For analysis of the morphology of the femoral trochlea linear dimensions (e.g. Biedert's trochlea heights) showed better reliability than angular measurement.
Different imaging parameters defining the morphology of the femoral trochlea have been published, however it is not clear which are most reliable ones. The aim of the study was to evaluate the inter-observer reliability of nine quantitative parameters typically applied in CT-scans and MRI. It was hypothesized that these parameters would show substantial reliability (ICC>0.7).
CT scans of 36 cases with a history of at least one lateral patella dislocation (LPD) and 30 cases without a history of patellofemoral instability (non-LPD) were included in the study. The following parameters were evaluated: medial, central and lateral trochlea heights as introduced by Roland Biedert, trochlea depth, transverse trochlea shift, trochlea facet asymmetry, sulcus angle and medial and lateral trochlea slope. All parameters were measured by four investigators independently. To evaluate the inter-observer agreement ICCs were calculated for a) the entire study group and b)I for the LPD and non-LPD subgroups separately.
For all patients together medial, central and lateral trochlea heights had the highest ICC values between 0.910 and 0.930. For trochlea depth the ICC was 0.861. Transverse trochlea shift had an ICC of 0.749. For the angular parameters sulcus angle, lateral trochlea slope and medial trochlea slope ICC values of 0.563, 0.715 and 0.722 were determined, respectively. Trochlea facet asymmetry showed an ICC of 0.657.
Except for central trochlea height all other parameters showed a higher ICC in the non-LPD subgroup. This indicates that the tested parameters are less consistent if patients have a more dysplastic trochlea. The highest ICC values were found for linear measures like the Biedert Trochlea heights. Inferior ICC values were found for angular measurements, with the commonly used sulcus angle showing the lowest reliability.
All investigated imaging parameters for the femoral trochlea morphology showed inter-observer reproducibility > 0.7 - except for the sulcus angle and the trochlea facet asymmetry.
We do therefore not recommend the routine use of the latter two parameters. Linear measures should be preferred over angular measures.