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Uncertainty and lack of data complicate use of short-stem total hip implants
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Hip implants featuring a shortened femoral stem are designed to preserve bone stock during total hip arthroplasty while offering a more physiologic replication of normal human anatomy compared with longer stem prostheses. Nearly a decade after their release, surgeons continue to experiment with their use and some find them as effective as longer stem hip prostheses.
“We have implanted over 2,000 [short stems] and have had excellent early results and function similar to their long stem counterparts,” Keith R. Berend, MD, of Joint Implant Surgeons, Inc. in New Albany, Ohio, said.
However, there is a growing sense among orthopedic surgeons that, despite a strong theoretical basis for their use, clinical data may be as of yet lacking on whether short-stem hip implants fulfill their potential. Questions remain about what types of patients benefit from their use, the optimal surgical technique for their insertion and whether they can replace or supplement the current total hip arthroplasty (THA) implant offerings.
Short-stem THA has generated interest in the United States and Europe. Although consensus on short-stem hip arthroplasty remains elusive, some experts believe this option, which tends to foster less invasive surgery, has significant clinical benefit.
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Image: Adams JB |
“The introduction of the short-stem implant has extended the range and indications of minimally invasive hip arthroplasty,” Dieter C. Wirtz, MD, of University Hospital, Bonn, Germany, told Orthopedics Today. “When used within their indications and implanted correctly, the short-stem implants are comparable in their risks of instability, fracture or failure to a conventional uncemented hip prosthesis.”
Preserve normal anatomy
In general, short-stem implants are designed to require less resection of the upper femur and/or less reaming of the femoral shaft. This serves a dual purpose of facilitating future revision while providing a postoperative state that closely mimics the originally functioning hip.
“Some believe that a more physiological result is obtained as the bone and proximal femur retains its normal morphology,” Orthopaedics Today Europe Editorial Board member Professor Fares S. Haddad, BSc, MCh (Orth), FRCS (Orth), FFSEM, of University College London, said.
Wirtz noted that “the prostheses mimic the physiological situation of force transduction from the hip joint into the femoral bone, where the metaphysis will take up the major part of the loading. This will prevent bone loss by stress shielding in this area.”
The specific preservation of femoral neck and a properly designed short-stem implant allow correct stress distribution and avoid stress, according to biomechanical stress distribution theories by Joseph Fetto, MD, and Peter S. Walker, PhD. These theories led to the creation of the Proxima short-stem hip (DePuy Orthopedics, Inc., Warsaw IN) designed by Francesco Santori.
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The Proxima design succeeded in its goal to preserve bone, but only focused on the medial lateral dimension and failed to achieve good fixation against flexion, extension or rotational forces on the prosthesis, according to Fetto.
Fetto and other researchers at New York University (NYU), developed a similar, lateral flare design, the Revelation Lateral Flare Total Hip System (DJO Surgical, Austin, Texas).
“When the Proxima was in the hands of residents or doctors who were not paying attention to the technical details of surgical technique, they tended to put them into varus or flexion because there was no stem to guide them for alignment,” Fetto said. “We used the geometry as a proximal body, and we put a stem on it so it would force people to stay in proper alignment. To maintain loads in the proximal zones 1 and 7 of the femur, we made the stem tapered and polished so it would discourage any ongrowth or loadsharing below that level in the femur.”
The learning curve
A significant learning curve exists for implanting these designs. Shorter stems translate to less accurate placement. Longer stems allow orthopedists to slide the device down the canal to orient the stem, according to S. David Stulberg, MD, of Northwestern University Hospital.
“It’s possible to put the stem in a little off kilter so the proper positioning is important and maybe an issue in these shorter stems,” Stulberg said. “The big issue is you have had many of these stems on the market that have been successful longer and have relatively little fixation proximally and when you shorten those stems, the question is whether they will work. Those are the ones you have to be watchful for.”
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Fetto sought to avoid this issue with the lateral flare stem. In its design phase, the researchers at NYU were able to show that there was no learning curve because the stem was developed to be inserted reliably from day one using alignment guides.
“We developed instruments to fix the broach handle so that while you are putting the prosthesis in, you will be in proper alignment similar to an external alignment guide for a total knee device,” Fetto said. “Other devices do not force you to do that, which leads to a lot of positioning errors. If you are not in the right position, the alignment guides will tell you.”
Rest fit vs. press fit
Shortened standard noncemented stems pose a risk for fracturing the femur. Fetto said he and Walker have eliminated this complication with the lateral flare stem’s ability to rest fit rather than press fit. A rest fit design, Fetto noted, allows the device to rest on the femur “in contrast to the traditional press fit of non-cemented femoral components.”
He added, “Wherein the latter are pounded into the femur, gaining initial stability and fixation analogous to a nail into a piece of wood. This is the primary reason why simply shortening an existing non-cemented design is at risk for causing a fracture of the proximal femur at the time of insertion. This risk of complication occurring is further increased in certain surgical approaches, which may limit adequate exposure of the femoral canal.”
Minimally invasive surgery
As minimally invasive surgery evolves, surgeons have reduced the size of stems to enter ever smaller incisions. But when you cut off the stem which, according to Fetto, gives the initial fixation and is essential for osseous integration, you remove the lifeline for a stable construct.
However, many surgeons continue to laud the ability of the short stem to accommodate any type of surgical technique including posterior, posterolateral and the direct anterior approach.
“There is the issue that as the anterior approaches become popular, inserting a stem of the conventional length is very difficult from the anterior approach,” Stulberg said. “You cannot really put a longer stem in consistently without potentially fracturing the femur or taking away soft tissue you are trying to preserve to get access to the femur.”
“If you are going to do an anterior approach, it is important to consider the design of the stem, both from the point of view of the length of the stem and the point of view of the geometry at the top, to make sure you can insert it accurately and safely,” he said.
Berend recommended a true broach-only technique, where the surgeon must fill the canal proximally without hanging up distally on the cortical diaphysis, which is important for long-term fixation.
Younger, more active patients
The overarching rationale for short-stem implants is the preservation of bone within the hip area.
“Young people have better bone and it is very possible in their lifetimes they may need their implants revised, so you want to have as much bone as possible,” Stulberg said. “Hopefully, you will have bone preserved that will allow you to put in another stem effectively that will be very durable over a long period of time.”
Some surgeons noted that the concept of a “young” patient remains ill-defined. While some view the label in terms of age, others interchange the word “young” with “active,” extending indicated use to populations that may be older, but who place high demand on an active lifestyle.
“We are using the short-stem THA in active patients below the biological age of 65 in males and 60 in females, with a high demand to their joint function and good bone quality,” Wirtz said. “In combination with a ceramic-on-ceramic bearing to minimize wear and attrition, we mainly see the advantages of the short-stem implant in the minimal invasive operative technique and the possible benefit for subsequent revisions.”
However, it is thought that using such implants in younger, more active patients may preselect for a population with greater odds for revision. In turn, the increased chance of future revision inherent to younger, more active populations may artificially skew reported revision rates, creating a perception that short stems are more prone to failure.
“With the lower age at the time of primary arthroplasty, the risk of a subsequent need for revision in the years to come rises,” Wirtz said.
However, a recent study conducted by Berend et al showed that patients of any age may benefit from short-stem THAs. Berend and his team examined 1,800 consecutive short-stem microplasty implants in 1,563 patients with an age range of 27 years to 96 years old. Half of the patients underwent the anterior supine minimally invasive approach. At 7 years, the surgeons revised 17 stems for a 1.1% failure rate. Complications included four deep infections, one intraoperative shaft perforation, one knee instability, two failures of ingrowth and nine periprosthetic fractures.
“If it is easier and maybe it preserves the bone, and maybe it loads the bone differently, those things remain to be proven,” Berend said. “But if the fixation is just as good with a 98.9% success rate at 7 years, why not use it?”
Typically, reports have shown that revision has been required for instability, fracture or failure of the original implant.
“Personally, I think there is a greater risk since the implantation is technically more demanding. But, it is too early to answer the question,” Gerold Labek, MD, of Innsbruck Medical University, Innsbruck, Austria, said.
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While there are no definitive answers on whether short-stem implants are in fact more prone to fracture, instability or other types of implant failure, neither is there sufficient data on their performance. The risk-benefit analysis is decidedly incomplete, and it may well turn out that some inherent shortcomings are acceptable if more positive effects can be proven, Labek said.
Long-term data lacking
Since they are relatively new to the orthopedic marketplace, there is limited clinical data on short-stem THA.
Data is lacking on one type of short stem, neck-preserving stems, which are mainly used in Europe, according to Berend.
“There are no good studies in the United States on neck-preserving stems,” Berend said. “We do not have any proven implants in the United States that we have much experience with so there may well be a downside and there may be patients where it is contraindicated.”
But with micro-stems or ministems, there is a 99% success at 7 years which “is comparable to any other series of any other implant,” according to Berend.
The smaller size of the implant may also present specific operative issues, namely with decreased surface area for fixation. According to Haddad, “there is a greater risk of failure by aseptic loosening.”
“In terms of gaining fixation, some of these require a very tight fit and as a result there is a slightly increased risk of fracture,” he said.
“Undersizing of the stem is a concern,” Berend said. “The shorter the stem, the more easily it can change in its alignment and get stuck in the proximal femur. It will feel tight, although it will not be appropriately sized, and that can lead to early failure of ingrowth or a periprosthetic fracture.”
Defining indications
Not all surgeons agree on indications for use. Labek said he does not use short-stem devices in his practice, but noted they may be used virtually interchangeably with conventional stems if all other patient parameters are equal — namely that there is sufficient bone stock to support the implant and subsequent load transfer.
Berend agrees short stems can be used in essentially the same kind of patient as a conventional stem.
“I do not think short stem will replace conventional stems, but in many surgeons’ hands, they are easier to put in and are a little more bone conserving, so there is no reason not to use them,” he said.
Short-stem THA has been studied in a wide variety of patients, but many surgeons believe young, active patients will benefit most from its use. Regardless of age or activity level, the patient’s anatomical condition is a key to the ultimate success of implantation.
“In patients with poor bone quality, severe osteoporosis or a femoral head necrosis reaching into the metaphyseal region, the indications are limited,” Wirtz said. “A thorough patient assessment, with special regard to the metaphyseal bone quality and biomechanical situation of the affected joint, as well as thorough surgical planning, precise osteotomy and correct positioning of the implant, helps in maximizing long-term stability of the implant.”
But according to Berend and Stulberg, short stems may be indicated in patients of any age. Stulberg et al are publishing a study in Clinical Orthopaedics and Related Research noting that the stems are just as effective in older patients as younger. Stulberg and colleagues performed THAs in 185 consecutive hips in patients undergoing primary total hip replacements with the Citation (Stryker, Kalamazoo, MI) short-stem metaphyseal-engaging device. There were no contraindications for the procedure. The team compared patients older than 70 years with those younger than 70 years with regard to clinical outcomes, complications, bone remodeling on X-rays and quality of fixation. The results between the two groups were identical at 4 years, Stulberg said.
“Correctly designed, they can be used in the large majority of patients,” he said. “Stems that have extensive contact in the metaphysis in the proximal portion of the femur just below the neck cut are the ones in my experience that are going to be the most stable initially, will not come loose, and provide the best opportunity for good bone retention and remodeling. Metaphyseal engaging and short stems would be reliable.”
To others, the lack of long-term follow up complicates how readily short stems are being used, largely because there remains sufficient uncertainty about not only how to use these devices, but also for whom they are indicated.
“Like many innovations, some [devices] have performed extremely well, whereas others unfortunately have seen early failures and a narrowing of their indications,” Haddad said. “This is an area where it is critical that the best standards for introduction of innovation by prospective randomized studies and careful registry data collection are maintained, such that major mistakes do not occur.” – by Bryan Bechtel and Renee Blisard
References:
- Lombardi AV. Short stems in total hip arthroplasty are successful. Presented at British Hip Society Travelling Fellows Symposia. September 11, 2011. New Albany, Ohio.
- Stulberg SD, Patel R, Smith M, Woodward CC. Metaphyseal engaging short stem femoral implants in patients older than 70 years. Clin Orthop Relat Res. In press.
- Keith R. Berend, MD, can be reached at Joint Implant Surgeons, Inc., 7277 Smith’s Mill Rd., Ste. 200, New Albany, OH 43054; 614-221-6331; email: berendkr@joint-surgeons.com.
- Joseph Fetto, MD, can be reached at NYU Medical Center, 530 1st Ave., Ste. 5B, NY, NY 10016; 212-263-7296; email: joseph.fetto@nyumc.org.
- Fares S. Haddad, BSc, MCh (Orth), FRCS (Orth), FFSEM, can be reached at Institute of Sport, Exercise & Health, Division of Surgery & Interventional Science, 4th floor, 74 Huntley St., London, UK WC1E 6AU; 44-207-935-6083; email: fares.haddad@ucl.ac.uk.
- Gerold Labek, MD, can be reached at Anichstrasse 35, Innsbruck A-6020, Austria; 43-512-504-81600; email: gerold.labek@efort.org.
- S. David Stulberg, MD, can be reached at Northwestern University Hospital, 680 N. Lake Shore Dr., #1068, Chicago, IL 60611; 312-664-6848; email: jointsurg@northwestern.edu.
- Dieter C. Wirtz, MD, can be reached at the Clinic of Orthopaedics and Traumatology, University Hospital, Sigmund-Freud-Str. 25, D-53105 Bonn, Germany; 49-228-287-14170; email: dieter.wirtz@ukb.uni-bonn.de.
- Disclosures: Berend is a consultant to and receives royalties and institutional research support from Biomet. Fetto is a consultant to DJO Surgical Corp. and the author of the lateral flare design concept for New York University, who owns the patent to the lateral flare device. Haddad, Labek and Wirtz have no relevant financial disclosures. Stulberg is a consultant to Innomed, Aesculap, Stryker and Zimmer.
What are your indications for using short-stem total hip arthroplasty?
Cases of specific anatomic abnormality
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Reliable femoral fixation can be obtained using a broad range of uncemented stems with different design rationales, including short femoral stems. Currently, I only use short stems to address a specific anatomic abnormality that would pose a problem for a conventional length stem, such as an excessively bowed femur or femoral deformity secondary to trauma, congenital hip abnormality or previous surgery. For routine total hip arthroplasties (THAs), I use a standard length cementless stem with an established 20 year survivorship of more than 90% that is suitable in the vast majority of patients and bone types.
Proponents of short stems claim they are bone preserving and may reduce stress shielding. However, most of the current short-stem designs available in the United States have the same proximal geometry and design rationale as standard length stems, gain fixation in the same location, and thus, load the proximal femur in the same manner. Short stems are also touted as facilitating less invasive surgery, specifically with respect to the direct anterior approach where femoral exposure can be challenging. While I am a posterior approach surgeon, I do question the rationale for allowing the surgical approach and exposure to dictate implant choice.
Early clinical results with short femoral stems are promising and they do represent another option for femoral fixation in THA. However with such reliable and reproducible results with conventional uncemented femurs, when I think about short stems, I am still left wondering, “When is less more?”
Mark Dolan, MD, is an orthopedic
surgeon with Northwestern Orthopaedic Institute in Chicago, Ill.
Disclosures: Dolan has no relevant financial disclosures.
Applicability for most cases
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My indications currently are that I use the short stem in about 99% of my patients. The rationale for why I switched from the standard stem to a longer stem is that I am using a tapered device, and the tapered device allows it to load the femur in the proximal region or upper region in order to deliver the stress to the proximal femur in order to preserve femoral bone stock.
We and others have started to rethink why you actually need a stem to engage further down or distally in the femur. We would rather have the implant itself engage the proximal femur, load the proximal femur and preserve the proximal femur. I think that we have shown ourselves and others that if the purpose of the stem is to prevent the implant going into what we call varus alignment, all taper stems that are placed in a varus alignment function fine. We do not see that as the purpose of a stem. We also know historically that there are stems on the market that have various diameters of the distal stem that are tapered that seem to work fine.
So we have moved into using short stems. I would say now, the majority of our patients like them, it is an easier revision because you violate less bone stock and it is easier to put in, so it facilitates shorter length incisions and different approaches. We have done over 1,800 and have had a tremendous success to date having started doing these in 2006.
Adolph Lombardi, MD, is an orthopedic
surgeon and president of Joint Implant Surgeons, Inc. in New Albany, Ohio.
Disclosure: Lombardi is a consultant to and has intellectual
property with Biomet.