User talk:Osamabari

project report on manufacturing of HIP JOINT
Abstract

Because the requirements demanded from implant materials for artificial hip joints are extremely high, only a very few materials are suitable for this purpose. the metallic materials are standardized by the ISO still predominantly include cobalt based alloys, in cast form for wear resistant ball heads and in forged for fracture-resistant anchorage stems. Forged titanium based alloys have been also used for some years for highly stressed femoral components stems. Both alloy types exhibit a higher resistance to pitting, crevice and galvanic corrosion, stress corrosion cracking and corrosion fatigue then wrought stainless steel of relatively low strength properties. For this reason inadequate material strength hip prostheses made of the latter material is compensated for by a larger cross section of the prosthetic stem, this depending on the geometric conditions of the femur.

    Table of content

	Introduction

	Objectives to be achieved

	Parts of hip joint

	Steps involved in manufacturing of hip joint

o	Manufacturing of acetabular shell o	Manufacturing of femur

	References

Introduction To produce life long, harmless hip joint considerable cross disciplinary studies have been carried out. The research includes adabtability and sustainability of artificial materials to human body, selection of materials, precision fabrication and efficient replacement operations. Artificial joints are normally composed of metallic and/or ceramic components that are fixed to existing bone. Materials used for manufacture and fixation of total hip prostheses are:

* Metals * Polyethylene (HMWPE) * Ceramics * Bone cement

	All these materials must posses strength and biocompatibility.

	The material must be strong enough to withstand the forces and stresses imposed on it in the patient's body. Measurements demonstrated that stresses on artificial hips widely exceed the patient's body weight.

	The material must be biocompatible, that means to be well tolerated by the tissues of the patient's body. All materials used with fabrication and fixation of total hip prostheses are well tolerated by the body when applied in bulk.

	The tolerance of the body's tissues, however, changes when the material is present in fine particle form, as dust. In the fine particle form, all materials used for fabrication and fixation of total hip prostheses may evoke inflammation reaction in the tissues. The inflammatory tissues may destruct skeleton around the prosthesis.

	Thus, another demand on the materials used for fabrication and fixation of THP is that they do not wear off too much and that they produce minimal quantity of wear particles.

Objectives to be achieved 	Accordingly, it is an object of the present invention to provide an artificial hip joint that will provide all of the functions inherent in a normal human hip joint and which possesses great strength and service life. 	Another object is to provide an artificial hip joint that is light in weight.

	A further object of the invention is the provision of an artificial hip joint that avoids immobilization due to undesirable fibrous and bone growths around the joint.

	Still another object is to provide an artificial hip joint which advantageously utilizes the normally undesirable fibrous and bone growths to assist in holding the joint in position within the body.

	Still another object of the present invention is the provision of an artificial hip joint which is relatively simple and inexpensive to manufacture and which is relatively easy to insert into the body.

'''Parts of hip joint ''' Artificial hip joints, include several components. A femoral component of an artificial hip comprises an elongate stem or shaft at its distal end that is affixed within the medullary canal of the femur. A proximal end of the stem includes a neck region, to which is attached a femoral head. The acetabular shell is a separate component of an artificial hip joint that is affixed within existing bone such as the acetabulum. The acetabular shell includes a cup-like region that receives the femoral head. The femoral head and the acetabular shell form an articulation couple and smooth low frictional movement of the femoral head within the shell is essential to ensure proper functioning of the artificial hip joint.

Steps involved in the manufacturing of hip joint

Steps involved involved in manufacturing of hip joint are

1.	Receiving Inspection and 2.	Stretch Rolling 3.	Hot Pressing 4.	Milling and 5.	Drag Finishing 6.	Cone Machining and 7.	Grinding of the Cone Basis 8.	Plasmapore Coating and 9.	Finishing 10.	Final Cleaning 11.	Packaging and Sterilization

1. Receiving Inspection A specimen is analyzed and tested for strength. The titanium is kept in a so-called "blocked store" until it is released by the quality control department.

2. Stretch Rolling The titanium alloy is heated and rolled into a conical shape.

3. Hot Pressing In the implant forge, computer-controlled hot pressing of the prosthesis material is monitored. Subsequent precision forging takes place in three stages: bending, rough pressing and finish pressing. The prosthesis is then trimmed (material residues are trimmed off) to give it the correct contour. The second pressing calibrates the prosthesis, thereby giving it its final shape.  4. Milling The production data for the prosthesis is input into the computer-controlled CNC machining center which is then equipped with special tools. Machining is then begun with the press of a button. The CNC machine requires 15 to 20 minutes for production unit. The finished prosthesis is then precisely measured and tested.  5. Drag Finishing Milling leaves a rough surface on the prosthesis. It is smoothed automatically in a grinding machine in which ceramic chips together with a lubricating gel fluid remove the roughness. Drag finishing takes several minutes. Only when all surface values satisfy requirements does the prosthesis move on to the next production phase.

6. Cone Machining The prosthesis cone must be turned using extreme care because it forms the critical interface to the prosthesis head. This demands the highest degree of machining precision. The CNC lathe gives the prosthesis cone the correct diameter, as well as the necessary roughness and roundness. Every prosthesis is measured in detail. All the production data is then recorded for full documentation purposes. This means the properties of an implanted prosthesis can be reconstructed even after many years.

7. Grinding of the Cone Basis The direct transition between prosthesis shaft and prosthesis cone requires a special finish, produced by special hand work.  8. Plasmapore Coating The so-called plasmapore coating robots coat the top third of the prosthesis shaft by spraying pure titanium powder onto the oxide-free surface of the prosthesis in a vacuum chamber. The titanium powder hits the piece at twice the speed of sound. Upon colliding with the prosthesis, the powder particles burst, thereby forming a rough, microporous surface with high stability - the so-called plasmapore coating. Then come various tests and measurements, e.g. of thickness, porosity and peel strength of the coat.

9. Finishing The prosthesis then passes through a dulling process to give its other areas the final surface finish. For this it is pre-cleaned ultrasonically and then sprayed with ceramic beads. In the final inspection phase, the prosthesis is subjected to extensive measurement and visual inspection and labeled with a laser beam. The code number is particularly important as it makes it possible to later recount the "biography" of the prosthesis in full detail.

10. Final Cleaning and Packaging Final cleaning of the prosthesis takes place in a continuous washing facility that then leads into a clean room in which workers wear special protective clothing. In the clean room, the prosthesis is packed in its primary and secondary packaging. It is then packed in its outside packaging (master carton) and labeled in a second step outside the clean room.

11. Sterilization The hip prosthesis is then sterilized by a company that specializes in the technique of gamma ray sterilization.

Manufacturing of Acetabular shell

The acetabular shell is constructed of separate, but permanently attached metallic and ceramic components. An external, bone-engaging portion of acetabular shell preferably is made of a metallic material and is affixed within the acetabular cavity of the pelvis. External, bone engaging portion is a substantially dome-like structure that includes an irregular bone-engaging surface and a concave mounting surface. An internal portion of acetabular shell is preferably formed of a ceramic material that is generally concave and substantially cup-like in shape. A first surface of the internal portion of acetabular shell is permanently affixed to the mounting surface of acetabular shell. Opposite the first surface of internal portion is a second, substantially smooth and concave articulation surface that seats and articulates with the femoral head component of a hip joint. As noted above, bone-engaging surface of the external portion of acetabular shell has an irregular surface that encourages bone ingrowth and enhances fixation within the acetabulum cavity. Surface can further include one or more screw holes for seating bone screws .The femoral head fits within the acetabular shell. The femoral head and the concave articulation surface  of the acetabular shell  form the articulation couple of the artificial hip joint. Generally, the femoral head can be manufactured from a ceramic or a metallic material. The concave articulation surface, preferably is ceramic, but can also be metal or a UHMWPE-lined metal.

In a preferred embodiment,, the internal portion of acetabular shell  is made of a ceramic material and the external portion of acetabular shell  is made of a metal or metal alloy. It is also preferred that the mounting surface of external portion and the first surface  of internal portion  have interlocking regions that enhance the permanent fixation of the two surfaces to each other.One of ordinary skill in the art will appreciate that the dimensions of the acetabular shell of the present invention will vary. Generally, the range of dimensions is as follows:

•	Outside Diameter (D) 38 mm to 72 mm •	Internal Cup Diameter (d) 22 mm to 32 mm •	Overall Height (H) 15 mm to 45 mm •	Nominal Height (h) 15 mm to 40 mm

An acetabular shell of the type described above is preferably manufactured through a casting technique that relies upon specialized processes to produce a suitable casting mold. A preferred method of manufacturing such an acetabular shell is to utilize a computer controlled three dimensional printing technology to manufacture casting molds for directly casting the acetabular shell. The casting molds can then be used to cast the external, metallic dome-like structure and dampening mechanism of the acetabular shell. In a preferred embodiment, the ceramic internal portion of the acetabular shell is made directly through 3-D printing and forms a non-disposable component of the mold. The ceramic internal portion of the shell is permanently attached to the mounting surface of the external metallic dome-like structure of the shell. The ceramic internal portion of the shell remains secured to the metal portions of the acetabular shell after disposable mold components are fractured and removed.During the 3-D printing process, the casting mold is formed of loose powder that is applied in successive layers, with binder selectively applied to each layer by a computer-controlled scanning nozzle similar to an ink jet. The application of binder to the powder layers selectively solidifies the powder in each layer in a region or profile corresponding to a section of the desired three-dimensional solid. The 3-D mold printing process involves the deposition of a layer of a powder material in a confined area and the application of a binding material to selected regions of the powder layer to solidify the powder in desired regions. A next layer of powder is then deposited over the first layer, and binder material is again applied to selected, generally partially overlapping regions of the second layer of powder to solidify the second layer in those new regions and to bind the solidified sections to the previously solidified sections of the first layer. These steps are repeated according to a predetermined pattern to obtain an object formed of many successive laminations of powder and binder material. The regions in which binder material is deposited in each scan layer correspond to the sections, at the current scan height, of the three-dimensional object being formed. The object to be formed is a casting mold that represents a negative image of an implantable article to be cast.

In one embodiment, the casting mold includes disposable and non-disposable portions. The non-disposable portion of the casting mold represents ceramic internal portion of the acetabular shell. After the loose powder material is removed from the casting mold, the hollow casting mold is preferably baked to drive off volatile material, and fired in a furnace at a suitable temperature for a suitable time to yield a strong ceramic mold. A preferred powder material for forming the mold is alumina which, when solidified with an application of aqueous colloidal silica as a binder material, may be fired at about 1925° F. for approximately two hours to form a fired alumina casting mold. The fired casting mold is extremely strong and thermally stable so that it defines a precise mold cavity. Depending on the degree of ceramic consolidation that is desired for proper mold strength, a certain amount of shrinkage may be expected on firing the green ceramic. After firing, the hollow mold, receives a molten metal or metal alloy which is allowed to solidify to form the prosthesis. Suitable metal alloys include, but are not limited to, cobalt-chromium alloys, titanium-vanadium alloys, stainless steel and other materials that are well known for use in the manufacture of implantable prostheses. It is understood that for some casting shapes the mold may be filled with a metal or metal alloy powder rather than a molten metal or metal alloy. In such an application heat is subsequently applied to solidify the casting according to well known techniques. After a casting, the implantable bone prostheses are removed from the casting mold(s) as finished product. Where the casting mold is green, i.e., unfired, it is readily crumbled and destroyed and separated from the prostheses. A fired ceramic casting mold may be provided with one or more sections which are joined to form the prostheses and that can be separated as needed to remove the finished product. Ultrasonic cleaning and selective etching may used to remove all residues of the mold from the cast metal article. The mold ceramic is more permeable and less dense than the ceramic insert and thus the two can be cleanly separated from each other.

Manufacturing of Femur

The bone-marrow channel of the femur is then worked by special conical milling cutters, the size of which is predetermined exactly with respect to the size of prosthesis pin. The bone-marrow channel of the femur is preferably reamed to a size that corresponds exactly to the size of pin. The natural cotyloid cavity is also worked with mushroom milling cutters, and the size of the biggest cutter should be 2-3 mm smaller in diameter than that of the outer dimensions of acetabulum prosthesis of the cotyloid cavity. This is necessary to ensure a reliable attachment of prosthesis to the bones of the pelvis.A machined prosthesis of the head of the femur is movably interconnected with acetabulum prosthesis and includes a pin to be driven into the bone-marrow channel of the femur, a curved neck integral with pin and a hipball fixedly positioned, e.g. by shrinking, on the neck and movably located within socket.

The head of the femur, in addition to pin and neck, also preferably includes an enlarged shoulder integral with and positioned between the pin and the neck, and the neck is preferably formed with a base  joined to the shoulder and eccentrically positioned with respect to the central axis  of the pin. Shoulder defines a side portion and a lower surface, and it is surface that rests on the upper portion of the severed femur when the artificial hip joint is installed. In a preferred construction of the artificial hip joint, an innermost portion of the neck also extends in a continuous manner from side portion of the shoulder. It is also preferable and the preferred embodiment illustrated provides for a curvature of neck so as to form an angle of substantially 130° with pin axis. The angle is measured between the pin axis and an imaginary line passing from the pin axis through the center of hip ball and tangentially to the innermost curved surface of the neck.Pin also defines two slots and opening in directions parallel to the direction of curvature of neck. The function of these slots is similar to the function of the holes in prosthesis, and slots and permit bone tissue to grow there through so as to fix pin and prosthesis within the femur. Pin is also tapered away from neck, and the neck is tapered away from the pin. The taper of the pin permits it to be driven downwardly and into the bone-marrow channel of the femur.