Jordy van Sambeeck

Chapter 9 148 important role in patellofemoral (in)stability. It could be argued that the currently performed static CT or MRI measurements (with heterogeneity in position) are not representative for the functional and dynamic problem of the patient. Next to static nature of the current imaging methods, a limitation of the currently used measurements is that they are performed on two-dimensional imaging. Nha et al. 4 demonstrated a new method of measurement of TT-TG based on a three-dimensional (3D) CT image modeling and showed lower measurement bias and improved reliability for the measurement of TT-TG in patients with femoral trochlear dysplasia. This might only be the beginning of a reset of measurement methods and normal values with increased reliability and validity, now based on three-dimensional imaging. The previously described issues stress the importance of a strict protocol for imaging in patients with patellofemoral instability to increase uniformity, reliability and validity of the measurements. The importance of alignment has been outlined previously. An optimal and uniform alignment should be the desired goal. This might be checked by 3D techniques such as are already in use for navigated surgery. A future imaging protocol could include CR, 4D CT and MRI. We propose that the position of the patient in a scan should be supine, with patellae facing forward, knees in 10° flexion, no hip abduction or adduction. For 4D scanning, then the first movement is from 90° to full extension by active range of motion against a resistance of ½ body weight. Then, under eccentric quadriceps force let the weight rebound until 100° flexion. A suggestion for which techniques and measurements a future imaging protocol for patients with patellofemoral instability could include is presented on this page: − Conventional radiography ° Standing posterior-anterior fixed flexion view and standing true lateral knee, both in 10° flexion ° Patellar height: Caton-Deschamps ° Trochlear dysplasia: differentiate between normal trochlea (no crossing sign, no bump), low-grade (only crossing sign, Dejour type A) and high-grade (crossing sign and bump or double contour sign, Dejour type B, C and D) trochlear dysplasia − 4D CT ° Standardized alignment, checked by 3D referencing ° Active weight-bearing range of motion ° Patellar tracking ° 3D measurement lateralization