chapter 8: Patellar Tilt‑Compression and the Excessive Lateral Pressure Syndrome (ELPS)
Loss of patellar cartilage, under load, will be noted radiographically as "joint line narrowing." In order to make comparisons between radiographs and surgical findings, as well as to facilitate meaningful comparisons for future studies, Ficat's patellar map may be helpful (see Fig. 8.3). One has to be careful in overinterpreting plain films because of the normal variation in patellar cartilage thickness and image overlap inherent in any axial radiograph. Lateral joint line diminution may be clearly visible on an axial view (Fig. 8.4). The lateral radiograph (posterior condyles superimposed) may also reveal tilt (Fig. 8.5). However, traditional radiographic views are sometimes normal. Therefore, radiographs alone cannot rule out a tilt‑compression syndrome in the patient with patellofemoral pain.
In the original edition of this book, Ficat and Hungerford (1) wondered, as did Wiberg (7) in 1941, "why with all the interest in arthrography there has been so little interest in using it to evaluate the patellofemoral joint." To perform an invasive study such as arthrography without axial views in patients with knee pain of less than obvious origin is as erroneous as ordering only an anteroposterior (AP) view or not viewing the lateral compartment by radiograph when medial compartment pathology is anticipated. One should always obtain good quality axial views when performing knee arthrograms.
Tomographic imaging, as described in Chapter 4, is particularly important in the evaluation of patients with patellar tilt‑compression syndrome. The posterior condyle reference line is symmetrical and reproducible for determining the patellar tilt angle. This reference line can only be obtained with a properly oriented tomographic image of the patellofemoral joint. The anterior trochlear anatomy varies so much that a determination of tilt using a line across the trochlea carries some risk of inaccuracy (Fig. 8.7).
CT offers the option of serial images with the knee in increasing flexion. This can be very helpful in determining if a patient has progressive tilt (increasing tilt with increased knee flexion) or transient tilt (tilt of the patella in early knee flexion that corrects with further flexion). In the asymptomatic control studies available (5), the patellar tilt angle (PTA) using CT was never less than 7 degrees, even at full extension. With the knee flexed 10 to 20 degrees, the PTA was not less than 12 to 14 degrees in asymptomatic normal volunteers (20 knees). CT is also very helpful postoperatively, when necessary, to see if appropriate correction has been accomplished (Fig. 8.8).
Inside Chapter 8: