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
1. What are the 5 material considerations for biomedical implants/devices?
Safety
Durability
Mechanical compatibility
Biodegradability
Biofunction
2. 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
3. List three uses of PMMA as biomedical implants/devices.
Intraocular lenses
PMMA bone cement is orthopedic surgery
Dentures
4. 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
5. 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spring loaded into a much smaller catheter, once the stent is delivered to the diseased vessel, the catheter sheath is withdrawn, and the stent expands elastically outward into the artery.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
6. 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.
7. 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.
8. 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
9. 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
- 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 - The peak of this process occurs Approximately 4 to 14 days following stent implantation
- 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
- 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 - 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 - \
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 - Skin, tendon, bone, dentin, heart valve, muscle, blood vessel, scar
Key features: Major fiber bundles to give strength - Cartilage
Main collagen of cartilage - Skin, muscle, blood vessels, bladder
More abundant in fetal tissue - All Basal laminas
Forms two dimensional network
Elastin
Proteoglycans
Proteoglycan complex/glycosaminoglycans
Adhesive proteins
Fibronectin - 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 - 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) - \
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 - 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 - 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 - 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 - 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 - 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 - 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 - 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 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 - 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 - 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.
- 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 - 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 - A PMA must provide valid scientific evidence that there is a “reasonable assurance” that a device is both safe and effective. True
- 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
- 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
- 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
- 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. - 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
- 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 - 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
- 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. - Two tip types for pins:
trochar (for cortical bone),
diamond end. - Holding power affected by:
size of pilot drill-hole,
depth of screw,
outside diameter of screw,
and bone quality. - 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. - 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.