How do cemented cementless and hybrid prostheses differ?
The terms cemented and cementless refer to methods of fixation of total joint arthroplasty prostheses for the hip and knee. Most experience is with cemented prostheses where a self-curing acrylic cement, polymethylmethacrylate, is used to improve fixation between the prosthetic component and bone. Advances in cementing techniques and materials have led to improved longevity and fewer problems with aseptic loosening. Patients who receive cemented prostheses can be walking without crutches within a few days.
Cementless prostheses include press fit and porous ingrowth prostheses. Press fit relies on a snug fit between prosthesis and bone without the use of cement. Porous ingrowth prostheses contain pores located on the proximal portion of the femoral component and acetabulum that allow ingrowth or ongrowth of bone. Hydroxyapatite or growth factors may be incorporated into the porous coating to stimulate bone ingrowth and better fixation. Overall, there is bone ingrowth into approximately 10% of the porous-coated surface. Patients receiving a cementless prosthesis are on crutches for up to 6 weeks postoperatively.
Cemented stems and cementless acetabular components have demonstrated the best longevity. Consequently, many surgeons use a cementless acetabular component with a cemented femoral component. This is termed a hybrid hip replacement.