Abstract
Background: The relative influence of patella and trochlear shape on the development of each structure is poorly understood. Articular morphology is felt to be an important factor influencing patellar instability. The purpose of this study was to evaluate the development of patellar facets in relation to age and sulcus depth in the pediatric knee. Methods: Dissection of 57 immature knees (1 month – 11 years; 36 male) was performed by fellowship-trained orthopaedic surgeons. A coordinated laser scanner, and analysis software (Hexagon Romer V3 CMM; Polyworks) were used to record cartilage anatomy. Patellar facets were identified as distinct regions of surface contour. In a subset of 30 specimens (2 years – 11 years; 22 male) trochlear cartilage sulcus angles were analyzed at points on the trochlea in relation to orientation angle from the femoral axis [F90° (perpendicular to the femoral axis, correlated to the posterior condylar axial slice), F120° (30° flexion), and F150° (60° flexion)]. Spearman’s correlations and nonparametric Mann-Whitney tests were evaluated for specimen age, patellar articular surface lengths, and trochlear sulcus angles. Results: There was strong correlation of patellar facet development with the angle of the cartilaginous femoral sulcus at 30° of flexion (p<0.001, rs=-0.696). With deepening femoral sulcus angles (range 137°-163°), there was an increase in the number of patellar facets present. Additionally, the presence of multiple medial facets was correlated with the sulcus angle at 30° (p<0.01) (Fig. 1). In the 13 specimens with a sulcus angle < 150°, all demonstrated well-formed patella with 5-7 facets identified. Within the group including those specimens younger than 2 years old, age (p<0.001) and width of the patellar articular surface (p<0.001) were correlated with the number of facets present. Multiple facet development on the lateral side of the patella was most strongly correlated with patellar articular surface width (p<0.001). Gender and the superior-most sulcus angle (F90°) didn’t correlate with patellar morphological development. The average number of facets identified was 3.8 (+/- 1.6), and the median number present was 4 (range 0-7). The most common patellar shape was 5 facets (n=16, age range 3 months – 11 years); medial, inferior-medial, lateral, inferior-lateral, and odd. Conclusion: Complex patellar morphology with multiple facets present is not uncommon in early pediatric development, with patellar width and the femoral sulcus angle at 30° as correlates. Significance: Patellar maturation may occur early and further investigation of the relationship of patellofemoral dysplasia on the early development of the corresponding structures is warranted. [Figure: see text]
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