Articulate patellar

Keywords— patellar, artificial knee cap, articulate patellar, total knee replacement. 

Articulate patellar was made by compacting bulk polyethylene powder into the die. The material that used to produce articulate patellar is all-polyethylene. In this study, only the dome shape will be manufactured by using CNC lathe machine (Miyano) in the Department of Engineering Design machining laboratory. 

Firstly, MRI (magnetic resonance imaging) is used to scan human body at each point in 3-axis, MIMICS software was used to simulate the data from MRI to generate the 3D model in. stl format. From the 3D model, the size of the kneecap of the patient can be measured and the suitable size of the articulate patellar during the total knee replacement can be decided. 

Secondly, by using reverse engineering method, a commonly designed articulate patellar was scanned using a 3D scanner and the 3D data was viewed and converted using IronCAD software. With the aid of (fig. 4), the size of the articulate patellar can be identified by measuring A and B and the size of the patellar (standard) is 32 which A=3mm B=8.5mm. 

Machining process using CNC lathe was used to manufacture the articulate patellar (the dome shape). 

Stress distribution between the femoral components to the articulate patellar can be defined by using FEA (finite element analysis) as shown in fig. 5. The contact area which extremely at high load can be determined. High stress at certain point also may cause wear to the articulate patellar. 

EUJI prescale film was used to define the distribution stress between the femur and articulate patellar by showing the mark of concentrated pressure. With both methods we can do the comparison between both methods to support the stress distribution result. 

The femoral unit clamping block or jig was produced which it can flex at certain angle. The jig produced has the same lateral profile as the femoral unit. The femoral s jig has 5 holes which is to lock the femoral s jig at 5 flexion angle of knee flexion. At the back of the femoral unit, there are 2 pins which allows the femoral s jig to clamp the femoral unit. The femoral s jig is clamped by compression test machine (Universal Testing Machine, model LS-28101-UTM) [1]. The patellar s jig with a diameter central holes 14.45mm and depth of 5.5mm was clamp to the UTM machine. Then the articulate patellar seated into the patellar s jighole underneath the femoral unit and allowed to move freely in the hole to centralise the unit about the femoral surface. The two sheets of FUJI Prescale low stress film... 

Gunston and MacKenzie s response to severe patello-femoral pain was to develop a separate patello-femoral arthroplasty, which consisted of a metallic patellar button articulating against an UHMWPE track implanted in the femur (1976). Because this solution required the implantation of two additional components, they cautioned against using this solution for patello-femoral replacement "indiscriminately" (1976). 

Using the Hood method, what is the maximum total damage score for the articulating surface of a bicondylar, cruciate-sparing total knee replacement, not including the patellar component ... 

The femoropatellar joint is a sellar joint the articulating surface of the patella is adapted to the patellar surface of the femur. This femoral articulation involves the anterior surface of both condyles. An oblique groove divides it into a large lateral and smaller medial area. The quadriceps muscles, the quadriceps tendon, and the patellar tendon maintain the joint s stability. Its major motions are vertical up-and-down movement on the femur, and movement in a sagittal plane with respect to the tibia. This allows a pulley function during flexion and extension of the knee. 

The patient is supine with the knee extended and relaxed. The examiner pushes the patella caudad in the trochlear groove and then holds it in this position. The patient is instructed to tighten the quadriceps muscle against the examiner s resistance. Palpable crepitation or pain on patellar motion is an indication of roughness of the articulating surfaces, potentially caused by chondromalacia of the patella. 

Fig. 5.2 Example total knee replacement system. The top portion of the figure highlights the polyethylene components available for the Persona personalized knee system manufactured by Zimmer, which includes both the tibia trays and the patellar resurfacing components. These liners are made from highly-crosslinked polyethylene with vitamin E added. In the bottom portion of the figure tibial trays are shown in their articulating position between the femoral and tibial metal components...

---