M u s c u l o s k e l e t a l I m a g i n g • R ev i ew Mulcahy and Chew Features and Imaging Assessment of Knee Replacement

Downloaded from www.ajronline.org by 37.44.207.89 on 01/24/17 from IP address 37.44.207.89. Copyright ARRS. For personal use only; all rights reserved

Musculoskeletal Imaging Review

Current Concepts in Knee Replacement: Features and Imaging Assessment Hyojeong Mulcahy 1 Felix S. Chew Mulcahy H, Chew FS

OBJECTIVE. This article reviews current concepts of knee replacement. Features of traditional and new prosthetic designs, materials, and surgical techniques are discussed. Normal and abnormal postoperative imaging findings are illustrated. Complications are reviewed and related to the current understanding about how and why these failures occur. CONCLUSION. It is well known that after knee replacement, patients with complications may be asymptomatic, and, for this reason, assessment of postoperative imaging is important. The foundation of radiologic interpretation of knee replacement is knowledge of the physiologic purpose, orthopedic trends, imaging findings, and complications.

S

Keywords: imaging assessment, total knee arthroplasty, total knee replacement DOI:10.2214/AJR.13.11307 Received May 21, 2013; accepted May 30, 2013. 1 Both authors: Department of Radiology, Musculoskeletal Imaging, University of Washington, Roosevelt Radiology Box 354755, 4245 Roosevelt Way NE, Seattle, WA 98105. Address correspondence to H. Mulcahy ([email protected]).

CME/SAM This article is available for CME/SAM credit. WEB This is a web exclusive article. AJR 2013; 201:W828–W842 0361–803X/13/2016–W828 © American Roentgen Ray Society

W828

urgical replacement of the knee joint, also called total knee arthroplasty (TKA) and total knee replacement, is considered the definitive treatment for symptomatic end-stage osteoarthritis of the knee [1]. Of the 11 million adults in the United States who have been estimated to have this diagnosis, 4 million have undergone a knee replacement [2]. A projected 700,000 primary TKA procedures were performed in 2012, an increase of 86% since 2003 [3]. Factors contributing to the increasing use and prevalence of knee replacements include growth, aging, and increasing longevity of the population; obesity; expanding indications for the procedure; and younger age at implantation [4]. A role for direct-to-consumer advertising has also been suggested in increasing demand [4, 5]. Although the total cost for a TKA is similar to that of a new automobile, TKA has been shown in multiple studies to be very cost-effective [6]. Imaging patients with knee replacements is now commonplace. Our purpose in this article is to identify key current concepts in primary total knee arthroplasty and to explain their relevance to diagnostic radiology. The knee is a synovial joint with three articular compartments: medial, lateral, and patellofemoral. The most common type of TKA replaces the femoral articular surfaces with a metal bicondylar component, the tibial articular surfaces with a metal tray carrying a polyethylene bearing surface, and the patellar articular surface with a polyethylene

button. An anterior surgical approach is typically used, generally sacrificing the anterior cruciate ligament and sometimes the posterior cruciate ligament (PCL). With variations in prosthetic design, bearing mode, patellar resurfacing, materials, fixation method, and surgical technique, there are over 150 different knee implant designs in current use [7]. Prosthetic Design The knee is an articulated column whose stability depends on static stabilizers (ligaments), dynamic stabilizers (muscle-tendon units), and geometric congruity. By constraining motion between components, knee prostheses may offer different levels of inherent stability to compensate for deficiencies in the native knee, including PCL-retaining, PCL-substituting, varus-valgus constrained, and rotating-hinge types [8]. PCL-Retaining Knee The femoral and tibial components of PCL-retaining designs allow retention of the native PCL. The success of these relatively unconstrained designs depends on a sound biomechanical environment. There must be good quality bone with minimal defects, intact soft tissues, and a PCL that remains functional and balanced (Fig. 1). Posterior-Stabilized Knee Posterior-stabilized designs substitute for PCL function by limiting excessive posterior tibial translation in flexion. They feature a tib-

AJR:201, December 2013

Downloaded from www.ajronline.org by 37.44.207.89 on 01/24/17 from IP address 37.44.207.89. Copyright ARRS. For personal use only; all rights reserved

Features and Imaging Assessment of Knee Replacement ial post and femoral cam, deeply dished articular surfaces, and a third condyle [8]. Earlier PCL-substituting designs had a central polyethylene post at the posterior middle portion of the tibial insert that, in flexion, engaged a transverse metal cam on the femoral component to prevent abnormal posterior tibial translation [9]. These earlier designs had problems and complications, such as post breakage, dislocation, and patellar clunk syndrome. Recently, interest has developed in using highly conforming tibial inserts to increase surface area contact with the femoral component throughout the full range of motion to increase stability (round-on-round), as compared with the relatively flat tibial insert used in unconstrained designs (round-on-flat). These designs may eliminate the need for resection of intercondylar notch bone stock or a vulnerable tibial post [10]. Studies have found no significant differences in function, patient satisfaction, or survivorship when comparing PCL-retaining and PCL-substituting designs [11, 12]. On radiographs, PCL-substituting implants may be recognized by the presence of the central slot in the femoral component oriented in the sagittal plane. The intercondylar post often is simply a projection extending from the polyethylene liner of the tibia and, therefore, may be radiolucent and difficult to recognize. In some cases, there may be a metal strut inside the polyethylene post (Fig. 2). Varus-Valgus Constrained Knee Varus-valgus constrained implants have a tall tibial post and a deep femoral box, providing inherent stability in the coronal plane. Because there is no link connecting the tibial and femoral components, these implants are sometimes referred to as unlinked constrained implants. To a variable extent, varus-valgus constrained implants limit varusvalgus tilt as well as rotation. In this design, the stem extension is important in transmitting stresses generated by the constrained articulation. These implants may be used for both primary and revision arthroplasty, particularly in patients with severe valgus deformities, collateral ligament deficiency, bone defects, and residual instability or irreconcilable flexion-extension imbalances [8]. On radiographs, varus-valgus constrained implants may be recognized by the presence of a tall tibial post and a deep femoral box. There is no hinge connecting the femoral and tibial components. The femoral and tibial components are secured to the bone by intramedullary stems, and there is a polyethylene bearing surface on the tibial component (Fig. 3).

Rotating-Hinge Knee Rotating-hinge knee implants are highly constrained devices mostly used for complex revision arthroplasty performed for severe bone loss or complex instability and for oncologic reconstruction. The tibial and femoral components are linked with a hinge built into the implants. Although there is flexionextension with this design, the hinge restricts varus-valgus and translational stresses. The prosthesis also allows the knee to rotate approximately 10° between flexion and extension, reproducing normal kinematics. Rotating hinge implants are inherently stable, so the presence or function of the native structures that provide stability to the knee is less important. On radiographs, rotating hinge total knee replacements are recognized by the presence of the hinge connecting the femoral and tibial components. The femoral and tibial components are secured to the bone by intramedullary stems, with the tibial stem sometimes seated in a polyethylene socket. There is a polyethylene liner on the tibial component. In the case of tumor reconstruction, portions of the distal femoral or proximal tibial shaft may be replaced by the prosthesis (Fig. 4). Medial Pivot Knee Traditional knee kinematics has held that, during flexion, both femoral condyles roll back on the tibial plateaus with a variable center of motion, following a J-shaped curve that the designs of conventional bicondylar TKA prostheses have duplicated. Recent studies of normal knee kinematics suggest that the medial pivot theory is a better model than the J-curve for understanding knee motion [13]. Instead of rolling back, the medial condyle spins in place like a ball-and-socket joint during flexion; the lateral femoral condyle pivots on the medial condyle as it rolls, spins, and translates [14, 15]. The medial pivot TKA is designed to move in the same way to reduce contact stresses and polyethylene wear. On the medial side, the tibial-bearing surface is congruent with the condyle to allow spinning, whereas on the lateral side, the tibial surface has a larger radius than the condyle, allowing posterior rotation and translation. Results after 5 and 7 years have been promising [16, 17]. High Flexion Knee Postoperative flexion is one parameter used to evaluate the success of TKA. The normal knee has 150° of flexion, but after TKA, more than 110° is rarely achieved. Attempts to design prostheses that allow high flexion (> 125°), particularly for younger pa-

tients, include lengthening the radius of curvature through the posterior condyles, increasing the posterior condylar offset, recessing the tibial insert, lengthening the trochlear groove, and altering the cam-post design [18]. These changes allow increased femoral rollback, translation, and, thus, clearance in deep flexion. Surgical techniques to increase flexion focus on soft-tissue balancing, component sizing and position, removal of impinging osteophytes, and reestablishment of the flexion gap [19]. Several high-flexion prostheses are now available and show variable results [20, 21]. Sex-Specific Knee Anatomic differences in male and female knees have long been recognized, and women undergo TKA more frequently than men (1.4:1) [2]. Sex-specific TKA designs with modified dimensions to accommodate the anatomic differences between sexes have been introduced [22] (Fig. 5), even in the absence of evidence suggesting that sex was a factor in failure rates [23]. Clinical results are starting to appear in the medical literature, and there appear to be no significant differences between the two groups in terms of satisfaction or clinical or radiologic outcome [22, 24]. Hemiarthroplasty Hemiarthroplasty of the knee refers to the concept of placing a spacer, usually in the medial compartment of the osteoarthritic knee, to ameliorate bone-on-bone apposition and internally realign it [25]. Both biologic and metal interpositional implants are currently available for the treatment of unicompartmental osteoarthritis. In biologic interpositional arthroplasty, an allograft meniscus is transplanted [26] (Fig. 6). Metal interpositional arthroplasty procedures developed in the 1950s [27, 28] were practically abandoned when cemented bicondylar joint replacements were introduced, but new devices and minimally invasive operations have renewed interest in them. The interpositional knee disks, such as UniSpacer (Zimmer) and OrthoGlide (Advanced Bio-Surfaces) implants, are cobalt-chromium devices with no moving parts that rest on the tibial plateau and rely on shape to maintain stability and position (Fig. 7). The results from short-term 2-year follow-up studies are not as good as those with standard bicondylar replacements [29]. Unicompartmental Knee Arthroplasty Unicompartmental knee arthroplasty was first introduced in the 1970s [30], and recent

AJR:201, December 2013 W829

Downloaded from www.ajronline.org by 37.44.207.89 on 01/24/17 from IP address 37.44.207.89. Copyright ARRS. For personal use only; all rights reserved

Mulcahy and Chew interest in minimally invasive surgical techniques has led to a concurrent resurgence in it [31]. Unicompartmental arthroplasty resurfaces both sides of a single articular compartment, usually the medial, but sometimes the lateral or even patellofemoral [32] (Fig. 8). For the medial or lateral compartment, prostheses typically have a metal condylar component and a metal-backed tibial-bearing surface. For patients with isolated unicompartmental osteoarthritis, unicompartmental arthroplasty may be an alternative to high tibial osteotomy or TKA. Adherence to strict surgical indications and appropriate patient selection, combined with meticulous surgical execution, are important factors in outcomes [33]. Bearings In early TKA designs, the polyethylene bearing surface was directly molded onto the tibial baseplate during manufacture (monoblock construction), yielding successful and durable long-term results. The need for multiple sizing options has resulted in modular components, which are locked into place at surgery [34]. There are two locking mechanisms: fixed bearing and mobile bearing. Fixed-bearing implants have polyethylene inserts that are locked into a tibial tray (Fig. 9); mobile-bearing implants have polyethylene inserts that can glide over the surface of the tibial component [35]. Fixed Bearings Fixed-bearing knee prostheses have been clinically successful but there are long-term failures resulting from loosening or polyethylene wear. A fixed-bearing prosthesis with a high conformity surface (so-called roundon-round) provides low contact stress, but high torque at the bone-implant interface may cause loosening. Conversely, a low-conformity surface (round-on-flat) produces less torque at the bone-implant interface but high contact stress may cause polyethylene failure [36, 37]. Mobile Bearings Mobile-bearing knee prostheses were introduced with the aim of reducing polyethylene wear and component loosening [38]. By creating a dual-surface articulation and a high-conformity surface, implant-bone interface stress and contact stress could be reduced simultaneously [34]. Although the mobile-bearing design has theoretic advantages over fixed-bearing designs, comparative studies did not show the superiority of one design over the other in terms of function, patient W830

preference, and prosthesis-related complications [39, 40]. There are a variety of dissimilar prostheses that feature mobile polyethylene bearings articulating with metal condylar components and metal tibial trays, including meniscal bearing, rotating platform, and multidirectional platform types [34, 41]. The meniscal bearing designs have separate medial and lateral mobile polyethylene bearings that slide independently in tracks (Fig. 8A). The rotating platform devices have a single bearing that rotates in the transverse plane without anteroposterior motion. The multidirectional platform devices have a single polyethylene bearing that allows both rotation and anteroposterior motion in the transverse plane. Mobile-bearing prostheses do not appear to have kinematic advantages over fixedbearing prostheses and are also subject to bearing dislocation and breakage, soft-tissue impingement, difficult implantation, and volumetric wear [42]. Mobile bearings are also available for unicompartmental arthroplasty. Patellar Resurfacing The two primary methods for resurfacing of the patella are the inset and the onlay techniques. In the inset technique, a circular component is recessed into a hole reamed into the patella [43]. Fixation is achieved using cement and a single small peg (Fig. 10A). This technique promotes ease of placement, improved extensor mechanism alignment, reduced bone removal, and more stable fixation from the bone surrounding the implant [44]. In the onlay technique, a polyethylene component is cemented onto the cut surface of the patella. It has a long history of successful clinical use and it is technically simpler than the inset technique. There are a variety of shapes and fixation methods for the onlay component, such as circular dome, oval dome, circular sombrero, oval sombrero, and metal-back porous-coated rotating bearing (Fig. 10B). Current onlay patellar components have three small pegs, rather than one large central peg, for cement fixation. The theoretic advantages of three small pegs include better fixation, less interference with the intraosseous blood supply, and increased resistance to breakage [45]. Metal-backed patellar components, both in cemented and cementless configurations, have largely been abandoned because of osteolysis, implant loosening, and metallosis [46–48] (Fig. 10C). Modern patellar component designs are all polyethylene. Even the concept of resurfacing of the patella at the time of knee replacement has un-

dergone reevaluation. Definitive evidence for either routinely resurfacing the patella or routinely not resurfacing the patella may be lacking [49, 50]. Materials Modern implants typically have a cobalt-chrome alloy femoral bicondylar component articulating with a polyethylene tibial-bearing surface that is usually attached to a titanium alloy tibial tray. The improvement of these materials is the subject of intense research. Cobalt alloys based on the cobalt-chromium-molybdenum system have been widely used for many years as femoral components and other medical implants. Ceramics have been used as bearing surfaces in hip replacements, with greatly reduced surface wear, but their brittleness makes them unsuitable for use in knee arthroplasty. A new alloy of oxidized zirconium (Oxinium, Smith and Nephew), has recently been developed for the femoral components. Thermally driven oxygen diffusion transforms the metallic zirconium alloy surface into a durable low-friction oxide (Fig. 11). The oxide layer is not a coating, but rather the surface zone of the metal alloy, conferring bearing properties of ceramic with the strength of metal [51]. Clinical trials have shown good results at 2 years [52] and 5 years [53]. Whether or not the theoretic advantage of Oxinium implants will translate to improved long-term clinical outcomes remains to be seen. Titanium alloys, including Ti6Al-4V and Ti-6Al-7Nb, have been used for knee components [54]; pure titanium may be used as a surface treatment to promote bony ingrowth. Porous tantalum has unique properties that make it an alternative metal for prosthetic components. Tantalum is a transition metal that, in its bulk form, has shown excellent biocompatibility and is safe to use in vivo. Current designs for orthopedic implants maintain a high volumetric porosity, low modulus of elasticity, and high frictional characteristics, making this metal conducive to biologic fixation [55]. The porosity of the structure allows bone ingrowth, and the modulus of elasticity allows physiologic transfer of stresses from implant to bone, decreasing the stress at the interface [56]. The Trabecular Metal tibial component (Zimmer) is a monoblock design consisting of a trabecular metal tray (porous tantalum) with two pegs and an articular surface of ultra–high-molecular-weight polyethylene that is directly compression molded. Early results have been encouraging [57, 58]. Current polyethylene bearings are made of ultra–high-molecular-weight polyethylene. Polyethylene is a durable high-performance plastic resin. Its strength, wear properties, low coefficient of friction, and the ability to mold or machine it into desired shapes have contributed to its success. Using gam-

AJR:201, December 2013

Downloaded from www.ajronline.org by 37.44.207.89 on 01/24/17 from IP address 37.44.207.89. Copyright ARRS. For personal use only; all rights reserved

Features and Imaging Assessment of Knee Replacement ma irradiation to sterilize polyethylene increases cross-linking to produce highly cross-linked polyethylene. This material has shown decreased wear rates when used in hip arthroplasty after 4–5 years [59]. However, gamma radiation also causes the formation of free radicals, which when combined with oxygen, may cause oxidative degradation of polyethylene with age. Because of this issue, manufacturers use ethylene oxide gas or gamma irradiation in an oxygen-free environment as their method of sterilization [60]. Wear reduction is proportional to the amount of cross-linking achieved; however, thermal stabilization also reduces the mechanical strength and fatigue resistance [61]. The addition of an antioxidant like vitamin E to the polyethylene to stabilize free radicals improves its resistance to fatigue crack propagation [62].

Fixation Implants may be fixed in place with or without cement. Bone cement is a mixture of an acrylic cement (polymethylmethacrylate) and various additives, including barium to render the mixture radiopaque and sometimes antibiotics. Bone cement in knee arthroplasty may be used as an adhesive rather than a space filler, so the cement may appear on radiographs as a subtle irregularly marginated radiodensity at the bone-metal or polyethylene-metal interfaces [63] (Fig. 1). Cementless fixation is initially achieved by press-fitting a component into a slightly undersized prepared cavity. Special surface characteristics of the components allow ingrowth of bone into a porous coat or on-growth of bone onto a textured surface (Fig. 12). Surface treatments include sintered beads, fiber mesh, porous metals, and hydroxyapatite [64]. The optimal mode of fixation of the components in TKA remains unresolved. The knee prostheses most frequently used all cemented components, and these have shown excellent clinical results in the long term [65, 66]. Cement provides good initial fixation and, with pressurization into cancellous bone, can seal the interface between implant and bone to prevent polyethylene debris from entering from the joint. Fixation can weaken with time and stress, and cement debris within the articulation can lead to accelerated polyethylene wear. Although many cementless designs failed early [67, 68], some have shown good long-term clinical results [69, 70]. The femoral component in almost all of the cementless designs reliably achieves fixation to bone and is commonly used in hybrid TKA [71]. The tibial component in cementless TKA has been more

problematic [72]. The success of cementless TKA appears to be design dependent. Those with excellent fixation of the tibial component, minimal constraint at the articular surface, or both have had high success rates [73]. In younger patients, the potential advantages of cementless fixation, including strong initial fixation, conservation of bone stock, predictable bony ingrowth, and reduction in stress shielding, could be of particular value [57]. Disadvantages of cementless fixation include higher costs, more precise surgical techniques, and unexplained periprosthetic pain. Surgical Techniques Digital Templating Preoperative templating for TKA is a visual method for selecting and sizing components. Originally performed by physically superimposing acetate overlays with outlines of components over hard-copy knee films, templating can now be performed on a workstation (Fig. 13). Templating software provides entire inventories of components for use with digital radiographs that are size-calibrated with an external marker. The femoral component is primarily sized on the lateral radiograph, whereas the tibial component is primarily sized on the anteroposterior radiograph [74]. The advantages of digital templating are the wide variety of available templates, the speed and precision of the technique, and elimination of hard-copy printouts of radiographs with their associated cost; disadvantages include dependence on the digital library, cost, and limitations in software functionality [75]. Studies comparing the accuracy of digital versus traditional templating for TKA show comparability [76, 77]. Minimally Invasive Surgery Minimally invasive surgery represents an alteration to the standard anterior median parapatellar approach to the knee. Not only is the incision shorter (< 14 cm) (Fig. 14), but there is much less surgical dissection and collateral damage to the knee, potentially decreasing postoperative pain, rehabilitation time, and cost [78]. However, the smaller surgical exposure has been cited as a risk for poorer component placement and subsequent failure [79]. Studies thus far have not shown definitive advantages in outcome for the minimally invasive techniques [80]. Computer-Assisted Orthopedic Surgery Uncorrected knee malalignment contributes to TKA failures [81]. Conventional techniques for alignment use a combination of

intramedullary and extramedullary instrumentation together with visual referencing to guide appropriate resection of bone and component placement. In computer-assisted orthopedic surgery, there are active robotic, semiactive robotic, and passive systems [82]. The earliest and most complex system was the active robotic system. Semiactive systems do not perform surgical tasks but may limit the placement of surgical tools. An example of a passive system is one for navigation that consists of computer platform, tracking system, and rigid body marker. Navigation systems may be CT based, fluoroscopy based, and imageless [83]. Recent meta-analyses indicate that the mechanical axis and the position of TKA components are better with computer-assisted orthopedic surgery than with conventional techniques [84, 85], but whether this leads to better outcomes remains to be seen [86]. Problems with navigation systems include difficulty with intraoperative landmark registration, increased operative time, increased costs, pin loosening and pin-site fracture, and steep learning curve [87]. Radiologic Imaging Radiographs of the knees are standard in the presurgical evaluation of candidates for TKA. Surgeons usually include weight-bearing anteroposterior radiographs and lateral radiographs of both knees and use them in planning their operation and determining the appropriate size for the prosthesis. Immediate postoperative radiographs are used to document the optimal appearance and position of the implant. Also, most surgeons obtain knee radiographs at the time of routine postsurgical follow-up as one means of surveillance for possible complications [88]. Baseline radiographs at the first outpatient visit (e.g., at 6 weeks) and follow-up radiographs every 1 or 2 years continued for the long term (> 10 years) are considered appropriate [89]. Routine views of the knee are the anteroposterior, lateral, and tangential axial (Merchant) views. As with preoperative radiographs, it is important to attempt to obtain the anteroposterior film with the patient weight bearing, because this more accurately depicts the joint space of the TKA as well as polyethylene wear with resultant joint space narrowing. The components must be included in their entirety on all views, including any stems or stem extensions. The three-foot standing anteroposterior view of the lower extremities (i.e., the threejoint view, with the hip, knee, and ankle on the same plate) may be helpful for preoperative

AJR:201, December 2013 W831

Downloaded from www.ajronline.org by 37.44.207.89 on 01/24/17 from IP address 37.44.207.89. Copyright ARRS. For personal use only; all rights reserved

Mulcahy and Chew planning, for assessment of the anatomic and mechanical axes, and postoperatively to confirm proper anatomic postoperative alignment of the lower extremity [90]. The alignment objective in TKA is to restore a projected anteroposterior weight-bearing axis of the lower extremity. On the threejoint view, a line drawn from the center of the femoral head to the center of the talar body (mechanical axis) should intersect the center or just medially to the center of the prosthetic knee, and the femoral and tibial components should be perpendicular to this line [91]. The anatomic axis of the femur is the line along the femoral shaft that passes through the center of the distal femur. On the femur, the angle between the mechanical axis and the anatomic axis is between 4° and 7° (Fig. 15). This angle is equivalent to the valgus angle set on the distal femoral cutting guide, thus achieving a distal femoral cut perpendicular to the mechanical axis of the femur. On the tibia, the goal is to cut the tibial surface exactly perpendicular to the long axis of tibia (tibial anatomic axis) [75]. The femoral component should be placed 7° ± 3° valgus, and the tibial component should be 90° ± 3° relative to the anatomic axis of the tibia on the anteroposterior radiograph, allowing an overall 4–7° valgus angulation (Fig. 16A). This could be measured by an angle intersecting the femoral anatomic axis with the tibial anatomic axis (femorotibial angle). On the lateral view, the horizontal portion of the femoral component should be 90° ± 3° relative to the long axis of the femur. The tibial component should be horizontal or slope downward 10° posteriorly (Fig. 16B) [92], and its position should be either central or posterior relative to the center of the tibial shaft. Most modern prostheses aim for a posterior tilt of 3–7° because the anterior portion of the tibial surface is weaker. The anterior flange of a properly sized femoral component should fit flush against and be parallel to the anterior cortex of the distal femur. An oversized femoral component can cause excessive softtissue tension and decreased range of motion. If the femoral component is undersized and placed posteriorly to the midplane of the femur, the anterior femoral cortex notching can happen, which predisposes the femoral shaft to fracture (Fig. 17). If it is undersized and placed anteriorly to the midplane, instability in flexion can result [93]. The size of the tibial component should match the size of the native plateau because component overhang may irritate the adjacent soft tissues (Fig.

W832

18). Tibial component undersizing leads to increased subsidence [92]. An axial view of the knee is important for assessing patellofemoral alignment, and it should be performed at a standard degree of flexion, usually 30–45° [7]. The prosthetic patellar component should be centered over the middle of the trochlea of the femoral component on an axial view. On a lateral view, the joint line (distance from the tibial tubercle to the tibial component) should be altered 8 mm or less, and the patella height (distance from the inferior edge of patellar component to the tibial articular surface) should be 10–30 mm to have good results [93, 94] (Fig. 19). The combined anteroposterior thickness of the patella and patellar polyethylene should not exceed that of the native patella to avoid stress on the extensor mechanism [90]. Rotational malalignment of the femoral and tibial components may cause excessive polyethylene wear [95] and other complications, including alteration of the foot progression angle during gait and complications associated with the patellofemoral joint [96]. Rotational alignment of the components is best assessed on cross-sectional images (usually CT) where the necessary landmarks are clearly depicted. Femoral component rotation is measured relative to the transepicondylar axis, and tibial component rotation is measured relative to the tibial tubercle. Normal rotation for the femoral component is 0.3° ± 1.2° internal rotation for women and 3.5° ± 1.2° internal rotation for men relative to the surgical epicondylar axis (Fig. 20A). The normal rotation value for the tibial component, which corresponds to the native articular surface, is 18° ± 2.6° internal rotation from the tip of the tubercle [97] (Fig. 20B). Internal rotation of the femoral or tibial components has been shown to be associated with increased patellofemoral complications, but external rotation of the femoral component is usually well tolerated [97–99]. In unicompartmental arthroplasty, the tibial component should be implanted perpendicular to the long axis of the tibia in the coronal plane to facilitate implant congruence throughout the flexion-extension arc. The tibial component should match the native tibial slope in the sagittal plane to protect the anterior cruciate ligament from degeneration and rupture. In general, the femoral component should be placed perpendicular to the tibial component in the coronal plane [33]. The valgus alignment on standing films should be neutral or slightly undercorrected [100].

Conclusion TKA is an area of highly active research and technical innovation with major industrial interest and economic implications. As the prevalence of knee implants increases in our aging but still active population, especially among women, radiologists will be seeing more and more images of knee replacements and must keep current with the newer concepts. References 1. Richmond J, Hunter D, Irrgang J, et al. American Academy of Orthopaedic Surgeons clinical practice guideline on the treatment of osteoarthritis (OA) of the knee. J Bone Joint Surg Am 2010; 92:990–993 2. Weinstein AM, Rome BN, Reichmann WM, et al. Estimating the burden of total knee replacement in the United States. J Bone Joint Surg Am 2013; 95:385–392 3. Steiner C, Andrews R, Barrett M, Weiss A; Healthcare Cost and Utilization Project. HCUP projections: mobility/orthopedic procedures 2011 to 2012—report 2012-03. U.S. Agency for Healthcare Research and Quality website. www.hcup-us. ahrq.gov/reports/projections/2012-03.pdf. Published September 20, 2012. Accessed May 8, 2013 4. Losina E, Thornhill TS, Rome BN, Wright J, Katz JN. The dramatic increase in total knee replacement utilization rates in the United States cannot be fully explained by growth in population size and the obesity epidemic. J Bone Joint Surg Am 2012; 94:201–207 5. Bozic KJ, Smith AR, Hariri S, et al. The 2007 ABJS Marshall Urist Award: the impact of directto-consumer advertising in orthopaedics. Clin Orthop Relat Res 2007; 458:202–219 6. Daigle ME, Weinstein AM, Katz JN, Losina E. The cost-effectiveness of total joint arthroplasty: a systematic review of published literature. Best Pract Res Clin Rheumatol 2012; 26:649–658 7. Math KR, Zaidi SF, Petchprapa C, Harwin SF. Imaging of total knee arthroplasty. Semin Musculoskelet Radiol 2006; 10:47–63 8. Morgan H, Battista V, Leopold SS. Constraint in primary total knee arthroplasty. J Am Acad Orthop Surg 2005; 13:515–524 9. Insall JN, Lachiewicz PF, Burstein AH. The posterior stabilized condylar prosthesis: a modification of the total condylar design—two to four-year clinical experience. J Bone Joint Surg Am 1982; 64:1317–1323 10. Hofmann AA, Tkach TK, Evanich CJ, Camargo MP. Posterior stabilization in total knee arthroplasty with use of an ultracongruent polyethylene insert. J Arthroplasty 2000; 15:576–583 11. Clark CR, Rorabeck CH, MacDonald S, MacDon-

AJR:201, December 2013

Downloaded from www.ajronline.org by 37.44.207.89 on 01/24/17 from IP address 37.44.207.89. Copyright ARRS. For personal use only; all rights reserved

Features and Imaging Assessment of Knee Replacement ald D, Swafford J, Cleland D. Posterior-stabilized and cruciate-retaining total knee replacement: a randomized study. Clin Orthop Relat Res 2001; 208–212 12. Forster MC. Survival analysis of primary cemented total knee arthroplasty: which designs last? J Arthroplasty 2003; 18:265–270 13. Mont MA, Booth RE Jr, Laskin RS, et al. The spectrum of prosthesis design for primary total knee arthroplasty. Instr Course Lect 2003; 52:397–407 14. Iwaki H, Pinskerova V, Freeman MA. Tibiofemoral movement. Part 1. The shapes and relative movements of the femur and tibia in the unloaded cadaver knee. J Bone Joint Surg Br 2000; 82:1189–1195 15. Hill PF, Vedi V, Williams A, Iwaki H, Pinskerova V, Freeman MA. Tibiofemoral movement. Part 2. The loaded and unloaded living knee studied by MRI. J Bone Joint Surg Br 2000; 82:1196–1198 16. Karachalios T, Roidis N, Giotikas D, Bargiotas K, Varitimidis S, Malizos KN. A mid-term clinical outcome study of the Advance Medial Pivot knee arthroplasty. Knee 2009; 16:484–488 17. Vecchini E, Christodoulidis A, Magnan B, Ricci M, Regis D, Bartolozzi P. Clinical and radiologic outcomes of total knee arthroplasty using the Advance Medial Pivot prosthesis: a mean 7 years follow-up. Knee 2012; 19:851–855 18. Wong JM, Khan WS, Chimutengwende-Gordon M, Dowd GS. Recent advances in designs, approaches and materials in total knee replacement: literature review and evidence today. J Perioper Pract 2011; 21:165–171 19. Long WJ, Scuderi GR. High-flexion total knee arthroplasty. J Arthroplasty 2008; 23:6–10 20. Luo SX, Su W, Zhao JM, Sha K, Wei QJ, Li XF. High-flexion vs conventional prostheses total knee arthroplasty: a meta-analysis. J Arthroplasty 2011; 26:847–854 21. Sumino T, Gadikota HR, Varadarajan KM, Kwon YM, Rubash HE, Li G. Do high flexion posterior stabilised total knee arthroplasty designs increase knee flexion? A meta analysis. Int Orthop 2011; 35:1309–1319 22. Thomsen MG, Husted H, Bencke J, Curtis D, Holm G, Troelsen A. Do we need a gender-specific total knee replacement? A randomised controlled trial comparing a high-flex and a genderspecific posterior design. J Bone Joint Surg Br 2012; 94:787–792 23. American Academy of Orthopaedic Surgeons. Gender-specific knee replacements: a technology overview. J Am Acad Orthop Surg 2008; 16:63–67 24. MacDonald SJ, Charron KD, Bourne RB, Naudie DD, McCalden RW, Rorabeck CH. The John Insall Award: gender-specific total knee replacement: prospectively collected clinical outcomes. Clin Orthop Relat Res 2008; 466:2612–2616

25. Bert JM. Unicompartmental knee replacement. Orthop Clin North Am 2005; 36:513–522 26. Richmond JC. Surgery for osteoarthritis of the knee. Rheum Dis Clin North Am 2008; 34:815– 825 27. MacIntosh D. Hemiarthroplasty of the knee using a space occupying prosthesis for painful varus and valgus deformities. J Bone Joint Surg Am 1958; 40:1428–1431 28. McKeever DC. Tibial plateau prosthesis. Clin Orthop Relat Res 1960; 18:86–95 29. Sisto DJ, Mitchell IL. UniSpacer arthroplasty of the knee. J Bone Joint Surg Am 2005; 87:1706–1711 30. Skollnick MD, Bryan RS, Peterson LF, Combs JJ Jr, Ilstrup DM. Polycentric total knee arthroplasty: a two-year follow-up study. J Bone Joint Surg Am 1976; 58:743–748 31. Geller JA, Yoon RS, Macaulay W. Unicompartmental knee arthroplasty: a controversial history and a rationale for contemporary resurgence. J Knee Surg 2008; 21:7–14 32. Walker T, Perkinson B, Mihalko WM. Patellofemoral arthroplasty: the other unicompartmental knee replacement. Instr Course Lect 2013; 62:363–371 33. Borus T, Thornhill T. Unicompartmental knee arthroplasty. J Am Acad Orthop Surg 2008; 16:9–18 34. Callaghan JJ, Insall JN, Greenwald AS, et al. Mobile-bearing knee replacement: concepts and results. Instr Course Lect 2001; 50:431–449 35. Huang CH, Liau JJ, Cheng CK. Fixed or mobilebearing total knee arthroplasty. J Orthop Surg Res 2007; 2:1 36. Bartel DL, Bicknell VL, Wright TM. The effect of conformity, thickness, and material on stresses in ultra-high molecular weight components for total joint replacement. J Bone Joint Surg Am 1986; 68:1041–1051 37. Sathasivam S, Walker PS. Optimization of the bearing surface geometry of total knees. J Biomech 1994; 27:255–264 38. Engh GA. Failure of the polyethylene bearing surface of a total knee replacement within four years: a case report. J Bone Joint Surg Am 1988; 70:1093–1096 39. Kim YH, Kook HK, Kim JS. Comparison of fixed-bearing and mobile-bearing total knee arthroplasties. Clin Orthop Relat Res 2001; 101–115 40. Wen Y, Liu D, Huang Y, Li B. A meta-analysis of the fixed-bearing and mobile-bearing prostheses in total knee arthroplasty. Arch Orthop Trauma Surg 2011; 131:1341–1350 41. Walker PS, Sathasivam S. Design forms of total knee replacement. Proc Inst Mech Eng H 2000; 214:101–119 42. Vertullo CJ, Easley ME, Scott WN, Insall JN. Mobile bearings in primary knee arthroplasty. J Am Acad Orthop Surg 2001; 9:355–364

43. Freeman MA, Samuelson KM, Elias SG, Mariorenzi LJ, Gokcay EI, Tuke M. The patellofemoral joint in total knee prostheses: design considerations. J Arthroplasty 1989; 4(suppl 4):S69–S74 44. Rosenstein AD, Postak PD, Greenwald AS. Fixation strength comparison of onlay and inset patellar implants. Knee 2007; 14:194–197 45. Lachiewicz PF. Implant design and techniques for patellar resurfacing in total knee arthroplasty. Instr Course Lect 2004; 53:187–191 46. Buechel FF, Pappas MJ, Makris G. Evaluation of contact stress in metal-backed patellar replacements: a predictor of survivorship. Clin Orthop Relat Res 1991; 190–197 47. Takai S, Yoshino N, Kusaka Y, Watanabe Y, Hirasawa Y. Dissemination of metals from a failed patellar component made of titanium-base alloy. J Arthroplasty 2003; 18:931–935 48. Piraino D, Richmond B, Freed H, Belhobek G, Schils J, Stulberg B. Total knee replacement: radiologic findings in failure of porous-coated metal-backed patellar component. AJR 1990; 155:555–558 49. Li S, Chen Y, Su W, Zhao J, He S, Luo X. Systematic review of patellar resurfacing in total knee arthroplasty. Int Orthop 2011; 35:305–316 50. Pavlou G, Meyer C, Leonidou A, As-Sultany M, West R, Tsiridis E. Patellar resurfacing in total knee arthroplasty: does design matter? A metaanalysis of 7075 cases. J Bone Joint Surg Am 2011; 93:1301–1309 51. Hernigou P, Nogier A, Manicom O, Poignard A, De Abreu L, Filippini P. Alternative femoral bearing surface options for knee replacement in young patients. Knee 2004; 11:169–172 52. Laskin RS. An oxidized Zr ceramic surfaced femoral component for total knee arthroplasty. Clin Orthop Relat Res 2003; 191–196 53. Innocenti M, Civinini R, Carulli C, Matassi F, Villano M. The 5-year results of an oxidized zirconium femoral component for TKA. Clin Orthop Relat Res 2010; 468:1258–1263 54. Munzinger UK, Boldt JG, Keblish PA. Primary knee arthroplasty, 1st ed. New York, NY: Springer-Verlag, 2004:25 55. Levine B, Sporer S, Della Valle CJ, Jacobs JJ, Paprosky W. Porous tantalum in reconstructive surgery of the knee: a review. J Knee Surg 2007; 20:185–194 56. Bobyn JD, Poggie RA, Krygier JJ, et al. Clinical validation of a structural porous tantalum biomaterial for adult reconstruction. J Bone Joint Surg Am 2004; 86-A(suppl 2):123–129 57. Helm AT, Kerin C, Ghalayini SR, McLauchlan GJ. Preliminary results of an uncemented trabecular metal tibial component in total knee arthroplasty. J Arthroplasty 2009; 24:941–944 58. Dunbar MJ, Wilson DA, Hennigar AW, Amirault

AJR:201, December 2013 W833

Downloaded from www.ajronline.org by 37.44.207.89 on 01/24/17 from IP address 37.44.207.89. Copyright ARRS. For personal use only; all rights reserved

Mulcahy and Chew JD, Gross M, Reardon GP. Fixation of a trabecular metal knee arthroplasty component: a prospective randomized study. J Bone Joint Surg Am 2009; 91:1578–1586 59. Dorr LD, Wan Z, Shahrdar C, Sirianni L, Boutary M, Yun A. Clinical performance of a Durasul highly cross-linked polyethylene acetabular liner for total hip arthroplasty at five years. J Bone Joint Surg Am 2005; 87:1816–1821 60. Manley MT, Sutton K. Bearings of the future for total hip arthroplasty. J Arthroplasty 2008; 23:47–50 61. Bradford L, Baker D, Ries MD, Pruitt LA. Fatigue crack propagation resistance of highly crosslinked polyethylene. Clin Orthop Relat Res 2004; 68–72 62. Oral E, Malhi AS, Wannomae KK, Muratoglu OK. Highly cross-linked ultrahigh molecular weight polyethylene with improved fatigue resistance for total joint arthroplasty: recipient of the 2006 Hap Paul Award. J Arthroplasty 2008; 23:1037–1044 63. Chew F, Roberts C. Total knee replacement. Part 1. Radiographic evaluation. Contemp Diagn Radiol 2006; 29:1–6 64. Mulcahy H, Chew FS. Current concepts of hip arthroplasty for radiologists. Part 1. Features and radiographic assessment. AJR 2012; 199:559–569 65. Ranawat CS, Meftah M, Windsor EN, Ranawat AS. Cementless fixation in total knee arthroplasty: down the boulevard of broken dreams—affirms. J Bone Joint Surg Br 2012; 94-B:82–84 66. Vince KG, Insall JN, Kelly MA. The total condylar prosthesis: 10- to 12-year results of a cemented knee replacement. J Bone Joint Surg Br 1989; 71:793–797 67. Berger RA, Lyon JH, Jacobs JJ, et al. Problems with cementless total knee arthroplasty at 11 years followup. Clin Orthop Relat Res 2001; 196–207 68. Ezzet KA, Garcia R, Barrack RL. Effect of component fixation method on osteolysis in total knee arthroplasty. Clin Orthop Relat Res 1995; 86–91 69. Goldberg VM, Kraay M. The outcome of the cementless tibial component: a minimum 14-year clinical evaluation. Clin Orthop Relat Res 2004; 214–220 70. Akizuki S, Takizawa T, Horiuchi H. Fixation of a hydroxyapatite-tricalcium phosphate-coated cementless knee prosthesis: clinical and radiographic evaluation seven years after surgery. J Bone Joint Surg Br 2003; 85:1123–1127 71. Illgen R, Tueting J, Enright T, Schreibman K, McBeath A, Heiner J. Hybrid total knee arthroplasty: a retrospective analysis of clinical and radiographic outcomes at average 10 years follow-up. J Arthroplasty 2004; 19:95–100

72. Lombardi AV Jr, Berasi CC, Berend KR. Evolution of tibial fixation in total knee arthroplasty. J Arthroplasty 2007; 22:25–29 73. Whiteside LA. Fixation for primary total knee arthroplasty: cementless. J Arthroplasty 1996; 11:125–127; discussion, 128–129 74. Peek AC, Bloch B, Auld J. How useful is templating for total knee replacement component sizing? Knee 2012; 19:266–269 75. Jamali AA. Digital templating and preoperative deformity analysis with standard imaging software. Clin Orthop Relat Res 2009; 467:2695–2704 76. Specht LM, Levitz S, Iorio R, Healy WL, Tilzey JF. A comparison of acetate and digital templating for total knee arthroplasty. Clin Orthop Relat Res 2007; 464:179–183 77. Trickett RW, Hodgson P, Forster MC, Robertson A. The reliability and accuracy of digital templating in total knee replacement. J Bone Joint Surg Br 2009; 91:903–906 78. Bonutti PM, Mont MA, McMahon M, Ragland PS, Kester M. Minimally invasive total knee arthroplasty. J Bone Joint Surg Am 2004; 86-A (suppl 2):26–32 79. Whiteside LA. Mini incision: occasionally desirable, rarely necessary: in the affirmative. J Arthroplasty 2006; 21:16–18 80. Khanna A, Gougoulias N, Longo UG, Maffulli N. Minimally invasive total knee arthroplasty: a systematic review. Orthop Clin North Am 2009; 40: 479–489 81. Ritter MA, Faris PM, Keating EM, Meding JB. Postoperative alignment of total knee replacement: its effect on survival. Clin Orthop Relat Res 1994; 153–156 82. Siston RA, Giori NJ, Goodman SB, Delp SL. Surgical navigation for total knee arthroplasty: a perspective. J Biomech 2007; 40:728–735 83. Bae DK, Song SJ. Computer assisted navigation in knee arthroplasty. Clin Orthop Surg 2011; 3:259–267 84. Fu Y, Wang M, Liu Y, Fu Q. Alignment outcomes in navigated total knee arthroplasty: a meta-analysis. Knee Surg Sports Traumatol Arthrosc 2012; 20:1075–1082 85. Mason JB, Fehring TK, Estok R, Banel D, Fahrbach K. Meta-analysis of alignment outcomes in computer-assisted total knee arthroplasty surgery. J Arthroplasty 2007; 22:1097–1106 86. Bauwens K, Matthes G, Wich M, et al. Navigated total knee replacement: a meta-analysis. J Bone Joint Surg Am 2007; 89:261–269 87. Lombardi AV Jr, Berend KR, Adams JB. Patientspecific approach in total knee arthroplasty. Orthopedics 2008; 31:927–930

88. Sarmah SS, Patel S, Hossain FS, Haddad FS. The radiological assessment of total and unicompartmental knee replacements. J Bone Joint Surg Br 2012; 94:1321–1329 89. Weissman BN, Shah N, Daffner RH, et al; American College of Radiology. ACR appropriateness criteria: imaging after total knee arthroplasty. American College of Radiology website. www. acr.org/~/media/ACR/Documents/AppCriteria/ Diagnostic/ImagingAfterTotalKneeArthroplasty. pdf. Published 1995. Updated 2011. Accessed May 5, 2013 90. Miller TT. Imaging of knee arthroplasty. Eur J Radiol 2005; 54:164–177 91. Clarke HD, Scott WN. Knee: axial instability. Orthop Clin North Am 2001; 32:627–637 92. Manaster BJ. Total knee arthroplasty: postoperative radiologic findings. AJR 1995; 165:899–904 93. Allen AM, Ward WG, Pope TL Jr. Imaging of the total knee arthroplasty. Radiol Clin North Am 1995; 33:289–303 94. Figgie HE 3rd, Goldberg VM, Heiple KG, Moller HS 3rd, Gordon NH. The influence of tibial-patellofemoral location on function of the knee in patients with the posterior stabilized condylar knee prosthesis. J Bone Joint Surg Am 1986; 68:1035– 1040 95. Jazrawi LM, Birdzell L, Kummer FJ, Di Cesare PE. The accuracy of computed tomography for determining femoral and tibial total knee arthroplasty component rotation. J Arthroplasty 2000; 15:761–766 96. Berger RA, Rubash HE, Seel MJ, Thompson WH, Crossett LS. Determining the rotational alignment of the femoral component in total knee arthroplasty using the epicondylar axis. Clin Orthop Relat Res 1993; 40–47 97. Berger RA, Crossett LS, Jacobs JJ, Rubash HE. Malrotation causing patellofemoral complications after total knee arthroplasty. Clin Orthop Relat Res 1998; 144–153 98. Rhoads DD, Noble PC, Reuben JD, Mahoney OM, Tullos HS. The effect of femoral component position on patellar tracking after total knee arthroplasty. Clin Orthop Relat Res 1990; 43–51 99. Anouchi YS, Whiteside LA, Kaiser AD, Milliano MT. The effects of axial rotational alignment of the femoral component on knee stability and patellar tracking in total knee arthroplasty demonstrated on autopsy specimens. Clin Orthop Relat Res 1993; 170–177 100. Deshmukh RV, Scott RD. Unicompartmental knee arthroplasty: long-term results. Clin Orthop Relat Res 2001; 272–278 (Figures appear on next page)

W834

AJR:201, December 2013

Downloaded from www.ajronline.org by 37.44.207.89 on 01/24/17 from IP address 37.44.207.89. Copyright ARRS. For personal use only; all rights reserved

Features and Imaging Assessment of Knee Replacement

Fig. 1—78-year-old woman with posterior cruciate ligament–retaining total knee arthroplasty. A and B, Anteroposterior (A) and lateral (B) radiographs of knee show that prosthesis is fixed with cement (arrows, A and B). Thickness of femoral component (black lines, B) is thinner than posterior stabilized designs.

A

A

B

B

Fig. 2—70-year-old woman with posterior cruciate ligament–substituting total knee arthroplasty. A and B, Anteroposterior (A) and lateral (B) radiographs of knee show that prosthesis is fixed with cement. Presence of central slot in femoral component (arrow, A) and thickness of femoral component (lines, B) are characteristic of cam-post type PCL-substituting designs.

AJR:201, December 2013 W835

Downloaded from www.ajronline.org by 37.44.207.89 on 01/24/17 from IP address 37.44.207.89. Copyright ARRS. For personal use only; all rights reserved

Mulcahy and Chew

Fig. 3—75-year-old man with varus-valgus constrained total knee arthroplasty. A and B, Anteroposterior (A) and lateral (B) radiographs of knee show that prosthesis is fixed with cement. Femoral and tibial components have extended stems (white arrows, A). Varus-valgus constrained designs have tall tibial metal post and deep femoral box (black arrow, A). There is no hinge connecting femoral and tibial components (arrow, B).

A

A

W836

B

B

Fig. 4—35-year-old woman with history of osteosarcoma and modular rotating hinged total knee arthroplasty. A and B, Anteroposterior (A) and lateral (B) radiographs of knee show that prosthesis is fixed with cement. Tibial and femoral components are linked with hinge (arrows) built into implants. Portions of distal femoral shaft are replaced by prosthesis.

AJR:201, December 2013

Downloaded from www.ajronline.org by 37.44.207.89 on 01/24/17 from IP address 37.44.207.89. Copyright ARRS. For personal use only; all rights reserved

Features and Imaging Assessment of Knee Replacement

A

B Fig. 6—22-year-old man with meniscal allograft. Coronal T1-weighted MRI shows lateral meniscal allograft (white arrow) with normal signal intensity and shape. Suture tracts (black arrow) are noted along lateral tibial plateau.

Fig. 5—63-year-old woman with sex-specific high-flexion total knee arthroplasty. A and B, Anteroposterior (A) and lateral (B) radiographs of knee show decreased mediolateral dimension of femoral prosthesis (double-ended arrow, A) and decreased anterior height of femoral flanges (double-ended black arrow, B), which are characteristic of sex-specific designs. Increased posterior femoral condylar radius (double-ended white arrow, B) is characteristic of high-flexion designs.

A

B

Fig. 7—62-year-old woman with interpositional arthroplasty. A and B, Anteroposterior (A) and lateral (B) radiographs of knee show metal interpositional arthroplasty (OrthoGlide, Advanced Bio-Surfaces). This device has no moving parts and requires no bone resection and no fixation.

AJR:201, December 2013 W837

Downloaded from www.ajronline.org by 37.44.207.89 on 01/24/17 from IP address 37.44.207.89. Copyright ARRS. For personal use only; all rights reserved

Mulcahy and Chew

A

B

C

Fig. 8—Three different patients with unicompartmental knee arthroplasty (UKA). A, 80-year-old woman. Anteroposterior radiograph of knee shows medial UKA with meniscal bearing (white arrow). B, 67-year-old man. Anteroposterior radiograph of knee shows lateral UKA with fixed bearing. C, 51-year-old woman. Anteroposterior radiograph of knee shows patellofemoral UKA.

Fig. 9—63-year-old woman with total knee arthroplasty with fixed-bearing design. Anteroposterior radiograph of knee shows cemented posterior stabilized prosthesis with fixed-bearing design. In general, fixed-bearing designs and rotating platform or multidirectional platform mobile-bearing designs are not differentiated on radiographs. However, sometimes fixed-bearing designs can have locking metal tibial post (arrow) for polyethylene fixation.

W838

AJR:201, December 2013

Downloaded from www.ajronline.org by 37.44.207.89 on 01/24/17 from IP address 37.44.207.89. Copyright ARRS. For personal use only; all rights reserved

Features and Imaging Assessment of Knee Replacement Fig. 10—Four different patients with patellar resurfacing in total knee arthroplasty. Magnified lateral radiographs of knees show different methods of patellar resurfacing. A, 67-year-old woman. Image shows inset patellar resurfacing with single peg (white arrow), cemented. B, 78-year-old man. Image shows onlay patellar resurfacing with cemented multiple pegs. Patellar articular surface is reamed. C, 66-year-old woman. Image shows metal backed patella with cementless fixation. D, 63-year-old man. Image shows nonresurfaced patella.

A

B

C

D

Fig. 11—55-year-old man with total knee arthroplasty with oxidized zirconium (Oxinium, Smith and Nephew) femoral condylar component. Anteroposterior radiograph of knee of shows oxidized zirconium femoral condylar component. There is no difference in radiographic density between femoral (oxidized zirconium) and tibial (cobalt-chromium-molybdenum alloy) components.

Fig. 12—65-year-old woman with cementless total knee arthroplasty. Anteroposterior radiograph of knee shows cementless fixation of prostheses and two additional tibial screws.

AJR:201, December 2013 W839

Downloaded from www.ajronline.org by 37.44.207.89 on 01/24/17 from IP address 37.44.207.89. Copyright ARRS. For personal use only; all rights reserved

Mulcahy and Chew

Fig. 13—67-year-old woman with digital templating. Anteroposterior (left) and lateral (right) radiographs of knee show digital templating method. Digital implant images are superimposed on calibrated digital radiographs of knee. 4.R = size of the tibial component, F = size of the femoral component, Ref = reference.

A

B

Fig. 14—Comparison of traditional total knee arthroplasty (TKA) with minimally invasive surgery quadricepssparing technique in two different patients. A, 80-year-old woman. Lateral radiograph of knee shows cemented posterior cruciate ligament–sparing TKA using traditional incisions. B, 64-year-old woman. Lateral radiograph of knee shows cemented fixed-bearing TKA using minimally invasive surgery quadriceps-sparing incisions.

W840

AJR:201, December 2013

Downloaded from www.ajronline.org by 37.44.207.89 on 01/24/17 from IP address 37.44.207.89. Copyright ARRS. For personal use only; all rights reserved

Features and Imaging Assessment of Knee Replacement

A

B

Fig. 16—63-year-old woman with total knee arthroplasty (TKA). A, Anteroposterior radiograph of TKA. Femorotibial angle is angle intersecting femoral anatomic axis with tibial anatomic axis. Femoral component should be placed 7° ± 3° valgus, and tibial component should be 90° ± 3° relative to anatomic axis of tibia on anteroposterior radiograph, allowing overall 4–7° valgus angulation. Polyethylene joint space should be equivalent medially and laterally (double-headed arrows). B, Lateral radiograph of TKA. Horizontal portion of femoral component should be 90° relative to anatomic axis of femur. Tibial component should be horizontal or slope downward 3–7° posteriorly, and its position should be either central or posterior relative to center of tibial shaft.

Fig. 15—51-year-old woman with three-joint view of both lower legs. Line drawn from center of femoral head to center of talar body is mechanical axis (MA) (black solid line), and it should intersect center or just medially to center of prosthetic knee, and femoral and tibial components should be perpendicular to this line. Anatomic axis of femur (AA) is line along femoral shaft that passes through center of distal femur (black dotted line). On femur, angle between mechanical axis and anatomic axis is between 4° and 7°. Femorotibial angle is angle intersecting femoral anatomic axis (double-ended black arrow) with tibial anatomic axis (double-ended white arrow).

Fig. 17—56-year-old man with total knee arthroplasty. Lateral radiograph of knee shows anterior femoral notching (arrow) of femoral component. This can predispose periprosthetic supracondylar femoral fracture.

Fig. 18—67-year-old woman with total knee arthroplasty. Anteroposterior radiograph of knee shows medial overhang (arrow) of tibial tray, which may irritate adjacent soft tissues.

AJR:201, December 2013 W841

Downloaded from www.ajronline.org by 37.44.207.89 on 01/24/17 from IP address 37.44.207.89. Copyright ARRS. For personal use only; all rights reserved

Mulcahy and Chew Fig. 19—64-year-old woman with patellar alignment in total knee arthroplasty (TKA). Preoperative (left) and postoperative (right) lateral radiographs of knee are shown. Change in position of joint line after TKA is determined by measuring tibial tubercle (TT)–tibial plateau distance on preoperative view and comparing it to tibial tubercle–tibial component articulating surface distance postoperatively (height of joint line) (double-ended black arrows). Height of joint line should be altered 8 mm or less. Patella height (PH; distance from inferior edge of patellar component to tibial articular surface) (double-ended white arrow) should be 10–30 mm to have good result.

A

B

Fig. 20—56-year-old woman with rotational alignment in total knee arthroplasty (TKA). A, Axial CT image of femoral component in TKA. Rotation of femoral component is determined through femoral epicondyles. Surgical transepicondylar axis (TEA) is line that extends from peak of lateral epicondyle to sulcus of medial epicondyles and is thought to represent center of rotation of knee (solid black line). Second line, prosthetic posterior condylar line, connects medial and lateral prosthetic posterior condylar surfaces (dotted black line). Rotation of femoral component is defined by angle of dotted black line relative to TEA. B, Axial CT images of proximal tibia. At level of polyethylene liner, perpendicular line is drawn through center point of liner (dotted black line) to line that is parallel to posterior tibial component (solid black line). At level of tibial tubercle, line bisecting tibial tubercle through center point is drawn (solid white line). Tibial component rotation is defined by angle between dotted black line and solid white line.

F O R YO U R I N F O R M AT I O N

This article is available for CME/SAM credit. To access the examination for this article, follow the prompts.

W842

AJR:201, December 2013