1. Bone Defects in TKR Dr (Prof) Raju Vaishya
(MS, MCh, FRCS) Sr Consultant
Dept of Orthopaedic & Joint Replacement Surgery
Indrarastha Apollo Hospitals, N Delhi

3. Bone deficiency in TKR
Frequent problem
Management is controversial

4. Causes of Bone Defects Arthritic Angular Deformity Hypoplasia AVN
Trauma
Previous Surgery (eg. HTO, TKR etc)

5. Types of Bone Defects
I) Based on size: a) <5mm, b) 5-10mm, c) >10mm
II) Based on location: a) Central, b) Peripheral
III) Based on margins: a) Contained, b) Uncontained

6. Rand’s Classification of Bone Defects
Type I: Focal metaphyseal defect (with intact cortical rim)
Type II: Extensive metaphyseal defect (with intact cortical rim)
Type III: Combined metaphyseal & cortical defects

7. Bone Defects
A) Contained or Cavitary: Intact rim of cortical bone surrounding the deficient area
B) Non contained or Segmental: More peripheral & lack bony cortical rim

8. Bone Defects in TKR
Most moderate & severely deformed primary knees have bone defects
Most revision knees have significant bone defects

9. Etiology of Bone Deficiency ( Primary TKR)
Varus: Defect on postero-medial aspect of tibial plateau
Valgus: Bone loss is usually located centrally on lateral tibial plateau
Previous HTO: Bone defect on postero-lateral corner of tibia

10. Etiology of Bone Deficiency (Revision TKR)
UKA: Localized defects in femur & tibia
Condylar Implant: Distal & post. on femur / Central or peripheral on tibia
Hinge Prosthesis: Diffuse cavitary type
Surface Arthroplasty: Central on tibia & Post. On femur

11. Facts about bony defects
Central deficiency frequently exists following loosening of an older resurfacing implant
Peripheral defect occurs with angular deformities & usually located posteromedially in varus knees
Femoral bone loss in revisions is located distally, posteriorly or combined
Tibial defects are commoner than femoral defects in Pr TKR

12. Tips for making bone cuts
Assess bony defects prior to making bone cuts
Measure the defects after bone cuts
Take great care in removing components (esp solidly integrated) or making bone cuts (esp metaphyseal bone)

13. Options to deal with Bone Defects
I) Increased Bone Resection
II) Translation of component (away from defect)
III) Bone Cement
IV) Bone Grafts (morselised, bone cuts, allograft)
V) Metal Wedges
VI) Augmented Femoral/Tibial Component

14. Increased Bone Resection
Beware of always trying to resect the defect!
Strength of bone diminishes by 33% , 2cms below the tibial plateau
Keep the tibial cut above the head of fibula

15. Translation of component
Utilized for peripheral defects involving <50% of single condyle
Requires the use of smaller tibial component for coverage & may alter force transmission across the implant & loosening.

16. Filling with Cement
Indicated for peripheral deficiency of <5mm & <10% of condylar area or small central defect
Provides poor mechanical support for prosthesis (can’t be pressurized, laminations form within cement & cement does shrink)
The end result may be a cantilever bending fatigue of tibial prosthesis requiring revision (Hence, least desirable option for managing bone defect)

17. Cementing with Reinforcement
Can be performed using screws or wire mesh
No significant improvement in mechanical strength of cement
Provides a level surface upon which to seat the implant
Indications for its use are similar to that of un reinforced cement

18. Bone Grafting
Indicated for peripheral bone defect >50% of condylar area & depth of >5mm & filling of central deficiency
Autografts are available from bone cuts in Pr TKR. In Revision, iliac bone graft is used
Allografts are usually from femoral heads. For massive bone loss, distal femur or prox. tibia is used

19. Advantages of Bone Grafts
Avoid the use of custom implants
Avoid possibility of cement fragmentation
Preserve subchondral bone
Provide a uniform cement thickness

20. Disadvantages of Bone Grafts
Local bone may be limited in amount
Fitting of the bone into a defect may be difficult
Incorporation of graft is unpredictable

21. Bone Grafting Technique
Exposure of bleeding bone
Precise fitting of the graft into the defect
Rigid fixation with screws/wires
Component coverage of the graft

22. Technique of Bone Grafting (Windsor, Insall & Sculco)
Convert a concave, irregular defect to a flat one & bone graft it

23. Failure of Bone Grafts Limb mal alignment with overload
Trying to fit graft in a sclerotic bone bed
Poor graft fit
Non incorporation of graft

24. Controversies in Bone Grafting
Appropriate time of Weight Bearing
Long term fate of grafts
Effects of stress relief on the grafts by longer-stemmed implants

25. Custom Implants
Valuable in complex deficiencies & for peripheral defects >1.5cm in depth
Provides excellent force transmission between implant & bone
Provide precise fit to the defect
Expensive & delay in procurement

26. Metal Wedge Augmentation
Provides adequate loading & load transfer
Indicated in peripheral or central defects with an area >10% of condyle & depth 5-15mm
No donor site morbidity
Customization is possible
Concerns over long term durability of wedge-cement-prosthesis interface

27. Metal Wedges/Augments

28. Modular Metal Wedges
An attractive option because of simplicity of intra-operative fabrication of a ‘custom’ implant to match the defect
Potential objection for its use is the question of durability of wedge fixation to the tibial tray

29. Revision TKR (Metal Wedge & Augment)

30. Extended Intramedullary Stems
Relieve stress in deficient bone in metaphyseal area
Indicated for defects greater than moderate size
Controversy exists in cementation of stem

31. Stress # with OA (Long intramedullary stem)

32. Bilateral TKR

34. Recommendations Small size defects (<5mm): Filling with bone cement
Medium size defects (5-10 mm): Autologous Bone Graft
Large size defects (>10mm): A) Primary TKR: Autologous Bone Graft (with long stem) B) Revision TKR: Metal Wedges/Augments (with long stem)

35. THANKS

36. Balancing Flexion/Extension Gap
I) Adequate Flexion & Extension: No change
II) Adequate Flexion & Loose Extension: Augment distal femur
III) Adequate Flexion & Tight Extension: Resect distal femur, Post. Release, D/C post. osteophyte

37. Balancing Flexion/Extension Gap
I) Loose Flexion & Adequate Extension: larger femoral component with post. Augment
II) Loose Flexion & Extension: Thicker tibial component
III) Loose Flexion & Tight Extension: Larger femoral component with distal augment, Resect distal femur

38. Balancing Flexion/Extension Gap
I) Tight Flexion & Adequate Extension: Smaller femoral component, Post. Tibial slant, Consider PS prosthesis
II) Tight Flexion & Loose Extension: Smaller femoral component with distal augment, Consider PS prosthesis
III) Tight Flexion & Extension: Thinner tibial component, Resect tibia

39. Balancing Flexion/Extension Gap
Extension Gap is governed by: Distal femoral resection & tibial cut
Flexion Gap is governed by: Post. Femoral resection & tibial cut

40. Classification of Bone Defects (Rand, 1990)