ortho appns

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Polymers are widely used in orthopedic application

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Page 1: Ortho appns
Page 2: Ortho appns

An orthopedic  implant is a medical device manufactured to replace a missing joint or bone or to support a damaged bone.

 Internal fixation is an operation in orthopedics that involves the surgical implementation of implants for the purpose of repairing a bone.

 Among the most common types of medical implants are the pins, rods, screws and plates used to anchor fractured bones while they heal.

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The material used in orthopedic implants must be biocompatible to avoid rejection by the body.Other risks associated with orthopedic implants include implants coming loose or breaking in the bone causing painful inflammation and infection to surrounding tissue.

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BONE PROPERTIES

Density – 2.3g/cm3Tensile Strength – 3-20MPaCompressive Strength – 15,000 psiShear Strength – 4,000 psiYoung’s Modulus – 10-40 MPa

Bone is anisotropic - its modulus is dependent upon the direction of loading.

Bone is weakest in shear, then tension, then compression.

Bone is viscoelastic: its force-deformation characteristics are dependent upon the rate of loading.

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ORTHOPEDIC TERMS

Osteoinductive – Characteristic in materials that promote new bone growth.

Osteoconductive – The property of a material that allows for the possible integration of new bone with the host bone.

Bioresorbable – The ability of a material to be entirely adsorbed by the body.

Trochanter The second segment of the leg, after the coxa and before the femur

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MATERIAL USEDComposite Metal :rough& polished

PolymerCeramics

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An orthopedic hip implant, exhibiting the use of all three classes of biomaterials: metals, ceramics and polymers.

In this case, the stem, which is implanted in the femur, is made with a metallic biomaterial.

The implant may be coated with a ceramic to improve attachment to the bone, or a polymeric cement.

At the top of the hip stem is a ball (metal or ceramic) that works in conjunction with the corresponding socket to facilitate motion in the joint.

The corresponding inner socket is made of either a polymer (for a metallic ball) or ceramic (for a ceramic ball) and attached to the pelvis by a metallic socket.

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Various fixation methods

(a) direct interference or (passive) noninterference fit;(b) mechanical fixation using screws, bolts, nuts, wires, etc.;(c) bone cement;(d) porous in growth (biological)

fixation;(e) direct chemical bonding using adhesives or after coating with direct bonding material

layer;(f) bone cement with resorbable

particles;(g) porous in growth controlled by

using electrical or electromagnetic

stimulation

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BONE CEMENT

Poly methylmethacrylate (PMMA) bone cement:

made from methylmethacrylate, poly methylmethacrylate, esters of meth acrylic acid, or copolymers containing poly methylmethacrylate and polystyrene

Used to fill gaps between bone and implant

•PMMA homopolymer•MMA/styrene copolymer•MMA/methyl acrylate copolymer

Stable interface between metal and bone

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Composition of a methacrylic cement

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PROPERTIES OF BONE CEMENTBone cement is supplied as two separate components, a polymer powder and a monomer, which is a colourless and inflammable liquid.

The powder consists of a spherical polymer, an initiator(dibenzoyl peroxide), a radio pacifier (zirconium oxide or Barium sulphate) and often an antibiotic.

As the powdered polymer and liquid monomer are mixed, a viscous dough is formed. Free radicals initiate the polymerization

This process is exothermic, with a maximum in vivo temperature of 40° to 47°C and this thermal energy is dissipated into the circulating blood, the prosthesis and the surrounding tissue 18 as the cement cures

The chemical composition, the powder to liquid ratio and the cement temperature in turn determine the viscosity. There are high viscosity and low viscosity cement types.

High viscosity bone cements have a short wetting phase and a longer working phase.Low viscosity cements have a longer wetting phase and a shorter working phase.

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Inherently weakStronger in compression than tensionWeakest in shear

Exothermic reactionMay lead to bone necrosis

By handling improperly or less than optimally

Weaker

Extra care should be taken toKeep debris out of the cement mantle (e.g., blood, fat)Make uniform cement mantle of several mmMinimize voids in the cement : mixing technique Pressurize

LIMITATIONS

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Knee and its injuries

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JOINT REPLACEMENTS The hip and shoulder joints have a ball and socket

articulation, while other joints such as the knee and elbow have a hinge-type articulation

They all possess to opposing smooth cartilaginous articular surfaces that are lubricated by viscous synovial fluid.

This fluid is made up of polysaccharides that adhere to the cartilage and upon loading can be permeated out onto to the surface to reduce friction.

The cartilage is not vascularized , and nutrition of the tissues appears to be a diffusional process.

The articulation of the joints is stabilized by the body s coordination of the ligaments, tendons, and muscles.

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Most femoral head replacements are made with installation of an acetabular cup. This is called total hip joint replacement (arthroplasty).

The diseased femoral part head is cut off, and the medullary canal of the femur is drilled and reamed to prepare it for the stem of the prosthesis.

The cartilage of the acetabulam is also reamed. The PMMA bone cement is prepared from polymer powder and monomer liquid.

It is packed into the medullary canal of the femur and the femoral stem is inserted. The acetabular component is similarly cemented.

The alignment and articulation of the artificial ball- and-socket joint are then verified.

UHMWPE and cross linked UHMWPE for the cup and stainless steel and Ti- based alloys used for femoral head and stem.

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Knee joint replacements

The development and acceptance of knee joint prosthesis have been slower than that of the hip joint due to the knees more complicated geometry and biomechanics of movement, and lesser stability in comparison with the hip.

It can be classified into hinged and non hinged type and it is further divided into uni – and biocompartmental.

Anatomy of the knee

Made up of 3 bones

•Femur (thigh bone)•Tibia (lower leg bone) •Patella (kneecap)

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Causes of knee pain

•Osteoarthritis (wear and tear)•Rheumatoid arthritis•Post-traumatic arthritis caused by:

•Fractures•Ligament injuries•Meniscus tears

Goals of total joint replacement are to help:

Relieve painRestore motionImprove functionImprove fitness and healthRestore quality of life

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Total Knee Replacement

•Partial knee replacement(unicompartmental)– Replacement of one or two parts of knee instead of total.– Retain more of patient natural knee.• Total knee replacement– Resurfaces the bones (tibia and femur) with an implant made of metal and plastic parts.– Medical-grade plastic spacer providing a smooth surface as cartilage

Femoral- replaces arthritic portion of thigh boneTibial- replaces arthritic portion of shin boneTibial insert- replaces cartilage and acts as shock absorberPatella- replaces knee cap

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Two major types of total knee replacement systems:Fixed Bearing- does not allow full range of motion Rotating Platform Bearing- closely simulates the action of the normal knee jointBenefits of fixed bearing knee joint replacements

Provides pain relief.Restores the motion of your knee.Improves quality of life.Good results in appropriate patientsRotating platform bearing

Provides pain relief.Restores the motion of your knee.Rotation similar to a normal knee.Reduces potential of early wear and loosening.Improves quality of life.

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Knee replacement procedure

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Hip jointsThe hip is one of the body's largest joints. It is a ball-and-socket joint.

The socket is formed by the acetabulum, which is part of the large pelvis bone.

The ball is the femoral head, which is the upper end of the femur (thighbone).

The bone surfaces of the ball and socket are covered with articular cartilage, a smooth tissue that cushions the ends of the bones and enables them to move easily.

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A joint is formed by the ends of 2 or more bones.The hip must bear the full force of your weight and consists of two main parts: A ball (femoral

head) at the top of your thigh bone (femur)

A rounded socket (acetabulum) in your pelvis

Hip joints

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Causes of hip joints

One of the most common causes of joint pain is arthritis. The most common types of arthritis are:

Osteoarthritis (OA) Rheumatoid Arthritis (RA)Post-traumatic Arthritis Avascular Necrosis

Osteoarthritis. This is an age-related "wear and tear" type of arthritis. It usually occurs in people more than50 year old . The cartilage cushioning the bones of the hip wears away. The bones then rub against each other, causing hip pain and stiffness. Osteoarthritis may also be caused or accelerated by subtle irregularities in how the hip developed in childhood.

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Rheumatoid arthritis.  This is an autoimmune disease in which the synovial membrane becomes inflamed and thickened. This chronic inflammation can damage the cartilage, leading to pain and stiffness. Rheumatoid arthritis is the most common type of a group of disorders termed "inflammatory arthritis

Avascular necrosis. An injury to the hip, such as a dislocation or fracture, may limit the blood supply to the femoral head. This is called avascular necrosis. The lack of blood may cause the surface of the bone to collapse, and arthritis will result. Some diseases can also cause avascular necrosis.

Post-traumatic arthritis. This can follow a serious hip injury or fracture. The cartilage may become damaged and lead to hip pain and stiffness over time.

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Total hip replacements

Procedure

The surgical procedure takes a few hours. Your orthopaedic surgeon will remove the damaged cartilage and bone and then position new metal, plastic, or ceramic implants to restore the alignment and function of your hip.

Hip replacement is a surgical procedure in which the hip joint is replaced by a prosthetic implant. Using metal alloys, high-grade plastics, and polymeric materials, orthopaedic surgeons can replace a painful, dysfunctional joint with a highly functional, long-lasting prosthesis.

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Acetabular shell

Acetabular shell

Plastic insert

Ceramic insert

Metal femoral stem

Ceramic femoral stem

Femoral stem

Hip implants

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Reduced hip pain.

Increased mobility and movement.

Correction of deformity.

Equalization of leg length (not guaranteed).

Increased leg strength.

Improved quality of life, ability to return to normal activities.

Enables you to sleep without pain.

Benefits of hip implants

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SPINEEach vertebra has two sets of facet joints. These spinal joints are called facet, apophyseal, or zygapophyseal joints .this joint are gliding joints and link vertebrae together. Facet joints are synovial joints surrounded by a capsule of collagenous tissue .the surface of synovial joints are coated with cartilage allowing joints for smooth motion. These joints allow flexion (bend forward) , extension (bend backward) and rotating or twisting motion. The spinal discs are located between pairs of vertebrae and it act as a shock absorbers and allow deformation of the spine.

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Normal function of the spine

Protect spinal cord and nerves Support the body weight and

external load Stability

Allow motion of the body for various activities Flexibility

Cervical (7)

Thoracic (12)

Lumbar (5)

Sacral (5)-fused

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SPINAL INJURIES The nucleus pulposus is made of a gel like material mostly composed of collagen fibers, proteins and water makes up 90 % of the disc weight at birth but decreases to 70 % by age 50. excess disc bulging or complete herniation may takes place by injury or aging, allowing the disc materials to escape the disc. This will may compress the nerves or spinal cord, causing pain and the blood supply to the disc decreases ; some disc may degenerate. The disc begins to lose water and shrinks . The range of motion and shock-absorbing ability of the spine are decreased .this may result in damage to the nerve and vertebrae.

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FLEXION INJURIES•Stable Injury•Affects Cervical, dorsal and Lumbar spine•Wedge -Superior Anterior of vertebra•Spinal cord injury unlikely

HYPEREXTENSION

•Stable injury•Affects mainly cervical spine•Anterior Longitudinal Ligament damage ? Whiplash injury• possibly rupture of intervertebral disc may cause cord compression

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Compression injury•Stable injury•Affects cervical or lumbar spine•Retro pulsed bony fragment may compress the cord

Shearing injury

Shearing = TearingUsually with rotationUnstableAffects any segment of the spineLeads to Dislocation or DislocationSpinal cord injury is common

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Spinal implant materials 316L Stainless steel:

Biocompatible Strong and stiff Poor imaging compatibility: artifact to CT and MRI

Titanium Alloy (Ti6Al4V ELI): Biocompatible No artifacts during CT and MRI Excellent fatigue strength, high strength, high

elasticity High resistance to fretting corrosion and wear

(surface treatments)

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Spinal instrumentation Goals of Spinal Instrumentation:

Correction of deformities or misaligned segments; Enhancement of solid fusion; Maintain anatomic alignment until a solid fusion takes place; and Allow early mobilization of patients

by providing an immediate stability

Cervical spine instrumentation

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Thoracolumbar spine instrumentation

Z-plate (Danek) Kaneda (AcroMed)

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Spinal fixation device

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Factors in spinal instrumentation

Materials: Bio-compatibility and Imaging compatibility Stiffness (or elasticity) and strength Corrosion

Implant Strength: Component (screw, rod, plate, wire, etc.) strength Metal-metal interface strength Construct strength Bone-metal interface strength: Bone–wire, -hook, and -screws

Construct Stability: Segmental stiffness or flexibility

Profile: Ease of Use:

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ANKLE JOINT REPLACEMENTS

The ankle joint is made up of three bones: the lower end of the tibia(shinbone), the fibula (the small bone of the lower leg), and the talus, the bone that fits into the socket formed by the tibia and fibula. The talus sits on top of the calcaneus (the heelbone). The talus moves mainly in one direction. It works like a hinge to allow your foot to move up and down

The large Achilles tendon at the back of the ankle is the most powerful tendon in the foot. It connects the calf muscles to the heelbone and gives the foot the power for walking, running, and jumping.

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Certain movements may cause a grinding or catching sensation as the arthritic bone surfaces move against one another. The ankle joint may swell. This swelling cause problems in the ankles

The benefit of an artificial joint is to ease the symptoms of ankle osteoarthritis

The Artificial AnkleEach artificial ankle prosthesis is made of two parts:The tibial component is the part of the artificial joint that replaces the socket portion of the ankle (the top section).The talus component replaces the top of the

talus.

Surgical procedure

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Ankle Joint ReplacementThe tibial component is usually made up of two parts: a flat metal piece called a metal tray that is attached directly to the tibia bone, and a plastic cup that fits onto the metal piece, forming a socket for the artificial ankle joint. The talus component is made of metal and fits into the socket of the tibial component.

The main advantage of an ankle transplant replacement is the potential for replacement of the entire ankle joint with viable living cartilage cells.

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Shoulder joint replacements The major shoulder joint motion originates from the ball-

and-socket articulation of the glenohumeral joint. The hemispherical , incongruent joint provides the largest

motion in the body

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shoulder is made up of three bones: your upper arm bone (humerus), your shoulder blade (scapula), and your collarbone (clavicle). The shoulder is a ball-and-socket joint: The ball, or head, of your upper arm bone fits into a shallow socket in your shoulder blade. This socket is called the glenoid.

the surfaces of the bones where they touch are covered with articular cartilage, a smooth substance that protects the bones and enables them to move easily. A thin, smooth tissue called synovial membrane covers all remaining surfaces inside the shoulder joint. In a healthy shoulder, this membrane makes a small amount of fluid that lubricates the cartilage and eliminates almost any friction in your shoulder.

The muscles and tendons that surround the shoulder provide stability and support.

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The surgeon begins by separating the deltoid and pectoral muscles, accessing the shoulder in a largely nerve-free area to minimize nerve damage. The shoulder is covered by the rotator cuff, which must be opened by cutting one of the anterior (front) rotator cuff muscles. This “opens the door,” allowing the surgeon to view and manipulate the arthritic parts of the shoulder ball and socket.

After the arthritic sections have been removed, the surgeon inserts the implant socket, ball, and stem components, closes and stitches the rotator cuff muscle, and stitches and cleans the incision, after which a bandage is applied as a temporary covering.

Surgical procedure

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FRACTURE PLATESA bone fracture  is a medical condition in which there is a break in the continuity of the bone. A bone fracture can be the result of high force impact or stress, or trivial injury as a result of certain medical conditions that weaken the bones, such as osteoporosis, bone cancer, or osteogenesis imperfecta, where the fracture is then properly termed a pathologic fracture.

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Bone plates are surgical tools, which are used to assist in the healing of broken and fractured bones

Currently osteotemy equipment is made primarily of titanium and stainless steel. The broken bones are first surgically reset into their proper position. Then a plate is screwed onto the broken bones to hold them in place, while the bone heals back together.

 

Bone plates can also be fabricated  using shape memory alloys, in particular nickel titanium

Traumatic fracture - This is a fracture due to sustained trauma. e.g.- Fractures caused by a fall, road traffic accident, fight etc.

Pathological fracture - A fracture through a bone which has been made weak by some underlying disease is called pathological fracture. e.g.- a fracture through a bone weakened by metastasis. Osteoporosis is the most common cause of pathological fracture.

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TYPES OF FRACTURES

Type I Fractures

These fractures break through the bone at the growth plate, separating the bone end from the bone shaft and completely disrupting the growth plate.

Type II Fractures

These fractures break through part of the bone at the growth plate and crack through the bone shaft as well.

Type III Fractures

These fractures cross through a portion of the growth plate and break off a piece of the bone end.

Type IV Fractures

These fractures break through the bone shaft, the growth plate, and the end of the bone.

Type V Fractures

These fractures occur due to a crushing injury to the growth plate from a compression force. They are rare fractures.

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Plates are some of the most common general purpose fixation devices. They contain holes for screws and pins that are used to fix the plate to intact bone and to fractures

For simple fractures of long bones, screws are often used to reduce the fractures and apply compression to the fracture site (lag screws). These screws, however, withstand external compressive and bending forces .

Plates that span the fracture site and reduced the fracture are called neutralization plates .since they resist or neutralize external forces at the fracture site protecting the lag screw fixation.

TYPE OF PLATES

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Reconstruction plates are flexible and can be cut to length to fit irregular surfaces. They are used primarily for fractures of the pelvis

Blade plates are used for fractures of the condylar regions of the long bones. They are simpler alternative devices that can be used in place of a plate with a separate condylar screw.

The LISS (Less Invasive Stabilization System) plate is a recently introduced type of plate that is a modification of the standard compression plate used for long bone fracture

A compression plate is most commonly used with diaphyseal fractures of the long bones. The geometry of its screw holes allows compression of a fracture spanned by the plate as the screw head contacts the plate during insertion

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SCREWS

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Screw compresses both sides of fix together•Best form of compression•Poor shear, bending, and rotational force ,resistance

Partially-threaded screw (lag by design) Fully-threaded screw (lag by technique)

LAG SCREW FIXATION

• Step One: Gliding hole = drill outer thread diameter of screw & perpendicular to fix

• Step Two: Pilot hole= Guide sleeve in gliding hole & drill far cortex = to the core diameter of the screw

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Step Three: counter sink near cortex so screw head will sit flush

Step Four: screw inserted and glides through the near cortex & engages the far cortex which compresses the fix when the screw head engages the near cortex

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Thank you