Background: The Scandinavian Total Ankle Replacement (STAR) prosthesis has been in clinical use since 1981, with investigational use in the U.S. since 1998. Few studies of the North American version of the STAR are available. This prospective cohort study analyzed intermediate to long-term outcomes of total ankle arthroplasty with use of the STAR prosthesis at two Canadian centers.
Methods: Consecutive patients who received the STAR prosthesis between 2001 and 2005 were enrolled at two large, urban teaching hospitals. Patients were annually evaluated clinically, and the Ankle Osteoarthritis Scale (AOS) and the Short Form (SF)-36 were administered.
Results: One hundred and eleven ankles underwent arthroplasty with the STAR prosthesis. One-half of the patients were male; the mean age was 61.9 ± 11.7 years. Sixty-eight of the ankles underwent a total of 121 additional procedures during ankle arthroplasty, including gastrocnemius release, subtalar arthrodesis, triple arthrodesis, tendoachilles lengthening, and removal of hardware. The mean duration of follow-up for all living patients without revision (seventy-three ankles) was 9.0 ± 1.0 years. Thirteen (12%) of the ankles required metal component revision at a mean of 4.3 ± 3.0 years (range, 0.6 to 10.2 years). Twenty (18%) of the prostheses underwent polyethylene bearing exchange, mostly due to fracture, at a mean of 5.2 ± 2.1 years (range, 1.5 to 9.3 years). Most (97%) of the revisions and exchanges occurred in patients with a diagnosis of primary, secondary, or posttraumatic osteoarthritis (p = 0.0003). The mean change from baseline to final follow-up was −36.5 ± 23.3 points for AOS pain, −38.6 ± 26.8 points for AOS disability, and 9.6 ± 10.3 points for the SF-36 physical component summary score. The SF-36 mental component summary score was unchanged.
Conclusions: Intermediate patient-reported outcomes were good after ankle arthroplasty with the STAR prosthesis performed by experienced surgeons, and long-term outcomes demonstrated a 12% rate of metal component revision and 18% rate of polyethylene bearing failure. The revision rate was substantially higher among the first twenty ankles than among subsequent ankles, but the early ankles had nearly two years’ longer follow-up than subsequent ankles. Additional study to elucidate possible reasons for polyethylene bearing failure is warranted.
Level of Evidence: Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.
1Division of Orthopaedic Surgery, St. Michael’s Hospital, 800-55 Queen Street East, Toronto, ON M5C 1R6, Canada. E-mail address: firstname.lastname@example.org
2Division of Orthopaedic Surgery, Horizon Health Network, 200-555 Somerset Street, Saint John, NB E2K 4X2, Canada
3Department of Orthopaedics, University of British Columbia, 1000-1200 Burrard Street, Vancouver, BC V6Z 2C7, Canada
End-stage ankle arthritis has a substantial impact on quality of life, equivalent to end-stage hip arthritis1. Total ankle arthroplasty is a viable treatment option for ankle arthritis2-4. The Scandinavian Total Ankle Replacement (STAR) design (Waldemar LINK, Hamburg, Germany; now distributed by Stryker, Kalamazoo, Michigan) has been in use since 1981; five versions have been utilized. The latest version, available in North America since investigational use began in 19985, is a three-component, mobile-bearing design with titanium plasma-sprayed ingrowth surfaces on the tibial and talar components. The talar component articulates with a slot that is machined into the polyethylene bearing to mimic the semiconstrained ankle joint on the talar side, maintaining an unconstrained relationship with the tibial component6. This variant, approved for use in Canada in 2000 and in the U.S. in 2009, does not include a hydroxyapatite coating.
European reports of short and intermediate-term clinical series of the STAR demonstrate survivorship approaching values seen for total knee arthroplasty7,8. These data are in contrast to findings regarding earlier prosthetic designs, which were associated with high complication rates and poor long-term survivorship9,10. The positive outcomes for the STAR prosthesis, combined with the high burden of end-stage ankle arthritis in patients, have led to consideration of arthroplasty as a viable surgical option. However, these results are tempered by recent reports of an 18% revision rate among available ankle joint registries11 and a probability of implant survivorship of <50% at fourteen years12.
North American studies reporting outcomes of the STAR design are limited5,13,14. Studies demonstrating intermediate and long-term clinical results of the STAR prosthesis that are validated by independent practitioners are needed15-17. Our prospective cohort study determined intermediate to long-term outcomes of ankle arthroplasty using the STAR prosthesis at two Canadian centers.
Materials and Methods
A prospective, observational study of all consecutive patients who underwent ankle arthroplasty with use of the STAR prosthesis (the version approved for use in North America) between November 2001 and October 2005 was performed at two large, urban teaching hospitals in Canada (Site A and Site B). Both sites collected data prospectively from 2001 onward; Site B collected patient-reported outcome scores from September 2003 onward. Patients were included if they had a diagnosis of end-stage ankle arthritis, were thirty years of age or older, and were able to provide informed consent. Exclusion criteria were an age younger than thirty years; peripheral neuropathy; peripheral vascular disease (i.e., no palpable pulses at the level of the ankle or an ankle-brachial index of <0.9); severe axial malalignment; active or previous infection of the ankle joint, tibia, or talus; multiple comorbidities; a poor soft-tissue envelope; and behavioral or cognitive concerns (e.g., alcoholism). Patients provided informed consent. This study was approved by each institution’s research ethics board.
All patients underwent a standard operative procedure of cementless, mobile-bearing, three-component total ankle replacement, with additional procedures performed as required to achieve a stable ankle joint and plantigrade foot. All surgical procedures were performed by two orthopaedic surgeons with foot and ankle specialty training, one surgeon at each site.
Patient demographics, comorbidities, and diagnoses were recorded preoperatively. Operative details were collected prospectively. Patients were evaluated in the clinic annually following surgery. Patients completed outcome questionnaires preoperatively and completed one or more questionnaires at least two years postoperatively. Clinical outcome measures were collected with use of the Foot and Ankle Follow-Up Questionnaire, developed by a coalition of ten orthopaedic associations. The specific components administered were the Ankle Osteoarthritis Scale (AOS), a reliable, validated, self-reported, ankle-specific measure of pain and disability18, and the Short Form-36 (SF-36) Standard Version 2.0 Health Survey, a general health scale with physical component summary (PCS) and mental component summary (MCS) scores19.
Revision ankle arthroplasty was defined as a reoperation to remove one or both metal components, or amputation. Polyethylene bearing exchange and major operative or postoperative complications were recorded.
Kaplan-Meier survival analyses determined the time to failure of the prosthesis and included all patients enrolled in the study. The censor date for revision was February 15, 2013. For outcome score analysis, only preoperative and the most recent follow-up scores collected through November 30, 2011, were used. All ankles were considered independently for all analyses. Ankles that underwent revision were included in outcome measure analyses to minimize selection bias. Two sensitivity analyses were conducted: exclusion of ankles that underwent metal component revision and exclusion of ankles that underwent such revision or polyethylene bearing exchange, to assess the impact of including data for these patients.
Descriptive statistics summarized patient demographic variables. Differences in baseline demographic characteristics (between the sites preoperatively and between the full cohort and the subgroup for outcome score analysis) were assessed using chi-square tests or Fisher exact tests for categorical variables and two-sample Student t tests for continuous variables. Paired Student t tests assessed changes in clinical outcome scores from baseline to follow-up and were reported using point estimates with corresponding 95% confidence intervals (CIs). In all tests, p ≤ 0.05 was considered significant.
Source of Funding
Integra LifeSciences and DePuy Synthes provided direct and indirect research funding support for this study.
One hundred and eleven ankles (sixty-one at Site A and fifty at Site B) in ninety-eight consecutive patients (fifty-four at Site A and forty-four at Site B) underwent arthroplasty with use of a STAR prosthesis between November 2001 and October 2005. This series comprised all ankle replacements performed at both sites during the study period, with the exception of the final STAR arthroplasty at Site B, which was performed at the patient’s request after some primary arthroplasties in other patients had been performed using another implant. All patients met the inclusion criteria and were included in this consecutive series. One-half (51%) of the patients were male. The mean age at surgery (and standard deviation [SD]) was 61.9 ± 11.7 years. The mean body mass index (BMI) was 27.9 ± 5.5 kg/m2. The study sites were similar in terms of patient sex, age, BMI, operative side, primary diagnosis, and cause of posttraumatic osteoarthritis (Table I).
The most frequent diagnosis was posttraumatic osteoarthritis (54%), followed by rheumatoid arthritis (20%), primary osteoarthritis (14%), and osteoarthritis secondary to deformity (7%) (Table I). The sites differed significantly (p < 0.001) in terms of distribution according to the Canadian Orthopaedic Foot and Ankle Society (COFAS) classification of complexity of end-stage ankle arthritis and level of deformity20. Site A had more ankles classified as Level 2 (48% compared with 12%), whereas Site B had more ankles classified as Level 1 (i.e., least complex; 34% compared with 20%) and Level 4 (i.e., most complex with extensive deformity; 42% compared with 18%).
Additional intraoperative procedures were performed in sixty-eight (61%) of the ankles (Table II). The most frequently performed procedures were gastrocnemius release (in forty-one), subtalar arthrodesis (in fifteen), triple arthrodesis (in twelve), and tendoachilles lengthening (in nine).
Revisions and Complications
Seventy-three (66%) of the ankles were intact and functioning with original components at a mean duration of follow-up of 9.0 ± 1.0 years (range, 6.8 to 11.3 years). Six patients (each with one prosthesis) died, 3.8 to 9.3 years after surgery. Thirty-two (29%) of the ankles required metal component revision and/or polyethylene bearing exchange (Fig. 1).
Thirteen (12%) of the ankles required metal component revision (Fig. 2-A), with a mean time to revision of 4.3 ± 3.0 years (range, 0.6 to 10.2 years). The resulting projected ten-year survival rate was 88%. Seven of the ankles were converted to tibiotalocalcaneal arthrodesis, four were revised with HINTEGRA total ankle replacements (Integra LifeSciences, Plainsboro, New Jersey), one was converted to pantalar arthrodesis, and one patient was treated with transtibial amputation (see Appendix).
Twenty (18%) of the prostheses underwent polyethylene bearing exchange (Fig. 2-B), at a mean of 5.2 ± 2.1 years after ankle arthroplasty (range, 1.5 to 9.3 years). Sixteen ankles experienced nineteen bearing fractures (see Appendix). One ankle had an incomplete bearing fracture with wear, with bearing exchange at thirty-six months after arthroplasty, and then a second bearing fracture, with bearing exchange at ninety-six months. Another ankle had three bearing fractures, with bearing exchange at thirty-two, fifty-two, and eighty-five months after arthroplasty. Of the four remaining bearings that failed, two exhibited asymmetric wear, while one exhibited severe wear, was exchanged at 4.2 years, and subsequently was revised to tibiotalocalcaneal arthrodesis at 6.3 years (Case 7). The fourth patient had evidence of osteolysis and required a polyethylene bearing exchange, cyst debridement, bone-grafting, and open Achilles lengthening.
The revision of metal components and exchange of polyethylene bearings varied significantly by primary diagnosis (p = 0.0011) (see Appendix). Patients with osteoarthritis underwent significantly more metal revisions and bearing exchanges (p = 0.0003). Of the thirteen metal revisions and the twenty polyethylene bearing exchanges, thirty-two (97%) occurred in patients with a primary diagnosis of osteoarthritis (eight of sixteen; 50%), osteoarthritis secondary to deformity (six of eight; 75%), or posttraumatic osteoarthritis (eighteen of sixty; 30%). When stratified by COFAS classification of the preoperative complexity of ankle arthritis20, there were no significant differences: six (21%) of the twenty-nine Level-1 ankles, twelve (34%) of the thirty-five Level-2 ankles, six (43%) of the fourteen Level-3 ankles, and nine (28%) of the thirty-two Level-4 ankles underwent metal revision or polyethylene bearing exchange.
The combined rate of metal revision and polyethylene bearing exchange was greater for the first twenty ankles of each surgeon (38%) compared with subsequent ankles (24%) (Table III). The mean duration of follow-up for both surgeons’ first twenty ankles (10.3 ± 0.5 years) was nearly two years longer than for subsequent ankles (8.4 ± 0.6 years) (Fig. 3).
There were eight (7%) other major complications (see Appendix). One patient experienced upper gastrointestinal bleeding postoperatively. One patient developed deep-vein thrombosis. Three patients required wound debridement and free flap reconstruction. Another patient was admitted to the hospital for delayed wound-healing and treated with intravenous antibiotics. One patient developed tarsal tunnel syndrome on the operative side and underwent polyethylene bearing exchange and talonavicular joint arthrodesis 5.4 years after ankle arthroplasty. One patient developed a medial malleolar stress fracture two years after polyethylene bearing exchange.
Clinical Outcome Measures
Scores on outcome measures preoperatively and at least two years following ankle replacement were available for seventy-four (67%) of the ankles (fifty-nine at Site A and fifteen at Site B). The mean duration of follow-up for the clinical outcome analysis was 7.6 ± 2.3 years (range, 2.0 to 9.6 years; median, 6.4 years); sixty-three (85%) of the seventy-four ankles were followed for five years or longer. Preoperative clinical outcome-measure data were not collected for thirty-six ankles (thirty-five at Site B and one at Site A); one patient was lost to follow-up (Site A). Patient demographics for the seventy-four ankles with complete outcome-measure scores were similar to those for the full cohort (see Appendix), with the exception of COFAS classification: the subgroup with complete outcome scores had a higher proportion of Level-2 ankles (thirty-three of seventy-four; 45%) than did the full cohort (thirty-five of 111; 32%).
The AOS pain and disability and SF-36 PCS scores improved from preoperatively to final follow-up (Fig. 4). The mean change (i.e., postoperative – preoperative score) in AOS pain, where a lower score indicates a better outcome, was −36.5 ± 23.3 points (95% CI, −42.0 to −31.1 points), from a mean of 56.3 ± 18.9 points (95% CI, 51.9 to 60.7 points) preoperatively to 19.8 ± 19.1 points (95% CI, 15.3 to 24.2 points) postoperatively. The mean change in the AOS disability score was −38.6 ± 26.8 points (95% CI, −44.9 to −32.4 points). The SF-36 PCS score improved from a mean of 29.6 ± 7.8 points (95% CI, 27.8 to 31.4 points) preoperatively to a mean of 39.1 ± 11.4 points (95% CI, 36.5 to 41.8 points) postoperatively. The SF-36 MCS score was effectively unchanged postoperatively.
Sensitivity analyses of changes in clinical outcome scores excluded eight ankles with complete outcome measure scores that underwent metal component revision, and then excluded those eight ankles plus thirteen ankles with complete outcome measure scores that underwent polyethylene bearing exchange (Table IV). The change from baseline to final follow-up was slightly greater for AOS pain, AOS disability, and SF-36 MCS when excluding patients who underwent metal revision or bearing exchange.
Total ankle arthroplasty with the STAR design led to good clinical outcomes at intermediate to long-term follow-up, but 29% of the ankles required polyethylene bearing exchange (18%) and/or metal component revision (12%).
Patients demonstrated large improvements in AOS disability, AOS pain, and SF-36 PCS scores following ankle arthroplasty with the STAR prosthesis, consistent with a weighted mean improvement of 45.2 points on standardized 100-point ankle and hindfoot measures in a meta-analysis of 497 total ankle replacements with various prostheses21. Comparable improvements in clinical outcomes at the time of final follow-up have been reported for the STAR in the short22 and intermediate8,23 term, although the present study is, to our knowledge, the first to utilize a validated, disease-specific, patient-reported outcome measure (the AOS) and a validated general-health outcome measure (the SF-36). The degree of clinical improvement seen here is consistent with that reported for multiple implant designs in the intermediate term4 and in a meta-analysis of combined implant data for 852 ankle arthroplasties24.
The definition of revision for ankle arthroplasty is complex, controversial25-27, and varied, but removal or exchange of one or more metal components is generally considered a revision28. We defined revision as reoperation to remove one or both metal components, or amputation. We considered polyethylene bearing exchange separately, as removal of only the bearing does not place the bone stock or total construct at risk, and patient recovery following bearing exchange is usually rapid, with weight-bearing within two weeks of surgery.
The 12% metal-component failure rate in this study is consistent with, or lower than, reported rates of metal-component revision for the STAR prosthesis: 10.7% at a weighted mean follow-up of sixty-four months in a systematic review11, 12% of fifty-two ankles at five to eight years of follow-up8, 12% of 200 ankles at a mean follow-up of 7.3 years29, 13% of eighty-four ankles at a mean follow-up of 9.1 years5, 20% of fifty-one ankles at three to eight years of follow-up23, 22% of 205 ankles in the Swedish Ankle Arthroplasty Register at ten years3, and 38% of seventy-seven ankles at eleven to fifteen years of follow-up12. The rate of conversion to arthrodesis in our study (7%) is also comparable with the 6% to 10% reported for STAR implants8,29 and the 5% of 572 ankle replacements using various implants determined by meta-analysis24. Metal-component failure of the STAR occurred at a mean of four years in our study, which is comparable with that in other reports8,29.
The high rate of polyethylene bearing replacement (18%) predominantly due to fracture, incomplete fracture, or severe wear raises considerable concerns about the polyethylene bearing for the STAR design. Brunner et al. reported polyethylene bearing fractures in 14% of seventy-seven ankles at eleven to fifteen years following arthroplasty with the STAR prosthesis12. Additional research evaluating clinical factors and implant-design factors that contribute to polyethylene bearing fracture and severe wear is warranted.
Numerous studies have recently shown that ankle arthroplasty with the STAR design is technically challenging and involves a learning curve, whereby increased surgeon experience and careful patient selection can improve outcomes and decrease failure rates2,3,23,30,31. Our study also found a higher combined rate of metal revision and polyethylene bearing exchange for the first twenty ankles of each surgeon. However, the early ankles had nearly two years’ longer follow-up than subsequent ankles. Thus, while implant survivorship may be somewhat improved in later patients, it is unknown if this observation will be sustained with longer follow-up of the subsequent patients. Ankle complexity, as determined by the COFAS classification of end-stage ankle arthritis20, did not appear to affect the revision rate. It is now well understood that patient selection and accurate implantation techniques are key. Care must be taken to ensure correct alignment of the implant, achieve well-balanced ligaments and stability, be attentive to coronal and sagittal plane alignment, and correct any residual deformity8,22,32,33. While surgeon experience is likely to reduce revision rates, clinical outcome scores do not appear to change with experience22.
Our results demonstrated that patients with rheumatoid arthritis required fewer metal revisions or polyethylene bearing exchanges compared with patients with osteoarthritis. Similarly, a review of 780 Swedish Ankle Arthroplasty Register procedures using various implants estimated a slightly greater ten-year survival rate for patients with rheumatoid arthritis (0.72) compared with patients with osteoarthritis (0.68) or posttraumatic osteoarthritis (0.66); women sixty years of age and younger with osteoarthritis were at a higher risk for revision3. The reduced function and overall activity levels associated with greater disability in patients with rheumatoid arthritis may, in part, account for the potentially better implant survival34. Recently, a comparative, matched cohort study with a mean duration of follow-up of sixty-four months found no difference in revision rates between patients with rheumatoid arthritis and patients with osteoarthritis after ankle replacement procedures involving various prostheses34.
BMI and age did not appear to influence the prevalence of metal revision or polyethylene bearing exchange, but our analyses were not designed to test for potential risk factors for revision. Our results are consistent with the findings of a recent report that demonstrated no significant difference in complication and revision rates among obese and nonobese patients35.
Our study has several strengths: it was performed prospectively, with a large cohort (111 cases) and a long mean duration of follow-up (nine years) for survivorship analysis. The surgery was performed by two experienced practitioners at two centers, with consistent outcomes across sites. Validated, patient-reported outcome measures were utilized.
Limitations of this study include the absence of a comparative control group and the lack of preoperative clinical outcome scores for one-third of the patients. However, intermediate to long-term clinical series such as this study commonly do not have concurrent control groups, as they reflect real-world practice rather than a narrowly defined study environment. The full cohort and the patients with complete preoperative and postoperative clinical outcome scores had similar demographics, with the exception of the COFAS classification of end-stage ankle arthritis.
In conclusion, intermediate patient-reported outcomes were good after ankle arthroplasty with the STAR prosthesis performed by experienced surgeons, and long-term outcomes demonstrated a 12% rate of metal component revision and 18% rate of polyethylene bearing failure. The revision rate was substantially higher among the first twenty ankles than among subsequent ankles, but the early ankles had nearly two years’ longer follow-up than subsequent ankles. Additional study to elucidate possible reasons for polyethylene bearing failure is warranted.
Tables showing data from patients who underwent metal component revision and polyethylene bearing exchange and who experienced other major complications, a table presenting the rates of metal revision and bearing exchange by primary diagnosis, and a table showing demographic data for patients with a complete set of clinical outcome scores are available with the online version of this article as a data supplement at jbjs.org.
NOTE: The authors thank Dagmar Gross for assistance with the preparation of this manuscript and Ed Vidgen for conducting the statistical analysis.
Investigation performed at St. Michael’s Hospital, Toronto, Ontario, and St. Paul’s Hospital, Vancouver, British Columbia, Canada
Disclosure: One or more of the authors received payments or services, either directly or indirectly (i.e., via his or her institution), from a third party in support of an aspect of this work. In addition, one or more of the authors, or his or her institution, has had a financial relationship, in the thirty-six months prior to submission of this work, with an entity in the biomedical arena that could be perceived to influence or have the potential to influence what is written in this work. No author has had any other relationships, or has engaged in any other activities, that could be perceived to influence or have the potential to influence what is written in this work. The complete Disclosures of Potential Conflicts of Interest submitted by authors are always provided with the online version of the article.
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