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

Anterior Approach Hip Resurfacing

I am recently more frequently asked, “Is hip resurfacing 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.   Hip resurfacing also known as hip 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 hip resurfacings are performed through a large posterior approach that is more soft tissue invasive than anterior approach.  Anterior approach hip resurfacing can preserve the femoral attachments of the hip musculature along with preservation of femoral bone stock.

The other important question is:  Is hip resurfacing the best prosthesis choice for an individual patient?  In general hip resurfacing 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 hip resurfacing is the right choice for younger patients is also not clear.  There is currently lack of conclusive evidence that patients function better after hip resurfacing than after standard hip replacement.  Also, we do not have long term (20 year) follow-up studies that demonstrate the longevity of resurfacing.  The current metal-metal surface replacement prostheses are more promising than past designs. Hip resurfacing 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 hip resurfacing 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 resurfacing 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).

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

 Joel Matta, MD

Surgical Approaches for Hip Replacement

The “approach” refers to the pathway that the surgeon takes through the soft tissues to reach the bone and perform hip replacement.  The approaches are:  anterior (Smith-Petersen), antero-lateral (Watson-Jones), lateral (Harding), and posterior (Kocher-Langenbeck).  The names in parentheses refer to surgeons who described the approach.  Wikipedia references these approaches and the soft tissue intervals they follow.
Hip replacement - Wikipedia, the free encyclopedia

Surgical approaches ideally follow inter nervus (between nerves) and inter muscular soft tissue intervals to limit the chance of muscle and nerve damage.  The important nerve damage to be avoided is to the motor nerves that provide the signal for hip muscle action.  These motor nerves are the superior gluteal nerve which enervates the gluteus medius, gluteus minimus, and tensor fascia latae muscles and the inferior gluteal nerve which enervates the gluteus maximus muscle.

The anterior (Smith-Petersen) approach is the only approach that is both inter nervus and inter muscular and it follows the interval between the tensor fascia latae and sartorius muscles.

The antero-lateral (Watson-Jones) approach comes closest to also meeting these criteria however the hip deltoid (combination of tensor fascia latae and gluteus maximus muscles with the iliotibial band) is split.  Also, this approach which follows the interval between the tensor and gluteus medius muscles is not inter nervus and places the superior gluteal nerve branch to the tensor muscle at risk.

The lateral (Harding) approach can impair function of the important abductor muscles by detachment of the gluteus minimus muscle and splitting the gluteus medius muscle.  Gluteus medius splitting also endangers the superior gluteal nerve.  Abductor muscle and/or superior gluteal nerve impairment can cause a limp.

The posterior (Kocher-Langenbeck) approach splits the gluteus maximus and detaches the external rotator muscles from the femur.  The external rotator muscles (particularly the obturator externus muscle) are active in preventing hip dislocation and also active during athletic activity requiring hip rotation (golf, tennis, skiing, martial arts).

Largely because of the above factors, I prefer the anterior (Smith-Petersen) approach.

Though the above definitions of approaches are more and more adhered to, there remains confusion and I would say misuse of the term “anterior approach”.  Some surgeons may refer to the antero-lateral (Watson-Jones) approach as anterior.  Some surgeons may even refer to the lateral (Harding) approach as anterior.

Proper definition prevents misinformation.

 Joel Matta, MD

Enhancing Safety and Accuracy of Anterior Approach Hip Replacement

The “approach” is the incision used for hip replacement and the deep pathway taken through the soft tissues.  “Anterior Approach” refers to the use of the Short Smith-Petersen Approach to the hip.

Simply choosing the anterior approach for hip replacement however, does not guarantee patient benefits.  Other elements of the technique are also necessary for minimizing soft tissue disruption, enhancing accuracy of artificial hip components and minimizing the chance of complication.  Specifically supine patient position, the orthopedic table, and intra operative checks with the fluoroscope (x-ray) enhance safety and accuracy of anterior approach and make anterior approach applicable to essentially all patients.

Definitions:  Supine means patient on their back rather than on their side (lateral).  Orthopedic table refers to the HANA or PROfx table.  A fluoroscope is a low dose x-ray machine used during surgery that displays an enhanced image on a TV screen and will also make x-ray prints.

Most surgeons performing hip replacement are accustomed to placing the patient lateral (on their side) on a standard flat table and not taking check x-rays during surgery.  Anterior approach hip replacement as I describe it is therefore a departure in methods which is often initially resisted by the uninitiated surgeon.

Supine patient position:  With the patient lying on his back during surgery, his skeletal position is more consistent which allows better anatomic references for accurate positioning of the acetabular (hip socket) component as well as assessment of leg length.  Urgent or emergency problems the anesthesiologist might face are also more easily handled.

The orthopedic table:  Though anterior approach is an ideal soft tissue interval for hip surgery regarding muscle preservation, it presents problems with access to the femur.  If the surgeon struggles for access, muscles can be damaged and the benefits of anterior approach lost.  The orthopedic table’s unique positioning capabilities deliver the upper femur for surgeon access while minimizing muscle trauma.  The table acts outside the sterile field, moving the leg with the parallel carbon fiber spar and also acts inside the wound by lifting the upper femur for access with the robotic femoral support hook.

The flouroscope:  Final judgment of the accuracy of a hip replacement (acetabular position, leg length, femoral offset, and component fit) is judged by x-ray.  I advocate strongly that this information should be obtained during surgery (with the fluoroscope) prior to closing the wound.  An advantage of the anterior approach is that with the patient supine on the carbon fiber table, accurate x-ray information is easily and immediately available.  This accuracy I find is greater than after surgery x-rays.  Most surgeons wait until after surgery for their check x-ray.  I would say this is too late and has obvious disadvantages.  Small inaccuracies that could have been easily corrected are accepted and large inaccuracies require a return to the operating room.

Computer guidance to position hip components is also helpful in enhancing accuracy.  The computer however creates a virtual picture with some tolerance for error while x-ray is an actual picture.  Also, the surgeon still needs to get an x-ray at some point to see if the computer is right.

Use of the anterior approach incision therefore does not by itself bring maximum patient benefit.  Anterior approach combined with the technologies and methods of the supine position, theorthopedic table,and theflouroscopedoes.

 Joel Matta, MD

Hip Replacement Materials

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 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 though I have not seen it in any of my patients.

Ceramic ball with cobalt-chromium socket: Compared to a metal-metal bearing, metal particle production is 1/10th (laboratory studies) which lowers the risk of metal hypersensitivity and lowers blood cobalt and chromium ion levels. Compared to ceramic-ceramic a bigger ball size is typically possible (more stability, almost no fracture risk) and there is no risk of socket fracture. This bearing is very promising but newest and has the least clinical follow-up. Though clinical studies showing no problems have been completed, ceramic-metal is still in the FDA approval process and its use is termed “off label”.

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