Many Radiographic and Magnetic Resonance Imaging Assessments for Surgical Decision Making in Pediatric Patellofemoral Instability Patients Demonstrate Poor Interrater Reliability


      To evaluate the interrater reliability of several common radiologic parameters used for patellofemoral instability and to attempt to improve reliability for measurements demonstrating unacceptable interrater reliability through consensus training.


      Fifty patients with patellar instability between the ages of 10 and 19 years were selected from a prospectively enrolled cohort. For measurements demonstrating unacceptable interrater reliability (intraclass correlation coefficient [ICC]: <0.6), raters discussed consensus methods to improve reliability and re-examined a subset of 20 images from the previous set of images. If reliability was still low after the second round of assessment, the measure was considered unreliable.


      Of the 50 included subjects, 22 (44%) were male and the mean age at the time of imaging was 14 ± 2 years. With 1 or fewer consensus training sessions, the interrater reliability of the following radiograph indices were found to be reliable: trochlea crossing sign (ICC: 0.625), congruence angle (ICC: 0.768), Caton-Deshamps index (ICC: 0.644), lateral patellofemoral angle (ICC: 0.768), and mechanical axis deviation on hip-to-ankle alignment radiographs (ICC: 0.665-0.777). Reliable magnetic resonance imaging (MRI) indices were trochlear depth (ICC: 0.743), trochlear bump (ICC: 0.861), sulcus angle (ICC: 0.684), patellar tilt (ICC: 0.841), tibial tubercle to trochlear groove distance (ICC: 0.706), effusion (ICC: 0.866), and bone marrow edema (ICC: 0.961).


      With 1 or fewer consensus training sessions, the interrater reliability of the following patellofemoral indices were found to be reliable for trochlear morphology: trochlea crossing sign and congruence angle on radiograph and trochlear depth, trochlear bump, and sulcus angle on MRI. Reliable patellar position measurements included: Caton-Deshamps index and lateral patellofemoral angle on radiograph and patellar tilt and tibial tubercle to trochlear groove distance on MRI. Additional global measurements (e.g., mechanical axis deviation on standing radiographs) and MRI assessments demonstrated acceptable reliability.

      Level of Evidence

      II, prospective diagnostic study.
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        • Magnussen R.A.
        • Verlage M.
        • Stock E.
        • et al.
        Primary patellar dislocations without surgical stabilization or recurrence: How well are these patients really doing?.
        Knee Surg Sports Traumatol Arthrosc. 2017; 25: 2352-2356
        • Waterman B.R.
        • Belmont P.J.
        • Owens B.D.
        Patellar dislocation in the United States: Role of sex, age, race, and athletic participation.
        J Knee Surg. 2011; 25: 51-58
        • Colvin A.C.
        • West R.V.
        Current concepts review: Patellar instability.
        J Bone Joint Surg. 2008; 90A: 2751-2762
        • Khormaee S.
        • Kramer D.E.
        • Yen Y.M.
        • Heyworth B.E.
        Evaluation and management of patellar instability in pediatric and adolescent athletes.
        Sports Health. 2015; 7: 115-123
        • Diederichs G.
        • Issever A.S.
        • Scheffler S.
        MR imaging of patellar instability: Injury patterns and assessment of risk factors.
        Radiographics. 2010; 30: 961-981
        • Dejour D.
        • Le Coultre B.
        Osteotomies in patello-femoral instabilities.
        Sports Med Arthrosc Rev. 2007; 15: 39-46
        • Fithian D.C.
        • Paxton E.W.
        • Cohen A.B.
        Indications in the treatment of patellar instability.
        J Knee Surg. 2004; 17: 47-56
        • Nelitz M.
        • Theile M.
        • Dornacher D.
        • Wölfle J.
        • Reichel H.
        • Lippacher S.
        Analysis of failed surgery for patellar instability in children with open growth plates.
        Knee Surg Sports Traumatol Arthrosc. 2012; 20: 822-828
        • Donner A.
        • Eliasziw M.
        Sample size requirements for reliability studies.
        Stat Med. 1987; 6: 441-448
      1. Age limits and adolescents.
        Paediatr Child Health. 2003; 8: 577
        • Bishop M.E.
        • Brady J.M.
        • Ling D.
        • Parikh S.
        • Stein B.E.S.
        Descriptive epidemiology study of the justifying patellar instability treatment by early results (JUPITER) cohort.
        Orthop J Sports Med. 2019; 7 (2325967119S00046 (3 suppl))
        • Landis J.R.
        • Koch G.G.
        The measurement of observer agreement for categorical data.
        Biometrics. 1977; 33: 159
        • Thévenin-Lemoine C.
        • Ferrand M.
        • Courvoisier A.
        • Damsin J.P.
        • Le Pointe H.D.
        • Vialle R.
        Is the Caton-Deschamps index a valuable ratio to investigate patellar height in children?.
        J Bone Joint Surg Am. 2011; 93: e35
        • Laurin C.A.
        • Levesque H.P.
        • Dussault R.
        • Labelle H.
        • Peides J.
        The abnormal lateral patellofemoral angle: A diagnostic roentgenographic sign of recurrent patellar subluxation.
        J Bone Joint Surg Am. 1978; 60A: 55-60
        • Pandit S.
        • Frampton C.
        • Stoddart J.
        • Lynskey T.
        Magnetic resonance imaging assessment of tibial tuberosity-trochlear groove distance: Normal values for males and females.
        Int Orthop. 2011; 35: 1799-1803
        • Dejour H.
        • Walch G.
        • Nove-Josserand L.
        • Guier C.
        Factors of patellar instability: An anatomic radiographic study.
        Knee Surg Sports Traumatol Arthrosc. 1994; 2: 19-26
        • Panni A.S.
        • Cerciello S.
        • Maffulli N.
        • Di Cesare M.
        • Servien E.
        • Neyret P.
        Patellar shape can be a predisposing factor in patellar instability.
        Knee Surg Sports Traumatol Arthrosc. 2011; 19: 663-670
        • Pfirrmann A.
        • Zanetti M.
        • Romero J.
        • Hodler J.
        Femoral trochlear dysplasia: MR findings.
        Radiology. 2000; 216: 858-864
        • Sillanpää P.J.
        • Salonen E.
        • Pihlajamäki H.
        • Mäenpää H.M.
        Medial patellofemoral ligament avulsion injury at the patella: Classification and clinical outcome.
        Knee Surg Sports Traumatol Arthrosc. 2014; 22: 2414-2418
        • Merchant A.
        • Mercer R.
        • Jacobsen R.
        • Cool C.
        Roentgenographic analysis of patellofemoral congruence.
        J Bone Joint Surg Am. 1974; 56-A: 1391-1396
        • Figueroa D.
        • Calvo R.
        • Vaisman A.
        • Carrasco M.A.
        • Moraga C.
        • Delgado I.
        Knee chondral lesions: Incidence and correlation between arthroscopic and magnetic resonance findings.
        Arthroscopy. 2007; 23: 312-315
        • Dejour D.
        Evaluation and treatment of patellar instability.
        Corolyon Clin Sauvegarde. Published online 2002; : 1-4
        • Brossmann J.
        • Muhle C.
        • Schröder C.
        • et al.
        Patellar tracking patterns during active and passive knee extension: Evaluation with motion-triggered cine MR imaging.
        Radiology. 1993; 187: 205-212
        • Haj-Mirzaian A.
        • Thawait G.K.
        • Tanaka M.J.
        • Demehri S.
        Diagnosis and characterization of patellofemoral instability: Review of available imaging modalities.
        Sports Med Arthrosc Rev. 2017; 25: 64-71
        • Smith T.O.
        • Davies L.
        • Toms A.P.
        • Hing C.B.
        • Donell S.T.
        The reliability and validity of radiological assessment for patellar instability. A systematic review and meta-analysis.
        Skeletal Radiol. 2011; 40: 399-414
        • Biedert R.M.
        • Bachmann M.
        Anterior-posterior trochlear measurements of normal and dysplastic trochlea by axial magnetic resonance imaging.
        Knee Surg Sports Traumatol Arthrosc. 2009; 17: 1225-1230
        • Paiva M.
        • Blønd L.
        • Hölmich P.
        • et al.
        Quality assessment of radiological measurements of trochlear dysplasia: A literature review.
        Knee Surg Sports Traumatol Arthrosc. 2018; 26: 746-755
        • Koëter S.
        • Bongers E.M.H.F.
        • De Rooij J.
        • Van Kampen A.
        Minimal rotation aberrations cause radiographic misdiagnosis of trochlear dysplasia.
        Knee Surg Sports Traumatol Arthrosc. 2006; 14: 713-717
        • Toms A.P.
        • Cahir J.
        • Swift L.
        • Donell S.T.
        Imaging the femoral sulcus with ultrasound, CT, and MRI: Reliability and generalizability in patients with patellar instability.
        Skeletal Radiol. 2009; 38: 329-338
        • Lippacher S.
        • Dejour D.
        • Elsharkawi M.
        • et al.
        Observer agreement on the Dejour trochlear dysplasia classification: A comparison of true lateral radiographs and axial magnetic resonance images.
        Am J Sports Med. 2012; 40: 837-843
        • Brady J.M.
        • Sullivan J.P.
        • Nguyen J.
        • et al.
        The tibial tubercle–to–trochlear groove distance is reliable in the setting of trochlear dysplasia, and superior to the tibial tubercle–to–posterior cruciate ligament distance when evaluating coronal malalignment in patellofemoral instability.
        Arthroscopy. 2017; 33: 2026-2034
        • Gordon J.E.
        • Chen R.C.
        • Dobbs M.B.
        • Luhmann S.J.
        • Rich M.M.
        • Schoenecker P.L.
        Interobserver and intraobserver reliability in the evaluation of mechanical axis deviation.
        J Pediatr Orthop. 2009; 29: 281-284
        • Marx R.G.
        • Grimm P.
        • Lillemoe K.A.
        • et al.
        Reliability of lower extremity alignment measurement using radiographs and PACS.
        Knee Surg Sports Traumatol Arthrosc. 2011; 19: 1693-1698
        • Vähäsarja V.
        • Lanning P.
        • Lähde S.
        • Serlo W.
        Axial radiography or CT in the measurement of patellofemoral malalignment indices in children and adolescents?.
        Brain Lang. 1996; 51: 639-643
        • Ye Q.
        • Yu T.
        • Wu Y.
        • Ding X.
        • Gong X.
        Patellar instability: The reliability of magnetic resonance imaging measurement parameters.
        BMC Musculoskelet Disord. 2019; 20: 317
        • Marzo J.
        • Kluczynski M.
        • Notino A.
        • Bisson L.
        Comparison of a novel weightbearing cone beam computed tomography scanner versus a conventional computed tomography scanner for measuring patellar instability.
        Orthop J Sports Med. 2016; 4232596711667356
        • Wagenaar F.C.B.M.
        • Koëter S.
        • Anderson P.G.
        • Wymenga A.B.
        Conventional radiography cannot replace CT scanning in detecting tibial tubercle lateralisation.
        Knee. 2007; 14: 51-54
        • Longo U.G.
        • Berton A.
        • Salvatore G.
        • et al.
        Medial patellofemoral ligament reconstruction combined with bony procedures for patellar instability: Current indications, outcomes, and complications.
        Arthroscopy. 2016; 32: 1421-1427
        • Fabricant P.D.
        • Ladenhauf H.N.
        • Salvati E.A.
        • Green D.W.
        Medial patellofemoral ligament (MPFL) reconstruction improves radiographic measures of patella alta in children.
        Knee. 2014; 21: 1180-1184
        • Neyret P.
        • Robinson A.H.N.
        • Le Coultre B.
        • Lapra C.
        • Chambat P.
        Patellar tendon length—The factor in patellar instability?.
        Knee. 2002; 9: 3-6
        • Askenberger M.
        • Arendt E.A.
        • Ekström W.
        • Voss U.
        • Finnbogason T.
        • Janarv P.M.
        Medial patellofemoral ligament injuries in children with first-time lateral patellar dislocations.
        Am J Sports Med. 2016; 44: 152-158
        • Stefancin J.J.
        • Parker R.D.
        First-time traumatic patellar dislocation: A systematic review.
        Clin Orthop. 2007; 455: 93-101
        • Seeley M.A.
        • Knesek M.
        • Vanderhave K.L.
        Osteochondral injury after acute patellar dislocation in children and adolescents.
        J Pediatr Orthop. 2013; 33: 511-518