Abstract
End-stage ankle arthritis is a debilitating condition that significantly impairs function and quality of life comparable to end-stage arthritis of the hip and knee. The Trabecular Metal (Zimmer Biomet, Warsaw IN) total ankle arthroplasty device was first implanted in 2013 and is unique in its lateral approach to the ankle joint, which necessitates a transfibular osteotomy. The lateral approach of the Trabecular Metal has a purported ability to maintain the integrity of blood supply to the skin, spare the deltoid ligament and minimize wound healing complications associated with the anterior approach. Furthermore, the lateral transfibular approach provides direct visualization of the center of rotation corresponding to the central point in the body of the talus which may limit risk of malalignment. Mid-term data at five-year follow-up is currently lacking for the Trabecular Metal. A retrospective review was performed at our institution of patients who received a Trabecular Metal total ankle implant through a transfibular lateral approach. A total of 13 patients were included in the study with an average follow up of 5.34 years and an implant survivorship of 92.30 %. The average AOFAS score at final follow up was 88.54 and 100 % of the patients reported that they would undergo the procedure again. Our study provides an important contribution to the limited available mid-term survivorship data of the Trabecular Metal total ankle system inserted through a lateral transfibular approach.
Introduction
The Trabecular Metal (Zimmer Biomet, Warsaw IN) total ankle arthroplasty device was first implanted in 2013. , Between 2009 and 2019, a total of 41,060 total ankle arthroplasties (TAAs) were performed in the United States according to the IBM MarketScan database. The Infinity (Stryker, Kalamazoo MI), INBONE (Stryker, Kalamazoo MI) and Trabecular Metal are the only implants that demonstrated consistently increased utilization within that time frame, with Infinity demonstrating the most utilization to date. Both the Infinity and INBONE devices are implanted via an anterior approach. The INBONE system also requires an accessory plantar incision for reaming the subtalar and tibiotalar joints to allow for insertion of its tibial stem component. While the Infinity and Trabecular Metal share some similar design characteristics with low profile tibial components and superiorly oriented pegs or fins, the Trabecular Metal is unique in its lateral approach to the ankle joint, which necessitates a transfibular osteotomy. The Trabecular Metal is a semiconstrained, fixed bearing implant and is the only total ankle implant on the market still being used in substantial numbers that is inserted through a lateral approach. This lateral approach allows visualization of the ankle’s center of rotation enabling more accurate reconstruction and correction of the ankle joint alignment while minimizing bony resection. ,, The lateral approach also obviates some of the wound-healing concerns that have been reported with use of the standard anterior ankle incision utilized with other systems. ,, The Infinity and Trabecular Metal received FDA approval in 2013 and 2012, respectively. Due to this recency, neither implant has demonstrated long term, sizable data of survivorship at ten-year follow up Fig. 1 .
Preoperative AP radiograph demonstrating joint space narrowing with ankle valgus.
End-stage ankle arthritis is a debilitating condition that significantly impairs function and quality of life comparable to end-stage arthritis of the hip and knee. Unlike osteoarthritis of the hip and knee, ankle arthritis is more likely to be post-traumatic in etiology, typically affecting a patient population roughly ten years younger on average. As such, the longevity of any implanted device must meet the demands and lifespan of these patients. Historically, ankle arthrodesis has been the treatment of choice in end stage ankle arthritis, providing pain relief at the cost of joint motion and the potential for acceleration of arthritic disease in adjacent joints. , Total ankle arthroplasty has emerged as an alternative to ankle fusion, aiming to alleviate pain without complete sacrifice of joint mobility Fig. 2 .
Preoperative lateral radiograph demonstrating posterior joint space narrowing.
The lateral transfibular approach to total ankle arthroplasty has a number of specific advantages. Lundberg in 1989 demonstrated that transfibular access to the ankle joint provides direct visualization of the center of rotation corresponding to the central point in the body of the talus. Patient Specific Instrumentation (PSI) is the emerging standard for anterior approach to TAA aiming to decrease procedural difficulty and provide more consistency in surgical steps. However, controversy remains as to whether PSI actually results in improved implant positioning, with many authors emphasizing the importance of intraoperative decision making by an experienced surgeon rather than over-reliance upon predetermined parameters. , Malalignment of ankle prostheses leads to isolated areas of increased surface pressures, which can lead to wear, subsidence, and aseptic loosening. ,,, Even without PSI, the lateral transfibular approach promotes optimization of implant positioning afforded by direct visualization of the axis of rotation of the joint. This accuracy in implant positioning, joint alignment, and deformity correction could lead to improvements in survivorship by avoiding malalignment Fig. 3 .
First postoperative appointment AP weightbearing radiograph demonstrating rectus ankle alignment with fibular plate.
In contrast to an anterior approach, the lateral approach to total ankle arthroplasty carries a risk of fibular nonunion due to the need for transfibular osteotomy. The loss of a stable bony strut supporting the prosthesis laterally can lead to valgus breakdown and ultimately implant failure. Schon recently published exceptional results demonstrating 100 % implant retention and 0 % fibular nonunion at five year follow up in 130 patients in by far the largest study to date. While several studies have evaluated implant survivorship broadly, midterm data specifically assessing the Trabecular Metal system remains limited and reported survival rates vary across series. ,, Understanding implant survival and the factors contributing to failure is critical for guiding patient selection and surgical planning. The purpose of this manuscript is to demonstrate midterm survivorship at five-year follow up of the Zimmer Trabecular Metal total ankle arthroplasty device with patient reported outcomes presented by non-inventor authorship. Our null hypothesis is that our results will align with the current limited available literature on survivorship and patient reported outcomes in the Trabecular Metal total ankle system Fig. 4 .
First postoperative appointment lateral weightbearing radiograph.
Methods
A category IV IRB-exempt retrospective chart review was performed at our institution, identifying patients who received the Trabecular Metal implant via a lateral approach with transfibular osteotomy by a single surgeon between April 1, 2019 and April 1, 2022. The search yielded a cohort of 13 consecutive patients. Inclusion criteria were patients within this time frame receiving a Trabecular Metal implant through a lateral transfibular approach. Exclusion criteria included follow up <40 months, patients undergoing revision total ankle arthroplasty, patients lost to follow up and unavailable AOFAS scores at most recent follow up. Ancillary procedures were identified but not incorporated into inclusion or exclusion criteria. Following inclusion and exclusion criteria, all 13 consecutive patients were retained for further analysis. The data was extracted and de-identified by a single author (RR) and statistical analysis was performed by a separate, single author (GR). Statistical analyses were performed using Microsoft Excel, Version 365 (Microsoft Corp., Redmond, WA).The collected data included date of surgery, concomitant procedures performed, age, gender, BMI, laterality, follow-up time and postoperative AOFAS scores. Preoperative AOFAS scores were not acquired prior to the procedure and were thus not included. The mean, range and standard deviation (σ) were calculated for descriptive analysis Fig. 5 .
Final follow up weightbearing AP radiograph demonstrating maintained alignment.
Results
Following inclusion and exclusion criteria, a total of 13 patients were included in the study with an average follow up of 5.34 years (range 50–82 months) and an implant survivorship of 92.30 %. The single incidence of failure was removed when calculating average follow up time as this person no longer retained the implant. The average age at time of surgery was 60.15 (range 50–68, standard deviation, σ = 5.16), the average BMI was 33.48 (range 27.7 to 44.92, σ = 4.88) and the cohort was 61.5 % male. The average AOFAS score at final follow up was 88.54. If the single incidence of failure was excluded, the average AOFAS score at final follow up was 90.92. One hundred percent of patients underwent at least one concomitant procedure which included tendoachilles lengthening (61.5 %), subtalar joint arthrodesis (53.8 %), lateral ankle stabilization (53.8 %), talonavicular arthrodesis (30.8 %), triple arthrodesis (15.4 %), peroneal tendon repair (7.7 %), first metatarsophalangeal joint arthrodesis (7.7 %) and supramalleolar osteotomy (7.7 %). There was only one instance of conversion to ankle fusion at 18 months after the index procedure; this patient had chronic soft tissue insufficiency with posterior tibial tendon dysfunction and peroneal pathology with chronic pain. Ultimately, she opted for a single stage procedure in the form of ankle arthrodesis over attempted soft tissue balancing and repair. A total of three patients (23.1 %) required additional surgery at a later date which included subtalar joint arthrodesis, bony exostectomy, removal of hardware, and the aforementioned case of ankle fusion. Fibular nonunion was not encountered in the present study. All thirteen patients (100 %) reported that they would opt to have the surgery again, including the patient who suffered implant failure leading to ankle fusion. Patient demographics, concomitant procedures and subsequent procedures are listed in Table 1 .
Table 1
Patient demographics, follow up time concomitant procedures and subsequent procedure for patients receiving the Trabecular Metal total ankle system through a lateral transfibular approach.
| Age | Sex | BMI | F/u (mo) | Laterality | CP | SP | |
|---|---|---|---|---|---|---|---|
| 65 | M | 34.7 | 78 | Left | STJ arthrodesis, TN arthrodesis, LAS | ||
| 66 | M | 34.4 | 72 | Right | Triple arthrodesis, TAL | ||
| 61 | M | 32.28 | 71 | Right | STJ arthrodesis, LAS | ||
| 64 | M | 27.7 | 67 | Right | LAS | ST arthrodesis | |
| 52 | M | 35.19 | 65 | Right | STJ arthrodesis, TN arthrodesis | ||
| 62 | M | 28.79 | 64 | Left | STJ arthrodesis, TAL | exostectomy ROH, MGD, TN arthrodesis | |
| 50 | F | 44.92 | 60 | Right | Peroneal tendon repair | Ankle fusion | |
| 58 | F | 30.19 | 51 | Left | 1st MPJ fusion, LAS | ||
| 59 | M | 39.16 | 57 | Right | STJ fusion, TAL, LAS | ||
| 68 | F | 28.3 | 54 | Right | TAL, Triple arthrodesis | ||
| 59 | M | 30.7 | 50 | Left | TAL, LAS, SMO | ||
| 60 | F | 37.09 | 46 | Left | TAL, Medial double arthrodesis, LAS | ||
| 58 | F | 31.87 | 46 | Right | TAL, Medial double arthrodesis, LAS | ||
| Average | 60.15 | 61.5 % Male | 33.48 | 60.077 | 64.29 % Right |
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