1. firm 1 grandround ASEPTIC LOOSENING OF THA presenter: ondari n
firm 1 grandround ASEPTIC LOOSENING OF THA presenter: ondari n.j FACILITATOr: DR. MUSEVE

2. Incidence of hip arthritis is 3-5% in >55yrs

5. A good prosthesis important

7. Biomechanics THA components bears atleast 3X body weight
Abductor lever arm ~2.5X body lever arm
Abductor lever arm may be dec by OA or neck shortening
Lever arm ratios can increase to 4:1
Lenghts of lever can be surgically changed to approach 1:1
This theoretically reduces load hip by 30%

8. Lateral and distal reattachment of osteotomized GT
Medialization of acetabulum

9. Stress transfer to bone
Bone quality determines most appropriate implant
Dorr radiographic classification of proximal femur
Type A femurs
Thick cortices
Narrow distal canal – ‘champaigne flute’ appearance
Found in young pts
Permits good fixation
Type B femurs
Exhibit bone loss, shape not compromised
Implant fixation not a problem
Type C femurs
Thin cortex, wide medullary canal – ‘stovepipe’ shape
Occurs in older osteoporotic women
Less favorable for implant fixation

10. Dorr classification of morphology of femur

11. Stress transfer to bone
Stress transfer to bone desirable
Measures to decrease stress shielding
Decrease modulus of elasticity of stem eg titanium alloy
Smaller diameter stems
Prosthetic collar
Stem shape
Tapered geometries better

12. Complications of THA Intraoperative Early postoperative
Mortality, nerve injuries, vascular injuries
Early postoperative
Thromboembolism, hemartoma formation, infection, dislocation, limb length discrepancy
Late postoperative
Heterotopic ossification
Loosening
Most serious long term problem

13. Loosening of THA components
Most serious complication
Commonly leads to revision
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
Can be septic or aseptic

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

15. Gruen 7 zones of femur

16. Delee and Charnley acetabular zones

17. Cemented Femoral loosening; Radiographic features
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 %

18. Are all radioluscent line due to loosening?
Radioluscent lines btn femoral cortex and cement can be produced by;
Cancellous bone not completely removed during sx
Normal age related expansion of femoral canal assoc cortical thinning. Poss et al study;
Medullay canal expands at 0.33mm/yr
Cortical thickness decrease by 0.14mm/yr
NB; these radioluscet lines do not typically have the surrounding sclerotic line noted on loose femoral stems
Medullary canal widening has not been implicated in the process of femoral loosening

19. 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
Cements laminations
Presence of voids in cement
Poor mixing, injecting technique, blood or fragments of bone
Failure to pressurize cement
Failure to prevent stem motion while cement is hardening
Failure to position component in neutral or mildly valgus position

20. Cementless femoral components

21. 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 >50
Eccentric PE wear of the cup
Fracture of cup and/or cement(rare)

23. 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
Failure to distribute cement around entire outer surface of cup
Mvt of cup or cement mantle while cement is hardening
Malpositioning of cup – neck of femoral component impinges on margin of socket

24. Pathophysiology Generation of particulate debris Mechanisms of wear
corrosion
Mechanisms of wear
Adhesion, abrasion, microfatigue and 3rd body wear
Wear debris sources
PE, cement, metal particles
PE bearing surfaces are the major factor responsible for periprosthetic osteolysis

25. Pathophysiology cont. Particle size important
0.5 – 10microm – pagocytosed
<0.5microm – too small to activate a response
>10microm – stimulate a giant cell response
Irregularly shaped particles more active than spherical poarticles

26. Modes of wear
Is the mechanical condition under which prosthesis was working when wear occurred
Four modes
Mode 1
Motion btn two bearing surfaces as intended by designer
Mode 2
10 bearing surface rubbing against 20 surface
Mode 3
Two 10 surfaces with interposed third-body particles
Mode 4
Two non-primary surfaces rubbing together

28. OSTEOLYSIS
Is the final pathway related to host cellular response to debris of all types
Mechanism
Generation of wear particles
Access of these particles to periprosthetic bone
Cellular response to particulate debris
Debris dispensed through joint fluid by pressure gradient
Pattern of lysis depends on implant design

29. Osteolysis; cellular response
MQs predominant cells
Surface interaction btn MQs and wear debris incite inflammatory response whether or not phagocytosis occurs
Multiple cytokines/chemokines produced
Osteoclasts activated, osteoblasts inhibited
Net result – bone resorption

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

31. Diagnosis History Physical exam Investigations
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

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

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

34. 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