Patella Height Correlates With Trochlear Dysplasia: A Computed Tomography Image Analysis.

PURPOSE: The aim of this study was to investigate the position of the patella relative to the trochlea for a possible correlation with radiologic parameters characterizing the form of the trochlea.

METHODS: The computed tomography scans of 36 cases with patellofemoral instability and 30 without (mean age, 24.7 ± 6.8 years) were studied. The height of the patella relative to the trochlea was evaluated as the distance between the axial slice where the patella (P) showed its widest diameter, as the patella at this level has the greatest potential to form the trochlea, and the proximal entrance of the femoral trochlea (TE). The correlations between this parameter and several radiologic parameters used to evaluate trochlear dysplasia, including trochlea height, transverse trochlea shift, trochlea depth, sulcus angle, lateral and medial trochlea slope, trochlea facet asymmetry, and the Dejour trochlea type, were calculated.

RESULTS: The P-TE distance correlated significantly with all trochlea parameters evaluated, with a more dysplastic trochlea in cases of higher position of the patella: medial, central, and lateral trochlea height (0.287 <r < 0.490, P < .019), transverse trochlea shift (r = 0.516, P < .001), trochlea depth (r = -0.299, P = .015), sulcus angle (r = 0.344, P = .005), medial and lateral trochlea slope (-0.274 <r < -0.295, P < .026), trochlea facet asymmetry (r = -0.399, P = .005), and Dejour trochlea type (r = 0.394, P = .001).

CONCLUSIONS: On the basis of our findings it was concluded that patella height was significantly related to the morphology of the femoral trochlea. The strongest correlations with patella height were observed for the parameters central trochlea height (r = 0.490, P < .001) and transverse trochlea shift (r = 0.516, P < .001). A higher positioned patella was associated with a more dysplastic trochlea.

LEVEL OF EVIDENCE: Level III, retrospective cross-sectional study.