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Rotational alignment of the tibial component affects the kinematic rotation of a weight-bearing knee after total knee arthroplasty
Rotational Alignment of the Tibial Component Affects the Kinematic Rotation of a Weight-Bearing Knee after Total Knee Arthroplasty Hiroyuki Nakahara, Ken Okazaki, Satoshi Hamai, Shinya Kawahara, Hidehiko Higaki, Hideki Mizu-uchi, Yukihide Iwamoto PII: DOI: Reference:
S0968-0160(15)00003-4 doi: 10.1016/j.knee.2015.01.002 THEKNE 2026
To appear in:
The Knee
Received date: Revised date: Accepted date:
14 July 2014 19 December 2014 12 January 2015
Please cite this article as: Nakahara Hiroyuki, Okazaki Ken, Hamai Satoshi, Kawahara Shinya, Higaki Hidehiko, Mizu-uchi Hideki, Iwamoto Yukihide, Rotational Alignment of the Tibial Component Affects the Kinematic Rotation of a Weight-Bearing Knee after Total Knee Arthroplasty, The Knee (2015), doi: 10.1016/j.knee.2015.01.002
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ACCEPTED MANUSCRIPT Rotational Alignment of the Tibial Component Affects the Kinematic Rotation of a
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Weight-Bearing Knee after Total Knee Arthroplasty
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Hiroyuki Nakahara1), Ken Okazaki1), Satoshi Hamai1), Shinya Kawahara1), Hidehiko Higaki2),
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Hideki Mizu-uchi1), Yukihide Iwamoto1)
1)
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Department of Orthopaedic Surgery, Graduate School of Medical Sciences, Kyushu
University
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3-1-1 Maidashi, Higashi-ku, Fukuoka, 812-0054 Japan 2)
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Department of Biorobotics, Faculty of Engineering, Kyushu Sangyo University
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2-3-1 Matsukadai, Higashi-ku, Fukuoka, 813-8503 Japan
Corresponding author: Ken Okazaki Department of Orthopaedic Surgery, Graduate School of Medical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan Phone: +81-92-642-5488 Fax: +81-92-642-5507 E-mail: [email protected]
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ACCEPTED MANUSCRIPT Abstract
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Purpose: The purpose of this study is to elucidate how the rotational malalignment of
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prosthesis after total knee arthroplasty affects the rotational kinematics in a weight-bearing
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condition.
Methods: In this study of 18 knees replaced with the posterior stabilizing fixed-bearing
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system, which has a relatively low-restricting design, rotational angles between the femoral
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and tibial components and between the femur and tibia during stair climbing were evaluated in vivo in three dimensions using radiologically based image-matching techniques. Rotational
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alignments of the components were assessed by postoperative CT. The correlations between
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the rotational alignments and the rotational angles during stair climbing were evaluated. Results: Rotational alignment of the tibial component significantly correlated with rotational
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angles between the components as well as between bones during stair climbing. Rotational malalignment of the tibial component toward internal rotation caused a rotational mismatch of the tibial component toward internal rotation relative to the femoral component in 0° extension and caused a rotational mismatch of the tibia (bone) toward external rotation relative to the femur (bone). The knee in which the tibial component was placed close to the AP axis of the tibia did not show any rotational mismatch between either components or bones. Conclusions: Rotational alignment of the tibial component affects the kinematic rotation of 2
ACCEPTED MANUSCRIPT the replaced knee during a weight-bearing condition even though using a low-restricting
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designed surface, and the AP axis can be a reliable reference in determining rotational
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alignment for the tibial component.
Key words: total knee arthroplasty, kinematics, rotational alignment, rotational mismatch,
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stair climbing
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ACCEPTED MANUSCRIPT 1. Introduction It has been suggested that the surgical epicondylar axis (SEA) approximates the
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femoral rotational axis of normal and osteoarthritic knees and that Akagi’s anterior-posterior
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tibial axis (AP axis) is perpendicular to the SEA in knee extension [1-3]. Therefore, the SEA and the AP axis have been used as one of the rotational landmarks for femoral and tibial
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components during total knee arthroplasty (TKA). Other rotational landmarks in aligning the components are also used: Whiteside line, clinical epicondylar axis, posterior condylar line
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and gap balancing technique for the femoral component; medial one third of the tubercle and
However, component rotational alignments have the potential to deviate
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component [4, 5].
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allowing component to seek its own position through a range of motion for the tibial
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from preoperative landmarks, and the tibial rotational alignment is particularly susceptible to error [6-9]. Because femoral and tibial component rotational alignment could influence the
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patellofemoral joint and quadriceps [10-13], component position could affect knee joint kinematics during weight-bearing [14]. It is generally considered that the component rotational alignment would affect the rotational position of the tibia relative to the femur. However, the influence of the component rotational alignment on the joint kinematics might be different depending on the surface designs regarding constraints for rotation. Rotational malalignment of the components may be compensated for if the design of the tibiofemoral articulation allows some rotation. In fact, it is sometimes seen that postoperative non-weight-bearing radiographs show rotational mismatch between the components, 4
ACCEPTED MANUSCRIPT suggesting that rotational laxity of the joint surface compensates the rotational malalignment
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of the components. However, it is unclear this rotational mismatch still exists under
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weight-bearing conditions. This issue has received little objective or quantitative study.
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Recently, a postoperative kinematic analysis using fluoroscopy has been used for evaluating femoral rotation, roll-back, condylar lift-off, and post-cam impingement [15-20].
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The replaced knee has been reported to show external rotation of the tibial component relative
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to the femoral component during extension from flexion in weight-bearing condition; however, it shows more variation of its movement compared to the normal knee. Rotational
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kinematics might be influenced by many factors, such as geometry or design of the
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components, ligament balance and rotational alignment of the component. However, no study has described the relation between the component rotational alignment and the component
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rotational motion during flexion-extension movement during weight-bearing. Therefore the following clinical questions have arisen: Does the rotational alignment of each component affect the rotational relationship between tibial component and the femoral component and the rotational relationship between the femur and tibia during stair climbing? 2. Materials and Methods 2.1. Subjects
A total of 18 patients who had undergone TKA were recruited. They gave informed consent and the institutional review board approved this study. All patients were women with a mean 5
ACCEPTED MANUSCRIPT age of 76.4 years (range, 66 to 83 years). The preoperative diagnosis was osteoarthritis in all
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patients. Patients with rheumatoid arthritis, previous arthroplasty, osteotomy, severe
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extra-articular deformity, and fractures about the knee were excluded. All patients received a
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posterior-stabilized (PS) fixed bearing TKA (NexGen LPS-Flex, Zimmer, Warsaw, IN). The
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mean follow-up was for 26.7 months (range, 3.1 to 65.9 months).
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2.2. Surgical technique
One experienced surgeon performed all cases. Using the measured resection technique, the
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components were aligned to allow the mechanical axis to pass through the center of the
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prosthetic knee in the coronal plane. The femoral component was aligned perpendicularly to
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the anatomical axis in the sagittal plane and positioned along the SEA in the axial plane based on the preoperative planning on a computed tomography (CT) images. The tibial bone cut
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was planned to be parallel to the lateral anatomical slope in the sagittal plane. The rotational alignment of the tibial component was adjusted to the AP axis of the tibia (the line connecting the center of PCL at its tibial attachment and the medial border of patellar tendon at the tibial tubercle). Soft tissue balancing was performed to achieve varus and valgus stability in both extension and flexion.
2.3. Computed tomography scan evaluation
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ACCEPTED MANUSCRIPT Transverse CT scans were taken at levels ranging from the hip joint to the ankle joint at 2-mm
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intervals before and two weeks after surgery, and a three-dimensional (3D) image of the lower
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extremity was reconstructed on the computer using the program 3D Template (version
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02.02.02, Japan Medical Materials, Corp., Osaka, Japan). Rotational alignment of the femoral component was determined by measuring the angle between the SEA and the line joining the
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posterior margins of the femoral component (Fig. 1a). The angle in the component external
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position was defined as a positive value. For the AP axis of tibia, the medial border of the patellar tendon at its attachment level and the middle of the posterior cruciate ligament (PCL)
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at its tibial attachment were identified preoperatively (Fig. 1b), and the AP axis was projected
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accurately to the postoperative CT (Fig. 1c). Rotational alignment of the tibial component was assessed by measuring the angle between the AP axis and the anteroposterior line of the tibial
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component (Fig. 1c). The angle in component external position was defined as a positive value. Coronal alignment and posterior inclination of the tibial component relative to the tibial mechanical axis were also measured.
2.4. Kinematic analysis
Continuous sagittal radiological images of stair climbing were obtained for each patient using a flat-panel detector (Ultimax-i, Toshiba, Tochigi, Japan) (Fig. 2a). This produced 10 frames per second with an image area of 420 mm (H) × 420 mm (V), and 0.148 mm × 0.148
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ACCEPTED MANUSCRIPT mm/pixel resolution (Fig. 2b). The angles of flexion and axial rotation of the components
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were measured using the image-matching method [20]. The accuracy and precision of the
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measurement technique was determined by in vitro investigations. The root-mean-square
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(RMS) accuracy errors for the femoral component were 0.075 mm for inplane translation, 0.071 mm for out-of-plane translation, and 0.076 for rotation, and the accuracies for the tibial
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component were 0.178 mm for in-plane translation, 0.208 mm for out-of-plane translation,
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and 0.169 for rotation. We found higher accuracy than reported in previous literature [19] because the resolution of images became higher, the number of images obtained in 1 second
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increased and the identification of the source of X-rays was completed more correctly [21].
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The rotational relationship of the tibial component relative to the femoral component was measured in 0° knee extension, and 30° and 60° knee flexion. External rotation of the tibia
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with respect to the femur was considered positive. Based on the postoperative CT data, described in the Computed tomography scan evaluation section, the angle between the perpendicular line of the SEA (defined as SEA’) and the AP axis in extension was measured and defined as “bony rotational relationship angle”. If the AP axis was externally rotated relative to the SEA’ the angle was positive.
2.5. Statistical analysis
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ACCEPTED MANUSCRIPT We used the Pearson correlation analysis to determine the correlation of the rotational
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alignment of either tibial or femoral component to the rotational relationship between the
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components in 0° extension, and in 30° and 60° of flexion, or to the bony rotational
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relationship angle in extension. The relationship between coronal alignment and posterior inclination of the tibial component and the kinematic rotation was also evaluated. Statistical
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analyses were performed with JMP 9.0 (SAS Institute Inc, Cary, NC, USA). Significance was
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set at a p-value of < 0.05.
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3. Results
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The rotational alignment angles of the femoral and tibial components were −0.4 ± 2.2° (range,
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−3.8 to 4.6°) and −0.9 ± 6.5° (range, −11.3 to 10.2°), respectively. There was no significant correlation of the rotational alignment angle of the femoral component to the rotational
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relationship between tibial component and femoral component at any flexion angles (Table 1). However, there was a significant correlation between the rotational alignment angle of the tibial component and the rotational relationship angle between tibial component and femoral component in 0° extension (Table 1, Fig. 3). Increased malalignment of the tibial component toward internal rotation (toward a negative value) resulted in an increased tibial component rotation relative to the femoral component toward internal rotation (toward a negative value). This correlation indicates that malalignment of tibial component causes rotational mismatch
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ACCEPTED MANUSCRIPT between the components in 0° extension. When the tibial component was aligned close to the
There was no significant correlation of the rotational alignment angle of the tibial
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0°.
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AP axis, the rotational relationship angle between the components in extension approximated
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component to the rotational relationship between the components in 30° and 60° flexion (Table 1).
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The bony rotational relationship angle (the angle between the SEA’ and the AP axis of tibia) in
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extension was 2.5 ± 10.7° (range, −16.6 to 16.4°). There was not a significant correlation between the bony rotational relationship angle and the rotational alignment angle of the
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femoral component (p=0.08). However, there was a significant correlation between the bony
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rotational relationship angle and the rotational alignment angle of the tibial component (Table 1, Fig. 4). In 0° extension, rotational malalignment of the tibial component caused a bony
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rotational mismatch in the opposite direction of the rotational alignment: Increased malalignment of the tibial component toward internal rotation (toward a negative value) resulted in an increased rotation of the tibia (bone) relative to the femur (bone) toward external rotation (toward a positive value) (Fig. 4). When the tibial component was aligned close to the AP axis, the bony rotational relationship angle in extension approximated 0°.
The coronal alignment angle and posterior inclination angle of the tibial component did not significantly correlate with the rotational relationship between components or the bones (Table 1). 10
ACCEPTED MANUSCRIPT 4. Discussion
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In this study, the rotational alignment of the tibial component significantly correlated with the
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rotational relationship between the femoral and tibial components as well as between the
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femur and tibia (bony rotational relationship angle) in weight-bearing during stair climbing. These rotational mismatches between components and between bones affected the subsequent
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rotational kinematics during flexion. As many previous studies suggested, the tibial rotational
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alignment was particularly susceptible to error. However, the tibial component should be carefully aligned when using a fixed bearing surface to avoid rotational mismatch for both
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components and bones. The AP axis of the tibia is a reliable reference for overall rotational
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alignment.
The rotational alignment of the tibial component strongly correlated with the
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rotational relationship between the tibial component and the femoral component in 0° extension. The rotational mismatch between the components probably occurs because each bone tends to return to its proper position during weight bearing by utilizing the rotational laxity built into the design of the components. The fixed bearing surface of the implant used in this study is designed to allow ±12° rotational mismatch relative to the femoral component in extension and in 90° flexion (data from the manufacturer) [22]. However, weight-bearing may allow smaller degrees of rotational mismatch between the components than designed. As a result, the degree of rotational mismatch between the components was less than that of the 11
ACCEPTED MANUSCRIPT rotational malalignment of the tibial component in most cases, and thus, a bony rotational
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mismatch also occurred. In fact, the degree of rotational mismatch between the components
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was less than ±12° in all the cases.
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There have been many reports investigating or comparing the rotational kinematics of replaced knees with the similar image-matching techniques. However, few studies have
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taken account of the rotational alignment of the components. Since the rotational alignment of
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the tibial component significantly affects the rotational kinematics as this study has shown, one should be cautious in evaluating the variation of rotational kinematics among the cases.
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The tibia had a tendency to externally rotate relative to the femur with increasing
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internal alignment of the tibial component relative to the AP axis. This fact shows that the rotational malalignment of the tibial component affects the rotational kinematics of the knee
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joint during weight bearing even if the non-high-restricting insert was used. Although the fixed bearing surface of this component is designed to have an admissibility for about ±12° rotational mismatch as mentioned above, bony rotational mismatch occurred in patients with ≤ 12° of angulation of rotational tibia malalignment. If the tibial component is aligned in the internal position, the patellofemoral joint may be misaligned and quadriceps strength may be affected due to an increased Q angle as the tibia is rotated outward relative to the femur [11,12].
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ACCEPTED MANUSCRIPT We used the AP axis of the tibia as a reference line to express the rotational
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alignment of tibial component. When the tibial component was aligned closely to the AP axis,
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the rotational mismatch between the components and bony rotational mismatch were not
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observed in knee extension. This shows that the AP axis can also be a reliable landmark of the tibial component as it is perpendicular to the SEA not only in rest [1-3] but also in weight
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bearing. The AP axis (Akagi’s line) is a line connecting the center of PCL at its tibial
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attachment and the medial border of the patellar tendon at the tibial tubercle [1]. Kawahara, et al reported that the line parallel to the Akagi’s AP axis on tibial cut surface runs between the
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center of the cut surface and the medial 1/6 of the patellar tendon at its attachment, that could
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be a landmark in placing the tibial tray on the cut surface [23]. There have been many other methods reported to determine the rotational alignment of the tibial component during the
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surgery. Medial 1/3 of the tibial tubercle is one of the well-recognized landmarks. Incavo, et al reported that when a template of tibial tray with a symmetrical design was placed on an axial MRI image of normal knee at the level of 8mm distal to the tibial joint surface aligning along to the femoral epicondyler axis, the short axis of the tibial tray intersected the patellar tendon at the range of 17% to 50% of its width from the medial edge in 75% of the subjects [4]. This study suggests that aligning the tibial plate from medial 1/6 to 1/2 of patellar tendon is appropriate in most cases. Our data also suggest that several degrees of tibial external rotation from the AP axis are acceptable because some cases in which the tibial component 13
ACCEPTED MANUSCRIPT was placed slightly in external rotation relative to the AP axis showed no rotational mismatch
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between the components and bones. The x-intercept of the regression line of either graph
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shows a slight external rotation of the rotational alignment angle of the tibial component. If
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slightly more external rotation is acceptable, the medial 1/3 of the tibial tubercle and the center of the cut surface might also be a good reference for tibial rotational alignment.
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However, there has been another debate that the tibial tubercle may not be a reliable rotational
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landmark because there is a wide variation in the morphology of proximal tibia and the relationship between the femoral transepicondylar axis and anterior tibial tuberosity axis
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among the cases [24]. Variations in the rotational relationship angle in our study may be
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influenced by this anatomical variation among the cases. Therefore, the self-adjusting technique to align the tibial plate with the femoral component in extension has been
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advocated [5]. Huddlestone et al reported that the tibial plate was aligned to 5.2° ± 5.0° externally rotated relative to the medial margin of the tibial tubercle using this technique [25] This study suggests aligning around medial 1/3 is appropriate as an average, but wide variation also exists. One should be aware of these anatomical variations and carefully align the tibial component taking into account of both the anatomic landmarks and intraoperative kinematics with the femoral component. The rotational alignment of the femoral component did not affect the rotational relationship between the components or between the bones. This may be because the 14
ACCEPTED MANUSCRIPT deviation of the femoral rotational alignment angle was smaller than that of the tibia. Previous
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studies showed that the tibial rotational alignment is more likely to deviate from preoperative
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landmarks than the femoral component [7,8]. As the femur has a clear landmark such as the
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SEA and the posterior condylar axis, the femoral component can be easily placed using references from the landmarks during surgery. However, it is reported that the rotational
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alignment of the femoral component could influence the postoperative knee functions in daily
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activities [26]. Therefore, we stress that it is important to place the femoral component accurately.
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There were some limitations to this study. First, we used a single type of implant.
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Difference in design for the conformity and rotational laxity should affect the results. For example, if the high-restricting insert was used, the rotational malalignment of the tibial
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component might more strongly affect the rotational kinematics of the knee joint during weight bearing. However, as this study shows, even with using a relatively low-restricting insert witha rotational laxity that this implant adopts, the rotational laxity could not compensate the rotational malalignment of the tibial component. This information had not been available from literatures or manufacturers. Therefore, the investigations should be extended to other implants in future. However, one can assume that same phenomenon would also occur in many other TKA implants with similar surface design. Second, preoperative kinematic and deformity may affect the postoperative kinematics and we did not evaluate the 15
ACCEPTED MANUSCRIPT preoperative conditions. However, the strong correlation between the tibial component
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alignment and the rotational mismatch between bones suggests that the individual variances in
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preoperative condition would not significantly affect on this phenomenon. Finally, the study
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was limited by the small number of patients. In the past literature, the influence of prosthesis alignment on axial rotation motion was evaluated for 67 subjects [14]. However, this study
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evaluated the subjects implanted with mobile-bearing TKA. The present study did reveal that
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the rotational alignment of the tibial component correlated strongly with the rotational relationship between the components and between the bones in fixed-bearing TKA and that
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the trend was constant even though the total patient number was small. Therefore, we
5. Conclusions
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consider the fact obtained in this study is reliable.
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The results of this study show how the rotational alignment of the tibial component affects rotational relationship between the bones and between the components of the replaced knee joint during weight bearing. The designed allowance for rotational mismatch within the fixed bearing surface does not fully compensate the rotational malalignment of the tibial component during weight bearing. The rotational alignment of the tibial component is an important factor in postoperative knee joint kinematics that could influence patient function and satisfaction, and the AP axis also can be a reliable landmark of the tibial component as it is perpendicular to the SEA at rest and during weight bearing. 16
ACCEPTED MANUSCRIPT Acknowledgement
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This work was supported by institutional funding from the Grant-in-Aid for Specially
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Promoted Research of Japan Society for the Promotion of Science (23000011).
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Figure legends
Figure 1. a. The angle between the surgical epicondylar axis (SEA) and the line joining the
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posterior margins of the femoral component axis was measured (defined as “rotational
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alignment angle of the femoral component”). b. The AP axis of the tibia (Akagi’s line:
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connecting the medial border of the patellar tendon at the attachment level to the projected center of the posterior cruciate ligament (PCL) at the tibial attachment) was identified
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preoperatively. Because the PCL attachment is located on a different slice of CT form the patellar tendon attachment, it was projected to the CT slice of the patellar tendon attachment. c. The AP axis of the tibia defined on the preoperative CT (b) was projected onto the postoperative CT (solid line) and the AP line of the tibial component was drawn (dotted line). The angle between the AP axis of the tibia and the AP line of the tibial component was measured (defined as “rotational alignment angle of the tibial component”).
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ACCEPTED MANUSCRIPT Figure 2. a. Stair climbing was analyzed. b. Movement of the knee was observed using a large
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flat-panel radiological image detector.
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Figure 3. The correlation of the rotational alignment angle of the tibial component (deviation angle from the AP axis of the tibia) to the rotational relationship angle between the
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components in 0° extension during stair climbing.
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Figure 4. The correlation of the rotational alignment angle of the tibial component (deviation angle from the AP axis of the tibia) to the rotational relationship angle between the bones
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(angle between the AP axis of the tibia and SEA’ of the femur) in 0° extension during stair
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climbing . The Pearson correlation analysis showed a significant and strong correlation.
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Figure 1
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Figure 2
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Figure 3
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Figure 4
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Table 1. P value (P) and correlation coefficient (r) of the correlation of each alignment angle to the rotational
Bony rotational
30°flexion
60°flexion
relationship angle
Rotational alignment angle of
P = 0.27
P = 0.99
P = 0.90
P = 0.08
femoral component
r = -0.27
r = -0.01
r=-0.03
r = 0.42
Rotational alignment angle of
P = 0.01
P = 0.18
P = 0.46
P < 0.01
tibial component
r = 0.61
r = 0.33
r = 0.19
r = -0.90
Coronal alignment of tibial
P = 0.55
P = 0.81
P = 0.86
P = 0.60
component
r = 0.17
r = 0.07
r = 0.05
r = -0.15
Posterior slope angle of tibial
P=0.40
P=0.57
P = 0.49
P = 0.96
component
r = -0.22
r = -0.15
r = -0.18
r = -0.01
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0°extension
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Components rotational relationship angle
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relationship between components and between bones
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ACCEPTED MANUSCRIPT Highlights
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Tibial rotational alignment affects rotational mismatch of components. Tibial rotational alignment affeccts rotational mismatch of bones. It affects rotational kinematics even if using a low-constrained surface design.
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S0968-0160(15)00003-4 doi: 10.1016/j.knee.2015.01.002 THEKNE 2026
To appear in:
The Knee
Received date: Revised date: Accepted date:
14 July 2014 19 December 2014 12 January 2015
Please cite this article as: Nakahara Hiroyuki, Okazaki Ken, Hamai Satoshi, Kawahara Shinya, Higaki Hidehiko, Mizu-uchi Hideki, Iwamoto Yukihide, Rotational Alignment of the Tibial Component Affects the Kinematic Rotation of a Weight-Bearing Knee after Total Knee Arthroplasty, The Knee (2015), doi: 10.1016/j.knee.2015.01.002
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT Rotational Alignment of the Tibial Component Affects the Kinematic Rotation of a
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Weight-Bearing Knee after Total Knee Arthroplasty
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Hiroyuki Nakahara1), Ken Okazaki1), Satoshi Hamai1), Shinya Kawahara1), Hidehiko Higaki2),
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Hideki Mizu-uchi1), Yukihide Iwamoto1)
1)
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Department of Orthopaedic Surgery, Graduate School of Medical Sciences, Kyushu
University
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3-1-1 Maidashi, Higashi-ku, Fukuoka, 812-0054 Japan 2)
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Department of Biorobotics, Faculty of Engineering, Kyushu Sangyo University
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2-3-1 Matsukadai, Higashi-ku, Fukuoka, 813-8503 Japan
Corresponding author: Ken Okazaki Department of Orthopaedic Surgery, Graduate School of Medical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan Phone: +81-92-642-5488 Fax: +81-92-642-5507 E-mail: [email protected]
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ACCEPTED MANUSCRIPT Abstract
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Purpose: The purpose of this study is to elucidate how the rotational malalignment of
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prosthesis after total knee arthroplasty affects the rotational kinematics in a weight-bearing
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condition.
Methods: In this study of 18 knees replaced with the posterior stabilizing fixed-bearing
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system, which has a relatively low-restricting design, rotational angles between the femoral
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and tibial components and between the femur and tibia during stair climbing were evaluated in vivo in three dimensions using radiologically based image-matching techniques. Rotational
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alignments of the components were assessed by postoperative CT. The correlations between
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the rotational alignments and the rotational angles during stair climbing were evaluated. Results: Rotational alignment of the tibial component significantly correlated with rotational
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angles between the components as well as between bones during stair climbing. Rotational malalignment of the tibial component toward internal rotation caused a rotational mismatch of the tibial component toward internal rotation relative to the femoral component in 0° extension and caused a rotational mismatch of the tibia (bone) toward external rotation relative to the femur (bone). The knee in which the tibial component was placed close to the AP axis of the tibia did not show any rotational mismatch between either components or bones. Conclusions: Rotational alignment of the tibial component affects the kinematic rotation of 2
ACCEPTED MANUSCRIPT the replaced knee during a weight-bearing condition even though using a low-restricting
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designed surface, and the AP axis can be a reliable reference in determining rotational
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alignment for the tibial component.
Key words: total knee arthroplasty, kinematics, rotational alignment, rotational mismatch,
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stair climbing
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ACCEPTED MANUSCRIPT 1. Introduction It has been suggested that the surgical epicondylar axis (SEA) approximates the
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femoral rotational axis of normal and osteoarthritic knees and that Akagi’s anterior-posterior
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tibial axis (AP axis) is perpendicular to the SEA in knee extension [1-3]. Therefore, the SEA and the AP axis have been used as one of the rotational landmarks for femoral and tibial
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components during total knee arthroplasty (TKA). Other rotational landmarks in aligning the components are also used: Whiteside line, clinical epicondylar axis, posterior condylar line
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and gap balancing technique for the femoral component; medial one third of the tubercle and
However, component rotational alignments have the potential to deviate
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component [4, 5].
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allowing component to seek its own position through a range of motion for the tibial
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from preoperative landmarks, and the tibial rotational alignment is particularly susceptible to error [6-9]. Because femoral and tibial component rotational alignment could influence the
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patellofemoral joint and quadriceps [10-13], component position could affect knee joint kinematics during weight-bearing [14]. It is generally considered that the component rotational alignment would affect the rotational position of the tibia relative to the femur. However, the influence of the component rotational alignment on the joint kinematics might be different depending on the surface designs regarding constraints for rotation. Rotational malalignment of the components may be compensated for if the design of the tibiofemoral articulation allows some rotation. In fact, it is sometimes seen that postoperative non-weight-bearing radiographs show rotational mismatch between the components, 4
ACCEPTED MANUSCRIPT suggesting that rotational laxity of the joint surface compensates the rotational malalignment
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of the components. However, it is unclear this rotational mismatch still exists under
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weight-bearing conditions. This issue has received little objective or quantitative study.
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Recently, a postoperative kinematic analysis using fluoroscopy has been used for evaluating femoral rotation, roll-back, condylar lift-off, and post-cam impingement [15-20].
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The replaced knee has been reported to show external rotation of the tibial component relative
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to the femoral component during extension from flexion in weight-bearing condition; however, it shows more variation of its movement compared to the normal knee. Rotational
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kinematics might be influenced by many factors, such as geometry or design of the
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components, ligament balance and rotational alignment of the component. However, no study has described the relation between the component rotational alignment and the component
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rotational motion during flexion-extension movement during weight-bearing. Therefore the following clinical questions have arisen: Does the rotational alignment of each component affect the rotational relationship between tibial component and the femoral component and the rotational relationship between the femur and tibia during stair climbing? 2. Materials and Methods 2.1. Subjects
A total of 18 patients who had undergone TKA were recruited. They gave informed consent and the institutional review board approved this study. All patients were women with a mean 5
ACCEPTED MANUSCRIPT age of 76.4 years (range, 66 to 83 years). The preoperative diagnosis was osteoarthritis in all
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patients. Patients with rheumatoid arthritis, previous arthroplasty, osteotomy, severe
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extra-articular deformity, and fractures about the knee were excluded. All patients received a
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posterior-stabilized (PS) fixed bearing TKA (NexGen LPS-Flex, Zimmer, Warsaw, IN). The
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mean follow-up was for 26.7 months (range, 3.1 to 65.9 months).
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2.2. Surgical technique
One experienced surgeon performed all cases. Using the measured resection technique, the
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components were aligned to allow the mechanical axis to pass through the center of the
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prosthetic knee in the coronal plane. The femoral component was aligned perpendicularly to
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the anatomical axis in the sagittal plane and positioned along the SEA in the axial plane based on the preoperative planning on a computed tomography (CT) images. The tibial bone cut
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was planned to be parallel to the lateral anatomical slope in the sagittal plane. The rotational alignment of the tibial component was adjusted to the AP axis of the tibia (the line connecting the center of PCL at its tibial attachment and the medial border of patellar tendon at the tibial tubercle). Soft tissue balancing was performed to achieve varus and valgus stability in both extension and flexion.
2.3. Computed tomography scan evaluation
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ACCEPTED MANUSCRIPT Transverse CT scans were taken at levels ranging from the hip joint to the ankle joint at 2-mm
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intervals before and two weeks after surgery, and a three-dimensional (3D) image of the lower
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extremity was reconstructed on the computer using the program 3D Template (version
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02.02.02, Japan Medical Materials, Corp., Osaka, Japan). Rotational alignment of the femoral component was determined by measuring the angle between the SEA and the line joining the
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posterior margins of the femoral component (Fig. 1a). The angle in the component external
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position was defined as a positive value. For the AP axis of tibia, the medial border of the patellar tendon at its attachment level and the middle of the posterior cruciate ligament (PCL)
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at its tibial attachment were identified preoperatively (Fig. 1b), and the AP axis was projected
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accurately to the postoperative CT (Fig. 1c). Rotational alignment of the tibial component was assessed by measuring the angle between the AP axis and the anteroposterior line of the tibial
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component (Fig. 1c). The angle in component external position was defined as a positive value. Coronal alignment and posterior inclination of the tibial component relative to the tibial mechanical axis were also measured.
2.4. Kinematic analysis
Continuous sagittal radiological images of stair climbing were obtained for each patient using a flat-panel detector (Ultimax-i, Toshiba, Tochigi, Japan) (Fig. 2a). This produced 10 frames per second with an image area of 420 mm (H) × 420 mm (V), and 0.148 mm × 0.148
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were measured using the image-matching method [20]. The accuracy and precision of the
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measurement technique was determined by in vitro investigations. The root-mean-square
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(RMS) accuracy errors for the femoral component were 0.075 mm for inplane translation, 0.071 mm for out-of-plane translation, and 0.076 for rotation, and the accuracies for the tibial
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component were 0.178 mm for in-plane translation, 0.208 mm for out-of-plane translation,
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and 0.169 for rotation. We found higher accuracy than reported in previous literature [19] because the resolution of images became higher, the number of images obtained in 1 second
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increased and the identification of the source of X-rays was completed more correctly [21].
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The rotational relationship of the tibial component relative to the femoral component was measured in 0° knee extension, and 30° and 60° knee flexion. External rotation of the tibia
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with respect to the femur was considered positive. Based on the postoperative CT data, described in the Computed tomography scan evaluation section, the angle between the perpendicular line of the SEA (defined as SEA’) and the AP axis in extension was measured and defined as “bony rotational relationship angle”. If the AP axis was externally rotated relative to the SEA’ the angle was positive.
2.5. Statistical analysis
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ACCEPTED MANUSCRIPT We used the Pearson correlation analysis to determine the correlation of the rotational
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alignment of either tibial or femoral component to the rotational relationship between the
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components in 0° extension, and in 30° and 60° of flexion, or to the bony rotational
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relationship angle in extension. The relationship between coronal alignment and posterior inclination of the tibial component and the kinematic rotation was also evaluated. Statistical
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analyses were performed with JMP 9.0 (SAS Institute Inc, Cary, NC, USA). Significance was
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set at a p-value of < 0.05.
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3. Results
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The rotational alignment angles of the femoral and tibial components were −0.4 ± 2.2° (range,
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−3.8 to 4.6°) and −0.9 ± 6.5° (range, −11.3 to 10.2°), respectively. There was no significant correlation of the rotational alignment angle of the femoral component to the rotational
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relationship between tibial component and femoral component at any flexion angles (Table 1). However, there was a significant correlation between the rotational alignment angle of the tibial component and the rotational relationship angle between tibial component and femoral component in 0° extension (Table 1, Fig. 3). Increased malalignment of the tibial component toward internal rotation (toward a negative value) resulted in an increased tibial component rotation relative to the femoral component toward internal rotation (toward a negative value). This correlation indicates that malalignment of tibial component causes rotational mismatch
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ACCEPTED MANUSCRIPT between the components in 0° extension. When the tibial component was aligned close to the
There was no significant correlation of the rotational alignment angle of the tibial
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0°.
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AP axis, the rotational relationship angle between the components in extension approximated
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component to the rotational relationship between the components in 30° and 60° flexion (Table 1).
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The bony rotational relationship angle (the angle between the SEA’ and the AP axis of tibia) in
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extension was 2.5 ± 10.7° (range, −16.6 to 16.4°). There was not a significant correlation between the bony rotational relationship angle and the rotational alignment angle of the
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femoral component (p=0.08). However, there was a significant correlation between the bony
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rotational relationship angle and the rotational alignment angle of the tibial component (Table 1, Fig. 4). In 0° extension, rotational malalignment of the tibial component caused a bony
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rotational mismatch in the opposite direction of the rotational alignment: Increased malalignment of the tibial component toward internal rotation (toward a negative value) resulted in an increased rotation of the tibia (bone) relative to the femur (bone) toward external rotation (toward a positive value) (Fig. 4). When the tibial component was aligned close to the AP axis, the bony rotational relationship angle in extension approximated 0°.
The coronal alignment angle and posterior inclination angle of the tibial component did not significantly correlate with the rotational relationship between components or the bones (Table 1). 10
ACCEPTED MANUSCRIPT 4. Discussion
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In this study, the rotational alignment of the tibial component significantly correlated with the
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rotational relationship between the femoral and tibial components as well as between the
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femur and tibia (bony rotational relationship angle) in weight-bearing during stair climbing. These rotational mismatches between components and between bones affected the subsequent
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rotational kinematics during flexion. As many previous studies suggested, the tibial rotational
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alignment was particularly susceptible to error. However, the tibial component should be carefully aligned when using a fixed bearing surface to avoid rotational mismatch for both
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components and bones. The AP axis of the tibia is a reliable reference for overall rotational
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alignment.
The rotational alignment of the tibial component strongly correlated with the
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rotational relationship between the tibial component and the femoral component in 0° extension. The rotational mismatch between the components probably occurs because each bone tends to return to its proper position during weight bearing by utilizing the rotational laxity built into the design of the components. The fixed bearing surface of the implant used in this study is designed to allow ±12° rotational mismatch relative to the femoral component in extension and in 90° flexion (data from the manufacturer) [22]. However, weight-bearing may allow smaller degrees of rotational mismatch between the components than designed. As a result, the degree of rotational mismatch between the components was less than that of the 11
ACCEPTED MANUSCRIPT rotational malalignment of the tibial component in most cases, and thus, a bony rotational
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mismatch also occurred. In fact, the degree of rotational mismatch between the components
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was less than ±12° in all the cases.
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There have been many reports investigating or comparing the rotational kinematics of replaced knees with the similar image-matching techniques. However, few studies have
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taken account of the rotational alignment of the components. Since the rotational alignment of
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the tibial component significantly affects the rotational kinematics as this study has shown, one should be cautious in evaluating the variation of rotational kinematics among the cases.
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The tibia had a tendency to externally rotate relative to the femur with increasing
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internal alignment of the tibial component relative to the AP axis. This fact shows that the rotational malalignment of the tibial component affects the rotational kinematics of the knee
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joint during weight bearing even if the non-high-restricting insert was used. Although the fixed bearing surface of this component is designed to have an admissibility for about ±12° rotational mismatch as mentioned above, bony rotational mismatch occurred in patients with ≤ 12° of angulation of rotational tibia malalignment. If the tibial component is aligned in the internal position, the patellofemoral joint may be misaligned and quadriceps strength may be affected due to an increased Q angle as the tibia is rotated outward relative to the femur [11,12].
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ACCEPTED MANUSCRIPT We used the AP axis of the tibia as a reference line to express the rotational
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alignment of tibial component. When the tibial component was aligned closely to the AP axis,
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the rotational mismatch between the components and bony rotational mismatch were not
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observed in knee extension. This shows that the AP axis can also be a reliable landmark of the tibial component as it is perpendicular to the SEA not only in rest [1-3] but also in weight
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bearing. The AP axis (Akagi’s line) is a line connecting the center of PCL at its tibial
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attachment and the medial border of the patellar tendon at the tibial tubercle [1]. Kawahara, et al reported that the line parallel to the Akagi’s AP axis on tibial cut surface runs between the
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center of the cut surface and the medial 1/6 of the patellar tendon at its attachment, that could
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be a landmark in placing the tibial tray on the cut surface [23]. There have been many other methods reported to determine the rotational alignment of the tibial component during the
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surgery. Medial 1/3 of the tibial tubercle is one of the well-recognized landmarks. Incavo, et al reported that when a template of tibial tray with a symmetrical design was placed on an axial MRI image of normal knee at the level of 8mm distal to the tibial joint surface aligning along to the femoral epicondyler axis, the short axis of the tibial tray intersected the patellar tendon at the range of 17% to 50% of its width from the medial edge in 75% of the subjects [4]. This study suggests that aligning the tibial plate from medial 1/6 to 1/2 of patellar tendon is appropriate in most cases. Our data also suggest that several degrees of tibial external rotation from the AP axis are acceptable because some cases in which the tibial component 13
ACCEPTED MANUSCRIPT was placed slightly in external rotation relative to the AP axis showed no rotational mismatch
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between the components and bones. The x-intercept of the regression line of either graph
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shows a slight external rotation of the rotational alignment angle of the tibial component. If
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slightly more external rotation is acceptable, the medial 1/3 of the tibial tubercle and the center of the cut surface might also be a good reference for tibial rotational alignment.
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However, there has been another debate that the tibial tubercle may not be a reliable rotational
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landmark because there is a wide variation in the morphology of proximal tibia and the relationship between the femoral transepicondylar axis and anterior tibial tuberosity axis
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among the cases [24]. Variations in the rotational relationship angle in our study may be
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influenced by this anatomical variation among the cases. Therefore, the self-adjusting technique to align the tibial plate with the femoral component in extension has been
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advocated [5]. Huddlestone et al reported that the tibial plate was aligned to 5.2° ± 5.0° externally rotated relative to the medial margin of the tibial tubercle using this technique [25] This study suggests aligning around medial 1/3 is appropriate as an average, but wide variation also exists. One should be aware of these anatomical variations and carefully align the tibial component taking into account of both the anatomic landmarks and intraoperative kinematics with the femoral component. The rotational alignment of the femoral component did not affect the rotational relationship between the components or between the bones. This may be because the 14
ACCEPTED MANUSCRIPT deviation of the femoral rotational alignment angle was smaller than that of the tibia. Previous
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studies showed that the tibial rotational alignment is more likely to deviate from preoperative
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landmarks than the femoral component [7,8]. As the femur has a clear landmark such as the
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SEA and the posterior condylar axis, the femoral component can be easily placed using references from the landmarks during surgery. However, it is reported that the rotational
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alignment of the femoral component could influence the postoperative knee functions in daily
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activities [26]. Therefore, we stress that it is important to place the femoral component accurately.
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There were some limitations to this study. First, we used a single type of implant.
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Difference in design for the conformity and rotational laxity should affect the results. For example, if the high-restricting insert was used, the rotational malalignment of the tibial
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component might more strongly affect the rotational kinematics of the knee joint during weight bearing. However, as this study shows, even with using a relatively low-restricting insert witha rotational laxity that this implant adopts, the rotational laxity could not compensate the rotational malalignment of the tibial component. This information had not been available from literatures or manufacturers. Therefore, the investigations should be extended to other implants in future. However, one can assume that same phenomenon would also occur in many other TKA implants with similar surface design. Second, preoperative kinematic and deformity may affect the postoperative kinematics and we did not evaluate the 15
ACCEPTED MANUSCRIPT preoperative conditions. However, the strong correlation between the tibial component
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alignment and the rotational mismatch between bones suggests that the individual variances in
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preoperative condition would not significantly affect on this phenomenon. Finally, the study
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was limited by the small number of patients. In the past literature, the influence of prosthesis alignment on axial rotation motion was evaluated for 67 subjects [14]. However, this study
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evaluated the subjects implanted with mobile-bearing TKA. The present study did reveal that
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the rotational alignment of the tibial component correlated strongly with the rotational relationship between the components and between the bones in fixed-bearing TKA and that
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the trend was constant even though the total patient number was small. Therefore, we
5. Conclusions
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consider the fact obtained in this study is reliable.
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The results of this study show how the rotational alignment of the tibial component affects rotational relationship between the bones and between the components of the replaced knee joint during weight bearing. The designed allowance for rotational mismatch within the fixed bearing surface does not fully compensate the rotational malalignment of the tibial component during weight bearing. The rotational alignment of the tibial component is an important factor in postoperative knee joint kinematics that could influence patient function and satisfaction, and the AP axis also can be a reliable landmark of the tibial component as it is perpendicular to the SEA at rest and during weight bearing. 16
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This work was supported by institutional funding from the Grant-in-Aid for Specially
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Promoted Research of Japan Society for the Promotion of Science (23000011).
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Figure legends
Figure 1. a. The angle between the surgical epicondylar axis (SEA) and the line joining the
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posterior margins of the femoral component axis was measured (defined as “rotational
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alignment angle of the femoral component”). b. The AP axis of the tibia (Akagi’s line:
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connecting the medial border of the patellar tendon at the attachment level to the projected center of the posterior cruciate ligament (PCL) at the tibial attachment) was identified
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preoperatively. Because the PCL attachment is located on a different slice of CT form the patellar tendon attachment, it was projected to the CT slice of the patellar tendon attachment. c. The AP axis of the tibia defined on the preoperative CT (b) was projected onto the postoperative CT (solid line) and the AP line of the tibial component was drawn (dotted line). The angle between the AP axis of the tibia and the AP line of the tibial component was measured (defined as “rotational alignment angle of the tibial component”).
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ACCEPTED MANUSCRIPT Figure 2. a. Stair climbing was analyzed. b. Movement of the knee was observed using a large
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Figure 3. The correlation of the rotational alignment angle of the tibial component (deviation angle from the AP axis of the tibia) to the rotational relationship angle between the
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components in 0° extension during stair climbing.
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Figure 4. The correlation of the rotational alignment angle of the tibial component (deviation angle from the AP axis of the tibia) to the rotational relationship angle between the bones
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(angle between the AP axis of the tibia and SEA’ of the femur) in 0° extension during stair
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climbing . The Pearson correlation analysis showed a significant and strong correlation.
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Table 1. P value (P) and correlation coefficient (r) of the correlation of each alignment angle to the rotational
Bony rotational
30°flexion
60°flexion
relationship angle
Rotational alignment angle of
P = 0.27
P = 0.99
P = 0.90
P = 0.08
femoral component
r = -0.27
r = -0.01
r=-0.03
r = 0.42
Rotational alignment angle of
P = 0.01
P = 0.18
P = 0.46
P < 0.01
tibial component
r = 0.61
r = 0.33
r = 0.19
r = -0.90
Coronal alignment of tibial
P = 0.55
P = 0.81
P = 0.86
P = 0.60
component
r = 0.17
r = 0.07
r = 0.05
r = -0.15
Posterior slope angle of tibial
P=0.40
P=0.57
P = 0.49
P = 0.96
component
r = -0.22
r = -0.15
r = -0.18
r = -0.01
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0°extension
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Components rotational relationship angle
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relationship between components and between bones
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Tibial rotational alignment affects rotational mismatch of components. Tibial rotational alignment affeccts rotational mismatch of bones. It affects rotational kinematics even if using a low-constrained surface design.
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