubMed: MeSH publication types

  • Journal Article
  • Validation Study


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