Changes in Cartilage and Subchondral Bone of Femoral Trochlear Groove After Patellectomy in Growing Rabbits

Objective To explore the effects of patellectomy on the bony and cartilaginous morphology of the trochlear groove in growing rabbits. Methods Forty-eight 4-week-old New Zealand white rabbits were randomly assigned to two groups. The control group underwent a sham surgical procedure, whereas the patellectomy group underwent patella excision surgery. Half of the rabbits in each group were sacrificed 3 months postoperatively; the rest were sacrificed 6 months postoperatively. Hematoxylin and eosin staining was performed on collected samples. Measurements included the bony and cartilaginous sulcus angles of the trochlear groove. In addition, the thickness of the articular cartilage at the deepest sulcus position (central thickness) and at the mid-position of the medial and lateral facets was measured and compared between groups. Results Three months after surgery, histological images revealed significant differences between the control group and the patellectomy group in cartilaginous sulcus angle (144.2 degrees +/- 1.5 degrees vs 151.9 degrees +/- 2.4 degrees, respectively; P < 0.001). No obvious difference in bony sulcus angle was found between the groups. Six months after surgery, significant between-group differences were observed in cartilaginous sulcus angle (136.3 degrees +/- 2.5 degrees in control group vs 160.7 degrees +/- 3.0 degrees in patellectomy group, P < 0.001) and bony sulcus angle (136.2 degrees +/- 2.2 degrees in control group vs 160.4 degrees +/- 2.6 degrees in patellectomy group, P < 0.001). However, there were no significant intra-group differences between cartilaginous and bony sulcus angles in either group. Three months after surgery, significant between-group differences were detected in articular cartilage thickness at the three different positions (medial facet: 324.3 +/- 14.0 mu m in control group vs 391.7 +/- 98.8 mu m in patellectomy group, P = 0.029; central position: 362.1 +/- 13.6 mu m in control group vs 730.3 +/- 76.8 mu m in patellectomy group, P < 0.001; lateral facet: 324.6 +/- 12.7 mu m in control group vs 358.5 +/- 38.7 mu m in patellectomy group, P = 0.009). No between-group differences in cartilage thickness were found at 6 months. Conclusions Abnormal mechanical stress (patellectomy) during a rabbit's development can cause flattening of the femoral trochlear cartilage, followed by changes in the subchondral osseous layer. Abnormal mechanical stress is a crucial factor in the development of trochlear groove dysplasia.