Mobile-bearing total knee arthroplasty: More rotation is evident during more demanding tasks Arthur W. Z¨urcher, Kim van Hutten, Jaap Harlaar, Caroline B. Terwee, G.H. Rob Albers, Ruud G. P¨oll PII: DOI: Reference:
S0968-0160(14)00108-2 doi: 10.1016/j.knee.2014.05.007 THEKNE 1912
To appear in:
The Knee
Received date: Revised date: Accepted date:
19 September 2013 5 May 2014 18 May 2014
Please cite this article as: Z¨ urcher Arthur W., van Hutten Kim, Harlaar Jaap, Terwee Caroline B., Rob Albers GH, P¨oll Ruud G., Mobile-bearing total knee arthroplasty: More rotation is evident during more demanding tasks, The Knee (2014), doi: 10.1016/j.knee.2014.05.007
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ACCEPTED MANUSCRIPT Mobile-bearing total knee arthroplasty: more rotation is evident during more demanding tasks
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Arthur W. Zürcher,1 Kim van Hutten,2 Jaap Harlaar,3 Caroline B. Terwee,4 G.H. Rob Albers,5
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Ruud G. Pöll6
Department of Orthopedic Surgery, Diakonessen Hospital, Bosboomstraat 1, 3582 KE
Utrecht, the Netherlands
Department of Rehabilitation Medicine, VU University Medical Center, Amsterdam, the
Netherlands 3
Department of Rehabilitation Medicine and Research Institute MOVE, VU University
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Medical Center, Amsterdam, the Netherlands 4
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Department of Epidemiology and Biostatistics and EMGO Institute of Health and Care
Research, VU University Medical Center, Amsterdam, the Netherlands Department of Orthopedic Surgery, AVE Orthopaedic Clinics, Huizen, the Netherlands
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Department of Orthopedic Surgery, Slotervaart Hospital and VU University Medical Center,
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Amsterdam, the Netherlands
Keywords: mobile-bearing, TKA, rotation, sit-to-walk
Correspondence to: Arthur W. Zürcher Tafelbergerhout 32 3845 JD Harderwijk The Netherlands T: +31.6.51388478 E-mail: [email protected]
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ACCEPTED MANUSCRIPT Abstract Background: Some reports showed few but significant more axial femorotibial rotation in
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favor of mobile-bearing (MB) versus fixed-bearing (FB) total knee arthroplasty (TKA),
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mostly during knee bend fluoroscopic studies. The goal of the current study was to submit a
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MB and FB group of TKA patients to a turning activity, in which additional rotation was to be expected.
Methods: Two consecutive cohorts of patients after TKA (10 FB and 11 MB knees in a total
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of 18 patients) were assessed using motion analysis five year postoperatively, while
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performing gait and sit-to-walk (STW) movements with and without turning steps. Results: Mean range of rotation in the FB group increased from 9.7° during gait, to 11.7° during STW straight, and to 14.3° during STW turning. Mean range of rotation in the MB
during STW turning.
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group increased from 13.4° during gait to 21.0° during STW straight, and stayed at 21.1°
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Conclusions: Too many uncontrolled variables in the current study hinder a meaningful discrimination of MB from FB TKA rotation. However, the study does illustrate how more
variants.
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demanding task loads could be helpful in exploring the geometric constraints of TKA
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ACCEPTED MANUSCRIPT Introduction A large variety exists in total knee arthroplasty (TKA), for instance regarding condylar
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geometry design, posterior cruciate retention versus substitution, bearing mobility, bone
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versus ligament referenced placement, cemented versus uncemented placement, with or
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without patella resurfacing etc. As far as bearing mobility concerns, fixed-bearings (FB) are most frequently used. This is probably because superior clinical results of mobile-bearing (MB) designs are still lacking [1-3], wear rate results inconclusive [4-6], and kinematic
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differences small [7-9]. The rationale of MB lies originally in being part of the low-contact-
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stress concept to reduce loosening and wear. Herein the use of a meniscal or rotating bearing element allowed both mobility and congruency, producing both low constrained forces and low contact stresses [10]. Several in vivo fluoroscopic studies compared mobile- to fixed-
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bearing variants [7-9,11-13] half of them showing small but significant more axial femorotibial rotation (’rotation’) in the MB group (Table 1). More rotation may strictly not be
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relevant for the functioning of the low-contact-stress concept, but the question is raised, whether it is even desirable to have a closer to natural amount of rotation in TKA.
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More rotation may assist in more complex daily life activities, although beyond a certain threshold it could preclude a clinically undesirable instability. In vivo fluoroscopic analysis of normal knees showed that only 11 degrees of rotation was used during gait and around 15 degrees during higher demanding tasks, such as a deep knee bend and chair sit/rise [14]. In Dennis’ multicenter knee bend study all TKA variants showed below 10 degrees of rotation, except for anterior cruciate retaining TKA [11]. It is questionable whether the possibilities and restrictions of MB and FB TKA, and their comparison to the normal knee, should not be tested while performing more challenging tasks. We demonstrated in a motion analysis study an increase of rotation from 14 to 21 degrees in the normal knee by adding turning steps to a sit-to-walk task [15].
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ACCEPTED MANUSCRIPT We expected that this additional knee rotation by adding turning elements to a task load would also occur in our TKA patients. This assumption was supported by a finite element
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study showing that rotational load was the primary contributor to TKA mechanics [16]. We
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also hypothesized that a MB variant would have more rotation than a typical FB variant in
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turning activities.
Material and Methods
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Two consecutive cohorts of patients after TKA, 10 FB knees (in 9 patients) and 11 MB knees
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(in 9 patients), underwent gait analysis five years postoperatively between February 2006 and June 2008. The FB cohort was operated on in Hilversum Hospital (currently Tergooi
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Hospital, Hilversum, The Netherlands) receiving a NexGen Complete Knee Solution
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Legacy Posterior Stabilized TKA (Zimmer Inc, Warsaw, IN), while the MB cohort was operated on in Slotervaart Hospital (Amsterdam, The Netherlands) receiving a LCS
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Complete Rotating Platform TKA (DePuy Inc, Warsaw, IN). In the Nexgen knee the posterior ligament (PCL) was substituted and the orientation of saw cuts was bone referenced. In the
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LCS knee the PCL was sacrificed and saw cuts were ligament balance referenced. Otherwise, surgical approach and aftercare in both hospitals were uniform. The local ethical committee in both hospitals gave permission for conducting the study. Inclusion criteria for the study were patients successfully operated for osteoarthritis with a postoperative Knee Society Knee Score of 80 points or more. Exclusion criteria were revision surgery, neurological disorders that interfered with walking, body mass index (BMI) of 30 or more. During the course of the study, the criterion of BMI was eased from 30 to 35 to secure patient enrollment. The patient characteristics regarding gender, age at surgery, side, BMI and interval from surgery to analysis are shown in Table 2. Gender was equally divided in the FB group, whereas the MB group consisted of mainly women. Interval from surgery to gait
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ACCEPTED MANUSCRIPT analysis was 74 months in the FB group an 64 months in the MB group (p = 0.001). Otherwise, there were no statistically significant differences between both groups. Normal
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data were taken from to a prior study, in which fifteen healthy volunteers (six females, nine
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males) participated. Their average age was 33.4 years (range 24-63) and average body mass
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index 23.3 (range 18-25) [15].
Gait analysis took place in the Human Movement Laboratory (Department of Rehabilitation Medicine, VU University Medical Center, Amsterdam, the Netherlands). An OptoTrak
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motion analysis system (model 3020, Northern Digital Inc, Waterloo, Ontario, Canada) was
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used to record the 3D position of active surface markers at a sampling rate of 50Hz. For the tibia a cluster of three markers was strapped over the middle lateral shank. For the femur a cluster of three markers was rigidly attached to an epicondylar frame. The Femoral
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Epicondylar Frame is a validated tool for noninvasive tracking of femoral axial rotation with an error of 3.3 degrees up to 40 degrees of knee flexion [17]. The majority of normal rotation
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took place between 0-45 degrees of knee flexion during knee bending and chair rising in a fluoroscopic study [14]. We found the same in a motion analysis study in healthy patients
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performing chair rises with and without turns; most rotation took place at the end of stance with the knee nearly in extension [15]. Besides that, higher flexion angles would be less relevant to study in TKA, because an increased flexion angle also means loss of condylar congruency [18]. The error for tibial rotation using surface markers is 2 degrees [19]. An open source Matlab software program, BodyMech (www.bodymech.nl), was used to calculate 3D knee kinematics [20]. Tibia and femur were considered to be rigid bodies with a local coordinate system, defined by anatomical points [21]. Coordinates of the two points, where the virtual axis of the device entered the femoral epicondyles, were calculated from the frame markers. The greater trochanter instead of femoral head was used for the femoral longitudinal axis definition. The shank markers were anatomically calibrated using the tibial tuberosity
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ACCEPTED MANUSCRIPT and medial and lateral malleoli. Knee kinematics followed from the relative orientation of the tibia with respect to the femur, while decomposition into Euler angles was applied following
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the Grood and Suntay convention [22].
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The subjects performed four tasks: gait, move from sit-to-walk (STW) straight ahead, STW
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crossoverstep turning and STW sidestep turning. Chair height was adjusted to 90% of the lower leg length. Only the prosthetic knee in the weight bearing leg was measured during stance phase, the contralateral side acting as the swing leg. The tasks were standardized and
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described previously in a study with healthy subjects [15]. Videos are available in the
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electronic version of the current article. The subjects practiced each task until smoothly performed in a natural pace. Three measurements per task were recorded and used for analysis.
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Ranges of rotation during the various tasks were compared between the FB and MB groups. The difference between peak internal and peak external femorotibial rotation was used to
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define range of axial knee rotation. The difference between internal rotation during crossoverstepping and external rotation during sidestepping was used to define overall range
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of rotation for STW turning. An independent t-test was utilized to compare variables (ranges of rotation during gait, STW straight and STW turning) as well as patient characteristics between both groups (FB and MB). Level of significance was set at p = 0.05. The original sample size calculation with power set at 0.80 had revealed a number of 16 patients per group to find a difference of 5 between groups with 5 of variance.
Results During the stance phase of normal gait, the range of rotation in the FB group was with an average of 9.7 degrees (SD 4.2) less than the range of 13.4 degrees (SD 6.7) in the MB group,
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ACCEPTED MANUSCRIPT albeit not to a significant level (Table 3 and 4). The results of non-operated knees in healthy subjects in Table 4 were collected in a prior study [15].
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During STW straight, range of rotation in the FB group was considerably less than in the MB
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group (p = 0.002). In the FB group the average peak internal rotation was 8.8 degrees (SD
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5.5) at 90 percent of stance phase on average (SD 14) and with an average knee flexion angle of 35 percent (SD 6). External rotation was 2.9 degrees (SD 2.5) at 20 percent of stance phase (SD 16) with a knee flexion angle of 65 degrees (SD 15). This accounted for a range of
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rotation of 11.7 degrees (SD 3.6). In the MB group this range was 21.0 degrees (SD 7.3), with
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17.9 degrees (8.0) peak internal rotation at 89 percent stance (SD 12) with 29 degrees knee flexion (SD 8) and 3.2 degrees (SD 2.9) external rotation at 20 percent stance (SD 16) with 65 degrees knee flexion (SD 15).
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STW turning still resulted in less range of rotation for the FB group (p = 0.051). In the FB group the average peak internal rotation was 11.8 degrees (SD 6.2), at 88 percent of stance
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phase (SD 12) with an average of 33 degrees knee flexion angle (SD 6), during crossoverstepping. External rotation during sidestepping was 2.5 degrees (SD 2.1) at 26
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percent stance (SD 24) with 59 degrees knee flexion (SD 20). This accounted for an overall range of rotation of 14.3 degrees (SD 5.4), versus 21.1 degrees (SD 8.5) in the MB group. In this group crossoverstepping resulted in of 19.4 degrees internal rotation (SD 8.6) at 98 percent stance (SD 7) with 30 degrees knee flexion (SD 7), and sidestepping resulted in 1.7 degrees external rotation (SD 2.7) at 24 percent stance (SD 31) with 66 degrees knee flexion (SD 20).
Discussion Significant but small differences in axial femorotibial rotation during knee bending activities in favor of MB TKA were shown in a number of papers [7-9]. In the current study, the
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ACCEPTED MANUSCRIPT difference in rotation was even larger when moving from sit to walk with and without turns. We expected increased differences during a more demanding task, because in a pilot study on
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healthy subjects with non-operated knees range of rotation increased from 14 to 22 degrees by
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adding a turning element to STW.
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STW represents a complex transitional task, which is a merging of a discrete task (rising from a chair) and a rhythmic one (walking) [23]. In the FB group, rotation gradually increased with increased task complexity (gait, STW straight, STW turning) to 14 degrees. In the MB group,
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an increase to 21 degrees in rotation from gait to STW occurred, while no further increase was seen adding turns. Perhaps the low-friction articulation between bearing undersurface and
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tibial component is the reason for this ‘switch on/off’ pattern of rotation in MB knees. Even without the initiation of gait, the sit-to-stand (STS) movement is an important and
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challenging task of daily living that requires relatively large joint torques (and consequently joint load) and accurate balance control [24]. Interestingly, kinematic recovery in STS
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performance was reported at one year after TKA [25] and the necessary coordination appeared not to be different from a control group [26]. To our knowledge, former kinematic
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analysis of the STS movement after TKA was restricted to the sagittal plane only [27-29], while STW after TKA has not been studied at all. A shortcoming in the design of the study is that the LCS and NexGen design features and surgical technique were, except for difference in bearing mobility, not otherwise identical. Also, less rotational constraint in a PCL-retained then in a PCL-substituted FB variant might have been expected [11]. On the other hand, both prostheses were considered to be highly representative for their cohort, being amongst the most implanted artificial knees worldwide. Another possible shortcoming refers to the utilized noninvasive measurement technique, which does not make it possible to assess mobility of the bearing relative to the tibial component in the MB group. Nevertheless, since the concept of low-contact-stress TKA is
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ACCEPTED MANUSCRIPT based on higher congruency between femoral component and bearing uppersurface, one might assume that the larger rotation found in the MB group was due to bearing undersurface
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mobility. This assumption was supported by studies utilizing highly accurate roentgen
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stereometric analysis [7,30]. A third shortcoming is that the study design was not a
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randomized trial, which means that the patient groups may be different in relevant known or unknown variables. The number of females was larger in the MB group than in the FB group,
difference as was found in this study [31].
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but an assumable higher laxity in females could not be held to account for as large a
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The concept of higher articulating congruency combined with bearing rotational mobility has a theoretical advantage of reduced polyethylene wear and improved function [32]. Clinical studies of the LCS knee showed excellent results with MB [33-34], but the superiority over a
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FB design in comparative studies remains unproven [1-3]. One randomized study compared the LCS (MB) to NexGen (FB) with a minimum 10-year clinical and radiological follow-up,
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finding both groups were equally successful [35]. Series of bilaterally operated patients, randomized for FB on one MB on the other side, need to provide even longer-term clinical
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results [36-39]. Kinematic studies are necessary to find support for either concept, although higher amounts of rotation in a MB knee would not necessarily prove the benefit of its concept.
In conclusion, there are too many uncontrolled variables in this study to provide a meaningful contribution on MB versus FB TKA kinematics. A well-controlled randomized trial with MB and FB variants of the same prosthesis would be necessary to do so. We found that a difference in knee rotation between MB and FB becomes apparent, when changing from a relatively simple task to a more demanding task such as getting-up from a chair and start walking with and without turning. The study therefore illustrates that more demanding task loads could be helpful in exploring the geometric constraints of TKA variants.
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Conflict of interest statement
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This study was financially supported by an unrestricted grant from DePuy (Johnson &
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Johnson Medical) and Biomet. Otherwise, all authors have no financial and personal
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relationships with other people or organizations that could inappropriately influence (bias) their work
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31. Almquist PO, Ekdahl C, Isberg PE, Friden T. Knee rotation in healthy individuals related to age and gender. J Orthop Res 2013; 31: 23-28 32. Callaghan JJ, Insall JN, Greenwald AS, Dennis DA, Komistek RD, Murray DW, Bourne RB, Rorabeck CH, Dorr LD. 2001. Mobile-bearing knee replacement: concepts and results. Instr Course Lect 50:431-449. 33. Buechel FF Sr. Long-term followup after mobile-bearing total knee replacement. Clin Orthop Relat Res 2002; 404: 40-50
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37. Kim YH, Kim DY, Kim JS. Simultaneous mobile- and fixed-bearing total knee replacement in the same patients. A prospective comparison of mid-term outcomes using a similar design of prosthesis. J Bone Joint Surg [Br] 2007; 89B: 904-910
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Table 1. Summary of studies comparing axial knee rotation in vivo Reference N Task FB MB p Value Dennis et al., 2004 [11] 212/76* Knee bend NS 7.6 7.6 Ranawat et al., 2004 [8] 20/20 Knee bend 0.01 3.8 7.4 Delport et al., 2006 [7] 10/10 Knee bend < 0.005 2.4 7.5 Shi et al., 2008 [9] 26/30 Passive knee bend < 0.05 5.2 7.9 Liu et al., 2009 [12] 11/7 Squat-to-stand NS 5 5 Wolterbeek et al., 2011 [13] 8/7† Step-up NS 8.3 10.4 N = number of fixed- versus mobile-bearing knees NS = not significant *Refers to posterior-stabilized variant versus posterior cruciate ligament (PCL) sacrificing variant †Refers to multiradius posterior-substituted variant versus multiradius PCL-sacrificing variant
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ACCEPTED MANUSCRIPT Table 2. Patient characteristics
5/5
9/2
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MB group (11 knees)
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3/7 28.8 (3.4) 65.3 (12.3) 74.3 (6.6)
6/5 30.2 (2.9) 62.8 (11.8) 63.9 (4.4)
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Gender Female/male Side Right/left Mean BMI (SD) Mean age at surgery, years (SD) Mean interval from surgery to analysis, months (SD)
FB group (10 knees)
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ACCEPTED MANUSCRIPT Table 3. Individual peak values of internal and external knee rotation in degrees. For each value the knee flexion angle in degrees is presented between brackets
Peak ext
Peak int
Peak ext
Peak int
Peak ext
Peak int
Peak ext
FB1
5.8 (28)
-0.1 (19)
1.7 (42)
-6.0 (47)
1.7 (30)
-5.1 (50)
4.2 (48)
-1.2 (35)
FB2
11.8 (22)
-0.5 (26)
4.2 (36)
-6.2 (51)
6.0 (32)
-5.4 (49)
0.2 (64)
-6.5 (36)
FB3
6.9 (48)
-1.2 (25)
9.2 (33)
-1.7 (74)
17.5 (26)
-1.4 (75)
9.9 (26)
-1.9 (75)
FB4
7.3 (24)
-0.2 (13)
15.3 (21)
0.1 (61)
17.7 (25)
1.1 (57)
11.4 (14)
1.1 (56)
FB5
13.2 (42)
-1.2 (18)
12.6 (36)
-0.1 (69)
14.6 (35)
-2.7 (56)
3.4 (61)
-3.7 (45)
FB6
2.7 (42)
-4.6 (20)
10.5 (31)
-1.5 (75)
13.1 (31)
-1.5 (74)
7.6 (23)
-2.2 (75)
FB7
8.4 (30)
-0.3 (18)
3.7 (40)
-3.1 (84)
m.d.
m.d.
3.5 (86)
-2.5 (43)
FB8
9.9 (37)
1.5 (19)
17.1 (36)
-0.4 (88)
18.7 (44)
-2.1 (87)
12.8 (25)
-0.3 (91)
FB9
14.8 (41)
-4.0 (24)
11.6 (40)
-4.1 (55)
12.1 (39)
-2.5 (75)
2.6 (31)
-3.4 (80)
FB10
2.8 (44)
-2.5 (17)
2.5 (34)
-5.6 (50)
4.8 (35)
-6.1 (53)
1.7 (81)
-4.3 (54)
MB1
7.5 (46)
-3.0 (20)
10.9 (20)
-0.8 (73)
15.5 (24)
1.2 (68)
7.6 (74)
2.8 (32)
MB2
-2.0 (24)
-12.0 (20)
19.6 (27)
-1.2 (77)
26.4 (25)
-0.2 (76)
15.7 (24)
0.0 (79)
MB3
m.d.
m.d.
25.2 (30)
-1.0 (82)
24.4 (29)
-0.3 (87)
19.3 (35)
-1.4 (86)
MB4
19.3 (18)
-3.6 (16)
31.7 (19)
-3.8 (71)
34.2 (20)
-2.6 (69)
20.2 (15)
-1.7 (70)
MB5
10.2 (35)
0.0 (22)
15.8 (32)
-1.3 (85)
15.3 (46)
-1.0 (84)
7.4 (33)
-0.4 (83)
MB6
5.2 (30)
-6.6 (14)
27.1 (30)
-3.4 (61)
29.0 (27)
-2.5 (62)
16.8 (20)
-2.3 (66)
MB7
2.6 (34)
-11.2 (14)
17.9 (33)
-4.8 (65)
21.0 (30)
-2.4 (66)
11.8 (18)
-1.4 (67)
MB8
5.7 (26)
-2.4 (23)
8.7 (29)
-4.8 (60)
5.2 (34)
-5.4 (57)
3.8 (85)
-1.9 (60)
MB9
25.1 (33)
-2.8 (26)
10.9 (48)
-7.9 (36)
12.9 (30)
-3.4 (36)
1.5 (81)
-7.7 (26)
MB10
10.9 (28)
-0.7 (20)
21.5 (24)
1.4 (73)
19.5 (31)
2.1 (73)
13.6 (20)
-0.2 (77)
MB11
8.3 (36)
0.9 (34)
7.4 (31)
-7.1 (71)
10.1 (34)
-6.9 (70)
3.3 (35)
-4.2 (83)
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Peak int
STW, sidestepping
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STW, crossoverstepping
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STW, straight
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Gait
m.d. Missing data
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ACCEPTED MANUSCRIPT MB 13.4 (6.7) 21.0 (7.3) 21.1 (8.5)
Normal
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13.5 (3.9) 20.9 (7.9)
p Value* 0.152 0.002 0.051
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Table 4. Mean ranges of axial knee rotation (SD) FB Gait 9.7 (4.2) Sit-to-walk, straight 11.7 (3.6) Sit-to-walk, turning 14.3 (5.4) * FB versus MB
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ACCEPTED MANUSCRIPT Highlights
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Most in vivo studies on axial knee rotation utilized gait or knee bending tasks Some reports showed few but significant more rotation in mobile-bearing variants of TKA We studied rotation in mobile- and fixed-bearing TKA patients, while performing a sit-to-walk task with and without turning steps The mobile-bearing group showed significant more rotation The study illustrates how higher demanding task loads could be helpful in exploring the geometric constraints of TKA variants
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S0968-0160(14)00108-2 doi: 10.1016/j.knee.2014.05.007 THEKNE 1912
To appear in:
The Knee
Received date: Revised date: Accepted date:
19 September 2013 5 May 2014 18 May 2014
Please cite this article as: Z¨ urcher Arthur W., van Hutten Kim, Harlaar Jaap, Terwee Caroline B., Rob Albers GH, P¨oll Ruud G., Mobile-bearing total knee arthroplasty: More rotation is evident during more demanding tasks, The Knee (2014), doi: 10.1016/j.knee.2014.05.007
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 Mobile-bearing total knee arthroplasty: more rotation is evident during more demanding tasks
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Arthur W. Zürcher,1 Kim van Hutten,2 Jaap Harlaar,3 Caroline B. Terwee,4 G.H. Rob Albers,5
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Ruud G. Pöll6
Department of Orthopedic Surgery, Diakonessen Hospital, Bosboomstraat 1, 3582 KE
Utrecht, the Netherlands
Department of Rehabilitation Medicine, VU University Medical Center, Amsterdam, the
Netherlands 3
Department of Rehabilitation Medicine and Research Institute MOVE, VU University
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Medical Center, Amsterdam, the Netherlands 4
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2
Department of Epidemiology and Biostatistics and EMGO Institute of Health and Care
Research, VU University Medical Center, Amsterdam, the Netherlands Department of Orthopedic Surgery, AVE Orthopaedic Clinics, Huizen, the Netherlands
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Department of Orthopedic Surgery, Slotervaart Hospital and VU University Medical Center,
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Amsterdam, the Netherlands
Keywords: mobile-bearing, TKA, rotation, sit-to-walk
Correspondence to: Arthur W. Zürcher Tafelbergerhout 32 3845 JD Harderwijk The Netherlands T: +31.6.51388478 E-mail: [email protected]
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ACCEPTED MANUSCRIPT Abstract Background: Some reports showed few but significant more axial femorotibial rotation in
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favor of mobile-bearing (MB) versus fixed-bearing (FB) total knee arthroplasty (TKA),
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mostly during knee bend fluoroscopic studies. The goal of the current study was to submit a
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MB and FB group of TKA patients to a turning activity, in which additional rotation was to be expected.
Methods: Two consecutive cohorts of patients after TKA (10 FB and 11 MB knees in a total
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of 18 patients) were assessed using motion analysis five year postoperatively, while
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performing gait and sit-to-walk (STW) movements with and without turning steps. Results: Mean range of rotation in the FB group increased from 9.7° during gait, to 11.7° during STW straight, and to 14.3° during STW turning. Mean range of rotation in the MB
during STW turning.
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group increased from 13.4° during gait to 21.0° during STW straight, and stayed at 21.1°
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Conclusions: Too many uncontrolled variables in the current study hinder a meaningful discrimination of MB from FB TKA rotation. However, the study does illustrate how more
variants.
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demanding task loads could be helpful in exploring the geometric constraints of TKA
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ACCEPTED MANUSCRIPT Introduction A large variety exists in total knee arthroplasty (TKA), for instance regarding condylar
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geometry design, posterior cruciate retention versus substitution, bearing mobility, bone
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versus ligament referenced placement, cemented versus uncemented placement, with or
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without patella resurfacing etc. As far as bearing mobility concerns, fixed-bearings (FB) are most frequently used. This is probably because superior clinical results of mobile-bearing (MB) designs are still lacking [1-3], wear rate results inconclusive [4-6], and kinematic
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differences small [7-9]. The rationale of MB lies originally in being part of the low-contact-
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stress concept to reduce loosening and wear. Herein the use of a meniscal or rotating bearing element allowed both mobility and congruency, producing both low constrained forces and low contact stresses [10]. Several in vivo fluoroscopic studies compared mobile- to fixed-
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bearing variants [7-9,11-13] half of them showing small but significant more axial femorotibial rotation (’rotation’) in the MB group (Table 1). More rotation may strictly not be
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relevant for the functioning of the low-contact-stress concept, but the question is raised, whether it is even desirable to have a closer to natural amount of rotation in TKA.
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More rotation may assist in more complex daily life activities, although beyond a certain threshold it could preclude a clinically undesirable instability. In vivo fluoroscopic analysis of normal knees showed that only 11 degrees of rotation was used during gait and around 15 degrees during higher demanding tasks, such as a deep knee bend and chair sit/rise [14]. In Dennis’ multicenter knee bend study all TKA variants showed below 10 degrees of rotation, except for anterior cruciate retaining TKA [11]. It is questionable whether the possibilities and restrictions of MB and FB TKA, and their comparison to the normal knee, should not be tested while performing more challenging tasks. We demonstrated in a motion analysis study an increase of rotation from 14 to 21 degrees in the normal knee by adding turning steps to a sit-to-walk task [15].
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ACCEPTED MANUSCRIPT We expected that this additional knee rotation by adding turning elements to a task load would also occur in our TKA patients. This assumption was supported by a finite element
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study showing that rotational load was the primary contributor to TKA mechanics [16]. We
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also hypothesized that a MB variant would have more rotation than a typical FB variant in
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turning activities.
Material and Methods
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Two consecutive cohorts of patients after TKA, 10 FB knees (in 9 patients) and 11 MB knees
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(in 9 patients), underwent gait analysis five years postoperatively between February 2006 and June 2008. The FB cohort was operated on in Hilversum Hospital (currently Tergooi
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Hospital, Hilversum, The Netherlands) receiving a NexGen Complete Knee Solution
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Legacy Posterior Stabilized TKA (Zimmer Inc, Warsaw, IN), while the MB cohort was operated on in Slotervaart Hospital (Amsterdam, The Netherlands) receiving a LCS
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Complete Rotating Platform TKA (DePuy Inc, Warsaw, IN). In the Nexgen knee the posterior ligament (PCL) was substituted and the orientation of saw cuts was bone referenced. In the
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LCS knee the PCL was sacrificed and saw cuts were ligament balance referenced. Otherwise, surgical approach and aftercare in both hospitals were uniform. The local ethical committee in both hospitals gave permission for conducting the study. Inclusion criteria for the study were patients successfully operated for osteoarthritis with a postoperative Knee Society Knee Score of 80 points or more. Exclusion criteria were revision surgery, neurological disorders that interfered with walking, body mass index (BMI) of 30 or more. During the course of the study, the criterion of BMI was eased from 30 to 35 to secure patient enrollment. The patient characteristics regarding gender, age at surgery, side, BMI and interval from surgery to analysis are shown in Table 2. Gender was equally divided in the FB group, whereas the MB group consisted of mainly women. Interval from surgery to gait
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ACCEPTED MANUSCRIPT analysis was 74 months in the FB group an 64 months in the MB group (p = 0.001). Otherwise, there were no statistically significant differences between both groups. Normal
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data were taken from to a prior study, in which fifteen healthy volunteers (six females, nine
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males) participated. Their average age was 33.4 years (range 24-63) and average body mass
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index 23.3 (range 18-25) [15].
Gait analysis took place in the Human Movement Laboratory (Department of Rehabilitation Medicine, VU University Medical Center, Amsterdam, the Netherlands). An OptoTrak
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motion analysis system (model 3020, Northern Digital Inc, Waterloo, Ontario, Canada) was
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used to record the 3D position of active surface markers at a sampling rate of 50Hz. For the tibia a cluster of three markers was strapped over the middle lateral shank. For the femur a cluster of three markers was rigidly attached to an epicondylar frame. The Femoral
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Epicondylar Frame is a validated tool for noninvasive tracking of femoral axial rotation with an error of 3.3 degrees up to 40 degrees of knee flexion [17]. The majority of normal rotation
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took place between 0-45 degrees of knee flexion during knee bending and chair rising in a fluoroscopic study [14]. We found the same in a motion analysis study in healthy patients
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performing chair rises with and without turns; most rotation took place at the end of stance with the knee nearly in extension [15]. Besides that, higher flexion angles would be less relevant to study in TKA, because an increased flexion angle also means loss of condylar congruency [18]. The error for tibial rotation using surface markers is 2 degrees [19]. An open source Matlab software program, BodyMech (www.bodymech.nl), was used to calculate 3D knee kinematics [20]. Tibia and femur were considered to be rigid bodies with a local coordinate system, defined by anatomical points [21]. Coordinates of the two points, where the virtual axis of the device entered the femoral epicondyles, were calculated from the frame markers. The greater trochanter instead of femoral head was used for the femoral longitudinal axis definition. The shank markers were anatomically calibrated using the tibial tuberosity
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ACCEPTED MANUSCRIPT and medial and lateral malleoli. Knee kinematics followed from the relative orientation of the tibia with respect to the femur, while decomposition into Euler angles was applied following
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the Grood and Suntay convention [22].
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The subjects performed four tasks: gait, move from sit-to-walk (STW) straight ahead, STW
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crossoverstep turning and STW sidestep turning. Chair height was adjusted to 90% of the lower leg length. Only the prosthetic knee in the weight bearing leg was measured during stance phase, the contralateral side acting as the swing leg. The tasks were standardized and
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described previously in a study with healthy subjects [15]. Videos are available in the
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electronic version of the current article. The subjects practiced each task until smoothly performed in a natural pace. Three measurements per task were recorded and used for analysis.
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Ranges of rotation during the various tasks were compared between the FB and MB groups. The difference between peak internal and peak external femorotibial rotation was used to
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define range of axial knee rotation. The difference between internal rotation during crossoverstepping and external rotation during sidestepping was used to define overall range
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of rotation for STW turning. An independent t-test was utilized to compare variables (ranges of rotation during gait, STW straight and STW turning) as well as patient characteristics between both groups (FB and MB). Level of significance was set at p = 0.05. The original sample size calculation with power set at 0.80 had revealed a number of 16 patients per group to find a difference of 5 between groups with 5 of variance.
Results During the stance phase of normal gait, the range of rotation in the FB group was with an average of 9.7 degrees (SD 4.2) less than the range of 13.4 degrees (SD 6.7) in the MB group,
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ACCEPTED MANUSCRIPT albeit not to a significant level (Table 3 and 4). The results of non-operated knees in healthy subjects in Table 4 were collected in a prior study [15].
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During STW straight, range of rotation in the FB group was considerably less than in the MB
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group (p = 0.002). In the FB group the average peak internal rotation was 8.8 degrees (SD
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5.5) at 90 percent of stance phase on average (SD 14) and with an average knee flexion angle of 35 percent (SD 6). External rotation was 2.9 degrees (SD 2.5) at 20 percent of stance phase (SD 16) with a knee flexion angle of 65 degrees (SD 15). This accounted for a range of
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rotation of 11.7 degrees (SD 3.6). In the MB group this range was 21.0 degrees (SD 7.3), with
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17.9 degrees (8.0) peak internal rotation at 89 percent stance (SD 12) with 29 degrees knee flexion (SD 8) and 3.2 degrees (SD 2.9) external rotation at 20 percent stance (SD 16) with 65 degrees knee flexion (SD 15).
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STW turning still resulted in less range of rotation for the FB group (p = 0.051). In the FB group the average peak internal rotation was 11.8 degrees (SD 6.2), at 88 percent of stance
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phase (SD 12) with an average of 33 degrees knee flexion angle (SD 6), during crossoverstepping. External rotation during sidestepping was 2.5 degrees (SD 2.1) at 26
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percent stance (SD 24) with 59 degrees knee flexion (SD 20). This accounted for an overall range of rotation of 14.3 degrees (SD 5.4), versus 21.1 degrees (SD 8.5) in the MB group. In this group crossoverstepping resulted in of 19.4 degrees internal rotation (SD 8.6) at 98 percent stance (SD 7) with 30 degrees knee flexion (SD 7), and sidestepping resulted in 1.7 degrees external rotation (SD 2.7) at 24 percent stance (SD 31) with 66 degrees knee flexion (SD 20).
Discussion Significant but small differences in axial femorotibial rotation during knee bending activities in favor of MB TKA were shown in a number of papers [7-9]. In the current study, the
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ACCEPTED MANUSCRIPT difference in rotation was even larger when moving from sit to walk with and without turns. We expected increased differences during a more demanding task, because in a pilot study on
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healthy subjects with non-operated knees range of rotation increased from 14 to 22 degrees by
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adding a turning element to STW.
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STW represents a complex transitional task, which is a merging of a discrete task (rising from a chair) and a rhythmic one (walking) [23]. In the FB group, rotation gradually increased with increased task complexity (gait, STW straight, STW turning) to 14 degrees. In the MB group,
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an increase to 21 degrees in rotation from gait to STW occurred, while no further increase was seen adding turns. Perhaps the low-friction articulation between bearing undersurface and
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tibial component is the reason for this ‘switch on/off’ pattern of rotation in MB knees. Even without the initiation of gait, the sit-to-stand (STS) movement is an important and
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challenging task of daily living that requires relatively large joint torques (and consequently joint load) and accurate balance control [24]. Interestingly, kinematic recovery in STS
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performance was reported at one year after TKA [25] and the necessary coordination appeared not to be different from a control group [26]. To our knowledge, former kinematic
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analysis of the STS movement after TKA was restricted to the sagittal plane only [27-29], while STW after TKA has not been studied at all. A shortcoming in the design of the study is that the LCS and NexGen design features and surgical technique were, except for difference in bearing mobility, not otherwise identical. Also, less rotational constraint in a PCL-retained then in a PCL-substituted FB variant might have been expected [11]. On the other hand, both prostheses were considered to be highly representative for their cohort, being amongst the most implanted artificial knees worldwide. Another possible shortcoming refers to the utilized noninvasive measurement technique, which does not make it possible to assess mobility of the bearing relative to the tibial component in the MB group. Nevertheless, since the concept of low-contact-stress TKA is
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ACCEPTED MANUSCRIPT based on higher congruency between femoral component and bearing uppersurface, one might assume that the larger rotation found in the MB group was due to bearing undersurface
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mobility. This assumption was supported by studies utilizing highly accurate roentgen
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stereometric analysis [7,30]. A third shortcoming is that the study design was not a
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randomized trial, which means that the patient groups may be different in relevant known or unknown variables. The number of females was larger in the MB group than in the FB group,
difference as was found in this study [31].
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but an assumable higher laxity in females could not be held to account for as large a
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The concept of higher articulating congruency combined with bearing rotational mobility has a theoretical advantage of reduced polyethylene wear and improved function [32]. Clinical studies of the LCS knee showed excellent results with MB [33-34], but the superiority over a
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FB design in comparative studies remains unproven [1-3]. One randomized study compared the LCS (MB) to NexGen (FB) with a minimum 10-year clinical and radiological follow-up,
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finding both groups were equally successful [35]. Series of bilaterally operated patients, randomized for FB on one MB on the other side, need to provide even longer-term clinical
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results [36-39]. Kinematic studies are necessary to find support for either concept, although higher amounts of rotation in a MB knee would not necessarily prove the benefit of its concept.
In conclusion, there are too many uncontrolled variables in this study to provide a meaningful contribution on MB versus FB TKA kinematics. A well-controlled randomized trial with MB and FB variants of the same prosthesis would be necessary to do so. We found that a difference in knee rotation between MB and FB becomes apparent, when changing from a relatively simple task to a more demanding task such as getting-up from a chair and start walking with and without turning. The study therefore illustrates that more demanding task loads could be helpful in exploring the geometric constraints of TKA variants.
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Conflict of interest statement
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This study was financially supported by an unrestricted grant from DePuy (Johnson &
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Johnson Medical) and Biomet. Otherwise, all authors have no financial and personal
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relationships with other people or organizations that could inappropriately influence (bias) their work
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Table 1. Summary of studies comparing axial knee rotation in vivo Reference N Task FB MB p Value Dennis et al., 2004 [11] 212/76* Knee bend NS 7.6 7.6 Ranawat et al., 2004 [8] 20/20 Knee bend 0.01 3.8 7.4 Delport et al., 2006 [7] 10/10 Knee bend < 0.005 2.4 7.5 Shi et al., 2008 [9] 26/30 Passive knee bend < 0.05 5.2 7.9 Liu et al., 2009 [12] 11/7 Squat-to-stand NS 5 5 Wolterbeek et al., 2011 [13] 8/7† Step-up NS 8.3 10.4 N = number of fixed- versus mobile-bearing knees NS = not significant *Refers to posterior-stabilized variant versus posterior cruciate ligament (PCL) sacrificing variant †Refers to multiradius posterior-substituted variant versus multiradius PCL-sacrificing variant
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ACCEPTED MANUSCRIPT Table 2. Patient characteristics
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MB group (11 knees)
IP
3/7 28.8 (3.4) 65.3 (12.3) 74.3 (6.6)
6/5 30.2 (2.9) 62.8 (11.8) 63.9 (4.4)
AC
CE P
TE
D
MA
NU
SC R
Gender Female/male Side Right/left Mean BMI (SD) Mean age at surgery, years (SD) Mean interval from surgery to analysis, months (SD)
FB group (10 knees)
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ACCEPTED MANUSCRIPT Table 3. Individual peak values of internal and external knee rotation in degrees. For each value the knee flexion angle in degrees is presented between brackets
Peak ext
Peak int
Peak ext
Peak int
Peak ext
Peak int
Peak ext
FB1
5.8 (28)
-0.1 (19)
1.7 (42)
-6.0 (47)
1.7 (30)
-5.1 (50)
4.2 (48)
-1.2 (35)
FB2
11.8 (22)
-0.5 (26)
4.2 (36)
-6.2 (51)
6.0 (32)
-5.4 (49)
0.2 (64)
-6.5 (36)
FB3
6.9 (48)
-1.2 (25)
9.2 (33)
-1.7 (74)
17.5 (26)
-1.4 (75)
9.9 (26)
-1.9 (75)
FB4
7.3 (24)
-0.2 (13)
15.3 (21)
0.1 (61)
17.7 (25)
1.1 (57)
11.4 (14)
1.1 (56)
FB5
13.2 (42)
-1.2 (18)
12.6 (36)
-0.1 (69)
14.6 (35)
-2.7 (56)
3.4 (61)
-3.7 (45)
FB6
2.7 (42)
-4.6 (20)
10.5 (31)
-1.5 (75)
13.1 (31)
-1.5 (74)
7.6 (23)
-2.2 (75)
FB7
8.4 (30)
-0.3 (18)
3.7 (40)
-3.1 (84)
m.d.
m.d.
3.5 (86)
-2.5 (43)
FB8
9.9 (37)
1.5 (19)
17.1 (36)
-0.4 (88)
18.7 (44)
-2.1 (87)
12.8 (25)
-0.3 (91)
FB9
14.8 (41)
-4.0 (24)
11.6 (40)
-4.1 (55)
12.1 (39)
-2.5 (75)
2.6 (31)
-3.4 (80)
FB10
2.8 (44)
-2.5 (17)
2.5 (34)
-5.6 (50)
4.8 (35)
-6.1 (53)
1.7 (81)
-4.3 (54)
MB1
7.5 (46)
-3.0 (20)
10.9 (20)
-0.8 (73)
15.5 (24)
1.2 (68)
7.6 (74)
2.8 (32)
MB2
-2.0 (24)
-12.0 (20)
19.6 (27)
-1.2 (77)
26.4 (25)
-0.2 (76)
15.7 (24)
0.0 (79)
MB3
m.d.
m.d.
25.2 (30)
-1.0 (82)
24.4 (29)
-0.3 (87)
19.3 (35)
-1.4 (86)
MB4
19.3 (18)
-3.6 (16)
31.7 (19)
-3.8 (71)
34.2 (20)
-2.6 (69)
20.2 (15)
-1.7 (70)
MB5
10.2 (35)
0.0 (22)
15.8 (32)
-1.3 (85)
15.3 (46)
-1.0 (84)
7.4 (33)
-0.4 (83)
MB6
5.2 (30)
-6.6 (14)
27.1 (30)
-3.4 (61)
29.0 (27)
-2.5 (62)
16.8 (20)
-2.3 (66)
MB7
2.6 (34)
-11.2 (14)
17.9 (33)
-4.8 (65)
21.0 (30)
-2.4 (66)
11.8 (18)
-1.4 (67)
MB8
5.7 (26)
-2.4 (23)
8.7 (29)
-4.8 (60)
5.2 (34)
-5.4 (57)
3.8 (85)
-1.9 (60)
MB9
25.1 (33)
-2.8 (26)
10.9 (48)
-7.9 (36)
12.9 (30)
-3.4 (36)
1.5 (81)
-7.7 (26)
MB10
10.9 (28)
-0.7 (20)
21.5 (24)
1.4 (73)
19.5 (31)
2.1 (73)
13.6 (20)
-0.2 (77)
MB11
8.3 (36)
0.9 (34)
7.4 (31)
-7.1 (71)
10.1 (34)
-6.9 (70)
3.3 (35)
-4.2 (83)
IP
SC R
NU
D
CE P
T
Peak int
STW, sidestepping
MA
STW, crossoverstepping
TE
STW, straight
AC
Gait
m.d. Missing data
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ACCEPTED MANUSCRIPT MB 13.4 (6.7) 21.0 (7.3) 21.1 (8.5)
Normal
T
13.5 (3.9) 20.9 (7.9)
p Value* 0.152 0.002 0.051
AC
CE P
TE
D
MA
NU
SC R
IP
Table 4. Mean ranges of axial knee rotation (SD) FB Gait 9.7 (4.2) Sit-to-walk, straight 11.7 (3.6) Sit-to-walk, turning 14.3 (5.4) * FB versus MB
18
ACCEPTED MANUSCRIPT Highlights
AC
CE P
TE
D
MA
NU
SC R
IP
T
Most in vivo studies on axial knee rotation utilized gait or knee bending tasks Some reports showed few but significant more rotation in mobile-bearing variants of TKA We studied rotation in mobile- and fixed-bearing TKA patients, while performing a sit-to-walk task with and without turning steps The mobile-bearing group showed significant more rotation The study illustrates how higher demanding task loads could be helpful in exploring the geometric constraints of TKA variants
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