types of hip replacement

Last reviewed 01/2018

In total hip replacement (THR) surgery

• the acetabulum (hip socket) is replaced with either a single-piece cup made from 1 material (polyethylene, ceramic or metal) or a 2-piece (modular) cup made from a metal outer shell and a polyethylene, ceramic or metal liner
• the head of the femur (thigh bone) is replaced with either a single-piece metal stem and head, or a modular component consisting of a metal stem (which may consist of more than 1 piece) with a metal, ceramic or ceramicised metal head
• THRs vary in what fixation method is used for each component of the prosthesis
  • in some THRs, all the components are fixed into position using cement (referred to as cemented THRs)
    • other types of THR are designed to be used without cement (referred to as cementless THRs); instead, they are inserted using press-fit fixation, and natural bone growth over time secures the prosthesis in place
    • some prostheses are hybrid, in which the femoral component is cemented into place while the cup is fixed without cement, or reverse hybrid, in which the femoral component is fixed without cement while the cup is cemented into place
• THRs may also vary by femoral head size, with a large head defined as being 36 mm or more in diameter

Hip resurfacing arthroplasty

• involves removing and replacing the surface of the femoral head with a hollow metal hemisphere, which fits into a metal cup fixed into the acetabulum. All resurfacing arthroplasty prostheses currently on the market are metal-on-metal (MoM), and can be hybrid or cementless
• as with THR prostheses, resurfacing arthroplasty prostheses may also vary by femoral head size

A good hip prosthesis must:

• be durable
• allow movement without undue friction
• be permanently fixed to the skeleton
• not cause a foreign body response

The first two characteristics are adequately met by most modern metal-on-polyethylene prostheses:

• the durability of the new joint is rarely the limiting factor in the success of a hip replacement
• the friction of articulation is about 40 times higher in a prosthesis as compared to a normal joint; while this permits free movement it imposes a strain on the fixation of the components to the bone

The permanence of the fixation is a major problem:

• cemented prostheses fix well initially, allowing rapid mobilisation, however a foreign body reaction to particles of cement may result in bone lysis around the cement margin. This has become less important with advances in cementing techniques.
• uncemented prostheses take longer to fix securely but are usually easier to revise

Reference:

1. NICE (February 2014). Total hip replacement and resurfacing arthroplasty for endstage arthritis of the hip