Ultra High weight Molecular Weight Polyethylene


    TKR COMPONENTS WOTH UHMWPE Tibial           Insert

UHMW Polyethylene - Long hydrocarbon chain held together by covalent bonds. 

Exists in two forms - 

        1. Disorganized amorphous phase

        2. More organized crystalline phase

How is this material manufactured ?

   Zeigler Process 

    1.Ethylene gas polymerized at a low temperature, low pressure environment catalyst Titanium Chloride        produces a fine UHMWPE powder.

    2. Then the powder processed in one of the following methods-

            - Ram extrusion produces bar stock, lowest quality

            - sheet compression moulding -higher quality 

            - Direct compression moulding - expensive shape of final component 

            - machining - - UHMWPE bar, sheets or moulded components shaped into final form

            - Sterilization and packaging - gamma irradiation ,gas plasma or ethylene oxide. 

    How can its material properties be manipulated ? 

            By making cross-linked Polyethylene

   Bombarding material with an electric beam or gamma irradiation which causes chain session of double covalent bonds, followed by rebonding either by oxidation or by cross linking.

    Annealing to prevent oxidation and reduction of shelf half life.

    Adding antioxidants e.g. Vitamin E 

    Advantages - 80-100 % reduction in vivo wear

Disadvantages - brittle , increased risk of fractures 


Comments

Post a Comment

Popular posts from this blog

Outline of Treatment of Spinal Tuberculosis

Image
 Tuberculosis     In general , Rest and Nutrition                                 Chemotherapy                                Surgery if needed .                                    Dorsal Spine - Approach to surgery     A bit ambiguous      Many prefer to do Anterior Transpleural. Some choose Anterolateral/posterolateral extrapleural                and posterolateral approaches      Posterolateral Approach(Martin 1970)      Dura exposed by Hemilaminectomy first and then operation extended laterally to remove posterior         ends of 2 to 4 ribs, corresponding transverse process and pedicles.      He thinks  Anterolateral approach a very risky one.     Approach to Atlanto-occipital and Atlanto-axial joint         Numerous structures on the way anteriorly     Supine position, Neck on 5-10 degrees hyperextension ,Trachesostomy done     Transoral Anterior Approach           Uvula, Soft palate bissected , Hypopharynx packed, 5 cm long incision given, Flaps                                 
Read more

COXA VARA

Image
Coxa Vara Painless limp, LLD gradually worsening ,  Unilateral or bilateral in 30-50 % cases Prominent trochanters Pelvic Tilt- LLD  Trendelenburg test or delaye trendelenburg test + ve B/L waddling  High Greater trochnater - supratrochanteric shortening,  Decreased abduction, (decrease in articular trochanteric distance ) and internal rotation (due to decreased anteversion) may have out toeing r/o cervical instability causing limping  Types of Coxa Vara  https://quizlet.com/au/304405013/coxa-vara-flash-cards/ Mangement      Depends on Hilgenreiner Angle (HEA ) https://www.orthobullets.com/pediatrics/4041/developmental-coxa-vara  > 60 degrees - wait and watch    45-60 degrees - wait and watch  Goals of surgery      Neck shaft angle  (more or equal ) to 140.              degrees     Correct version      Ossification and healing of inferomedial.               fragment      Restore ATD (Articulo-trochanteric            distance    AND abductor mechanism                 (length -tension
Read more

Paediatric Supracondylar Humerus Fracture

Image
Supracondylar Fracture  Patient Presentation         Age 6-10 years         MOI - Fall on outstretched hand with elbow on extension, breaks.   Olecranon serves as the fulcrum      and the stress concentrates in distal humerus. Anteriorly the perisoteum hinges.     Pain , swelling, deformity, bruising      Deformity (usually S shaped ) , skin puckering      Compartment syndrome         Blood vessels spasm/ contusion/ tear/ thrombosis     If capillary refill present , hand arm Dunlop traction done.      No role of Angiography , further delays the treatment.      Nerve Injuries, proximal fragment spike hits nerve.             3a Posteromedial displacement - Radial Nerve involvement             3b Posterolateral displacement - Median Nerve involvement     Gartland and Wilkins Classification      Extension type fracture      1. Undisplaced Fracture      2. Displaced Fracture , posterior cortex is.                intact     3. Displaced fracture, posterior cortex breaks      Flexion type occ
Read more

Hind Foot amputation

Image
Boyd Amputation -Tibiocalcaneal arthodesis, heel pad preserved. ( https://www.semanticscholar.org/ ) ( Modifizierte Pirogoff-Amputation | SpringerLink ) Pirgoff Amputation  Amputation at ankle. part of calcanuem left in the stump , Calcaneum cut vertically.  Advantages  long lever arm , self suspension , good proprioception , end wt bearing.  Disadvantages  poor cosmesis , too long to use standard foot , no possibility of prosthetic foot fitting 
Read more

Timing and Outcome of Surgery in Hip Fractures

Hip Joint Ball and Socket joint. Hip fracture is any fracture involving Interochanteric region head, neck or acetabulum. 310,000 Hip fractures in the United State in 2003     1/3 rd - receive a hip replacement.     10.3 - 15.2 billion dollars / year Elderly – Vast Majority  Co-morbidities Femoral Neck Fracture Fracture Healing is delayed due to          - I ntracapusular neck- No Cambium layer          - Synovial fluid clears out haematoma and inhibits fracture union          - Haematoma causes pressure on head Mechanism of injury  • Directly on lateral hip • Twisting mechanism • Fatigue or insufficiency fracture, then fall • In younger - RTA /  fall from a height Risk Factors of Hip Fractures   • Osteoporosis and Falls   Lifetime risk -17.5 percent for women : 6 percent for men  • Average -   women 77 years old  :  men 72 years old • Low socioeconomic status • Cardiovascular diseas
Read more