Bone defects in tkr
- 1. DR ANKIT JOSE M.S ORTHO FELLOW IN JOINT ARTHROPLASTY SUNSHINE HOSPITAL BONE DEFECTS IN TKR
- 2. Causes of Bone Defects Stress shielding Osteolysis Infection Mechanical motion Iatrogenic from implant removal Osteonecrosis
- 3. 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
- 4. 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
- 5. CLASSIFICATION OF BONE DEFECTS
- 6. Classification of Bone Defects I) Based on size: Rand a) <5mm, b) 5-10mm, c) >10mm II) Based on location: Dorr a) Central, b) Peripheral III) Based on margins: Insall a) Contained, b) Uncontained
- 9. DRAWBACKS of AORI Does not address instability- ROTATIONAL Patellar bone loss Situation where implant remain well fixed
- 10. NO SINGLE CLASSIFICATION IS IDEAL
- 11. 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
- 12. Bone Defects in TKR Most moderate & severely deformed primary knees have bone defects Most revision knees have significant bone defects
- 13. 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 Primary TKR
- 14. PREOPERATIVE ASSESSMENT AP/LATERAL XRAY Opp knee xray CT with 3-D reconstruction in revision TKR Intraoperative findings
- 15. WHAT TO ADDRESS IN BONE DEFECTS Restoration of longitudinal, angular and rotational stability. Restoration of the joint line. Restoration of soft tissue stability. Reconstitution of bone.
- 16. 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)
- 19. IMPLANT SELECTION Collateral ligament and extensor mechanism Degree of bone loss Integrity of residual bone
- 20. WHAT IMPLANT? Posterior stabilized Unlinked constrained Rotating hinge Modular prosthesis
- 21. IMPLANT STABILITY Longitudinal stability – peripheral rim Angular stability- eccentric – stem Rotational stability – femur and tibia
- 22. OPTIONS ? Cement and screw Bone graft Modular wedges and block augments Porous metal metaphyseal cones and sleeves Megaprosthesis
- 23. CEMENT AND SCREW After bony cut measure <5mm and <50% bone surface area 5-10mm – cement + screw (4.5mm cc screw ) Screw- pillars
- 24. 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
- 25. Why not >10mm Thermal necrois Shrinkage of cement during polymerization and lamination Ritter et al – 47 primary cases 6.1 yr follow up Non progressive radiolucent line <1mm in 27% of TKA
- 29. 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)
- 30. BONE GRAFT Autogenous bone grafting Allogenic bone grafting Impaction bone grafting Structural bone allograft
- 32. 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
- 33. Advantages of Bone Grafts Avoid the use of custom implants Avoid possibility of cement fragmentation Preserve subchondral bone Provide a uniform cement thickness
- 34. 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.
- 35. 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
- 36. Technique of Bone Grafting (Windsor, Insall & Sculco) Convert a concave, irregular defect to a flat one & bone graft it
- 37. 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
- 38. 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
- 40. AUGMENTS Space fillers and substitutes bone INDICATIONS Uncontained defect 5-10mm >40% bone implant interface is unsupported by host bone Periphery of defect involve >25% of adjacent cortex
- 41. Augments in femoral side –posterior and distal Wedge or block augments ?
- 42. 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
- 45. METAPHYSEAL FIXATION Porous sleevs Porous cones STEM REQUIRED ? Based on zone of fixation Primary stability Stemless tibial fixation
- 49. INDICATION Bone stock is poor Impaction grafting fail to achieve implant stability Additional logitudinal and angular support required
- 50. ADVANTAGES Biologic fixation Fill large defects Immediate additional structural support. Primarily rotational stability
- 51. DISADVANTAGES Lack of bone stock restoration Removal of additional native bone Removal challenging
- 56. PATELLA LOSS Previously resurfaced patella Patellar fracture Avascular necrosis
- 57. Bone graft and augmentation Cemented biconvex polyethylene patellar button Trabecular metal patellar prosthesis Patellar resection arthroplasty Gull wing sagital osteotomy Patellectomy –last resort
- 59. MEGAPROSTHESIS
- 62. THANK YOU