Welcome to Hip and Pelvis Blog Spot!

This is a new addition to HipandPelvis.com that provides the visitor with current thinking and trends as expressed by the orthopaedic surgeons of The Hip and Pelvis Institute at St John’s Health Center.  It also provides information not covered in our traditional patient education section.

Information on this site is based on current medical information as interpreted by the MD’s of the hip and pelvis institute.  At any point in time, medical information is always incomplete and subject to interpretation and therefore there are differences of opinions and recommendations between experts.  I believe that the internet serves an important function by making medical information more accessible to everyone.   

Joel Matta, MD, Founder and Director, Hip and Pelvis Institute

Latest Entry:

02/13/08

I am recently more frequently asked, “Is surface replacement hip arthroplasty possible through the anterior approach.”   The answer is yes and I believe that the anterior approach is the preferable way to perform this procedure.   Surface replacement is a procedure that is primarily advocated for younger patients.  There is less removal of bone from the femur.  The head of the femur is machined to a smaller size and a metal cap placed over it rather than completely removing the femoral head as is done with standard hip replacement.  One of the main arguments supporting it is that taking less bone can be advantageous for the young patient if later revision of the femoral component is necessary which is more possible in young patients.  What is typically not discussed by most surgeons is that preserving muscle attachments to the femur is also very important, particularly in young patients who may require revision surgery.  Currently the large majority of surface replacements are performed through a large posterior approach that is more soft tissue invasive than anterior approach.  Anterior approach surface replacement can preserve the femoral attachments of the hip musculature along with preservation of femoral bone stock.

The other important question is:  Is surface replacement the best prosthesis choice for an individual patient?  In general surface replacement is not recommended for older patients for whom there is a probability of living the rest of their life without the need for revision surgery.  The answer as to whether surface replacement is the right choice for younger patients is also not clear.  There is currently lack of conclusive evidence that patients function better after surface replacement than after standard hip replacement.  Also, we do not have long term (20 year) follow-up studies that demonstrate the longevity of surface replacement.  The current metal-metal surface replacement prostheses are more promising than past designs. Surface replacement prostheses have been available for over 30 years though past designs have been abandoned because of a high failure rate.  The early results of the current designs however, show fewer failures and revisions at 5 to 10 years (1-5%) but still a somewhat higher revision rate than standard hip replacement.

The widely accepted advantage of surface replacement is that because of the bone preservation, revision of a failed femoral component is easier and more secure than after failure of a standard femoral component.  The reservations regarding surface replacement are that the femoral component is probably more likely to need revision and that metal-metal is the only bearing surface available (see my blog comments on bearing surfaces).

Surface replacement is therefore another prosthesis option through anterior approach that has a high probability of an excellent functional result.  Revision of a failed surface replacement arthroplasty to a standard hip replacement can also be performed through the anterior approach.

Dr. Joel Matta

First Entry - 02/08/08

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 no 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 10,000 risk for fracture of the ceramic socket possibly due to extreme forceful motions.

Cobalt-chromium ball with cobalt-chromium socket:  Very low wear.  Even though wear is higher than ceramic it is impossible to wear this metal-metal bearing out during a lifetime.  The largest ball sizes are available which can be helpful if the patient demands extreme motion (doing the splits, leg behind your head).  No chance of fracture.  There is however a possible hypersensitivity (inflammatory) reaction to metal wear particles which causes pain and fluid around the hip reported at between 1 in 500 and 1 in several thousand.  I tend to believe 1 in 500 though good statistics are lacking.  There is also a theoretical risk of cobalt or chromium ion systemic toxicity causing cancer though this has never been proven.

Ceramic ball with cobalt-chromium socket:  Compared to a metal-metal bearing, metal particle production is 1/50th  which lowers the risk of metal hypersensitivity and ion toxicity.  Compared to ceramic-ceramic there is no risk of socket fracture.  The available ball size is larger than metal-poly, ceramic-poly and ceramic-ceramic but smaller than metal-metal.  This bearing is very promising but newest and has the least clinical follow-up.

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.

Overall I think that patients are often too concerned with proper selection of the specific prosthesis.  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.

Dr. Joel Matta