Project - 2
Additive manufacturing uses data computer-aided-design (CAD) software or 3D object scanners to direct hardware to deposit material, layer upon layer, in precise geometric shapes. As its name implies, additive manufacturing adds material to create an object. By contrast, when you create an object by traditional means, it is often necessary to remove material through milling, machining, carving, shaping or other means. Although the terms 3D printing and rapid prototyping are casually used to discuss additive manufacturing, each process is actually a subset of additive manufacturing. While additive manufacturing seems new to many, it has actually been around for several decades. In the right applications, additive manufacturing delivers a perfect trifecta of improved performance, complex geometries and simplified fabrication. As a result, opportunities abound for those who actively embrace additive manufacturing.
The applications of Additive Manufacturing (AM) have increased extensively in the area of orthopaedics. The AM applications are for making anatomic models, surgical instruments & tool design, splints, implants and prosthesis. A brief review of various research articles shows that patient-specific orthopaedic procedures provide multiple applications areas and provide directions for future developments. AM gives a flexible solution in orthopaedics area, where customised implants can be formed as per the required shape and size and can help substitution with customised products. A 3D model created by this technology gain an accurate perception of patient's anatomy which is used to perform mock surgeries and is helpful for highly complex surgical pathologies. It makes surgeon's job accessible and increases the success rate of the operation. AM provides a perfect fit implant for the specific patient by unlimited geometric freedom. Various scanning technologies capture the status of bone defects, and printing of the model is done with the help of this technology. It gives an exact generation of a physical model which is also helpful for medical education, surgical planning and training. This technology can help to solve present day challenges as data of every patient is different from another.
Additive manufacturing and orthopaedic implants:
Additive manufacturing is a type of manufacturing technology in which materials like powder, plastic or metal are deposited layer by layer to fabricate the 3D model from Computer Aided Design (CAD) model. This method is different from traditional manufacturing technology because rather than removing of material; it adds materials layer by layer. In surgical applications, this technology is used to create a model which gives a better understanding of complex pathology and anatomy of the patient. It easily produces specific custom implants and patient-specific instruments which help surgeon during the surgery of the patient.
In biomedical engineering, orthopaedics is surgical discipline applied through various disciplines such as joint arthroplasty, ranging from trauma surgery to tumour surgery for correction of the deformity. Orthopaedic applications provide a detailed analysis of the musculoskeletal system and craniomaxillofacial surgery.
Applications of additive manufacturing give a flexible solution with quick and cost-effective production of implants and also surgical instruments with high-quality of patient-specific. AM offers multiple benefits as compared to conventional implant production methods. By 3D CAD data, patient-specific parts are produced without using any tool along with required medically compatible materials and with a high quality of accuracy and precision. It makes surgeon job easier and optimise patient's treatment with minimum unpleasant side effects. AM methods can produce individual instrument and easily manufacture various medical devices. This technology is recasting in orthopaedic care that rapidly fabricates implantable devices by the use of bioactive materials and polymer. In orthopaedics, AM has extensive benefit for bone ingrowths capabilities. It enables to fabricate complex metal parts of the different shape, size and design. Regarding improving lives, it has a dramatic effect on the human condition. This is helpful for both clinical environment and manufacturing method. It creates implant of spinal devices, standard knee and helpful in the development of orthopaedic implant.
Types of orthopedic implants:
The three most common types of orthopedic implants are screws, plates, and prostheses.
- Screws: Orthopedic screws can have either a flat or Phillips head and are used to tighten up damaged areas, such as a torn labrum or rotator cuff. Orthopedist to use screws to repair fractured bone or restore stability in a weak area.
- Plates: There are five primary types of plates:
Buttress plates are used to hold together fractures at the end of long bones, in particular, at the knee and ankle, where the fracture site experiences large compressive and other distorting forces. These plates are contoured so they can move with the body, however, some may be L- or T-shaped.
Neutralization plates are not a specific plate, but rather, a category of plates that work to span the fractured area, balancing the load so that screws or other devices can secure and stabilize the area.
Bridging plates are used to stabilize the area while providing length and alignment. Additionally, bridging plates promote secondary bone healing because they preserve the blood supply to the fracture fragments by not disrupting the damaged area.
Tension plates usually are wires used to secure an area as it heals.
Compression plates are metallic plates used to repair a bone by using dynamic pressure between bone fragments to promote healing. - Prostheses: Orthopedists use a variety of orthopedic prosthetic implants to replace missing joints or bones, or to provide support to a damaged bone. Most commonly, orthopedists use prostheses for knees and hips, allowing the patients to regain full range of motion, pain-free, in a relatively short amount of time. In some cases, the prosthetic material can be combined with healthy bone to replace diseased or damaged bone, or prostheses can replace certain parts of a joint bone entirely.
Generating 3D objects by using additional manufacturing in orthopaedic:
In orthopaedic the patient-specific analysis is essential to obtain an accurate medical imaging data of the individual patient. Magnetic resonance imaging (MRI), modern multi-row detector Computer Tomography (MDCT), Computer tomography (CT) scan, X-rays and 3D scanners provide an accurate, fast, high-resolution data and easily prepare a 3D view of patient's anatomy. AM convert the digital medical image into a 3D physical model. This conversion takes place in three steps shown in the table below.
Table: Generation of 3D objects by using additive manufacturing applications
| Sl. No | Steps used | Description |
| 1 | Image acquisition | High-quality medical image with high resolution in 3D virtual form is generated from various scanning technologies Image acquisition is the most critical step because physical model accuracy depends on this CT, MRI and 3D scanners are mainly used to capture the image for this purpose |
| 2 | Image post-processing | DICOM (Digital Imaging and Communications in Medicine) images are extracted for data reconstruction by the use of image post-processing software It is useful for examining skeletal structures and detailed information about joint alignment and fractures CAD software transforms the 3D model into a series of polygons and converts data into standard triangulate language (STL) format The input to the 3D printing machine for part fabrication, the data file is in STL format DICOM images also play an important role in medical imaging data for the specific patient and 3D printing technology |
| 3 | 3D printing | CAD software divides the 3D model into "very thin" cross-sectional layers Additive manufacturing technologies fabricate 3D physical model by adding material layer by layer. |
3-D reconstruction images from these scanning technologies provide superior visualisation. This provides better surgical management and accurate diagnosis. These scanning technologies give 3D pictures displayed on a computer screen which cannot affect the perception of a physical model for complicated cases. For this, it is necessary to print these 3D models by the additive manufacturing technologies for the complete understanding. These 3D printed models provide better information to the surgeon. Before printing it is necessary to prepare DICOM which is extracted from the medical imaging and then convert it into STL format to complete the printing process by 3D printing machines.
Application of additive manufacturing in orthopaedics:
Additive manufacturing provides tremendous development in manufacturing field and now explore its applications in various medical fields. The 3D printed model's first goal is to resemble the cases in the clinic and give a detailed overview to the surgeon. The principal application of this model is for the testing procedure in advance as it provides a feeling of the mechanical response of real bone to the surgeon. The operation can also be performed on the 3D model to examine and visualise before performing actual surgery.
Table : Applications of Additive Manufacturing in Orthopaedics.
| Sl.No | Application | Description |
| 1 | Anatomic models for the planning of surgery | Traditionally the preoperative planning by an orthopaedic surgeon is done with the help of 2D Plain CT images and X-ray to assess the pathology and bony anatomy of the patient By the application of AM advanced image post-processing software is used to produce 3D images and 3D non-axial reformatted images The 3D anatomy can be viewed, and patient-specific physical bone models can be regenerated from patient's 3D data by using additive manufacturing technologies This physical model can help surgeons to have a visual and tactile understanding of the patient-specific pathology and anatomy. |
| 2 | Cost-effectiveness for orthopaedics | Traditionally there are standardised instruments that are not useful for every patient AM produced higher productivity customised implants and instruments at a lower cost as compared to the conventionally manufactured system The surgeon can easily achieve high-quality product to meet the required standard in orthopaedics It is a cost-effective tool for the hospital which fulfils the customised requirement of the surgeon |
| 3 | Surgical guides | AM is applied successfully for the fabrication of patient-specific surgical guides and implants It is used for a tumour, total joint arthroplasty and deformity correction It helps surgeons for the designing of surgical cutting guides which perfectly match the anatomy of the patient with reasonable accuracy For synthetic devices and individually printed implants, this technology is used efficiently for even complicated cases such as a spinal tumour and pelvic tumour By the applications of this technology, surgical tools can also be redesigned and manufactured |
Total Hip Replacement Prostheses:
In a total hip replacement (also called total hip arthroplasty), the damaged bone and cartilage is removed and replaced with prosthetic components.
The damaged femoral head is removed and replaced with a metal stem that is placed into the hollow center of the femur. The femoral stem may be either cemented or "press fit" into the bone.
A metal or ceramic ball is placed on the upper part of the stem. This ball replaces the damaged femoral head that was removed.
The damaged cartilage surface of the socket (acetabulum) is removed and replaced with a metal socket. Screws or cement are sometimes used to hold the socket in place.
A plastic, ceramic, or metal spacer is inserted between the new ball and the socket to allow for a smooth gliding surface.
Components of Implants
Many different types of designs and materials are currently used in artificial hip joints. All of them consist of two basic components: the ball component (made of highly polished strong metal or ceramic material) and the socket component (a durable cup of plastic, ceramic or metal which may have an outer metal shell). The prosthetic components may be "press fit" into the bone to allow your bone to grow onto the components or they may be cemented into place. The decision to press fit or to cement the components is based on several factors, such as the quality and strength of your bone. A combination of a cemented stem and a non-cemented socket may also be used. The acetabular component shows the plastic (polyethylene) liner inside the metal shell. The porous surface of this acetabular component allows for bone ingrowth. The holes around the cup are used if screws are needed to hold the cup in place.
Additive manufacturing method and material used in making hip prosthesis:
When it comes to production parts made through AM, the success of the application often is not as well established as the appearance of the part would suggest. Making a part through 3D printing is one thing. Achieving a process that will produce that part to demanding specifications and do so consistently is more challenging. The difference accounts for why usable 3D-printed parts are common, while established 3D-printing production processes are less. Additive manufacturing allows the titanium cup of a hip implant to be made with precise surface geometry carefully engineered to encourage the growth of the patient’s bone into this surface. The specific process the company uses to make implants in this way is electron beam melting (EBM) on machines.
When the hip joint doesn’t function, due to disease or fracture, a successful and widely used treatment is total hip arthroplasty (THA). In a THA, both the acetabulum and femur are replaced. Because of the high pain and debilitation caused by osteoarthritis. The whole concept was composed of: a stainless steel femoral prosthesis with small diameter head, the high density polyethylene (HDPE) socket, and acrylic cement to fix them. There are two techniques to fixate the stem into the femur currently used in THA: cemented fixation where a
polymethylmetacrylate (PMM) mixture is used as a grout between the bone and the implant, and cementless fixation, which relies upon bone ingrowths into the implant. There are different opinions in the research community about which one of the methods is to prefer. Recent research show that the two methods are
comparable with some exceptions.
THA is a successful orthopedic operation, with good survival within a 10-year period [18], but still there are problems, especially for younger, more active patients, whom are supposed to have the implant for a long time. Often patients have to wait to get an implant, even though they need one, because the surgeons know that it doesn’t last for the patient’s lifetime and revision surgeries are often more complicated than primary surgery. Most people can only go through 1-3 revision surgeries. The most common reason for revision surgery is asceptic loosening. Mechanical failure, such as fatigue fractions, is rare. Asceptic loosening is caused by both mechanical and biological factors and usually occurs several years after implantation. An important biological factor is the biological response to wear particles, and this is counteracted by reducing the friction coefficient of the materials. Mechanical factors include micro motion between the implant and bone,
and a phenomenon called stress shielding. Stress shielding is caused by the unnaturally high stiffness of the implant compared to the bone material as explained in Paper II. In brief, the stiff implant bears too big a share of the load and the surrounding bone tissue, which is a living material, adapts to the low stress level and resorbs [21]. Ways to counteract aseptic loosening due to mechanical factors are: achieving a firm primary stability and lowering the stiffness of the implant while keeping its strength. By creating surface structures to contribute to good bone ingrowth, and open celled net structures designed to achieve higher flexibility, EBM manufacturing can contribute to solving these issues.
THA is a successful orthopedic operation, with good survival within a 10-year period, but still there are problems, especially for younger, more active patients, whom are supposed to have the implant for a long time . Often patients have to wait to get an implant, even though they need one, because the surgeons know that it doesn’t last for the patient’s lifetime and revision surgeries are often more complicated than primary surgery. Most people can only go through 1-3 revision surgeries. The most common reason for revision surgery is asceptic loosening. Mechanical failure, such as fatigue fractions, is rare. Asceptic loosening is caused by both mechanical and biological factors and usually occurs several years after implantation. An important biological factor is the biological response to wear particles, and this is counteracted by reducing the friction coefficient of the materials. Mechanical factors include micro motion between the implant and bone,
and a phenomenon called stress shielding. The stiff implant bears too big a share of the load and the surrounding bone tissue, which is a living material, adapts to the low stress level and resorbs. Ways to counteract aseptic loosening due to mechanical factors are: achieving a firm primary stability and lowering the stiffness of the implant while keeping its strength.
Testing of Hip Prosthesis:
Wear and fatigue testing is performed to validate hip implant durability and performance over an extended period of time. Range of motion, axial push-in/out, modular connection strength, component interlock strength, and assembly/disassembly force properties are also evaluated by static testing.
Hip joint prostheses testing measures how your product will withstand different levels of fatigue, compression, torsion, and bending over an extended period of time. The testing is done under the specifications of ISO 7206. ISO 7206 provides industry guidance for the classification, dimensions, and test methods for partial and total hip joint prostheses.
Hip stem fatigue testing, governed by ISO 7206-4, applies an axial load to an implant that has been potted in such a way as to represent the loosening of the implant proximally. The orientation translates axial load into a combination of compression, torsion, and bending stresses on the stem of the specimen. Tests typically run to 5,000,000 cycles and must meet the load requirement of 2,300 N (517 lbs).
Stem fatigue testing simulates a loosened implant, femoral neck fatigue testing per ISO 7206-6 simulates loads experienced by a properly fixed implant during gait. Hip prostheses are expected to run out to 10,000,000 cycles without failure and tested at 5,340 N (1,200 lbs).
Femoral head testing applies static axial forces to ensure the prosthesis withstands the forces it’s exposed to while in use. Testing according to ISO 7206-10 helps determine the static compressive or tension loads that cause failure of the femoral neck and head assembly.
Orbital hip wear testing aims to characterize the tribological properties of a hip implant system by utilizing wear simulator technology to reproduce walking kinematics using flexion/extension, abduction/adduction, and internal/external rotation. Advanced SEM analysis and surface scanning can be performed to evaluate particulate and wear scars.
ASTM F1814 Standard Guide for Evaluating Modular Hip and Knee Joint Components provides an overview of relevant tests depending on the type of hip implant design.
ASTM F1820 Standard Test Method for Determining the Forces for Disassembly of Modular Devices provides a standard methodology for determining the attachment strength or locking mechanism strength between modular acetabular shell and liner.
MDT tests are conducted in accordance with ANSI/ISO/IEC 17025-2005. Testing schedules and resource needs are determined during project kickoff meetings with MDT engineers and the customer. Services are performed in accordance with standard operating procedures and test protocols specific to the project. Standard tests do not begin without a protocol signed by both the customer and an MDT representative. For feasibility or non-standard tests, MDT will develop a method and protocol with customer input and will review the final process with the customer prior to initiation of the test.
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