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Classification of dysplasia of the femoral trochlea in patients with patellar instability depends on the evaluation plane
  1. Yuzo Yamada1,
  2. Yukiyoshi Toritsuka2,
  3. Shuji Horibe3,
  4. Norimasa Nakamura4,
  5. Kazuomi Sugamoto5,
  6. Hideki Yoshikawa6,
  7. Konsei Shino7
  1. 1 Orthopeadic Surgery, Yao Municipal Hospital, Yao, Japan
  2. 2 Orthopaedic Sports Medicine, Kansai Rosai Hospital, Amagasaki, Japan
  3. 3 Faculty of Comprehensive Rehabilitation, Osaka Prefecture University, Habikino, Japan
  4. 4 Orthopaedic Surgery, Osaka Health Science University, Osaka, Japan
  5. 5 Locomotor Biomaterial Limited to the Joint Surgery, Osaka University Graduate School of Medicine, Suita, Japan
  6. 6 Orthopeadic Surgery, Osaka University Graduate School, Suita, Japan
  7. 7 Orthopaedic Sports Medicine, Osaka Yukioka Medical University, Ibaraki, Japan
  1. Correspondence to Dr Yukiyoshi Toritsuka; toritukayukiyosi{at}


Objective Trochlear dysplasia is a major predisposing factor of patellar instability (PI). Dysplasia types are generally evaluated using the Dejour classification, but it is unclear whether this classification covers the entire spectrum. The objective of this study was to confirm whether the trochlear types on an axial view categorised according to the classification represent the entire trochlear shape.

Methods Ninety knees from 81 patients with PI and 15 knees from 10 healthy volunteers (HVs) were evaluated. Three-dimensional knee models were created by MRIs. The femoral trochlear planes (FTPs) were defined as virtual cross sections including the transepicondylar axis, closer to the perpendicular plane of the articular surface. FTP 0 was defined as the reference plane including the proximal edge of the femoral trochlea and FTP θ as the plane making optional angle θ to FTP 0. Trochlear dysplasia types according to the classification were evaluated at every 10 degrees of FTPs up to 60 degrees (FTP 10, 20, 30, 40, 50 and 60). A trochlea with a sulcus angle <145° was defined as normal. Changes in the trochlear type according to FTPs, and agreement with clinical classification were evaluated.

Results Eighty-six knees (96%) in patients with PI and 12 (80%) in HVs showed changing trochlear types in different FTPs. Patterns of change varied among patients with PI and HVs. This suggests morphological variation of dysplastic trochleae. Agreement of trochlear type on each FTP with the clinically used Dejour classification was 42% on FTP 10, 49% on FTP 20, 33% on FTP 30, 22% on FTP 40, 22% on FTP 50% and 22% on FTP 60 in patients with PI, and 20% at FTP 10, 80% at FTP 20 and 100% on FTP 30 through FTP 60 in HVs. This suggests that the trochlear types in the clinically used plane do not always match the ones on the planes describing the contact surface to the patella.

Conclusion The trochlear types on an axial view provided by the Dejour classification do not represent the entire trochlear geometry. Multiple axial planes should be clinically used to more precisely describe the entire trochlear shape.

  • knee
  • dislocation
  • MRI
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  • Contributors YY provided patients who were subjects of the study, performed data collection and analysed the data. YT (corresponding author) created the study design, provided patients who were subjects of the study and drafted the manuscript. SH provided patients who were subjects of the study. NN provided patients who were subjects of the study. KSu assisted in study design using a 3D computer analysing system. HY assisted in study design using a 3D computer analysing system. KSh assisted in study design and preparation of the manuscript.

  • Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

  • Competing interests None declared.

  • Patient consent for publication Participants provided informed consent.

  • Provenance and peer review Not commissioned; externally peer reviewed.

  • Data availability statement Data are available in a public, open access repository.

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