Research On Optimal Design Of Acetabulum Files

The hip joint is an important link in the dynamic chain of the lower extremities and torso,and it’s load includes not only the weight at rest,but also the load during exercise,such as walking,climbing,running and jumping.So the hip joint plays a very important role in the normal activities of human daily life.When the lesion happens,the stress distribution of the hip joint cartilage and the subchondral bone will change,which will result in hip pain or even functional limitation and loss.With the acceleration of population aging in China,the incidence of hip joint disease is also rising rapidly.Because of the advantages of small trauma,less bleeding and less postoperative pain,artificial hip arthroplasty has gradually become a standard operation for the treatment of hip diseases.The long time process of artificial hip replacement is complicated,in which acetabular file is used to cut the cartilage of the acetabular fossa and the subchondral bone to reconstruct the acetabular fossa to match the shape and size of the acetabular prosthesis.However,this key surgical procedure has not received much attention from the domestic researchers.Therefore,in order to provide theoretical basis for clinical operation design basis for medical device companies,it is necessary to study the mechanical properties and cutting characteristics of acetabular resected objects-acetabular cartilage and subchondral bone,and study the cutting process and the design of the existing acetabular files.(1)A scanning electron microscope was used to observe the structure of the cartilage and subchondral bone of the acetabulum.It was found that the growth direction of the surface fiber and the middle and lower fibers of the acetabular cartilage was different.The surface fiber(about 0.2mm thick)of the acetabular cartilage grew laterally,while the middle and lower layer fiber(about 1.4mm thick)of the acetabular cartilage was vertical.The dividing line between the acetabular cartilage and the subchondral bone is not smooth,and the cartilage and thesubchondral bone are interlaced in the demarcation area(about 0.2mm thick),and the clear structure of bone unit of the subchondral bone is observed.These characteristics of acetabulum cartilage are similar to those of knee joint cartilage.Then the mechanical properties of bovine acetabular cartilage and subchondral bone were carried out.The average values of tensile modulus and ultimate stress of bovine acetabular cartilage which were at the tensile rate of 2mm/min,5mm/min and 10mm/min,were 5.22±0.96 MPa and 2±0.54 Mpa,4.87MPa±0.19 MPa and 1.18±0.2MPa,2.67±0.21 MPa and 0.73±0.22 MPa,respectively.The tensile modulus and ultimate stress of the subchondral bone were 418.16 MPa and 31.01 Mpa,467.65 MPa and 38.80 MPa,583.89 MPa and 46.47 MPa at the tensile rate of 2mm/ min,5mm/min and 10mm/min respectively.The hardness of the subchondral bone in the different regions of the acetabular fossa was also tested.It was found that the average hardness of the highest area of the subchondral bone of the bovine acetabular fossa was 72.0HV,and the average hardness of the lowest area was59.6HV.(2)Through the analysis of the design of the porous acetabular files that are commonly used in the present operation,it is confirmed that the surface cutting teeth of the porous acetabular file are distributed along the spiral distance,and the corresponding equations are given.The three-dimensional model of the 50 mm porous acetabular file is established by using the three-dimensional modeling software.Then,the cutting process of a porous acetabular file cutting tooth on the acetabular socket with a porous acetabular file is analyzed by a high speed photogrammetry.The cutting process can be divided into 4 stages,which are surface contact,extrusion of water,cutting into the cartilage membrane,cutting the interstitial cells of cartilage,and finally forming a curly strip continuous cutting.Then,according to the relationship between the cutting direction and the extension direction of the bone element,three cutting modes,such as the interleaving direction,the parallel direction and the vertical direction,are introduced.Then,the cutting force and cutting moment of different diameter(42mm to 60mm)acetabular files at different speeds(400r/min,600r/min,800r/min,1000r/min)and differentfeed speeds(12mm/min,24mm/min,36mm/min)were measured.It was found that the higher the rotational speed,the higher cutting force and the cutting force,and the higher the feed speed,the greater the cutting force and the cutting moment and the larger the diameter of the acetabulum file,the greater the cutting force and the cutting moment.The reasonable rotational speed 600r/min and feed speed12mm/min are recommended for the actual operation,and it is suggested that the cutting surface repair should be made by using the same diameter oblique edge acetabular file.(3)The cutting force model of the porous acetabular file was established through the orthogonal cutting experiment of single cutting teeth.The distribution and tooth profile of the existing porous acetabular file were optimized.Then,the optimized acetabular file model was printed by the metal 3D printing technology.And the experiment of cutting wax model was carried out with the optimized acetabular file.The results showed that the cutting moment of the acetabulum file is increased slowly after the optimization of the tooth distribution,and the cutting surface of the acetabulum file is smooth after the optimization of the cutting profile.(4)The Abaqus simulation software is used to simulate the subchondral bone cutting by the cutting teeth of the porous acetabular file.Different cutting tooth model with different structure parameters is established by changing the angle of the arc arch of the cutting teeth,and the parameters of the optimized cutting tooth structure are explored.The simulation results shows that when the inclination angle of the arc arch hole is 30 degrees,the cutting effect is better.