Continue reading »]]> Improving the Accuracy of Total Hip Arthroplasty

In my hands, the intra-operative xray machine called the C arm or fluoroscope is a very useful tool for improving the accuracy of total hip arthroplasty.

Direct Anterior Approach

The direct anterior approach is well-suited to using a C-arm because the patient is flat on their back and it is very easy to image the pelvis.  The C-arm has been used for fracture surgery for a long period of time, but it is difficult to position the machine easily when the patient is lying on their side.  When the patient is in the supine position (flat on their back) I can use the C arm during all of the critical steps of a total hip arthroplasty to make sure that I am making the correct choices in terms of neck cut, depth of acetabular reaming, acetabular component positioning, and femoral stem, head, and neck selection.  As an example, here is a gallery of images saved on the C arm during a typical direct anterior minimally invasive total hip.

Hip Xrays

In the first two images we see the preoperative AP pelvis and hip xrays.  The first image taken intra-operatively is the 3rd image which shows the reamer being used to remove the remaining bone from the acetabulum.  I like to use the C-arm at this point to verify that the acetabulum has been reamed appropriately and I also get a good sense of how well the cup will sit in the acetabulum.  The next image shows the acetabulum being inserted.  The C-arm is used here to control the final position of the cup, setting the abduction and anteversion.  Next the size of the femoral trial is evaluated, and finally, once the the components are in place and the hip is relocated, the operative side is compared to the non-operative side.  This process makes SURE that there are no surprises when the postoperative xray is taken in the post-anesthetic care unit.

Continue reading »]]> Please fill out the form below to schedule an Online consultation.

If you are interested in consulting with me regarding your diagnosis and treatment I have several options available.

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1. In order to save time and cost for patients, all diagnostic studies such as MRI, CT scan and X-rays and preoperative tests are usually done in the patients home town prior to surgery, if it’s needed. If you haven’t made it this far and you have questions about hip pain, please do not hesitate to contact me.
2. Once I have received your online request for a consultation, I will contact your over the phone. We’ll discuss your situation and if you have your diagnostics studies, you can either email or Fed Ex them to my office.
3. I use a service called Blackboard Connect, which allows me to explain the findings on the X-ray and the MRI scan while both of us are looking at the same image via the internet. Think of it as an office visit from your home computer.
4. At this point I will discuss with you my recommendations.

In my experience, patients report very high rates of satisfaction with this process since it affords them the opportunity to consult with a practicing surgeon without the expense associated with travel and time off work.  I can coordinate most of your pre-operative work-up via email prior to you traveling to Monterey for further consultation or for surgery.

Continue reading »]]> After performing the direct anterior total hip procedure for over 5 years now, I have learned where some of the pitfalls are in this procedure.  In my mind, the area of greatest potential concern is the degree of initial stability achieved between the femoral component and the femoral canal.  This implant needs to have a very high degree of initial stability because I encourage patients to fully weight bear immediately after surgery and return to activities as quickly as they can.  In my mind, the best strategy for prevention of blood clots is physical activity, since this allows the body own natural defense mechanisms against blood clot formation to work.

I use an uncemented femoral stem which means that the stem has to have a solid press-fit into the femoral canal and no bone cement is used.  The femoral stem is coated with a special metal layer that mimics the micro-architecture of bone.  As the bone remodels around the stem, it locks onto the minute variations in the surface of the metal and essentially makes it a permanent part of the femur.  This process is called osteointegration, and it is absolutely a requirement for a successful long term implant.  Because patients are allowed to weight bear immediately after surgery they will put a lot of stress and strain on the hip prosthesis before the bone has solidly grown into the micro-architecture of the femoral stem.

The biology of osteointegration is not completely understood and all of the major manufacturers of orthopedic implants have their own proprietary metal surfaces and coating that are designed to facilitate osteointegration.  We speculate that some stress is essential for osteointegration to occur, but too much stress occurring before the femoral stem has completely bonded to the bone may cause micromotion at interface between the bone and metal which may inhibit the process of osteointegration.  If this occurs, a layer of fibrous tissue may stabilize the stem, but in the worse case scenario, the stem is loose inside the femoral canal and becomes a source of pain for the patient.  Therefore, we try to balance early activity with the benefits of decreased blood clots, faster rehabilitation, higher patient satisfaction, and possibly even enhanced ingrowth if the stresses are appropriate, with the theoretical concerns of too much stress early on may be detrimental to the biology of integration.

Choosing the correct stem for the correct patient is a little bit art and a little bit science, and it is also influenced heavily by the maxim that if you do the same thing over and over again, you tend to get better at it.  Most surgeons in the US try to limit themselves to one or two stems for most of their index procedures.  Currently, the design that I am using is the Biomet Taperloc stem.  I believe that this stem does a good job of meeting the needs of a proximal fit and fill stem with good initial stability, ease of insertion for the direct anterior approach, has a good track record, and is manufactured by a solid company with a long history in orthopedics in the United States.  Biomet orthopedics (www.biomet.com) is on record as saying that they have over 22 years of experience with this stem design, that it has been successfully implanted in a very large group of patients, and that it has functioned well in the young and the elderly.  In my mind, the greatest advantage of this stem is the reduced diameter of the distal portion of the stem which allows for solid contact between the proximal metaphyseal area of the femur and the porous coating and decreases the incidence of post-operative thigh pain.

Balance® Microplasty™ Hip Prosthesis Surgical Technique

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The hip is a ball and socket joint in the engine room of human locomotion.  The natural motion of the hip allows us to walk, run, swim, cycle, dance (for those of us with rhythm), and enjoy our lives as upright bipeds with grace.  When the cartilage in the hip joint starts to deteriorate, the implications are profound.  People complain of pain, especially when they first start to ambulate.  They develop a limp, and as the disease progresses they start to avoid activities that they enjoy and that are good for the rest of the body and soul.

In the anatomic illustration above, we see that the hip joint is surrounded by a thick white capsule of tissue that encases the femoral head and the acetabulum.  The blood supply to the femoral head comes from the femoral artery, specifically a branch called the medial femoral circumflex artery, which is an important land mark during surgical treatment of hip disease.  Below, we have two thumbnail images of X-rays of a normal pelvis and a pelvis with osteoarthritis of the hip joint.  If you click on the images, a large version of the picture will launch which makes it much easier to see the annotation describing the various anatomic landmarks.

In this xray of an elderly female with osteoarthritis, the joint space of the left hip has been obliterated as the cartilage has deteriorated.  This hip has progressed to the point where there is bone on bone contact.  In addition, the soft tissues (the muscles and the ligaments) about the hip have started to stiffen and contract which is why she stands with an unequal pelvis, giving the left leg an appearance that it is longer than the right.  By convention, X-rays are usually displayed as if the patient were facing the viewer, but most X-rays have a marker on the film itself indicating which is the right or the left side of the patient.

Continue reading »]]> A magnetic resonance imaging (MRI) is very useful for detecting subtle abnormalities of the hip joint that may not be readily apparent on plain xray.  In the past 10 years, MRI scans have allowed us to appreciate the subtleties of cartilage and labral degeneration that cause severe hip pain well before obvious osteoarthritis of the hip develops.

For example, these are the xrays of a young woman who came to see me complaining of bilateral hip pain.  She was referred to my office after non-weight bearing films were obtained at the hospital.  She has a very low body mass index and she has no history of hip trauma but she was a dancer, cheerleader, and runner when she was in high school.

Her plain xrays demonstrate the surprising finding of a tiny cyst in the acetabulum in the area of the acetabulum where most of the stress of weight bearing is concentrated.  This may correlate with the fact that her symptoms are worse after she has been standing for most of the day.

An MRI arthrogram of the hip was obtained.  An arthrogram involved injecting the joint with a contrast material that expands the capsule surrounding the hip joint and allows us to see the anatomic detail inside the hip much more clearly.  The following two images show that the radiologist has successfully injected the contrast material into the joint because the contrast material encircles the femoral head and outlines the inside of the joint.  If the injection was not successful, we would see a smudge of contrast in the tissues outside of the hip joint.

After the arthrogram was performed, a series of different MRI sequences were used to evaluate the inside of the hip joint.

These images show that their are tiny, symmetric cysts in in the weight bearing portion of the acetabulum on both sides.  However, they do not show any evidence of labral pathology, avsacular necrosis, or classic osteoarthritis of the hip.  The cause of the subchondral cysts is a bit of a mystery.  There is a recent publication in the journal hip that suggests that these cysts may be a normal anatomic variant.  I concluded that because the anesthetic portion of the intra-articular injection did not alleviate her pain it was not possible to attribute her pain to the findings on the MRI scan.  I reassured her that she did not need treatment at the present time, but if her pain persists, we will plan on obtaining a follow up MRI scan in 1 year to make sure that the cysts have not enlarged.

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References

Cyst-like lesion of the acetabular roof – an abnormal finding or an anatomical variant?  Hip Int. 2010 Apr-Jun;20(2):258-60.  Tzaveas AP, Villar RN.  The Wellington Hospital, London, UK.

Abstract: Cyst-like lesions are frequently found in the area of the acetabulum on MRI scans. However, their presence is not always abnormal. We report four patients with such lesions found on MRI where, during hip arthroscopy, an area resembling a horseshoe-like extension of the cotyloid fossa was found. Clinicians must be aware that not all cystic acetabular lesions are pathological and may simply represent a normal anatomical or developmental variant of the hip joint. They do not always represent an indication for hip arthroscopic surgery.

Continue reading »]]> Here are a series of xrays that are illustrated and annotated to identify the anatomic landmarks and concepts that are used during total hip arthroplasty.  Please click on the thumbnail image to launch a full sized image that is annotated with the correct landmarks.

The first Xray is of a 35 year old male with no arthritis of the hip. The second Xray is of the pelvis in a 53 year old female with osteopenia.  She is post-menopausal and has a borderline osteoporosis of the hips.  Notice that the bone in the area of the calcar is much thinner and the cortex of the femoral shaft is much thinner as well.  The third Xray is of an elderly female with severe osteoarthritis of the left hip.  The first thing to notice about this film is that in contras to the 1st two films which have equal leg lengths, this Xray demonstrates apparently unequal leg lengths.  Often the legs are in truth exactly the same length, but they appear different because the arthritic process causes a contraction of the muscles and tendons about the hip.  In my practice it is of paramount importance that the xray is taken in the standing position and the patient and I agree on what will be our criteria for deciding on equal leg lengths.

In the next Xray I illustrate how leg lengths are most commonly determined and also illustrate femoral offset — the distance between the longitudinal axis of the femur and the center of acetabulum.  This is also an important measurement because increased offset is often associated with persistent post-operative thigh pain, whereas insufficient offset is often associated with a sense that the hip is weak, or unstable.

Continue reading »]]> Here are two examples of patients of mine who have had both hips replaced via a minimally invasive direct anterior approach.  The first patient is a very active physician from Alaska who developed severe bilateral osteoarthritis of the hip joints.  He was initially very reluctant to undergo surgery (no doctor likes a taste of their own medicine) but ultimately he chose to have me replace both of his joints.  In this case, we did both operations at the same time.

Here are his pre-operative xrays.  Notice how the cartilage has worn away and there is no joint space left inside the acetabulum.  Also, the lack of cartilage on the femoral head has allowed subchondral cysts to develop which are associated with severe arthritis.

and here are his post-operative xrays.  In this case, the patient’s size (he is a physically big man) and the strength of his bone made the direct anterior approach quite challenging.  Since I new he would push very hard in rehabilitation I put a cable around the proximal portion of the femur on both sides in order to prevent a crack from when he put all of his weight on both hips immediately after surgery.

And here he is skiing in the backcountry in alaska, 6 months after his operation.

Continue reading »]]> Summary of this page: Total hip arthoplasty is meant to relieve pain, allow the patient to walk with a more normal gait, and result in a highly satisfied patient.  One of the most troublesome problems after total hip arthoplasty for both patients and orthopedic surgeons is when the patient has unequal leg lengths after surgery, which is referred to as a “leg-length discrepancy”.  While there are a few immediate complications that can occur as the result of a leg-length discrepancy, such as a stretch injury to the sciatic nerve or peroneal nerve, back pain as the result of an uneven pelvis, or an abnormal gait, the most frequent outcome is a dissatisfied patient and an unhappy surgeon.  While careful preoperative planning and intra-operative techniques can decrease the chance of the patient noticing a leg-length discrepancy after the operation, a good course of action is to have the patient and the surgeon agree in advance on what constitutes equal leg lengths, define a standard for evaluating leg lengths, and then using a standardized X-ray technique for measuring leg lengths.  This ensures that every one is on the same page when it comes to this issue.  In our experience, the anterior approach has a few benefits over the posterior approach when it comes to making sure the leg lengths are equal after surgery.  This is primarily because the patient is flat on their back during surgery, which makes it much easier to control the alignment of the pelvis, and also because a C-arm — an intraoperative X-ray machine — is used in anterior hip surgery so that an objective measurement of leg lengths can be made before the procedure is finished.

Recent data produced by a oversight agency called the Joint Commission on Accreditation of Healthcare Organizations (JCAHO) listed 6 major “events” that are relevant to orthopedics out of 19 frequent adverse medical events that deserve particular attention.  These “events” are occurrences that can be seen as medical errors because they may be preventable in some instances, and in this study, leg length inequality accounted for 4.7% of the total number of medical errors investigated by JCAHO.  Other events, such as patient falls while in the hospital, are relevant to orthopedic surgeons, but their prevention is a bit more complex.

The most frequent error in limb lengths after total hip replacement is that the operated hip is longer than the native hip.  Sometimes this may be necessary in order to achieve stability of the replaced joint.  When the patient is being operated on for arthritis complicated by congenital dislocation of the hip for example, it may be necessary to lengthen the leg in order to return the hip center to its normal location.  When the leg is lengthened, it may place increased stress on the sciatic nerve, stretching the nerve, and this can produce what we call a nerve palsy.  This will typically manifest as burning pain down the course of the sciatic nerve, numbness in the lower leg or foot, and sometimes muscle weakness in the foot and leg.  If patients are left with uneven leg lengths after surgery and their gait is abnormal, they can develop low back pain or other gait abnormalities that will cause them discomfort.  However, most of the time, the most common complaint from a patient with a leg length discrepancy is just that they are dissatisfied.  Indeed, dissatisfaction with unequally leg lengths after total hip arthroplasty is the SINGLE MOST COMMON reason for litigation against orthopedic surgeons.  Lets figure out a way to avoid that from happening.

Over the years, the surgeons who choose to perform total hip arthroplasty through a posterior approach have developed a number of ways to either directly or indirectly measure leg lengths before the incision is sewn up.  These include using careful pre-operative planning with overlays that anticipate what changes in leg lengths are going to occur during the course of the joint replacement, placing markers on the pelvis and the femur so that the distance between the two objects can be measured before and after the joint is replaced, taking an intra-operative X-ray to confirm the limb lengths, and feeling the length of the legs through the drapes.  In my experience with these techniques, they are not always 100% foolproof.  Pre-operative templating is certainly helpful, but minor variations in the bone and the local anatomy can result in subtle changes in the way that the implants fit into the patient.  The use of pins that are tapped into the femur and the pelvis as a standard of measurement is not 100% secure because they can move during surgery.  Taking an X-ray with a patient lying on their side (which is the standard position for posterior total hip arthroplasty) can be very difficult, especially if it is a large patient and their position has changed on the table during the operation.  This frequently happens because once a patient is covered with all of the barriers that we use to create at sterile field — the process of “prepping and draping” — it can be very difficult to make sure that the patient is correctly aligned when the X-ray is taken.  If the patient is not perfectly square with respect to the table then the X-ray technician will not be able to get an accurate picture of the pelvis, and using the the intra-operative X-ray to assess leg lengths can be problematic.  While it is desirable to aim for a “bulls-eye” and restore the legs to exactly equal lengths, this is not always perfectly possible.  There is some debate about what constitutes an acceptable leg length discrepancy after surgery, with some surgeons advocating for anything less than 1cm (less than 1/2 an inch) as a very acceptable threshold.  It is pretty difficult to identify any problems that are realistically caused by a difference in leg lengths of less than 1 centimeter, since a large proportion of the general population has a leg length discrepancy of about 1/2 of an inch by virtue of the natural underlying asymmetry of the human body — before the ever develop arthritis or have a joint replacement.

In my hands, one of the major advantages of the direct anterior total hip arthroplasty technique is what I perceive to be an increased ability to determine leg lengths accurately.  The patient is lying flat on their back, so even if they are very large, the pelvis is still perfectly square to the table, and therefore perfectly square to the X-ray beam.  Also, the intra-operative C-arm can be used to make sure that the femoral and acetabular components are in the correct place, and in general, it is much easier (and represents less of a risk to the sterility of the procedure) to take multiple X-rays with the C-arm than it is do the same thing with a portable X-ray unit, which is what is required during most conventional setups for posterior total hip arthroplasty.

Here is an X-ray of the pelvis of someone who is going to have their right hip replaced.  A horizontal line has been drawn across the bottom of the pelvis, just touching a part of the pelvis called the ischial tuberosities.  Notice that the pelvis is perfectly “square” with respect to the viewer, and there is a high degree of symmetry in the anatomic landmarks from one side to the other.  The distance between the horizontal line and the top of the bump of bone on the inside of the femur (the lesser trochanter) is the most commonly used method for determining leg lengths.  This is because the horizontal line is a PELVIC reference, and the top of the lesser trochanter is a FEMORAL reference.  Notice that on this X-ray, the top of the lesser trochanter on the patient’s right side (this x-ray is oriented as if the patient is looking at us) is displaced superiorly with respect to the left side.  This is because the arthritic process has thinned the cartilage inside the hip joint, and the erosion of the cartilage has resulted in a progressive shortening of the limb.  The goal of a total hip arthroplasty in this instance would be to replace the joint in such a way that the distance between the horizontal line and the top of the less trochanter is equal on both side.

Here is an X-ray of a patient without arthritis, and the relationship between the horizontal line and the top of the lesser trochanter is equal.  I am trying to achieve the same relationship between the pelvis and the femur after a hip operation.

Here is a picture of a relatively large (but by no means very large) patient getting prepared to have a direct anterior total hip arthroplasty.  Notice how the patient is flat on their back so that the pelvis is perfectly square.  If this same patient were to lie on their side, it would be much more difficult to control the position of the pelvis because the “soft tissue envelope” around the patient makes it difficult to feel the landmarks of the pelvis and it also makes it difficult for the intra-operative positioners to hold onto the pelvis securely.  Bottom line — it is harder to orient large patients correctly 100% of the time when they are on their side, especially all throughout the procedure.

Here is a picture of the same patient during the middle of the procedure.  In this instance, the C-arm has been prepped and draped so that in can easily be pulled in and out of the surgical field whenever we need to verify the position of the components.  For example, in the next picture, a spot view has been taken of the acetabular reamer after preparation of the socket side of the hip replacement.  This will verify that the socket has been appropriately reamed to accept the new component.

In the second picture, the femoral stem has been inserted, and the C-arm is being used to verify that all of the components are in the correct position and that the relationship between the anatomic landmarks on the acetabular side and the femoral side of the joint replacement are all correct.