Patients often ask “What are the hip replacement parts made of and what is the best?” Both cemented and uncemented hip prostheses can have excellent long term results. The current trend however is toward uncemented. With uncemented hips, the structural portion of the femoral and acetabular components that contact the bone are made of titanium with a rough surface that the bone grows onto or into. The ball and socket bearing surface is of a different material that is more wear resistant than titanium. The artificial femoral head (ball) can be made of cobalt-chromium or ceramic and the acetabular liner (socket) that fits into the titanium acetabular shell is made of cross linked polyethylene, ceramic or cobalt chromium. In summary the titanium parts are consistent but the bearing surface can be varied according to patient needs and choice. All bearing surfaces have potential advantages and disadvantages.

Cobalt-chromium ball with cross linked polyethylene socket: The greatest clinical follow-up data supports this bearing’s reliability. Continued improvements in the ball surface and durability of the polyethylene predicts continued gains in longevity. It is impossible for most patients to wear this bearing out.

Ceramic ball with cross linked polyethylene socket: Laboratory wear studies indicate lower polyethylene wear than with a cobalt-chromium ball. There is a possible ceramic fracture risk though there are only rare reported fractures with the latest generation of ceramic.

Ceramic ball with ceramic socket: This bearing has the lowest wear of any bearing and the wear particles are probably less reactive with body tissues than cobalt-chromium or polyethylene. There is about 1 in 1000 risk for fracture of the ceramic socket, possibly due to extreme forceful motions. There is also a similar risk of fracture of the smallest size ceramic ball (28 millimeters) and less fracture risk as the ball gets bigger. Squeaking of ceramic-ceramic bearings has also been reported.

At present there is no clear cut answer though for my patients all possibilities are available. I can make the choice for you or with you or you can research hip bearings yourself. All of the above choices have very low risk and can be considered good choices.

I believe that the way the surgery is done: preserving the soft tissues, avoiding complications and implanting the artificial parts accurately is most important. Anterior approach hip replacement is the best at achieving these goals and with the anterior approach the patient has all options open regarding the type of hip prosthesis.

Metal on metal bearings (metal ball with metal socket liner):  During the past decade metal on metal bearings went through a period of great popularity.  The potential advantages that led to selection of this bearing by surgeons and patients was the large ball head which enhances stability and the low wear rates.  The metal used for this bearing is cobalt-chromium.  Some patients however have shown high blood levels of these metals following metal on metal bearings.  Though bad systemic effects from the elevated metal levels have not been clearly shown there is concern regarding possible toxic effects.  Toxicity to tissue in the hip area associated with metal particle wear from the bearing however as been demonstrated in a small percentage of cases.  The biggest problems with metal on metal bearings have been with the very large ball heads that are implanted with one piece hip sockets made entirely of cobalt-chromium.  In addition to metal wear particles these cobalt-chromium hip sockets also do not bond to the bone as reliably as titanium hip sockets.  Hip resurfacing prostheses have metal on metal bearings and hip sockets made entirely of cobalt-chromium and therefore potential for the above mentioned problems.

Joel Matta, MD