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A new quantitative radiographic measurement of patella for patellar instability using the lateral plain radiograph: ‘patellar width ratio’

  • Knee
  • Published:
Knee Surgery, Sports Traumatology, Arthroscopy Aims and scope

Abstract

Purpose

Patellar width ratio, a new measurement of anterior–posterior patellar width, was developed using lateral radiographs. The hypothesis was that patellar width ratio would increase with increasing patellar tilt angle and that patients with patellar instability would have larger patellar width ratio compared to controls.

Methods

Fifty knees who underwent surgery for patellar instability were enrolled as Group P. The fifty knees without patellar instability were enrolled as controls (Group C). Patellar width ratio was measured using preoperative lateral radiographs. The width between proximal and distal apexes of patella was defined as A. The width between anterior and posterior margins of patella was defined as B. Patellar width ratio was defined as the ratio B/A. Patellar tilt angle was measured on preoperative computed tomography images. Values were compared between groups and their correlation examined, and a receiver operating characteristic (ROC) curve was generated to identify the threshold value.

Results

Mean patellar width ratio in Groups C and P was 0.54 ± 0.04 and 0.66 ± 0.11 (P < 0.01). Mean patellar tilt angle in Groups C and P was 12.8° ± 4.9° and 32.0° ± 10.3° (P < 0.01). Patellar width ratio was strongly correlated with patellar tilt angle (R = 0.83, P < 0.01). For patellar width ratio, the area under ROC curve was 0.86, and the cut-off value was 0.59 (sensitivity 76.0 %, specificity 90.0 %).

Conclusion

Patellar width ratio in Group P was significantly larger than in Group C. Patellar width ratio would allow clinicians to evaluate patellar tilt on lateral radiographs.

Level of evidence

III.

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Abbreviations

PF:

Patellofemoral

PWR:

Patellar width ratio

ACL:

Anterior cruciate ligament

BMI:

Body mass index

CT:

Computed tomography

MRI:

Magnetic resonance imaging

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Authors’ contributions

RK and KN participated in the design of the study and the measurements, performed the statistical analysis, and drafted the manuscript. T. Matsushita and DA participated in the design of the study and performed the statistical analysis, and drafted the manuscript. T. Matsumoto, KT, and MK conceived of the study, participated in its design and coordination, and helped to draft the manuscript. All authors read and approved the final manuscript.

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    Authors and Affiliations

    1. Department of Orthopaedic Surgery, Kobe University Graduate School of Medicine, 7-5-1, Kusunoki-cho, Chuo-ku, Kobe, 650-0017, Japan

      Ryosuke Kuroda, Kanto Nagai, Takehiko Matsushita, Daisuke Araki, Tomoyuki Matsumoto, Koji Takayama & Masahiro Kurosaka

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    1. Ryosuke Kuroda
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    2. Kanto Nagai
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    3. Takehiko Matsushita
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    4. Daisuke Araki
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    5. Tomoyuki Matsumoto
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    6. Koji Takayama
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    7. Masahiro Kurosaka
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    Correspondence to Ryosuke Kuroda.

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    The authors declare that they have no conflict of interest.

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    Ryosuke Kuroda and Kanto Nagai equally contributed to this work.

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    Kuroda, R., Nagai, K., Matsushita, T. et al. A new quantitative radiographic measurement of patella for patellar instability using the lateral plain radiograph: ‘patellar width ratio’. Knee Surg Sports Traumatol Arthrosc 25, 123–128 (2017). https://doi.org/10.1007/s00167-016-4179-x

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    • DOI: https://doi.org/10.1007/s00167-016-4179-x

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