The Journal of Arthroplasty xxx (2015) xxx–xxx
Contents lists available at ScienceDirect
The Journal of Arthroplasty journal homepage: www.arthroplastyjournal.org
Development of a Modern Knee Society Radiographic Evaluation System and Methodology for Total Knee Arthroplasty R. Michael Meneghini, M.D. a, Michael A. Mont, M.D. b, David B. Backstein, M.D. c, Robert B. Bourne, M.D. d, Doug A. Dennis, M.D. e, Giles R. Scuderi, M.D. f a
Indiana University School of Medicine, Fishers, Indiana Rubin Institute for Advanced Orthopedics, Center for Joint Preservation and Replacement, Sinai Hospital of Baltimore, Baltimore, Maryland Mount Sinai Hospital, University of Toronto, Toronto, Ontario d University Hospital, London, Ontario, Canada e Colorado Joint Replacement, Denver, Colorado f North Shore–LIJ Heath System, Medical Group Orthopaedics, New York, New York b c
a r t i c l e
i n f o
Article history: Received 7 May 2015 Accepted 22 May 2015 Available online xxxx Keywords: Knee Society Radiographic Evaluation and Scoring System total knee arthroplasty knee society radiographic evaluation classification radiolucency
a b s t r a c t To accompany the new clinical Knee Society Score, a committee was formed to develop an updated radiographic assessment and evaluation system. The purpose is to accumulate radiographic data in a standardized manner to facilitate more accurate interpretation, documentation and clinical correlation. We systematically reviewed the TKA radiographic evaluation literature as well as the original Knee Society Radiographic Evaluation and Scoring System. A modern system was developed, approved by the Knee Society membership, which ensured proper radiographic documentation of coronal and sagittal implant alignment, fixation interface integrity with respect to radiolucent lines and osteolysis, and a zonal classification system to document precise deficiency locations. It is hoped that data may be accumulated in a standardized manner with eventual formulation of implant risk “criteria” or “scores’. © 2015 Elsevier Inc. All rights reserved.
In 1989, the original Knee Society Clinical Rating System was developed to assess the clinical and functional status of patients after total knee arthroplasty (TKA) [1]. It was accompanied by a radiographic evaluation and scoring method published in the same year [2]. Recently, a new Knee Society Scoring System was developed to objectively evaluate patients with TKA clinically with respect to function, expectations, pain and satisfaction. The purpose of creating the new scoring system was to modernize this outcome measure with greater utility, sensitivity and validity in contemporary knee arthroplasty patients, who have increasing physical demands and activities [3,4]. Subsequently, a modernized and updated radiographic evaluation system for total knee arthroplasty was necessary, particularly in light of the diverse and complex variety of knee designs that have emerged over the past 25 years. Due to the increase in primary and revision knee arthroplasty surgery that is projected to occur [5], it is essential to develop a consistent One or more of the authors of this paper have disclosed potential or pertinent conflicts of interest, which may include receipt of payment, either direct or indirect, institutional support, or association with an entity in the biomedical field which may be perceived to have potential conflict of interest with this work. For full disclosure statements refer to http://dx.doi.org/10.1016/j.arth.2015.05.049. Level of Evidence: V. Reprint requests: R. Michael Meneghini, M.D., Indiana University School of Medicine, 13100 East 136th Street, Suite 2000, Fishers, IN 46037.
and standardized methodology to obtain and perform a radiographic evaluation of these procedures. When compared to the original Knee Society Scoring system [2], a newer practical approach was needed to be established to update and standardize guidelines for the specific radiographs to be obtained, the techniques used to obtain them, and the methods for evaluation and reporting upon the status of the implants. Due to the lack of studies with sufficient statistical power to correlate specific radiographic findings with outcomes, as well as the numerous implant designs, it was beyond the scope of this system to define specific x-ray parameter values that would deem implants as “normal”, “abnormal” or “at-risk.” Rather, it is proposed that this radiographic evaluation system be used to accumulate radiographic data in a standardized manner in order to facilitate more accurate x-ray interpretation, documentation and clinical correlation. In addition to primary TKA implants, schematics and methodology are provided for the evaluation of revision knee arthroplasty systems.
Methods A committee of six Knee Society members was formed with the specific task of developing an updated radiographic assessment and evaluation system. The committee was composed of knee arthroplasty
http://dx.doi.org/10.1016/j.arth.2015.05.049 0883-5403/© 2015 Elsevier Inc. All rights reserved.
Please cite this article as: Meneghini RM, et al, Development of a Modern Knee Society Radiographic Evaluation System and Methodology for Total Knee Arthroplasty, J Arthroplasty (2015), http://dx.doi.org/10.1016/j.arth.2015.05.049
2
R.M. Meneghini et al. / The Journal of Arthroplasty xxx (2015) xxx–xxx
incorporated into the final Knee Society Radiographic Evaluation System presented in this manuscript and in the accompanying schematics. Standard Postoperative Radiographs Serial radiographs are recommended for interval comparison of radiographic metrics such as radiolucent lines and component position. The techniques employed by the staff in obtaining the radiographic views of the TKA are critical to ensuring accurate evaluation. The three essential views that must be obtained for a complete and accurate TKA radiographic evaluation are listed below with a suggested description of an optimal technique.
Fig. 1. (A) Schematic of coronal plane radiographic measurements (in degrees) that denote femoral and tibial anatomic axis based on the implant alignment. (B) Schematic of sagittal plane radiographic measurements (in degrees) that denote femoral component flexion and tibial slope.
surgeons who had extensive experience in primary and revision total knee arthroplasty and who undertook a systematic review of the pertinent TKA radiographic evaluation literature, as well as a review of the original Knee Society Radiographic Evaluation and Scoring System [2]. A structured search of 4 electronic databases of EMBASE, CINAHLplus, PubMed, and SCOPUS was conducted to identify reports between January 1980 and September 2013 concerning radiographic evaluation of knee arthroplasties. The authors used a combination of the Boolean search strings knee, arthroplasty* replacement*, radiograph*, revis*, xray*, and osteolysis*, to identify evaluation metrics regarding knee arthroplasty procedures. Bibliographies of all reports identified were individually searched to extract additional studies for the final analysis that may have been overlooked after the initial search. Based on the information obtained in those searches and reviews, a modern and updated evaluation system was developed for both primary and revision TKA and then this was distributed to the entire Knee Society membership for scrutinized evaluation, feedback, and suggested edits. The feedback from the membership was consolidated and
• Weight-bearing antero-posterior (AP) view: The technique should emphasize targeting the x-ray beam parallel and in line with the approximate slope of the tibial component baseplate. This provides optimal visualization of the various tibial fixation interfaces to accurately assess the location and the magnitude of radiolucent lines. The knee should be positioned with the patella facing towards the x-ray beam in order to minimize limb rotation and to more accurately assess alignment in the coronal plane. • Lateral view: The technique should be taken with the knee flexed 30° with the patient lying on the affected side with an emphasis on obtaining a true lateral of the femoral component, where the posterior femoral condyles are superimposed. This facilitates a tangential view of the implant fixation interfaces to accurately assess radiolucent lines, femoral component positions, sizes, tibial slopes, as well as the patella implant, patellar bone, and the patella tendon relationship. • Patello-femoral view: The preferred view is the Merchant view, and is obtained with the patient lying supine with knees flexed to 45°, typically held with a fixed or adjustable platform, and the x-ray beam angled at 30° from the horizontal [6]. This view is used to evaluate the patellar implant fixation integrity, the patellar bone, and the patellar alignment with respect to tilt and subluxation. Radiographic Evaluation Metrics Alignment/Component Position • Coronal alignment is evaluated on the AP radiograph. The coronal “anatomic” alignment of the femoral component is comprised of the distal femoral component surface with respect to the anatomic axis of the femoral shaft. Similarly, the tibial component alignment is determined by the angle between the baseplate and the
Fig. 2. (A) Schematic of radiographic patella tilt measurement (in degrees) relative to the femoral component denoted on the Merchant view radiograph. (B) Schematic of radiographic patella displacement measurement (in millimeters) relative to the central trochlea of the femoral component denoted on the Merchant view radiograph.
Please cite this article as: Meneghini RM, et al, Development of a Modern Knee Society Radiographic Evaluation System and Methodology for Total Knee Arthroplasty, J Arthroplasty (2015), http://dx.doi.org/10.1016/j.arth.2015.05.049
R.M. Meneghini et al. / The Journal of Arthroplasty xxx (2015) xxx–xxx
3
mechanical axis of the tibia, as approximated in a similar manner to the femur (the fibular shaft axis may also be used if proximal tibial bowing is present) (See Fig. 1A). • Sagittal alignment is evaluated on the lateral radiograph. Femoral component alignment is measured as the angle between the most distal femoral fixation surface with respect to the femoral shaft axis. The distal femoral fixation surface may be obscured by the cam mechanism housing in a posterior-substituting TKA design, which may necessitate using that surface as an approximation depending on the implant design (See Fig. 1B). • Patellofemoral alignment is determined on the patellofemoral (Merchant view) and is assessed with tilt and subluxation metrics. Patella tilt is defined as the angle between the anterior limits of the femoral component condyles and the prosthesis–bone interface line of the patellar component [7](See Fig. 2A). Patella subluxation (displacement) is defined as the distance between those lines intersecting the center of the patella and the line through the deepest part of the trochlear groove [7] (See Fig. 2B).
Implant Fixation Interface: Radiolucent Lines and Osteolysis The fixation interface of all implants should be examined for radiolucent lines on the AP, lateral, and patellofemoral radiographs. This includes the implant–cement and cement–bone interfaces, as well as the implant–bone interface in uncemented implants. The significance of radiolucent lines is likely dependent on whether they encompass an entire interface surface (partial versus complete), and whether they are stable or progressive on serial radiographs with nearly identical implant orientations, limb positions, and radiographic projections. However, it has been reported that while stable, non-progressive radiolucent lines are frequent in the first year after TKA, even progressive radiolucent lines may not be indicative of implant fixation failure [8]. Furthermore, it has been reported that the method of radiolucent line assessment in the previous Knee Society Radiographic Scoring System is unreliable due to its complexity, and a simplified methodology reported to offer improved reliability and reproducibility was needed [9]. Therefore, for the benefit of standardization of comparative evaluation, implant monitoring and outcome assessment, a simplified and standardized method of describing the general locations/regions of radiolucent lines, as well as regions of osteolytic regions, is described. This is an important goal of the modernized and updated Knee Society Radiographic Evaluation System presented in this manuscript. When utilizing this evaluation system, the documentation of lucent lines should be graded as “partial” or “complete” with respect to the zone denoted on the schematic images (Figs. 3 and 4) and regions of osteolysis should be documented in millimeters in the zone locations. Implant Zone Classification The tibial, femoral, and patella implants are divided into three general zones on the various radiographs. In general, zones 1 and 2 are on the periphery (either medial/lateral, anterior/posterior, inferior/posterior), whereas, zone 3 is used to designate the “central keel” region of an associated implant design, while the central region of a two-pegged design encompasses the pegs and the central region between them. On the AP view, a designation of “3M” is used to designate the medial aspect of the keel, and “3L” the lateral aspect of the keel. For a twopegged tibial baseplate design, “3M” and “3L” are used to designate the area around each of the respective pegs and “3” is used to designate the central area under the baseplate between the pegs. On the lateral view, “3A” and “3P” are used to designate the respective anterior and posterior regions of the keel. Although it may not be initially intuitive, the most inferior region of the keel is designated “5”. The rationale for this lies in the numerical designation of “4” being used for the region of the stem extensions in the revision setting (See Fig. 4A–D) and to maintain consistency and uniformity. The details of the regions are listed below:
Fig. 3. (A) Coronal and (B) sagittal radiographic schematic of keeled and two-peg implants with zones for documentation of radiolucent lines and osteolysis. (C) Sagittal plane radiographic schematic of femoral implant with zones denoted for documentation radiolucent lines and osteolysis. (D) Patellofemoral view radiographic schematic of multi- or singlepeg patella implant with zones denoted for documentation radiolucent lines and osteolysis. Radiolucent lines should be denoted and documented as “partial” or “complete” and osteolysis documented in millimeters.
Tibial Component AP View: (See Fig. 3A) • Zone 1: medial baseplate • Zone 2: lateral baseplate • Zone 3: central keel/stem region (“M” and “L” designate the respective regions of the central keel) • Zone 4: Revision TKA Stem Extension (“M” and “L” designate the respective regions of the stem extension) (See Fig. 4A) • Zone 5: inferior aspect of tibial keel/stem Tibial Component Lateral View: (See Fig. 3B) • Zone 1: anterior baseplate
Please cite this article as: Meneghini RM, et al, Development of a Modern Knee Society Radiographic Evaluation System and Methodology for Total Knee Arthroplasty, J Arthroplasty (2015), http://dx.doi.org/10.1016/j.arth.2015.05.049
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R.M. Meneghini et al. / The Journal of Arthroplasty xxx (2015) xxx–xxx
Discussion
Fig. 4. (A) Coronal and (B) sagittal radiographic schematic of revision tibial implants that have stem extensions with zones for documentation of radiolucent lines and osteolysis. (C) Coronal and (D) sagittal radiographic schematic of revision femoral implants that have stem extensions with zones for documentation of radiolucent lines and osteolysis. Radiolucent lines should be denoted and documented as “partial” or “complete” and osteolysis documented in millimeters.
• Zone 2: posterior baseplate • Zone 3: central keel/stem/peg fixation region (“A” and “P” designate the respective regions of the central keel) • Zone 4: Revision TKA Stem Extension (“A” and “P” designate the respective regions of the stem extension) (See Fig. 4B) • Zone 5: inferior aspect of tibial keel/stem Femoral Component Lateral (See Figs. 3C and 4D) and AP View (See Fig. 4C) • Zone 1: anterior flange • Zone 2: posterior flange • Zone 3: central box/peg/distal fixation region (“A” and “P” designate the respective chamfers if visible) • Zone 4: Revision TKA Stem Extension (“M” and “L” designate the respective regions of the stem extension on the AP view (See Fig. 4C); “A” and “P” designate the respective regions of the stem extension on the lateral view (See Fig. 4D)) Patella Component Patellofemoral View: (see Figs. 3D and 5) • Zone 1: medial • Zone 2: lateral • Zone 3: central peg/baseplate region (“M” and “L” designate the respective regions on the merchant view, whereas “S” and “I” designate the superior and inferior regions on the lateral view) • Patella bone thickness is measured and noted in Fig. 5.
Fig. 5. Patellofemoral radiographic view schematic denoting patella bone thickness, measured in millimeters.
The overall goal of this project was to develop a consistent and standardized methodology to obtain and perform a radiographic evaluation of total knee arthroplasties (TKAs). When compared to the original Knee Society Scoring system [2], a suggested more practical approach was to establish updated and standardized guidelines for the specific radiographs to be obtained, techniques used to obtain them, and methods for evaluation and reporting on the status of implants. In addition, compared to the original Knee Society Radiographic Evaluation System, the complexity and variety of implants have increased, which drives a need to adapt the radiographic evaluation method accordingly. This modernized evaluation system is more descriptive and more detailed, compared to the previous version and will also allow evaluation of multiple implant designs. However, this evaluation system remains descriptive rather than predictive or prognostic in its current scope and form. Due to the lack of studies with sufficient statistical power to correlate specific radiographic findings with outcomes, as well as the numerous implant systems and designs, it is beyond the scope of this evaluation system to define specific radiographic parameter values as either “normal”, “abnormal” or “at-risk”. After thorough review and discussion of the Radiographic Score Committee, as well as via feedback from the entire Knee Society membership, it was concluded that this radiographic evaluation system should remain descriptive and focus on the uniformity of assessment and documentation. However, the committee has proposed that this tool can potentially be used to accumulate data in a standardized manner, which might be analyzed and used to formulate a “criteria” or “score” to determine if an implant is at risk and our goal is that future research efforts will be focused in this regard. So that this evaluation guideline might promote standardization of reporting in the modern era of healthcare multi-center analysis and registry outcomes, it should be feasible and applicable for the majority of, if not all knee arthroplasty surgeons. Certain practice resource restrictions, such as financial, equipment and staffing, may preclude more advanced techniques such as full-length mechanical axis images being performed on a routine basis. Therefore, the recommended images and techniques in these guidelines are based on a simplified and cost-effective basis and represent a “minimum” requirement for standardized assessment and reporting of the status and radiographic functioning of the implant. The committee members acknowledge that more advanced imaging may be helpful to further assess pathologic failure mechanisms in TKA and recommend performing those if clinically indicated. Acknowledgments The authors would like to sincerely thank and acknowledge Joy Marlowe for her contributions in the manuscript, which involved creation and development of the schematic drawings and images. References 1. Insall JN, Dorr LD, Scott RD, et al. Rationale of the Knee Society clinical rating system. Clin Orthop Relat Res 1989(248):13. 2. Ewald FC. The Knee Society total knee arthroplasty roentgenographic evaluation and scoring system. Clin Orthop Relat Res 1989(248):9. 3. Noble PC, Scuderi GR, Brekke AC, et al. Development of a new Knee Society scoring system. Clin Orthop Relat Res 2012;470(1):20. 4. Scuderi GR, Bourne RB, Noble PC, et al. The new Knee Society Knee Scoring System. Clin Orthop Relat Res 2012;470(1):3. 5. Kurtz SM, Ong KL, Lau E, et al. Impact of the economic downturn on total joint replacement demand in the United States: updated projections to 2021. J Bone Joint Surg Am 2014;96(8):624. 6. Merchant AC, Mercer RL, Jacobsen RH, et al. Roentgenographic analysis of patellofemoral congruence. J Bone Joint Surg Am 1974;56(7):1391. 7. Gomes LS, Bechtold JE, Gustilo RB. Patellar prosthesis positioning in total knee arthroplasty. A roentgenographic study. Clin Orthop Relat Res 1988(236):72. 8. Aebli N, Krebs J, Schwenke D, et al. Progression of radiolucent lines in cementless twinbearing low-contact-stress knee prostheses: a retrospective study. J Arthroplasty 2004; 19(6):783. 9. Bach CM, Biedermann R, Goebel G, et al. Reproducible assessment of radiolucent lines in total knee arthroplasty. Clin Orthop Relat Res 2005(434):183.
Please cite this article as: Meneghini RM, et al, Development of a Modern Knee Society Radiographic Evaluation System and Methodology for Total Knee Arthroplasty, J Arthroplasty (2015), http://dx.doi.org/10.1016/j.arth.2015.05.049
Contents lists available at ScienceDirect
The Journal of Arthroplasty journal homepage: www.arthroplastyjournal.org
Development of a Modern Knee Society Radiographic Evaluation System and Methodology for Total Knee Arthroplasty R. Michael Meneghini, M.D. a, Michael A. Mont, M.D. b, David B. Backstein, M.D. c, Robert B. Bourne, M.D. d, Doug A. Dennis, M.D. e, Giles R. Scuderi, M.D. f a
Indiana University School of Medicine, Fishers, Indiana Rubin Institute for Advanced Orthopedics, Center for Joint Preservation and Replacement, Sinai Hospital of Baltimore, Baltimore, Maryland Mount Sinai Hospital, University of Toronto, Toronto, Ontario d University Hospital, London, Ontario, Canada e Colorado Joint Replacement, Denver, Colorado f North Shore–LIJ Heath System, Medical Group Orthopaedics, New York, New York b c
a r t i c l e
i n f o
Article history: Received 7 May 2015 Accepted 22 May 2015 Available online xxxx Keywords: Knee Society Radiographic Evaluation and Scoring System total knee arthroplasty knee society radiographic evaluation classification radiolucency
a b s t r a c t To accompany the new clinical Knee Society Score, a committee was formed to develop an updated radiographic assessment and evaluation system. The purpose is to accumulate radiographic data in a standardized manner to facilitate more accurate interpretation, documentation and clinical correlation. We systematically reviewed the TKA radiographic evaluation literature as well as the original Knee Society Radiographic Evaluation and Scoring System. A modern system was developed, approved by the Knee Society membership, which ensured proper radiographic documentation of coronal and sagittal implant alignment, fixation interface integrity with respect to radiolucent lines and osteolysis, and a zonal classification system to document precise deficiency locations. It is hoped that data may be accumulated in a standardized manner with eventual formulation of implant risk “criteria” or “scores’. © 2015 Elsevier Inc. All rights reserved.
In 1989, the original Knee Society Clinical Rating System was developed to assess the clinical and functional status of patients after total knee arthroplasty (TKA) [1]. It was accompanied by a radiographic evaluation and scoring method published in the same year [2]. Recently, a new Knee Society Scoring System was developed to objectively evaluate patients with TKA clinically with respect to function, expectations, pain and satisfaction. The purpose of creating the new scoring system was to modernize this outcome measure with greater utility, sensitivity and validity in contemporary knee arthroplasty patients, who have increasing physical demands and activities [3,4]. Subsequently, a modernized and updated radiographic evaluation system for total knee arthroplasty was necessary, particularly in light of the diverse and complex variety of knee designs that have emerged over the past 25 years. Due to the increase in primary and revision knee arthroplasty surgery that is projected to occur [5], it is essential to develop a consistent One or more of the authors of this paper have disclosed potential or pertinent conflicts of interest, which may include receipt of payment, either direct or indirect, institutional support, or association with an entity in the biomedical field which may be perceived to have potential conflict of interest with this work. For full disclosure statements refer to http://dx.doi.org/10.1016/j.arth.2015.05.049. Level of Evidence: V. Reprint requests: R. Michael Meneghini, M.D., Indiana University School of Medicine, 13100 East 136th Street, Suite 2000, Fishers, IN 46037.
and standardized methodology to obtain and perform a radiographic evaluation of these procedures. When compared to the original Knee Society Scoring system [2], a newer practical approach was needed to be established to update and standardize guidelines for the specific radiographs to be obtained, the techniques used to obtain them, and the methods for evaluation and reporting upon the status of the implants. Due to the lack of studies with sufficient statistical power to correlate specific radiographic findings with outcomes, as well as the numerous implant designs, it was beyond the scope of this system to define specific x-ray parameter values that would deem implants as “normal”, “abnormal” or “at-risk.” Rather, it is proposed that this radiographic evaluation system be used to accumulate radiographic data in a standardized manner in order to facilitate more accurate x-ray interpretation, documentation and clinical correlation. In addition to primary TKA implants, schematics and methodology are provided for the evaluation of revision knee arthroplasty systems.
Methods A committee of six Knee Society members was formed with the specific task of developing an updated radiographic assessment and evaluation system. The committee was composed of knee arthroplasty
http://dx.doi.org/10.1016/j.arth.2015.05.049 0883-5403/© 2015 Elsevier Inc. All rights reserved.
Please cite this article as: Meneghini RM, et al, Development of a Modern Knee Society Radiographic Evaluation System and Methodology for Total Knee Arthroplasty, J Arthroplasty (2015), http://dx.doi.org/10.1016/j.arth.2015.05.049
2
R.M. Meneghini et al. / The Journal of Arthroplasty xxx (2015) xxx–xxx
incorporated into the final Knee Society Radiographic Evaluation System presented in this manuscript and in the accompanying schematics. Standard Postoperative Radiographs Serial radiographs are recommended for interval comparison of radiographic metrics such as radiolucent lines and component position. The techniques employed by the staff in obtaining the radiographic views of the TKA are critical to ensuring accurate evaluation. The three essential views that must be obtained for a complete and accurate TKA radiographic evaluation are listed below with a suggested description of an optimal technique.
Fig. 1. (A) Schematic of coronal plane radiographic measurements (in degrees) that denote femoral and tibial anatomic axis based on the implant alignment. (B) Schematic of sagittal plane radiographic measurements (in degrees) that denote femoral component flexion and tibial slope.
surgeons who had extensive experience in primary and revision total knee arthroplasty and who undertook a systematic review of the pertinent TKA radiographic evaluation literature, as well as a review of the original Knee Society Radiographic Evaluation and Scoring System [2]. A structured search of 4 electronic databases of EMBASE, CINAHLplus, PubMed, and SCOPUS was conducted to identify reports between January 1980 and September 2013 concerning radiographic evaluation of knee arthroplasties. The authors used a combination of the Boolean search strings knee, arthroplasty* replacement*, radiograph*, revis*, xray*, and osteolysis*, to identify evaluation metrics regarding knee arthroplasty procedures. Bibliographies of all reports identified were individually searched to extract additional studies for the final analysis that may have been overlooked after the initial search. Based on the information obtained in those searches and reviews, a modern and updated evaluation system was developed for both primary and revision TKA and then this was distributed to the entire Knee Society membership for scrutinized evaluation, feedback, and suggested edits. The feedback from the membership was consolidated and
• Weight-bearing antero-posterior (AP) view: The technique should emphasize targeting the x-ray beam parallel and in line with the approximate slope of the tibial component baseplate. This provides optimal visualization of the various tibial fixation interfaces to accurately assess the location and the magnitude of radiolucent lines. The knee should be positioned with the patella facing towards the x-ray beam in order to minimize limb rotation and to more accurately assess alignment in the coronal plane. • Lateral view: The technique should be taken with the knee flexed 30° with the patient lying on the affected side with an emphasis on obtaining a true lateral of the femoral component, where the posterior femoral condyles are superimposed. This facilitates a tangential view of the implant fixation interfaces to accurately assess radiolucent lines, femoral component positions, sizes, tibial slopes, as well as the patella implant, patellar bone, and the patella tendon relationship. • Patello-femoral view: The preferred view is the Merchant view, and is obtained with the patient lying supine with knees flexed to 45°, typically held with a fixed or adjustable platform, and the x-ray beam angled at 30° from the horizontal [6]. This view is used to evaluate the patellar implant fixation integrity, the patellar bone, and the patellar alignment with respect to tilt and subluxation. Radiographic Evaluation Metrics Alignment/Component Position • Coronal alignment is evaluated on the AP radiograph. The coronal “anatomic” alignment of the femoral component is comprised of the distal femoral component surface with respect to the anatomic axis of the femoral shaft. Similarly, the tibial component alignment is determined by the angle between the baseplate and the
Fig. 2. (A) Schematic of radiographic patella tilt measurement (in degrees) relative to the femoral component denoted on the Merchant view radiograph. (B) Schematic of radiographic patella displacement measurement (in millimeters) relative to the central trochlea of the femoral component denoted on the Merchant view radiograph.
Please cite this article as: Meneghini RM, et al, Development of a Modern Knee Society Radiographic Evaluation System and Methodology for Total Knee Arthroplasty, J Arthroplasty (2015), http://dx.doi.org/10.1016/j.arth.2015.05.049
R.M. Meneghini et al. / The Journal of Arthroplasty xxx (2015) xxx–xxx
3
mechanical axis of the tibia, as approximated in a similar manner to the femur (the fibular shaft axis may also be used if proximal tibial bowing is present) (See Fig. 1A). • Sagittal alignment is evaluated on the lateral radiograph. Femoral component alignment is measured as the angle between the most distal femoral fixation surface with respect to the femoral shaft axis. The distal femoral fixation surface may be obscured by the cam mechanism housing in a posterior-substituting TKA design, which may necessitate using that surface as an approximation depending on the implant design (See Fig. 1B). • Patellofemoral alignment is determined on the patellofemoral (Merchant view) and is assessed with tilt and subluxation metrics. Patella tilt is defined as the angle between the anterior limits of the femoral component condyles and the prosthesis–bone interface line of the patellar component [7](See Fig. 2A). Patella subluxation (displacement) is defined as the distance between those lines intersecting the center of the patella and the line through the deepest part of the trochlear groove [7] (See Fig. 2B).
Implant Fixation Interface: Radiolucent Lines and Osteolysis The fixation interface of all implants should be examined for radiolucent lines on the AP, lateral, and patellofemoral radiographs. This includes the implant–cement and cement–bone interfaces, as well as the implant–bone interface in uncemented implants. The significance of radiolucent lines is likely dependent on whether they encompass an entire interface surface (partial versus complete), and whether they are stable or progressive on serial radiographs with nearly identical implant orientations, limb positions, and radiographic projections. However, it has been reported that while stable, non-progressive radiolucent lines are frequent in the first year after TKA, even progressive radiolucent lines may not be indicative of implant fixation failure [8]. Furthermore, it has been reported that the method of radiolucent line assessment in the previous Knee Society Radiographic Scoring System is unreliable due to its complexity, and a simplified methodology reported to offer improved reliability and reproducibility was needed [9]. Therefore, for the benefit of standardization of comparative evaluation, implant monitoring and outcome assessment, a simplified and standardized method of describing the general locations/regions of radiolucent lines, as well as regions of osteolytic regions, is described. This is an important goal of the modernized and updated Knee Society Radiographic Evaluation System presented in this manuscript. When utilizing this evaluation system, the documentation of lucent lines should be graded as “partial” or “complete” with respect to the zone denoted on the schematic images (Figs. 3 and 4) and regions of osteolysis should be documented in millimeters in the zone locations. Implant Zone Classification The tibial, femoral, and patella implants are divided into three general zones on the various radiographs. In general, zones 1 and 2 are on the periphery (either medial/lateral, anterior/posterior, inferior/posterior), whereas, zone 3 is used to designate the “central keel” region of an associated implant design, while the central region of a two-pegged design encompasses the pegs and the central region between them. On the AP view, a designation of “3M” is used to designate the medial aspect of the keel, and “3L” the lateral aspect of the keel. For a twopegged tibial baseplate design, “3M” and “3L” are used to designate the area around each of the respective pegs and “3” is used to designate the central area under the baseplate between the pegs. On the lateral view, “3A” and “3P” are used to designate the respective anterior and posterior regions of the keel. Although it may not be initially intuitive, the most inferior region of the keel is designated “5”. The rationale for this lies in the numerical designation of “4” being used for the region of the stem extensions in the revision setting (See Fig. 4A–D) and to maintain consistency and uniformity. The details of the regions are listed below:
Fig. 3. (A) Coronal and (B) sagittal radiographic schematic of keeled and two-peg implants with zones for documentation of radiolucent lines and osteolysis. (C) Sagittal plane radiographic schematic of femoral implant with zones denoted for documentation radiolucent lines and osteolysis. (D) Patellofemoral view radiographic schematic of multi- or singlepeg patella implant with zones denoted for documentation radiolucent lines and osteolysis. Radiolucent lines should be denoted and documented as “partial” or “complete” and osteolysis documented in millimeters.
Tibial Component AP View: (See Fig. 3A) • Zone 1: medial baseplate • Zone 2: lateral baseplate • Zone 3: central keel/stem region (“M” and “L” designate the respective regions of the central keel) • Zone 4: Revision TKA Stem Extension (“M” and “L” designate the respective regions of the stem extension) (See Fig. 4A) • Zone 5: inferior aspect of tibial keel/stem Tibial Component Lateral View: (See Fig. 3B) • Zone 1: anterior baseplate
Please cite this article as: Meneghini RM, et al, Development of a Modern Knee Society Radiographic Evaluation System and Methodology for Total Knee Arthroplasty, J Arthroplasty (2015), http://dx.doi.org/10.1016/j.arth.2015.05.049
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R.M. Meneghini et al. / The Journal of Arthroplasty xxx (2015) xxx–xxx
Discussion
Fig. 4. (A) Coronal and (B) sagittal radiographic schematic of revision tibial implants that have stem extensions with zones for documentation of radiolucent lines and osteolysis. (C) Coronal and (D) sagittal radiographic schematic of revision femoral implants that have stem extensions with zones for documentation of radiolucent lines and osteolysis. Radiolucent lines should be denoted and documented as “partial” or “complete” and osteolysis documented in millimeters.
• Zone 2: posterior baseplate • Zone 3: central keel/stem/peg fixation region (“A” and “P” designate the respective regions of the central keel) • Zone 4: Revision TKA Stem Extension (“A” and “P” designate the respective regions of the stem extension) (See Fig. 4B) • Zone 5: inferior aspect of tibial keel/stem Femoral Component Lateral (See Figs. 3C and 4D) and AP View (See Fig. 4C) • Zone 1: anterior flange • Zone 2: posterior flange • Zone 3: central box/peg/distal fixation region (“A” and “P” designate the respective chamfers if visible) • Zone 4: Revision TKA Stem Extension (“M” and “L” designate the respective regions of the stem extension on the AP view (See Fig. 4C); “A” and “P” designate the respective regions of the stem extension on the lateral view (See Fig. 4D)) Patella Component Patellofemoral View: (see Figs. 3D and 5) • Zone 1: medial • Zone 2: lateral • Zone 3: central peg/baseplate region (“M” and “L” designate the respective regions on the merchant view, whereas “S” and “I” designate the superior and inferior regions on the lateral view) • Patella bone thickness is measured and noted in Fig. 5.
Fig. 5. Patellofemoral radiographic view schematic denoting patella bone thickness, measured in millimeters.
The overall goal of this project was to develop a consistent and standardized methodology to obtain and perform a radiographic evaluation of total knee arthroplasties (TKAs). When compared to the original Knee Society Scoring system [2], a suggested more practical approach was to establish updated and standardized guidelines for the specific radiographs to be obtained, techniques used to obtain them, and methods for evaluation and reporting on the status of implants. In addition, compared to the original Knee Society Radiographic Evaluation System, the complexity and variety of implants have increased, which drives a need to adapt the radiographic evaluation method accordingly. This modernized evaluation system is more descriptive and more detailed, compared to the previous version and will also allow evaluation of multiple implant designs. However, this evaluation system remains descriptive rather than predictive or prognostic in its current scope and form. Due to the lack of studies with sufficient statistical power to correlate specific radiographic findings with outcomes, as well as the numerous implant systems and designs, it is beyond the scope of this evaluation system to define specific radiographic parameter values as either “normal”, “abnormal” or “at-risk”. After thorough review and discussion of the Radiographic Score Committee, as well as via feedback from the entire Knee Society membership, it was concluded that this radiographic evaluation system should remain descriptive and focus on the uniformity of assessment and documentation. However, the committee has proposed that this tool can potentially be used to accumulate data in a standardized manner, which might be analyzed and used to formulate a “criteria” or “score” to determine if an implant is at risk and our goal is that future research efforts will be focused in this regard. So that this evaluation guideline might promote standardization of reporting in the modern era of healthcare multi-center analysis and registry outcomes, it should be feasible and applicable for the majority of, if not all knee arthroplasty surgeons. Certain practice resource restrictions, such as financial, equipment and staffing, may preclude more advanced techniques such as full-length mechanical axis images being performed on a routine basis. Therefore, the recommended images and techniques in these guidelines are based on a simplified and cost-effective basis and represent a “minimum” requirement for standardized assessment and reporting of the status and radiographic functioning of the implant. The committee members acknowledge that more advanced imaging may be helpful to further assess pathologic failure mechanisms in TKA and recommend performing those if clinically indicated. Acknowledgments The authors would like to sincerely thank and acknowledge Joy Marlowe for her contributions in the manuscript, which involved creation and development of the schematic drawings and images. References 1. Insall JN, Dorr LD, Scott RD, et al. Rationale of the Knee Society clinical rating system. Clin Orthop Relat Res 1989(248):13. 2. Ewald FC. The Knee Society total knee arthroplasty roentgenographic evaluation and scoring system. Clin Orthop Relat Res 1989(248):9. 3. Noble PC, Scuderi GR, Brekke AC, et al. Development of a new Knee Society scoring system. Clin Orthop Relat Res 2012;470(1):20. 4. Scuderi GR, Bourne RB, Noble PC, et al. The new Knee Society Knee Scoring System. Clin Orthop Relat Res 2012;470(1):3. 5. Kurtz SM, Ong KL, Lau E, et al. Impact of the economic downturn on total joint replacement demand in the United States: updated projections to 2021. J Bone Joint Surg Am 2014;96(8):624. 6. Merchant AC, Mercer RL, Jacobsen RH, et al. Roentgenographic analysis of patellofemoral congruence. J Bone Joint Surg Am 1974;56(7):1391. 7. Gomes LS, Bechtold JE, Gustilo RB. Patellar prosthesis positioning in total knee arthroplasty. A roentgenographic study. Clin Orthop Relat Res 1988(236):72. 8. Aebli N, Krebs J, Schwenke D, et al. Progression of radiolucent lines in cementless twinbearing low-contact-stress knee prostheses: a retrospective study. J Arthroplasty 2004; 19(6):783. 9. Bach CM, Biedermann R, Goebel G, et al. Reproducible assessment of radiolucent lines in total knee arthroplasty. Clin Orthop Relat Res 2005(434):183.
Please cite this article as: Meneghini RM, et al, Development of a Modern Knee Society Radiographic Evaluation System and Methodology for Total Knee Arthroplasty, J Arthroplasty (2015), http://dx.doi.org/10.1016/j.arth.2015.05.049
