DOI:10.2214/AJR.07.2729
AJR 2008; 190:1112-1123
© American Roentgen Ray Society
Postoperative Evaluation of the Total Ankle Arthroplasty
Joseph M. Bestic1,
Jeffrey J. Peterson1,
James K. DeOrio1,2,
Laura W. Bancroft1,
Thomas H. Berquist1 and
Mark J. Kransdorf1,3
1 Department of Radiology, Mayo Clinic, 4500 San Pablo Rd., Jacksonville, FL
32224-3899.
2 Present address: Department of Orthopedics, Duke University Medical Center,
Durham, NC.
3 Department of Radiologic Pathology, Armed Forces Institute of Pathology,
Washington, DC.
Received June 10, 2007;
accepted after revision November 1, 2007.
The opinions and assertions contained herein are the private views of the
authors and are not to be construed as official or as reflecting the views of
the Department of the Army or the Department of Defense.
J. K. DeOrio is a consultant for Link Orthopedics and Integra, is a
consultant for and has a financial interest in INBONE Technologies, and is a
member of the speakers' bureau of Tornier. He was also a member of the design
team for the Zimmer total ankle and has been a consultant for the DePuy
Orthopedic Company.
Presented at the 2007 annual meeting of the American Roentgen Ray Society,
Orlando, FL, where a certificate of merit was awarded.
Address correspondence to J. M. Bestic
(bestic.joseph{at}mayo.edu).
CME
This article is available for CME credit. See
www.arrs.org
for more information.
Abstract
OBJECTIVE. The purpose of this article is to review the basic design
features of second-generation total ankle arthroplasty components and to
illustrate the normal and abnormal postoperative imaging features associated
with such devices. The usefulness of CT in postoperative evaluation will be
highlighted.
CONCLUSION. Postoperative evaluation of the total ankle arthroplasty
necessitates a familiarity with the various designs currently in use.
Radiography serves as an integral component in the postoperative evaluation of
such devices, with CT offering further characterization of radiographic
abnormalities.
Keywords: ankle • ankle arthroplasty devices • arthroplasty • musculoskeletal imaging
Introduction
Total ankle arthroplasty was developed to provide an alternative to ankle
arthrodesis for the treatment of severe arthrosis, with the inherent advantage
of preserving joint motion. Initially introduced with much optimism in the
1970s, cemented first-generation ankle arthroplasties were subsequently found
to be plagued with unacceptably high complication rates and were largely
abandoned [1,
2]. Enthusiasm for total ankle
arthroplasty has been renewed with the development of uncemented
second-generation devices, which have addressed many of the initial technical
failures through innovative designs and refined surgical techniques. Newer
designs require less bone resection, leaving stronger subchondral bone to
secure the prosthesis. In addition, mobile-bearing prostheses offer the
distinct possibility of less wear and loosening, which is attributable to
improved component conformity and minimal constraint. To date,
second-generation total ankle arthroplasty devices have been reported to have
promising intermediate-term results
[3,
4]. However, the long-term
outcome of total ankle arthroplasty is under continued scrutiny, with recent
success tempered by the poor performance of cemented first-generation devices
and the realization that complications will and do occur with
second-generation devices [3,
5,
6]. Regardless, encouraging
results with second-generation devices have led to their increasing
popularity, with a multitude of total ankle devices to choose from
worldwide.
Total Ankle Arthroplasty Devices
Effective postoperative imaging evaluation of the total ankle arthroplasty
requires an appreciation for basic component design philosophy and a
familiarity with the unique features of the various devices in use. Existing
second-generation devices incorporate two basic design
philosophies—namely, three-component (mobile-bearing) and two-component
(fixed-bearing) designs. Three-com ponent designs are characterized by
individual tibial and talar devices, which are separated by a fully conforming
mobile polyethylene spacer. Two-component devices have only a single partially
conforming articulation between the tibial and talar devices, with the
polyethylene spacer fixed to the tibial component.
At least 20 different ankle replacement systems are in use worldwide, with
new systems in continual development. Examples of commonly used
second-generation total ankle arthroplasty devices include the STAR
(Scandinavian Total Ankle Replacement, Waldemar Link) (Figs.
1A and
1B), the Buechel-Pappas Total
Ankle Replacement (Endotec) (Figs.
2A and
2B), the TNK ankle (Japan
Medical Materials) (Figs. 3A
and 3B), and the Agility Total
Ankle System (DePuy) (Figs. 4A
and 4B). Of these devices, only
the Agility Total Ankle was approved by the U.S. Food and Drug Administration
(FDA) for use in the United States before 2006. Since then, three new devices
have received FDA approval. These include the INBONE Total Ankle (INBONE
Technologies, formerly Topez Orthopedics) (Figs.
5A and
5B), the Salto Talaris Total
Ankle (Tornier) (Figs. 6A and
6B), and the Eclipse Total
Ankle (Integra Life Sciences Holdings). Although these devices are
FDA-approved for use with cement, they are exclusively used offlabel without
cement and feature bone ingrowth components. The STAR ankle replacement
recently received tentative FDA approval for use without cement and is
expected to be available to surgeons later this year
[7].
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Fig. 1A —STAR arthroplasty device (Scandinavian Total Ankle
Replacement, Waldemar Link) is cementless, three-component (mobile-bearing)
design developed by H. Kofoed in 1981. Mobile, ultrahigh-molecular-weight
polyethylene (UHMWPE) meniscus (thick black arrow) articulates
superiorly with trapezoidal, flat, cobalt–chromium tibial plate
(white arrow) and inferiorly with longitudinally ridged, convex,
cobalt–chromium talar component (thin black arrow). Talar
component possesses fin (asterisk, B) that inserts caudally
into talus. Two characteristic cylindric bars (arrowheads) positioned
on superior aspect of tibial component serve to anchor implant in subchondral
tibia. Photograph of STAR arthroplasty device, oblique lateral view.
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Fig. 1B —STAR arthroplasty device (Scandinavian Total Ankle
Replacement, Waldemar Link) is cementless, three-component (mobile-bearing)
design developed by H. Kofoed in 1981. Mobile, ultrahigh-molecular-weight
polyethylene (UHMWPE) meniscus (thick black arrow) articulates
superiorly with trapezoidal, flat, cobalt–chromium tibial plate
(white arrow) and inferiorly with longitudinally ridged, convex,
cobalt–chromium talar component (thin black arrow). Talar
component possesses fin (asterisk, B) that inserts caudally
into talus. Two characteristic cylindric bars (arrowheads) positioned
on superior aspect of tibial component serve to anchor implant in subchondral
tibia. Anteroposterior radiograph of STAR arthroplasty device.
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Fig. 2A —Buechel-Pappas total ankle prosthesis (Endotec). Similar to
STAR (Scandinavian Total Ankle Replacement, Waldemar Link) device,
Buechel-Pappas ankle replacement is cementless, three-component
(mobile-bearing) design. Tibial component is stabilized by stem that extends
into tibial metaphysis (arrowhead). Ultrahigh-molecular-weight
polyethylene meniscus (thick arrow) glides along metallic talar
component (thin arrow) stabilized by ridge on its undersurface
(asterisk) that articulates with corresponding longitudinal groove on
talar component. Design allows limited inversion and eversion of ankle joint
without loss of congruity and requires minimal talar bone resection.
Photograph of Buechel-Pappas arthroplasty device, frontal view.
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Fig. 2B —Buechel-Pappas total ankle prosthesis (Endotec). Similar to
STAR (Scandinavian Total Ankle Replacement, Waldemar Link) device,
Buechel-Pappas ankle replacement is cementless, three-component
(mobile-bearing) design. Tibial component is stabilized by stem that extends
into tibial metaphysis (arrowhead). Ultrahigh-molecular-weight
polyethylene meniscus (thick arrow) glides along metallic talar
component (thin arrow) stabilized by ridge on its undersurface
(asterisk) that articulates with corresponding longitudinal groove on
talar component. Design allows limited inversion and eversion of ankle joint
without loss of congruity and requires minimal talar bone resection.
Anteroposterior radiograph of Buechel-Pappas arthroplasty device.
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Fig. 3A —TNK (Japan Medical Materials) ankle prosthesis is cementless,
two-component (fixed-bearing) device used almost exclusively in Japan. This
device consists of fused ceramic tibial (thin white arrow) and flat
ultrahigh-molecular-weight polyethylene tray (thick white arrow)
components that articulate with convex ceramic talar component (black
arrow). Several bone fixation methods have been used, including
hydroxyapatite-coated beads, fixation screws, and biologic coating. This
prosthesis requires large amount of bone resection and has been associated
with high rate of subsidence. Photograph of TNK device, oblique frontal
view.
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Fig. 3B —TNK (Japan Medical Materials) ankle prosthesis is cementless,
two-component (fixed-bearing) device used almost exclusively in Japan. This
device consists of fused ceramic tibial (thin white arrow) and flat
ultrahigh-molecular-weight polyethylene tray (thick white arrow)
components that articulate with convex ceramic talar component (black
arrow). Several bone fixation methods have been used, including
hydroxyapatite-coated beads, fixation screws, and biologic coating. This
prosthesis requires large amount of bone resection and has been associated
with high rate of subsidence. Anteroposterior radiograph of TNK device.
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Fig. 4A —Agility Total Ankle System (DePuy) has been available for use
since 1984, making it longest-used total ankle replacement system in United
States. Agility ankle is porous-coated, two-piece (fixed-bearing) implant with
partially conforming articulation. Modular, concave polyethylene insert
(asterisk) locks into tibial component (thin arrow). Talar
component (thick arrow) articulates with tibial component with
approximately 20° of external rotation. Syndesmotic fusion (double
arrowheads, B) increases surface area of tibial component
prosthesis–bone interface in attempt to resist subsidence while allowing
fibula to share portion of load. Failure of syndesmotic fusion is associated
with increased rate of failure
[8]. Photograph of Agility
device, oblique frontal view.
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Fig. 4B —Agility Total Ankle System (DePuy) has been available for use
since 1984, making it longest-used total ankle replacement system in United
States. Agility ankle is porous-coated, two-piece (fixed-bearing) implant with
partially conforming articulation. Modular, concave polyethylene insert
(asterisk) locks into tibial component (thin arrow). Talar
component (thick arrow) articulates with tibial component with
approximately 20° of external rotation. Syndesmotic fusion (double
arrowheads, B) increases surface area of tibial component
prosthesis–bone interface in attempt to resist subsidence while allowing
fibula to share portion of load. Failure of syndesmotic fusion is associated
with increased rate of failure
[8]. Anteroposterior radiograph
of Agility device.
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Fig. 5A —INBONE Total Ankle (INBONE Technologies, formerly Topez
Orthopedics) is two-component (fixed-bearing) device with bone ingrowth
anchoring stems in both tibial (thin arrow) and talar
(arrowhead) components. Polyethylene insert (thick arrow) is
attached to tibial component. Modular tibial stem consists of individual
segments that can be customized for each patient. Photograph of INBONE device,
frontal view.
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Fig. 5B —INBONE Total Ankle (INBONE Technologies, formerly Topez
Orthopedics) is two-component (fixed-bearing) device with bone ingrowth
anchoring stems in both tibial (thin arrow) and talar
(arrowhead) components. Polyethylene insert (thick arrow) is
attached to tibial component. Modular tibial stem consists of individual
segments that can be customized for each patient. Anteroposterior radiograph
of INBONE device.
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Fig. 6A —Salto Talaris Total Ankle replacement (Tornier) is
two-component (fixed-bearing) device with anatomic design consisting of
cobalt–chromium tibial (thick arrow) and talar (thin
arrow) components. Slide-on ultrahigh-molecular-weight polyethylene
insert (asterisk) is attached to tibial component and shows matching
articular geometry with talar implant. Tapered fixation plug
(arrowhead) on superior aspect of tibial component serves to secure
implant against bone surface. Photograph of Salto Talaris device, lateral
view.
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Fig. 6B —Salto Talaris Total Ankle replacement (Tornier) is
two-component (fixed-bearing) device with anatomic design consisting of
cobalt–chromium tibial (thick arrow) and talar (thin
arrow) components. Slide-on ultrahigh-molecular-weight polyethylene
insert (asterisk) is attached to tibial component and shows matching
articular geometry with talar implant. Tapered fixation plug
(arrowhead) on superior aspect of tibial component serves to secure
implant against bone surface. Lateral radiograph of Salto Talaris device.
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Imaging of the Total Ankle Arthroplasty
The postoperative evaluation of total ankle arthroplasties consists of
serial clinical and radiographic assessment. Imaging is imperative in
identifying early postoperative complications, which may not be apparent on
clinical examination. Thus, a thorough understanding of the normal and
abnormal postoperative imaging features associated with such devices is of
considerable value. CT can supplement the postoperative evaluation of total
ankle arthroplasty devices by providing a more detailed evaluation of implant
components and surrounding osseous change.
Routine postoperative radiographs provide valuable information for the
orthopedic surgeon concerning the anatomic relationship between osseous
structures and implant components and the presence and extent of bone loss or
heterotopic bone formation. Most important, radiographs serve to evaluate
changes on serial examinations, which may signify the development of
postoperative complications. Anteroposterior and lateral views of the ankle
should ideally be obtained with the patient in the standing position to ensure
physiologic positioning. Non–weight-bearing lateral radiographs obtained
with the ankle in maximal dorsiflexion and plantar flexion can facilitate
evaluation of the range of motion. Fluoroscopically positioned views serve to
optimize radiographic alignment of the component–bone or
bone–cement interfaces
[8].
Perhaps the most important role of imaging in the postoperative evaluation
of total ankle arthroplasties is to detect changes in component position,
which may signify evidence of component loosening. Although component
migration is often readily apparent, more subtle changes in component
angulation or position relative to surrounding osseous structures can be
detected by carefully analyzing angular and linear measurements on serial
radiographic examinations
[9–11]
(Figs. 7A,
7B,
7C,
7D,
7E,
7F, and
7G). Although such
measurements are not routinely made on all follow-up examinations, this
information may aid in the detection of subtle abnormalities (especially if
there is clinical concern for loosening) and can be used to provide the
surgeon with evidence of quantifiable change. An angular change of more than
5° in the measured angle of either component suggests component migration
or subsidence [11]. More than
5-mm subsidence of the talar component on lateral view is also considered
worrisome for loosening [10].
Component loosening can also manifest as radiolucent lines at the
component–bone interface. Radiolucent lines greater than 2 mm or a
progressive increase in the width or extent of existing radiolucencies is
considered significant [8]. It
is important to differentiate such radiolucencies from those related to
surgical technique, which may surround components in the immediate
postoperative setting.
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Fig. 7A —Radiographic measurements for total ankle arthroplasty
(illustrated using STAR [Scandinavian Total Ankle Replacement, Waldemar Link]
device). Angular and linear values can be defined to evaluate changes in
component alignment and position that may signify component migration
[8–10].
Anteroposterior view of STAR device depicts method of angular evaluation.
Alpha angle ( ) is formed by intersection of lines drawn parallel to
flat plate of tibial component and long axis of tibial shaft on
anteroposterior view (normal = 90°).
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Fig. 7B —Radiographic measurements for total ankle arthroplasty
(illustrated using STAR [Scandinavian Total Ankle Replacement, Waldemar Link]
device). Angular and linear values can be defined to evaluate changes in
component alignment and position that may signify component migration
[8–10].
Lateral view of STAR device depicts method of angular evaluation. Beta angle
(β) is formed by intersection of lines drawn parallel to flat plate of
tibial component and long axis of tibial shaft (normal = 90°). Gamma angle
( ) is formed by intersection of line drawn through long axis of talar
component with line drawn from posterior talar component through middle of
talar neck. Gamma angle in postoperative setting has been shown to range from
11.1° to –33.4°, with average measurement of 18.8°
[10].
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Fig. 7C —Radiographic measurements for total ankle arthroplasty
(illustrated using STAR [Scandinavian Total Ankle Replacement, Waldemar Link]
device). Angular and linear values can be defined to evaluate changes in
component alignment and position that may signify component migration
[8–10].
Anteroposterior (C) and lateral (D) views of STAR device depict
method of linear evaluation of component position. Linear values are
established by measuring position of components relative to surrounding
osseous structures. Measurement "a" is perpendicular distance
between tip of lateral malleolus and line drawn through base of tibial
component. Measurement "b" is perpendicular distance from anterior
aspect of talar component to line intersecting calcaneal tubercle and dorsal
aspect of talonavicular joint. Measurement "c" is perpendicular
distance from posterior aspect of talar component to line intersecting
calcaneal tubercle and dorsal aspect of talonavicular joint.
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Fig. 7D —Radiographic measurements for total ankle arthroplasty
(illustrated using STAR [Scandinavian Total Ankle Replacement, Waldemar Link]
device). Angular and linear values can be defined to evaluate changes in
component alignment and position that may signify component migration
[8–10].
Anteroposterior (C) and lateral (D) views of STAR device depict
method of linear evaluation of component position. Linear values are
established by measuring position of components relative to surrounding
osseous structures. Measurement "a" is perpendicular distance
between tip of lateral malleolus and line drawn through base of tibial
component. Measurement "b" is perpendicular distance from anterior
aspect of talar component to line intersecting calcaneal tubercle and dorsal
aspect of talonavicular joint. Measurement "c" is perpendicular
distance from posterior aspect of talar component to line intersecting
calcaneal tubercle and dorsal aspect of talonavicular joint.
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Fig. 7E —Radiographic measurements for total ankle arthroplasty
(illustrated using STAR [Scandinavian Total Ankle Replacement, Waldemar Link]
device). Angular and linear values can be defined to evaluate changes in
component alignment and position that may signify component migration
[8–10].
Sequential lateral views of STAR device depict small change ( 4°) in
gamma angle over course of approximately 3 years. Such angular measurements,
although they are often not routinely used, facilitate detection of subtle
changes in component position and can be helpful in providing evidence of
quantifiable change to surgeon.
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Fig. 7F —Radiographic measurements for total ankle arthroplasty
(illustrated using STAR [Scandinavian Total Ankle Replacement, Waldemar Link]
device). Angular and linear values can be defined to evaluate changes in
component alignment and position that may signify component migration
[8–10].
Sequential lateral views of STAR device depict small change ( 4°) in
gamma angle over course of approximately 3 years. Such angular measurements,
although they are often not routinely used, facilitate detection of subtle
changes in component position and can be helpful in providing evidence of
quantifiable change to surgeon.
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Fig. 7G —Radiographic measurements for total ankle arthroplasty
(illustrated using STAR [Scandinavian Total Ankle Replacement, Waldemar Link]
device). Angular and linear values can be defined to evaluate changes in
component alignment and position that may signify component migration
[8–10].
Coronal CT image obtained at time of follow-up radiograph depicted in F
shows thin region of osteolysis involving medial aspect of talar component
(arrows). Constellation of findings in this case is concerning for
aseptic loosening. Concave undersurface of talar component clearly precludes
adequate radiographic evaluation of this region, highlighting usefulness of CT
in such circumstances.
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To better localize abnormalities about the components, a zonal system
(similar to the Gruen classification of the hip) may be used
[9,
12,
13]. Using the STAR device as
a representative example, bone surrounding the tibial component can be divided
into distinct zones on the anteroposterior radiograph. Individual zones are
demarcated by lines drawn perpendicular to the tibial plate on each side of
the cylindric bars, which are seen on end in the anteroposterior projection.
Using this system of demarcation yields five zones that span the length of the
tibial plate. These five zones are labeled 1–5, medial to lateral. In a
similar fashion, the tibial component can be divided into individual zones on
the lateral radiograph. Again using the cylindric bars of the tibial plate as
a reference, lines are drawn perpendicular to the tibial plate at the anterior
and posterior aspects of the cylindric bars now seen in their long axis. Three
individual zones are thus demarcated in the lateral projection (A–C,
anterior to posterior) (Figs.
8A and
8B). Dividing the components
into distinct zones can serve to facilitate effective communication between
the radiologist and orthopedic surgeon.
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Fig. 8A —Zonal system (illustrated with STAR [Scandinavian Total Ankle
Replacement, Waldemar Link] device) offers advantage of more precise
localization of abnormalities of components. In anteroposterior projection,
tibial component can be divided into five zones by lines drawn perpendicular
to tibial plate. Lines are drawn on each side of cylindric bars, yielding five
individual zones (1–5, medial to lateral).
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Fig. 8B —Zonal system (illustrated with STAR [Scandinavian Total Ankle
Replacement, Waldemar Link] device) offers advantage of more precise
localization of abnormalities of components. In lateral projection, tibial
component can be divided into three zones by lines drawn perpendicular to
tibial plate. Lines are drawn at anterior and posterior aspects of cylindric
bars, yielding three individual zones (A–C, anterior to posterior).
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In radiographically equivocal or troublesome cases, CT may be used to
further characterize or confirm suspected postoperative complications. CT has
been shown to be superior to conventional radiography for the early detection
and more accurate quantification of periprosthetic radiolucencies
[14]. CT technique should be
modified to optimize imaging, with attempts made to reduce attenuation and
streak artifacts related to metal with a high-attenuation coefficient. The
effective energy of the X-ray beam should be increased (kVp 140, mAs 200).
These adjustments improve the penetration of dense metal and improve the
accuracy of projection data. When practical, aligning the axis of the implant
so that the X-ray beam traverses the smallest possible cross-sectional area
serves to reduce artifacts. Artifacts may be further mini mized with the use
of narrow collimation settings
[15]. Extended range
postprocessing can also be used to decrease metallic streak artifact. A
standard or smooth reconstruction filter is preferred because metallic
artifact is accentuated with the use of a sharp or bone algorithm. If
available on individual scanners, the CT scale may be increased (up to 40,000
H) to accommodate the high linear attenuation coefficients of metal, which lie
outside the normal range of reconstructed CT attenuations
[15]. Thin slice selection and
thin collimation are necessary to achieve isotropic imaging, which facilitates
multiplanar reformatted imaging in any plane.
Postoperative Complications
The complex biomechanics of the ankle, with its substantial shearing and
axial loading forces, predispose total ankle replacements to a variety of
complications. Careful preoperative patient selection and meticulous surgical
technique can help to minimize complications associated with total ankle
arthroplasty. Such complications may be categorized as intraoperative, early
postoperative, or delayed. Intraoperative complications include injury to
neurovascular and tendinous structures, malpositioning or improper sizing of
prosthetic components, excessive bone resection, and malleolar fractures.
Infection (Fig. 9), impaired
wound healing, swelling, stress fractures across the medial malleolus, and
syndesmotic nonunions (Agility Total Ankle only) may be observed in the early
postoperative period. Delayed postoperative complications include, but are not
limited to, deep infection, development of periprosthetic radiolucencies
(Figs. 10A,
10B, and
10C), aseptic loosening and
subsidence (Figs. 11A and
11B), periprosthetic fractures
(Figs. 12A and
12B), polyethylene wear with
osteolysis, spacer migration or fracture (Figs.
13A,
13B,
14A,
14B,
14C, and
14D), heterotopic bone
formation, syndesmotic nonunion (Agility Total Ankle only), and reflex
sympathetic dystrophy [5,
6]. Among the more frequent of
these complications are wound healing problems, deep infection, polyethylene
wear, and aseptic loosening [5,
6]. Failure secondary to
loosening is generally considered a major late complication of total ankle
arthroplasty [4].
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Fig. 9 —Infection in 67-year-old man. Lateral radiograph of STAR
total ankle (Scandinavian Total Ankle Replacement, Waldemar Link) shows
several pockets of gas (arrows) in soft tissues of ankle secondary to
superficial infection.
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Fig. 10A —Periprosthetic lucencies. Anteroposterior radiograph of STAR
total ankle (Scandinavian Total Ankle Replacement, Waldemar Link) in
46-year-old woman shows ovoid radiolucency (circled in white) located
in zones 4 and 5 of tibial component. At surgery, this radiolucency was found
to represent polyethylene osteolysis. Note lateral migration of tibial
component with associated remodeling of fibula (white arrow).
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Fig. 10B —Periprosthetic lucencies. Initial postoperative
anteroposterior radiograph of STAR total ankle in 65-year-old woman shows
slight discordance between surgical drill pathways (arrows) and
cylindric bars of tibial component. This should not be confused with
osteolysis.
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Fig. 10C —Periprosthetic lucencies. Lateral radiograph of a
Buechel-Pappas total ankle (Endotec) in 41-year-old woman shows well-defined
radiolucent region located in anterior tibia just above tibial component plate
(arrowhead). Cultures were negative at time of implant removal. Note
concomitant subsidence of talar component (black arrow) and prominent
heterotopic bone extending into ankle joint around anterior and posterior
aspects of tibial plate (white arrows).
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Fig. 11A —Aseptic loosening. Anteroposterior radiograph of STAR total
ankle (Scandinavian Total Ankle Replacement, Waldemar Link) in 46-year-old
woman shows marked lateral tibial component migration with extensive
surrounding osteolysis (thick black arrow) and remodeling of fibula
(thick white arrow). Stress fracture is present in medial malleolus
(thin black arrow). Note lateral talar suture anchor (thin white
arrow) from prior lateral ligamentous reconstruction.
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Fig. 11B —Aseptic loosening. Anteroposterior radiograph of Agility
Total Ankle (DePuy) in 65-year-old woman shows marked subsidence and lateral
tilt of talar component (black arrow). Large radiolucent focus is
evident in medial malleolus (white arrow) with thin region of
periprosthetic radiolucency about lateral aspect of tibial component
(arrowhead). These changes have developed despite presence of
successful syndesmotic fusion (asterisk). Both components were
revised within 1 year of this radiograph, with sparse bone ingrowth evident on
removal of components. Cultures were negative at time of surgery.
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Fig. 12A —Periprosthetic fracture. Alterations in stress distribution
related to component size or position may lead to periprosthetic fractures.
Malleolar fractures may also occur as result of excessive bone resection or
during implantation of prosthesis
[5]. Despite presence of medial
malleolar screw, periprosthetic fracture (white arrow) can be seen in
medial malleolus on anteroposterior radiograph of a STAR total ankle
(Scandinavian Total Ankle Replacement, Waldemar Link) in 75-year-old woman.
Note tiny round radiolucency (black arrow) related to wire pins used
to secure saw guide during placement of device.
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Fig. 12B —Periprosthetic fracture. Alterations in stress distribution
related to component size or position may lead to periprosthetic fractures.
Malleolar fractures may also occur as result of excessive bone resection or
during implantation of prosthesis
[5]. Corresponding coronal CT
image confirms periprosthetic fracture (arrow) involving medial
malleolus. Extension of fracture line to level of tibial component is clearly
shown.
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Fig. 13A —Migration of polyethylene spacer with ankle subluxation in
72-year-old man. Anteroposterior radiograph of STAR total ankle (Scandinavian
Total Ankle Replacement, Waldemar Link) shows ankle subluxation and lateral
migration of polyethylene spacer (arrow) with resultant malalignment.
Such changes often occur as result of lateral ligamentous instability. Note
suture anchor (arrowhead) from lateral ligamentous reconstruction
performed at time of STAR device placement.
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Fig. 13B —Migration of polyethylene spacer with ankle subluxation in
72-year-old man. Coronal CT scan confirms significant lateral migration of
polyethylene spacer (arrow) and facilitates more detailed evaluation
of morphology and integrity of polyethylene component. Note loss of normally
parallel superior and inferior surfaces of polyethylene spacer due to
asymmetric wear medially (asterisk).
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Fig. 14A —Fracture of polyethylene component in 69-year-old man.
Anteroposterior radiograph of STAR total ankle (Scandinavian Total Ankle
Replacement, Waldemar Link) suggests damage to polyethylene spacer, as
evidenced by abnormal lateral migration of wire marker embedded in spacer
(arrow).
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Fig. 14B —Fracture of polyethylene component in 69-year-old man. Axial
(B) and sagittal (C) CT images confirm fractured polyethylene
component (asterisk). Note concomitant polyethylene osteolysis in
tibia (arrow, C) that predominantly involves posterior aspect
of zone B.
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Fig. 14C —Fracture of polyethylene component in 69-year-old man. Axial
(B) and sagittal (C) CT images confirm fractured polyethylene
component (asterisk). Note concomitant polyethylene osteolysis in
tibia (arrow, C) that predominantly involves posterior aspect
of zone B.
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Currently available second-generation total ankle devices share many common
characteristics and therefore develop many of the same complications. As a
whole, three-component (mobile-bearing) designs are at an increased risk of
polyethylene spacer dislocation, albeit unusual, and may generate more wear
particles from the two separate articulations. Two-component (fixed-bearing)
designs show only partial conformity involving a single articulation, which
increases stability but also theoretically increases polyethylene contact
stress and wear. The risk of polyethylene spacer dislocation is much lower
with two-component designs
[2].
Individual design features associated with specific devices often
predispose each to unique problems that may be anticipated on follow-up
imaging. The three-component STAR device shows a relative lack of inversion
and eversion, which may result in excessive contact stress (edge loading) on
the polyethylene spacer and may transfer an increased load to the
prosthesis–bone interface
[2]. Excessive contact stress
increases wear on the polyethylene component, ultimately predisposing to
osteolysis. In contrast, the Buechel-Pappas ankle uses a fully congruent
deepsulcus polyethylene spacer that allows limited inversion and eversion
motion with a concomitant reduction in contact stress
[2,
16]. Implantation of the
Buechel-Pappas ankle requires violation of the anterior tibial cortex for
placement of the tibial component, which may compromise cortical integrity
proximal to the implant [2]. In
addition, the smaller anteroposterior dimensions of the Buechel-Pappas tibial
plate in comparison with the anteroposterior dimensions of the resected distal
tibia allows bone overgrowth, which may ultimately lead to limitations in
range of motion [16]
(Fig. 10C). This bone
overgrowth often limits motion in the mobile-bearing ankles, essentially
converting them to two-piece designs. Nonunion or delayed union of the
syndesmotic fusion unique to the Agility Total Ankle has been associated with
migration of the tibial component, ballooning osteolysis, and circumferential
radiolucency about the tibial component
[12]. Agility Total Ankle
component subsidence or migration frequently involves the talar component
[3,
13]
(Fig. 11B). This may be
attributable to the relatively narrow design of the talar component, which
only partially covers the cut talar surface
[13]. Newer designs
incorporate a wider-based talar component in an effort to combat subsidence
[7]. The design of the TNK
ankle requires removal of a significant amount of bone stock, predisposing
this prosthesis to a relatively high rate of subsidence
[2]. Limited data are currently
available concerning the results of newer total ankle designs. These include
three new two-piece designs recently approved for use by the FDA: INBONE
(INBONE Technologies), Salto-Talaris (Tornier), and Eclipse (Integra Life
Science Holdings) ankles, and a recent recommendation for approval by the FDA
of the STAR mobile-bearing design (Scandinavian Total Ankle Replacement,
Waldemar Link). Nonetheless, continual advances in both implant design and
surgical technique hold much promise for improved outcomes.
Conclusion
Promising intermediate-term results associated with second-generation
devices have made total ankle arthroplasty a viable alternative to ankle
arthrodesis. The concomitant increase in popularity of such devices
necessitates a familiarity with both normal and abnormal postoperative imaging
features. Radiographs serve as an integral component in the postoperative
evaluation of the total ankle arthroplasty. The addition of CT to the
radiologist's armamentarium can augment post-operative evaluation,
specifically when dealing with equivocal radiographic findings.
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Abstract
Introduction
