Bone Defects in TKR Dr (Prof) Raju Vaishya (MS, MCh, FRCS) Sr Consultant Dept of Orthopaedic & Joint Replacement Surgery Indrarastha Apollo Hospitals, N Delhi Email: raju.vaishya@gmail.com

Bone deficiency in TKR Frequent problem Management is controversial

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

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

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

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

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

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

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

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

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)

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

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

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.

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)

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

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

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

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

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

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

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

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

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

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

Metal Wedges/Augments

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

Revision TKR (Metal Wedge & Augment)

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

Stress # with OA (Long intramedullary stem)

Bilateral TKR

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)

THANKS

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

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

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

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

Classification of Bone Defects (Rand, 1990)