An MRI-based technique for assessment of lower extremity deformities—reproducibility, accuracy, and clinical application

Abstract

The hypothesis of this study was that length, torsion, and axis of a leg phantom can be measured accurately and reproducibly by magnetic resonance imaging (MRI) and that this can be applied to patients with leg deformities. Two phantoms and 30 patients (genu varum, n = 15; genu valgum, n = 15) were investigated using an optimized MRI technique. Reference measurements were performed with a micrometer screw and a goniometer. Patient leg length and axis were compared with long radiographs in bipedal stance. Intra- and interobserver reproducibility and accuracy were calculated using the mean absolute difference (MAD) and the 95% confidence interval. In patients, comparisons were done using a paired Student's t-test. MAD, intraobserver MAD, and interobserver MAD were 0.03, 0.03, 0.04 mm (length); 0.98, 1.2, 0.98 degrees (torsion); and 0.18, 0.23, 0.22 degrees (axis), respectively. In patients, leg length was underestimated by MRI (-2.4 +/- 0.7%; 1.9 +/- 0.7 cm; P < 0.001). The hip-knee-ankle angle (HKA) did not show significant differences in varus knees (-0.5 +/- 1.0 degrees ; P > 0.05), while it was significantly underestimated in valgus knees (-3.6 +/- 2.8 degrees ; P < 0.05). The phantom study revealed that leg length, torsion, and axis can be measured accurately and reproducibly by MRI. Although underestimation of leg length and HKA in valgus knees occurred, this optimized MRI technique can be applied to patients with leg deformities.

Measurement of lower limb alignment: there are within-person differences between weight-bearing and non-weight-bearing measurement modalities

“…Other modalities that measure mechanical leg axis (MLA) include intra-operative computer navigation in computer-assisted surgery (CAS) and magnetic resonance imaging (MRI) in patient-specific instrumentation (PSI). Several studies have found differences between these measurement modalities [ 1 , 6 , 11 , 13 , 24 , 28 , 30 – 32 ]. However, most of these studies compared mean or median values of the measurement modalities and did not analyse within-person measurement differences.…”

Combined magnetic resonance imaging approach for the assessment of in vivo knee joint kinematics under full weight-bearing conditions

“…Hinterwimmer et al 49 however, compared MRI-based measurements in supine position to long radiographbased measurements obtained in upright position and found significant underestimation for leg length and for HKA-angle in valgus knees. Liodakis et al 48 however, compared HKA-angles measured from upright-MRI and weight-bearing long radiographs and found good correlation for the HKA-angle and a very high mean inter-and intra-observer agreement for the upright-MRI-based approach.…”

Reliability of an Integrated Ultrasound and Stereophotogrammetric System for Lower Limb Anatomical Characterisation

“…Most studies use conventional means such as radiographs or MRI [13, 33–35]. Terjesen et al, however, showed that 95% of the ultrasound leg length measurements on 45 subjects were within 7 mm of the radiographic measurements [21].…”