Total ankle arthroplasty: defining its clinical niche

By Hank Black

Research generally upholds total ankle arthroplasty as a viable alternative to the traditional first-line surgical treatment, ankle arthrodesis, for correctly selected patients with end-stage ankle arthritis. But complication rates associated with ankle arthroplasty remain an area of concern.

The up-and-down utilization of total ankle arthroplasty (TAA) since the early 1970s is typical of many technological advances in medicine: excitement, disappointment, repeat. Now, enthusiasm is again high and recent research suggests that improvements in materials, design, and surgical technique will allow total ankle replacement to find its proper position in the treatment of painful end-stage ankle arthritis, which affects 1% of the adult population.¹

“Replacement surgery gets a lot of attention from patients with this diagnosis and does have a role in perhaps one-third of cases,” said Canadian foot and ankle surgeon Alastair S. E. Younger, MD, who is affiliated with BC Foot & Ankle Specialists in Vancouver, British Columbia. “Yet the surgery is difficult to learn and we’ll need another four to five years to get a meaningful series of patients to compare survivorship of implant designs.”

In many cases, major complication rates of TAA exceed that of the traditional first-line treatment, ankle fusion (AF), but researchers say this is somewhat offset by the improved function associated with TAA and the potential development (or prior existence) of arthritic pathology in adjacent joints following fusion that could require additional fusions.

Other recent research generally upholds TAA as a viable alternative to conservative medical treatment and arthrodesis for correctly selected patients, including findings on perioperative complications, reoperation rates, gait, function, cost utility, diabetic or elderly patients, as well as patient expectations, satisfaction, and education.

In fact, Barg et al aver that, with current advanced materials and designs, there is no gold standard treatment; both TAA and ankle arthrodesis are important options in the hands of experienced surgeons who use careful planning and patient selection.²

The ideal indication for TAA is advanced, complete osteoarthritis of the ankle in patients with good bone quality, neutral alignment, good stability, and preserved mobility of the ankle.³ Generally accepted criteria include primary, post-traumatic, or inflammatory ankle arthritis and relatively low activity demands.⁴

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Design and materials

Results of two-component, cemented, first-generation total ankle replacements starting in the early 1970s were disappointing, with a very high rate of failure primarily due to poor design, instability, and aseptic loosening. Published failure rates were as high as 60% to 90% after five and 10 years, respectively.^5,6

Replacement systems that emerged in the mid-1980s included semiconstrained cementless designs, either mobile or fixed bearing. In the late 1990s, systems were introduced with a mobile bearing polyethylene meniscus between the tibial and talar components.

Whereas newer ankle replacements rely heavily on ultra-high molecular weight polyethylene, interest is turning to a highly cross-linked polyethylene already employed in hip and knee replacements. University of Chicago orthopedic surgery resident Oliver N. Schipper, MD, said, “This material has made a significant difference in longevity of hip implants. We think it most likely will show decreased risk of osteolysis secondary to polyethylene particles, but more research on its wear properties is needed.”

Now the field awaits large, well-conducted, controlled, long-term prospective studies of designs, including comparisons of two- and three-component implants.^2,7

Reoperations, complications

Regardless of design, the unique kinematic and anatomic characteristics of the hindfoot and ankle make arthroplasty a challenging procedure that requires a long surgical learning curve.⁸ Studies have found that surgeon experience reduces the revision rate,⁹ and some leaders believe the overall number of specialized centers for the procedure should be limited.¹⁰

Studies of complications and rates of repeat surgery at the original site of arthroplasty or fusion have been needed, partly because surgeons and health care systems use different terminology to define such complications. Younger reported on this issue at the recent American Academy of Orthopaedic Surgeons (AAOS) annual meeting in March in Las Vegas on behalf of a Canadian Orthopaedic Foot and Ankle Society (COFAS) multicenter research team that has accumulated more than 600 patients in its Prospective Ankle Reconstruction Database on surgical management of end-stage ankle arthritis.

The team developed a simple classification system for such ankle reoperation (Table 1).¹¹ They compared reoperations after TAA or AF and determined the rate was higher for TAA, with most problems relating to design issues. No reoperation was performed in 75% (86% for AF; 70% for TAA) of procedures.

As for perioperative complication rates, Schipper reported at the AAOS meeting in March that an analysis of the large National Inpatient Sample (NIS) database showed that TAA was associated with slightly but significantly lower risks of blood transfusion, nonhome discharge, and overall complications compared with AF.¹² AF transfusion risk was not high, and the great majority of patients were not transfused.

“We hypothesize the data are due to surgeons who do not perform ankle fusion frequently and may excessively burr bone in attempting to increase the rate of fusion,” he said.

Risk factors

Diabetes as a risk factor for perioperative complications in TAA and AF was explored in an AAOS presentation by Jimmy J. Jiang, MD, an orthopedic surgeon at the University of Chicago and part of the research team plumbing the NIS database. The researchers found that, for both operations, patients with diabetes have higher complication rates, longer hospital stays, and more frequent nonhome discharge.¹³ Wukich et al reported the presence of complicated diabetes was a significant predictor of operative-site infection after foot and ankle surgery.¹⁴

“Diabetic patients’ potential lack of tissue perfusion in the lower extremity is a concern that begs for careful preoperative screening for abnormal blood glucose levels. If a patient is in good blood glucose control and otherwise healthy, experienced surgeons would consider performing a replacement procedure,” Jiang said.

Obesity, as might be expected, also is an independent risk factor for postoperative complications after both TAA and AF. Werner et al, using the PearlDiver database of more than one billion patient records, concluded that the increased rates of medical comorbidities, intraoperative factors, and larger soft tissue envelopes were the likely causes of the complications, which included major, minor, local, systemic, venous thromboembolic, infectious, and medical complications. The incidence of revision TAA was also significantly higher in obese (4.9%) than nonobese patients (3.1%).¹⁵

Patients with rheumatoid arthritis also can benefit from TAA and have similar outcomes to patients with noninflammatory arthritis, according to a study by Pedersen et al.¹⁶ Preoperatively, rheumatoid arthritis patients had overall worse pain and disability than the comparison group, but this did not affect their final outcomes, researchers concluded.

Surrounding joint pathology

Figure 1. Pre- and postoperative views of a fixed-bearing, two-component, modular stem total ankle system. It is the second version of a third-generation total ankle system. (Images courtesy of Todd A. Irwin, MD.)

Today, TAA accounts for more than one-third of surgeries for end-stage ankle arthritis.¹⁵ Enthusiasm in TAA is due, say many surgeons, not only to the emergence of new generations of implant design and patient demand,¹⁹ but also concern that ankle arthrodesis leads to increased stress on nearby joints and eventually to adjacent- or surrounding-joint arthritis that requires additional fusions.^17,18 The rate of additional fusion is about 11% within five years of the primary fusion.¹⁹

“The rate is not as high as historically quoted,” Younger said. “Is the preoperative subtalar arthritis not diagnosed, or did it develop in response to the postfusion stress transferred to surrounding joints? It’s just as likely to have been there all along, but our awareness of the problem has increased as CT and MR imaging has improved.”

Some recent studies have delved into the importance in TAA of attaining proper alignment of both the prosthesis and the arthritic ankle’s soft and bony tissues. In a retrospective cohort study of 89 consecutive ankle replace­ments,²⁰ a group led by C. Thomas Haytmanek Jr, MD, found that, even when preoperative ankle deformity exceeded 10°, a statistically significant correction in the coronal alignment of the arthritic ankle was possible immediately after surgery and maintained at a mean
follow-up of eight years.

“We noted a slight increase in revision rate in patients with a more than ten degrees of preoperative coronal plane deformity as measured on weight-bearing mortise views of the ankle,” said Haytmanek, an orthopedic surgeon associated with the Coughlin Clinic at St. Alphonsus Medical Group in Boise, ID. “This was not significant enough to discourage use of the prosthesis in this population, but we recommend discussing the increased revision rate with these patients preoperatively.”

In the subgroup of 21 patients with severe malalignment, a mean preoperative coronal angulation of 16.1° was corrected to 4.6° at final follow-up. This subgroup experienced a higher secondary surgery rate (33.3%) than the entire cohort (27.8%), with component revision or failure occurring in three cases compared to eight cases in the entire cohort.

As for alignment of the prosthesis, recent results by an Austrian group indicated that mild malalignment of total ankle arthroplasties did not affect the revision rate at four years.²¹

Gait and function

Figure 2. Radiographs show lateral and mortise views of a well-aligned, mobile-bearing total ankle replacement. There is evidence of bone ingrowth on the tibial component of the prosthesis. (Images courtesy of C. Thomas Haytmanek Jr, MD.)

Studies have shown that pain and disability are similar after both TAA and AF.²² A pilot study reported at the AAOS meeting showed gait and balance were also similar, with no statistically significant difference in velocity, cadence, and other measures.²³ Researcher Brandon King, MD, an orthopedic surgery resident at the University of Michigan in Ann Arbor, told LER, “However, there was a trend toward better pain and function scores in the TAA group, though it did not reach statistical significance.”

He said the arthrodesis cohort actually had better balance scores, though most of the differences weren’t significant, and that risk of falling might be a useful point to make when talking about treatment options with elderly patients with ankle arthrosis.

Although many studies have shown that gait is improved over preoperative status after both TAA and ankle fusion, a recent investigation demonstrated why ankle replacement may feel more normal than ankle fusion. Orthopedic surgeon James R. Jastifer, MD, and his former colleagues at St. Alphonsus Regional Medical Center’s Coughlin Clinic in Boise, ID, examined patients’ clinical and functional gait scores on stairs, an inclined ramp, and an uneven surface preoperatively and at six and 12 months postoperatively.²⁴ TAA patients had significantly better outcomes than arthrodesis patients for several objective functional measures and higher scores for walking upstairs, walking downstairs, and walking uphill, improvements that the authors believe are due to preserved ankle motion. (Jastifer now is affiliated with Borgess Health System in Kalamazoo, MI.)

As longer-term durability and efficacy of TAA emerge, the prospect of providing ankle replacement surgery to younger patients becomes more attractive. In a prospective study targeting that issue, Demetracopoulos et al divided 395 consecutive patients with a mean follow-up of 3.5 years into three groups based on age at the time of surgery (<55, 55-70, and >70 years) and found that patients younger than 55 years had a greater improvement in Short-Form 36 Vitality and American Orthopaedic Foot & Ankle Society function scores than patients older than 70 years.²⁵

At the same time, an analysis of gait in TAA patients older than 70 years (mean age 74.6 years) reported equivalent improvements to a comparison group aged 50 to 60 years (mean age 55.4 years) who underwent the same procedure.²⁶

“This is a good sign that the procedure is viable in the older population. We will present data this summer demonstrating clinical improvements to accompany these gait improvements,” said Jason T. Bariteau, MD, assistant professor of orthopedic surgery at Emory University in Atlanta, and first author of the study.

Bariteau noted that the only area not improved in the geriatric group was sagittal plane position at initial contact, indicating younger patients preoperatively had more of an equinus position, which was improved with TAA. TAA in the geriatric cohort did not result in improved equinus position.

Costs

Although patients’ length of stay is similar for both TAA and AF, the cost of ankle replacement systems accounts for an increased expense of at least $12,000.¹⁴ Yet, a straight-up comparison of cost of the two operations doesn’t tell the whole story, according to
researchers.

Nwachukwu et al, for example, found that adding indirect costs, including future related additional surgeries, to direct costs, made TAA the preferred strategy from both a health system and a societal perspective.²⁷ The group found direct costs from the NIS database charge data; indirect costs were related to lost productivity and wages due to disability from disease (including adjacent joint OA) or recovery from surgery. In the cost scenarios analyzed, TAA proved to be the most cost-effective surgical treatment when performed in middle-aged and younger patients, with saved productivity costs for patients and their employers.

The new data are important because, in some cases, patients are denied access to TAA by payers due to the cost of the ankle prosthesis, and ankle fusion is offered as the only alternative to medical management, according to another study from the Canadian Orthopaedic Foot and Ankle Society database. The analysis by Younger and colleagues compared TAA and ankle fusion with hip and knee joint replacement and found that the total cost of the initial hospitalization for ankle arthroplasty was similar to that of both hip and knee arthroplasty.²⁸

Patient education

The halo effect of hip and knee arthroplasty successes as well as Internet-based and traditional marketing by implant manufacturers prompts many patients with end-stage ankle arthritis to go to their physicians asking for a total replacement for their debilitated ankle, Younger noted.

No doubt there is a disconnection between established medical guidelines and information available on the Internet. Elliott et al²⁹ evaluated total ankle replacement information available through public Internet sites and rated the quality of information according to authorship type and site certification status. Websites scoring excellent or high on a five-point scale comprised 35% of the 105 websites studied; 48% ranked as poor or unacceptable. The researchers suggested that professional organizations and physicians form a partnership to ensure that provider websites reflect current indications and contraindications for ankle arthroplasty in order to enhance patient education.²⁹

Younger said outcomes measures based on patient expectation and satisfaction may be more useful than current operative outcome measures based on pain and function. He has led research that found TAA patients had higher expectation scores preoperatively than those having ankle fusion, and that expectations were more likely to be met by ankle replacement than fusion. TAA patients more often reported improved satisfaction scores after surgery.³⁰ Interestingly, analysis indicated that, preoperatively, patient expectation was independent of pain and function scores. Nevertheless, postoperative expectations met and satisfaction scores strongly correlated with pain and function scores at follow-up.

“We really have to find a way to study this. Everybody talks about ‘patient satisfaction’ but I think we have to quantify and find a way to measure ‘patient dissatisfaction,’” Younger said.

Patient education is key to meeting this challenge, Younger said.

“We need more educators in clinics and need to find a way to show they would be cost-effective,” he said. “What’s the cost of a surgical failure when the patient does not fully understand our instructions? If an operation fails because of patient noncompliance, you’re really saying the patient failed because they didn’t get correct education. We can explain everything, but sometimes all the patient hears is ‘blah, blah, blah.’”

Hank Black is a medical writer in Birmingham, AL.

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