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Symposium: Redefining total hip replacement for active patients

Issue: Issue 5 2007

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David Hamblen, PhD, FRCS: Over the years, advances in total hip replacement (THR) surgery have broadened the range of hip system options and promoted the development of smaller implants that are less invasive in terms of bone removal. As more young patients experience hip joint disease, technological advances strive to maintain quality of life and mobility and preserve bone and soft tissue for these active patients. Plasma-coated, short hip stems may offer alternative and enhanced solutions to patients.

One such option is the uncemented titanium Metha prosthesis, which offers a modular implant with six stem lengths with a microporous texture and a microcrystalline calcium phosphate coating. The prosthesis also features a choice of nine neck connections, allowing the ceramic or metal head to be placed in anteversion, retroversion, or neutral, and at an angle of 130°, 135°, or 140°.

Our panel of international hip surgeons will be discussing their experience with this and other similar implants and the indications and technique for its use.

What is the proportion of younger patients with arthritis in your practice, and how often do you perform THR on patients younger than 60 years old?

I have treated an increasing number of younger patients in the last 5 years. —Reinhard Steffen, MD

Reinhard Steffen, MD: Many patients interested in modern hip replacement search the Internet and come across new concepts such as hip surface replacement, minimally invasive surgery, and short hip stem prostheses. I have treated an increasing number of younger patients in the last 5 years. Currently, one-third of THR patients in my private practice are younger than age 60.

Ralf H. Wittenberg, MD: I live in a more rural area of Germany where the patient group is more willing to accept some disabilities and pain than are other populations. They may cope with hip pain for 10 years before seeking THR. Living in a rural area, older patients tend to be biologically young and active, which is why I would perform THR with a short hip stem prosthesis on patients up to 70 years old.

Philip Housden, MD: The average practice in the United Kingdom has approximately 2% of THR patients younger than age 60, but in my practice the rate is 20%. Patients frequently come to me with clear demands of what they want; some patients come with Internet research in hand and the hopes of achieving a completely normal hip, which is not always feasible. Surgeons must balance the risks involved with THR when treating younger patients. I often counsel younger patients on the limitations of hip replacement and discuss waiting until they are slightly older before undergoing the procedure. I have performed hip resurfacing as a surgical option in younger, active patients since 1997.

Henry R. Boucher, MD: About 20% of my patients undergoing THR are younger than age 60. In the United States, marketing is aggressive, and demand for less invasive surgery and surface replacement is increasing. Short hip stem THR, which may be less invasive on both bony structures and soft tissues, is an attractive option for younger patients. Currently, in the United States, however, short stem prostheses are rarely used.

Marcin Milecki, MD: In my hospital practice in Poland, about 40% of patients undergoing hip replacements are younger than age 60.

Francesco Falez, MD: About 30% to 35% of my patients undergoing THR are younger than age 60. A growing number of younger patients are requesting total joint replacement today than in the past because people tend to remain active well past age 60. The surgeon’s goal is to offer patients minimally invasive, soft tissue- and bone-sparing procedures, and a quick recovery period. THR is moving away from use of a diaphyseal, invasive stem to one that conserves more bone stock, allowing for better function and easier future revision.

THR vs surface replacement

Hamblen: What are the relative indications for surface replacement?

Falez: The indication for surface replacement depends on variables such as patient age, bone quality, pathology, and the severity of joint deterioration. I restrict surface replacement to patients younger than age 50, active, and motivated for surgery. Surgeons must inform patients that surface replacement may require revision in the short term. Between 2% and 4% of patients who undergo the procedure require revision because of neck fracture or avascular necrosis of the femoral head.

Patients who undergo THR with a short stem, however, may have the same risk for revision as patients who undergo THR with a conventional stem with a 96% survival at 10 to 15 years.¹

Steffen: My experience with the modular cementless short hip stem (B. Braun Aesculap) for THR has not shown a severe risk of implant failure due to patient activity. Also, I find that anchorage with a metaphyseal implant is better than with a diaphyseal implant because the metaphyseal implant has more dedicated proximal load transfer.

Housden: The surface replacement early failure rate within the first few postoperative years is higher than that for THR during the same time.² In my experience with performing about 300 surface replacements, I have not observed as many late failures (up to 10 years) with surface replacement. Most early surface replacement failures are from fractures. I feel that avascular necrosis is a relative contraindication. I find that when patients are fully aware of the benefits and risks of surface replacement, they are more likely to accept possible failure and subsequent revision. I have revised about nine surface replacements, some with a short metaphyseal bearing stem. In my experience, patients who had fractures or dislocations after surface replacement often are the patients who have deformed proximal femoral anatomies.

The difference between surface replacement and THR is that surface replacement conserves bone and THR conserves soft tissues. A THR with a short stem, however, conserves host bone and soft tissue.

Bone quality is an important factor for THR. Patients with hip dysplasia…may not be good candidates for short-stem THR. —Marcin Milecki, MD

I think that THR with a short hip stem is more flexible than surface replacement.

Boucher: When offered a choice between surface replacement and THR with a conventional stem, most of my younger patients choose surface replacement. With appropriate patient selection based on criteria such as non-distorted anatomy and good bone quality, and meticulous surgical technique, early complication rates are low and patient satisfaction is excellent.

Short-stem option for most patients

Hamblen: Are there any anatomical contraindications to THR with a short metaphyseal hip stem prosthesis?

Steffen: Most patients are good candidates for short-stem THR. Dysplasia on the acetabular site, however, may be a contraindication in some patients.

Milecki: Bone quality is an important factor for THR. Patients with hip dysplasia have extremely thin femoral bone, and may not be good candidates for short-stem THR.

Falez: In younger patients, avascular necrosis, trauma, posttraumatic deformities, and hip dysplasia are often indications for THR, and implant choice should be based on age, level of activity, and bone quality. I never perform surface replacement on patients with hip dysplasia because the deformity cannot be corrected with this procedure; surface replacement does not alter the biomechanical changes that led to joint degeneration. I may perform short-stem THR, however, depending on the severity of the patient’s dysplasia. A patient with significant dysplasia is not a good candidate for short-stem THR because the anatomy of the femur is not designed to hold a metaphyseal stem in the manner required in this procedure.

Hamblen: Is obesity a contraindication for THR with a metaphyseal short stem?

Steffen: I implant a metaphyseal short stem in patients who weigh up to 120 kg, which is similar to weight considerations for conventional hip replacement.

Housden: I restrict metaphyseal short-stem THR to patients with body mass index less than 40%, but there is little evidence to show that obese people who are mobile have poor outcomes with THR. Obese patients who are less mobile, however, are more likely to have more osteoporosis. Therefore, I often implant a cemented or hybrid THR in obese patients who are younger than age 60 and have few demands.

Hamblen: How does aging affect bone quality? Is advanced age a contraindication for the short-stem implant?

Wittenberg: I think that all patients with good bone quality are candidates for implanting a short-stem prosthesis (Figure 1). Surgeons can achieve good proximal fixation in patients who have adequate bone stock. Patients with poor bone quality or patients who have metabolic diseases are not good candidates for this implant.

My preferred indication is an active patient up to age 70. There is no morphologic or biomechanical evidence to restrict surgeons from performing short-stem prosthesis THR on patients older than age 55. I inform older patients, however, that if I find insufficient bone structure during THR, I will instead implant a conventional hip stem prosthesis. The clear message is that the implant must be a lasting solution for patients. I do not advocate implanting short-stem prostheses as an intermediate solution. For me, the short-stem prosthesis must be viewed from a lifelong perspective.

Steffen: Bone quality is a significant issue for older patients. As a person ages, the inner diameter of the femur and the diameter of the femoral neck increases because of osteoporosis. Therefore, with an older patient, the surgeon cannot secure an anchor in the metaphyseal part of the stem. Globally, the older population is becoming more active and demanding, and I implant a short stem in patients up to 70 years old. Bone density measurements are not necessary, and active patients often have better bone quality than inactive patients.

Falez: I implant a short hip stem in patients up to about 75 years old. I think that bone quality rather than patient age determines whether a short-stem implant is appropriate. An active 75-year-old patient with good bone quality should be offered the possibility to have a less invasive, high-functioning short stem.

Boucher: A 70-year-old man who is active in sports but who recently cut back his activity level still has adequate bone quality for both conventional and short-stem THR and for surface replacement. A 70-year-old woman, on the other hand, has a different bone mass, and short-stem THR and surface replacement are riskier procedures.

Hamblen: Do you perform preoperative bone density scanning in older women to determine bone quality?

Wittenberg: I do not perform bone scans. One should not assume that there is always a correlation between bone density and fixation. Occasionally, bone density measurements may suggest that the patient has good bone quality, but fixation may be poor because the structure of the bone is inadequate, perhaps due to heavy alcohol consumption. Severe osteoporosis can be observed on x-ray, however. If an x-ray shows that the patient has osteoporosis, I will not implant a short hip stem prosthesis, but I may use the short stem in patients who have poor or fair quality cancellous bone if they have adequate cortical bone stock.

Implant design

Hamblen: Please discuss the design of the Metha implant. How does it differ from the Mayo Conservative Hip (Zimmer Inc.) and other short stem designs?

Steffen: The Metha and the Mayo hip stems share some similar design concepts, but surgeons have more clinical experience with the Mayo stem (Figure 2). The handling of each design’s instruments is similar; however, I find that the Metha is more curved and therefore, easy to implant.

The stem has a modular design. Surgeons can manipulate the position of the femoral head after placing the stem and can influence offset, anteversion, and retroversion. Surgeons can also optimize the positioning of the femoral head to the position of the cup. With the cup in a fixed position, the relationship between head position and cup position can be optimized. In my experience, the stem provides a good range of motion and smooth motion when moving the neck after placing the cup and head.

Falez: I have performed about 200 THRs with the Mayo implant since 1999 and have observed 1% biologic failure due to implant loosening when polyethylene configurations were used.

The modular neck design of the Metha implant is an advantage. During the first 50 implantations, I was able to use the same standard neck length for all patients but achieved stable hips by changing the offsets. I never observed a leg length discrepancy.

Housden: The Metha implant is a tapered stem that provides good primary stability with its osteoinductive surface, producing secondary stability. The capability to adjust neck length allows surgeons to achieve optimal anteversion, leg length, and stability.

The capability to adjust neck length allows surgeons to achieve optimal anteversion, leg length, and stability. —Philip Housden, MD

Wittenberg: The ability to vary the angles is also an advantage. An additional important advantage is that the surgeon does not need to touch the trochanteric area or the muscle attachments during surgery.

Hamblen: How does a double coating with Plasmapore µ-CaP (B. Braun Aesculap) affect implant fixation?

Steffen: The porous titanium plasma coating has been used for more than 20 years. The porous titanium provides good primary stability due to the surface roughness and ingrowth. The additional layer of thin calcium phosphate is designed to accelerate bony ingrowth.^3-7

Hamblen: Is there an advantage to having a calciumphosphate surface coating?

Boucher: My impression is that an additional CaP surface coating may help speed the process of bone ingrowth, although I am unaware that a true clinical benefit has been demonstrated long term.

Learning curve

Hamblen: Is the short-stem procedure appropriate for most orthopedic surgeons to perform, or should the procedure be restricted to hip specialists? Is there a long learning curve for the short-stem implantation technique?

Falez: I do not think surgeons will experience a long learning curve. Surgeons will be able to perform short-stem THR easily after observing two to three procedures and performing about 10. The procedure is similar to implanting a conventional hip stem, and implanting the short stem requires only six instruments. Surgeons must learn how to position the stem and understand how and where to cut the neck to implant the Metha stem.

In my opinion, surface replacement is a more demanding surgery than short-stem implantation.

Milecki: I recommend that surgeons first observe several short-stem implantations performed by surgeons with experience in this procedure. This will allow new surgeons to become familiar with the tools necessary for short-stem implantation.

Housden: I have performed 15 to 20 implantations and find that the procedure is technically straightforward. In my experience, surface replacement is a more challenging procedure. Patient selection for surface replacement is also challenging.

I advise surgeons to preplan with templates before implanting a short stem and to choose the valgus neck angle preoperatively so that surgery time is not increased by the need to use too many trials.

In addition, surgeons performing the procedures will learn other pearls, such as to avoid inserting the neck adapter in upside-down.

Steffen: A hip surgeon who performs about 100 THRs each year will perhaps need to perform only 5 to 10 Metha implantations before feeling comfortable with the procedure. Surgeons experienced with conventional hip implantation will notice that the resection line at the femoral neck is different in the short-stem procedure. In addition, it is more difficult to determine the appropriate stem size, and surgeons can use intraoperative fluoroscopic control to check if it is appropriate.

Anterior vs posterolateral approach

Hamblen: What is your preferred surgical approach for implanting the short hip stem?

Steffen: Surgeons can choose any approach. Surgeons must expose the femoral neck but do not have to expose the greater trochanter area, which is sometimes difficult because there are more muscles and soft tissue in that area. Exposure for femur preparation is easier with a short stem in anterior or posterior approaches compared with standard stems. In my experience, the most comfortable approach is the direct lateral transgluteal approach.

Falez: I use either the posterolateral or direct lateral approach. A minimally invasive approach can also be beneficial because surgeons will damage less soft tissue during stem insertion.

Milecki: I use a posterolateral approach because the acetabulum can be observed easily.

Wittenberg: I prefer the anterolateral Watson-Jones approach.

Boucher: Many surgeons in the United States use the posterolateral approach for THR. The second most common approach is the direct lateral, which is my preferred approach. Because short-stem prostheses can be inserted through any incision, they can be accessed more easily with less invasive surgeries. The short stem appears easier to insert and place around the calcar than a standard straight stem because its insertion point does not require lateralization. I think that implanting a short stem using a minimally invasive approach will become common in the United States.

It is most appropriate for surgeons who are new to implanting a short stem to use their standard approach in the beginning and then move on to less invasive approaches as they become more comfortable with the implant.

Surgical technique

Hamblen: Please describe the surgical technique for implanting a short stem. What are the key points that should be stressed for less experienced surgeons?

Steffen: Determining where the surgeon should resect the femoral neck is the first step in the procedure (Figure 3). It is mandatory to preserve about 2 mm of the lateral femoral neck and perform the cut angulation about 50° from this landmark. Surgeons should also preserve about 1 cm medially. I recommend to expose the groove between the femoral neck and the greater trochanter and, from this groove, move 2 to 3 mm up to perform the femoral neck resection.

I make two cuts in a minimally invasive approach. Because this approach may induce soft tissue tension, I make the second cut just below the femoral head, remove a piece of femoral neck, and then remove the head.

My next step is to open the canal centrally with one or two smooth awls. Then, I rasp up to the size I measured by x-ray and then make the first reduction. I strongly recommend to use an x-ray control because only under x-ray control can surgeons determine appropriate angulation and correct sizing. If the stem is undersized, the risk for failure increases significantly. Of the 500 short stem implantations I have performed, three patients experienced implant failure because of undersizing.

Hamblen: At this point, do surgeons inexperienced in this technique risk destroying the lateral side of the neck?

Steffen: The risk for destroying the lateral side of the cortex occurs only at the beginning of the procedure. After that, surgeons do not need to steer the rasps. The rasps follow the direction of the femoral neck and move slightly into anteversion, until coming in contact with the posterior-lateral cortex.

The entrance of the femoral neck should be filled, but the surgeon will succeed by going up one more size. I have never split the femoral neck with the rasp but split it twice during implant insertion. There is always a difference between rasp position and stem position. In my first 10 procedures, I learned to position the stem 2 to 3 mm above the rasp insertion level.

Wittenberg: Surgeons will not damage the lateral side of the cortex if they leave the femoral neck long and cut it only slightly. I recommend using x-ray to observe osteophytes of the head and then measure down from the osteophytes of the head or from the landmarks on the head.

Hamblen: Next, how do you prepare the socket before you put in the chosen neck connection to stop the risk of fretting corrosion from contamination with biological debris?

Wittenberg: Previously, I hammered in the final prosthesis with the trial neck, removed the trial neck, checked that the surface was clean, and then inserted the original neck. Currently, all trials are performed with the rasp, and I assemble the implant on the table, as the trial reduction provides precise feedback on the necessary neck length.

Determining appropriate modularity

Hamblen: How does the surgeon determine the appropriate modular options for the neck?

Steffen: I normally determine neck and head components when I have the final rasp in. Depending on the visible part of the head that I can also feel in front of the cup, I determine whether more anteversion is necessary. Retroversion may be required when I feel too much of the head surface. Therefore, with a shape of the trial head, I can estimate the anteversion of the head against the cup position (Figure 4). Depending on the amount of the trial head I can feel in front of the cup, I can decide whether to use anteversion or retroversion. Angulation can be determined by x-ray.

Housden: I prefer to determine preoperatively whether I will use 130°, 135°, or 140° offset. I recommend that surgeons have as few variables as possible during surgery because, especially with new nurses and a new surgeon, determining the different variables during surgery will make the procedure more difficult.

Falez: Intraoperatively, I feel the positioning of the femoral head in relation to the cup that is already in position. I use trials to determine which size will provide better stability and hip function. In my experience, the different angles of offset are more useful in providing stability than the options of anteversion or retroversion.

Milecki: I usually determine offset preoperatively using x-rays, and I choose head size and neck type intraoperatively. After using the last rasp (with the neutral neck) and the trial head, I test possible dislocation positions, especially in flexion and internal rotation. If I still have doubts, I use different trial necks after implanting the stem. I often use anteversion necks.

Navigation vs x-ray

Hamblen: When should surgeons use hip navigation systems?

Steffen: I use hip navigation in 80% of my procedures to determine cup position only, and patients are in the supine position. The system is helpful for patients with dysplastic hips because I can choose the new cup position.

Boucher: In the United States, most patients are on their sides during THR. Navigation, however, is easier to perform when the patient is supine because the position allows for better access to the anterior pelvic plane. Navigation can be used to optimize component position, but it adds time and a learning curve in the operating room.

Hamblen: Would navigation be advantageous for surgeons with limited experience implanting a short-stem prosthesis?

Wittenberg: I think that only surgeons who use navigation routinely will benefit from using navigation during short-stem THR. Otherwise, the less experienced surgeon will struggle with learning navigation as well as the new surgery.

Hamblen: Do you recommend that surgeons use intraoperative x-rays?

Housden: I think it is difficult to take intraoperative x-rays while performing surgery using the posterior approach.

Falez: I occasionally use intraoperative x-rays for making further corrections of the stem position, when needed, but not for sizing. The x-rays are used more for stem positioning, especially with a short stem.

Ceramic-on-ceramic head

Hamblen: Do you prefer to use a metal or ceramic head?

Steffen: In my 20 years of experience, ceramic-on-ceramic demonstrates excellent outcomes.^8-12 Neither breakages nor squeaking is a problem in the institution where I practice.

Boucher: Ceramic-on-ceramic bearings were FDA-approved for use in the United States in 2001. Concerns exist regarding ceramic-on-ceramic, however. Surgeons worry about the risk of fracture, although the risk is low. Surgeons are also concerned with squeaking, and a center recently reported a 7% squeaking rate. The exact cause for the squeaking is unclear, but edge loading and component design seem to be the most plausible causes.^13-15

Clinically, I have used both metal and ceramic heads in THR and have achieved good results. I have not had any squeaking with ceramic bearings, but I have one patient who had transient squeaking in a metal-on-metal bearing.

Housden: Some patients who undergo surface replacement may be relatively conservative with activity level for about 1 year. After approximately 9 months to 1 year, when they feel confident, they may increase activity level and may start articulating parts of the metal bearing that have not been used before, resulting in squeaking. With time, however, the squeaking often subsides.

Milecki: In my experience, only one patient, who is about 2 meters tall, experienced squeaking with the ceramic head.

Falez: I prefer metal-on-metal heads. In my experience using ceramic-on-ceramic heads, patients have not experienced squeaking, but I reported two breakages due to exploding heads last year. The breakages were sudden and occurred about 4 years postoperatively. I performed revision with polyethylene cups and ceramic heads.

Hamblen: Can surgeons use metal heads with the Metha implant?

Steffen: Yes, but the standard for young patients in my practice is ceramic-on-ceramic, not metal-on-polyethylene.

Milecki: In Poland, ceramic-on-ceramic is most common, with some surgeons preferring ceramic-on-polyethylene. Currently in Otwock, Poland, surgeons use ceramic-on-ceramic articulation often because of an earlier experience with polyethylene wear in the holes of pressfit cups.

Hamblen: What size implant do you prefer? What influences your choice of implant size?

Steffen: I prefer to implant the 32-mm head, but only with ceramic-on-ceramic, because it provides better range of motion and has a lower dislocation rate than the 28-mm head.

Housden: I implant the 28-mm head, which is a universal standard for most THRs performed in our unit. The 28-mm head is a compromise between the better volumetric wear rates of the 22-mm heads and improved stability of the larger heads. With the newer bearing surfaces, my colleagues and I may be able to move toward using the larger heads without increasing wear rates.

Falez: My standard size is 36-mm or larger, providing young, active patients the maximum range-of-motion and joint stability.

Milecki: In my practice, we recently switched from the 28-mm head to the 32-mm head because of the lower risk of subluxation and increased range of motion. Also, the risk of joint impingement is eliminated because the head and the inlay do not knock into each other, therefore lasting longer.

Boucher: If I use a hard-on-hard bearing, I would use the largest head size possible for stability and range-of-motion purposes. Also, with metal-on-metal bearings, larger head sizes may decrease wear due to better lubrication.¹⁶

If I use a polyethylene bearing, head size will depend on the cup size to maintain adequate polyethylene thickness. I have concerns about polyethylene thickness, including cross-linked polyethylene, for which only 5-year results are available. If I use a size 50 or 52 cup, I will use a 28-mm head.

Surgical time

Hamblen: Does it take less time to insert the metaphyseal implant than a conventional hip replacement? How does using the new implant system affect your operating room staff?

Steffen: I think that the concept is simpler than the standard implant concept because the metaphyseal implant is available in only six sizes, and operating time for the femoral component is similar to, if not faster than, standard implantation. Minimally invasive approaches, however, add 10 to 15 minutes to the operating time because of the time spent exposing the acetabulum and preparing the socket.

Milecki: My operating room staff finds the instrumentation to be user-friendly.

Housden: I think that implanting the stem is a straightforward procedure, and operating room nurses agree that it is simple and well thought out.

Hamblen: Have you observed less femoral blood loss during metaphyseal implantation than during conventional hip implantation because the procedure does not require so much reaming of the femur?

Falez: I notice a small reduction in blood loss, about 100 mL to 200 mL, which is not a significant difference in terms of the entire procedure. I do not think that the short stem size is responsible for the reduction in blood loss, however.

Clinical results

Hamblen: What are your clinical outcomes with the modular short stem and other metaphyseal implants?

Falez: I have 8 years of experience implanting the Mayo hip stem and 2 years of experience implanting the Metha hip stem. Clinical results with these metaphyseal implants are excellent. My 8-year experience with the Mayo stem has resulted in four failures. Two of these were mechanical failures, one was an infection, and the other was a femoral fracture.

Wittenberg: My colleagues and I conducted a prospective study on 100 patients who received a short stem using minimally invasive surgery (Figure 5). Early clinical and radiologic results were good. The mean Harris Hip Score increased from 51 to 97, and pain decreased from 7.0 to 0.8 VAS at 1 year postoperatively. In addition, 97% of patients reported that they were either fully satisfied or partly satisfied with procedure outcomes.

In another study, my colleagues and I compared partial postoperative weight bearing in 89 patients and full postoperative weight bearing in 78 patients. Study results showed that patients were satisfied with either partial or full weight bearing with a short-stem prosthesis (Figure 6).

Splits in the bone near the lesser trochanter at the time of stem insertion were a complication in the series but were neither associated with instability nor visible on x-ray. Patients’ bone healed after partial weight bearing. Also, two young, active men required revision to a standard stem prosthesis for loosening after 12 and 14 months because the implants were too small.

Hamblen: Were any stem breakages reported?

Wittenberg: A few breakages have occurred in the first 4,000 stems implanted, due to failure of the neck-stem adapter made of titanium alloy. The breakages occurred between 13 and 18 months after implantation. The taper of the modular cone adapter is manufactured with a precision of some microns, which means that when it is fitted together, there is a process of cold welding. Laboratory testing has shown the strength of this modular connection goes far beyond the recommended standard loads, but this assumes a clean connection. Chemical and electron microscopy investigation of this junction in the failed cases showed the presence of biological material, from both bone and soft tissue debris, which had resulted in micromotion, accelerated wear, and fretting corrosion. Because of this finding, we now recommend using the rasp, rather than the stem to check the head position. This allows clean assembly of the definitive stem and neck adapter before implant insertion, with less risk of contamination of the connection. For increased safety, the adapter is now made of cobalt-chrome alloy with higher stiffness (less micromotion) and higher wear resistance.

Milecki: My clinical results with the Metha stem are excellent, with only one complication. A patient’s bone was fractured intraoperatively, but the patient did not experience additional complications. The same stem type was used for revision, and stem loosening did not occur.

Steffen: I have 2.5 years of experience implanting the modular short stem (Figure 7). The one-year results of our first 100 patients demonstrate 80% excellent results, which is better than my results in young patients who received a standard stem. Fifteen percent of patients have good results, and 2% to 5% of patients have poor results. Complications reported include one loosening, one sinkage due to osteoporosis, and one fracture due to the patient falling down 6 weeks after surgery. These patients underwent revision, which was simple to perform. Standard stems were used for revision, and they are easy to anchor.

Because the orientation of the femoral head is optimized, the Metha stem may function better than non-modular short stems. In addition, leg length discrepancy is not a concern with this system.

Hamblen: Do patients report any thigh pain?

Steffen: In my experience, pain has not been reported in the follow-up period.

Falez: One of my patients who received a short stem reported thigh pain, but the pain was caused by stem positioning in which the stem was impinging on the posterior cortex. A few months after conservative treatment, the pain subsided.

Boucher: Thigh pain is related to implant design, materials, size, and coating. Most standard femoral stems have thigh pain rates of 2% to 10%. Proximally coated tapered stems have a lower incidence of thigh pain than extensively coated cylindrical stems.17 In my practice, I implant proximally coated tapered straight stems, and thigh pain rate is less than 5%.

Hamblen: What is your technique for dealing with splits in the calcar recognized at the time of the stem insertion?

Steffen: For one significant calcar split, I used a circumferential wire, and for other minor cracks, I reduced postoperative weight bearing, and they healed without problems.

Hamblen: If the femoral component is well anchored by bony ingrowth, do surgeons experience difficulty in removing the stem for revision?

Steffen: A revision was required 4 months after surgery for one patient who had a perforation of the lateral cortex. Removing the stem was not difficult at 4 months, and I predict that removing the stem will not be difficult in the long term. Surgeons can easily follow the stem with a chisel and reach the end of the porous coated proximal surface.

Housden: The tapered design is also amenable to revision. As soon as the stem is disimpacted, the stem-bone bond separates. In contrast, some older, non-tapered components with large coating areas are more difficult to remove because the surgeon must work all the way down the shaft to the tip.

Steffen: Another patient had subsidence and required implant revision. The implant was too small for the patient’s bone. The patient was a 55-year-old man, but because of alcohol abuse, he had poor bone quality. The surgeon who performed the primary surgery did not know that the patient abused alcohol. We learned from this experience to press a finger into the cancellous bone to assess bone quality and, if bone quality is considered poor, then the surgeon should implant a standard hip stem.

Falez: A surgical goal of short-stem prostheses implantation is not to retain bone for possible future revision but to make revision of short-stem prostheses easier. I may revise a short stem with another metaphyseal short stem.

Hamblen: Have you ever begun implanting a Metha stem and changed the implant selection during the procedure?

Milecki: One patient’s bone quality was poor, which required changing to a straight stem. The patient was a 58-year-old woman with minor endocrinologic concerns.

Housden: I treated one patient who had a couple of pins in his femoral neck from a previous slipped femoral epiphysis, and I considered implanting the short stem. The tip of the stem, however, was close to the pin entry site, and removing the pins was difficult. I decided that the short stem would cause a stress riser at its tip, so I used a longer stem. A patient with an abnormality in the metaphyseal-diaphyseal junction may be at risk for subtrochanteric fracture.

Postoperative management

Hamblen: What postoperative care do you recommend to your patients? Do you recommend any special exercises or activity restrictions? What is your weight-bearing protocol?

Steffen: Patients should use crutches for 4 to 6 weeks. I allow full weight bearing at day 5. Patients can return to work after 4 to 6 weeks and return to full activities, including sports, after 3 months. During the first 3 months, patients must avoid extensive joint motion so that all muscles return to normal function. After 3 months, patients can walk, hike, and play sports such as tennis or golf. I recommend that patients avoid skiing for 1 year, however.

Falez: I also recommend that patients avoid activity for 3 months after surgery.

Milecki: Patients may stand up at postoperative day 1, then use two crutches for 6 weeks and one crutch for up to 3 months postoperatively. I recommend that patients avoid sports for 6 months after surgery and skiing for 1 year. Patients returning to sports activities should avoid extreme situations, such as sports in which the player must score.

Hamblen: Regarding radiologic evidence of success, does the modular short stem demonstrate any stress shielding or bone loss similar to that with some early cementless standard implants?

Steffen: Subsidence is not a problem with the modular short stem. About 1 year postoperatively, patients will develop an increase in bone density in the area of the proximal femur.

Hamblen: How early do you observe spot welding of the bone?

Steffen: I see spot welding 6 months postoperatively.

Falez: I am unsure if the Metha stem will function differently from the Mayo conservative stem. In my experience, 2-year postoperative results showed that 20% of patients implanted with the Mayo stem developed lateral cortical hypertrophy related to the positioning of the stem. In my experience, the bending of the stem forced the distal portion against the lateral cortex which caused total asymptomatic lateral cortical hypertrophy. Currently, I have not observed this in patients implanted with the Metha stem, but longer follow-up may indicate otherwise.

Hamblen: What would be the preferred radiologic follow-up for patients implanted with the modular short stem?

Steffen: I think an anterior-posterior view after 2 years is sufficient for patients implanted with a short stem. For clinical symptoms, I recommend a lateral view as well.

Falez: Metha hip function and reliability will become clearer at the 5-year follow-up. For the time being, surgeons can rely on data and experience with other metaphyseal short implants.

Looking to the future

Hamblen: Most surgeons predict that short-stem prostheses will become the new standard in THR. Do you agree? What would you like to see for the future of THR in general?

Falez: I think that short-stem prostheses are part of the future. The short stem is a step toward an implant design that more closely resembles the physiologic joint. As surgeons move toward smaller implants and away from surface replacement, another option between THR with short stems and surface replacement will develop.

The short stem is a step toward an implant design that more closely resembles the physiologic joint. —Francesco Falez, MD

Housden: The question is philosophical. Surgeons implant prostheses to create a joint that is as closely physiologic as possible. Some surgeons argue that a larger head more closely resembles the original joint. I think that interfaces are a crucial issue in new developments in THR. Interface difficulties often cause implant failure. The metaphyseal short-stem prosthesis may be indicated in many current THR cases. In addition to developments with minimally invasive surgery, nanotechnology may play a larger role in the future of THR. Robotics may be used to perform THR through smaller incisions, with remotely controlled surgery. I predict that hip surgery will be significantly different in 10 to 15 years.

Milecki: I think that stems are evolving to better resemble physiology, although they can never mimic nature exactly. I look forward to using larger heads, and I hope new cup designs will improve anchorage in the pelvis. I also hope that future prosthesis materials will achieve elasticity similar to bone.

Boucher: I think that as the metaphyseal short stem becomes available in the United States, advances in THR will continue. The stem provides a good interface for bone attachment, according to the early results, but bearing options will continue to advance. Most current implants benefit older patients, but younger patients will benefit from development of THR. Less invasive procedures, which usually focus on soft tissue, will focus on bone and continue to evolve. Navigation will also be used more commonly in THR.

Hamblen: Plasma-coated, metaphyseal short hip stems, such as this new prosthesis concept, have broadened the range of hip system options to meet the needs of active patients more effectively.

I would like to thank Orthopaedics Today International for organizing this discussion and B. Braun Aesculap for its sponsorship. I would also like to thank the panel members for their participation in this discussion and monograph project.

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