Total Hip replacement: ARTICUALTIONS Ceramic on polyethylene Ceramic on ceramic for young Metal on metal (resurfacing) Metal (cobalt chrome) on polyethylene WEAR Wear debris similar to bacteria o < 10 microns activates macrophages o > 10 microns activates giant cells Osteolysis and aseptic loosening and bone resorption TESTING In vitro testing does not recreate real life It is though swing phase creates micro separation thus wear particles WEAR PREVENTION Prevent access ie cementing Decrease particle number by increasing contact surface Alternative bearings THR: Adrian Taylor INDICATIONS ADLs Failed conservative management Threshold for surgery and medically fit RADIOLOGY LINES Lines o Cross over of anterior and posterior acetabular lines means acetabulum is not retroverted o Coxa vera <120 0 coxa valga > 135 0
Protrusion acetabulum o Charnley 1 1-5mm 2 6-15mm 3 - >15mm Acetabular dysplasia o Crowe 1 - <50% subluxation 2 50-75% subluxation 3 - >75% subluxation 4 - >100% subluxed HIP FORCES 5cm 15cm BW Single leg stance 2x BW
Walking 3x BW Running and stairs 5-7x BW If BW is 500N o Abductor distance is 1/3 then abductor force must be 3 x = 1500N o Use of a walking stick in contralateral hand reduces abductor force by 67% OPERATIVE GOALS Pain relief and improve function o Stability o Reproduce biomechanics offset o Preserve bone stock o Leg length reproduction WHICH HIP WOULD YOU USE NJR data ODEP (orthopaedic data evaluation panel) response Ceramic longer wearing in <70 Uncemented in <70 SURIGCAL PREPARATION Pre-operative planning with a template WHO Approach o NB medial circumflex artery is under quadratus femoris o NJR 40% anterolateral (gluteal dysfunction and poor femoral canal visualisation) o NJR Posterior 35% (perceived dislocation risk, sciatic nerve risk) Acetabulum o Transverse acetabular ligament 20-40 degrees anteverted 40-50 inclinated o Find true floor True floor corresponds to teardrop on the radiograph True floor known as the 3rapeziectomy plate (U shaped cartilage known as the fovea) Non articular space known as the cotyloid fossa with central oyster soft tissue in order to re-establish optimal hip mechanics, the hip centre must be placed medially, inferiorly, and anteriorly o coverage of cup
>60% coverage Trabecular implant coverage >40% o Restore hip centre If hip centre not restored 8x early failure rate o Acetabular screw placement Superiorly parallel to spine Femur o Length Maximum overlengthening 3.5-4cm o Offset Human body 5cm from abductors shorter and these are dysfunctioned o Fixation Uncemented Cemented CONSIDERATIONS FOR TAKE DOWN ARTHRODESIS Gluteal function? o EMG o US o MRI Walking gets worse pain gets better Outcome same as revision Use imaging for acetabular placement as the anatomy is destroyed Revision hip surgery bone loss CLASSIFICATION Paprosky o 1 proximal either meidial of lateral o 2 extensive prximal medial or lateral o 3a large bone defect both medial and lateral
o 3b extended bone defect into diaphysis Dorr classification o A Good bone stock bets for uncemented o B moderate bone stock o C osteoporotic best for cemented Revision Tools Trefines used to cut out distal furlong Minus rex- cut through metal JRI cup removal tool OSCAR US cement removal system Flexible osteotomes or Large K wires held break interface in uncemented components Broken screw removal set from Stryker Mole wrench and bull nose pliers Tribiology: DEFINITIONS Tribiology the science of surface interaction during motion o 3 parameters Friction Lubrication wear FRICTION Surface resistance to motion LUBRICATION Process of reducing friction o Boundary layer o Mixed o Fluid film (hydrodynamic) Needs articulation gap <250 microns Stribeck curve WEAR Erosion of a surface
o Abrasive wear rubbing away o Adhesive wear cohesion of particles o 3 rd body from loose material Polyethylene wear o <0.1mm year to avoid osteolysis Polyethylene: MAKING PROCESS Ziegler process o Titanium catalyst Polyethylene has 2 distinct parts o Amorphous disorganised o Crystalline organised Element level o Carbons joined hands with hydrogen ions attached o c-c-c-c-c-co Cross linked and looks like c-c-c-c-c-c -c-c-c-c-c-c- WEAR Originally highly crosslinked poly worked in vitro but not in vivo as it was highly crystalline and cracked HOW TO DECREASE WEAR Hips are highly cross linked poly but not overly crystalline Knees are moderately cross linked MEASURING WEAR 2D x rays via the martell method needs > 0.1mm to detect 3D radiostereometric analysis