1. بنام خداوند جان وخرد

2. Reasons for Hip Replacement Osteoarthritis (OA) Trauma and post-traumatic arthritis Congenital deformities Bone tumors Avascular necrosis S. Acker 2

3. Before Modern Total Hip Arthroplasty To treat hip fracture: –Resect (remove) the remainder of the fractured femoral neck. –Displace the greater trochanter distally. –Place the femoral shaft into the acetabulum. Variations: –Place the femoral head on the end of the femoral shaft before inserting into the acetabulum. –Interpose a portion of the abductor muscle to form an articulating surface –“Results were variable.” (Steinberg and Steinberg, 2000) S. Acker 3

4. Before Modern Total Hip Arthroplasty Cup Arthroplasty –Interposition of a cup between the the acetabulum and femur –First cup made of glass: brittleness led to frequent fracture –Vitallium Double-cup arthroplasty –One cup cemented over the femoral head –One cup cemented into the acetabulum. S. Acker 4

5. Sir John Charnley The “Father of Modern Total Hip Replacement” Contributions: –“Low-friction arthroplasty,” where a metal head articulates against a plastic socket –Introduced PMMA bone cement for fixation –Introduced high-density polyethylene as a bearing surface –Many advances in biomaterials, surface replacement, biomechanics, operating techniques and operating instruments Knighted in 1977 by Queen Elizabeth S. Acker 5

6. The Hip Joint S. Acker 6 Acetabulum Femoral head Femoral neck Femoral shaft Greater trochanter Acetabulum

7. Osteoarthritis Radiographic evidence: Narrowing of the joint space The joint space on an x-ray is cartilage –Appears as a space because it is less dense than bone –Progressive narrowing of the joint space means loss of cartilage on the articulating surfaces. S. Acker 7 Singer, 2008

12. Loading of the femoral component S. Acker 12 W Shear Approximate region of maximum bending Bending Torsion Compression

13. The HGP stem (courtesy of Zimmer)

14. Bone cement Bone cement “is a grout not a glue: fixation is achieved by mechanical interlock rather than adhesion.” (Learmonth et al., 2007) Two interfaces: –Bone-cement (the foundation for durable fixation) –Cement-implant Improvements in bone cement application –Pressurization forces cement into the bone –Cleaning of the bone surface –Retrograde insertion Mixed and cured in the operating room S. Acker 14

15. Pros & Cons of Bone Cement Exothermic reaction can cause tissue damage Cement mantle can fracture and result in corrosion Allows for a milder transition in material properties since the modulus of elasticity is between that of the implant and bone Allows for early mobility after surgery –Decreases bone resorption associated with reduced loading (Wolff’s Law.) S. Acker 15

16. Uncemented THA Development driven by early failure of cemented stems –Believed to be a result of “cement disease” (osteolysis) Fixation is via bony ingrowth (biologic fixation) –Hydroxyapetite (HA) and tricalcium phosphate (TCP) coatings can encourage ingrowth Uncemented stems have been more succesful than uncemented acetabular cups. Preferred over cemented THA, despite similar success rates (Learmonth et al., 2007) S. Acker 16

17. Biologic Fixation Requires sufficient pore size in the coating Must restrict micromotion between the implant and the bone during progression of bone ingrowth Must have an initial good fit (not too much space between the implant and the bone that should grow into it.) Revisions are difficult. A lot of bone may be removed with the implant. S. Acker 17

18. Modularity: Separate stem and head Advantages of Modularity More room in the surgical field Surgeon performs final assembly –Uses trial components to test sizes Can have a cobalt- chrome head (good wear resistance) and titanium alloy stem (better elastic modulus) Disadvantages of Modularity Potential for disassembly Can have motion between components –Fretting, corrosion Metal combination –Potential for galvanic corrosion S. Acker 18

19. Material combinations: Metal on PE Osteolysis initially attributed to cement particles Actually due to a local reaction to polyethylene particles. Annual wear of conventional polyethylene: 0.2mm/year Cross-linked polyethylene has much better wear resistance: <0.001mm/million cycles S. Acker 19

20. Material combinations: Metal on Metal Initial introduction: 1960s –Many early failures Annual wear: 0.004 mm/million cycles Can use a large femoral head diameter –Reduces the risk of impingement and provides more stability Concern: Release of metal ions –Can be detected systematically –No long-term adverse affects have been reported S. Acker 20

21. Ceramics Low co-efficient of friction Scratch-resistant No ion release Low wear: <0.001mm/million cycles Potential for brittle fracture S. Acker 21

22. TOTAL HIP ARTHROPLASTY S. Acker 22

26. Qaem,s General Hospital

27. Abduction Pillow