| Objectives: Patellar dislocation is more common phenomenon in clinical. In clinical research,researchers found most patients who suffer patellar dislocation combine with trochlear dysplasia. So most of the researchers believed that femoral trochlear dysplasia was one of the most important predisposing factors for recurrent patellar dislocation. However, the reason for femoral trochlear dysplasia was not very clear at present. Clinical research found that dislocation of the hip was the primary reason of acetabular dysplasia. Considering the similarity between patellofemoral joint and hip joint, we recently found that early patellar dislocation could lead to femoral trochlear dysplasia in the developmental rabbits. During the clinical treatment of acetabular dysplasia in children, researchers found that acetabular dysplasia could be improved after hip dislocation reduction. The aim of the present animal study was to investigate whether the early reduction of the patellar dislocation could prevent the femoral trochlear dysplasia caused by patellar dislocation in growing rabbits.Methods: Sixty 1-month-old New Zealand white rabbits(provided by the Laboratory Animal Center of Hebei Medical University) weighing 290–320g, were randomly divided into four groups(N=30knees/group): control group, early-reduced group, late-reduced group and dislocation group. The control group underwent no surgical procedures. The other three groups underwent dislocation surgery. After intravenous anaesthesia, the rabbits’ knees were shaved and sterilized following standard protocol. For surgical dislocation, a 4-cm midline incision was made over the knee, followed by dissection of subcutaneous tissues to expose the patella and its retinaculum. A 2-cm longitudinal incision was made in the joint capsule along each side of the patella. The patella was pushed laterally to induce patellar dislocation and keep patellar dislocation. The lateral capsule was then sutured(3-4 times) with overlapping tissue to prevent return of the patella to its normal position during active and passive knee extension and flexion. The early-reduced group underwent patellar reduction 1 month after subluxation surgery via the original midline incision. The skin and subcutaneous tissues were dissected to expose the patella and its retinaculum. The lateral joint capsule was loosened, and the medial capsule was sutured to reduce the patella and keep it in the trochlear track. The late-reduced group underwent patellar reduction 2 months after dislocation surgery. The dislocation group underwent no patellar reduction surgery. The skin incision was closed with interrupted mattress sutures. Bandages were applied at the completion of surgery. All rabbits were housed under the same conditions. Each animal had an individual stainless steel cage and was allowed an unrestricted activity in the cage. The rabbits underwent 20 min of passive knee joint movement three times daily to prevent joint stiffness. Intramuscular buprenorphine(0.05mg/kg) was administered twice daily for 3 days for post-operative analgesia. Oral ciprofloxacin(10mg/kg) was administered as antibiotic prophylaxis for the first 3 days after surgery. CT scan was performed 1, 2 and 6 months after surgical dislocation to measure the sulcus angle, trochlear width and trochlear depth of the trochlear groove. All rabbits were killed with air venous embolism 6 months after surgical dislocation. The morphology of the femoral trochlea and cartilage of the four groups were evaluated and compared. The tissue sections were made and stained with haematoxylin and eosin or toluidine blue. Microscopic analysis of the cartilage was performed to evaluate and compare the difference among the four groups.Results: Measuring results of CT examination showed that there was no statistically significant difference in average sulcus angle, trochlear width and trochlear depth between the control group and the other three groups one month after dislocation surgery. There was no statistically significant difference in average sulcus angle, trochlear width and trochlear depth between the control groups and the early-reduced group two months after the dislocation surgery, too. However, there was statistically significant difference in average sulcus angle, trochlear width and trochlear depth between the control group and the late-reduced group and the dislocation group two months after the dislocation surgery(P<0.05). Compared with the early-reduced group, there was statistically significant difference in average sulcus angle, trochlear width and trochlear depth in late-reduced group and dislocation group two months after the dislocation surgery(P<0.05). At six months after the dislocation surgery, the sulcus angle, trochlear width and trochlear depth of early-reduced group recovered nearly normal. There was no statistically significant difference in average sulcus angle, trochlear width and trochlear depth between the control groups and the early-reduced group six months after the dislocation surgery. Compared with dislocation group, there was obvious improvement in sulcus angle, trochlear width and trochlear depth in late-reduced group(P<0.05). However, there was statistically significant difference in average sulcus angle, trochlear width and trochlear depth compared with the late-reduced group and the control group(P<0.05). There was statistically significant difference between the early-reduced group and the late-reduced group. Six months after the dislocation surgery, cross visible indicated that the shape of the femoral trochlea grove in control group was normal and articular cartilage surface was smooth. The trochlear groove had normal depth and the lateral femoral trochlear facet was usually more protruded and higher than the internal trochlear facet. The shape of the femoral trochlea grove in early-reduced group was nearly normal and articular cartilage surface was smooth. The shape of the femoral trochlea grove in late-reduced group was shallow and low. Lateral femoral trochlea was low, and height of trochlear groove was reduced. The articular cartilage surface was rough and uneven with dim color. The shape of the femoral trochlea grove in dislocation group was abnormal. The trochlear groove was shallow and the lateral femoral trochlea was low, shallow, and wide. The articular cartilage surface was rough and the hyperosteogeny of the femoral trochlea was obvious. The HE staining of the articular cartilage showed that HE staining in control group was homogeneous and appearance of the articular cartilage was smooth and the cells were regularly and orderly arranged with basically the same size and the four layers were clear. The appearance of the cartilage of the early-reduced group was similar to that of the control group. The surface of the cartilage was smooth, with regularly arranged cells of the same size. In the late-reduced group, the articular cartilage of the femoral trochlea and the patellar cartilage were thin and not very smooth. The cartilage cells were irregular. The four structural layers were not very clear. In the dislocation group, the appearance of the cartilage was rough and partially peeled off cartilage which resulted in orientation of the cells lacked a pattern. The size of cartilage cells were irregular arrangements and the four structural layers could not be identified.Conclusions: Based on our study results, we conclude that patellar subluxation or dislocation early in an animal’s development can lead to femoral trochlear dysplasia or flattening and that early reduction can minimize femoral trochlear dysplasia in growing rabbits. |
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