Introduction Types of fixation cement fixation polymethylmethacrylate (PMMA) biologic fixation (cementless fixation) bone ingrowth bone ongrowth History cemented fixation first described by Gluck in 1891 Charnley popularized technique in 1950s used cement borrowed from dentists failures in 1980s thought to be due to "cement disease" driving force to perfect cementless techniques cementless fixation used throughout 1900s, with varying results in 1983, FDA approved Anatomic Medullary Locking (AML) implant first microporous surface with potential for bone ingrowth proximally coated stems designed shortly thereafter due to concerns of thigh pain and osteolysis Prevalence of fixation technique increasing trend towards cementless fixation 93% of THA in United States in 2012 were cementless Indications Dorr classification attempts to guide indications for cemented or uncemented femoral component fixation. Ratio is calculated as canal diameter 10 cm distal to midportion of lesser trochanter divided by inner canal diameter at midportion of lesser trochanter Dorr Classification Ratio Characteristics Suggested Femoral Component Fixation Type A < 0.5 Cortices seen on both AP and lateral XR Uncemented Type B 0.5 to 0.75 Thinning of posterior cortex on lateral XR Uncemented type C >0.75 Thinning of cortices on both views Cemented Cement Fixation Mechanism acts as grout by producing interlocking fit between surfaces Indications femoral component elderly patients deeper penetration of cement in osteopenic patients provides excellent fixation irradiated bone bone ingrowth potential is limited with press-fit components in irradiated bone "stovepipe femur" also known as Dorr C femur enlarged metaphyseal region and lack of supporting isthmus make cementless fixation difficult acetabular component controversial cemented acetabular component fails at a higher rate than press-fit cement resists shear poorly Technique cementing techniques have evolved with time 1st generation hand-mixed cement finger packed cement no canal preparation or cement restrictor 2nd generation cement restrictor placement cement gun femoral canal preparation brush and dry 3rd generation vacuum-mixing to reduce cement porosity cement pressurization femoral canal preparation pulsatile lavage cement fixation optimized by limited porosity of cement leads to reduced stress points in cement cement mantle > 2mm increased risk of mantle fractures if < 2mm mantle stiff femoral stem flexible stems place stress on cement mantle stem centralization avoid malpositioning of stem to decrease stress on cement mantle smooth femoral stem sharp edges produce sites of stress concentration absence of mantle defects defined as any area where the prosthesis touches cortical bone with no cement between creates an area of higher concentrated stress and is associated with higher loosening rates proper component positioning within femoral canal varus or valgus stem positioning increases stress on cement mantle Radiographic analysis Barrack and Harris grading system grade A complete filling of medullary canal "white-out" of cement-bone interface grade B slight radiolucency of cement-bone interface grade C radiolucencies > 50% of bone-cement interface or incomplete cement mantles grade D gross radiolucencies and/or failure of cement to surround tip of stem Biologic Fixation Mechanism 2 different types ingrowth bone grows into porous structure of implant ongrowth bone grows onto the microdivots in the grit blasted surface Indications femoral component younger patients older patients with good bone stock revision total hip arthroplasty cemented femoral stems have lower success rates in the revision setting acetabular component all situations except poor acetabular bone stock irradiated bone Technique methods press fit technique slightly larger implant than what was reamed/broached is wedged into position line-to-line technique size of implant is the same as what was reamed/broached screws often placed in acetabulum if reamed line-to-line biologic fixation is optimized with pore size 50-300um preferably 50-150um porosity of 40-50% increased porosity may lead to shearing of metal gaps < 50um defined as gap space between bone and prosthesis micromotion < 150um increased micromotion may lead to fibrous ingrowth maximal contact with cortical bone types of coating porous-coated metallic surfaces allows bone ingrowth fixation extent of coating proximal coating only less distal stress shielding extensively coated stem produces more stress shielding of proximal bone useful for revision arthroplasty where proximal bone stock may be compromised grit blasted metallic surface allows bone ongrowth fixation all grit blasted stems are extensively coated fixation strength is less than with porous coated stems, necessitating greater area of surface coating hydroxyapatite (HA) osteoconductive agent used as an adjunct to porous-coated and grit blasted surfaces may allow more rapid closure of gaps between bone and prosthesis has shown shorter time to biologic fixation in animal models, but no advantage clinically in humans Radiographic analysis signs of a well-fixed cementless femoral component spot-welds new endosteal bone that contacts porous surface of implant absence of radiolucent lines around porous portion of femoral stem proximal stress shielding in extensively-coated stems absence of stem subsidence on serial radiographs signs of a well-fixed cementless acetabular component lack of migration on serial radiographs lack of progressive radiolucent lines intact acetabular screws Complications of Implant Fixation Aseptic loosening causes poor initial fixation mechanical loss of fixation over time particle-induced osteolysis clinical presentation acetabular loosening groin/buttock pain femoral loosening thigh pain start-up pain evaluation sequential radiographs bone scan treatment revision of loose components Stress shielding definition proximal femoral bone loss in the setting of a well-fixed stem risk factors stiff femoral stem most important risk factor large diameter stem extensively porous coated stem greater preoperative osteopenia clinical implications clinical implications of proximal stress shielding unknown treatment no specific treatment is necessary Intraoperative fracture risk factors use of press fit technique treatment acetabular fracture stable cup add screws for additional fixation unstable cup remove cup, stabilize fracture, and reinsert cup with screws femur fracture proximal femur fracture stable prosthesis limit weight-bearing consider cerclage cables/wires unstable prosthesis remove prosthesis, stabilize fracture, reinsert new stem that bypasses fracture by two cortical diameters