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Changes in total knee arthroplasty design affect in-vivo kinematics in a redesigned total knee system: A fluoroscopy study
Accepted Manuscript Changes in total knee arthroplasty design affect in-vivo kinematics in a redesigned total knee system: A fluoroscopy study
Francesco Zambianchi, Francesco Fiacchi, Vincenzo Lombari, Luca Venturelli, Andrea Marcovigi, Andrea Giorgini, Fabio Catani PII: DOI: Reference:
S0268-0033(18)30249-3 doi:10.1016/j.clinbiomech.2018.03.014 JCLB 4500
To appear in:
Clinical Biomechanics
Received date: Accepted date:
12 September 2017 19 March 2018
Please cite this article as: Francesco Zambianchi, Francesco Fiacchi, Vincenzo Lombari, Luca Venturelli, Andrea Marcovigi, Andrea Giorgini, Fabio Catani , Changes in total knee arthroplasty design affect in-vivo kinematics in a redesigned total knee system: A fluoroscopy study. The address for the corresponding author was captured as affiliation for all authors. Please check if appropriate. Jclb(2017), doi:10.1016/ j.clinbiomech.2018.03.014
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ACCEPTED MANUSCRIPT
Changes in total knee arthroplasty design affect in-vivo kinematics in a redesigned total knee system: a fluoroscopy study Francesco Zambianchi1, Francesco Fiacchi1, Vincenzo Lombari1, Luca Venturelli1, Andrea Marcovigi1, Andrea Giorgini1, Fabio Catani1 1
Department of Orthopaedic Surgery
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Via del Pozzo, 71 - 41124 - Modena, Italy
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Azienda Ospedaliero Universitaria di Modena, University of Modena and Reggio Emilia
Corresponding Author
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Zambianchi Francesco M.D.
email: [email protected]
Word Count Abstract: 248 Main Text: 3229
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ACCEPTED MANUSCRIPT Changes in total knee arthroplasty design affect in-vivo kinematics in a redesigned total knee system: a fluoroscopy study Abstract Background: Journey II Bi-Cruciate-Stabilized knee system was designed to overcome the complications of Journey Bi-Cruciate-Stabilized, including ilio-tibial band inflammation and episodes of dislocation. The purpose of this study was to assess differences in knee kinematics between the first and second-generation design by means of video-fluoroscopy. Re-designed
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prosthesis in-vivo kinematics was analysed during activities of daily living and results were eventually compared with those of the previous system, as reported in a previously published study.
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It was hypothesised that changes in components’ design influences replaced knee’s kinematic
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patterns.
Methods: Sixteen patients (3 males, 13 females) implanted with the redesigned prosthesis were
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assessed by video-fluoroscopy during stair-climbing, chair-rising and leg-extension at 8 months of follow-up. Patterns of axial rotation and antero-posterior motion of the medial and lateral femoral condyles were obtained. Range of Motion and International Knee Society Score were recorded pre-
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and post-operatively. Student t-tests were applied to compare the mean of each interesting variables. Findings: The comparison of the kinematics of the two designs revealed similar patterns of axial
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rotation, with progressive femoral external rotation in flexion and reduced absolute values of displacement for the new system. Reduced posterior displacements of the medial and lateral
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condyles were observed in Journey II patients. In terms of absolute location, the lateral condyle in the redesigned prosthesis showed a more anterior position on the tibial-baseplate embedded coordinate system at maximal flexion.
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Interpretation: Design changes in the recently-introduced total knee system contributed to modify
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its in-vivo knee kinematics as demonstrated by video-fluoroscopy.
Keywords: Bi-Cruciate Stabilized, TKA, design, fluoroscopy, kinematics.
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ACCEPTED MANUSCRIPT 1. Introduction Although surgical techniques and implant designs have improved through the years, as evidenced by excellent survivorship and long-term results [1], patients’ satisfaction after total knee arthroplasty (TKA) is still no more than 70 - 75 % [2, 3]. Low rates of satisfaction are especially obtained in relatively young and high-demanding patients, who often complain post-operative pain and reduced knee function, in particular during deep knee flexion activities [3, 4].
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In 2005 a new prosthetic design (Journey Bi-Cruciate Stabilized - BCS - Knee System, Smith & Nephew, Inc., Memphis, TN, USA) was introduced on the market, proposing to restore normal knee function throughout knee flexion and promoting a normal knee kinematic pattern [5]. Its main
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design features included the introduction of an anatomical joint line and articulating surface: the
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tibial insert was designed with a concave medial and convex lateral shape, providing medial stability and increasing posterior translation of the lateral condyle with flexion [6]. Moreover, the
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prosthesis was designed with an inherent screw-home mechanism, supporting a relative anterior and internally rotated femoral position in extension [7].
Complications following this total knee design were highlighted in recent publications. In
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particular, some patients presented with increased incidence of iliotibial band (ITB) syndrome, explained by excessive femoral translation during knee flexion, which could cause increased
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eccentric loading of the ITB [8]. Moreover, episodes of knee dislocation were reported in some
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patients performing varus-flexion or flexion-pivoting movements, occurring when the femoral cam jumped over the relatively short tibial post during knee flexion [9]. Excessive femoral rollback was also considered responsible of mechanical stress on the capsule and soft tissue structures, leading to post-operative knee stiffness in some cases [10].
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In 2013 a re-designed prosthesis was introduced on the market to overcome the clinical complications mentioned above: Journey II BCS Knee System (Smith & Nephew Inc., Memphis,
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TN, USA) with its design adjustments, proposed to reduce the complications described for its predecessor, maintaining the guided motion concept and decreasing the anterior-posterior translation of the tibio-femoral joint. The purpose of the present study is to quantitatively assess the differences in knee kinematics between the two prosthetic designs. Such assessment was performed by video-fluroscopy, investigating replaced knee in-vivo kinematics during activities of daily living and comparing the results with those obtained by a cohort of patients implanted with Journey BCS , reported in a previously published study [11]. It was hypothesized that the design changes between the old and new design play a role in the modification of the in-vivo knee kinematic patterns, reducing the posterior displacement of both femoral condyles over the tibial-base plate, which was considered 3
ACCEPTED MANUSCRIPT responsible for the described complications.
2. Methods 2.1. Study Design In the present study, 16 patients implanted with a bi-cruciate stabilized TKA (Journey II BCS Knee System, Smith & Nephew Inc., Memphis, TN, USA) in a single center were selected and
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included in group A. Inclusion criteria were as follows: TKA implanted for symptomatic primary knee osteoarthritis, age > 18 and < 75 years, body mass index (BMI) < 40, no prior history of joint replacement of the affected side, no ligamentous incompetency necessitating higher levels of
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constrain and complete recovery of knee range of motion after the operation. At an average 8
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months post-operatively (min. 3 months, max. 13 months) patients were asked to undergo fluoroscopic examination of the operated knee. Written informed consent was signed by all subjects
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prior to being included in the study, which was approved by the local Institutional Review Board. The cohort included 3 males and 13 females, with a mean age of 69.3 years (standard deviation, SD - 10.1, min. 59, max. 82) (Table 1). The right knee was treated in 9 cases, the left knee in 7. None of
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the patients included in the study reported post-operative joint infection, nor severe instability. As in the previously published study [11], all prostheses were implanted by the same senior surgeon,
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using an image-free knee navigation system (Stryker-Leibinger, Freiburg, Germany), performing a
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standard medial parapatellar approach and aiming a neutral mechanical coronal limb alignment. Only the deep fibers of medial collateral ligament were released routinely to achieve a better joint exposure. No other ligamentous releases were performed in any of the examined patients. Patella was resurfaced and the prosthetic components were cemented in all cases. Passive flexion-extension
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range of motion (RoM) was recorded pre-operatively and before video-fluoroscopy examination. Clinical assessment was performed using the International Knee Society (IKS) Score [12] pre-
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operatively and at the time of fluoroscopy investigation. Occurrence of ITB friction syndrome was recorded post-operatively. During fluoroscopy assessment patients were asked to perform three activities of daily living, including two closed chain motions, stair climbing and chair rising and one open chain movement, leg extension against gravity. For stair climbing, three 21cm-high steps were used. To assess stepping up, only the first step was used to perform three consecutive up/down cycles where the ascent phase was captured. For the rising, chair height was set specifically for each patient in order for him or her to begin with the knee flexed at about 90°. Also in this task, only the ascent phase was analyzed. For the extension against gravity task, patients were examined in a semi-supine position (i.e. sitting at 45°), with their knee hanging as flexed as possible over the end of the 4
ACCEPTED MANUSCRIPT examination chair (Figure 1). Data collection and analysis procedures were as previously reported [11, 13, 14] and included the use of a standard flat panel detector (Opera Swing, GMM S.p.a, Italy) with a frame rate of 15 images per second. The implant surface model was projected onto each fluoroscopic image, determining its threedimensional position and orientation by an iterative procedure aimed at matching the implant silhouette with the silhouette of the subject’s implant components [15] (Figure 2). Previous validation work showed that 3D position and orientation of the metal prosthesis
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components has an accuracy better than 0.5 mm and 1°, respectively [15, 16]. The implant landmark-based coordinate system of femoral and tibial components’ CAD models was determined
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with standard conventions [17]. Condylar contacts were assumed on the medial and lateral
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compartments as the two pairs of points at minimum distance between the femoral prosthetic condyles and the tibial base-plate [18, 19]. The positions of these contact points (CPs) were then
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expressed for every knee flexion degree, onto the tibial base-plate reference frame in terms of percentage locations over its anterior-posterior (A/P) length, thus irrespective of different sizes: 0% and 100% corresponded to the most anterior and most posterior location, respectively. Patterns of
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A/P motion of the CPs were therefore obtained independently for the medial and lateral condyles. For each patient and motor task, the medial and lateral CP coordinates were determined and plotted
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versus the knee flexion angle. Also, the difference between A/P locations of the CPs at maximum extension and flexion was considered the posterior femoral rollback (PFR) [20]. Contact-line
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rotation, defined as rotation of the line connecting the medial and lateral CP with respect to the medio-lateral axis on the tibial transverse plane, was calculated for each flexion angle, but here, it has been reported over predefined flexion angles with 10° increments.
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Kinematics data for the closed-motion motor tasks (chair rising and stair climbing) relative to the first-generation knee system were obtained from a fluoroscopy-based study by the senior author
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with the same examination and acquisition methodology [11]. Patients from the previously published study were included in group B.
2.2. Implant features The recently introduced knee system brought design adjustments aiming to limit the predecessor’s clinical complications. In particular, the lateral and medial anterior flange of the femoral component were reduced in thickness and tapered at the edges, with aim to decrease tension forces on the ITB, the width decreased to limit implant overhang. Changes were also made to the tibial post, which was placed anteriorly and designed taller than its predecessor, to reduce the risk of knee dislocation. The kinematic pattern of the new design was planned through virtual simulating tests into a 5
ACCEPTED MANUSCRIPT validated musculoskeletal modeling system (LifeMod/KneeSIM; LifeModeler, Inc., San Clemente, CA, USA) [21].
2.3. Statistical Analysis Descriptive statistics such as mean, SD and range were calculated for each variable. Student t-tests were applied to compare the mean of each variable between the two sets of data relative to each
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prosthetic design. P values were two-sided and considered significant if smaller than 0.05.
3. Results
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3.1. In-vivo kinematics
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Consistent kinematic motions were observed for all patients and for each motor task, with no abnormal patterns in any of the examined knees. The femur showed an overall external rotation
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relative to the tibia from extension to flexion in all three examined motor tasks (Figure 3). Not all second-generation BCS knee systems exhibited screw-home mechanism, with femoral internal rotation in full extension. However, all patients displayed femoral component sharp external
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rotation in the first degrees of knee flexion and all the examined axial rotation patterns were similar. Values of femoral external rotation, based on the tibial plate-embedded coordinate system, at
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minimal and maximal knee flexion (0°-80°), are reported in Table 2. A larger posterior displacement of the lateral condyle compared to the medial was observed in
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function of knee flexion in all the examined tasks. The average A/P displacements of the medial and lateral condylar CP are reported for the three investigated tasks in Table 2 and Figure 4. In the three examined tasks the medial condyle CPs were placed in the central portion of the tibial
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base-plate reference frame, showing a progressive posterior translation from 0° to 15° of knee flexion, with a successive anterior translation from 15° to 55° of knee flexion and an ultimate slight
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posterior translation from 55° to 80°. The lateral condyle CPs instead demonstrated a posterior placement in the tibial base-plate reference frame throughout knee flexion movement. At full extension, the lateral CPs were located in the central portion of the tibial base-plate and showed a posterior displacement up to approximately 15° of knee flexion, followed by a phase of anterior translation, from 15° to 45° and a successive posterior translation from 45° to 80° of knee flexion (Figure 5 and Figure 6). No notable kinematic differences were reported between close (chair rising and stair climbing) and open chain (leg extension) motions.
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ACCEPTED MANUSCRIPT 3.2. Group A vs Group B in-vivo kinematics comparison The in-vivo kinematics of the two designs was compared during closed chain motions. Surgical techniques and methods of analyses were consistent between the two study designs. In both activities the two total knee systems showed similar kinematic patterns of axial rotation, with progressive femoral external rotation with knee flexion. Over the flexion arc, the prostheses in group A demonstrated reduced absolute values of femoral external rotation during knee flexion and a more neutral position in full extension compared to group B, which reported values of femoral
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component internal rotation (Table 3, Table 4 and Figure 7).
Reduced absolute values of A/P translation of the CP on the medial and lateral compartments were
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reported in both tasks by group A compared to group B (Table 3 and Table 4).
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The group B motion patterns were consistently posteriorly directed with knee flexion in both compartments, implying significant PFR. The recent knee system’s kinematics instead, is
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characterized by a relatively constant positioning of the medial CP across the central portion of the tibial base plate and by a posterior displacement of the lateral CP in the first 20° of knee flexion, followed by a small anterior translation in the central region of knee flexion and then a slight
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posterior translation after 60-65° of knee flexion. (Figure 8, Table 3 and Table 4). No differences were reported between the two groups relative to pre- and post-operative RoM and post-operative clinical outcome. Statistically significant differences were described for the pre-
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operative “Knee” and “Function” IKS Score domains (P<0.05), with lower scores reported in group
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A (Table 1). No cases of ITB friction syndrome were recorded. Statistically significant differences between the first and second-generation designs’ kinematics were reported in both motor tasks. No significant differences were observed in chair rising range of
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axial rotation and in stair climbing absolute displacement of the lateral condyle at maximal
4. Discussion
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extension (Table 3 and Table 4).
The first-generation of total knee system analyzed in the present study was introduced as the knee design which could replicate the function of normal joint, through a dual cam-post mechanism substituting both the cruciate ligaments and permitting to achieve deep flexion by preserving knee rotation and posterior femoral translation with flexion [22, 23, 24]. In addition, its polyethylene insert geometry proposed to guide posterior motion of the medial and lateral condyles in order to mimic the kinematics of the natural knee in flexion. Several studies confirmed that the implant’s kinematic behaviour was profoundly guided by the cam-post mechanism and the bearing gemoetriy, as intended by the designer [4, 7, 23, 24, 25], but daily practice highlighted significant clinical 7
ACCEPTED MANUSCRIPT complications. In particular, Luyckx et al. described symptoms of ITB traction syndrome in 7.2% of a large cohort of patients at a mean of 6 months follow-up. After rehab, pain during flexion persisted in 2% of them, resulting in surgical ITB release. The authors attributed the symptom to the large translation of the medial condyle and to the unrestrained posterior displacement of the lateral condyle, coupled with excessive femoral external rotation with progressive joint flexion [26], responsible of increased eccentric loading of the ITB [8]. In addition, Arnout et al. reported complications associated with knee dislocation [9], occurring during varus-flexion or flexion-
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rotation motions. Such movements allowed the femoral cam to jump over the relatively short tibial post. Digennaro et al. in their retrospective study comparing two designs, explained the high
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incidence of post-operative stiffness in the study total knee system, with the excessive femoral
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rollback, responsible of mechanical stress on the capsule and soft tissue structures [10]. The introduction on the market of the second-generation design was described as the evolutionary
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step towards natural motion in TKA. In-vitro results confirmed the design change claims of reduced stress on the ITB and desired natural knee kinematics, with posterior displacement of the lateral condyle and relatively reduced translation of the medial condyle with flexion. Such kinematic
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patterns appeared to contrast with the displacements observed for the predecessor, exceeding those of the un-operated joint [25]. Recent literature comparing healthy and replaced knees with the
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second-generation BCS design during weight bearing activities, confirmed the designer’s purpose of kinematic similarities between the BCS knee replacement and the native knee. In particular,
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similar patterns of condyle translation and axial rotation were reported during early flexion and beyond 90° of knee flexion. Different behaviors were described in full extension – absent femoral internal rotation due to anterior cruciate ligament resection in the BCS knee – and in the transition
native joint [26].
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phase (30°-60° of flexion), with a negligible displacement of femoral condyles compared to the
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The objective of the present study was to confirm the kinematic purposes relative to the motion of the second-generation of BCS total knee system (group A), through an in-vivo evaluation of the kinematics of patients implanted with this system during activities of daily living by means of video-fluoroscopy. Results were compared with those achieved by patients implanted with the firstgeneration TKA (group B) undergoing the same investigation, as described in previously published study [11]. The most important finding of the present research is the confirmation that the design adjustments proposed on the examined total knee system, have implications in implanted knee’s kinematic behaviour. Fluoroscopy data confirm the hypothesis that the design changes between the first and the second-generation total knee system plays a role in the modification of the in-vivo knee 8
ACCEPTED MANUSCRIPT kinematic pattern during closed-chain motions. In particular, similar configurations of axial rotation of the femoral component with flexion are a characteristic of both designs. However, the inherent screw-home mechanism of the group B cohort, which maintained a relative posterior and internally rotated position in full extension, was modified towards a more anterior rotational placement of the femoral component in full extension in group A (Figure 7). Not all second-generation BCS knee systems exhibited screw-home mechanism, with femoral internal rotation in full extension. Regarding the displacement of the CPs on the tibial plateau, the prostheses in group A demonstrated
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reduced translation of both the medial and lateral femoral condyles compared to group B in closed chain motions (Table 3 and Table 4). Moreover, the medial CP translation reported by group A was
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more similar to that described by Komistek for the normal knee [7]. This finding is in contrast with
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recent observations, describing a progressive posterior translation of the medial femoral condyle after 60° of knee flexion in the BCS compared to the healthy joint [26].
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In terms of absolute location, the lateral CP in the re-designed prosthesis, together with a reduced posterior displacement, showed a more anterior position on the tibial-base plate embedded coordinate system as compared to group B at maximal flexion. These results represent the
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kinematic confirmation of the design adjustments of the second-generation prosthesis and find a confirmation in recent publication relative to BCS kinematics in weight bearing conditions.
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The analysis of open and close chain motions was performed in order to investigate the influence of muscle activity and loading conditions on replaced knee kinematics. Surprisingly, no significant
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kinematic differences were described for open and close chain motions [27, 28], demonstrating that muscular activity and weight bearing conditions, do not significantly modify the kinetic patterns of the examined knee system. It was hypothesized that the high SD ranges in all the performed
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analysis influences this finding. The high range of SD itself was explained by the reduced constrain in the redesigned prosthesis compared to its predecessor and leading to a “less” guided motion of
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the femur during knee flexion. Such design feature allows the patient to find the best equilibrium, balancing the external and internal forces, without increasing soft tissue strain. The present study is limited by several factors, including the small number of patients included and the absence of sample size calculation and randomization. Second, single-plane fluoroscopy imaging has uncertainties on the medio-lateral translations. Third, comparison with the previously reported study is indirect and with variable examination time point. Even though the analysis was performed based on analogue examination conditions and with similar shape-matching techniques and software, differences in kinematic activities, as well as inter-individual variability in 3D positioning of the components onto each fluoroscopic image still remain and inevitably affects the investigation and its conclusion. Moreover, implants’ coordinate system is based on femoral and 9
ACCEPTED MANUSCRIPT tibial components CAD models (implant landmarks-based coordinate system) and not on femur and tibia bony anatomical landmarks. This leads to the description of the relative motion of femoral and tibial component one with respect to the other, and not necessarily to the bone kinematics of femur and tibia. Last, the study lacks correlation between patient-reported outcome and satisfaction and specific knee kinematics. To overcome this limitation, a prospective trial would be useful to evaluate the clinical and functional outcome of the examined total knee system. The resulting data
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would tell more about the influence of design changes over patients’ satisfaction.
5. Conclusions
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The design adjustments performed onto the second-generation prosthesis to limit excessive
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posterior displacement of the femoral condyles, as well as femoral component rotation in weightbearing conditions, contributed to modify replaced knee’s kinematics during daily living activities,
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as confirmed by fluoroscopy data.
Acknowledgements
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This research did not receive any specific grant from funding agencies in the public, commercial, or
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not-for-profit sectors.
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ACCEPTED MANUSCRIPT Table 1 Demographic and clinical data of the two cohorts of patients. The data reported in Journey BCS column are derived from a previously published study [5]. International Knee Society (IKS) score is reported for both “Knee” and “Function” sections, pre- and post-operatively. Values are reported as mean (standard deviations SD, min., max.). n.s.: not statistically significant. RoM: Range of
Group A 16
Age (years)
69.3 (SD 10.1, min. 59, max. 82) 3 / 13
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68.2 (SD 10.0, min. 58, max. 79)
n.s.
4 / 12
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Gender (male/female)
P-value
16
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Number of patients
Group B
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Parameter
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Motion.
109.6° (SD 10.6, min. 90°, max. 135°)
116.4° (SD 9.9, min. 100°, max. 135°)
n.s.
Post-operative RoM
115.2° (SD 12.1, min. 90°, max. 130°)
118.8° (SD 11.3, min. 90°, max. 130°)
n.s.
Pre-operative IKS “Knee”
38.0 (SD 14.6, min. 25, max. 71)
49.0 (SD 12.0, min. 25, max. 63)
0.0268
Pre-operative IKS “Function”
42.4 (SD 8.1, min. 33, max. 69)
50.7 (SD 9.4, min. 35, max. 70)
0.0120
Post-operative IKS “Knee”
93.2 (SD 6.4, min. 80, max. 100)
94.9 (SD 5.6, min. 83, max. 100)
n.s.
Post-operative IKS “Function”
91.4 (SD 7.1, min. 79, max. 100)
90.7 (SD 9.6, min. 70, max. 100)
n.s.
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Pre-operative RoM
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ACCEPTED MANUSCRIPT Table 2 Average femoral external rotation and A/P displacements of the medial and lateral condylar CP are reported for the three investigated tasks from knee extension to flexion. Values are reported as mean (standard deviations SD, min., max.).
Femoral Chair Rising
Stair Climbing
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displacement
Leg Extension
Range of Axial 12.2 (SD 10.2, min. 2.9, max. 11.8)
5.1 (SD 9.4, min. 1.6, max. 19.9)
4.0 (SD 6.7, min. 0.6, max. 8.8)
5.3 (SD 8.0, min. 1.3, max. 9.6)
4.9 (SD 5.2, min. 2.9, max. 8.7)
11.0 (SD 4.5, min. 1.0, max. 14.2)
5.6 (SD 7.3, min. 2.2, max. 11.0)
8.2 (SD 5.0, min. 4.8, max. 14.4)
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rotation (°)
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A/P Medial CP (mm)
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(mm)
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A/P Lateral CP
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7.0 (SD 9.7, min. 2.5, max. 17.0)
ACCEPTED MANUSCRIPT Table 3 Comparison of fluoroscopy data relative to group A and group B, during chair rising motion. Values are reported as mean (standard deviations SD, min., max.). n.s.: not statistically significant; PFR: posterior femoral rollback.
Chair Rising – Mean (SD, min., max.) Group B
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Group A (n = 16)
(n = 16)
Range of Motion (°)
0 - 80
A/P Medial CP (mm)
4.0 (SD 6.7, min. 0.6, max. 8.8)
10.0 (SD 2.6, min. -7.7, max. 2.3)
0.0023
A/P Lateral CP (mm)
11.0 (SD 4.5, min. 1.0, max. 14.2)
18.5 (SD 3.0, min. -15.3, max. 3.1)
< 0.0001
A/P Medial CP (% Tibial size)
7.8 (SD 13.4, min. 1.1, max. 18.4)
18.5 (SD 6.1, min. 32.9, max. 55.9)
0.0068
A/P Lateral CP (%Tibial size)
22.0 (SD 9.5, min. 1.8, max. 29,5)
43.8 (SD 6.5, min. 14.0, max. 57.8)
< 0.0001
Range of Axial Rotation (°)
12.2 (SD 10.2, min. 2.9, max. 11.8)
15.8 (SD 4.4, min. 7.3, max. 21.7)
n.s.
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0 - 90
P-value
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A/P Medial CP (%Tibial size)
-
48.0 (SD 4.9)
55.9 (SD 7.9)
0.0019
At reached max flexion (°)
50.7 (SD 5.6)
35.8 (SD 5.6)
< 0.0001
48.0 (SD 5.5)
57.8 (SD 6.7)
< 0.0001
70.0 (SD 4.0)
14.2 (SD 4.7)
< 0.0001
At reached max extension (°)
-0.6 (SD 4.9)
-4.2 (SD 5.3)
n.s.
At reached max flexion (°)
11.6 (SD 5.2)
11.0 (SD 6.0)
n.s.
1.1 (SD 5.2)
8.9 (SD 3.5)
< 0.0001
11.0 (SD 4.5)
18.5 (SD 2.6)
< 0.0001
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At reached max extension (°)
At reached max extension (°)
Medial PFR Lateral PFR
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Axial Rotation (°, external +)
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At reached max flexion (°)
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A/P Lateral CP (%Tibial size)
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ACCEPTED MANUSCRIPT Table 4 Comparison of fluoroscopy data relative to group A and group B, during stair climbing motion. Values are reported as mean (standard deviations SD, min., max.). n.s.: not statistically significant; PFR: posterior femoral rollback
Stair Climbing – Mean (SD, min., max.) Group B
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Group A
P-value
(n = 16)
0 - 70
A/P Medial CP (mm)
5.3 (SD 8.0, min. 1.3, max. 9.6)
A/P Lateral CP (mm)
5.6 (SD 7.3, min. 2.2, max. 11.0)
0 - 70
-
9.7 (SD 3.0, min. -6.0, max. 3.7)
0.0482
14.3 (SD 3.5, min. -10.6, max. 3.5)
0.0002
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Range of Motion (°)
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(n = 16)
10.9 (SD 16.3, min. 2.6, max. 21.3)
23.3 (SD 6.4, min. 35.2, max. 58.5)
0.0082
A/P Lateral CP (%Tibial size)
10.8 (SD 14.6, min. 4.9, max. 21.1)
32.7 (SD 8.0, min. 25.1, max. 58.8)
< 0.0001
5.1 (SD 9.4, min. 1.6, max. 19.9)
13.0 (SD 4.0, min. 5.6, max. 21.6)
0.0043
58.5 (SD 4.8)
< 0.0001
38.9 (SD 5.9)
0.0001
53.7 (SD 11.3)
57.3 (SD 7.3)
n.s.
64.5 (SD 3.3)
25.6 (SD 6.3)
< 0.0001
7.6 (SD 9.1)
-4.0 (SD 1.0)
< 0.0001
10.5 (SD 4.0)
6.5 (SD 4.8)
0.0157
3.2 (SD 6.0)
8.5 (SD 2.0)
0.0022
5.6 (SD 7.3)
14.3 (SD 3.4)
0.0002
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Range of Axial Rotation (°)
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A/P Medial CP (% Tibial size)
A/P Medial CP (%Tibial size)
40.2 (SD 8.1)
At reached max flexion (°)
47.0 (SD 4.5)
At reached max extension (°)
Axial Rotation (°, external +)
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At reached max flexion (°)
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At reached max extension (°) At reached max flexion (°) Medial PFR Lateral PFR
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A/P Lateral CP (%Tibial size)
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At reached max extension (°)
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ACCEPTED MANUSCRIPT References 1. Jones CA, Beaupre LA, Johnston DW, Suarez-Almazor ME. Total joint arthroplasties: current concepts of patient outcomes after surgery. Rheum Dis Clin N Am 2007;33:71–86 2. Noble PC, Conditt MA, Cook KF, Mathis KB. The John Insall Award: patient expectations affect satisfaction with total knee arthroplasty. Clin Orthop Relat Res. 2006;452:35–43 3. Noble PC, Gordon MJ, Weiss JM, Reddix RN, Conditt MA, Mathis KB. et al. Does total knee replacement restore normal knee function? Clin Orthop Relat Res. 2005;431:157–165
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4. Weiss JM, Noble PC, Conditt MA, Kohl HW, Roberts S, Cook KF, Gordon MJ, Mathis KB. What functional activities are important to patients with knee replacements? Clin Orthop
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Relat Res. 2002;404:172–188
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5. Victor J, Bellemans J. Physiologic kinematics as a concept for better flexion in TKA. Clin Orthop Relat Res. 2006;452:53–58.
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6. Steinbrück A, Schröder C, Woiczinski M, Fottner A, Pinskerova V, Müller PE, Jansson V. Femorotibial kinematics and load patterns after total knee arthroplasty: An in vitro comparison of posterior-stabilized versus medial-stabilized design. Clin Biomech.
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2016;33:42-48. doi: 10.1016/j.clinbiomech.2016.02.002. 7. Komistek RD, Dennis DA, Mahfouz M. In-vivo fluoroscopic analysis of the normal human
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knee. Clin Orthop Relat Res. 2003;410:69–81. 8. Luyckx L, Luyckx T, Bellemans J, Victor J. Iliotibial band traction syndrome in guided
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motion TKA: A new clinical entity after TKA. Acta Orthop. Belg. 2010;76:507–512. 9. Arnout N, Vandenneucker H, Bellemans J. Posterior dislocation in total knee replacement: a price for deep flexion? Knee Surg Sports Traumatol Arthrosc 2006;19(6):911–913.
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10. Digennaro V, Zambianchi F, Marcovigi A, Mugnai R, Fiacchi F, Catani F. Design and kinematics in total knee arthroplasty. Int Orthop. 2014;38(2):227–233.
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11. Catani F, Ensini A, Belvedere C, Feliciangeli A, Benedetti MG, Leardini A, Giannini S. In vivo kinematics and kinetics of a bi-cruciate substituting total knee arthroplasty: A combined fluoroscopic and gait analysis study. J Orthop Res. 2009;27(12):1569–1575. 12. Insall JN, Dorr LD, Scott RD, Scott WN. Rationale of the Knee Society clinical rating system. Clin Orthop Relat Res. 1989;248:13–14. 13. Catani F, Belvedere C, Ensini A, Feliciangeli A, Giannini S, Leardini A. In-vivo knee kinematics in rotationally unconstrained total knee arthroplasty. J Orthop Res. 2011;29(10):1484–1490.
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ACCEPTED MANUSCRIPT 14. Fantozzi S, Catani F, Ensini A, Leardini A, Giannini S. Femoral rollback of cruciateretaining and posterior-stabilized total knee replacements: in vivo fluoroscopic analysis during activities of daily living. J Orthop Res. 2006;24:2222–2229. 15. Banks SA, Hodge WA. Design and activity dependence of kinematics in fixed and mobilebearing knee arthroplasties. J Arthroplasty 2004;19:809–816. 16. Victor J, Banks SA, Bellemans J. Kinematics of posterior cruciate ligament- retaining and substituting total knee arthroplasty. A prospective randomised outcome study. J Bone Joint
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Surg [Br] 2005;87-B:646–655.
17. Grood ES, Suntay WJ. A joint coordinate system for the clinical description of three-
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dimensional motions: application to the knee. J Biomech Eng. 1983;105(2):136-44.
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18. Tanaka Y, Nakamura S, Kuriyama S, Ito H, Furu M, Komistek RD, Matsuda S. How exactly can computer simulation predict the kinematics and contact status after TKA? Examination
10.1016/j.clinbiomech.2016.09.006.
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in individualized models. Clin Biomech. 2016;39:65-70. doi:
19. Banks S, Bellemans J, Nozaki H, Whiteside LA, Harman M, Hodge WA. Knee motions
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during maximum flexion in fixed and mobile-bearing arthroplasties. Clin Orthop Relat Res. 2003;410:131–138.
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20. Nozaki H, Banks SA, Suguro T, Hodge WA. Observations of femoral rollback in cruciateretaining knee arthroplasty. Clin Orthop Relat Res. 2002;404:308–314.
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21. Johal P, Williams A, Wragg P, Hunt D, Gedroyc W. Tibio-femoral movement in the living knee. A study of weight bearing and non-weight bearing knee kinematics using
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‘interventional’ MRI. J of Biomech 2005;38(2):269–276. 22. Kuroyanagi Y, Mu S, Hamai S, Robb WJ, Banks SA. In Vivo Knee Kinematics During Stair and Deep Flexion Activities in Patients With Bicruciate Substituting Total Knee
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Arthroplasty. J Arthroplasty 2012;27(1):122-128. 23. Arbuthnot J and Brink R. Assessment of the antero-posterior and rotational stability of the anterior cruciate ligament analogue in a guided motion bi-cruciate stabilized total knee arthroplasty. J Med Eng Technol. 2009;33: 610–615 24. Christen, B., Neukamp, M., Aghayev, E. Consecutive series of 226 journey bicruciate substituting total knee replacements: early complication and revision rates. BMC Musculoskelet Disord. 2014;15: 395. doi: 10.1186/1471-2474-15-395. 25. Victor J, Mueller JKP, Komistek RD, Sharma A, Nadaud MC, Bellemans J. In Vivo Kinematics after a Cruciate-substituting TKA. Clin Orthop Relat Res. 2010;468:807–814.
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ACCEPTED MANUSCRIPT 26. Grieco TF, Sharma A, Dessinger GM, Cates HE, Komistek RD. In Vivo Kinematic Comparison of a Bicruciate Stabilized Total Knee Arthroplasty and the Normal Knee Using Fluoroscopy. J Arthroplasty 2018;33(2):565-571. doi: 10.1016/j.arth.2017.09.035. 27. Yoshiya S, Matsui N, Komistek RD, Dennis DA, Mahfouz M, Kurosaka M. In Vivo Kinematic Comparison of Posterior Cruciate-Retaining and Posterior Stabilized Total Knee Arthroplasties Under Passive and Weight-Bearing Conditions. J Arthroplasty 2005;20(6):777-783
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28. Horiuchi H, Akizuki S, Tomita T, Sugamoto K, Yamazaki T, Shimizu N. In vivo kinematic analysis of cruciate-retaining total knee arthroplasty during weight-bearing and non-weight-
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bearing deep knee bending. J Arthroplasty 2012;Jun;27(6):1196-1202.
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doi:10.1016/j.arth.2012.01.017
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ACCEPTED MANUSCRIPT Highlights Total knee arthroplasty kinematics of two systems was analyzed by means of fluoroscopy. Comparison includes 16 new total knee designs and 16 old systems, as described in a previous study. Similar patterns of knee axial rotation were described between the two total knee systems. As proposed, the new system obtained reduced medial and lateral displacement compared to
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the old. Design changes in the redesigned prosthesis contributed to modify its in-vivo knee
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kinematics.
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ACCEPTED MANUSCRIPT Figures Legend Figure 1: fluoroscopy system tracking a subject’s knee during three activities of daily living, including (A) chair rising, (B) stair climbing and (C) leg extension. Figure 2: 3D-to-2D CAD model-to-flat panel image registration was used to determine the kinematics of knees implanted with a bi-cruciate stabilized (BCS) total knee system during three activities of daily living.
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Figure 3: Femoral component axial rotation (°) relative to the tibial component in closed and openchain motor tasks at different knee flexion degrees.
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Figure 4: A/P translation (mm) of the medial and lateral femoral condyles on the tibial component
representative of femoral condyle anterior translation.
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in closed and open-chain motor tasks at different knee flexion degrees. Ascending curves are
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Figure 5: A/P translation (%) of the medial and lateral femoral condyles on the tibial component in terms of absolute placement in the three motor tasks at different knee flexion degrees. Figure 6: Average contact locations overimposed on a right tibial polyethylene insert CAD model.
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Average contact locations on the medial and lateral side are shown for 20° flexion increments for each motor task.
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Figure 7: Patterns of femoral axial rotation (°) of the two examined total knee designs in closed chain motor tasks (Chair Rising and Stair Climbing) at different knee flexion degrees. * Statistically
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significant difference between Group A and Group B. Figure 8: Patterns of A/P translation of the medial and lateral femoral condyles of the two examined total knee systems in closed chain motor tasks (Chair Rising and Stair Climbing) at different knee
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flexion degrees. Values are given in terms of femoral condyles absolute placement on the tibial
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component. * Statistically significant difference between Group A and Group B.
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Francesco Zambianchi, Francesco Fiacchi, Vincenzo Lombari, Luca Venturelli, Andrea Marcovigi, Andrea Giorgini, Fabio Catani PII: DOI: Reference:
S0268-0033(18)30249-3 doi:10.1016/j.clinbiomech.2018.03.014 JCLB 4500
To appear in:
Clinical Biomechanics
Received date: Accepted date:
12 September 2017 19 March 2018
Please cite this article as: Francesco Zambianchi, Francesco Fiacchi, Vincenzo Lombari, Luca Venturelli, Andrea Marcovigi, Andrea Giorgini, Fabio Catani , Changes in total knee arthroplasty design affect in-vivo kinematics in a redesigned total knee system: A fluoroscopy study. The address for the corresponding author was captured as affiliation for all authors. Please check if appropriate. Jclb(2017), doi:10.1016/ j.clinbiomech.2018.03.014
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
Changes in total knee arthroplasty design affect in-vivo kinematics in a redesigned total knee system: a fluoroscopy study Francesco Zambianchi1, Francesco Fiacchi1, Vincenzo Lombari1, Luca Venturelli1, Andrea Marcovigi1, Andrea Giorgini1, Fabio Catani1 1
Department of Orthopaedic Surgery
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Via del Pozzo, 71 - 41124 - Modena, Italy
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Azienda Ospedaliero Universitaria di Modena, University of Modena and Reggio Emilia
Corresponding Author
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Zambianchi Francesco M.D.
email: [email protected]
Word Count Abstract: 248 Main Text: 3229
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ACCEPTED MANUSCRIPT Changes in total knee arthroplasty design affect in-vivo kinematics in a redesigned total knee system: a fluoroscopy study Abstract Background: Journey II Bi-Cruciate-Stabilized knee system was designed to overcome the complications of Journey Bi-Cruciate-Stabilized, including ilio-tibial band inflammation and episodes of dislocation. The purpose of this study was to assess differences in knee kinematics between the first and second-generation design by means of video-fluoroscopy. Re-designed
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prosthesis in-vivo kinematics was analysed during activities of daily living and results were eventually compared with those of the previous system, as reported in a previously published study.
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It was hypothesised that changes in components’ design influences replaced knee’s kinematic
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patterns.
Methods: Sixteen patients (3 males, 13 females) implanted with the redesigned prosthesis were
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assessed by video-fluoroscopy during stair-climbing, chair-rising and leg-extension at 8 months of follow-up. Patterns of axial rotation and antero-posterior motion of the medial and lateral femoral condyles were obtained. Range of Motion and International Knee Society Score were recorded pre-
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and post-operatively. Student t-tests were applied to compare the mean of each interesting variables. Findings: The comparison of the kinematics of the two designs revealed similar patterns of axial
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rotation, with progressive femoral external rotation in flexion and reduced absolute values of displacement for the new system. Reduced posterior displacements of the medial and lateral
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condyles were observed in Journey II patients. In terms of absolute location, the lateral condyle in the redesigned prosthesis showed a more anterior position on the tibial-baseplate embedded coordinate system at maximal flexion.
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Interpretation: Design changes in the recently-introduced total knee system contributed to modify
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its in-vivo knee kinematics as demonstrated by video-fluoroscopy.
Keywords: Bi-Cruciate Stabilized, TKA, design, fluoroscopy, kinematics.
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ACCEPTED MANUSCRIPT 1. Introduction Although surgical techniques and implant designs have improved through the years, as evidenced by excellent survivorship and long-term results [1], patients’ satisfaction after total knee arthroplasty (TKA) is still no more than 70 - 75 % [2, 3]. Low rates of satisfaction are especially obtained in relatively young and high-demanding patients, who often complain post-operative pain and reduced knee function, in particular during deep knee flexion activities [3, 4].
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In 2005 a new prosthetic design (Journey Bi-Cruciate Stabilized - BCS - Knee System, Smith & Nephew, Inc., Memphis, TN, USA) was introduced on the market, proposing to restore normal knee function throughout knee flexion and promoting a normal knee kinematic pattern [5]. Its main
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design features included the introduction of an anatomical joint line and articulating surface: the
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tibial insert was designed with a concave medial and convex lateral shape, providing medial stability and increasing posterior translation of the lateral condyle with flexion [6]. Moreover, the
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prosthesis was designed with an inherent screw-home mechanism, supporting a relative anterior and internally rotated femoral position in extension [7].
Complications following this total knee design were highlighted in recent publications. In
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particular, some patients presented with increased incidence of iliotibial band (ITB) syndrome, explained by excessive femoral translation during knee flexion, which could cause increased
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eccentric loading of the ITB [8]. Moreover, episodes of knee dislocation were reported in some
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patients performing varus-flexion or flexion-pivoting movements, occurring when the femoral cam jumped over the relatively short tibial post during knee flexion [9]. Excessive femoral rollback was also considered responsible of mechanical stress on the capsule and soft tissue structures, leading to post-operative knee stiffness in some cases [10].
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In 2013 a re-designed prosthesis was introduced on the market to overcome the clinical complications mentioned above: Journey II BCS Knee System (Smith & Nephew Inc., Memphis,
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TN, USA) with its design adjustments, proposed to reduce the complications described for its predecessor, maintaining the guided motion concept and decreasing the anterior-posterior translation of the tibio-femoral joint. The purpose of the present study is to quantitatively assess the differences in knee kinematics between the two prosthetic designs. Such assessment was performed by video-fluroscopy, investigating replaced knee in-vivo kinematics during activities of daily living and comparing the results with those obtained by a cohort of patients implanted with Journey BCS , reported in a previously published study [11]. It was hypothesized that the design changes between the old and new design play a role in the modification of the in-vivo knee kinematic patterns, reducing the posterior displacement of both femoral condyles over the tibial-base plate, which was considered 3
ACCEPTED MANUSCRIPT responsible for the described complications.
2. Methods 2.1. Study Design In the present study, 16 patients implanted with a bi-cruciate stabilized TKA (Journey II BCS Knee System, Smith & Nephew Inc., Memphis, TN, USA) in a single center were selected and
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included in group A. Inclusion criteria were as follows: TKA implanted for symptomatic primary knee osteoarthritis, age > 18 and < 75 years, body mass index (BMI) < 40, no prior history of joint replacement of the affected side, no ligamentous incompetency necessitating higher levels of
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constrain and complete recovery of knee range of motion after the operation. At an average 8
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months post-operatively (min. 3 months, max. 13 months) patients were asked to undergo fluoroscopic examination of the operated knee. Written informed consent was signed by all subjects
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prior to being included in the study, which was approved by the local Institutional Review Board. The cohort included 3 males and 13 females, with a mean age of 69.3 years (standard deviation, SD - 10.1, min. 59, max. 82) (Table 1). The right knee was treated in 9 cases, the left knee in 7. None of
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the patients included in the study reported post-operative joint infection, nor severe instability. As in the previously published study [11], all prostheses were implanted by the same senior surgeon,
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using an image-free knee navigation system (Stryker-Leibinger, Freiburg, Germany), performing a
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standard medial parapatellar approach and aiming a neutral mechanical coronal limb alignment. Only the deep fibers of medial collateral ligament were released routinely to achieve a better joint exposure. No other ligamentous releases were performed in any of the examined patients. Patella was resurfaced and the prosthetic components were cemented in all cases. Passive flexion-extension
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range of motion (RoM) was recorded pre-operatively and before video-fluoroscopy examination. Clinical assessment was performed using the International Knee Society (IKS) Score [12] pre-
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operatively and at the time of fluoroscopy investigation. Occurrence of ITB friction syndrome was recorded post-operatively. During fluoroscopy assessment patients were asked to perform three activities of daily living, including two closed chain motions, stair climbing and chair rising and one open chain movement, leg extension against gravity. For stair climbing, three 21cm-high steps were used. To assess stepping up, only the first step was used to perform three consecutive up/down cycles where the ascent phase was captured. For the rising, chair height was set specifically for each patient in order for him or her to begin with the knee flexed at about 90°. Also in this task, only the ascent phase was analyzed. For the extension against gravity task, patients were examined in a semi-supine position (i.e. sitting at 45°), with their knee hanging as flexed as possible over the end of the 4
ACCEPTED MANUSCRIPT examination chair (Figure 1). Data collection and analysis procedures were as previously reported [11, 13, 14] and included the use of a standard flat panel detector (Opera Swing, GMM S.p.a, Italy) with a frame rate of 15 images per second. The implant surface model was projected onto each fluoroscopic image, determining its threedimensional position and orientation by an iterative procedure aimed at matching the implant silhouette with the silhouette of the subject’s implant components [15] (Figure 2). Previous validation work showed that 3D position and orientation of the metal prosthesis
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components has an accuracy better than 0.5 mm and 1°, respectively [15, 16]. The implant landmark-based coordinate system of femoral and tibial components’ CAD models was determined
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with standard conventions [17]. Condylar contacts were assumed on the medial and lateral
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compartments as the two pairs of points at minimum distance between the femoral prosthetic condyles and the tibial base-plate [18, 19]. The positions of these contact points (CPs) were then
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expressed for every knee flexion degree, onto the tibial base-plate reference frame in terms of percentage locations over its anterior-posterior (A/P) length, thus irrespective of different sizes: 0% and 100% corresponded to the most anterior and most posterior location, respectively. Patterns of
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A/P motion of the CPs were therefore obtained independently for the medial and lateral condyles. For each patient and motor task, the medial and lateral CP coordinates were determined and plotted
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versus the knee flexion angle. Also, the difference between A/P locations of the CPs at maximum extension and flexion was considered the posterior femoral rollback (PFR) [20]. Contact-line
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rotation, defined as rotation of the line connecting the medial and lateral CP with respect to the medio-lateral axis on the tibial transverse plane, was calculated for each flexion angle, but here, it has been reported over predefined flexion angles with 10° increments.
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Kinematics data for the closed-motion motor tasks (chair rising and stair climbing) relative to the first-generation knee system were obtained from a fluoroscopy-based study by the senior author
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with the same examination and acquisition methodology [11]. Patients from the previously published study were included in group B.
2.2. Implant features The recently introduced knee system brought design adjustments aiming to limit the predecessor’s clinical complications. In particular, the lateral and medial anterior flange of the femoral component were reduced in thickness and tapered at the edges, with aim to decrease tension forces on the ITB, the width decreased to limit implant overhang. Changes were also made to the tibial post, which was placed anteriorly and designed taller than its predecessor, to reduce the risk of knee dislocation. The kinematic pattern of the new design was planned through virtual simulating tests into a 5
ACCEPTED MANUSCRIPT validated musculoskeletal modeling system (LifeMod/KneeSIM; LifeModeler, Inc., San Clemente, CA, USA) [21].
2.3. Statistical Analysis Descriptive statistics such as mean, SD and range were calculated for each variable. Student t-tests were applied to compare the mean of each variable between the two sets of data relative to each
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prosthetic design. P values were two-sided and considered significant if smaller than 0.05.
3. Results
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3.1. In-vivo kinematics
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Consistent kinematic motions were observed for all patients and for each motor task, with no abnormal patterns in any of the examined knees. The femur showed an overall external rotation
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relative to the tibia from extension to flexion in all three examined motor tasks (Figure 3). Not all second-generation BCS knee systems exhibited screw-home mechanism, with femoral internal rotation in full extension. However, all patients displayed femoral component sharp external
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rotation in the first degrees of knee flexion and all the examined axial rotation patterns were similar. Values of femoral external rotation, based on the tibial plate-embedded coordinate system, at
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minimal and maximal knee flexion (0°-80°), are reported in Table 2. A larger posterior displacement of the lateral condyle compared to the medial was observed in
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function of knee flexion in all the examined tasks. The average A/P displacements of the medial and lateral condylar CP are reported for the three investigated tasks in Table 2 and Figure 4. In the three examined tasks the medial condyle CPs were placed in the central portion of the tibial
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base-plate reference frame, showing a progressive posterior translation from 0° to 15° of knee flexion, with a successive anterior translation from 15° to 55° of knee flexion and an ultimate slight
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posterior translation from 55° to 80°. The lateral condyle CPs instead demonstrated a posterior placement in the tibial base-plate reference frame throughout knee flexion movement. At full extension, the lateral CPs were located in the central portion of the tibial base-plate and showed a posterior displacement up to approximately 15° of knee flexion, followed by a phase of anterior translation, from 15° to 45° and a successive posterior translation from 45° to 80° of knee flexion (Figure 5 and Figure 6). No notable kinematic differences were reported between close (chair rising and stair climbing) and open chain (leg extension) motions.
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ACCEPTED MANUSCRIPT 3.2. Group A vs Group B in-vivo kinematics comparison The in-vivo kinematics of the two designs was compared during closed chain motions. Surgical techniques and methods of analyses were consistent between the two study designs. In both activities the two total knee systems showed similar kinematic patterns of axial rotation, with progressive femoral external rotation with knee flexion. Over the flexion arc, the prostheses in group A demonstrated reduced absolute values of femoral external rotation during knee flexion and a more neutral position in full extension compared to group B, which reported values of femoral
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component internal rotation (Table 3, Table 4 and Figure 7).
Reduced absolute values of A/P translation of the CP on the medial and lateral compartments were
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reported in both tasks by group A compared to group B (Table 3 and Table 4).
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The group B motion patterns were consistently posteriorly directed with knee flexion in both compartments, implying significant PFR. The recent knee system’s kinematics instead, is
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characterized by a relatively constant positioning of the medial CP across the central portion of the tibial base plate and by a posterior displacement of the lateral CP in the first 20° of knee flexion, followed by a small anterior translation in the central region of knee flexion and then a slight
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posterior translation after 60-65° of knee flexion. (Figure 8, Table 3 and Table 4). No differences were reported between the two groups relative to pre- and post-operative RoM and post-operative clinical outcome. Statistically significant differences were described for the pre-
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operative “Knee” and “Function” IKS Score domains (P<0.05), with lower scores reported in group
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A (Table 1). No cases of ITB friction syndrome were recorded. Statistically significant differences between the first and second-generation designs’ kinematics were reported in both motor tasks. No significant differences were observed in chair rising range of
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axial rotation and in stair climbing absolute displacement of the lateral condyle at maximal
4. Discussion
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extension (Table 3 and Table 4).
The first-generation of total knee system analyzed in the present study was introduced as the knee design which could replicate the function of normal joint, through a dual cam-post mechanism substituting both the cruciate ligaments and permitting to achieve deep flexion by preserving knee rotation and posterior femoral translation with flexion [22, 23, 24]. In addition, its polyethylene insert geometry proposed to guide posterior motion of the medial and lateral condyles in order to mimic the kinematics of the natural knee in flexion. Several studies confirmed that the implant’s kinematic behaviour was profoundly guided by the cam-post mechanism and the bearing gemoetriy, as intended by the designer [4, 7, 23, 24, 25], but daily practice highlighted significant clinical 7
ACCEPTED MANUSCRIPT complications. In particular, Luyckx et al. described symptoms of ITB traction syndrome in 7.2% of a large cohort of patients at a mean of 6 months follow-up. After rehab, pain during flexion persisted in 2% of them, resulting in surgical ITB release. The authors attributed the symptom to the large translation of the medial condyle and to the unrestrained posterior displacement of the lateral condyle, coupled with excessive femoral external rotation with progressive joint flexion [26], responsible of increased eccentric loading of the ITB [8]. In addition, Arnout et al. reported complications associated with knee dislocation [9], occurring during varus-flexion or flexion-
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rotation motions. Such movements allowed the femoral cam to jump over the relatively short tibial post. Digennaro et al. in their retrospective study comparing two designs, explained the high
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incidence of post-operative stiffness in the study total knee system, with the excessive femoral
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rollback, responsible of mechanical stress on the capsule and soft tissue structures [10]. The introduction on the market of the second-generation design was described as the evolutionary
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step towards natural motion in TKA. In-vitro results confirmed the design change claims of reduced stress on the ITB and desired natural knee kinematics, with posterior displacement of the lateral condyle and relatively reduced translation of the medial condyle with flexion. Such kinematic
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patterns appeared to contrast with the displacements observed for the predecessor, exceeding those of the un-operated joint [25]. Recent literature comparing healthy and replaced knees with the
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second-generation BCS design during weight bearing activities, confirmed the designer’s purpose of kinematic similarities between the BCS knee replacement and the native knee. In particular,
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similar patterns of condyle translation and axial rotation were reported during early flexion and beyond 90° of knee flexion. Different behaviors were described in full extension – absent femoral internal rotation due to anterior cruciate ligament resection in the BCS knee – and in the transition
native joint [26].
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phase (30°-60° of flexion), with a negligible displacement of femoral condyles compared to the
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The objective of the present study was to confirm the kinematic purposes relative to the motion of the second-generation of BCS total knee system (group A), through an in-vivo evaluation of the kinematics of patients implanted with this system during activities of daily living by means of video-fluoroscopy. Results were compared with those achieved by patients implanted with the firstgeneration TKA (group B) undergoing the same investigation, as described in previously published study [11]. The most important finding of the present research is the confirmation that the design adjustments proposed on the examined total knee system, have implications in implanted knee’s kinematic behaviour. Fluoroscopy data confirm the hypothesis that the design changes between the first and the second-generation total knee system plays a role in the modification of the in-vivo knee 8
ACCEPTED MANUSCRIPT kinematic pattern during closed-chain motions. In particular, similar configurations of axial rotation of the femoral component with flexion are a characteristic of both designs. However, the inherent screw-home mechanism of the group B cohort, which maintained a relative posterior and internally rotated position in full extension, was modified towards a more anterior rotational placement of the femoral component in full extension in group A (Figure 7). Not all second-generation BCS knee systems exhibited screw-home mechanism, with femoral internal rotation in full extension. Regarding the displacement of the CPs on the tibial plateau, the prostheses in group A demonstrated
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reduced translation of both the medial and lateral femoral condyles compared to group B in closed chain motions (Table 3 and Table 4). Moreover, the medial CP translation reported by group A was
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more similar to that described by Komistek for the normal knee [7]. This finding is in contrast with
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recent observations, describing a progressive posterior translation of the medial femoral condyle after 60° of knee flexion in the BCS compared to the healthy joint [26].
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In terms of absolute location, the lateral CP in the re-designed prosthesis, together with a reduced posterior displacement, showed a more anterior position on the tibial-base plate embedded coordinate system as compared to group B at maximal flexion. These results represent the
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kinematic confirmation of the design adjustments of the second-generation prosthesis and find a confirmation in recent publication relative to BCS kinematics in weight bearing conditions.
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The analysis of open and close chain motions was performed in order to investigate the influence of muscle activity and loading conditions on replaced knee kinematics. Surprisingly, no significant
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kinematic differences were described for open and close chain motions [27, 28], demonstrating that muscular activity and weight bearing conditions, do not significantly modify the kinetic patterns of the examined knee system. It was hypothesized that the high SD ranges in all the performed
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analysis influences this finding. The high range of SD itself was explained by the reduced constrain in the redesigned prosthesis compared to its predecessor and leading to a “less” guided motion of
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the femur during knee flexion. Such design feature allows the patient to find the best equilibrium, balancing the external and internal forces, without increasing soft tissue strain. The present study is limited by several factors, including the small number of patients included and the absence of sample size calculation and randomization. Second, single-plane fluoroscopy imaging has uncertainties on the medio-lateral translations. Third, comparison with the previously reported study is indirect and with variable examination time point. Even though the analysis was performed based on analogue examination conditions and with similar shape-matching techniques and software, differences in kinematic activities, as well as inter-individual variability in 3D positioning of the components onto each fluoroscopic image still remain and inevitably affects the investigation and its conclusion. Moreover, implants’ coordinate system is based on femoral and 9
ACCEPTED MANUSCRIPT tibial components CAD models (implant landmarks-based coordinate system) and not on femur and tibia bony anatomical landmarks. This leads to the description of the relative motion of femoral and tibial component one with respect to the other, and not necessarily to the bone kinematics of femur and tibia. Last, the study lacks correlation between patient-reported outcome and satisfaction and specific knee kinematics. To overcome this limitation, a prospective trial would be useful to evaluate the clinical and functional outcome of the examined total knee system. The resulting data
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would tell more about the influence of design changes over patients’ satisfaction.
5. Conclusions
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The design adjustments performed onto the second-generation prosthesis to limit excessive
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posterior displacement of the femoral condyles, as well as femoral component rotation in weightbearing conditions, contributed to modify replaced knee’s kinematics during daily living activities,
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as confirmed by fluoroscopy data.
Acknowledgements
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This research did not receive any specific grant from funding agencies in the public, commercial, or
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not-for-profit sectors.
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ACCEPTED MANUSCRIPT Table 1 Demographic and clinical data of the two cohorts of patients. The data reported in Journey BCS column are derived from a previously published study [5]. International Knee Society (IKS) score is reported for both “Knee” and “Function” sections, pre- and post-operatively. Values are reported as mean (standard deviations SD, min., max.). n.s.: not statistically significant. RoM: Range of
Group A 16
Age (years)
69.3 (SD 10.1, min. 59, max. 82) 3 / 13
-
68.2 (SD 10.0, min. 58, max. 79)
n.s.
4 / 12
-
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Gender (male/female)
P-value
16
SC
Number of patients
Group B
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Parameter
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Motion.
109.6° (SD 10.6, min. 90°, max. 135°)
116.4° (SD 9.9, min. 100°, max. 135°)
n.s.
Post-operative RoM
115.2° (SD 12.1, min. 90°, max. 130°)
118.8° (SD 11.3, min. 90°, max. 130°)
n.s.
Pre-operative IKS “Knee”
38.0 (SD 14.6, min. 25, max. 71)
49.0 (SD 12.0, min. 25, max. 63)
0.0268
Pre-operative IKS “Function”
42.4 (SD 8.1, min. 33, max. 69)
50.7 (SD 9.4, min. 35, max. 70)
0.0120
Post-operative IKS “Knee”
93.2 (SD 6.4, min. 80, max. 100)
94.9 (SD 5.6, min. 83, max. 100)
n.s.
Post-operative IKS “Function”
91.4 (SD 7.1, min. 79, max. 100)
90.7 (SD 9.6, min. 70, max. 100)
n.s.
AC
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Pre-operative RoM
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ACCEPTED MANUSCRIPT Table 2 Average femoral external rotation and A/P displacements of the medial and lateral condylar CP are reported for the three investigated tasks from knee extension to flexion. Values are reported as mean (standard deviations SD, min., max.).
Femoral Chair Rising
Stair Climbing
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displacement
Leg Extension
Range of Axial 12.2 (SD 10.2, min. 2.9, max. 11.8)
5.1 (SD 9.4, min. 1.6, max. 19.9)
4.0 (SD 6.7, min. 0.6, max. 8.8)
5.3 (SD 8.0, min. 1.3, max. 9.6)
4.9 (SD 5.2, min. 2.9, max. 8.7)
11.0 (SD 4.5, min. 1.0, max. 14.2)
5.6 (SD 7.3, min. 2.2, max. 11.0)
8.2 (SD 5.0, min. 4.8, max. 14.4)
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rotation (°)
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A/P Medial CP (mm)
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(mm)
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A/P Lateral CP
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7.0 (SD 9.7, min. 2.5, max. 17.0)
ACCEPTED MANUSCRIPT Table 3 Comparison of fluoroscopy data relative to group A and group B, during chair rising motion. Values are reported as mean (standard deviations SD, min., max.). n.s.: not statistically significant; PFR: posterior femoral rollback.
Chair Rising – Mean (SD, min., max.) Group B
PT
Group A (n = 16)
(n = 16)
Range of Motion (°)
0 - 80
A/P Medial CP (mm)
4.0 (SD 6.7, min. 0.6, max. 8.8)
10.0 (SD 2.6, min. -7.7, max. 2.3)
0.0023
A/P Lateral CP (mm)
11.0 (SD 4.5, min. 1.0, max. 14.2)
18.5 (SD 3.0, min. -15.3, max. 3.1)
< 0.0001
A/P Medial CP (% Tibial size)
7.8 (SD 13.4, min. 1.1, max. 18.4)
18.5 (SD 6.1, min. 32.9, max. 55.9)
0.0068
A/P Lateral CP (%Tibial size)
22.0 (SD 9.5, min. 1.8, max. 29,5)
43.8 (SD 6.5, min. 14.0, max. 57.8)
< 0.0001
Range of Axial Rotation (°)
12.2 (SD 10.2, min. 2.9, max. 11.8)
15.8 (SD 4.4, min. 7.3, max. 21.7)
n.s.
NU
SC
RI
0 - 90
P-value
MA
A/P Medial CP (%Tibial size)
-
48.0 (SD 4.9)
55.9 (SD 7.9)
0.0019
At reached max flexion (°)
50.7 (SD 5.6)
35.8 (SD 5.6)
< 0.0001
48.0 (SD 5.5)
57.8 (SD 6.7)
< 0.0001
70.0 (SD 4.0)
14.2 (SD 4.7)
< 0.0001
At reached max extension (°)
-0.6 (SD 4.9)
-4.2 (SD 5.3)
n.s.
At reached max flexion (°)
11.6 (SD 5.2)
11.0 (SD 6.0)
n.s.
1.1 (SD 5.2)
8.9 (SD 3.5)
< 0.0001
11.0 (SD 4.5)
18.5 (SD 2.6)
< 0.0001
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At reached max extension (°)
At reached max extension (°)
Medial PFR Lateral PFR
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Axial Rotation (°, external +)
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At reached max flexion (°)
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A/P Lateral CP (%Tibial size)
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ACCEPTED MANUSCRIPT Table 4 Comparison of fluoroscopy data relative to group A and group B, during stair climbing motion. Values are reported as mean (standard deviations SD, min., max.). n.s.: not statistically significant; PFR: posterior femoral rollback
Stair Climbing – Mean (SD, min., max.) Group B
PT
Group A
P-value
(n = 16)
0 - 70
A/P Medial CP (mm)
5.3 (SD 8.0, min. 1.3, max. 9.6)
A/P Lateral CP (mm)
5.6 (SD 7.3, min. 2.2, max. 11.0)
0 - 70
-
9.7 (SD 3.0, min. -6.0, max. 3.7)
0.0482
14.3 (SD 3.5, min. -10.6, max. 3.5)
0.0002
SC
Range of Motion (°)
RI
(n = 16)
10.9 (SD 16.3, min. 2.6, max. 21.3)
23.3 (SD 6.4, min. 35.2, max. 58.5)
0.0082
A/P Lateral CP (%Tibial size)
10.8 (SD 14.6, min. 4.9, max. 21.1)
32.7 (SD 8.0, min. 25.1, max. 58.8)
< 0.0001
5.1 (SD 9.4, min. 1.6, max. 19.9)
13.0 (SD 4.0, min. 5.6, max. 21.6)
0.0043
58.5 (SD 4.8)
< 0.0001
38.9 (SD 5.9)
0.0001
53.7 (SD 11.3)
57.3 (SD 7.3)
n.s.
64.5 (SD 3.3)
25.6 (SD 6.3)
< 0.0001
7.6 (SD 9.1)
-4.0 (SD 1.0)
< 0.0001
10.5 (SD 4.0)
6.5 (SD 4.8)
0.0157
3.2 (SD 6.0)
8.5 (SD 2.0)
0.0022
5.6 (SD 7.3)
14.3 (SD 3.4)
0.0002
MA
Range of Axial Rotation (°)
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A/P Medial CP (% Tibial size)
A/P Medial CP (%Tibial size)
40.2 (SD 8.1)
At reached max flexion (°)
47.0 (SD 4.5)
At reached max extension (°)
Axial Rotation (°, external +)
CE
At reached max flexion (°)
AC
At reached max extension (°) At reached max flexion (°) Medial PFR Lateral PFR
PT E
A/P Lateral CP (%Tibial size)
D
At reached max extension (°)
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ACCEPTED MANUSCRIPT References 1. Jones CA, Beaupre LA, Johnston DW, Suarez-Almazor ME. Total joint arthroplasties: current concepts of patient outcomes after surgery. Rheum Dis Clin N Am 2007;33:71–86 2. Noble PC, Conditt MA, Cook KF, Mathis KB. The John Insall Award: patient expectations affect satisfaction with total knee arthroplasty. Clin Orthop Relat Res. 2006;452:35–43 3. Noble PC, Gordon MJ, Weiss JM, Reddix RN, Conditt MA, Mathis KB. et al. Does total knee replacement restore normal knee function? Clin Orthop Relat Res. 2005;431:157–165
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4. Weiss JM, Noble PC, Conditt MA, Kohl HW, Roberts S, Cook KF, Gordon MJ, Mathis KB. What functional activities are important to patients with knee replacements? Clin Orthop
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Relat Res. 2002;404:172–188
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5. Victor J, Bellemans J. Physiologic kinematics as a concept for better flexion in TKA. Clin Orthop Relat Res. 2006;452:53–58.
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6. Steinbrück A, Schröder C, Woiczinski M, Fottner A, Pinskerova V, Müller PE, Jansson V. Femorotibial kinematics and load patterns after total knee arthroplasty: An in vitro comparison of posterior-stabilized versus medial-stabilized design. Clin Biomech.
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2016;33:42-48. doi: 10.1016/j.clinbiomech.2016.02.002. 7. Komistek RD, Dennis DA, Mahfouz M. In-vivo fluoroscopic analysis of the normal human
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knee. Clin Orthop Relat Res. 2003;410:69–81. 8. Luyckx L, Luyckx T, Bellemans J, Victor J. Iliotibial band traction syndrome in guided
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motion TKA: A new clinical entity after TKA. Acta Orthop. Belg. 2010;76:507–512. 9. Arnout N, Vandenneucker H, Bellemans J. Posterior dislocation in total knee replacement: a price for deep flexion? Knee Surg Sports Traumatol Arthrosc 2006;19(6):911–913.
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10. Digennaro V, Zambianchi F, Marcovigi A, Mugnai R, Fiacchi F, Catani F. Design and kinematics in total knee arthroplasty. Int Orthop. 2014;38(2):227–233.
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11. Catani F, Ensini A, Belvedere C, Feliciangeli A, Benedetti MG, Leardini A, Giannini S. In vivo kinematics and kinetics of a bi-cruciate substituting total knee arthroplasty: A combined fluoroscopic and gait analysis study. J Orthop Res. 2009;27(12):1569–1575. 12. Insall JN, Dorr LD, Scott RD, Scott WN. Rationale of the Knee Society clinical rating system. Clin Orthop Relat Res. 1989;248:13–14. 13. Catani F, Belvedere C, Ensini A, Feliciangeli A, Giannini S, Leardini A. In-vivo knee kinematics in rotationally unconstrained total knee arthroplasty. J Orthop Res. 2011;29(10):1484–1490.
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ACCEPTED MANUSCRIPT 14. Fantozzi S, Catani F, Ensini A, Leardini A, Giannini S. Femoral rollback of cruciateretaining and posterior-stabilized total knee replacements: in vivo fluoroscopic analysis during activities of daily living. J Orthop Res. 2006;24:2222–2229. 15. Banks SA, Hodge WA. Design and activity dependence of kinematics in fixed and mobilebearing knee arthroplasties. J Arthroplasty 2004;19:809–816. 16. Victor J, Banks SA, Bellemans J. Kinematics of posterior cruciate ligament- retaining and substituting total knee arthroplasty. A prospective randomised outcome study. J Bone Joint
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Surg [Br] 2005;87-B:646–655.
17. Grood ES, Suntay WJ. A joint coordinate system for the clinical description of three-
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dimensional motions: application to the knee. J Biomech Eng. 1983;105(2):136-44.
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18. Tanaka Y, Nakamura S, Kuriyama S, Ito H, Furu M, Komistek RD, Matsuda S. How exactly can computer simulation predict the kinematics and contact status after TKA? Examination
10.1016/j.clinbiomech.2016.09.006.
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in individualized models. Clin Biomech. 2016;39:65-70. doi:
19. Banks S, Bellemans J, Nozaki H, Whiteside LA, Harman M, Hodge WA. Knee motions
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during maximum flexion in fixed and mobile-bearing arthroplasties. Clin Orthop Relat Res. 2003;410:131–138.
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20. Nozaki H, Banks SA, Suguro T, Hodge WA. Observations of femoral rollback in cruciateretaining knee arthroplasty. Clin Orthop Relat Res. 2002;404:308–314.
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21. Johal P, Williams A, Wragg P, Hunt D, Gedroyc W. Tibio-femoral movement in the living knee. A study of weight bearing and non-weight bearing knee kinematics using
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‘interventional’ MRI. J of Biomech 2005;38(2):269–276. 22. Kuroyanagi Y, Mu S, Hamai S, Robb WJ, Banks SA. In Vivo Knee Kinematics During Stair and Deep Flexion Activities in Patients With Bicruciate Substituting Total Knee
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Arthroplasty. J Arthroplasty 2012;27(1):122-128. 23. Arbuthnot J and Brink R. Assessment of the antero-posterior and rotational stability of the anterior cruciate ligament analogue in a guided motion bi-cruciate stabilized total knee arthroplasty. J Med Eng Technol. 2009;33: 610–615 24. Christen, B., Neukamp, M., Aghayev, E. Consecutive series of 226 journey bicruciate substituting total knee replacements: early complication and revision rates. BMC Musculoskelet Disord. 2014;15: 395. doi: 10.1186/1471-2474-15-395. 25. Victor J, Mueller JKP, Komistek RD, Sharma A, Nadaud MC, Bellemans J. In Vivo Kinematics after a Cruciate-substituting TKA. Clin Orthop Relat Res. 2010;468:807–814.
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ACCEPTED MANUSCRIPT 26. Grieco TF, Sharma A, Dessinger GM, Cates HE, Komistek RD. In Vivo Kinematic Comparison of a Bicruciate Stabilized Total Knee Arthroplasty and the Normal Knee Using Fluoroscopy. J Arthroplasty 2018;33(2):565-571. doi: 10.1016/j.arth.2017.09.035. 27. Yoshiya S, Matsui N, Komistek RD, Dennis DA, Mahfouz M, Kurosaka M. In Vivo Kinematic Comparison of Posterior Cruciate-Retaining and Posterior Stabilized Total Knee Arthroplasties Under Passive and Weight-Bearing Conditions. J Arthroplasty 2005;20(6):777-783
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28. Horiuchi H, Akizuki S, Tomita T, Sugamoto K, Yamazaki T, Shimizu N. In vivo kinematic analysis of cruciate-retaining total knee arthroplasty during weight-bearing and non-weight-
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bearing deep knee bending. J Arthroplasty 2012;Jun;27(6):1196-1202.
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doi:10.1016/j.arth.2012.01.017
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ACCEPTED MANUSCRIPT Highlights Total knee arthroplasty kinematics of two systems was analyzed by means of fluoroscopy. Comparison includes 16 new total knee designs and 16 old systems, as described in a previous study. Similar patterns of knee axial rotation were described between the two total knee systems. As proposed, the new system obtained reduced medial and lateral displacement compared to
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the old. Design changes in the redesigned prosthesis contributed to modify its in-vivo knee
AC
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MA
NU
SC
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kinematics.
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ACCEPTED MANUSCRIPT Figures Legend Figure 1: fluoroscopy system tracking a subject’s knee during three activities of daily living, including (A) chair rising, (B) stair climbing and (C) leg extension. Figure 2: 3D-to-2D CAD model-to-flat panel image registration was used to determine the kinematics of knees implanted with a bi-cruciate stabilized (BCS) total knee system during three activities of daily living.
PT
Figure 3: Femoral component axial rotation (°) relative to the tibial component in closed and openchain motor tasks at different knee flexion degrees.
RI
Figure 4: A/P translation (mm) of the medial and lateral femoral condyles on the tibial component
representative of femoral condyle anterior translation.
SC
in closed and open-chain motor tasks at different knee flexion degrees. Ascending curves are
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Figure 5: A/P translation (%) of the medial and lateral femoral condyles on the tibial component in terms of absolute placement in the three motor tasks at different knee flexion degrees. Figure 6: Average contact locations overimposed on a right tibial polyethylene insert CAD model.
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Average contact locations on the medial and lateral side are shown for 20° flexion increments for each motor task.
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Figure 7: Patterns of femoral axial rotation (°) of the two examined total knee designs in closed chain motor tasks (Chair Rising and Stair Climbing) at different knee flexion degrees. * Statistically
PT E
significant difference between Group A and Group B. Figure 8: Patterns of A/P translation of the medial and lateral femoral condyles of the two examined total knee systems in closed chain motor tasks (Chair Rising and Stair Climbing) at different knee
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flexion degrees. Values are given in terms of femoral condyles absolute placement on the tibial
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component. * Statistically significant difference between Group A and Group B.
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Figure 1
Figure 2
Figure 3
Figure 4
Figure 5
Figure 6
Figure 7
Figure 8