Introduction Biomechanics of total hip arthroplasty depend on prosthesis design bearing surface and lubrication characteristics fixation method Designs include femoral component cemented press-fit (uncemented) login to view 3 more bullets acetabular components cemented login to view 2 more bullets press-fit (uncemented) login to view 1 more bullet Modular dual-mobility liners login to view 2 more bullets bearing surfaces polyethylene metal ceramic History 1891 Dr. Gluck performs first reported attempt at a hip replacement with ivory used to replace the femoral head 1940 Austin Moore performs first metallic hip replacement surgery (hemiarthroplasty) with a proximal femoral replacement bolted to the femur 1952 Austin Moore prosthesis developed 1960s Sir John Charnley introduces concept of low friction arthroplasty concept login to view 1 more bullet components login to view 3 more bullets Press-fit Femoral Stems Overview rely on biologic fixation compression hoop stresses provide initial stability Types tapered stems most are proximally coated stems that taper distally examples login to view 2 more bullets extensively coated stems porous coating extends into the diaphysis for distal engagement examples login to view 2 more bullets modular stems distal stem and proximal body can be "mixed-and-matched" examples login to view 2 more bullets collared vs. collarless stems pros and cons to both designs Unique complications intraoperative fracture more likely in press-fit through lateral approach typically due to underreaming loosening high loosening rate when used in irradiated bone (due to lack of ingrowth) junctional corrosion seen in modular components (including cemented modular components) common in modular neck stems and can result in metallosis and pseudotumor formation Cemented Femoral Stems Overview rely on cement fixation cement is a grout that provides initial and long-term stability limited remodeling potential preferred for irradiated bone due to the bone's limited ability for ingrowth preferred for poor proximal femoral bone stock (i.e. Dorr C femurs) composition cobalt-chrome or stainless steel login to view 2 more bullets titanium login to view 3 more bullets Unique complications stem breakage cemented stems are smaller than press-fit stems and unable to tolerate as much cantilever bending login to view 1 more bullet Bearing Surfaces Metal-on-polyethylene metal (cobalt-chrome) femoral head on polyethylene acetabular liner benefits longest track record of bearing surfaces lowest cost most modularity disadvantages higher wear and osteolysis rates compared to metal-on-metal and ceramics smaller head (compared to metal-on-metal) leads to higher risk of impingement Metal-on-metal benefits better wear properties than metal-on-polyethylene login to view 3 more bullets larger head allows for increased ROM before impingement disadvantages more expensive than metal-on-polyethylene increased metal ions in serum and urine (5-10x normal) login to view 3 more bullets may form pseudotumors hypersensitivity (Type IV delayed type hypersensitvity) login to view 6 more bullets contraindications login to view 3 more bullets Ceramic on Ceramic benefits best wear properties of all bearing surfaces lowest coefficient of friction of all bearing surfaces inert particles login to view 1 more bullet disadvantages more expensive than metal-on-polyethylene worst mechanical properties (alumina is brittle, low fracture toughness) login to view 1 more bullet squeaking login to view 6 more bullets less modularity with fewer neck length options stripe wear login to view 2 more bullets Ceramic on polyethylene benefits standard of care alumina ceramic heads results in less polyethylene wear than metal-on-polyethylene (MoP) bearings disadvantages zirconia undergoes tetragonal to monoclinic phase transformation with time login to view 5 more bullets Titanium on Polyethylene not recommended due to high wear rates