Clinical Outcome and Fusion Rate Following Simultaneous Subtalar Fusion and Total Ankle Arthroplasty
Methods: This study included 25 patients who underwent primary TAR and simultaneous subtalar fusion between May 2011 and November 2014. Sixteen males (64%) and 9 females (36%) were enrolled with a mean age of 58 years (25-82). Patients were clinically assessed preoperatively and at 6 and 12 months postoperatively. Total follow-up time was 24.2 ± 11.6 months. Radiographic examination included a postoperative computed tomographic (CT) scan obtained 12 months after surgery. Three surgeons independently reviewed the CT scans and interobserver reliability was calculated. Functional scores were also assessed.
Results: At 12 months postoperatively, the subtalar fusion rate in patients treated with TAR and simultaneous subtalar fusion was 92%. There was a statistically significant increase in American Orthopedic Foot & Ankle Society ankle/hindfoot score from 27.9 to 75.1. Ankle range of motion significantly increased from 12 to 32.8 degrees. Additionally, there was a statistically significant decrease in visual analog scale pain score from 8.6 to 2.1.
Conclusions: TAR and simultaneous subtalar joint fusion were reliable procedures for the treatment of ankle and subtalar joint arthritis. Furthermore, CT scans showed an excellent reliability among orthopedic surgeons in determining the degree of successful fusion of subtalar arthrodesis.
Level of Evidence: Level IV, case series.
Keywords: ankle, replacement, subtalar, subtalar arthrodesis, fusion, ankle replacement, computed tomography.
Subtalar arthrodesis is commonly performed for manage- ment of posttraumatic subtalar arthritis, rheumatoid arthri- tis, posterior tibial tendon dysfunction, tarsal coalition, and primary subtalar arthritis, with a reported fusion rate rang- ing from 84% to 100%. Several studies have noted that fusion is often required following the progression of subta- lar arthritis after ipsilateral tibiotalar arthrodesis.3,10,28 In these patients, the altered loading and reduced talar blood supply can create a less favorable environment for the sub- talar fusion resulting in a fusion rate of 61.5% to 66.7%.18,41
Patients with arthritis or severe dysfunction involving both the ankle and the subtalar joints can benefit from tibiotalocalcaneal (TTC) arthrodesis or total ankle replacement and subtalar fusion.9,25,33,38 TTC fusion is con- sidered by many a salvage operation for failed previous sur- gery or Charcot neuroarthropathy, resulting in a rigid ankle and hindfoot, considerably limiting global foot function.34 Moreover, fusion is associated with complications such as nonunion, malunion, and gait disturbance in addition to stress transfer and adjacent joint degeneration.12,21,36
References 1, 4, 14, 16-18, 20, 26, 31, 35
1USPeC, IRCCS Istituto Ortopedico Galeazzi, Milan, Italy
2Universita’ degli Studi di Milano, Milan, Italy
3Seconda Università degli Studi di Napoli, Napoli, Italy
4Department of Orthopaedics, Medical University of South Carolina, Charleston, South Carolina, USA
Federico G. Usuelli, MD, USPeC, IRCCS Istituto Ortopedico Galeazzi, Via Riccardo Galeazzi 4, 20161 Milan, Italy.
With the evolution of total ankle design and a refinement of oper- ative techniques, total ankle replacement (TAR) has become a reasonable alternative to arthrodesis with comparable improvements in function and quality of life.15,40
The aim of this study was to investigate the fusion rate of the subtalar joint in patients simultaneously treated with total ankle replacement (TAR) and subtalar joint fusion as well as to investigate functional outcome at 1 year postoperatively.
After preparing the articular surfaces of the tibiotalar joint for the implant, a lateral sinus tarsi approach was used to perform subtalar joint fusion. Debridement of the poste- rior and the anterior facets was achieved with curettes and small osteotomes. The joint surface was penetrated with a 2.0-mm drill bit. The talar and the tibial components were inserted. The foot was held at hindfoot neutral to slight, physiologic valgus. Rigid internal fixation with 2 headless fully threaded positioning screws (diameter 7.5 mm, Large Qwix; Integra, Newdeal) was used for all cases (Figure 1).
Figure 1. Weight-bearing lateral ankle radiograph showing
subtalar fusion stabilized with 2 headless fully threaded positioning screws.
Clinical and Radiologic Evaluation
Patients were clinically evaluated preoperatively (T0) and postoperatively at 6 months (T1) and 12 months (T2). Pain and function were assessed using the American Orthopedic Foot & Ankle Society (AOFAS) ankle and hindfoot score, visual analog scale (VAS) pain score, and the 12-Item Short Form Health Survey (SF-12).6,8,21,23,30 Range of motion (ROM) was determined pre- and postoperatively using a goniometer along the lateral border of the leg and foot.
Radiographic examination included a postoperative CT scan obtained 12 months after surgery. Sagittal and coronal cuts (2 mm thick) of each subtalar joint wereevaluated. All radiologic evaluations were made using the standard tools in our Picture Archiving and Communication System (PACS). Patient identifiers were blinded in all CT scans. All the scans were evaluated by 3 orthopedic surgeons who were not directly involved in the operative procedure deter- mining the extent of fusion based on criteria suggested by Coughlin and colleagues12 (Figure 2). On the CT scan, the measured section was considered fused when the apposing arthrodesis surfaces had bridging bone so that the cut ends of the cortices were no longer seen. The percentage area fused was calculated from those values. On the CT scan, the excluded areas included both the actual hardware and the areas obscured by artifact. The obscured area was excluded from calculations. The sum of the fused area was divided by the sum of the joint not obscured. This ratio was expressed as a percentage. In agreement with Coughlin et al, we used a criterion of 50% fusion (on the CT scans) as a threshold for considering a joint fused.
Figure 2. Coronal and sagittal computed tomography (CT) scan sequences of 2 subtalar arthrodesis. On the left, evaluation of the fusion site, excluding hardware and artifact, shows less than 50% union of the bony surfaces. On the right, evaluation of the fusion site, excluding hardware and artifact, shows more than 50% union of the bony surface.
The statistical analysis was performed by Matlab version 2008 (MathWorks, Natick, MA). The statistical tests per- formed included analysis of variance and kappa test.11,22 For k-score, confidence intervals were defined at 95%. The k-score interpretation was based on the Koch-Landis inter- pretation. All statistical tests were considered significant with P < .001.
Two asymptomatic nonunions were identified in the 25 cases for a subtalar fusion rate of 92%. Of the 2 patients who had an asymptomatic nonunion, 1 patient had 36% and the other had 41% of their subtalar joint fused, respectively. No major complications were reported, including avascular necrosis of the talus.
Identifying a subtalar fusion showed an excellent interobserver reliability (k = 0.913) (Table 1). The probabil- ity that the interrater reliability was better than fair was sig- nificant (P < .001).
Table 2. Clinical Outcomes Using the AOFAS Ankle and Hindfoot Score, VAS Pain Score, ROM, and SF-12 Score (PCS and MCS).
This study reports the outcomes of 25 patients treated for end-stage ankle and subtalar osteoarthritis with total ankle arthroplasty and simultaneous subtalar fusion. Our findings demonstrate that total ankle replacement and simultaneous subtalar arthrodesis allowed for significant improvements in the short term in radiologic and clinical outcomes. Clinically, there was a significant improvement in AOFAS scores, SF-12, VAS pain scores, and ROM after total ankle arthroplasty and subtalar fusion at 1 year postoperatively. Radiographically, there was a high rate of fusion at 12 months’ follow-up, evaluated by computed tomography.
A recent cadaver injection study investigated how 4 dif- ferent total ankle systems available in the United States affected the talar blood supply.37 All TAR systems damaged the extraosseous talar blood supply in some manner. Altered biomechanics and a damaged talar blood supply after ankle replacement may create a less favorable environment for ipsilateral hindfoot fusion.37 Therefore, a tibiotalar arthrod- esis may cause similar vascular and biomechanical insults to the talus. These findings suggest that the talar vascular insult during TAR implantation may not be enough to cause an outright nonunion. At the same time, the relatively high fusion rate may demonstrate that the subtalar joint is in a more biomechanically favorable position after a TAR than an ankle arthrodesis to allow for better healing.41 Easley et al reported a fusion rate of 84% in 184 consecutive isolated subtalar fusions.18 The patient cohort included only 6 cases in which the subtalar arthrodesis was adjacent to a prior ipsi- lateral ankle arthrodesis; of these 6 patients, 4 (66.7%) pro- gressed to successful subtalar fusion. When these 6 cases were excluded, the union rate improved to 90%.
With regards to clinical and radiologic outcomes of TAR and subtalar fusion, previous literature suggested good results. Lewis et al, in a consecutive series of 404 primary TARs in 396 patients, identified 70 patients with an ipsilat- eral hindfoot arthrodesis.29 Radiographic and clinical evalu- ation suggested that all hindfoot arthrodeses progressed to fusion. The AOFAS scores improved from 38.1 to 71.0 points in the hindfoot fusion group, significantly lower than in the control group (42.5 to 81.6; P < .001). Furthermore, they reported a significantly lower survivorship rate in the fusion group (90.0%) compared with the control group (97.6%) at 3.2-year follow-up.
One of the strengths of our study was the use of CT scans to evaluate subtalar fusion rates. Radiographs may overesti- mate the degree of joint fusion.12,24,27 Coughlin et al in a prospective study compared plain radiographs and CT scans for the quantitative evaluation of fusion in hindfoot arthrod- esis.12 They used the criterion of 50% fusion (on the CT scans) as a threshold for considering a joint fused. However, they pointed out that 50% bridging of the joint may be too stringent. In their personal experience, they have seen many arthrodesis joints that had a smaller degree of fusion (20% to 35%) who were asymptomatic.
It is important to recognize the inherent limitation of this study, including its retrospective design and limited and het- erogeneous sample size. Follow-up of only 1 year makes it difficult to compare functional results to longer-term studies. Our study was also affected by the limitations of the CT. Artifact due to the metal fixation made evaluation of fusion more difficult. With regard to clinical outcomes, we acknowl- edge that the American Orthopaedic Foot & Ankle Society (AOFAS) score, despite its lack of validation, has been used widely in the literature and allows for comparisons between this and other studies. We tried to offset this clinical indicator with use of the VAS.5 Forty-nine different scoring systems have been identified as being used to assess clinical outcomes in foot and ankle surgery. However, few metrics have been validated or proven to offer a valid, reliable method of assess- ing patients with foot and ankle pathology.5
In conclusion, this study demonstrated good clinical and radiological outcomes after TAR and simultaneous subtalar arthrodesis at 1 year postoperatively. Furthermore, CT scans showed an excellent reliability among orthopedic sur- geons in determining the degree of successful arthrodesis of the subtalar joint. The fusion rate of the subtalar joint was not affected by the TAR.
Declaration of Conflicting Interests
The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
The author(s) received no financial support for the research, authorship, and/or publication of this article.
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