Aseptic loosening total hip arthroplasty

Aseptic loosening total hip arthroplasty.

1. ASEPTIC LOOSENING OF THA presenter: Dr.imran ali

2. A good prosthesis is important

3. Although success rates for total hip arthroplasty (THA) now approach 97%, osteolysis and aseptic loosening continue to plague surgeons. Reported prosthetic failure rates due to these complications are as high as 20%.1 1Sinha RK, Shanbhag AS, Maloney WJ, Hasselman CT, Rubash HE. Osteolysis : Cause and Effect, Instructional Course Lectures, Volume 47. Rosemont, Ill: American Academy of Orthopaedic Surgeons Press; 1998: 307-320.

4. When cemented femoral components were the predominant types of prostheses used, as many as 12% of patients demonstrated symptomatic loosening, and as many as 20% required revision surgery. [2] 2 Aseptic loosening in THA. In: American Academy of Orthopaedic Surgeons. Adult Reconstruction Orthopaedic Knowledge Update . Rosemont, Ill: American Academy of Orthopaedic Surgeons Press; 1996: 147-156 .

5. Osteolysis is the end result of a biologic process that begins when the number of wear particles generated in the joint space overwhelms the capsule's capacity to clear them. 

6. Osteolysis Steps in osteolysis : particulate debris formation Access of these particles to periprosthetic bone macrophage activated osteolysis   prosthesis micromotion particulate debris dissemination

7. osteoclast osteoblast interaction cytokines/ chemokines MACROPHAGES DEBRIS phagocytosis inhibit

8. Sources of particulate debris  Wear Mechanisms of wear A.   Adhesion: microscopically PE sticks to prosthesis and debris gets pulled off B.  Abrasion: C. Third body wear particles in joint space cause abrasion and wear D. M icro  Fatigue 2. Corrosion: electrochemical reaction

9. wear rates by material Non-cross linked UHMWPE wear rate is 0.1-0.2 mm/yr Ceramic bearings lowest wear rates of any bearing combination (0.5 to 2.5 µ per component per year)  Ceramic-on-polyethylene, ranging from 0 to 150 µ. Metal-on-metal produces smaller wear particles as well as lower wear rates   (ranging from 2.5 to 5.0 µ per year) 

10. Modes of wear 1.  Motion between 2 surfaces designed for motion 2.  Primary bearing surface against an non intended bearing surface i.e. femoral head against acetabular shell when liner has worn out 3.  Interposed third body particles i.e. bone or cement 4.  Two non bearing surfaces together i.e. back sided fretting, morse taper fretting, screws

11. Loosening of THA components With Cemented THAs, the acetabulum is the first component to fail from loosening. With cementless hips, the femoral component loosens more often as a result of osteolysis . Loosening occurs at implant-cement interface in femoral component, while at bone-cement interface in acetabulum .

12. Zones of loosening Femoral component Seven Gruen zones Acetabular component Three Delee and Charnley zones

13. Gruen 7 zones of femur Zone 1 Debonding Zone 4 Subsidence Zone 7 Fragmentation of cement

14. Barrack grading

15. Delee and Charnley acetabular zones

16. Harris grading Cemented Femoral loosening; Radiographic Definite loosening Stem failure – fracture/deformation Cement mantle fracture esp zone 4 Radiolucency >1mm Changes in stem position- usually varus position Pistoning effect Probable loosening Continous radioluscent line at bone-cement interface Endosteal cavitation -linear and focal osteolysis Possible loosening Radioluscent lines at bone-cement interface 50-100%

17. Harris grading 1.  Possible   Bone-cement lucency < 50% total may be due to poor cementing technique

18. Harris grading 2. Probable Cement-implant radiolucent line >2mm wide - progressive

19. 3.  Definite Cement fracture(zone 4)  Femoral stem fracture Radiolucency >2 mm Greun zone 1> debonding New lucency cement - implant interface Stem migration,/ varus Pistoning effect

20. Mechanism of stem failure A.   Subsidence/ Pistoning 1-2 mm normal in first year > 5 mm abnormal Quantified by measuring distance against a fixed landmark e.g tip of greater troch , tear drop

21. Subsidence

22. Mechanism of stem failure B.  Medial midstem pivot Medial migration of the proximal stem in association with lateral displacement of the distal stem tip

23. Mechanism of stem failure Calcar pivot Either medial or lateral movement of the distal tip of the embedded stem with reasonable support proximally 

24. Mechanism of stem failure   Distal pivot/bending cantilever - distal fix strong, but proximally loose - breakdown of proximal cement

25. Are all radioluscent line due to loosening? Radiolucent lines btn femoral cortex and cement Cancellous bone not completely removed during sx Normal age related expansion of femoral canal assoc cortical thinning.1 Medullary canal expands at 0.33mm/yr Cortical thickness decrease by 0.15mm/yr No surrounding sclerotic line 1. Poss et al study

26. Technical problems that contribute to stem loosening Failure to remove adequate cancellous bone medially Inadequate quantity of cement Thin column cracks easily Tip of stem should be supported by a plug of cement Presence of voids in cement Poor mixing, injecting, pressurizing technique, Blood, bone fragments ion cement( laminations) Failure to prevent stem motion while cement is hardening Failure to position component in neutral or mildly valgus position

27. Cementless femoral components

28. Engh classification Types based on presence of radiolucent lines (RLL)  I.  Stable bony ingrowth   Take one year to see A.   Spot welds at end of porous coating B.  Absence of RLL next to porous coating - may have RLL next to non porous coated areas C.   Calcar atrophy secondary to stress shielding

29. Stable bony ingrowth Spot welds Stress shielding

30. Stable fibrous ingrowth A.  No spot welds B.   Parallel sclerotic lines / RLL about porous coating C.  No migration  

31. Unstable fibrous ingrowth A.  Component migration B.  Progressive increase RLL - divergent RLL C.   Pedestal formation (bony hypertrophy at tip)

32. Cemented Acetabular loosening; radiographic features Bone-cement lucency >2mm and/or progressive Medial migration and protrusion of cement and cup Change in inclination of cup >5 Eccentric PE wear of the cup Fracture of cup and/or cement(rare)

33. Technical problems during sx leading to cup loosening Inadequate support of the cup by bone & cement Insufficient bone stock Acetabullum not reamed deeply enough Failure to remove all cartilage, loose bone fragments, fibous tissue and blood Failure to make sufficient no of holes in acetabulum to secure good cement-bone bon Failure to pressurize cement, distribute cement Movementt of cup or cement mantle while cement is hardening Malpositioning of cup

34. Uncemented Acetabular Component Concepts Bone ingrowth into component averages only 12%  - even with 84% bone contact  Non continuous radiolucent lines  commonly found in press fit acetabular components  are often not progressive

35. Radiographic signs of ingrowth fixation   Moore et al CORR 2006 - 3 or more 97% stable - 2 or less, 83% unstable

36. Radiographic signs of ingrowth fixation Five signs - absence of radiolucent lines - presence of a superolateral buttress inferomedial buttress - medial bone stress-shielding - radial trabeculae

37. Radiographic signs of loosening   5 signs - radiolucent lines that appear after two years - progression of radiolucent lines after two years - radiolucent lines in all three zones - radiolucent lines 2 mm or wider in any zone - migration > 2mm

38. Engh Classification  I. Stable bony ingrowth   A  No RLL B  One RLL zone 1/2 C  RLL zones 1 & 2

39. II Stable fibrous ingrowth - <2mm zone 3 III Unstable fibrous ingrowth - >2mm RLL in zone 3

40. Diagnosis History Pain on wt bearing –groin, buttock or thigh Typically ‘start-up’ pain Pain relieved by rest, aggravated by hip rotation Physical exam Antalgic gait Limb length discrepancy Investigations Laboratory R/O infection Imaging Progressive radiolucency Migration of implant

41. Treatment Asymptomatic patient Radiographic loosening often appears be4 symptoms More frequent follow-up Revision surgery if bone destruction is progressive Symptomatic patient Revision surgery

42. Indications for surgery Symptomatic patient Loose implants Large lytic lesions Progressive osteolysis even if no symptoms

43. Revision Total Hip Arthroplasty cementless components are generally preferred in revision settings. The bone sclerotic and does not provide optimal conditions for cement interdigitation only the loose components need to be revised If implant remains stable despite osteolysis , bone grafting of the defects with retention of the implant is recommended