Abstract
In recent years, the use of computed tomography (CT) has made it possible to obtain without distortion images of axial sections of the patella with the knee in the first 15°–20° of flexion.
We performed CT examinations on 27 patients aged between 11 and 17 years. We considered patients who had anterior knee pain with or without a feeling of patellar instability. CT examinations were performed with the knee flexed to 15° with and without quadriceps contraction. The tomograms obtained were analysed considering: (1) the congruence angle (CA), (2) the patellar tilt angle (PTA), (3) the sulcus angle (SA) and (4) trochlear depth (TD). We performed CT examinations on a control group of 20 patients aged between 11 to 17 years. Statistical analysis was performed by using the analysis of variation (ANOVA) test or the Student’s t-test on paired or unpaired data.
The difference between control knees and symptomatic knees was significant for all of the CT variables (unpaired t-test). Malalignment detected with the quadriceps relaxed was typed according to the classification of Schutzer et al. as follows: type I – lateralised patella, 13 knees (24.1%); type II – lateralised and tilted patella, 24 knees (44.4%); and type III – tilted patella, 12 knees (22.2%). In 26 knees (48.2%), CT examination with quadriceps in contraction gave the same findings as CT examination with the quadriceps relaxed, i.e. type and severity of malalignment were identical. In the remaining 28 knees (51.8%), CT examination with the quadriceps in contraction gave different results from the CT examination with the quadriceps relaxed.
The greater sensitivity and specificity of CT as compared with conventional radiographic methods in the diagnosis of patellofemoral malalignment have been demonstrated. Our results show that there is a relationship between clinical findings and CT data. CT assessment with the quadriceps relaxed permitted us to divide the knees into three types of patellofemoral malalignment. To our knowledge, not many studies have been performed with the quadriceps contracted. In the present study, in 48.2% of knees there were no differences between CT assessment with the quadriceps relaxed and with the quadriceps contracted in either type or severity of malalignment. In contrast, in the remaining 51.8% of symptomatic knees we found differences.
Before planning an operation in patients with anterior knee pain with or without patellar instability, CT assessment both with the quadriceps relaxed and contracted permits a reliable documentation of malalignment, permitting the surgeon to select the optimal treatment.
