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Malalignment sign on knee magnetic resonance imaging: a new predictor for excessive femoral anteversion in patients with patellar dislocation

Abstract

Purpose

To evaluate the clinical relevance of the newly identified malalignment sign in predicting excessive femoral anteversion in patients with patellar dislocations.

Methods

A total of 55 patients with patellar dislocation who underwent surgical treatment between 2016 and 2019 were included in this study. Femoral anteversion, tibial torsion, and the femorotibial index were measured via a CT scan. The malalignment sign on the knee MRI was defined as a malalignment between the lateral side of the intercondylar fossa of the femur and the lateral intercondylar eminence of the tibial plateau.

Results

A positive malalignment sign was observed in 36 of the 55 patients. Increased femoral anteversion was significantly correlated with the number of frames with a positive malalignment sign (r = 0.511, P < 0.001). The value of femoral anteversion was significantly greater in the group with a positive malalignment sign (P = 0.02). For a femoral anteversion value of 32°, the sensitivity and specificity of the malalignment sign reached the maximal level of 89.5% and 47.2%, respectively.

Conclusion

Increased femoral anteversion correlated significantly with a positive malalignment sign on knee MRI. However, tibial torsion did not affect the malalignment sign. A positive malalignment sign is evidence for femoral derotation osteotomy.

Level of evidence

Level IV.

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Correspondence to Aiguo Zhou.

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The study was approved by the Ethics Board of the First Affiliated Hospital of Chongqing Medical University (IRB approval number: 2019-230).

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Xu, Z., Zhang, H., Guo, M. et al. Malalignment sign on knee magnetic resonance imaging: a new predictor for excessive femoral anteversion in patients with patellar dislocation. Knee Surg Sports Traumatol Arthrosc 29, 1075–1082 (2021). https://doi.org/10.1007/s00167-020-06080-8

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Keywords

  • Patellar dislocation
  • Patellar instability
  • Femoral anteversion
  • Femoral derotation osteotomy
  • Malalignment sign