Weight-bearing MRI with a knee flexion angle of 20\xb0: a study on additional MRI investigation modalities to support a more accurate understanding of patellofemoral instability

J Leiprecht,J Huth,L P Ambros,F Mauch,R Best

doi:10.1186/s12891-021-04733-4

Abstract

BackgroundDiagnosing patellofemoral instability disorders correctly, weight-bearing MRI (WB-MRI) has become an option. Aiming for a best possible accuracy in displaying potentially underlying causes, the named MRI modalities were sporadically even investigated in different knee flexion angles. However, despite confirmed MRI-outcome-differences between WB-MRI and non-WB-MRI, none of the described MRI modalities have so far established themselves. Mainly this is due to an unfeasibility in daily clinical routine in regard to time and economic aspects. Thus, we intended to evaluate an additional but reduced patellofemoral MR-imaging solely in a relevant 20° of knee flexion under WB- and non-WB-MRI conditions.MethodsSeventy-three subjects with and without patellofemoral instability were investigated under supine as well as under WB-MRI conditions in a 20° of knee flexion angle. Patellofemoral risk indices in the sagittal plane (Insall-Salvati-Index, Caton-Deschamps-Index, Patellotrochlear Index) and the axial plane (Patella tilt of Fulkerson and Sasaki) were detected and compared between the different MRI conditions. Significance, reliability and Cohen’s effect size was calculated.ResultsNearly all assessed indices showed significant differences between patients and controls in the different MRI positions. Comparing pairwise, all measured indices failed to show significant differences between the two MRI positions. However, patella tilt angles of the patient group showed an elevation from supine to WB-MRI (14.00 ± 7.54° to 15.97 ± 9.10° and 16.34 ± 7.84° to 18.54 ± 9.43°). Here, Cohen’s d showed small to medium effects between supine and WB-MRI.ConclusionIn comparison to standard MRI in supine position, axial risk indices seem to be accentuated under WB-MRI and a knee flexion angle of 20°. In particular, symptomatic cases with inconspicuous conventional MRI imaging, additional MRI imaging only in the axial plane in a 20° of knee flexion could be beneficious and useful in clinical daily routine.

Highlights

Diagnosing patellofemoral instability disorders correctly, weight-bearing Magnetic Resonance Imaging (MRI) (WB-MRI) has become an option
Inter-class-correlation coefficient (ICC) for inter- and intra-observer reliability of our measurements was very good to excellent (Table 2)
The previously described 20% of patients suffering from chronic patellofemoral problems and having inconspicuous risk values on standard MRI [4] might benefit from the additional performance of a weight-bearing MRI (WB-MRI) in 20° flexion angle of the knee

Summary

Introduction

Diagnosing patellofemoral instability disorders correctly, weight-bearing MRI (WB-MRI) has become an option. Aiming for a best possible accuracy in displaying potentially underlying causes, the named MRI modalities were sporadically even investigated in different knee flexion angles. Despite confirmed MRI-outcomedifferences between WB-MRI and non-WB-MRI, none of the described MRI modalities have so far established themselves. This is due to an unfeasibility in daily clinical routine in regard to time and economic aspects. Magnetic Resonance Imaging (MRI) of the extended knee in supine and non-weight-bearing condition plays a decisive role in assessing underlying causes of the patellofemoral disbalance in clinical daily routine [2, 5]. Guidelines have been established to facilitate the choice of subsequent optimal conservative and operative therapeutic options

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