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Objective:To establish a model of patellar dislocation by femoral osteotomy or surgical release of medial retinaculum in immature rabbits, and observe morphological and trabecular microarchitectural changes in the trochlea.Methods:Forty rabbits at 3 months of age were included. All right knees underwent surgery, 20 knees were treated with femoral osteotomy and internal rotation of distal femur to increase femoral anteversion angle (Osteotomy group, OS group), and another 20 knees were treated with surgical release of medial retinaculum and overlap suture of lateral retinaculum (Soft tissue group, ST group). All left knees were acting as internal controls. Micro-CT scans for distal femur were acquired after 4 months post surgery. the height of Medial, central, and lateral trochlear, sulcus angle, and lateral and medial trochlear slope were measured to describe the trochlear morphology, and bone volume fraction (BV/TV), trabecular thickness (Tb.Th), trabecular number (Tb.N), trabecular spacing (Tb.Sp), and bone mineral density (BMD) were calculated to evaluate the microarchitectural structure. All parameters were compared between groups.Results:In OS group, one rabbit sustained a hip dislocation without patellar dislocation. Three knees developed complete patellar dislocation in daily flexion position, and the remaining 16 patellae were dislocated when the knee was placed in the maximal extension position. In ST group, 15 knees were complete patellar dislocation in daily flexion position, and 5 knees were without dislocation. A local boss was formed proximal to the entrance of the groove and the articular cartilage was smooth, and no obvious osteoarthritis was observed in OS group. In ST group no boss was formed, while obvious cartilage degeneration and defect was seen. Compared to the control group, the central trochlear height and sulcus angle were greater in both groups, but without significant difference between the two groups. The Tb.Th was increased in both medial and lateral condyle, and Tb.N was decreased in medial condyle compared with its control knees in OS group. The BV/TV, Tb.Th, Tb.N and BMD were decreased and Tb.Sp was increased in both medial and lateral condyle compared with its control knees in ST group. Compared to the OS group, the BV/TV, Tb.Th, Tb.N and BMD were smaller and Tb.Sp was greater in both medial and lateral condyle in ST group, with significant differences.Conclusion:The model of patellar dislocation could be successfully achieved by femoral rotational osteotomy to increase femoral anteversion or surgical release of medial retinaculum and overlap suture of lateral retinaculum, and subsequent morphological and trabecular microarchitectural changes in the trochlea are different. Different bony and soft tissue factors should be addressed for different patients with patellar dislocation in clinical practice.
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Objective To investigate the impact of graft position shift on anterior cruciate ligament reconstruction induced by femoral fixation of interference screw. Methods Nineteen fresh cadaveric knees were used and assigned to three groups. 1) Study of graft position shift: 5 knees were randomly selected, interference screws of 7 mm, 8 mm and 9 mm were used in autologous tendon fixation, then the graft position shift were measured. 2) Study of isometry: 7 knees were randomly divided into the isometric reconstruction group (D group). In the D group, Retrobutton, interference screw and interference screw in location-corrected bone tunnel were used respectively as fixation. The isometry of grafts was evaluated. 3) Study of tibia anterior translation: 7 knees were randomly divided into the anatomic reconstruction group (J group). In the J group,the tibia anterior translation was measured in four different conditions in the same joint: intact knee joint,knee joint without ACL, ACL anatomic reconstruction by interference screw fixation, and ACL anatomic reconstruction by interference screw fixation with corrected bone tunnel location. Results 1) With 7 mm, 8mm and 9 mm interference screw fixation, graft position shift were (2.36±0.11) mm, (2.72±0.06) mm and (3.00±0.06) mm respectively. 2) Graft length change: graft length change in Retrobutton group and corrected bone tunnel group were less than 3 mm, while graft length change in those fixed with interference screw were stretched in more than 3 mm. 3) Study of tibia anterior translation: there was no difference among the intact group, the anatomic group and the corrected group at 0° and 15°. However, the difference was found between the intact group and other groups at 30°、60° and 90° of flexion, as well as between these two reconstructed methods at 20° joint flexion (P＜0.05). Conclusion In both isometric and anatomic ACL reconstruction with interference screw, the graft is pushed tightly toward the femoral tunnel wall, which shifts the graft away from the desired position. In our study we find out that the corrected location of the femoral bone tunnel significantly improves the isometry of ACL reconstruction and anatomic reconstruction.