Establishment Of A Rabbit Simple Articular Cartilage Defect Model Via A Posteromedial Knee Approach

Backgrounds: Articular cartilage defects resulting from trauma,inflammation and osteoarthritis are common clinical occurrences.Because of poor regenerative capacity of chondrocytes,articular cartilage does not usually regenerate by forming original-quality tissue.They are frequently associated with joint pain,dysfunction and decreased patient quality of life.Tissue-engineered cartilage for the repair of articular cartilage defects is considered the most effective and most recently developed therapeutic technique in current clinical practice.The establishment of appropriate animal models is essential for the experimental study of cartilage defect repair.New Zealand white rabbits are most widely used in animal experiments of articular cartilage defects.Currently,most investigators have utilized an anteromedial patellar incision to expose the articular cartilage in establishing an animal experimental rabbit articular cartilage defect model.Due to limited exposure of the surgical field,the sites used to create the cartilage defect more likely involved the femoral trochlea or the anterior portion of the femoral condyle.The surgical procedures used at these sites to create the cartilage defect were quite simple and were unlikely to cause injury to the important neurovascular tissues of the knee.However,these sites were located in the non-weight-bearing region of the rabbit knee.Furthermore,the cartilage surfaces of the sites chosen for defect creation were not sufficiently smooth,which may somehow affect the attachment of the regenerated cartilage implantation.Different investigators chose different ways of modeling and cartilage defects position,diameter,depth of cartilage defects are also different in animal experiments,which resulted in difficult to compare the efficacy of various new treatments.The cartilage defect models established before are actually models of cartilage-bone defects.The incomplete subchondral bone will lead to migration of bone marrow mesenchymal stem cells(BMSCs),which have been proved to be effective in the treatment of articular cartilage defects.These models will bring in confounding factors in the study of new treatment methods,resulting in bias in the results of the study.We attempted to further investigate the weight-bearing region of the rabbit knee by observing the movement of the rabbit knee joint in this study.The anatomical features of the muscles,nerves and blood vessels around the knee joint can provide the basis for modifying modeling approach.The range of exposure difference between anteromedial patellar incision and posteromedial approach were compared in vitro.Thickness distribution of habitual weight-bearing cartilage in rabbit femoral condyles was presented by optical coherence tomography(optical coherence tomography,OCT)as a non-invasive measurement method and data reference was provided for the construction of simple cartilage defect.Objective: This study sought to explore a method of establishing an animal model that requires a simple operation with minimal trauma and that allows access to appropriate locations for creating simple cartilage defects with appropriate depth after considering the habitual weight-bearing area,main anatomic structure and cartilage thickness of rabbit knee joint.Methods: A total of 60 New Zealand white rabbits of both genders aged 12 months were randomly average divided into 6 groups with 10 in each group.In the first group,we fixed the rabbit knees in maximum flexion or in the maximum extension position with elastic bandage.Under x-ray examination,the angle between the femoral mechanical axis above the knee and the tibial mechanical axis below the knee was further observed to determine the main loading area of femoral condyle cartilage.We were able to describe the distribution of the muscles and nerve fibers that surround the knee joint and observe the positional relationship between the surgical working space in the posterior popliteal fossa and the muscles or nerve fibers based on the anatomy of cadaveric specimens in group two.CT scan and angiography of the rabbit knee joints after ear vein intravenous injection of Optiray(350mg/ml)in the third group enabled the clear visualization of the blood vessel distribution and positional relationship between the operative incision and the adjacent blood vessel.The operative field and exposure were compared between a patellar anteromedial approach and a posteromedial knee approach by measuring the angle between the axis of the marking needle and the long axis of the femur on fresh isolated rabbit knee specimens obtained from the fourth group.For the fifth group,we took fresh specimens of knee joints(100 knees)after rabbits were killed painless in group 1,2,3,4,6 and the weight-bearing 0.4 x 0.6cm~2 regions of medial condyle were divided into 6 pieces of 0.2 x 0.2cm~2 block and the thickness of midpoint of each area was measured by OCT method.The medial femoral condylar cartilage defects were constructed on live rabbits in the sixth group using a posteromedial knee incision to verify the feasibility of the new approach.Results: From the maximum flexion position to the maximum extension,the angle between the connecting line of the midpoints of the weight-bearing region to the femoral condyle and femoral axis was 90 degrees to 130 degrees which suggest that the habitual weight-bearing area of the femoral condyle is located in the caudal half region(posterior aspect).The main tissues at risk for injury are the gracilis aponeurosis in the outermost layer and the semimembranosus and semitendinous at the bottom of gracilis aponeurosis,which are directly below the posteromedial incision.The posterior portion of the medial femoral condyle may be fully exposed in the knee extension position after partial incision through the triangular space composed of tibial collateral ligament,semitendinosus muscle and the medial head of the gastrocnemius muscle after cut open the gracilis fascia and and the semimembranosus at the distal end of the femur.The distance between deep tibial nerve or common peroneal nerve and posteromedial incision location is far enough,the shortest distance between the main nerve branches and the operative incision is 0.45 ± 0.11 cm in average.The 3-dimensional computed tomography angiography suggests that a posteromedial knee approach may avoid the descending genicular artery and the shortest distance is 0.31 ± 0.06 cm in average.It is safer that surgical incision should be selected within 0.5cm from the tibial collateral ligament and at the same height.This approach may provide excellent exposure for the caudal half of the medial femoral condyle after marking needle insertion at the maximum flexion position and the maximum extension position in vitro.The average thickness of the cartilage in the habitual weight-bearing area was 304.9±6.2?m,and there was no significant difference in the cartilage thickness between the 6 secondary partition(P<0.05).Experiment results in vivo show that the posteromedial incision can reveal the main loading area of femoral medial condyle cartilage and cartilage defects with 3mm diameter and depth of 0.3mm were successfully constructed.The simple cartilage defects are easy to construct,less bleeding,and no death or disability after operation.Conclusions: The posteromedial approach is an optimal method for pure cartilage defect construction on the medial femoral condyle of rabbit knee joint.This method can fully reveal the habitual weight-bearing area of the femoral condyle of rabbit knee joint,construct simple cartilage defect,reduce the confounding factors and surgical trauma could be controlled,which merits animal experimentation.