Implants exam review

Define biomedical implants; what makes something a biomedical implant

. Medical devices and structures that are inserted directly into the body of the patient Differ from prostheses in that the prostheses are commonly attached to the body rather than being an implant The biomedical implants are most commonly a product developed from studies in the BME field

What are the 5 material considerations for biomedical implants/devices? Safety Durability Mechanical compatibility Biodegradability Biofunction
How PMMA was adopted as an implantation material; who was the inventor? WW2 pilots would get PMMA in their eyes and no adverse effects were noted, invented by Dr. Harold Ridley
List three uses of PMMA as biomedical implants/devices. Intraocular lenses PMMA bone cement is orthopedic surgery Dentures
What is intraocular lens and what disease they treat? An intraocular lens is a tiny artificial lens for the eye, it works by replacing the eyes natural lens that is removed during cataract surgery
Differences between balloon expandable stents and self-expandable stents; how each are inserted into the body; typical materials used for each and why Balloon expandable stents are guided to the target area by a catheter and then the balloon is inflated to open the valve. Then the artificial valve is deployed and the catheter/balloon combo are removed. The stents are mounted over an angioplasty balloon. The stents are often made of 316 stainless steel or other non corrosive, stiff alloy metals like tantalum, or Cr-Co super alloys, Elgiloy (Co-Cr-Ni alloy), MP35N (Nickel-cobalt base alloy), and L605 (cobalt-chromium-tungsten-nickel alloy) Self expanding stents are produced at the desired final diameter, and spring loaded into a much smaller catheter, once the stent is delivered to the diseased vessel, the catheter sheath is withdrawn, and the stent expands elastically outward into the artery. These stents are made of more elastic materials like Nitrol, a nickel-titanium allow with shape memory capability
What is the origin of the word stent? Who invented the vascular stent? The word comes from the 19th century from a dentist, Charles Thomas Stent. This was most famous for improving and modifying the denture base of the Gutta-Percha creating the stents compounding that made it practical as a material for Dental impressions. In 1847 it was introduced as a material for making dental impressions, used to fill the empty space inside the root of a tooth after it has undergone endodontic therapy. First use for a vascular stent came from Weldon et al in 1966 when they described a Prosthetic-stented aortic homograft used for mitral valve replacement.
What was going on with Abbott’s Absorb bioresorbable vascular stent? The companies said they are ending the production of the stent due to poor sales performance. The company plans to continue clinical trials to assess long term outcomes after the scaffold has dissolved.
Be familiar with the key parameters in stent design. Biocompatibility High expansion ratio (deployed diameter/ crimped diameter) Navigation of tortuous vessels or entering branches with an acute angle, thus the stent must have good longitudinal flexibility. The crimped diameter of the stent is often referred to as it's profile, which should be as low as possible The above considerations generally require a minimum amount of material A high degree of radial strength Sufficiently radiopaque These two considerations above require a high amount of material in the stent, thus there must be a trade off in the design process The expansion of the stent from the crimped to the deployed state must result in as little axial foreshortening as possible, or it will be difficult to predict the final position Other considerations include the ability to retrieve the stent in case of a mal deployment and minimal interference with CT and MRI imaging The Delivery system must work well with the particular stent design and must Hold the stent in place in a way that does not injure or snag on the artery wall as it is guided to the disease site Perhaps the most important design characteristic for stents is that they do not provoke the development of a new blockage either acutely through thrombosis or later on due to hyperplasia Unfortunately there is little direct information on How stent design affects these processes
What system is used for stent and tube cutting; working principle? The Sigma stent and tube cutting system is used for stent and tube cutting. This is done by first designing the stent using CAD and then the cutting system will laser cut the stent from a protruding piece of metal with a stream of water cooling as necessary
1. Host reactions for stent implants: what are the four stages? Systemic antiplatelet drugs – four major drugs? What cause in-stent restenosis? First the exposure of the Subendothelium and the stent material to the blood stream Initiates thrombus formation This usually takes minutes/hours including the aggregation of platelets, fibrin, and erythrocytes (RBCs) The degree of Platelet adhesion depends on not only the surface characteristics of the stent but also on the Strut configuration Areas of flow stagnation which depend heavily on strut design influence the degree of platelet adhesion Areas that are subjected to Intermittent flow stagnation and low wall shear stress Showed Greater platelet accumulation in their in vitro experiments The second stage of the reaction to the stent is Inflammation
2. The peak of this process occurs Approximately 4 to 14 days following stent implantation
3. Deposits of surface adherent and Tissue infiltrating monocytes can be seen around stent struts, demonstrating the degree to which the struts are injuring the wall
4. These monocytes release Cytokines, mitogens, and tissue growth factors that further increase neointimal formation The Third Stage is the Proliferation of vascular smooth muscle cells in the media and neointima This process depends on the Stent Material as well as the Stress placed on the artery wall by the stent The Final Stage of arterial adaption is Remodeling One can think of this phase as the Artery’s attempt to reach a new homeostatic state in the presence of the persistent injury caused by the stent The final thickness of the neointima depends heavily on The degree to which the stent injures the artery wall as indicated by the disruption of the internal and external elastic laminae Systematic antiplatelet drugs Electrochemical surfaces have reduced the risk associated with the stent itself However the use of systematic antiplatelet drugs has played a more dominant role in reducing acute stent thrombosis Aspirin enjoys widespread use as an anticoagulant It's use as an adjunct to stent deployment is limited because it inhibits only one of the many pathways to platelet activation Currently daily usage of aspirin is recommended for all persons at risk of circulatory disorders, including stent patients Ticlopidine is another platelet activation inhibitor, can be effective when used in conjunction with aspirin but suffers from a number of undesirable effects Clopidogrel like Ticlopidine inhibits platelet activation but has fewer side effects Heparin is commonly used during stent procedures But not afterwards Recent success has resulted from the use of glycoprotein IIb/IIIa inhibitors such as Abciximab, which is administered prior to and during the interventional procedure In Stent Restenosis The Growth of tissue into the stented region can cause a new blockage This process is responsible for the clinical failure of 20-30% of stenting procedures within 6 months following implantation Among the factors that influence the risk for restenosis is Stent Design In a clinical study of more than 4500 coronary stent implantations it was shown that restenosis rates for different stent designs ranged from 20-50% The exact relationship between stent design and the development of Intimal hyperplasia is not well understood, generally it is understood that the percent Area covered by the stent and the mechanical mismatch between the stent and artery wall are important factors
5. BioMimics 3D stent was designed for treating femoropopliteal artery disease. What are the engineering innovation and benefits of this design? Two major types of drug eluting stents? Biomimics 3D represents an innovative approach to the requirement for durable support for the arterial lumen after intervention. The helical line stent is designed not only to promote swirling blood flow but also to accommodate the complex biomechanical challenge associated with stenting this anatomically mobile artery Nonplanar curvature in arterial systems promotes swirling flow which Increases shear wall stress which is not only atheroprotective but protective against neointimal hyperplasia following intervention. Due to it's shape biomimics 3D similarly affects blood flow. With improved biomechanical performance, the device may be especially useful in hostile arterial environments like the distal SFA (superficial femoral artery) Drug eluting stents Paclitaxel drug eluting coated stents for coronary artery placement are sold under the name Taxus by Boston Scientific in the united states Paclitaxel drug eluting stents for Femoropopliteal Artery placement are sold under the name Zilver PTX by Cook Medical
6. \ What are structural ECMs. Function and hierarchical structure of collagen. Type I, II, III, IV collagen. Structural ECM components consist of mainly proteins (Collagen, Elastin, Fibronectin, Laminin) Proteoglycans, and bound and unbound water ECM are any material part of a tissue that is not part of any cell, ECM represents the Secreted product of resident cells within each tissue and organ and is composed of a mixture of structural and functional proteins arranged in a unique, tissue specific three dimensional ultrasound Fibrous structural macromolecules Collagen Accounts for roughly ⅓ of the total body protein 40% in skin 10-20% in bone and teeth 7-8% in blood vessels Essential components in tendon, ligaments, cartilage, intestines etc Very stiff material that provides mechanical strength and carries tension, collagen fibril has high tensile mechanical strength) Provides platform for bone mineralization Supports attachment of numerous cells Tertiary structure Three chains packed together into a chemically stable structure unit: homotrimer and heterotrimer Triple right-handed helical: Collagen material: ~300 nm in length and ~1.5 nm in diameter Quaternary Structure Super-molecular unit structure: Collagen fibril: 20-100 nm in diameter Quasi-hexagonal lattice with an interchain distance of 1.3 nm Quarterly staggered packing produces a characteristic banding appearance: 64-67 nm of D-periodTypes of collagens 1-4
7. Skin, tendon, bone, dentin, heart valve, muscle, blood vessel, scar Key features: Major fiber bundles to give strength
8. Cartilage Main collagen of cartilage
9. Skin, muscle, blood vessels, bladder More abundant in fetal tissue
10. All Basal laminas Forms two dimensional network Elastin Proteoglycans Proteoglycan complex/glycosaminoglycans Adhesive proteins Fibronectin
11. Reinforcement of concentric cylindrical layers in osteon. (figure this out) The Osteon consists of a central canal called the osteonic canal which is surrounded by concentric rings (Lamellae) of a matrix. Between the rings of matrix, the bone cells are located in spaces called Lacunae
12. Function and structure of elastin. Microstructural characteristics of artery and lung alveoli. Elastins are similar to rubber bands and can be stretched very far, store energy, and release most of the elastic energy when bouncing back important to dynamic tissues such as lung alveoli Elastic fibers are 10-12 nm in diameter Amorphous elastin forms the core Microfibrillar components surround the core Fibers tend to branch Fibers aggregate to form network structures Ropes (ligaments) Concentric sheets (blood vessels) Honeycombs (elastic cartilage)
13. \ Function and structure of small PG, large PG and aggrecan. Microstructural characteristics of cartilage. Proteoglycans Macromolecules: found in all connective tissues and extracellular matrices and on the surface of many cells Consist of a Core protein covalently attached to one or more polysaccharides called GAGs Highly negatively charged GAG chains and trap a lot of water (like gel), making the tissues hydrated, lubricated, and resisting/absorbing repetitive mechanical loading such as in cartilageAggrecan Predominant proteoglycan in cartilage Forms large aggregates >4 um long, bigger than bacteria Give cartilage unique gel-like properties, trap and attract water Central component is Hyaluronan (HA) Large Proteoglycans Lubricants (absorb water) Shock absorbers (resist compression) Space filters Regulate diffusion and flow of both water and macromolecules
14. Biomechanical properties of various structural ECMs and the analogs we used for them. Elastin fibers Insoluble proteins Resilience Long range deformability Elasticity Chemically inert and resistance to dissolution Hydrophobicity Stability Large strains with small applied stress Complete return to original dimensions Small hysteresis (small energy dissipation) Collagen Enables flexible deformation Provides high mechanical strength to tissues like tendons Proteoglycans Attract and trap water like gel Hydrates and lubricates tissues resists/absorbs repetitive mechanical loading such as in cartilage
15. Give examples of blood interfacing implants. What are the material requirements for long-term implants? Blood interfacing implants Heart valve prosthesis Total artificial heart Ventricular assist devices Vascular prosthesis Short term: Extracorporeal devices Dialysers Blood oxygenators Ventricular assist devices Catheters Long term Heart valve prostheses Vascular grafts Cardiac pacemakers Total artificial heart Material requirements for long term implants Biocompatibility, nontoxicity, and durability Non-irritating to tissue, resistant to platelet and thrombosis deposition Non-degradable in the physiological environment Neither absorb blood constituents, nor release foreign substances Mimic the function of the organ Suitable size and weight Easily available, inexpensive, machinable, sterilizable, and long storage life
16. Know the anatomy of the heart. Heart valve stenosis; heart valve regurgitation. Anatomy of heart Pulmonary heart valve: three leaflets Aortic valve: three leaflets Tricuspid valve: three leaflets Mitral valve: two leaflets Heart valve stenosis Diseased heart valves can result in stenosis which is impeded forward flow and/or backward flow Burdens heart and may lead to heart failure Heart valve regurgitation When the valves in the heart do not close completely leading to a leaky valve where blood can flow backwards when it should flow forwards and vise versa
17. Three major types of heart valve replacements – mechanical heart valves, bioprosthetic heart valves, transcatheter heart valves; advantage and disadvantage of each type. Mechanical heart valves Early development in the 1960s Modern device can last a lifetime All will require lifelong treatments with anticoagulants Three kinds of MHVs: caged-ball, tilting disk, Bi-leaflet valve MHV drawbacks Cavitation An event that lead to MHV failure or MHV related erosion A rapid formation of vaporous microbubbles in the fluid due to the drop of pressure, bubbles will collapse or implode during recovery Cause pressure or thermal shockwaves and fluid microjets Bioprosthetic heart valve Two types of bioprosthetic heart valves Homograft implant from deceased patient Preservation include sterilization, free drying, immersing in antibiotic solution Not so popular due to long term durability and availability Xenograft from animal models Undergo chemical procedures to be suitable for implantation The common risk includes immune rejection to foreign materials Structural deterioration due to fatigue, damage (~15-20 years) Most popular model is porcine heart due to high similarity to human heart Harvested from 7-12 month old pigs Reduced stress at the juncture between stent and leaflet Transcatheter Heart valve A catheter is guided into the heart and a small balloon is inflated to open the valve in what is called valvuloplasty A catheter carrying a balloon and folded artificial valve The catheter is deployed and withdrawn once the new valve is in place Transcatheter aortic valve implantation or replacement was recently approved by the FDA for intermediate risk patients with severe aortic stenosis. This technique was already worldwide adopted for inoperable and high risk patients
18. How mechanical heart valve replacements are made; three major designs – caged-balled, tilting-disc, bi-leaflet; major materials used; what are their properties/drawbacks? What is cavitation? Caged-ball valves Use a metal cage (Co-Cr alloy) to house a silicone elastomer ball When blood pressure (mmHg) is greater inside heart chamber than outside of the heart chamber the ball is pushed against the cage and allows blood to flow When blood pressure is Greater outside of the heart chamber than it is inside the heart chamber the ball moves back against the base and forms a seal 1960 (Edwards and Starr), 1966 (Smeloff and Cutter inc) Simple design only moving part is the ball High tendency to form blood clots Patients need high degree of anticoagulant, target INR 2.5-3.5 Production of starr-edwards valve was discontinued in 2007 Tilting disk valve First designed in 1969 by Bjork-Shiley A single circular occluder controlled by a metal strut A metal ring covered by fabric Suture threads are stitched to hold the valve in place Two metal supports support the disk for opening and closing during heart valves Open angle of 60 degrees and ~70 BPM Working properties Improved hemodynamic property Excellent wear resistance and mechanical strength Excellent blood compatibility with pyrolytic carbon disc More flexible Bi-leaflet heart valve First introduced in 1979 Design: two semicircular leaflets that rotate about struts attached to the valve housing Improvements Provide much more natural blood flow than caged ball or tilting disk Only a small amount of blood thinner is needed Have a great opening area, open completely
19. How bioprosthetic valve replacement are made – two major designs – bovine pericardium, porcine aortic valve; major materials used? Common problems with implanted prosthetic heart valves. Bovine pericardial tissue Specified and controlled design characteristics (e.g. orifice area, valve height, degree of coaptation) Glutaraldehyde fixation to reduce foreign body reactions (.625%) Mimic geometry and flow dynamics of natural human aortic valve Less stenotic compared to porcine bioprosthesis due to pericardial design and increased orifice area. Consist of a base ring and stent with supporting posts Porcine aortic valve Very similar to human heart Valves harvested from 7-12 month old pigs The same .625% glutaraldehyde fixation is used to reduce foreign body reactions Attach tissues to flexible supporting stents and preserve Reduced stress at the juncture between stent and leaflet Potential problems for both Porcine valve can have bulky calcifications nodules on the leaflets surface leading to severe aortic stenosis Pericardial valve can have excessive Pannus overgrowth with a fibrotic reaction encasing the sewing ring structure
20. What does “CDRH” represent? What is “21 Code of Federal Regulations (CFR) 862–892”. CDRH stands for the Center for devices and radiologic health 21 code of federal regulations contains descriptions of a wide variety of medical devices arranged by practice area
21. 21 CFR codes for “orthopedic medical devices “and “cardiovascular medical devices? CFR code for Orthopedic medical devices is 888 CFR code for Cardiovascular devices is 870
22. Define Investigational Device Exemptions (IDE), Premarket Approval (PMA), 510k, ISO 9000, Good Manufacturing Practice (GMP), Good Laboratory Practice (GLP), IRB, IACUC. Investigational device exemption Must be obtained in order to distribute devices for clinical trials Pre-market approvals are necessary when the device developer wishes to market an innovative device in the United States That is not substantially equivalent to any other device that has been cleared through the 510(k) process PMA must demonstrate that the device is Safe and Effective Considerably more complex than the 510(k) process A detailed manufacturing section describing the methods for building and testing the device must be included 510(K)- four types of 510(k) premarket notifications Traditional, abbreviated, special, De Novo. The 510(K) application process Claims substantial similarity. Some well understood devices can now be approved under 510(k) rules even if they were not marketed before 1976 Prove your product is a substantially equivalent (SE) new device Might be treated as a not substantially (NSE) device ISO 9000 covers design and mandates design review/documentation Is a family of standards for quality management systems. ISO 9000 is Maintained by ISO (International Organization for Standardization) and is administered by accreditation and certification bodies Is a qualifier for international markets or specific domestic customers Certification can be a valuable marketing tool The standards are a sound blueprint for a quality system GMP refers to the good manufacturing practice regulations by the FDA These regulations which have force of law, requite that manufacturers, processors, and packagers of drugs, medical devices, some food, and blood take proactive steps to ensure that their products are safe, pure, and effective GLP refers to good laboratory practice regulations which govern the conduct of nonclinical laboratory safety studies Applies whenever data is used to support a nonclinical laboratory safety study IRB is the institutional review board Is a committee that has been formally designated to Approve, monitor, and review BME and behavioral research involving humans with the aim to protect the rights sand welfare of the research subjects IACUC is the institutional animal care and use committee Is a self regulating entity that according to U.S. federal law, must be established by institutions that use lab animals for research or instructional purposes to oversee and evaluate all aspects of the institutions animal care and use program
23. More than 3000 medical devices are cleared on to the U.S. market every year through the 510(k) premarket notification process. This represents approximately half the new devices that appear in the U.S. market in a given year. The 510(k) process is relatively rapid, flexible, and adaptable to many different device types and risk levels.
24. What is predicate device? A predicate device is the previously cleared device included for comparison purposes in a 510(k) 510(K) May contain multiple predicate devices that address various features When searching for potential predicate devices, two FDA databases, The 510(K) database and the classification database can be helpful
25. In 510(k) submission components, understand the “Statement of Substantial Equivalence” and “Comparative Information”. Statement of Substantial Equivalence This optional selection can “sell” the 510(k) to the ODE by providing a well reasoned rationale for a substantial equivalence determination. This section may not be necessary when there is a very simple comparison between a single predicate device and the new device Comparative information This is the heart of the 510(k). This section must contain data that demonstrates that the 510(k) device is “substantially equivalent” to the predicate devices
26. A PMA must provide valid scientific evidence that there is a “reasonable assurance” that a device is both safe and effective. True
27. The PMA process is considerably more complex than the 510(k) process. Unlike most 510(k), a detailed manufacturing section describing the methods for building and testing the device must be included. True
28. The post-market requirements of a PMA are considerably more complex than those related to a 510(k). Specifically, a PMA annual report must be filed with the Office of Device Evaluation (ODE) each year and changes in labeling, materials, manufacturing, and quality methods, and specifications as well as changes in manufacturing location must all be reported to, and approved by, the ODE, in advance. True
29. After a PMA device is approved, the approval letter, summary of safety and effectiveness, and official labeling are placed on the CDRH Web site. The PMA submission itself is not available via the Freedom of Information process. True
30. Clinical trial data outside of U.S. Note that clinical trial is classified as four phases in pharmaceutical field and three studies in medical devices. The cost recovery provision of the IDE regulation [21 CFR 812.20(b)(8)] permits the sponsor to charge for the device. The sponsor can charge enough to recover research and development costs. This provision cannot be used to commercialize an investigational device. True The data does not need to come from inside the U.S. good, credible, and ethical data will be accepted from any location. But the study must be conducted in accordance with the Declaration of Helsinki or local ethical procedures, whichever is stricter is used.
31. The SMDA Federal is legislation which was designed so that the FDA could quickly be informed of any medical product that has caused or suspected to have caused a serious illness, injury or death. Reporting must be completed within ten working days after an event is determined to be reportable. True
32. The goal of the QSR is to create a self-correcting system that reliably produces robust device designs and production methods, ensuring that devices perform in a manner consistent with their intended use. True QSR regulates both the device development and the manufacturing process for all class 2 and 3 devices from the start of development phase until the device is no longer supported by the manufacturer Also covers the manufacturing process for many class 1 devices It does not cover the research process for any medical devices
33. Most GMP requirements are very general and open-ended, allowing each manufacturer to decide individually how to best implement the necessary controls (flexibility). GMP is also sometimes referred to as "cGMP". The "c" stands for "current," reminding manufacturers that they must employ technologies and systems which are up-to-date in order to comply with the regulation. Components of GMP: Organization and Personnel, Buildings and Facilities, Equipment, Production/Packaging Controls, Documentation, Storage and Distribution, Quality and Laboratory Controls. True
34. What are the six types of bone implants? What are each primarily used for? Wires – used for reattaching large fragments; Pins – hold fragments of bone together provisionally or permanently; Screws – fixation of bone fragments; Plates – facilitate fixation of bone fragments; Intramedullary Nails – internal struts to stabilize long bone fractures; Joint Replacements – replace damaged joints with prosthetics.
35. Two tip types for pins: trochar (for cortical bone), diamond end.
36. Holding power affected by: size of pilot drill-hole, depth of screw, outside diameter of screw, and bone quality.
37. Screw pullout strength varies with time: depends on growth of bone into screw threads. If micro-movement occurs then contacting bone tissue is replaced with fibrous tissue, loosening the screw.
38. Two types of bone screws - Cortical Bone Screw: small threads, can be further classified - Self-tapping: slightly greater holding power; Non-self-tapping.

Cancellous Screw: large threads to increase thread to bone contact, can also have different thread types
V threads: has a v shaped thread; Buttress threads: have a slope on one side and a flat edge on the other.

What are the different types of bone screws and what kind of thread forms are there Hexagonal drive, star torx drive (TD) cruciform drive (SD) single slot drive. Thread forms HC/HA are for cortical bone

HB is for cancellous bone

COR=cortical screw CAN= cancellous screw LOC=locking ST=self tapping Outer code explained

Rigid plates shield underlying bone from stress needed for healthy growth, high contact flat plates inhibit vascularization of the outer bone. Clinically more flexible plate are now used to allow micromovement and lower contact. Reasoning for this shift is to increase healing rate and decrease loss of bone mass. True
316LVM is Low Vacuum Melted to achieve high levels of purity, reduced inclusions, and reduced delta ferrite particles. We Satin Finish our plates giving the following advantages: lack of annoying light reflection during surgery; Creates a uniform surface layer of compressive stress, which acts to combat stress cracks and corrosion, therefore, increasing the life of implant; Greater ultrasound reflection; Cleaner part, free from residues with a low CFU (microorganism) count, resulting in easier autoclave sterilization. True
IMs are internal struts to stabilize long bone fractures. More resistant to multi-directional bending compared to plates, however they are less resistant to torsional loads. There is a variety of IM shapes to increase area of contact with the internal cortex of the bone. Screws proximal and distal to fracture help stability. True Shear stress used to help prevent torsion by using two methods Three point, high pressure contact with curved pins Positive interlocking between nail and intramedullary canal
Cartilage is hard to repair, so damaged joints lead to long term problems with no natural solution. Rubbing causes pain, joint replacement removes need for cartilage and stops pain. Joint replacements are permanent implants, an extensive amount of bone and cartilage is removed during the procedure. If the prosthesis fails, re-implanting is impossible Design of implant is based on kinematics and load transfer characteristics of joint.
What is intraoperative fracture? Give an example. Incidence of Intraoperative periprosthetic fracture varies between .0-4% depending on the patient risk factor and implants used Intraoperative fractures during total knee replacement leads to increased operative time, higher complications rates and poor functional outcomes Studies have shown that the fracture risk is higher in female patients, rheumatoid patients, and patients with severe knee deformity. Medial femoral condyle intraoperative fractures Are most common The method that this is fixed is up to the surgeons discretion but the three methods are 1. Standard implants with screws alone 2. Standard implants with locking plates and screws 3. Stemmed implants with screws were used
What part of your body contains these kinds of joint Pivot joint, hinge joint, saddle joint, plane joint, condyloid joint, ball-and-socket joint – examples in human synovial joints. Pivot joint: between C1 and C2 vertebrae in the neck Hinge joint: Elbow, the ankle joint is a hinge type synovial joint , the knee joint is a hinge type synovial joint, which mainly allows for flexion and extension. Saddle joint: between trapezium carpal bone and 1st metacarpal bone in the wrist Ball and Socket: the hip joint is a ball and socket, shoulder joint is a ball and socket between the scapula and the humorous. However the socket of the glenoid cavity of the scapula is itself quite shallow and is made deeper by the addition of the glenoid labrum Condyloid joint: between the radius and carpal bones of wrist Plane joint: between tarsal bones on the foot
What are the four failure modes of internal fixation devices, and where do they occur? (Table 44.2) Overload Location of failure: bone fracture site, implant screw hole, screw thread Reasons for failure: small size implant, unstable reduction, early weight bearing Fatigue Bone fracture site, implant screw hole, screw thread Early weight bearing Small size implant Unstable reduction Fracture non union Corrosion Screw head-plate hole, bent area Different alloy implants Over-tightening screw Misalignment of screw Over-bent Loosening Screw Motion Wrong choice of screw type Osteoporotic bone
An external fixation device may be used to keep fractured bones stabilized and in alignment. The device can be adjusted externally to ensure the bones remain in an optimal position during the healing process. External fixation is usually used when internal fixation is contraindicated- often to treat open fractures, or as a temporary solution.