Warning: Creating default object from empty value in /home/anterior/public_html/wp-content/plugins/wpsp/configs/default.php on line 27
direct anterior total hip | nuances of fixation on the femoral side » direct anterior total hip

«

»

Print this Post

nuances of fixation on the femoral side

the femoral component — bonding to the bone in a high torque muscle envelope.

When I first began to use the direct anterior total hip approach in 2005, I exclusively used an implant on the femoral side that is classified as a non-cemented, proximally porous coated, tapered wedge design.  There are several features that make this an ideal stem for the anterior approach.  It has a cut out at the shoulder on the lateral side of the prosthesis which makes it easier to insert if there is any residual femoral neck bone stock remaining — since this area can sometimes be a difficult to visualize during the anterior approach.  It is designed to be inserted with a hand broaching technique (which avoids the need to ream the femur with a power reamer), and the double offset broaches that were developed for the insertion of this stem are well suited to the anterior approach.  Most importantly, the tapered wedge design had proven itself to be a successful design, with very high (>98%) success rates in a large number of patients in published clinical reports in the united states.  It is worth noting that most of these patients were treated with a posterior approach to the hip, and there may be a few subtle differences between the anterior and posterior approach that makes this stem less likely to be successful if it is put in anteriorly.

This stem is meant to sit in the femoral canal in a fashion where there is direct contact between the porous surfaces of the proximal portion of the stem and the femoral bone.  If the bone is able to attach to this part of the femoral stem, it is said to have achieved osteointegration, and that is widely seen as a prerequisite for a long term successful outcome following total joint replacement.

 

In a very small minority of my patients, these stems appeared to fail to osteointegrate — the bone failed to solidly attach to the femoral stem.  The number of patients was very small, but it was significant, since many of these patients had specifically sought out an anterior approach because their independent research had led them to believe that their ability to return to physical activity, hiking, cycling, and other sports would be improved if they had an anterior approach.  Indeed, most of the patients who failed to achieve solid osteointegration on the femoral side were those who had exceptionally fast recoveries.  They went home from the hospital earlier, they completed their goals in rehabilitation faster, and they returned to a normal gait faster.  However, by six months, they started to complain of thigh pain.  The thigh pain appears to be due to the fact that if the stem is loose, the micromotion between the stem and the bone is a source of discomfort.  Often this discomfort is very similar to osteoarthritic pain — it is worse when the patient first starts moving and then tends to improve once they have taken a few steps.  The degree of pain was highly variable, but the radiographic findings were relatively constant.  The stems appeared to fit tightly in the femoral canal on the AP X-ray, but the lateral view would demonstrate a radiolucency around the stem that to my eye, suggested that the stem was primarily loose about the longitudinal axis of the femur.

accolade stem total hip osteointegration lateral radiograph accolade osteointegration

Here are two radiographs (click on the thumbnails to enlarge them) of a stem that has not properly integrated with the bone.

In this picture, I’ve put dots around the radiolucent lines in the femur that indicate that the stem is rotating on its longitudinal axis.

Just recently, a report was published out of the department of orthopedic surgery at Lennox Hill hospital in New York City, reporting similar findings.  In this report, the senior author found that this same type of stem failed to achieve osteointegration in 4.7% of a series of nearly 300 patients.  This surgeon reported that he switched from the posterior approach to the anterior approach towards the end of the study period but the number of anterior approach patients was too small (16 patients) to draw any conclusions about whether this mode of failure was more or less likely with the anterior or the posterior approach.  The orthopedic surgeon who published this report concluded that the cause of failure was due to the geometry of the proximal portion of the femur, which in some cases, resulted in a tight fit between the distal, smooth, and non-porous coated portion of the stem, leaving the proximal portion of the stem without the contact and stresses required to achieve osteointegration.  In his study, larger male patients were more likely to fail to achieve osteointegration, and he concluded that this was because their proximal femoral geometry was ill-suited to the tapered design of the Accolade stem.  Interesting, the author also concluded that this may be an “underreported” phenomenon, since he was not aware of any other papers specifically documenting this type of failure of osteointegration.

For a complete PDF of this article click here: Distal Fixation of Proximally Coated Tapered Stems May Predispose to a Failure of Osteointegration.

It is difficult to know for certain, but I hypothesize that another potential reason why this stem may fail to integrate in a minority of my patients after an anterior approach is because their speedy recovery and fast rehabilitation puts too great of a stress about the “rolling axis” (to use a term borrowed from aviation) of the component before the stem can be adequately stabilized by ingrowing bone.  In my cases, the stems never moved on the AP view but they definitely were unstable on the lateral view, and the radiolucent lines that are present seem to suggest that the stem rocks back and forth when downward pressure is put on the femoral head.  This is the type of load that would be encountered when the patient goes up stairs, leading with the operated leg — a movement that we call single leg stair climbing.  I believe, but I do not know for certain, that some patients with a less favorable geometry of the proximal femoral canal, coupled with a very fast recovery and a quick return to normal activities that are the hallmarks of the anterior approach, are more likely than others to develop this complication.

 

The degree of disability created by this micromotion is very variable.  Some patients are barely bothered at all, and in a couple of cases, I have had to revise the femoral components of patients with thigh pain and place a different implant on the femoral side.  The revisions have resulted in a dramatic improvement in the presenting complaint of thigh pain after a total hip arthroplasty, and in each case, the femoral component that was removed was indeed loose with no evidence of solid ingrowth.

 

This year, at the annual meeting of the American Academy of Orthopedic Surgeons, there was a series of presentations on “high performance total hip arthroplasty”, which was variably defined by the presenters but essentially seemed to mean a total hip in a patient that returned to playing singles tennis, running, active combat military service, or surfing, for example.  In those cases, the femoral components were said to be in a very “high torque environment” and it was noted that a key feature of total joint replacement in a very active person was some degree of thigh pain.  I believe that this condition may be more likely following an anterior approach to the hip since there is less surgical disruption of the short external rotators of the hip, a faster return to normal hip function, and possibly an increased ability to perform athletic activities.

 

As a result of these cases where the stem did not osteointegrate completely, I have switched to a “fit and fill” design or a “reduced distal diameter design”  that is intended to occupy more of the space in the proximal portion of the femoral canal.  In my mind, increased filling of the femoral canal and a larger area of contact between the ingrowth medium and bone provides increased resistance to movement of the stem about the longitudinal, or axis of roll, of the component.  Time will tell.

AP xray osteoarthritis left hip lateral xray osteoarthritis pre-op AP radiograph citation fit and fill prosthesis fit and fill stem design lateral xray

This series of pictures illustrates the use of a “fit and fill” femoral stem design on an elderly female patient with osteoarthritis of the left hip.  Click on the thumbnails to enlarge.

Leave a Reply

Your email address will not be published. Required fields are marked *