Total Ankle Arthroplasty

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1 Musculoskeletal Imaging Pictorial Essay estic et al. Total nkle rthroplasty Musculoskeletal Imaging Pictorial Essay Downloaded from by on 11/26/17 from IP address Copyright RRS. For personal use only; all rights reserved Joseph M. estic 1 Jeffrey J. Peterson 1 James K. DeOrio 1,2 Laura W. ancroft 1 Thomas H. erquist 1 Mark J. Kransdorf 1,3 estic JM, Peterson JJ, DeOrio JK, ancroft LW, erquist TH, Kransdorf MJ Keywords: ankle, ankle arthroplasty devices, arthroplasty, musculoskeletal imaging DOI: /JR Received June 10, 2007; accepted after revision November 1, 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 rmy 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 INONE 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 merican Roentgen Ray Society, Orlando, FL, where a certificate of merit was awarded. 1 Department of Radiology, Mayo Clinic, 4500 San Pablo Rd., Jacksonville, FL ddress correspondence to J. M. estic (bestic.joseph@mayo.edu). 2 Present address: Department of Orthopedics, Duke University Medical Center, Durham, NC. 3 Department of Radiologic Pathology, rmed Forces Institute of Pathology, Washington, DC. CME This article is available for CME credit. See for more information. JR 2008; 190: X/08/ merican Roentgen Ray Society Postoperative Evaluation of the Total nkle rthroplasty OJECTIVE. The purpose of this article is to review the basic design features of secondgeneration 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. T otal 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, secondgeneration 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 secondgeneration devices have led to their increasing popularity, with a multitude of total ankle devices to choose from worldwide. Total nkle rthroplasty 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 twocomponent (fixed-bearing) designs. Threecom 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. t 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 STR (Scandinavian Total nkle Replacement, Waldemar Link) (Fig. 1), the uechel-pappas Total nkle Replacement (Endotec) (Fig. 2), the TNK ankle (Japan Medical Materials) (Fig. 3), and the gility Total nkle System (DePuy) (Fig. 4). Of these devices, only the gility Total nkle was approved by the U.S. Food and Drug dministration (FD) for use in the United States before Since then, three new devices have received FD approval. These include the INONE Total nkle (INONE Technologies, formerly Topez 1112 JR:190, pril 2008

2 Total nkle rthroplasty Downloaded from by on 11/26/17 from IP address Copyright RRS. For personal use only; all rights reserved Orthopedics) (Fig. 5), the Salto Talaris Total nkle (Tornier) (Fig. 6), and the Eclipse Total nkle (Integra Life Sciences Holdings). lthough these devices are FD-approved for use with cement, they are exclusively used offlabel without cement and feature bone ingrowth components. The STR ankle replacement recently received tentative FD approval for use without cement and is expected to be available to surgeons later this year [7]. Imaging of the Total nkle rthroplasty 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. nteroposterior 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. lthough 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] (Fig. 7). lthough 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. n 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. 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 STR 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. gain 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 ( C, anterior to posterior) (Fig. 8). Dividing the components into distinct zones can serve to facilitate effective communication between the radiologist and orthopedic surgeon. 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, ms 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. rtifacts 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. 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 (gility Total nkle only) may be observed in the early postoperative period. Delayed postoperative complications include, but are not limited to, deep infection, development of periprosthetic radiolucencies (Fig. 10), aseptic loosening and subsidence (Fig. 11), periprosthetic fractures (Fig. 12), polyethylene wear with osteolysis, spacer migration or fracture (Figs. 13 and 14), heterotopic bone formation, syndesmotic nonunion (gility Total nkle only), and reflex sympathetic dystrophy [5, 6]. mong 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]. JR:190, pril

3 estic et al. Downloaded from by on 11/26/17 from IP address Copyright RRS. For personal use only; all rights reserved Currently available second-generation total ankle devices share many common characteristics and therefore develop many of the same complications. s 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 STR 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 uechel- 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 uechel-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 uechel- 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 gility Total nkle has been associated with migration of the tibial component, ballooning osteolysis, and circumferential radiolucency about the tibial component [12]. gility Total nkle component subsidence or migration frequently involves the talar component [3, 13] (Fig. 11). 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 FD: INONE (INONE Technologies), Salto-Talaris (Tornier), and Eclipse (Integra Life Science Holdings) ankles, and a recent recommendation for approval by the FD of the STR mobile-bearing design (Scandinavian Total nkle 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 postoperative evaluation, specifically when dealing with equivocal radiographic findings. References 1. Sodha S, Wei SY, Okereke E. Evolution of total ankle arthroplasty. Univ Pennsylvania Orthop J 2000; 13: Easley ME, Vertullo CJ, Urban WC, Nunley J. Total ankle arthroplasty. J m cad Orthop Surg 2002; 10: Spirt, ssal M, Hansen ST. Complications and failure after total ankle arthroplasty. J one Joint Surg m 2004; 86: Jackson MP, Singh D. Total ankle replacement. Current Orthopaedics 2003; 17: Conti SF, Wong YS. Complications of total ankle replacement. Clin Orthop 2001; 391: DeOrio JK. Focus on total ankle arthroplasty. Orthopedics 2006; 29: DeOrio JK, Easley ME. Total ankle arthroplasty. In: Instructional course lectures. merican cademy of Orthopaedic Surgeons, 2008 (in press) 8. erquist TH, DeOrio JK. Reconstructive procedures. In: erquist TH, ed. Radiology of the foot and ankle, 2nd ed. Philadelphia, P: Lippincott Williams & Wilkins, 2000: Knecht SI, Estin M, Callaghan JJ, et al. The gility total ankle arthroplasty: seven to sixteen-year follow-up. J one Joint Surg m 2004; 86: nderson T, Montgomery F, Carlsson. Uncemented STR total ankle prostheses: three to eight-year follow-up of fifty-one consecutive ankles. J one Joint Surg m 2003; 85: Valderrabano V, Hintermann, Dick W. Scandinavian total ankle replacement. Clin Orthop 2004; 424: Pyevich MT, Saltzman CL, Callaghan JJ, lvine FG. Total ankle arthroplasty: a unique design two to twelve-year follow-up. J one Joint Surg m 1998; 80: Kopp FJ, Patel MM, Deland JT, O Malley MJ. Total ankle arthroplasty with the gility prosthesis: clinical and radiographic evaluation. Foot nkle Int 2006; 27: Hanna RS, Haddad SL, Lazarus ML. Evaluation of periprosthetic lucency after total ankle arthroplasty: helical CT versus conventional radiography. Foot nkle Int 2007; 28: Lee MJ, Kim S, Lee S, et al. Overcoming artifacts from metallic orthopedic implants at highfield-strength MR imaging and multidetector CT. RadioGraphics 2007; 27: uechel FF, uechel FF, Pappas MJ. Ten-year evaluation of cementless uechel-pappas meniscal bearing total ankle replacement. Foot nkle Int 2003; 24: JR:190, pril 2008

4 Total nkle rthroplasty Downloaded from by on 11/26/17 from IP address Copyright RRS. For personal use only; all rights reserved Fig. 1 STR arthroplasty device (Scandinavian Total nkle Replacement, Waldemar Link) is cementless, three-component (mobile-bearing) design developed by H. Kofoed in 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, ) 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 STR arthroplasty device, oblique lateral view., nteroposterior radiograph of STR arthroplasty device. Fig. 2 uechel-pappas total ankle prosthesis (Endotec). Similar to STR (Scandinavian Total nkle Replacement, Waldemar Link) device, uechel-pappas ankle replacement is cementless, three-component (mobile-bearing) design. Tibial component is stabilized by stem that extends into tibial metaphysis (arrowhead). Ultrahigh-molecularweight 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 uechel-pappas arthroplasty device, frontal view., nteroposterior radiograph of uechel-pappas arthroplasty device. JR:190, pril

5 Downloaded from by on 11/26/17 from IP address Copyright RRS. For personal use only; all rights reserved Fig. 3 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., nteroposterior radiograph of TNK device. Fig. 4 gility Total nkle System (DePuy) has been available for use since 1984, making it longest-used total ankle replacement system in United States. gility 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, ) 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 gility device, oblique frontal view., nteroposterior radiograph of gility device JR:190, pril 2008

6 Total nkle rthroplasty Downloaded from by on 11/26/17 from IP address Copyright RRS. For personal use only; all rights reserved Fig. 5 INONE Total nkle (INONE 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 INONE device, frontal view., nteroposterior radiograph of INONE device. Fig. 6 Salto Talaris Total nkle 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., Lateral radiograph of Salto Talaris device. JR:190, pril

7 estic et al. Downloaded from by on 11/26/17 from IP address Copyright RRS. For personal use only; all rights reserved Fig. 7 Radiographic measurements for total ankle arthroplasty (illustrated using STR [Scandinavian Total nkle Replacement, Waldemar Link] device). ngular and linear values can be defined to evaluate changes in component alignment and position that may signify component migration [8 10]., nteroposterior view of STR device depicts method of angular evaluation. lpha angle (α) 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 )., Lateral view of STR device depicts method of angular evaluation. eta 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 (γ) 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]. C and D, nteroposterior (C) and lateral (D) views of STR 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. E and F, Sequential lateral views of STR 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. G, Coronal CT image obtained at time of followup 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. C D E F G 1118 JR:190, pril 2008

8 Total nkle rthroplasty Downloaded from by on 11/26/17 from IP address Copyright RRS. For personal use only; all rights reserved Fig. 8 Zonal system (illustrated with STR [Scandinavian Total nkle 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)., 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 ( C, anterior to posterior). Fig. 9 Infection in 67-year-old man. Lateral radiograph of STR total ankle (Scandinavian Total nkle Replacement, Waldemar Link) shows several pockets of gas (arrows) in soft tissues of ankle secondary to superficial infection. JR:190, pril

9 estic et al. Downloaded from by on 11/26/17 from IP address Copyright RRS. For personal use only; all rights reserved Fig. 10 Periprosthetic lucencies., nteroposterior radiograph of STR total ankle (Scandinavian Total nkle Replacement, Waldemar Link) in 46-year-old woman shows ovoid radiolucency (circled in white) located in zones 4 and 5 of tibial component. t surgery, this radiolucency was found to represent polyethylene osteolysis. Note lateral migration of tibial component with associated remodeling of fibula (white arrow)., Initial postoperative anteroposterior radiograph of STR 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. C, Lateral radiograph of a uechel-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). C 1120 JR:190, pril 2008

10 Total nkle rthroplasty Downloaded from by on 11/26/17 from IP address Copyright RRS. For personal use only; all rights reserved Fig. 11 septic loosening., nteroposterior radiograph of STR total ankle (Scandinavian Total nkle 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., nteroposterior radiograph of gility Total nkle (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). oth 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. Fig. 12 Periprosthetic fracture. lterations 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 STR total ankle (Scandinavian Total nkle 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., Corresponding coronal CT image confirms periprosthetic fracture (arrow) involving medial malleolus. Extension of fracture line to level of tibial component is clearly shown. JR:190, pril

11 estic et al. Downloaded from by on 11/26/17 from IP address Copyright RRS. For personal use only; all rights reserved Fig. 13 Migration of polyethylene spacer with ankle subluxation in 72-year-old man., nteroposterior radiograph of STR total ankle (Scandinavian Total nkle 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 STR device placement., 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) JR:190, pril 2008

12 Total nkle rthroplasty Downloaded from by on 11/26/17 from IP address Copyright RRS. For personal use only; all rights reserved C Fig. 14 Fracture of polyethylene component in 69-year-old man., nteroposterior radiograph of STR total ankle (Scandinavian Total nkle Replacement, Waldemar Link) suggests damage to polyethylene spacer, as evidenced by abnormal lateral migration of wire marker embedded in spacer (arrow). and C, xial () 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. D, Gross photograph of resected fractured polyethylene component. FOR YOUR INFORMTION This article is available for CME credit. See for more information. D JR:190, pril