The purpose of our study was to assess the reproducibility and reliability of traditional radiographic methods of diagnosing trochlear dysplasia compared with the gold standard of MRI. Plain radiographs and MRI scans of 36 knees in 28 patients with proven trochlear dysplasia were compared with 18 controls in a single surgeon's practice. The sulcus angle on MRI and axial radiographs was measured. The lateral radiograph was assessed for adequacy, the crossing sign and the trochlear bump sign. The mean axial (radiograph) and MRI sulcus angles in the dysplastic group were 145° and 158° respectively (p=0.0001) compared to 135° and 138° in the control group (p=0.09). The crossing sign was present in 34 out of 36 lateral radiographs in the dysplastic group and 8 out of 18 in the control group equating to a sensitivity of 94% and specificity of 56%. The quality of the lateral radiograph did not significantly alter the sensitivity or specificity of the crossing sign (p=0.01). The bump sign was present in 22 out of 36 lateral radiographs in the dysplastic group and 1 out of 18 in the control group equating to a sensitivity of 61% and specificity of 94%. Our study shows that an increased radiographic sulcus angle is reliable in diagnosing trochlear dysplasia but underestimates it. The bump sign is a reliable predictor of trochlear dysplasia. The crossing sign is sensitive but not specific in diagnosing dysplasia.
We retrospectively analysed the MR scans of 25 patients with patellofemoral dysplasia and ten control subjects, to assess whether there was any change in the morphology of the patella along its vertical length. Ratios were calculated comparing the size of the cartilaginous and subchondral osseous surfaces of the lateral and medial facets. We also classified the morphology using the scoring systems of Baumgartl and Wiberg. There were 18 females and seven males with a mean age of 20.2 years (10 to 29) with dysplasia and two females and eight males with a mean age of 20.4 years (10 to 29) in the control group. In the patient group there was a significant difference in morphology from proximal to distal for the cartilaginous (Analysis of variance (ANOVA) p = 0.004) and subchondral osseous surfaces (ANOVA, p = 0.002). In the control group there was no significant difference for either the cartilaginous (ANOVA, p = 0.391) or the subchondral osseous surface (ANOVA, p = 0.526). Our study has shown that in the dysplastic patellofemoral articulation the medial facet of the patella becomes smaller in relation to the lateral facet from proximal to distal. MRI is needed to define clearly the cartilaginous and osseous morphology of the patella before surgery is considered for patients with patellofemoral dysplasia.
The radiological and MRI appearances of 24 knees with patellar tendonitis resistant to conservative therapy were analysed to identify the characteristic MRI appearance and to determine if the patellar morphology was abnormal. A significant thickening of the tendon was found in all cases; this was a more reliable diagnostic feature than a high signal within the superior posterior and central aspect of the tendon at its proximal attachment The site of the lesion shown by MRI is more compatible with impingement of the inferior pole of the patella against the patellar tendon than a stress overload of the tendon. There were no significant differences in the length of the patella, inferior pole or length of the articular surface when the patellar morphology was compared with that of a matched control group.
