Evaluation of patello-femoral alignment by CT scans: interobserver reliability of several parameters.

Patello-femoral malalignment (PFM) is a common cause of disability often related to patello-femoral syndrome (PFS). Several causes have been taken into account; a proper diagnosis requires instrumental imaging and a methodical evaluation of different parameters. The aim of the present study was to identify the most reliable parameters for measuring patello-femoral and inferior limb alignment by CT. Twenty randomly selected patients suffering from PFS for a total of 40 knees were studied by static CT scans in order to assess patellar tilt, patellar displacement, patellar and trochlear morphology and inferior limb alignment. All known parameters were measured; the variability of the measurements between observers was evaluated by boxplots, Pearson's correlation coefficients, and infraclass correlation coefficient [ICC(2,1)] based on a two-way random effect model. Bland-Altman mean differences and 95 % limits of agreement were computed for each pair of measurements. Patellar tilt parameters appeared equally reliable; patellar displacement is best measured with BoTot that showed an ICC of 0.889; morphology is best measured with WibergTot, with an ICC of 0.862; lastly, for the inferior limb alignment parameters' analysis, FTV outperformed the others in terms of reliability. The present study allowed us to select a limited number of reliable parameters in the evaluation of patello-femoral and inferior limb alignment. The use of these parameters may also result in a more reliable comparison of studies on PFM and in a better evaluation of the treatment outcomes.

Magnetic resonance imaging (MRI) artefacts in hip prostheses: a comparison of different prosthetic compositions.

PURPOSE: The purpose of the study was to compare the artefacts produced by different hip prostheses on magnetic resonance imaging (MRI). MATERIALS AND METHODS: An identical MRI protocol was used to perform a quali-quantitative in vitro evaluation of artefacts caused by different hip prosthetic materials at different field strengths: prosthesis number 1, composed of cobalt-chrome-molybdenum (head and stem); prosthesis number 2, composed of ceramic (head) and titanium (stem); prosthesis number 3, composed of cobalt-chrome (head) and titanium (stem). All prostheses were imaged with both a clinical 1 Tesla (T) (Signa Horizon, General Electrics) and 1.5 T (Achieva, Philips) MRI system, using spin echo (SE) and gradient echo (GRE) sequences: sagittal T1 SE, coronal T2 fast SE (FSE), axial T1 SE, axial T2 FSE, sagittal T2 GRE, axial T2* GRE, coronal T1 GRE, axial T1 GRE. The artefacts produced by each prosthesis were assessed in each sequence at the different field strengths, by measuring the two longest diameters of the artefact in each section and sequence and comparing them to the actual diameters so as to obtain a ratio expressing the effective degree of artefact. RESULTS: Cobalt-chrome produced the largest artefacts both in SE (1.73 at 1 T and 2.37 at 1.5 T) and GRE sequences (2.8 at 1 T and 3.06 at 1.5 T) followed by titanium (SE, 1.6 at 1 T, 2.13 at 1.5 T; GRE, 2 at 1 T, 2.94 at 1.5 T) and cobalt-chrome-molybdenum (SE, 1.51 at 1 T, 1.67 at 1.5 T; GRE, 2.13 at 1 T and 2.48 at 1.5 T); ceramic produced the smallest artefacts in all sequences (SE, 1.0 at 1 T and 1.18 at 1.5 T; GRE, 1.3 at 1 T and 1.22 at 1.5T). Increasing the magnetic field strength, titanium showed the greatest variations in artefact size, and ceramic the smallest ones. CONCLUSIONS: The composition of prosthetic implants is decisive in determining the quality of MR imaging.