Project - 2

Introduction

In additive manufacturing, data from CAD programmes or 3D object scanners is used to control machinery that deposits material in successive layers to form complex geometries. Additive manufacturing, as the name implies, involves adding material to an already existing product throughout the manufacturing process. When making anything the old-fashioned way, however, you often have to take stuff away by milling, machining, carving, sculpting, or whatever else you need to do. Additive manufacturing includes a wide variety of processes, including 3D printing and rapid prototyping, both of which are often used interchangeably. Many people are surprised to learn that additive manufacturing has been around for decades, despite its seeming novelty. When used properly, additive manufacturing provides the holy grail of enhanced performance, complicated designs, and streamlined construction. Therefore, those who are open to and enthusiastic about additive manufacturing will have many doors opened to them.

There has been a significant uptick in the use of Additive Manufacturing (AM) for orthopaedic purposes. Anatomical models, surgical tools and tool design, splints, implants, and prostheses are all examples of areas where additive manufacturing has found use. A cursory examination of a selection of scholarly literature demonstrates that patient-specific orthopaedic procedures offer a wide variety of potential uses and point the way toward promising future innovations. In the field of orthopaedics, AM provides a versatile answer by allowing for the creation of implants in any desired shape and size. This technology's 3D models of patients' anatomies are used to practise "virtual" operations, which is very useful for diagnosing and treating difficult surgical diseases. Facilitating the surgeon's work and improving surgical outcomes. Thanks to its infinite geometric possibilities, AM enables the creation of implants that are a perfect fit for each individual patient. The current state of bone defects is captured by a number of scanning technologies, and a model is printed using these methods. Medical training, surgical planning, and classroom instruction all benefit from the precise physical model it generates. Because every patient's records are unique, this technology can be used to address current issues.

What is additive manufacturing and orthopedic implants

The process of additive manufacturing involves the deposition of successive layers of a material, such as powder, plastic, or metal, in order to create a three-dimensional object from a digitally-created model. This technique deviates from the norm of manufacturing in that, rather than eliminating material, it adds it in successive layers. This technology helps surgeons gain a more thorough comprehension of the patient's intricate anatomy and pathology through the creation of a model. The system makes it simple to create individualised implants and surgical tools for each patient.

Orthopaedics is a subspecialty of biomedical engineering concerned with the diagnosis, treatment, and prevention of deformities of the musculoskeletal system. The musculoskeletal and craniomaxillofacial systems are thoroughly examined in orthopaedic software programmes.

Additive manufacturing's medical applications provide a versatile, patient-specific, and rapid method of producing implants and surgical equipment at a reasonable cost. When compared to more traditional implant manufacturing technologies, AM has many advantages. Without the need for any sort of tool, and using only the most stringently medically appropriate materials, custom-made pieces can be made for each individual patient utilising 3D CAD data. It facilitates the surgeon's work and helps to ensure that the patient experiences as few negative effects as possible after the therapy. Using AM, it's possible to make customised instruments and mass-produce a wide range of medical gadgets. This technique is reshaping orthopaedic care by allowing for the quick fabrication of implanted devices out of bioactive materials and polymer. Orthopaedic applications of AM benefit greatly from its bone ingrowth potential. It makes it possible to manufacture metal components of varying complexity in terms of shape, size, and design. The impact on the human situation in terms of betterment of life is profound. The clinical setting and production process can both benefit from this. In the field of orthopaedics, it is used to develop spinal implant devices and standard knee implants.

Types of orthopedic implants

Orthopedic implants can range from screws and plates to prostheses and limb lengtheners.

Screws: Whether it's a torn labrum or rotator cuff, an orthopaedic screw with a flat or Phillips head can help restore motion and strength. Orthopedists employ screws to mend broken bones and strengthen weak spots.

Plates: There are five primary types of plates namely,

The fracture site near the end of long bones, such as the knee or ankle, is subjected to significant compressive and other distorting pressures, necessitating the use of buttress plates to keep the fractured area stable. These plates are curved to follow the curvature of the body as it moves, but they can also take on a L or T shape.
The term "neutralisation plate" refers to a broader category of plates used to span the fracture site and distribute the weight uniformly so that screws or other devices can be used to fix and stabilise the area.
Stabilizing plates are utilised to add length and straightness to the area. Because they don't interfere with the blood flow to the broken pieces of bone, bridging plates also help with secondary bone healing.
In most cases, tension plates take the form of wires that are placed around a wound to keep it in place while it heals.
Bone fractures can be repaired with dynamic pressure applied between bone pieces utilising compression plates.

Prosthesis: When a patient is missing a joint or a bone, or when a bone needs reinforcement, an orthopedist may use one of many different types of orthopaedic prosthetic implants. Orthopedists frequently employ prostheses for the knee and hip, allowing patients to restore complete range of motion, pain-free, in a short length of time. Prosthetic materials can be fused with healthy bone to replace diseased or damaged bone, or they can be used alone to replace specific areas of a joint bone.

Generating 3D objects by using additional manufacturing in orthopaedic

It is crucial in orthopaedics to conduct a patient-specific analysis in order to acquire reliable diagnostic imaging results. The contemporary multi-row detector Computer Tomography (MDCT), Computer tomography (CT) scan, X-rays, and 3D scanners that provide an accurate, quick, and high-resolution data and make it simple to build a 3D picture of the patient's anatomy are all examples. AM creates a tangible replica of a 3D medical imaging from a digital file. There are three columns in the table below that represent the progression of this conversion.

Table: Generation of 3D objects by using additive manufacturing applications

S.No.	Steps Used	Description
1	Image Acquisition	Multiple scanning techniques produce high-resolution, 3D virtual medical images. Accurate physical models depend on high-quality images, making image acquisition the most important stage. Imaging techniques such as computed tomography (CT), magnetic resonance imaging (MRI), and three-dimensional (3D) scanning are typically employed for this goal.
2	Image post-processing	Data reconstruction from DICOM (Digital Imaging and Communications in Medicine) pictures is accomplished with the use of image post-processing programmes. Using it, one can see the bones clearly and get specifics on things like joint alignment and fractures. By using standard triangulation language (STL) format, CAD software flattens the 3D model into a collection of polygons. The STL file format is the standard for data input to 3D printers. Medical imaging data for a single patient, such as 3D printed models, relies heavily on DICOM images.
3	3D Printing	The 3D model is separated into "extremely thin" cross-sectional layers using the CAD software. Technologies for additive manufacturing construct a physical replica of a 3D object by successively stacking layers of material.

Image reconstruction in three dimensions (3D) using these scanning methods allows for more accurate depiction. Enhanced surgical management and precise diagnosis are the results. These scanning methods provide 3D images on a computer screen, but they do not replace the usefulness of a physical model in more complex situations. These 3D models can only be fully comprehended when printed using additive manufacturing techniques. The surgeon benefits from more accurate data provided by these 3D printed models. In order to use 3D printing equipment, medical imaging data (DICOM) must be retrieved and converted to STL format before printing can begin.

Application of additive manufacturing in orthopaedics

Explore its applications in numerous medical disciplines immediately, thanks to the amazing progress that additive manufacturing has brought to the manufacturing sector. The primary purpose of the 3D printed model is to mimic the appearance of the cases seen in the clinic and provide the surgeon with a comprehensive overview. This model's primary use is in pre-operative testing, as it gives surgeons a feel for the mechanical response of real bone. It is possible to simulate an operation on the 3D model and observe its results before really carrying one out.

Table: Applications of Additive Manufacturing in Orthopaedics

S.No.	Applications	Description
1	Anatomic models for the planning of surgery	In the past, an orthopaedic surgeon would rely on X-rays and 2D Plain CT scans to evaluate a patient's pathology and bony architecture before surgery. Amplified reality (AM) is used in conjunction with cutting-edge image post-processing software to create both traditional 3D and non-axial 3D images. With the use of additive manufacturing techniques, patients' 3D anatomical data can be visualised, and personalised physical bone models can be produced for them. Surgeons can benefit from a better visual and tactile awareness of the pathology and anatomy of their patients thanks to this physical model.
2	Cost-effectiveness for orthopaedics	Standardized instruments, however, are not always helpful for every patient. When compared to the traditional manufacturing approach, AM's high-yield, bespoke implants and instruments were cheaper and more efficient. The orthopaedic surgeon will have little trouble producing a high-quality end result that conforms to industry standards. It's a practical instrument that meets the surgeon's unique needs at a reasonable price.
3	Surgical guides	Successfully, AM is used to make customised surgical guides and implants for each patients. Treatments for tumours, arthroplasty of the entire joint, and deformity adjustments all make use of this technique. It aids surgeons in creating surgical cutting guides that are somewhat accurate in their depiction of the patient's anatomy. Even in the most complex circumstances, such those involving a spinal tumour or a pelvic tumour, this method can be employed to great effect for the creation of synthetic devices and individually printed implants. Applications of this technology in the redesign and production of surgical tools are also possible.

Total Hip Replacement Prostheses

• Total hip replacement (also known as total hip arthroplasty) is a surgical procedure in which deteriorated bone and cartilage are surgically removed and artificial components are surgically implanted in their place.
• A metal stem is implanted into the femur's hollow interior to take the place of the severed femoral head. It is possible to cement or "press fit" the femoral stem into the bone.
• In order to decorate the top of the stem, a metal or ceramic ball is used. The injured femoral head was surgically removed, and this ball serves as a replacement.
• The acetabulum's injured cartilage surface is surgically removed and a metal socket is inserted in its place. The socket may be secured with screws or cement.
• To create a frictionless sliding surface between the replacement ball and socket, a plastic, ceramic, or metallic spacer is placed in between them.

Components of Implants

Today's artificial hip joints come in a wide variety of shapes, sizes, materials, and even technologies. The ball (often made of a hard, highly polished metal or ceramic) and the socket are the only two constants (a durable cup of plastic, ceramic or metal which may have an outer metal shell). You can either "press fit" the prosthetic parts into the bone and let your bone grow onto them, or you can cement them into place. Several aspects, like the quality and strength of your bone, must be considered before deciding whether to press fit or cement the components. A non-cemented socket can be used with a cemented stem, or vice versa. You can see the polyethylene (plastic) liner inside the metal acetabular component. The acetabular component has a porous surface that promotes bone ingrowth. If screws are needed to secure the cup, they can be inserted into the holes around its perimeter.

Additive manufacturing method and material used in making hip prosthesis

The success of AM applications is not always as well established as the appearance of the part would suggest when it comes to manufacturing parts manufactured by AM. Building a component with a 3D printer is one thing. It is more difficult to develop a method that reliably produces the required part in accordance with stringent specifications. This disparity explains why established 3D-printing production methods are scarce while usable 3D-printed parts are widespread. The titanium cup of a hip implant can be created with precise surface geometry via additive printing, allowing for optimal bone ingrowth. Electron beam melting (EBM) is the process the business utilises to mass-produce these implants.
Total hip arthroplasty is a common and effective treatment for hip dysfunction caused by disease or injury (THA). The acetabulum and femur are both surgically removed and rebuilt during a THA procedure. Because of the extreme discomfort and immobility that osteoarthritis causes. The proposal included a stainless steel femoral prosthesis with a small diameter head, a high density polyethylene (HDPE) socket, and acrylic cement to secure the components. Cemented fixation, in which a polymethylmetacrylate (PMM) combination is utilised as a grout between the bone and the implant, and cementless fixation, in which bone ingrowths into the implant, are the two procedures currently employed in THA to secure the stem into the femur. The scholarly community is divided about whether of the two approaches is preferable. Recent studies have shown that, with a few caveats, the two approaches are roughly equivalent.
There are still issues, especially for younger, more active patients who are expected to have the implant for a long time, despite the fact that THA is a successful orthopaedic treatment with good survival within a 10-year timeframe. Because physicians are well aware that implants don't last a patient's lifetime and that revision surgeries are typically more complex than main surgery, patients often have to wait even when they are in desperate need of an implant. The average person has only 1-3 chances at a revision surgery. Aseptic loosening is the most common cause of second-surgery. Failures due to mechanical causes, such as fatigue fractions, are uncommon. Mechanical and biological factors combine to create asceptic loosening, which often happens years after implantation. Reducing the friction coefficient of the materials helps reduce the biological response to wear particles, which is a significant factor in biology. Micromovement of the implant relative to the bone and stress shielding are examples of mechanical variables. According to Paper II, stress shielding occurs because implants typically have a far higher stiffness than bone material. The surrounding living bone tissue adapts to the low stress level and resorbs because the stiff implant bears too much of the strain. It is possible to prevent aseptic loosening caused by mechanical causes by establishing a high level of primary stability and decreasing the implant's stiffness without compromising its strength. Manufacturing EBM can help solve these problems by developing surface structures that promote optimal bone ingrowth and open-celled net structures that are meant to achieve more flexibility.
There are still issues, especially for younger, more active patients who are expected to have the implant for a long time, despite the fact that THA is a successful orthopaedic treatment with good survival within a 10-year timeframe. Because physicians are well aware that implants don't last a patient's lifetime and that revision surgeries are typically more complex than main surgery, patients often have to wait even when they are in desperate need of an implant. The average person has only 1-3 chances at a revision surgery. Aseptic loosening is the leading cause of revision surgery. Rarely will a mechanical failure occur, such as through fatigue fractions. Mechanical and biological factors combine to create asceptic loosening, which often happens years after implantation. Reducing the friction coefficient of the materials is one way to combat the biological reaction to wear particles, which is a significant determinant of wear. Micromovement of the implant relative to the bone and stress shielding are examples of mechanical variables. Because bone is a living material, it adjusts to the lower stress level and resorbs around the implant if it carries too much of the strain. Achieving a firm primary stability and decreasing the stiffness of the implant while maintaining its strength are two ways to combat aseptic loosening caused by mechanical causes.

Testing of Hip Prosthesis

Hip implants must pass wear and fatigue tests to prove they will last and work effectively for a long time. Static testing is also used to analyse attributes including assembly/disassembly force, range of motion, axial push-in/out, modular connection strength, and component interlock strength.
Hip joint prostheses testing evaluates the durability of your product over time by subjecting it to a variety of stresses, such as those caused by fatigue, compression, torsion, and bending. Standardization International Organization for Standardization (ISO) 7206 guidelines are used for the tests. Specifically, ISO 7206 advises on the proper categorization, size, and testing procedures for artificial hip joints, both partial and whole.
In ISO 7206-4-mandated hip stem fatigue testing, an axial force is applied to a potted implant to simulate proximal implant loosening. As a result of the orientation, the specimen's stem is subjected to loads in compression, torsion, and bending in addition to the axial load. Typical test loads are 2,300 N, and the maximum number of cycles is 5,000,000. (517 lbs).
Fatigue testing of the stem mimics the stresses experienced by a loose implant, while testing of the femoral neck in accordance with ISO 7206-6 mimics the loads received by a securely implanted prosthesis during locomotion. Tested at 5,340 N, the life expectancy of a hip prosthesis is 10 million cycles without failure (1,200 lbs).
Static axial forces are applied to the prosthesis' femoral head during testing to simulate the loads it will experience in real life. It is possible to ascertain the static compressive or tension loads that lead to failure of the femoral neck and head assembly by conducting tests in accordance with ISO 7206-10.
The goal of orbital hip wear testing is to describe the tribological features of a hip implant system by simulating walking kinematics through flexion/extension, abduction/adduction, and internal/external rotation using wear simulator technology. Particles and wear scars can be evaluated with high-tech scanning electron microscopy examination.
Depending on the specifics of the hip implant design, the ASTM F1814 Standard Guide for Evaluating Modular Hip and Knee Joint Components can provide a useful overview of the essential testing.
The attachment strength or locking mechanism strength between a modular acetabular shell and liner can be measured using the standardised procedure outlined in ASTM F1820, Standard Test Method for Determining the Forces for Disassembly of Modular Devices.
ANSI/ISO/IEC 17025-2005 is the standard by which MDT testing are performed. Initial meetings between MDT engineers and the client establish testing timelines and resource requirements. All work is carried out in accordance with established procedures and test protocols developed for the purpose of this particular project. The customer and MDT representative must sign a protocol before any routine tests may commence. When conducting feasibility or non-standard tests, MDT will work with the client to create a customised methodology and protocol, and then have the client evaluate the entire procedure before it begins.

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