Knee Surg Sports Traumatol Arthrosc DOI 10.1007/s00167-014-2841-8
KNEE
Toe-out angle changes after total knee arthroplasty in patients with varus knee osteoarthritis Masayuki Tazawa • Makoto Sohmiya • Naoki Wada • Irma Ruslina Defi • Kenji Shirakura
Received: 24 July 2013 / Accepted: 28 December 2013 Ó Springer-Verlag Berlin Heidelberg 2014
Abstract Purpose Toeing-out is a commonly proposed kinematic variable that has been suggested to reduce external knee adduction moment. Analyses of the toe-out angle after total knee arthroplasty (TKA) are useful for obtaining a proper understanding of the abnormal gait caused by varus knee osteoarthritis (OA), as well as performing rehabilitation after arthroplasty. Changes in the toe-out angle after arthroplasty have not yet been defined or analysed. Methods The study population consisted of 32 knees in 32 patients with varus knee OA who underwent TKA. The femorotibial angle was evaluated on standing anteroposterior radiographs before and after arthroplasty. The subjects underwent three-dimensional motion capture analyses to measure gait parameters (walking speed, cadence, stride length, step length, step width and the relative length of the single-limb support (SLS) percentage of one gait cycle) and the maximal hip adduction angle in the stance phase, the trunk lean angle in the coronal plane and the toe-out angle before and 4 weeks after arthroplasty. Results The femorotibial angle on the side of arthroplasty improved after surgery. Among the measured gait M. Tazawa (&) I. R. Defi K. Shirakura Department of Rehabilitation Medicine, Gunma University Graduate School of Medicine, 3-39-22 Showa, Maebashi, Gunma 371-8511, Japan e-mail: [email protected] M. Sohmiya N. Wada Division of Rehabilitation Medicine, Gunma University Hospital, 3-39-15 Showa, Maebashi, Gunma 371-8511, Japan I. R. Defi Department of Physical Medicine and Rehabilitation, Faculty of Medicine, Hasan Sadikin General Hospital, Padjadjaran University, Jl. Pasteur 38, Bandung 40161, Indonesia
parameters, only the SLS percentage increased significantly. The hip adduction angle and toe-out angle on the side of arthroplasty increased significantly after surgery. Conclusions The knee alignment and hip adduction angle in the coronal plane and SLS phase were normalized after arthroplasty. The increase in the toe-out angle after arthroplasty may be attributable to the restoration of a normal knee alignment. These findings contribute to obtaining a proper understanding of the abnormal gait caused by varus knee OA and are useful for orthopaedic surgeons and rehabilitation therapists when treating patients after arthroplasty. Level of evidence Prospective study, Level II. Keywords Three-dimensional motion analysis Toe-out angle Total knee arthroplasty Varus knee osteoarthritis
Introduction Patients with knee osteoarthritis (OA) complain of pain and demonstrate a slow walking speed, short step length and short stride length. The greatest amount of degeneration is found in the medial femorotibial compartment. The medial compartment of the knee bears 60–80 % of the total load, even in healthy knees [1]. The external knee adduction moment is an indirect measurement of the load on the medial compartment and is considered to be a risk factor for knee OA [15, 28]. Total knee arthroplasty (TKA) is a well-recognized procedure used to relieve pain and improve lower extremity alignment and walking in patients with knee OA [6, 10, 18, 23]. TKA is also performed to reduce excessive loading of the medial compartment of the knee by
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correcting the varus deformity [25]. Chang et al. [8] showed that correcting the varus knee alignment results in the recovery of a normal hip adduction angle and lateral trunk movement during walking. Only a few studies have compared the toe-out angle between individuals with and without knee OA. Bechard et al. [3] reported that the toe-out angle is smaller in patients with varus knee OA than in healthy controls. Lynn and Costigan [19] reported that patients with knee OA tend to have consistently lower toe-out angles during walking than do healthy adults. Realignment of the knee after TKA has been suggested to change the foot alignment, which potentially alters the dynamic foot function [7, 27]. However, no studies of changes in the toe-out angle after TKA have been reported. The purpose of this study was therefore to analyse changes in the toe-out angle after TKA. The current study is the first study to investigate changes in the toe-out angle after TKA among patients with varus knee OA. Analyses of the toe-out angle after TKA contribute to obtaining a proper understanding of the abnormal gait caused by varus knee OA and are useful for orthopaedic surgeons and rehabilitation therapists when treating patients after arthroplasty.
Materials and methods The subjects included patients with clinically and radiographically diagnosed varus knee OA who underwent TKA at Gunma University Hospital between June 2008 and June 2011 and fulfilled the following criteria: (1) the ability to walk without a walking aid before and 4 weeks after TKA, (2) a varus knee deformity with an FTA of [180° before surgery, (3) no history of leg or lumbar injury affecting the ability to walk and (4) no other lower extremity artificial joints. A total of 62 patients were enrolled, of whom 32 fulfilled the criteria and were included in this study. The final study population consisted of four males and 28 females. The mean age of the subjects was 72.2 ± 7.1 years, the mean body weight was 61.9 ± 10.4 kg, the mean height was 150.7 ± 8.2 cm and the mean body mass index was 27.3 ± 4.2. The severity of OA was determined on radiography according to the Kellgren–Lawrence grading system [16] and was graded as three or four in all cases. Surgery was performed by the knee surgeons of the university hospital using PFC Sigma (DePuy, Warsaw, IN, USA) cemented-type components without patella resurfacing. Joint exercises using a continuous passive motion machine were initiated on postoperative day 1. A standardized rehabilitation programme was started on the second or third day postoperatively. The programme included control of pain and swelling, the improvement of the range
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of motion of the knee, hip and ankle, muscle strengthening and walking training using parallel bars and walking aids (a walker and cane). Femorotibial angle measurements Anteroposterior radiographs were obtained with the subject standing on one leg without knee flexion before and 4 weeks after TKA. Care was taken to ensure that the patella was facing anteriorly. The FTA before and after surgery was measured by a single rehabilitation doctor and recorded in the radiographic archiving and communication system. The FTA is the lateral angle at the intersection between the femoral axis and tibial axis on an anteroposterior radiograph [10, 19]. Gait analysis A 10-camera motion capture system (VICON 612, Oxford Metrics, Oxford, UK) was used to sample the kinematic data of the gait. Retroreflective markers were fixed to the skin over anatomic landmarks as follows: single markers on the centre of the forehead, top of the head, spinous process of the seventh cervical vertebra, and midline of the sacrum between the bilateral posterior superior iliac spines and bilateral markers on the acromion, lateral epicondyle of the humerus at the elbow, radial styloid process of the wrist, greater trochanter at the hip, lateral condyle of the femur at the knee, lateral malleolus of the ankle and fifth metatarsal joint of the foot. The marker dimensional data were recorded continuously at 60 Hz. The VICON system has the highest level of precision, and the mean coefficient of variation was \2.5 % [5]. Axes in three dimensions (x, y and z) were configured to capture the positions of the markers in space. The x axis represented the mediolateral direction, the y axis represented the anteroposterior direction and the z axis represented the vertical direction. The coronal plane was defined by the x and z axes, the horizontal plane was defined by the x and y axes and the sagittal plane was defined by the y and z axes. The patients were asked to walk 10 m towards the y axis without any walking aids, at their own natural speed, on a flat and straight walkway in the rehabilitation unit of the university hospital. After one or two familiarization trials, at least three walking trials were performed for data collection. The data for each marker were recorded on the VICON Workstation version 4.6. The trial data were checked immediately after one walking trial on the VICON Workstation. In cases in which the data exhibited significant variation, the trial was omitted and a retrial was performed. Data for three trials were then obtained.
Statistical analysis The preoperative parameters were compared with the corresponding postoperative parameters. The step length and
(a) 5 0 -5 -10
0
20
40
60
80
100
80
100
80
100
% gait cycle
Trunk lean angle (degree)
The walking speed (m/s), cadence (steps/min), step length (m), stride length (m), step width (m), relative length of the single-limb support (SLS) phase (%) in the gait cycle, hip adduction angle (°) in the coronal plane, toe-out angle (°) in the horizontal plane and trunk lean angle (°) in the coronal plane were obtained. The walking speed was calculated using the velocity of the sacral marker in the direction of the gait (y axis) around the middle of the walkway. One walking cycle was defined as the sequence from the beginning of foot contact to the end of foot contact of the same leg. The step length was measured from the point of initial contact of one foot to the point of initial contact of the opposite foot, and the step width was calculated as the distance between the right and left lateral malleoli. The stride length was measured as the length between the heel strikes of the same leg. The SLS phase for each leg began with toe-off of the opposite side and ended with the initial contact of the opposite side. The SLS phase is the part of the gait cycle during which the body weight is entirely supported by one limb while the contralateral limb swings forward [18]. The length of the SLS phase was expressed as a percentage of the gait cycle (%GC). The hip adduction angle in the coronal plane was defined as the angle between a line from the greater trochanter to the lateral condyle marker of the femur and a vertical line from the greater trochanter to the ground and was measured at the maximal point in the stance phase. The trunk lean angle in the coronal plane was defined as the angle between a line perpendicular to the line connecting the bilateral acromial markers and the vertical line to the ground (z axis) and was measured at the maximal point in the stance phase. The toe-out angle was defined as the angle formed by the intersection of the line connecting the lateral malleolar and fifth metatarsal joint markers and the direction of forward movement (y axis) at mid-stance, i.e. approximately 30 % of the gait cycle. The patterns of the hip adduction angle, trunk lean angle and toe-out angle during the gait cycle are shown in Fig. 1. The hip adduction angle and trunk lean angle reached a maximum at approximately 30 % of the gait cycle. The average of the each measurement was calculated at the midpoint of the walking trial when the gait was stabilized. The average of three trials was then calculated. The study was approved by the Institutional Review Board of Gunma University Hospital (No. 659). All patients provided their signed informed consent to participate.
(b)
4 2 0 -2 -4
0
20
40
60
% gait cycle Toe-out angle (degree)
Measurements
Hip adduction angle (degree)
Knee Surg Sports Traumatol Arthrosc
(c)
20 15 10 5
0
20
40
60
% gait cycle
Fig. 1 Patterns of the hip adduction angle, trunk lean angle and toeout angle during the gait cycle. 0 % of the gait cycle is the point of foot contact, approximately 60 % of the gait cycle is the point of foot off of the same leg. The hip adduction angle (a) and trunk lean angle (b) in the coronal plane were measured at the maximal point in the stance phase. The toe-out angle (c) in the horizontal plane was measured at mid-stance, i.e. approximately 30 % of the gait cycle
relative length of the SLS phase were also compared between the operated and contralateral sides. The IBM SPSS Statistics version 20.0 computer software program was used for the analysis. The Wilcoxon signed-rank test was employed to determine the differences between the prearthroplasty and postarthroplasty measurements and the data for the operated and contralateral sides. A p value of \0.05 was considered to be statistically significant.
Results The mean FTA of the TKA side on standing radiographs improved from 186.5° ± 5.2° to 174.4° ± 3.3° after TKA, with significant differences between the preoperative and postoperative angles (p \ 0.001). The mean FTA of the non-TKA side was 181.6° ± 5.6°. There were no significant differences between the preoperative and postoperative measurements for any gait parameter, except for the length of the SLS phase
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Knee Surg Sports Traumatol Arthrosc Table 1 Comparison of gait parameters obtained before and after total knee arthroplasty Gait parameter
Pre-TKA
Post-TKA
p value
Gait speed (m/s)
0.7 ± 0.3
0.7 ± 0.2
n.s.
Cadence (steps/min)
89 ± 21
96 ± 18
n.s.
Stride length (m)
0.9 ± 0.2
1.0 ± 0.2
n.s.
Step width (m)
0.3 ± 0.1
0.3 ± 0.1
n.s.
Step length (m)
0.4 ± 0.1
0.4 ± 0.1
n.s.
TKA total knee arthroplasty, n.s. not significant Table 2 Comparison of the relative length of the SLS phase Gait parameter
Side
Pre-TKA
Post-TKA
p value
SLS phase (%GC)
TKA side
32.0 ± 6.4
35.7 ± 3.8
0.005*
Non-TKA side p value
33.9 ± 6.7
36.8 ± 3.7
0.004*
0.016*
n.s.
TKA total knee arthroplasty, SLS single-limb support, GC gait cycle, n.s. not significant * Significant; between pre- and post-TKA; between the TKA and non-TKA sides
(Table 1). The length of the SLS phase on both the operated and contralateral sides increased significantly after arthroplasty. Before surgery, the length of the SLS phase differed significantly between the operated and contralateral sides; however, no significant differences were detected after arthroplasty (Table 2). The mean hip adduction and toe-out angles on the operated side increased significantly after TKA. There were no significant changes in the mean hip adduction or toe-out angles on the contralateral side. In addition, no significant differences in the trunk lean angle were detected between the preoperative and postoperative measurements (Table 3).
Discussion The most important finding of this study is that the toe-out angle on the operated side increased after TKA. The toeout angle has been observed to be smaller in patients with Table 3 Comparison of the femorotibial angle, trunk lean angle, hip adduction angle and toe-out angle before and after TKA
Angle (°)
Side
Trunk lean angle
TKA side
3.8 ± 3.6
3.3 ± 3.0
n.s.
Non-TKA side
3.4 ± 3.5
2.6 ± 3.8
n.s. \0.001*
Hip adduction angle TKA total knee arthroplasty, n.s. not significant * Significant
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knee OA than in healthy individuals [3, 19]. McClelland et al. [20] reported that TKA patients walk with greater external knee rotation than that exhibited by healthy agematched controls. In patients with varus knee OA, TKA causes external rotation of the tibia and increases the toeout angle. The external knee adduction moment of the stance limb during walking can be described as the product of the frontal plane components of the ground reaction force (GRF) and lever arm [11]. The GRF vector passes from the centre of pressure under the foot to the centre of mass of the body. The lever arm length is the distance between the GRF line and the centre of the knee joint. The lever arm is longer in a varus knee than in a normal knee (Fig. 2a). Lateral trunk lean results from the lateral displacement of weight on the stance limb during walking, which shifts the ground GRF vector laterally and thus reduces the load on the medial joint of the knee [5] (Fig. 2b). Toeing-out is suggested to reduce the external knee adduction moment in the coronal plane [2, 14, 21, 24] (Fig. 2c). Nevertheless, patients with knee OA cannot rotate their foot out due to their leg malalignment [3, 19]. In the current study, the improvement of knee alignment by arthroplasty caused the foot to be externally rotated. This finding shows that the adduction moment on the artificial joint was smaller than that observed before surgery. The normal knee and foot alignment permitted early walking and weight bearing after TKA without disturbing the artificial joint. With the exception of the length of the SLS phase, no gait parameters changed significantly after TKA. These results are consistent with the findings of a prior study that showed that patients who underwent TKA exhibited a slow walking speed, slow cadence, short stride length and short step length for 3–12 months after surgery [29]. Walking parameters have been shown to improve 1–2 years after TKA [26]; the recovery of walking requires a longer period than that observed in the present study. Pain and the ability to walk are strongly correlated with the length of the SLS phase [9]. Patients with knee OA have a shorter SLS phase than that of healthy individuals [17]. The present study showed that the SLS phase improved significantly after TKA on both the operated and contralateral sides. Although the length of the SLS phase
Toe-out angle
Pre-TKA
Post-TKA
p value
TKA side
4.4 ± 3.4
7.8 ± 3.6
Non-TKA side
6.9 ± 4.0
6.9 ± 3.4
TKA side
15.7 ± 12.6
23.9 ± 15.0
\0.001*
Non-TKA side
15.7 ± 10.2
17.4 ± 9.4
n.s.
n.s.
Knee Surg Sports Traumatol Arthrosc
a
b
c
Fig. 2 Relationship between the GRF and the centre of the knee joint in the coronal plane. a A patient with varus knee osteoarthritis (OA), b A patient with varus knee OA with lateral trunk lean, c A patient
with varus knee OA with toeing-out The GRF vector passes closer to the knee joint in b and c than in a
differed significantly between the operated and contralateral sides before arthroplasty, this difference diminished postoperatively. TKA provided relief of pain on both the operated and contralateral sides. In the present study, the FTA on the operated side normalized and the hip adduction angle on the operated side increased significantly after arthroplasty. Terauchi et al. [26] reported the restoration of a normal hip adduction angle in patients with knee OA who underwent high tibial osteotomy intended to realign the knee. Chang et al. noted that the hip adduction angle improves after TKA. The correction of varus deformity of the knee via high tibial osteotomy or TKA tends to place the femoral shaft in a state of constant adduction during the stance phase. The lateral trunk lean angle during the stance phase did not change on either side after TKA. Lateral trunk lean decreases the knee joint adduction load during walking and is often seen in patients with knee OA. Mundermann et al. [22] suggested that shifting the trunk over the stance leg is a compensatory mechanism in patients with knee OA, as it is not observed in subjects without knee OA. Hunt et al. [12, 13] reinforced this idea, reporting a smaller trunk lean angle in healthy adults than in individuals with mild-to-moderate knee OA. Berman et al. [4] noted that trunk lean was caused by muscle weakness of the hip abductor muscle. The hip abductor muscles of knee OA patients are weaker than those of normal subjects. The recovery of muscle strength of the
lower extremities in OA patients after TKA requires 7 months to 2 years of rehabilitation [5]. In the present study, although TKA corrected the varus deformity of the knee and improved hip adduction, the trunk lean angle did not change in the short term after TKA. Measurements were obtained 4 weeks after TKA, when the muscle strength did not recover and trunk lean was maintained. The current study is the first to describe the toe-out angle after arthroplasty. However, this study is associated with some limitations. First, the study population did not include a control group. It was difficult to recruit a sufficient number of age-matched individuals without degeneration of the knee joint or other musculoskeletal disorders. The gait pattern in younger subjects differs markedly from that observed in older patients. Second, the GRF was not measured in this study. Our laboratory has only four force plates. Requiring the patients to walk on the force plates at centre of the walkway influences their walking pattern. Information regarding the GRF, however, is important and useful, and measuring the GRF is necessary in future studies.
Conclusion Patients with varus knee OA who underwent TKA achieved a normal knee alignment, hip adduction and relative duration of SLS. The increased toe-out angle
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observed after arthroplasty may be due to realignment of the knee. Analyses of the toe-out angle after TKA are useful for knee surgeons and rehabilitation therapists, as they allow clinicians to obtain a proper understanding of the abnormal gait caused by varus knee OA.
14.
15.
References 16. 1. Chang A, Hurwitz D, Dunlop D, Song J, Cahue S, Hayes K, Sharma L (2007) The relationship between toe-out angle during gait and progression of medial tibiofemoral osteoarthritis. Ann Rheum Dis 66:1271–1275 2. Andrews M, Noyes FR, Hewett TE, Andriacchi TP (1996) Lower limb alignment and foot angle are related to stance phase knee adduction in normal subjects: a critical analysis of the reliability of gait analysis data. J Orthop Res 14:289–295 3. Bechard DJ, Birmingham TB, Zecevic AA, Jones IC, Giffin JR, Jenkyn TR (2012) Toe-out, lateral trunk lean, and pelvic obliquity during prolonged walking in patients with medial compartment knee osteoarthritis and healthy controls. Arthr Care Res (Hoboken) 64:525–532 4. Berman AT, Bosacco SJ, Israelite C (1991) Evaluation of total knee arthroplasty using isokinetic testing. Clin Orthop Relat Res 271:106–113 5. Carse B, Meadows B, Bowers R, Rowe P (2013) Affordable clinical gait analysis: an assessment of the marker tracking accuracy of a new low-cost optical 3D motion analysis system. Physiotherapy 99:347–351 6. Catani F, Digennaro V, Ensini A, Leardini A, Giannini S (2012) Navigation-assisted total knee arthroplasty in knees with osteoarthritis due to extra-articular deformity. Knee Surg Sports Traumatol Arthrosc 20:546–551 7. Chandler JT, Moskal JT (2004) Evaluation of knee and hindfoot alignment before and after total knee arthroplasty: a prospective analysis. J Arthroplast 19:211–216 8. Chang QZ, Sohmiya M, Wada N, Tazawa M, Sato N, Yanagisawa S, Shirakura K (2011) Alternation of trunk movement after arthroplasty in patients with osteoarthritis of the knee. J Orthop Sci 16:382–388 9. Elbaz A, Mor A, Segal O, Agar G, Halperin N, Haim A, Debbi E, Segal G, Debi R (2012) Can single limb support objectively assess the functional severity of knee osteoarthritis? Knee 19:32–35 10. Huang TW, Hsu WH, Peng KT, Hsu RW, Weng YJ, Shen WJ (2011) Total knee arthroplasty with use of computer-assisted navigation compared with conventional guiding systems in the same patient: radiographic results in Asian patients. J Bone Joint Surg Am 93:1197–1202 11. Hunt MA, Birmingham TB, Giffin JR, Jenkyn TR (2006) Associations among knee adduction moment, frontal plane ground reaction force, and lever arm during walking in patients with knee osteoarthritis. J Biomech 39:2213–2220 12. Hunt MA, Birmingham TB, Bryant D, Jones I, Giffin JR, Jenkyn TR, Vandervoort AA (2008) Lateral trunk lean explains variation in dynamic knee joint load in patients with medial compartment knee osteoarthritis. Osteoarthr Cartil 16:591–599 13. Hunt MA, Wrigley TV, Hinman RS, Bennell KL (2010) Individuals with severe knee osteoarthritis (OA) exhibit altered proximal walking mechanics compared with individuals with less
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KNEE
Toe-out angle changes after total knee arthroplasty in patients with varus knee osteoarthritis Masayuki Tazawa • Makoto Sohmiya • Naoki Wada • Irma Ruslina Defi • Kenji Shirakura
Received: 24 July 2013 / Accepted: 28 December 2013 Ó Springer-Verlag Berlin Heidelberg 2014
Abstract Purpose Toeing-out is a commonly proposed kinematic variable that has been suggested to reduce external knee adduction moment. Analyses of the toe-out angle after total knee arthroplasty (TKA) are useful for obtaining a proper understanding of the abnormal gait caused by varus knee osteoarthritis (OA), as well as performing rehabilitation after arthroplasty. Changes in the toe-out angle after arthroplasty have not yet been defined or analysed. Methods The study population consisted of 32 knees in 32 patients with varus knee OA who underwent TKA. The femorotibial angle was evaluated on standing anteroposterior radiographs before and after arthroplasty. The subjects underwent three-dimensional motion capture analyses to measure gait parameters (walking speed, cadence, stride length, step length, step width and the relative length of the single-limb support (SLS) percentage of one gait cycle) and the maximal hip adduction angle in the stance phase, the trunk lean angle in the coronal plane and the toe-out angle before and 4 weeks after arthroplasty. Results The femorotibial angle on the side of arthroplasty improved after surgery. Among the measured gait M. Tazawa (&) I. R. Defi K. Shirakura Department of Rehabilitation Medicine, Gunma University Graduate School of Medicine, 3-39-22 Showa, Maebashi, Gunma 371-8511, Japan e-mail: [email protected] M. Sohmiya N. Wada Division of Rehabilitation Medicine, Gunma University Hospital, 3-39-15 Showa, Maebashi, Gunma 371-8511, Japan I. R. Defi Department of Physical Medicine and Rehabilitation, Faculty of Medicine, Hasan Sadikin General Hospital, Padjadjaran University, Jl. Pasteur 38, Bandung 40161, Indonesia
parameters, only the SLS percentage increased significantly. The hip adduction angle and toe-out angle on the side of arthroplasty increased significantly after surgery. Conclusions The knee alignment and hip adduction angle in the coronal plane and SLS phase were normalized after arthroplasty. The increase in the toe-out angle after arthroplasty may be attributable to the restoration of a normal knee alignment. These findings contribute to obtaining a proper understanding of the abnormal gait caused by varus knee OA and are useful for orthopaedic surgeons and rehabilitation therapists when treating patients after arthroplasty. Level of evidence Prospective study, Level II. Keywords Three-dimensional motion analysis Toe-out angle Total knee arthroplasty Varus knee osteoarthritis
Introduction Patients with knee osteoarthritis (OA) complain of pain and demonstrate a slow walking speed, short step length and short stride length. The greatest amount of degeneration is found in the medial femorotibial compartment. The medial compartment of the knee bears 60–80 % of the total load, even in healthy knees [1]. The external knee adduction moment is an indirect measurement of the load on the medial compartment and is considered to be a risk factor for knee OA [15, 28]. Total knee arthroplasty (TKA) is a well-recognized procedure used to relieve pain and improve lower extremity alignment and walking in patients with knee OA [6, 10, 18, 23]. TKA is also performed to reduce excessive loading of the medial compartment of the knee by
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correcting the varus deformity [25]. Chang et al. [8] showed that correcting the varus knee alignment results in the recovery of a normal hip adduction angle and lateral trunk movement during walking. Only a few studies have compared the toe-out angle between individuals with and without knee OA. Bechard et al. [3] reported that the toe-out angle is smaller in patients with varus knee OA than in healthy controls. Lynn and Costigan [19] reported that patients with knee OA tend to have consistently lower toe-out angles during walking than do healthy adults. Realignment of the knee after TKA has been suggested to change the foot alignment, which potentially alters the dynamic foot function [7, 27]. However, no studies of changes in the toe-out angle after TKA have been reported. The purpose of this study was therefore to analyse changes in the toe-out angle after TKA. The current study is the first study to investigate changes in the toe-out angle after TKA among patients with varus knee OA. Analyses of the toe-out angle after TKA contribute to obtaining a proper understanding of the abnormal gait caused by varus knee OA and are useful for orthopaedic surgeons and rehabilitation therapists when treating patients after arthroplasty.
Materials and methods The subjects included patients with clinically and radiographically diagnosed varus knee OA who underwent TKA at Gunma University Hospital between June 2008 and June 2011 and fulfilled the following criteria: (1) the ability to walk without a walking aid before and 4 weeks after TKA, (2) a varus knee deformity with an FTA of [180° before surgery, (3) no history of leg or lumbar injury affecting the ability to walk and (4) no other lower extremity artificial joints. A total of 62 patients were enrolled, of whom 32 fulfilled the criteria and were included in this study. The final study population consisted of four males and 28 females. The mean age of the subjects was 72.2 ± 7.1 years, the mean body weight was 61.9 ± 10.4 kg, the mean height was 150.7 ± 8.2 cm and the mean body mass index was 27.3 ± 4.2. The severity of OA was determined on radiography according to the Kellgren–Lawrence grading system [16] and was graded as three or four in all cases. Surgery was performed by the knee surgeons of the university hospital using PFC Sigma (DePuy, Warsaw, IN, USA) cemented-type components without patella resurfacing. Joint exercises using a continuous passive motion machine were initiated on postoperative day 1. A standardized rehabilitation programme was started on the second or third day postoperatively. The programme included control of pain and swelling, the improvement of the range
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of motion of the knee, hip and ankle, muscle strengthening and walking training using parallel bars and walking aids (a walker and cane). Femorotibial angle measurements Anteroposterior radiographs were obtained with the subject standing on one leg without knee flexion before and 4 weeks after TKA. Care was taken to ensure that the patella was facing anteriorly. The FTA before and after surgery was measured by a single rehabilitation doctor and recorded in the radiographic archiving and communication system. The FTA is the lateral angle at the intersection between the femoral axis and tibial axis on an anteroposterior radiograph [10, 19]. Gait analysis A 10-camera motion capture system (VICON 612, Oxford Metrics, Oxford, UK) was used to sample the kinematic data of the gait. Retroreflective markers were fixed to the skin over anatomic landmarks as follows: single markers on the centre of the forehead, top of the head, spinous process of the seventh cervical vertebra, and midline of the sacrum between the bilateral posterior superior iliac spines and bilateral markers on the acromion, lateral epicondyle of the humerus at the elbow, radial styloid process of the wrist, greater trochanter at the hip, lateral condyle of the femur at the knee, lateral malleolus of the ankle and fifth metatarsal joint of the foot. The marker dimensional data were recorded continuously at 60 Hz. The VICON system has the highest level of precision, and the mean coefficient of variation was \2.5 % [5]. Axes in three dimensions (x, y and z) were configured to capture the positions of the markers in space. The x axis represented the mediolateral direction, the y axis represented the anteroposterior direction and the z axis represented the vertical direction. The coronal plane was defined by the x and z axes, the horizontal plane was defined by the x and y axes and the sagittal plane was defined by the y and z axes. The patients were asked to walk 10 m towards the y axis without any walking aids, at their own natural speed, on a flat and straight walkway in the rehabilitation unit of the university hospital. After one or two familiarization trials, at least three walking trials were performed for data collection. The data for each marker were recorded on the VICON Workstation version 4.6. The trial data were checked immediately after one walking trial on the VICON Workstation. In cases in which the data exhibited significant variation, the trial was omitted and a retrial was performed. Data for three trials were then obtained.
Statistical analysis The preoperative parameters were compared with the corresponding postoperative parameters. The step length and
(a) 5 0 -5 -10
0
20
40
60
80
100
80
100
80
100
% gait cycle
Trunk lean angle (degree)
The walking speed (m/s), cadence (steps/min), step length (m), stride length (m), step width (m), relative length of the single-limb support (SLS) phase (%) in the gait cycle, hip adduction angle (°) in the coronal plane, toe-out angle (°) in the horizontal plane and trunk lean angle (°) in the coronal plane were obtained. The walking speed was calculated using the velocity of the sacral marker in the direction of the gait (y axis) around the middle of the walkway. One walking cycle was defined as the sequence from the beginning of foot contact to the end of foot contact of the same leg. The step length was measured from the point of initial contact of one foot to the point of initial contact of the opposite foot, and the step width was calculated as the distance between the right and left lateral malleoli. The stride length was measured as the length between the heel strikes of the same leg. The SLS phase for each leg began with toe-off of the opposite side and ended with the initial contact of the opposite side. The SLS phase is the part of the gait cycle during which the body weight is entirely supported by one limb while the contralateral limb swings forward [18]. The length of the SLS phase was expressed as a percentage of the gait cycle (%GC). The hip adduction angle in the coronal plane was defined as the angle between a line from the greater trochanter to the lateral condyle marker of the femur and a vertical line from the greater trochanter to the ground and was measured at the maximal point in the stance phase. The trunk lean angle in the coronal plane was defined as the angle between a line perpendicular to the line connecting the bilateral acromial markers and the vertical line to the ground (z axis) and was measured at the maximal point in the stance phase. The toe-out angle was defined as the angle formed by the intersection of the line connecting the lateral malleolar and fifth metatarsal joint markers and the direction of forward movement (y axis) at mid-stance, i.e. approximately 30 % of the gait cycle. The patterns of the hip adduction angle, trunk lean angle and toe-out angle during the gait cycle are shown in Fig. 1. The hip adduction angle and trunk lean angle reached a maximum at approximately 30 % of the gait cycle. The average of the each measurement was calculated at the midpoint of the walking trial when the gait was stabilized. The average of three trials was then calculated. The study was approved by the Institutional Review Board of Gunma University Hospital (No. 659). All patients provided their signed informed consent to participate.
(b)
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0
20
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% gait cycle Toe-out angle (degree)
Measurements
Hip adduction angle (degree)
Knee Surg Sports Traumatol Arthrosc
(c)
20 15 10 5
0
20
40
60
% gait cycle
Fig. 1 Patterns of the hip adduction angle, trunk lean angle and toeout angle during the gait cycle. 0 % of the gait cycle is the point of foot contact, approximately 60 % of the gait cycle is the point of foot off of the same leg. The hip adduction angle (a) and trunk lean angle (b) in the coronal plane were measured at the maximal point in the stance phase. The toe-out angle (c) in the horizontal plane was measured at mid-stance, i.e. approximately 30 % of the gait cycle
relative length of the SLS phase were also compared between the operated and contralateral sides. The IBM SPSS Statistics version 20.0 computer software program was used for the analysis. The Wilcoxon signed-rank test was employed to determine the differences between the prearthroplasty and postarthroplasty measurements and the data for the operated and contralateral sides. A p value of \0.05 was considered to be statistically significant.
Results The mean FTA of the TKA side on standing radiographs improved from 186.5° ± 5.2° to 174.4° ± 3.3° after TKA, with significant differences between the preoperative and postoperative angles (p \ 0.001). The mean FTA of the non-TKA side was 181.6° ± 5.6°. There were no significant differences between the preoperative and postoperative measurements for any gait parameter, except for the length of the SLS phase
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Knee Surg Sports Traumatol Arthrosc Table 1 Comparison of gait parameters obtained before and after total knee arthroplasty Gait parameter
Pre-TKA
Post-TKA
p value
Gait speed (m/s)
0.7 ± 0.3
0.7 ± 0.2
n.s.
Cadence (steps/min)
89 ± 21
96 ± 18
n.s.
Stride length (m)
0.9 ± 0.2
1.0 ± 0.2
n.s.
Step width (m)
0.3 ± 0.1
0.3 ± 0.1
n.s.
Step length (m)
0.4 ± 0.1
0.4 ± 0.1
n.s.
TKA total knee arthroplasty, n.s. not significant Table 2 Comparison of the relative length of the SLS phase Gait parameter
Side
Pre-TKA
Post-TKA
p value
SLS phase (%GC)
TKA side
32.0 ± 6.4
35.7 ± 3.8
0.005*
Non-TKA side p value
33.9 ± 6.7
36.8 ± 3.7
0.004*
0.016*
n.s.
TKA total knee arthroplasty, SLS single-limb support, GC gait cycle, n.s. not significant * Significant; between pre- and post-TKA; between the TKA and non-TKA sides
(Table 1). The length of the SLS phase on both the operated and contralateral sides increased significantly after arthroplasty. Before surgery, the length of the SLS phase differed significantly between the operated and contralateral sides; however, no significant differences were detected after arthroplasty (Table 2). The mean hip adduction and toe-out angles on the operated side increased significantly after TKA. There were no significant changes in the mean hip adduction or toe-out angles on the contralateral side. In addition, no significant differences in the trunk lean angle were detected between the preoperative and postoperative measurements (Table 3).
Discussion The most important finding of this study is that the toe-out angle on the operated side increased after TKA. The toeout angle has been observed to be smaller in patients with Table 3 Comparison of the femorotibial angle, trunk lean angle, hip adduction angle and toe-out angle before and after TKA
Angle (°)
Side
Trunk lean angle
TKA side
3.8 ± 3.6
3.3 ± 3.0
n.s.
Non-TKA side
3.4 ± 3.5
2.6 ± 3.8
n.s. \0.001*
Hip adduction angle TKA total knee arthroplasty, n.s. not significant * Significant
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knee OA than in healthy individuals [3, 19]. McClelland et al. [20] reported that TKA patients walk with greater external knee rotation than that exhibited by healthy agematched controls. In patients with varus knee OA, TKA causes external rotation of the tibia and increases the toeout angle. The external knee adduction moment of the stance limb during walking can be described as the product of the frontal plane components of the ground reaction force (GRF) and lever arm [11]. The GRF vector passes from the centre of pressure under the foot to the centre of mass of the body. The lever arm length is the distance between the GRF line and the centre of the knee joint. The lever arm is longer in a varus knee than in a normal knee (Fig. 2a). Lateral trunk lean results from the lateral displacement of weight on the stance limb during walking, which shifts the ground GRF vector laterally and thus reduces the load on the medial joint of the knee [5] (Fig. 2b). Toeing-out is suggested to reduce the external knee adduction moment in the coronal plane [2, 14, 21, 24] (Fig. 2c). Nevertheless, patients with knee OA cannot rotate their foot out due to their leg malalignment [3, 19]. In the current study, the improvement of knee alignment by arthroplasty caused the foot to be externally rotated. This finding shows that the adduction moment on the artificial joint was smaller than that observed before surgery. The normal knee and foot alignment permitted early walking and weight bearing after TKA without disturbing the artificial joint. With the exception of the length of the SLS phase, no gait parameters changed significantly after TKA. These results are consistent with the findings of a prior study that showed that patients who underwent TKA exhibited a slow walking speed, slow cadence, short stride length and short step length for 3–12 months after surgery [29]. Walking parameters have been shown to improve 1–2 years after TKA [26]; the recovery of walking requires a longer period than that observed in the present study. Pain and the ability to walk are strongly correlated with the length of the SLS phase [9]. Patients with knee OA have a shorter SLS phase than that of healthy individuals [17]. The present study showed that the SLS phase improved significantly after TKA on both the operated and contralateral sides. Although the length of the SLS phase
Toe-out angle
Pre-TKA
Post-TKA
p value
TKA side
4.4 ± 3.4
7.8 ± 3.6
Non-TKA side
6.9 ± 4.0
6.9 ± 3.4
TKA side
15.7 ± 12.6
23.9 ± 15.0
\0.001*
Non-TKA side
15.7 ± 10.2
17.4 ± 9.4
n.s.
n.s.
Knee Surg Sports Traumatol Arthrosc
a
b
c
Fig. 2 Relationship between the GRF and the centre of the knee joint in the coronal plane. a A patient with varus knee osteoarthritis (OA), b A patient with varus knee OA with lateral trunk lean, c A patient
with varus knee OA with toeing-out The GRF vector passes closer to the knee joint in b and c than in a
differed significantly between the operated and contralateral sides before arthroplasty, this difference diminished postoperatively. TKA provided relief of pain on both the operated and contralateral sides. In the present study, the FTA on the operated side normalized and the hip adduction angle on the operated side increased significantly after arthroplasty. Terauchi et al. [26] reported the restoration of a normal hip adduction angle in patients with knee OA who underwent high tibial osteotomy intended to realign the knee. Chang et al. noted that the hip adduction angle improves after TKA. The correction of varus deformity of the knee via high tibial osteotomy or TKA tends to place the femoral shaft in a state of constant adduction during the stance phase. The lateral trunk lean angle during the stance phase did not change on either side after TKA. Lateral trunk lean decreases the knee joint adduction load during walking and is often seen in patients with knee OA. Mundermann et al. [22] suggested that shifting the trunk over the stance leg is a compensatory mechanism in patients with knee OA, as it is not observed in subjects without knee OA. Hunt et al. [12, 13] reinforced this idea, reporting a smaller trunk lean angle in healthy adults than in individuals with mild-to-moderate knee OA. Berman et al. [4] noted that trunk lean was caused by muscle weakness of the hip abductor muscle. The hip abductor muscles of knee OA patients are weaker than those of normal subjects. The recovery of muscle strength of the
lower extremities in OA patients after TKA requires 7 months to 2 years of rehabilitation [5]. In the present study, although TKA corrected the varus deformity of the knee and improved hip adduction, the trunk lean angle did not change in the short term after TKA. Measurements were obtained 4 weeks after TKA, when the muscle strength did not recover and trunk lean was maintained. The current study is the first to describe the toe-out angle after arthroplasty. However, this study is associated with some limitations. First, the study population did not include a control group. It was difficult to recruit a sufficient number of age-matched individuals without degeneration of the knee joint or other musculoskeletal disorders. The gait pattern in younger subjects differs markedly from that observed in older patients. Second, the GRF was not measured in this study. Our laboratory has only four force plates. Requiring the patients to walk on the force plates at centre of the walkway influences their walking pattern. Information regarding the GRF, however, is important and useful, and measuring the GRF is necessary in future studies.
Conclusion Patients with varus knee OA who underwent TKA achieved a normal knee alignment, hip adduction and relative duration of SLS. The increased toe-out angle
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Knee Surg Sports Traumatol Arthrosc
observed after arthroplasty may be due to realignment of the knee. Analyses of the toe-out angle after TKA are useful for knee surgeons and rehabilitation therapists, as they allow clinicians to obtain a proper understanding of the abnormal gait caused by varus knee OA.
14.
15.
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