Bone cement

components, mechanisim of delivery, uses and complications of bone cement in orthopaedics

1. Bone cement Dr. Naveen bagilumane

2. Bone cement

3. Bone Cement In reality, “Bone Cement” is a misnomer .Word cement is used to describe a substance that bonds two things together, But bone cement acts as a space-filler that creates a tight space which holds the implant against the bone . Originally developed for Dental applications. Using in orthopaedics for more than 40 years. Gold standard in the field of joint replacement surgery. Neither Osteoinductive , nor Osteoconductive and does no remodeling of bone.

4. History trace back to….. Themistokles Gluck , a German surgeon, 1870 Fixed a total knee prosthesis made of ivory using cement made of plaster and colophony “ ...for a better fixation, I mixed plaster with colophony, which cures up to the hardness of glass. ”

5. History trace back to….. 1958 – Sir John Charnley used self curing PMMA to anchor femoral head prosthesis to femur First cement - Nulife

6. What is bone cement? Self curing organic or inorganic formulations which may or may not contain antibiotics used to fill up a cavity or to create a mechanical fixation of prosthesis to living bone. Chemical name - PMMA

7. Interest in orthopaedics Joint Replacement Surgery Spinal Compression Fractures Chronic Osteomyelitis Tumours

8. Composition POWDER (2) LIQUID (1) Polymer : PMMA Monomer: Methyl methacrylate (MMA) Initiator : BPO ( Benzoyl peroxide) Accelerator: N, N-Dimethyl para-toluidine (DMPT) Radio-opacifier: Barium sulphate (BaSO4)/Zirconia (ZrO2) Stabilizer: Hydroquinone

9. Why separate components? Polymerisation of MMA is too slow ( hrs to days) Pure MMA is of low viscosity can easily diffuse in blood Much easier to shape Heat polymerisation can boil monomer Pure MMA volumetric shrinkage

10. Processing and handling Four phases : Mixing Waiting Working Setting

11. 1.Mixing Viscosity starts to increase Chemical reaction : 1. Wetting - Surface area of Polymer beads dissolved by MMA 2. Polymerization Phase ends – formation of Homogenous mass (tooth paste like consistency) which is transferred to cement gun

12. What is polymerisation? Free radical polymerisation. Carbon-to-carbon double bonds broken and new carbon single bonds form Exothermic reaction. Temperature reach up to 70-120 C. May cause thermal bone damage. Viscosity increases.

13. How to mix? Hand mixing : Open bowl using spatula 1 to 2 Hz, period of 2min Disadvantages : - Introduction of Voids - Porosity 7% and higher - Excessive mixing increases porosity

14. Centrifugation Liquid & powder hand mixed then centrifuged 2300 – 4000 rpm for 0.5 – 3 min Adv : Dramatic decrease in porosity by 1% Disadv : Sedimentation of radiopacifiers It works only in low viscosity and its achieved by chilling MMA monomer

15. Vacuum mix Contents placed in bowl – mixed after vacuum conditions Adv : Low Porosity Low exposure of vapours Distribution of Radiopacifiers

16. 2. Waiting phase Viscosity increases Chemical reaction : Chain propagation starts Polymerisation continues Ends by sticky dough

17. 3.Working phase Cement is no longer sticky but of sufficiently low viscosity to enable surgeon to easily apply cement Chemical reaction : Exothermic reaction Polymerisation continues Viscosity increases

18. 4. Setting Chain Growth Finished No Movability Cement Hardened High Temperature. Volumetric & Thermal shrinkage

19. Functions of Bone cement Allows secure fixation of implant and bone Mechanical interlock and space filling Load transferring Maintenance/restoration of bone stock Release of antibiotics

20. How to deliver cement? 1 st Generation Hand / Finger packing Femoral component used – stainless steel & co – cr alloy Failed due to geometry of implants narrow medial margins sharp corners

21. 2 nd Generation Cement gun Placement of bone cement - retrograde fashion Plastic plug – cement pressurisation Pulsatile lavage – cleanse femoral canal of loose cancellous bone, blood, fat, marrow contents & dried prior to cementing it increases the shear strength at bone cement interface improved survival rate of implant

22. 3 rd Generation Pressurisation of cement during insertion Porosity reduction Surface modification of implant itself

23. 4 th Generation Use of proximal & distal centralizer in an attempt to make uniform cement mantle

24. Antibiotics Loaded Bone cement Ideal antibiotic properties : Preparation must be thermally stable Antibiotic properties not affected by heat Must be water soluble for diffusion into tissues Bactericidal Gradual elution over an appropriate time period Minimal local inflammatory response

25. Contd.. Have action against common pathogens like S.aureus , S. epidermidis ,coliforms and anaerobes. Must not significantly compromise mechanical integrity Must be available as a powder. Must have a low incidence of allergy.

26. Which antibiotics to use? Gentamycin (most common) and tobramycin are commonly used Vancomycin (ultrafine powder) is used as lyophilised vancomycin. It greatly reduces fatigue strength. Ciprofloxacin may inhibit soft tissue healing Penicillins and cephalosporins exhibits stability and good elution properties. But are avoided due to their potential allerginicity .

27. ALBC : ANTIBIOTIC LOADED BONE CEMENT

28. How to asses radiologically? Barrack’s Cement mantle grading Gruen zones

29. Barrack’s femoral component cementation Quality grading Grade Radiographic charcterstics A Complete filling of medullary canal, without radiolucent line between cement & bone ( White-Out) B Radiolucent line covering upto 50% of cement-bone interface C Radiolucent line covering between 50 -99% of cement – bone interface or incomplete cement mantle D Complete Radiolucent line (100%) at cement-bone interface and/or absence of cement distally to end of stem

30. Gruen zones 7 zones in AP / lateral Radiographs What is measured? Radiolucent lines at bone cement and prosthesis cement interface Progression of no. of Zones - Loosening

31. Mechanism of loosening

32. Bone cement in Tumours

33. Contraindications Pregnancy Active infection Hypersensitivity (d/t histamine release n Complement activation C3a/C5a) Metabolic disorder

34. Bone Cement Implantation Syndrome – (BCIS) HYPOXIA, HYPOTENSION or both and/or unexpected LOSS OF CONSCIOUSNESS occurring around the time of cementation, prosthesis insertion, reduction of the joint or, occasionally, tourniquet deflation in a patient undergoing cemented bone surgery.

35. Clinical picture varies.. Hypoxia Hypotension Cardiac arrhythmias increased Pulmonary Vascular Resistance (PVR) Cardiac arrest

36. Classification Grade 1 : moderate hypoxia (SpO2-94%) or hypotension [fall in systolic blood pressure (SBP) 20%]. Grade 2 : severe hypoxia (SpO2-88%) or hypotension (fall in SBP 40%) or unexpected loss of consciousness. Grade 3 : cardiovascular collapse requiring CPR.

37. Etiology of BCIS Absorption of monomer into circulation Embolization Histamine release & Hypersensitivity Complement activation Multimodal