Malalignment Correction of the Lower Limb Before, During, and After Total Ankle Arthroplasty

Current Trends in Total Ankle Replacement

Ankle arthritis can result in significant pain and restriction in range of motion. Total ankle replacement (TAR) is a motion-preserving surgical option used as an alternative to total ankle arthrodesis to treat end-stage ankle arthritis. There are several generations of TAR techniques based on component design, implant material, and surgical technique. With more recent TAR implants, an attempt is made to minimize bone resection and mirror the native anatomy. There are more than 20 implant devices currently available. Implant survivorship varies among prosthesis types and generations, with improved outcomes reported with use of the more recent third- and fourth-generation ankle implants. Pre- and postoperative assessments of TAR are primarily performed by using weight-bearing radiography, with weight-bearing CT emerging as an additional imaging tool. Preoperative assessments include those of the tibiotalar angle, offset, and adjacent areas of arthritis requiring additional surgical procedures. US, nuclear medicine studies, and MRI can be used to troubleshoot complications. Effective radiologic assessment requires an understanding of the component design and corresponding normal perioperative imaging features of ankle implants, as well as recognition of common and device-specific complications. General complications seen at radiography include aseptic loosening, osteolysis, hardware subsidence, periprosthetic fracture, infection, gutter impingement, heterotopic ossification, and syndesmotic nonunion. The authors review several recent generations of TAR implants commonly used in the United States, normal pre- and postoperative imaging assessment, and imaging complications of TAR. Indications for advanced imaging of TAR are also reviewed. ©RSNA, 2023 Supplemental material is available for this article. Test Your Knowledge questions for this article are available through the Online Learning Center.

The Role of Supramalleolar Osteotomies in Ankle Arthritis

The supramalleolar osteotomy (SMO) is a joint-preserving surgical procedure that allows realignment of the ankle joint in severe deformity secondary to arthritis. This osteotomy realigns the mechanical axis to provide better weight distribution through the ankle joint. With an aligned mechanical axis, the overloaded asymmetric ankle joint will shift toward the preserved joint area in a valgus or varus ankle joint. The SMO also can be used via a staged approach to correct severe deformity in an end-stage arthritic ankle before total ankle arthroplasty to optimize the implant's longevity and improve overall functional outcomes.

Post-operative management after total ankle arthroplasty: A systematic review of the literature

BACKGROUND

Currently, there is no consensus on the most appropriate post-operative management for patients undergoing total ankle arthroplasty. The aim of this study is therefore to offer a systematic review of the pertaining literature to identify current post-operative protocols and describe possible differences.

METHODS

A systematic review to identify recent studies concerning the post-operative management after total ankle arthroplasty was conducted. Five topics were analyzed: length of hospital stay, type and duration of immobilization, weight-bearing management, post-operative pharmacological therapies, adopted rehabilitation scheme.

RESULTS

Eighty-four studies met the inclusion criteria and were included in the review process. Most of the papers appear to have conflicting opinions with no consensus and homogeneous protocols.

CONCLUSION

Due to various methodological limitations, it is not possible to provide sufficiently supported evidence-based recommendations, and it is therefore difficult to determine the superiority of one post-operative protocol over the others after total ankle arthroplasty.

One-stage tibial deformity correction and ankle arthrodesis for ankle osteoarthritis and tibial malalignment after low tibial osteotomy

Introduction

There are no reports on one-stage corrective tibial opening wedge osteotomy and arthrodesis for osteoarthritis of the ankle and tibial malalignment after distal tibial osteotomy.

Presentation of case

The patient was a 70-year-old woman who presented with complaints of ankle pain and lower limb deformity after tibial osteotomy performed for ankle arthritis 17–18 years earlier. Clinical examination revealed marked swelling around the ankle joint and pain and tenderness at the joint line. Imaging showed tibial malalignment and severe osteoarthritic changes in the ankle. The patient had valgus deformity of 21° and recurvatum deformity of 4°. In two months, she admitted to Department of Orthopedics at Tokushima University Hospital in Japan and we performed one-stage corrective tibial opening wedge osteotomy and ankle arthrodesis with an anterolateral plate through a lateral longitudinal incision. After removal of the previous implants, the remaining articular cartilage and osteophytes were removed from the tibial and talar surfaces. After debridement of the talar trochlea and tibial plateau, the center of rotation and angular deformity of the tibia was cut transversely and a 1-cm bone graft obtained from the removed fibula was inserted into the osteotomy site, which decreased the tibial malalignment. An anterolateral locking plate was inserted over the anterior and lateral sides of the tibia, and the ankle was fused using 2 cannulated screws.

Discussion

The patient wore an above-knee splint for 6 weeks to avoid weight-bearing followed by gradual weightbearing with a brace thereafter. Osseous fusion was achieved after about 3.5 months. Radiographs obtained at the 2-year follow-up visit showed complete union of the tibia and talus. Full correction of valgus and recurvatum deformity was achieved, and the patient was able to perform daily activities with almost no pain.

Conclusion

We reported a rare case of ankle osteoarthritis and tibial malalignment that was successfully treated with one-stage corrective tibial opening wedge osteotomy and ankle arthrodesis using an anterolateral plate via a transfibular approach.

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Ankle osteoarthritis and malalignment can be followed by osteotomy.

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One-stage ankle arthrodesis and deformity correction should be considered.

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Anterolateral plate was useful for arthrodesis and correction.

Total Ankle Arthroplasty With Valgus Deformity

BACKGROUND

A substantial coronal plane deformity is common in the context of end-stage ankle osteoarthritis. Recent literature shows a trend toward extending the indication of total ankle arthroplasty in increasingly severe coronal deformities, showing promising results when correct alignment is achieved. Nevertheless, the results of lateral transfibular total ankle replacement (LTTAR) in valgus has not been extensively studied. We aimed to evaluate if the outcomes of LTTAR in ankles with valgus deformity were similar to those with no major deformity at short-term follow-up.

METHODS

This retrospective cohort study included 228 LTTARs. Patients were classified into 2 groups according to the preoperative coronal plane tibiotalar angle (TTS): neutral (less than 10 degrees of coronal deformity, 209 patients) and valgus (above 10 degrees of valgus, 19 patients). Clinical evaluation was performed using the American Orthopaedic Foot & Ankle Society (AOFAS) score, visual analog scale (VAS), 12-Item Short Form Health Survey 12 (SF-12) regarding its Physical and Mental Component Summary items. The radiographic evaluation considered anteroposterior and lateral ankle radiographs. Complications were also registered and classified as major or minor. The minimum follow-up was 2 years.

RESULTS

The average AOFAS, VAS, and SF-12 scores improved significantly postoperatively (P < .001), without differences between groups. At final radiographic follow-up, the valgus alignment group did not show significant differences with the neutral alignment group regarding TTS, lateral distal tibial angle, or anterior distal tibial angle (P > .05).

CONCLUSION

LTTAR in cases with valgus deformity achieved and maintained correction at short-term follow-up, as obtained in neutral alignment ankles. Clinical outcomes improved significantly regardless of preoperative valgus deformity.

LEVEL OF EVIDENCE

Prognostic Level III, retrospective cohort study.

Comparison of Mechanical Axis of the Limb Versus Anatomical Axis of the Tibia for Assessment of Tibiotalar Alignment in End-Stage Ankle Arthritis

BACKGROUND

Coronal plane ankle joint alignment is typically assessed using the tibiotalar angle (TTA), which relies on the anatomical axis of the tibia (AAT) and the articular surface of the talus as landmarks. Often, the AAT differs from the mechanical axis of the lower limb (MAL). We set out to test our hypothesis that the TTA using the MAL would differ from the TTA measured using the AAT in patients with ankle osteoarthritis.

METHODS

Standardized standing long leg radiographs of 61 ankles with end-stage osteoarthritis were analyzed. We measured the MAL and the AAT. A line was drawn along the talar articular surface (TA) and the TTA was calculated using both the MAL (MAL-TA) and the AAT (AAT-TA). The mechanical axis of the tibia (MAT) was also recorded and the MAL-MAT angle calculated. The difference between MAL-TA and AAT-TA and its correlation with the MAL-MAT angle were assessed. Intra- and interobserver agreement were measured for MAL-TA and AAT-TA.

RESULTS

The mean MAL-TA was 91.4 degrees (95% CI, 88.5-94.4) and the mean AAT-TA was 91.2 degrees (95% CI, 88.6-93.9). The difference ranged from -8.1 to 7.8 degrees, and was greater than 2 and 3 degrees in 42% and 18% of the patients, respectively. The difference, as an absolute value, also strongly correlated with the MAL-MAT angle (r = 0.91, P < .001). Intra- and interobserver reliability were excellent for both MAL-TA (intraclass correlation coefficient [ICC], 0.93 and 0.91, respectively) and AAT-TA (ICC, 0.91 and 0.89, respectively).

CONCLUSION

We recommend that surgeons consider using the MAL-TA, which relies on long leg radiographs, especially with proximal deformity, to more accurately measure coronal plane ankle joint alignment.

LEVEL OF EVIDENCE

Level III, retrospective comparative study.

A Staged Approach to Combined Extra-articular Limb Deformity Correction and Total Ankle Arthroplasty for End-Stage Ankle Arthritis

BACKGROUND

Patients presenting with end-stage ankle osteoarthritis (OA) in the setting of a concomitant extra-articular limb deformity pose a challenging problem that has not yet been described in the literature. We describe a case series of patients treated with external and internal fixation techniques followed by total ankle arthroplasty (TAA) in a staged approach to treat this complex presentation.

METHODS

Eight patients with limb deformity and end-stage ankle OA who underwent staged deformity correction and TAA from 2016 to 2019 at our institution were retrospectively identified. Average age was 58.5 (range, 49-68) years, with an average follow-up of 2.6 (range, 0.8-4.2) years. All patients underwent limb reconstruction with either tibial osteotomy with a circular frame (n=6) or intramedullary nail (n=2). Limb deformities consisted of the following: posttraumatic tibial malunion (2), limb length discrepancy (1), acquired tibial deformity (1), genu varum (2), or genu valgum (2). Radiographic parameters were assessed pre- and postoperatively on 51-inch standing and ankle radiographs: limb length discrepancy (LLD), genu varum/valgum deformity, recurvatum deformity, mechanical axis deviation, medial proximal tibial angle, lateral distal tibial angle, anterior distal tibial angle, and tibiotalar alignment. Pre- and postoperative patient-reported outcomes were assessed using 2 metrics, the Limb Deformity-Scoliosis Research Society (LD-SRS) and Patient-Reported Outcomes Measurement Information System (PROMIS) scores (Physical Function, Pain Intensity, Pain Interference, Global Physical Function, and Global Mental Function).

RESULTS

Following staged limb deformity correction and TAA, all patients achieved correction of LLD and angular deformities of the lower limb, along with restoration of normal alignment of the ankle joint. There was significant mean improvement in all patient-reported LD-SRS and PROMIS domains, except for LD-SRS mental health. LD-SRS function improved from 2.6 (±0.7) to 4.6 (±0.2), P = .008; pain improved from 2.9 (±0.9) to 4.8 (±0.2), P = .012; self-image improved from 2.9 (±0.4) to 4.7 (±0.3), P < .001; and total LD-SRS improved from 3.3 (±0.4) to 4.8 (±0.2), P = .002. Average satisfaction was 4.9 (±0.3). PROMIS physical function improved from 32.3 (±6.8) to 51.3 (±5.3), P = .008; pain interference improved from 66.0 (±9.1) to 41.3 (±6.2), P = .004; pain intensity improved from 60.0 (±13.3) to 33.1 (±5.3), P = .007; global physical health improved from 39.3 (±6.8) to 60.7 (±5.1), P = .002; global mental health improved from 54.8 (±5.9) to 65.6 (±2.8), P = .007. There was one incidence of pin site infection and one reoperation.

CONCLUSION

Deformity correction with either external frame or intramedullary nail fixation followed by TAA in a staged approach was a viable surgical option in the treatment of end-stage ankle OA with concurrent extra-articular limb deformity. This unique approach was capable of achieving deformity correction with improved patient-reported outcomes, minimal complications, and good patient satisfaction.

LEVEL OF EVIDENCE

Level IV, retrospective case series.

Mechanical and anatomical axis of the lower limb in total ankle arthroplasty

INTRODUCTION

Inadequate correction of mechanical alignment may lead to failure of Total Ankle Replacements (TAR). The mechanical axis of the lower limb (MAL), the mechanical axis of the tibia (MAT) and the anatomical axis of the tibia (AAT) are three well described coronal plane measurements using plain radiography. The assumption is that the MAL, MAT and AAT are equivalent. The relationship between these axes can vary in the presence of proximal deformity. The purpose of this study was to assess the relationship between MAL, MAT and AAT in a cohort of patients considered for TAR.

METHODS

75 consecutive standardised preoperative long leg radiographs of patients with end stage ankle osteoarthritis, between 2016 and 2017 at a specialist tertiary center for elective orthopedic surgery were analysed. Patients were split into 2 groups. The first group had a clinically and radiologically detectable deformity proximal to the ankle (such as previous tibial or femoral fracture, severe arthritis, or previous reconstructive surgery), whereas the second (normal) group did not. The MAL, MAT and AAT were measured and the difference between these values were calculated.

RESULTS

There were 54 patients in the normal group, and 21 patients in the deformity group. The mean difference between the MAL and AAT was 1.7 ± 1.3° (range, 0.1-5.4°). In the normal group, 15 patients (27%) had a difference of >2° between the MAL and AAT, compared with 52% in the deformity group. The mean difference between the MAL and MAT was 0.9 ± 1.7° (range, -4 to -3.5°). In the deformity group, 42% of patients had a difference between MAT and MAL of >2°, compared with 20% in the normal group.

CONCLUSION

MAT, MAL and AAT should not be assumed to be the same in all patients. The authors recommend considering the use of full-length weightbearing lower limb radiographs to plan TAR.

Hindfoot balancing in total ankle replacement: the role of supramalleolar osteotomies

PURPOSE

To compare the obtained deformity correction and clinical/functional outcomes between patients who underwent total ankle replacement (TAR) with or without a concurrent supramalleolar osteotomy (SMO) to address a varus and/or recurvatum deformity of the distal tibia.

METHODS

Data of 23 patients treated with an additional SMO to correct a varus and/or recurvatum deformity of the distal tibia at the time of TAR were prospectively collected. Twenty-three matched patients who underwent TAR only served as controls.

RESULTS

The American Orthopaedic Foot and Ankle Society (AOFAS)-hindfoot scale and pain assessed on a Visual Analogue Scale (VAS) did not significantly differ between the two groups at the final follow-up (AOFAS-hindfoot scale SMO/TAR group = 82 ± 10; TAR group = 82 ± 12; VAS pain SMO/TAR group = 1 (range, 0-4); TAR group = 1 (range, 0-5)). Ankle range of motion (ROM) did not improve in the SMO/TAR group (pre-operative = 27 ± 13 degrees, last follow-up = 30 ± 9 degrees; P = .294), but did improve in the TAR group (pre-operative = 31 ± 14 degrees, last follow-up = 39 ± 14 degrees; P = .049). Two patients who underwent SMO/TAR showed non-union of the tibial osteotomy, and two patients who underwent TAR only suffered from an intra-operative medial malleolar fracture.

CONCLUSION

An additional SMO during TAR in patients with a varus and/or recurvatum deformity of the distal tibia is not beneficial in most cases and should only be considered in pronounced multiplanar deformities.

Results of Tibia and Fibula Osteotomies Performed Concomitant to Total Ankle Replacement

BACKGROUND

Neutral ankle alignment along with medial and lateral support are paramount to the success of total ankle replacement (TAR). Fibula, intra-articular medial malleolus, and supramalleolar tibia osteotomies have been described to achieve these goals; however, the literature is scant with outcomes and union rates of these osteotomies performed concomitant to TAR. The purpose of this study was to describe our results.

METHODS

A retrospective review was performed to identify patients who had a concomitant tibia, fibula, or combined tibia and fibula osteotomy at the same time as TAR. Routine radiographs were used to assess osteotomy union rates and changes in alignment. Outcomes questionnaires were evaluated preoperatively and at most recent follow-up. Twenty-six patients comprising 4% of the total TAR cohort were identified with a mean follow-up of 3.9 years.

RESULTS

There were 12 combined tibia and fibula osteotomies, 9 isolated tibia osteotomies, and 5 isolated fibula osteotomies. The union rate for these osteotomies was 92%, 100%, and 100%, respectively. Mean coronal alignment improved from 15.2 to 2.1 degrees (P < .001). There was significant improvement in patient-reported outcome scores, including Short Form-36, Short Musculoskeletal Function Assessment, and visual analog scale pain. There was 1 failure in the study.

CONCLUSION

These data demonstrate successful use of tibia, fibula, or combined tibia and fibula osteotomies at the same time as TAR in order to gain neutral ankle alignment. The overall union rate was 96% with significant improvement in alignment, pain, and patient-reported outcomes. We believe concomitant osteotomies can be considered a successful adjunctive procedure to TAR.

LEVEL OF EVIDENCE

Level III, retrospective comparative series.

Evaluation of Hindfoot Alignment After Fixed- and Mobile-Bearing Total Ankle Prostheses

BACKGROUND

End-stage ankle arthritis can involve malalignment of the ankle in both the coronal and sagittal planes. Up to 33% to 44% of patients who present for total ankle replacement (TAR) have greater than 10° of coronal plane deformity. Normalization of the sagittal and coronal alignment is key in improving survivorship and functional outcomes in TAR. In the present study, we analyzed how both the ankle and hindfoot alignment for both a fixed-bearing and mobile-bearing TAR system changed over time. Specifically, we measured coronal and sagittal alignment of both the ankle and hindfoot complex.

METHODS

A retrospective study was performed on 2 independent groups of patients undergoing 2 different systems for total ankle replacement: Zimmer (lateral approach, fixed-bearing) and Hintegra (anterior approach, mobile bearing). Specific demographic data and radiographic data were measured. Within-group comparisons were performed using 1-way repeated measures ANOVA, analyzing the temporal course of clinical data within the Hintegra and Zimmer groups.

RESULTS

At the ankle joint, as measured by the α and β angles (P > .05), the position of the components remained relatively similar in both the fixed- and mobile-bearing TAR at 24-month follow-up. The sagittal alignment, as measured by the TT (tibiotalar) ratio, demonstrated a posterior shifting of the talus in the mobile bearing group (P = .036). Although the fixed- and mobile-bearing TAR had both significant hindfoot alignment improvement between the preoperative radiographs and at 24 months, over time, the fixed-bearing ankle had a significant increase in both the hindfoot alignment view angle and hindfoot alignment distance (P < .001), suggesting a possible dynamism of the hindfoot in the fixed-bearing TAR.

CONCLUSION

The lateral-approach fixed and anterior approach mobile-bearing implants maintained coronal and sagittal alignment in the short term; the temporal course of the lateral approach fixed-bearing ankle showed an increase in the valgus positioning of the hindfoot. The anterior approach mobile-bearing implant maintained its hindfoot alignment over the course of the study.

LEVEL OF EVIDENCE

Level III, case-control study.

Influence of Preoperative Tibiotalar Alignment in the Coronal Plane on the Survival of Total Ankle Replacement: A Systematic Review

BACKGROUND

It remains controversial whether significant preoperative tibiotalar varus and valgus deformity should be contraindications for total ankle replacement (TAR). The primary aim of this systematic review was to analyze the influence of preoperative tibiotalar varus and valgus alignment on the survival of TAR.

METHODS

The databases MEDLINE and Embase were searched from onset through September 2018. Two authors performed study selection and data extraction using a predefined data extraction tool. Implant survival in the alignment groups was reported as "revisions per 100 component years." Additional procedures, complications, and revisions were also reported. Assessment of the methodological quality was performed using the Newcastle-Ottawa Scale (NOS).

RESULTS

In total, 17 studies were considered eligible, in which a total of 1692 TARs were included from 1627 patients. The weighted mean follow-up was 52.4 (range, 1-147) months. The neutral alignment group included 711 TARs, the varus group included 545 TARs, and the valgus group included 332 TARs. Total revisions were 52, 37, and 36 in the preoperative tibiotalar neutral, varus, and valgus alignment groups, respectively. Revisions per 100 observed component years were 1.6, 1.7, and 2.5 in the preoperative tibiotalar neutral, varus, and valgus alignment groups, respectively. A total of 129 complications and 447 additional procedures were reported in 601 TARs.

CONCLUSION

There was a strong indication that preoperative varus alignment in the coronal plane had a comparable implant survival to neutral alignment. Preoperative valgus alignment demonstrated a more negative influence on implant survival.

LEVEL OF EVIDENCE

Level III, systematic review.

Role of Rotation in Total Ankle Replacement

BACKGROUND

The importance of total ankle replacement (TAR) implant orientation in the axial plane is poorly understood with major variation in surgical technique of implants on the market. Our aim was to better understand the axial rotational profile of patients undergoing TAR.

METHODS

In 157 standardized computed tomography (CT) scans of patients with end-stage ankle arthritis planning to undergo primary TAR surgery, we measured the relationship between the knee posterior condylar axis, the tibial tuberosity, the transmalleolar axis (TMA), and the tibiotalar angle. The foot position was measured in relation to the TMA with the foot plantigrade. The variation between the medial gutter line and the line bisecting both gutters was assessed.

RESULTS

The mean external tibial torsion was 34.5 ± 10.3 degrees (11.8-62 degrees). When plantigrade, the mean foot position relative to the TMA was 21 ± 10.6 degrees (0.7-38.4 degrees) internally rotated. As external tibial torsion increased, the foot position became more internally rotated relative to the TMA (Pearson correlation, 0.6; P < .0001). As the tibiotalar angle became more valgus, the foot became more externally rotated relative to the TMA (Pearson correlation, -0.4; P < .01). The mean difference between the medial gutter line and a line bisecting both gutters was 4.9 ± 2.8 degrees (1.7-9.4 degrees). More than 51% of patients had a difference greater than 5 degrees. The mean angle between the medial gutter line and a line perpendicular to the TMA was 7.5 ± 2.6 degrees (2.8-13.7 degrees).

CONCLUSION

There was a large variation in rotational profile of patients undergoing TAR, particularly between the medial gutter line and the TMA. Surgeon designers and implant manufacturers should develop consistent methods to guide surgeons toward judging the appropriate axial rotation of their implant on an individual basis. We recommend careful clinical assessment and preoperative CT scans to enable the correct rotation to be determined.

LEVEL OF EVIDENCE

Level IIc, outcomes research.

Should the Tibiotalar Angle Be Measured Using an AP or Mortise Radiograph? Does It Matter?

Understanding the tibiotalar angle (TTA) is key to planning for deformity correction. The TTA is an important radiographic tool to determine alignment or malalignment of the ankle and hindfoot. Two methods of measuring the TTA have been described: the midline TTA (MTTA) and the lateral TTA (LTTA). The aim of this study was to compare the 2 angles as measured on mortise and anteroposterior (AP) radiographs in a series of normal and pathological cases. A radiographic review was performed of sequential ankle AP and mortise radiographs taken between January 2016 and September 2017 across 4 specialist orthopedic centers. Patients were categorized into a normal group, where patients had normal radiological appearances, and an arthritis group, where patients had radiographic arthritis. The MTTA and the LTTA were measured. The overall mean ± standard deviation MTTA was 88.7° ± 5.1°, and mean LTTA was 87.5° ± 5.2° (p < .01). There was no statistically significant difference between the MTTA and LTTA in the normal group or on AP radiographs alone (p = .09). There was a statistically significant difference between the MTTA and LTTA in the arthritis group (p < .01) and when measured on mortise radiographs (p = .02). The MTTA had no difference when measured on the AP and mortise radiographs. There was a statistically significant difference in the LTTA between AP and mortise radiographs (p = .04). We have shown the MTTA to be a reliable and reproducible tool in all patients, on AP and mortise radiographs. The type of radiograph does not alter the measurement of deformity. In contrast, we have shown the LTTA to be unreliable and statistically different when measured on AP and mortise radiographs.

Ankle Arthritis

Ankle arthritis is a major source of morbidity impacting a younger working age population than hip and knee arthritis. Unlike the hip and knee, more than 70% of ankle arthritis cases are post-traumatic, with the remainder being inflammatory or primary arthritis. Nonoperative treatment begins with lifestyle and shoe-wear modifications and progresses to bracing, physical therapy, anti-inflammatory medications, and intra-articular injections. Ankle arthrodesis and total ankle arthroplasty are the 2 main surgical options for end-stage ankle arthritis, with debridement, realignment osteotomy, and distraction arthroplasty being appropriate for limited indications.

Total Replacement of Varus Ankle: Three-Component Prosthesis Design

In the past few decades, total ankle replacement (TAR) has become an increasingly recommended and accepted treatment in patients with end-stage ankle osteoarthritis. However, controversy still exists about the appropriate indications for TAR, specifically in ankles with coronal plane deformities. Although not explicitly proved, the long-term success of TAR seems to largely depend on the extent to which the surgeon is able to balance the ankle joint complex.