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Reliability of Single-leg and Double-leg Balance Tests in Subjects with Anterior Cruciate Ligament Reconstruction and Controls a
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Vasiliki Kouvelioti , Eleftherios Kellis , Nikolaos Kofotolis & Ioannis a
Amiridis a
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Laboratory of Neuromechanics, Department of Physical Education and Sports Sciences at Serres, Aristotle University of Thessaloniki, Greece Published online: 04 Feb 2015.
To cite this article: Vasiliki Kouvelioti, Eleftherios Kellis, Nikolaos Kofotolis & Ioannis Amiridis (2015): Reliability of Single-leg and Double-leg Balance Tests in Subjects with Anterior Cruciate Ligament Reconstruction and Controls, Research in Sports Medicine: An International Journal, DOI: 10.1080/15438627.2015.1005292 To link to this article: http://dx.doi.org/10.1080/15438627.2015.1005292
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Research in Sports Medicine, 00:1–16, 2015 © 2015 Taylor & Francis ISSN: 1543-8627 print/1543-8635 online DOI: 10.1080/15438627.2015.1005292
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Reliability of Single-leg and Double-leg Balance Tests in Subjects with Anterior Cruciate Ligament Reconstruction and Controls VASILIKI KOUVELIOTI, ELEFTHERIOS KELLIS, NIKOLAOS KOFOTOLIS, and IOANNIS AMIRIDIS Laboratory of Neuromechanics, Department of Physical Education and Sports Sciences at Serres, Aristotle University of Thessaloniki, Greece
The purpose of this study was to assess the test–retest reliability of postural balance in patients with anterior cruciate ligament reconstruction (ACL) and controls. Ten healthy subjects and 15 individuals with ACL reconstruction performed single-leg and double-leg balance tests. The center of pressure (COP) was recorded using a pressure platform. For the total COP path, the intraclass correlation coefficient (ICC) ranged from 0.79 to 0.91. For the COP standard deviation, the ICCs ranged from 0.68 to 0.94. For the COP velocity, the ICCs ranged from 0.72 to 0.91. The sway area and ellipse scores displayed ICCs values of 0.67 to 0.95 and 0.53 to 0.92, respectively. The ICCs were higher for double leg tests compared with single-stance ones. These results indicate that 30 s balance tests in double and single-leg stance are reliable tools to assess static balance. The use of such tests to monitor rehabilitation programs following ACL reconstruction is recommended. KEYWORDS stabilometry, bipedal upright stance, single leg stance, knee injury, ACL, ICC
INTRODUCTION Anterior cruciate ligament (ACL) injuries are common in young athletes (Dai, Herman, Liu, Garrette, & Yu, 2012; Noyes, Mooar, Matthews, & Butler, 1983; Received 1 March 2014; accepted 9 July 2014. Address correspondence to: Kouvelioti Vasiliki, Aristotle University of Thessaloniki Department of Physical Education and Sport Sciences at Serres, Agios Ioannis, 62110, Serres, Greece. E-mail: [email protected] 1
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Moses, Orchard, & Orchard, 2012). The anterior cruciate ligament (ACL) provides stability and minimizes stress across the knee joint (Stojianovic & Ostojic, 2012) and is proposed to play an integral role in the central somatosensory feedback loop by providing information regarding knee joint position and movement (Howells, Webster, & Ardern, 2011). A decrease in proprioceptive ability has been reported after ACL injury, because the human ACL has a mechanoreceptor system that is able to respond to the tension of the ligament (Friden, Roberts, Ageberg, Walden, & Zatterstrom, 2001). Surgical reconstruction is commonly performed to partially restore ACL function and to increase stability of the knee. The various reconstructive procedures for ACL cannot replace the mechanoreceptor system (Schutte, Dabezies, Zimmy, & Happel, 1987). Consequently, postural stability has been measured following ACL injury (Ageberg, Roberts, Holmström, & Fridén, 2004) or reconstruction surgery (Lephart et al., 1992). The double leg stance posture is frequently used to assess balance (Ageberg et al., 2004). Impaired postural control, measured by balance in single-limb stance, has been reported after acute (Ageberg, Zatterstrom, Moritz, & Friden, 2001) and chronic (Lysholm, Ledin, Ödkvist, & Good, 1998; Zatterstrom, Friden et al. 1994) ACL injuries, as well as after ACL reconstruction (Shiraishi et al. 1996). Research findings on the usefulness of single-leg balance tests after ACL reconstruction are conflicting (Shiraishi et al., 1996; Lysholm et al., 1998; Mattacola et al., 2002) indicating that there is a need for establishing reliable protocols for postural stability assessment. Reliability represents a key requirement for any outcome measure to ensure that any observed differences in variables measures between test sessions reflect real changes in postural control capacity, rather than random or systematic error in the measurement procedure. When examining the reliability of standing balance tests, intraclass correlation coefficients (ICC) would describe the extent to which tests might discriminate among groups of subjects and, as a result, would convey information regarding the appropriateness of these tests for use in studies evaluating various interventions (Streiner & Norman 1991; Stratford & Goldsmith 1997). The reliability of single-leg postural stability tests have been mainly examined in healthy individuals and in patients with ACL injury. In particular, Birmingham (2000) reported ICC values ranging from 0.41 to 0.90 in healthy individuals while Ageberg, Roberts, Holmstrom and Friden, (2003) and Ageberg, Zatterstrom, & Moritz, 1998) reported higher coefficients (range: 0.79 to 0.95). The ICCs between consecutive measurements was acceptable to high in single leg postural stability, (r = 0.42–0.90) (Benvenuti et al. 1999). Some research studies have examined reliability of single-balance tests in subjects with ACL injury (Hadian et al., 2008; Salavati et al., 2009). For example, Hadian et al. (2008) measured the reliability of COP measures of
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postural stability in patients with ACL injury and reported ICCs ranging from 0.71 to 0.96 for single-balance measurements. Salavati et al. (2009) examined test–retest reliability of COP measures of postural stability during quiet standing in a group with musculoskeletal disorders consisting of low back pain, ACL injury and functional ankle instability, and reported somewhat lower ICCs, ranging from 0.50 to 0.84. The above studies were performed mostly in ACL injured subjects, which differ compared with ACL reconstructed individuals. Furthermore, most studies examined double leg stance while no studies examined single leg stance. However double leg stance and single leg stance differ in terms of balance properties and mechanisms to maintain balance. It is rather difficult to make specific and direct comparisons across studies on the test–retest reliability of postural control measures. This is due to differences in the experimental setup, the instructions given to subjects and the duration or the number of trials. These differences may affect the reliability of the measurements (Pinsault & Vuillerme, 2009). In addition, the reliability of single-leg balance measurements has not been examined in individuals with ACL reconstruction. It is not certain that the reliability of a test in healthy subjects or ACL injured patients would apply for patients who underwent ACL reconstruction. Translating reliability coefficients into clinically meaningful representations of measurement error is a necessary and important step when the goal is to link clinical research to clinical practice (Ageberg et al., 2003). To our knowledge there are no studies that have investigated test–retest reliability of single-leg and double-leg balance tests in subjects with ACL reconstruction and controls. Therefore, the objective of this study was to examine the test– retest reliability of balance variables measured in double-leg and single-limb stance in subjects who underwent ACL reconstruction and controls.
METHODS Patients Fifteen subjects (age 24.37 ± 3.50 yr; mass 68.75 ± 10.03 kg; height 176 ± 10.03 cm; shoe number 41.87 ± 1.64 eur) who underwent ACL surgical reconstruction with semitendinosus allograft participated in this study. All patients had been subjected similar supervised rehabilitation. The median time elapsed from the surgery and the test occasion was two years.
Control Group The control group consisted of ten healthy (age 26.75 ± 2.37 yr; mass 63.12 ± 4.85 kg; height 172 ± 9.02 cm; shoe number 39.75 ± 2.34 eur) who
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volunteered to participate in this study after signing written informed consent. The subjects were university students of sport science and physical education. All subjects had no history of neurological disease, major orthopedic lesions, vestibular or visual disturbance. The protocol was approved by the Aristotle University Ethics Committee. All participants were physically active individuals as they participated systematically in team sports (basketball, handball, soccer and volleyball) for a minimum period of 5 years.
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Instrumentation All tests were performed on an EPS pressure platform (Loran Engineering S.r.I., Bologna, Italy). The system uses 2304 force sensing resistors in an active area of 70 × 50 cm to record plantar pressure at 25 Hz.
Procedure The subjects performed single-leg (Figure 1(A)) and double-leg (Figure 1(B)) balance tests. The design included three testing sessions for the ACL reconstructed group and two testing sessions for the healthy group, spaced one week apart. All sessions were performed by the same researcher. During the double-leg stance the subjects were instructed, to stand erect, as motionless as possible, on a normal comfortable posture, with opened eyes looking straight ahead at a cross marked at approximately eye level on a black board 5 m
FIGURE 1 Double-leg (A) and single-leg (B) balance test.
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away and barefoot with feet shoulder width apart on the platform with the arms by their sides. Each subject was requested to keep a quiet stance posture for 30 seconds. The assessment included three measurements, and 5 min rest was provided between successive trials. The best trial was further analyzed. During single-limb stance, the subjects were instructed to stand on one foot, which was placed pointing straight forward in relation to reference lines in the frontal and sagittal planes. The swinging leg was flexed 90° at the hip and knee joints with both arms hanging relaxed at the sides. The subjects were instructed to stand as still as possible, looking straight ahead at a point on the wall 65 cm away. The test order between legs was randomized. If single-limb balance was not maintained for 30 seconds the trial was not recorded and the measurement was repeated.
Data Analysis A computer program (Footchecker 3.2, Engineering S.r.I., Bologna, Italy) was used to compute the following variables. 1. Total COP path (TCP) in mm, defined as the average distance (Frykberg, Lindmark, Lanshammar, & Borg, 2007) of the COP from the reference lines and the amplitude is its standard deviation. 2. Average velocity of COP (COPvel) in mm/s which reflects the amplitude and frequency of COP movements and it is calculated as the total length of the path of COP divided by the test trial time. 3. Standard deviation of the COP from the mean value of COP in anteroposterior (SDx) and mediolateral (SDy) axis in mm, often defined as sway amplitude. 4. Sway area in mm2, estimated using an algorithm that constructs a smooth closed curve (of irregular shape) that encloses all recorded COP points, the surface area of which is calculated 5. Sway ellipse, often called sway index, defined as a confidence ellipse equivalent to one standard deviation from the mean Cop. Sway ellipse is considered as a measure of how well an individual can stand quietly (Tropp, Ekstrand, & Gillquist, 1984)
Statistical Analysis Test–retest reliability was examined using two methods: (1) mean difference and 95% confidence interval (CI); and (2) the two-way random effect model (absolute agreement definition), average measure ICC and 95% CI (ICC2,2 according to Shrout & Fleiss, 1979). According to Fleiss (1986), ICC values above 0.75 represent excellent reliability, while values between 0.4 and 0.75 represent good reliability. In
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TABLE 1 ICC Values for all Variables, during Different Balance Test Sessions, for the Healthy and the ACL Reconstructed (ACLr) Groups. SDx: Standard Deviation on x Axis; SDy: Standard Deviation on y Axis; TCP: Total Center of Pressure Path, COP Vel: Centre of Pressure Velocity Healthy
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Sway ellipse SDx SDy TCP COP Vel Sway Area
ACL
Double leg
Right leg
Left leg
Double leg
Right leg (injured)
Left leg
0.92 0.94 0.85 0.78 0.78 0.95
0.91 0.68 0.69 0.75 0.75 0.67
0.83 0.75 0.78 0.76 0.76 0.82
0.88 0.70 0.68 0.72 0.72 0.84
0.81 0.81 0.83 0.91 0.91 0.87
0.53 0.78 0.68 0.90 0.90 0.87
this study, most variables showed ICC values above 0.75 which indicates excellent reliability (Table 1). These values were high for both patients and controls, which enforces the use of balance tests for monitoring balance performance after ACL reconstruction.
RESULTS Total COP Path The mean values for the total COP path ranged from 42.53 ± 18.92 (double leg balance test) to 475.08 ± 180.93 mm (left leg balance test) for the healthy group (Figure 2). The ICC values for the total COP path ranged from 0.75 (right leg balance test) to 0.78 (double leg balance test) for the healthy group (Table 1). For the ACL group the mean values for the total COP path ranged from 34.32 ± 7.47 (double leg balance test) to 564.72 ± 179.84 mm (right leg balance test) (Figure 2). The ICC values ranged for the ACL group ranged from 0.72 (double leg balance test) to 0.91 (right leg balance test) (Table 1).
Average Velocity of COP The average COP velocity values ranged from 1.42 ± 0.62 (double leg balance test) to 15.83 ± 6.03 mm/s (left leg balance test) for the healthy group (Figure 3). The ICC values ranged from 0.75 (right leg balance test) to 0.78 (double leg balance test) (Table 1). For the ACL group from 34.32 ± 7.47 (double leg balance test) to 564.72 ± 179.84 mm/s (right leg balance test) (Figure 3). The ICC values for
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FIGURE 2 Total COP path values for the healthy and the ACL reconstructed group during the three different balance tests ((A): double leg balance test; (B): left leg balance test; (C): right leg balance test, vertical error bars indicate standard deviation) in three different testing sessions (Test 1, Test 2, Test 3).
the ACL group ranged from 0.72 (double leg balance test) to 0.91 (right leg balance test) (Table 1).
Standard Deviation of the COP (SDx, SDy) The mean SD values for the healthy group, for the x axis, ranged from 0.22 ± 0.96 (right leg balance test) to 0.61 ± 0.30 mm (double leg balance test) and for the y axis the mean SD values ranged from 0.12 ± 0.76 (double leg balance test) to 0.46 ± 0.17 mm (right leg balance test) (Table 2). For the x axis for the healthy group the ICC values ranged from 0.68 (right leg balance test) to 0.94 (double leg balance test) and from 0.69 (right leg balance test) to 0.85 (double leg balance test) for the y axis (Table 1).
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FIGURE 3 COP velocity values for the healthy and the ACL reconstructed group during the three different balance tests ((A): double leg balance test; (B): left leg balance test; (C): right leg balance test, vertical error bars indicate standard deviation) in three different testing sessions (Test 1, Test 2, Test 3).
For the ACL group the mean SD values for the x axis ranged from 0.21 ± 0.07 (left leg balance test) to 0.66 ± 0.021 mm (double leg balance test) and from 0.29 ± 0.10 (left leg balance test) to 0.76 ± 0.32 mm (right leg balance test) for the y axis (Table 2). The ICC values ranged from 0.70 (double leg balance test) to 0.81 mm (right leg balance test), for the x axis (Table 1) and from 0.68 (double leg balance test) to 0.83 mm (right leg balance test) for the y axis.
Sway Area The sway area mean values ranged from 3995.61 ± 2090.61 (double leg balance test) to 49302.86 ± 23879.07 mm2 (left leg balance test) (Table 3) for the healthy group. The ICC values ranged from 0.67 (right leg balance test) to 0.95 (double leg balance test) (Table 1). For the ACL group the mean values ranged from 16850.87 ± 5813.59 (left leg balance test) to 36425.48 ± 13733.25 mm2 (right leg balance test) (Table 3). For the sway area the ICC values ranged from 0.84 (double leg balance) to 0.87 (left and right leg balance test, Table 1).
SD Y
SD X
1 2 3 1 2 3
Testing sessions 0.058 ± 0.025 0.061 ± 0.030 – 0.012 ± 0.007 0.015 ± 0.009 –
Double leg balance test 0.22 ± 0.96 0.23 ± 0.14 – 0.46 ± 0.17 0.41 ± 0.15 –
Right leg balance test
Healthy Group
0.30 ± 12.49 0.29 ± 14.33 – 0.66 ± 0.18 0.58 ± 0.34 –
Left leg balance test 0.065 0.066 0.064 0.065 0.056 0.068
± ± ± ± ± ±
0.020 0.021 0.020 0.015 0.011 0.024
Double leg balance test
0.34 0.32 0.41 0.41 0.40 0.76
± ± ± ± ± ±
0.14 0.05 0.11 0.24 0.17 0.32
Right leg (injured) balance test
ACLr Group
0.21 0.21 0.23 0.35 0.29 0.43
± ± ± ± ± ±
0.07 0.08 0.08 0.14 0.10 0.26
Left leg balance test
TABLE 2 SDX and SDY Values for the Healthy and the ACL Reconstructed Group during the Three Different Balance Tests. SDx: Standard Deviation on x Axis, SDy: Standard Deviation on y Axis. Units of Measured Variables are as Follows: SDx (mm) and SDy (mm)
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Sway area
Superficial ellipse
1 2 3 1 2 3
Testing sessions
0.37 ± 0.51 0.46 ± 0.51 – 4051.94 ± 2136.84 3995.61 ± 2090.61 –
Double leg balance test 1.45 ± 0.89 1.24 ± 0.78 – 38955.42 ± 18119.55 32829.19 ± 14638.98 –
Right leg balance test
Healthy Group
2.19 ± 1.17 2.10 ± 1.26 – 49302.86 ± 23879.07 45761.05 ± 31332.07 –
Left leg balance test 0.29 0.30 0.24 3047.12 3066.10 3135.50
± ± ± ± ± ±
0.22 0.27 0.25 420.17 205.48 395.14
Double leg balance test
1.49 1.74 1.51 34759.80 29385.84 36425.48
± ± ± ± ± ±
0.82 0.93 0.99 14813.88 11899.16 13733.25
Right leg (injured) balance test
ACLr Group
0.97 1.03 1.50 18676.83 16850.87 19918.48
± ± ± ± ± ±
0.44 0.38 0.83 5800.17 5813.59 7402.77
Left leg balance test
TABLE 3 Sway Area and Superficial Ellipse Values for the Healthy and the ACL Reconstructed Group during the Three Different Balance Tests. Units of Measured Variables are as Follows: Superficial Ellipse (cm2) Sway Area (mm2)
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Sway Ellipse
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The Sway Ellipse mean values ranged from 0.37 ± 0.51 (double leg balance test) to 2.19 ± 1.17 cm2 (left leg balance test) (Table 3) for the healthy group. The ICC values ranged from 0.83 (left leg balance test) to 0.92 (double leg balance test) (Table 1). The mean values of the Sway Ellipse for the ACL group ranged from 0.24 ± 0.25 (double leg balance test) to 1.74 ± 0.93 cm2 (right leg balance test) and the ICC values ranged from 0.53 (left leg balance test) to 0.88 (double leg balance test) (Table 1).
DISCUSSION The results of this study indicated that double and single leg balance tests display moderate to high reliability in individuals with ACL reconstruction and controls. To our knowledge, no study examined the test–retest reliability of postural stability measures using computerized pressure plates in ACL reconstructed individuals. Nevertheless, our results are in agreement with those reported by Harrison, Duenkel, Dunlop, and Russell (1994) on single-leg standing balance measurements using simple ordinal scale in ACL reconstructed individuals. Further, studies on reliability of posture balance tests in ACL injured individuals also confirm our findings. In particular, Hadian et al. (2008), found low to moderate correlation coefficients (0.81 to 0.89) during single and double stance tests in ACL injured individuals while Salavatti et al. (2009) reported low to moderate reliability of posture balance measurements in a group of patients of diverse pathologies, including ACL injury. It has been suggested that reliability may be a population-specific property (Hadian et al., 2008). Consequently, it is difficult to make comparisons between different studies due to the differences in the population, the measured variables, the experimental setup and the duration or the number of trials. Nevertheless, our results indicate that evaluation of postural balance using computerized pressure plates in patients who underwent ACL reconstruction displays acceptable reliability. In the present study, some variables (total cop path, cop velocity and sway area) were more reliable for the ACL reconstructed group compared with the healthy group during the single limb balance tests. This is an interesting finding as one might expect a higher variability in balance parameters in the patient group due to ACL injury and subsequent ACL reconstruction surgery. There are various factors that might have contributed to these findings. First, the ACL reconstruction group included individuals who underwent surgery two years prior to the measurement session. They also underwent standard physical therapy treatment post surgery for an average period of 6 months and they were all physically active at the time of testing.
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Since ACL rehabilitation includes both muscle strengthening and balance training, one might suggest that they were trained in performing balance exercises (Ageberg, 2003). In contrast, the control group consisted of matched-paired individuals based on age and level of physical activity, who did not systematically take part in a balance or proprioception training program. This is further supported by the observation that reliability coefficients were higher in the ACL reconstruction group mainly during the right (injured) limb single balance test while differences in ICCs were smaller for the left leg single balance test and even smaller for the double leg test (Table 1). This leads us to suggest that the ACL reconstruction surgery and rehabilitation program followed by this particular group of patients aimed to restore postural stability of the ACL injured leg and less on the uninjured leg and, hence, they were more familiar and trained in balancing on their injured leg rather than performing exercises on the healthy limb or both legs. One might expect that reliability would be higher in the double leg support test. This is because during the single leg balance test, body mass is transmitted through only one leg, which involves a higher activity of fewer muscle groups to counteract any shifts in the centre of mass that may occur during the test. The continuous adjustments in muscle contraction coupled with a smaller base of support may increase postural sway and increase performance variability (O’Connell, George, & Stock, 1998). It was interesting that the ICC values were higher for double-leg balance tests compared with single-leg balance tests for the control group but not for the ACL reconstruction group (Table 1). As already mentioned, this may be a result of postsurgery rehabilitation followed by ACL reconstruction individuals with a focus on single leg, rather than double leg, balance exercises. Further research is necessary to examine variability during single and double leg balance tests after ACL surgery. It is not clear why differences in reliability coefficients between groups depend on the parameters used to assess balance (Table 1). As far as the right limb stance test is concerned, it appears that only the sway ellipse showed less reliability in the ACL group than the healthy group. This may be related to the nature of the ellipse, which is the outcome of fitting the COP path with a known geometrical measure without taking into consideration the total COP path, the speed of the COP or its full deviations relative to the mean value (Tropp et al., 1984). However, it our opinion that the implications of this finding for testing ACL reconstruction for single balance stability are rather limited. This is based on two factors: first, despite the aforementioned differences, all estimated parameters displayed moderate to high reliability. Second, variability in COP-related measures is common and may be non-systematic. Even when considering the data from both groups, reliability was higher for some postural stability variables as opposed to others (Table 1). In particular, we noticed that measurements in sway area, COP
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velocity, total COP path and superficial ellipse were more reliable and sensitive than the SDx and SDy (Table 1). As mentioned before, COP SDx and SDy are the standard deviations of the mean value of COP in anteroposterior and mediolateral axes respectively. This high variability of the SDx and SDy values leads to low ICC values. Even the smaller perturbation or change in subject position during testing has a pronounced effect on SD but a smaller effect on other variables. This has an implication for testing balance posture using posturography. In particular, the decision on which parameters should be based on the clinical or experimental use of the test as well as its reliability. The use of SD serves as a measure of the shifts of the COP during the whole test. For example, two individuals may show a very similar COP path and COP speed, but one may show a steady position of COP throughout the test while the other individual displays continuous small shifts relative to the baseline. If this information is essential for the clinician, evaluation may include multiple trials to reduce a potential reliability issue, as seen in this study. In contrast, evaluation of other variables, such as COP path or Speed is generally less prone to variability and, therefore, they can be used with more confidence. The results of this study showed large differences in COP path and COP speed between limbs for both groups. This is not in line with previous studies for both healthy individuals and individuals who underwent ACL reconstruction (Harrison et al., 1994; Henriksson, Ledin, & Good 2001; Hoffman, Schrader, & Koceja, 1999; Mattacola et al., 2002). The factors that might have contributed to this observation are not clear. The participants in the present study were systematically trained players. It is not clear whether training might have caused less balance ability on one leg over the other. There are suggestions in the literature that one leg is tuned for mobilizing features and the other leg for postural stability (Grouios et al., 2009), while others argue that one leg is predominantly used for the most difficult aspect of a task (Hart & Gabbard, 1997). If we take into consideration that the bilateral leg differences reported in this study were reproduced in three (for ACL group) or two (control group) consecutive testing sessions, then this deserves further consideration. Even in this case, however, the variability that characterizes balance ability precludes generalization of the present findings. Further research on bilateral leg differences in balance ability is guaranteed. As we mentioned previously it is rather difficult to make specific and direct comparisons across studies on the test–retest reliability of postural control measures. This is due to differences in the experimental set-up, the instructions given to subjects, the duration or the number of trials and the different measured variables. Previous studies that measured test–retest reliability examined only a few specific COP variables during single or double leg balance tests, but not during both conditions, and without examining the variability of the measures in healthy and ACL reconstructed groups. In the
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present study, we measured five COP variables during two different balance tests, single leg balance test and double leg balance test, between healthy and ACL reconstructed groups.
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CONCLUSIONS The results indicated a moderate to high reliability of single and double leg balance tests in patients who underwent ACL reconstruction. However, reliability was higher for the double-leg balance test compared with single-leg balance tests while the use of COP variability measures (SDx and SDy) was the least reliable and should be used with caution.
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Grouios, G., Hatzitaki, V., Kollias, N., & Koidou, I. (2009). Investigating the stabilising and mobilising features of footedness. Laterality, 14(4), 362–380. doi:10.1080/ 13576500802434965 Hadian, R.M., Negahban, H., Talebian, S., Salavati, M., Jafari, A.H., Sanjari, A.M., Mazaheri, M., & Parnianpour, M. (2008). Reliability of center of pressure measures of postural stability in patients with unilateral anterior cruciate ligament injury. Journal of Applied Sciences, 8, 3019–3025. Harrison, E.L., Duenkel, N., Dunlop, R., & Russell, G. (1994). Evaluation of single-leg standing following anterior cruciate ligament surgery and rehabilitation. Phys Ther. Mar, 74, 245–252. Hart, S., & Gabbard, C. (1997). Examining the stabilising characteristics of footedness. Laterality, 2, 17–26. Henriksson, M., Ledin, T., & Good, L. (2001). Postural control after anterior cruciate ligament reconstruction and functional rehabilitation. American Journal of Sports Medicine, 29, 359–366. Hoffman, M., Schrader, J., & Koceja, D. (1999). An Investigation of postural control in postoperative anterior cruciate ligament reconstruction patients. Journal of Athletic Training, 34, 130–136. Howells, B., Webster, K., & Ardern, C. (2011). Is postural control restored following anterior cruciate ligament reconstruction? A systematic review. Knee Surg Sports Traumatol Arthrosc, 19, 1168–1177. Lephart, S., Perrin, D., Fu, F., Gieck, J., McCue, F., & Irrgang, J. (1992). Relationship between selected physical characteristics and functional capacity in the anterior cruciate ligament insuficient athlete. Journal of Orthopaedic and Sports Physical Therapy, 16, 174–181. Lysholm, M., Ledin, T., Ödkvist, L.M., & Good, L. (1998). Postural control: a comparison between patients with chronic anterior cruciate ligament insufficiency and healthy individuals. Scand J Med Sci Sports, 8, 432–438. Mattacola, C.G., Perrin, D.H., Gansneder, B.M., Gieck, J.H., Saliba, E.N., & McCue, F. C. (2002). Strength, functional outcome, and postural stability after anterior cruciate ligament reconstruction. J Athl Train, 37, 262–268. Moses, B., Orchard, J., & Orchard J. (2012). Systematic review: annual incidence of ACL injury and surgery in various populations. Research in Sports Medicine, 20, 157–179. Noyes, F.R., Mooar, P.A., Matthews, D.S., & Butler, D.L. (1983). The symptomatic anterior cruciate-deficient knee. Part I: the long-term functional disability in athletically active individuals. J Bone Joint Surg Am, 65, 154–162. O’Connell, M., George, K., & Stock, D. (1998) Postural sway and balance testing: a comparison of normal and anterior cruciate ligament deficient knee Gait Posture, 8, 136–142. Pinsault, N., & Vuillerme, N. (2009). Test-retest reliability of centre of foot pressure measures to assess postural control during unperturbed stance. Med Eng Phys, 31, 276–286. Salavati, M., Hadian, M.R., Mazaheri, M., Negahban, H., Ebrahimi, I., Talebian, S., & Parnianpour, M. (2009). Test-retest reliability of center of pressure measures of postural stability during quiet standing in a group with musculoskeletal disorders
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consisting of low back pain, anterior cruciate ligament injury and functional ankle instability. Gait Posture, 29, 460–464. Schutte, M.J., Dabezies, E.J., Zimny, M.L., & Happel, L.T. (1987). Neural anatomy of the human anterior cruciate ligament. J Bone Joint Surg Am, 69, 243–247. Shiraishi, M., Mizuta, H., Kubota, K., Otsuka, Y., Nagamoto, N., & Takagi, K. (1996). Stabilometric assessment in the anterior cruciate ligament-reconstructed knee. Clin J Sport Med, 6(1), 32–39. Shrout, P.E., & Fleiss, J.L. (1979). Intraclass correlations: uses in assessing rater reliability. Psychol Bull. 86, 420–428. Stojianovic, M., & Ostojic, S. (2012). Preventing ACL injuries in team-sport athletes: a systematic review of training interventions. Research in Sports Medicine, 20, 223–238. Stratford, P.W., & Goldsmith, C.H. (1997). Use of the standard error as a reliability index of interest: an applied example using elbow flexor strength data. Phys Ther, 77, 745–750. Streiner, D., & Norman, G. (1989). Health Measurement Scales: A Practical Guide to Their Development and Use. Oxford: Oxford Medical Publications. Tropp, H., Ekstrand, J., & Gillquist, J. (1984). Stabilometry in functional instability of the ankle and its value in predicting injury. Med Sci Sports Exerc, 16(1), 64–66. Zatterstrom, R., Friden, T., Lindstrand, A., & Moritz, U. (1994). The effect of physiotherapy on standing balance in chronic anterior cruciate ligament insufficiency. American Journal of Sports Medicine, 22(4), 531–536.
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Reliability of Single-leg and Double-leg Balance Tests in Subjects with Anterior Cruciate Ligament Reconstruction and Controls a
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Laboratory of Neuromechanics, Department of Physical Education and Sports Sciences at Serres, Aristotle University of Thessaloniki, Greece Published online: 04 Feb 2015.
To cite this article: Vasiliki Kouvelioti, Eleftherios Kellis, Nikolaos Kofotolis & Ioannis Amiridis (2015): Reliability of Single-leg and Double-leg Balance Tests in Subjects with Anterior Cruciate Ligament Reconstruction and Controls, Research in Sports Medicine: An International Journal, DOI: 10.1080/15438627.2015.1005292 To link to this article: http://dx.doi.org/10.1080/15438627.2015.1005292
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Reliability of Single-leg and Double-leg Balance Tests in Subjects with Anterior Cruciate Ligament Reconstruction and Controls VASILIKI KOUVELIOTI, ELEFTHERIOS KELLIS, NIKOLAOS KOFOTOLIS, and IOANNIS AMIRIDIS Laboratory of Neuromechanics, Department of Physical Education and Sports Sciences at Serres, Aristotle University of Thessaloniki, Greece
The purpose of this study was to assess the test–retest reliability of postural balance in patients with anterior cruciate ligament reconstruction (ACL) and controls. Ten healthy subjects and 15 individuals with ACL reconstruction performed single-leg and double-leg balance tests. The center of pressure (COP) was recorded using a pressure platform. For the total COP path, the intraclass correlation coefficient (ICC) ranged from 0.79 to 0.91. For the COP standard deviation, the ICCs ranged from 0.68 to 0.94. For the COP velocity, the ICCs ranged from 0.72 to 0.91. The sway area and ellipse scores displayed ICCs values of 0.67 to 0.95 and 0.53 to 0.92, respectively. The ICCs were higher for double leg tests compared with single-stance ones. These results indicate that 30 s balance tests in double and single-leg stance are reliable tools to assess static balance. The use of such tests to monitor rehabilitation programs following ACL reconstruction is recommended. KEYWORDS stabilometry, bipedal upright stance, single leg stance, knee injury, ACL, ICC
INTRODUCTION Anterior cruciate ligament (ACL) injuries are common in young athletes (Dai, Herman, Liu, Garrette, & Yu, 2012; Noyes, Mooar, Matthews, & Butler, 1983; Received 1 March 2014; accepted 9 July 2014. Address correspondence to: Kouvelioti Vasiliki, Aristotle University of Thessaloniki Department of Physical Education and Sport Sciences at Serres, Agios Ioannis, 62110, Serres, Greece. E-mail: [email protected] 1
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Moses, Orchard, & Orchard, 2012). The anterior cruciate ligament (ACL) provides stability and minimizes stress across the knee joint (Stojianovic & Ostojic, 2012) and is proposed to play an integral role in the central somatosensory feedback loop by providing information regarding knee joint position and movement (Howells, Webster, & Ardern, 2011). A decrease in proprioceptive ability has been reported after ACL injury, because the human ACL has a mechanoreceptor system that is able to respond to the tension of the ligament (Friden, Roberts, Ageberg, Walden, & Zatterstrom, 2001). Surgical reconstruction is commonly performed to partially restore ACL function and to increase stability of the knee. The various reconstructive procedures for ACL cannot replace the mechanoreceptor system (Schutte, Dabezies, Zimmy, & Happel, 1987). Consequently, postural stability has been measured following ACL injury (Ageberg, Roberts, Holmström, & Fridén, 2004) or reconstruction surgery (Lephart et al., 1992). The double leg stance posture is frequently used to assess balance (Ageberg et al., 2004). Impaired postural control, measured by balance in single-limb stance, has been reported after acute (Ageberg, Zatterstrom, Moritz, & Friden, 2001) and chronic (Lysholm, Ledin, Ödkvist, & Good, 1998; Zatterstrom, Friden et al. 1994) ACL injuries, as well as after ACL reconstruction (Shiraishi et al. 1996). Research findings on the usefulness of single-leg balance tests after ACL reconstruction are conflicting (Shiraishi et al., 1996; Lysholm et al., 1998; Mattacola et al., 2002) indicating that there is a need for establishing reliable protocols for postural stability assessment. Reliability represents a key requirement for any outcome measure to ensure that any observed differences in variables measures between test sessions reflect real changes in postural control capacity, rather than random or systematic error in the measurement procedure. When examining the reliability of standing balance tests, intraclass correlation coefficients (ICC) would describe the extent to which tests might discriminate among groups of subjects and, as a result, would convey information regarding the appropriateness of these tests for use in studies evaluating various interventions (Streiner & Norman 1991; Stratford & Goldsmith 1997). The reliability of single-leg postural stability tests have been mainly examined in healthy individuals and in patients with ACL injury. In particular, Birmingham (2000) reported ICC values ranging from 0.41 to 0.90 in healthy individuals while Ageberg, Roberts, Holmstrom and Friden, (2003) and Ageberg, Zatterstrom, & Moritz, 1998) reported higher coefficients (range: 0.79 to 0.95). The ICCs between consecutive measurements was acceptable to high in single leg postural stability, (r = 0.42–0.90) (Benvenuti et al. 1999). Some research studies have examined reliability of single-balance tests in subjects with ACL injury (Hadian et al., 2008; Salavati et al., 2009). For example, Hadian et al. (2008) measured the reliability of COP measures of
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postural stability in patients with ACL injury and reported ICCs ranging from 0.71 to 0.96 for single-balance measurements. Salavati et al. (2009) examined test–retest reliability of COP measures of postural stability during quiet standing in a group with musculoskeletal disorders consisting of low back pain, ACL injury and functional ankle instability, and reported somewhat lower ICCs, ranging from 0.50 to 0.84. The above studies were performed mostly in ACL injured subjects, which differ compared with ACL reconstructed individuals. Furthermore, most studies examined double leg stance while no studies examined single leg stance. However double leg stance and single leg stance differ in terms of balance properties and mechanisms to maintain balance. It is rather difficult to make specific and direct comparisons across studies on the test–retest reliability of postural control measures. This is due to differences in the experimental setup, the instructions given to subjects and the duration or the number of trials. These differences may affect the reliability of the measurements (Pinsault & Vuillerme, 2009). In addition, the reliability of single-leg balance measurements has not been examined in individuals with ACL reconstruction. It is not certain that the reliability of a test in healthy subjects or ACL injured patients would apply for patients who underwent ACL reconstruction. Translating reliability coefficients into clinically meaningful representations of measurement error is a necessary and important step when the goal is to link clinical research to clinical practice (Ageberg et al., 2003). To our knowledge there are no studies that have investigated test–retest reliability of single-leg and double-leg balance tests in subjects with ACL reconstruction and controls. Therefore, the objective of this study was to examine the test– retest reliability of balance variables measured in double-leg and single-limb stance in subjects who underwent ACL reconstruction and controls.
METHODS Patients Fifteen subjects (age 24.37 ± 3.50 yr; mass 68.75 ± 10.03 kg; height 176 ± 10.03 cm; shoe number 41.87 ± 1.64 eur) who underwent ACL surgical reconstruction with semitendinosus allograft participated in this study. All patients had been subjected similar supervised rehabilitation. The median time elapsed from the surgery and the test occasion was two years.
Control Group The control group consisted of ten healthy (age 26.75 ± 2.37 yr; mass 63.12 ± 4.85 kg; height 172 ± 9.02 cm; shoe number 39.75 ± 2.34 eur) who
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volunteered to participate in this study after signing written informed consent. The subjects were university students of sport science and physical education. All subjects had no history of neurological disease, major orthopedic lesions, vestibular or visual disturbance. The protocol was approved by the Aristotle University Ethics Committee. All participants were physically active individuals as they participated systematically in team sports (basketball, handball, soccer and volleyball) for a minimum period of 5 years.
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Instrumentation All tests were performed on an EPS pressure platform (Loran Engineering S.r.I., Bologna, Italy). The system uses 2304 force sensing resistors in an active area of 70 × 50 cm to record plantar pressure at 25 Hz.
Procedure The subjects performed single-leg (Figure 1(A)) and double-leg (Figure 1(B)) balance tests. The design included three testing sessions for the ACL reconstructed group and two testing sessions for the healthy group, spaced one week apart. All sessions were performed by the same researcher. During the double-leg stance the subjects were instructed, to stand erect, as motionless as possible, on a normal comfortable posture, with opened eyes looking straight ahead at a cross marked at approximately eye level on a black board 5 m
FIGURE 1 Double-leg (A) and single-leg (B) balance test.
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away and barefoot with feet shoulder width apart on the platform with the arms by their sides. Each subject was requested to keep a quiet stance posture for 30 seconds. The assessment included three measurements, and 5 min rest was provided between successive trials. The best trial was further analyzed. During single-limb stance, the subjects were instructed to stand on one foot, which was placed pointing straight forward in relation to reference lines in the frontal and sagittal planes. The swinging leg was flexed 90° at the hip and knee joints with both arms hanging relaxed at the sides. The subjects were instructed to stand as still as possible, looking straight ahead at a point on the wall 65 cm away. The test order between legs was randomized. If single-limb balance was not maintained for 30 seconds the trial was not recorded and the measurement was repeated.
Data Analysis A computer program (Footchecker 3.2, Engineering S.r.I., Bologna, Italy) was used to compute the following variables. 1. Total COP path (TCP) in mm, defined as the average distance (Frykberg, Lindmark, Lanshammar, & Borg, 2007) of the COP from the reference lines and the amplitude is its standard deviation. 2. Average velocity of COP (COPvel) in mm/s which reflects the amplitude and frequency of COP movements and it is calculated as the total length of the path of COP divided by the test trial time. 3. Standard deviation of the COP from the mean value of COP in anteroposterior (SDx) and mediolateral (SDy) axis in mm, often defined as sway amplitude. 4. Sway area in mm2, estimated using an algorithm that constructs a smooth closed curve (of irregular shape) that encloses all recorded COP points, the surface area of which is calculated 5. Sway ellipse, often called sway index, defined as a confidence ellipse equivalent to one standard deviation from the mean Cop. Sway ellipse is considered as a measure of how well an individual can stand quietly (Tropp, Ekstrand, & Gillquist, 1984)
Statistical Analysis Test–retest reliability was examined using two methods: (1) mean difference and 95% confidence interval (CI); and (2) the two-way random effect model (absolute agreement definition), average measure ICC and 95% CI (ICC2,2 according to Shrout & Fleiss, 1979). According to Fleiss (1986), ICC values above 0.75 represent excellent reliability, while values between 0.4 and 0.75 represent good reliability. In
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TABLE 1 ICC Values for all Variables, during Different Balance Test Sessions, for the Healthy and the ACL Reconstructed (ACLr) Groups. SDx: Standard Deviation on x Axis; SDy: Standard Deviation on y Axis; TCP: Total Center of Pressure Path, COP Vel: Centre of Pressure Velocity Healthy
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Sway ellipse SDx SDy TCP COP Vel Sway Area
ACL
Double leg
Right leg
Left leg
Double leg
Right leg (injured)
Left leg
0.92 0.94 0.85 0.78 0.78 0.95
0.91 0.68 0.69 0.75 0.75 0.67
0.83 0.75 0.78 0.76 0.76 0.82
0.88 0.70 0.68 0.72 0.72 0.84
0.81 0.81 0.83 0.91 0.91 0.87
0.53 0.78 0.68 0.90 0.90 0.87
this study, most variables showed ICC values above 0.75 which indicates excellent reliability (Table 1). These values were high for both patients and controls, which enforces the use of balance tests for monitoring balance performance after ACL reconstruction.
RESULTS Total COP Path The mean values for the total COP path ranged from 42.53 ± 18.92 (double leg balance test) to 475.08 ± 180.93 mm (left leg balance test) for the healthy group (Figure 2). The ICC values for the total COP path ranged from 0.75 (right leg balance test) to 0.78 (double leg balance test) for the healthy group (Table 1). For the ACL group the mean values for the total COP path ranged from 34.32 ± 7.47 (double leg balance test) to 564.72 ± 179.84 mm (right leg balance test) (Figure 2). The ICC values ranged for the ACL group ranged from 0.72 (double leg balance test) to 0.91 (right leg balance test) (Table 1).
Average Velocity of COP The average COP velocity values ranged from 1.42 ± 0.62 (double leg balance test) to 15.83 ± 6.03 mm/s (left leg balance test) for the healthy group (Figure 3). The ICC values ranged from 0.75 (right leg balance test) to 0.78 (double leg balance test) (Table 1). For the ACL group from 34.32 ± 7.47 (double leg balance test) to 564.72 ± 179.84 mm/s (right leg balance test) (Figure 3). The ICC values for
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FIGURE 2 Total COP path values for the healthy and the ACL reconstructed group during the three different balance tests ((A): double leg balance test; (B): left leg balance test; (C): right leg balance test, vertical error bars indicate standard deviation) in three different testing sessions (Test 1, Test 2, Test 3).
the ACL group ranged from 0.72 (double leg balance test) to 0.91 (right leg balance test) (Table 1).
Standard Deviation of the COP (SDx, SDy) The mean SD values for the healthy group, for the x axis, ranged from 0.22 ± 0.96 (right leg balance test) to 0.61 ± 0.30 mm (double leg balance test) and for the y axis the mean SD values ranged from 0.12 ± 0.76 (double leg balance test) to 0.46 ± 0.17 mm (right leg balance test) (Table 2). For the x axis for the healthy group the ICC values ranged from 0.68 (right leg balance test) to 0.94 (double leg balance test) and from 0.69 (right leg balance test) to 0.85 (double leg balance test) for the y axis (Table 1).
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FIGURE 3 COP velocity values for the healthy and the ACL reconstructed group during the three different balance tests ((A): double leg balance test; (B): left leg balance test; (C): right leg balance test, vertical error bars indicate standard deviation) in three different testing sessions (Test 1, Test 2, Test 3).
For the ACL group the mean SD values for the x axis ranged from 0.21 ± 0.07 (left leg balance test) to 0.66 ± 0.021 mm (double leg balance test) and from 0.29 ± 0.10 (left leg balance test) to 0.76 ± 0.32 mm (right leg balance test) for the y axis (Table 2). The ICC values ranged from 0.70 (double leg balance test) to 0.81 mm (right leg balance test), for the x axis (Table 1) and from 0.68 (double leg balance test) to 0.83 mm (right leg balance test) for the y axis.
Sway Area The sway area mean values ranged from 3995.61 ± 2090.61 (double leg balance test) to 49302.86 ± 23879.07 mm2 (left leg balance test) (Table 3) for the healthy group. The ICC values ranged from 0.67 (right leg balance test) to 0.95 (double leg balance test) (Table 1). For the ACL group the mean values ranged from 16850.87 ± 5813.59 (left leg balance test) to 36425.48 ± 13733.25 mm2 (right leg balance test) (Table 3). For the sway area the ICC values ranged from 0.84 (double leg balance) to 0.87 (left and right leg balance test, Table 1).
SD Y
SD X
1 2 3 1 2 3
Testing sessions 0.058 ± 0.025 0.061 ± 0.030 – 0.012 ± 0.007 0.015 ± 0.009 –
Double leg balance test 0.22 ± 0.96 0.23 ± 0.14 – 0.46 ± 0.17 0.41 ± 0.15 –
Right leg balance test
Healthy Group
0.30 ± 12.49 0.29 ± 14.33 – 0.66 ± 0.18 0.58 ± 0.34 –
Left leg balance test 0.065 0.066 0.064 0.065 0.056 0.068
± ± ± ± ± ±
0.020 0.021 0.020 0.015 0.011 0.024
Double leg balance test
0.34 0.32 0.41 0.41 0.40 0.76
± ± ± ± ± ±
0.14 0.05 0.11 0.24 0.17 0.32
Right leg (injured) balance test
ACLr Group
0.21 0.21 0.23 0.35 0.29 0.43
± ± ± ± ± ±
0.07 0.08 0.08 0.14 0.10 0.26
Left leg balance test
TABLE 2 SDX and SDY Values for the Healthy and the ACL Reconstructed Group during the Three Different Balance Tests. SDx: Standard Deviation on x Axis, SDy: Standard Deviation on y Axis. Units of Measured Variables are as Follows: SDx (mm) and SDy (mm)
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Sway area
Superficial ellipse
1 2 3 1 2 3
Testing sessions
0.37 ± 0.51 0.46 ± 0.51 – 4051.94 ± 2136.84 3995.61 ± 2090.61 –
Double leg balance test 1.45 ± 0.89 1.24 ± 0.78 – 38955.42 ± 18119.55 32829.19 ± 14638.98 –
Right leg balance test
Healthy Group
2.19 ± 1.17 2.10 ± 1.26 – 49302.86 ± 23879.07 45761.05 ± 31332.07 –
Left leg balance test 0.29 0.30 0.24 3047.12 3066.10 3135.50
± ± ± ± ± ±
0.22 0.27 0.25 420.17 205.48 395.14
Double leg balance test
1.49 1.74 1.51 34759.80 29385.84 36425.48
± ± ± ± ± ±
0.82 0.93 0.99 14813.88 11899.16 13733.25
Right leg (injured) balance test
ACLr Group
0.97 1.03 1.50 18676.83 16850.87 19918.48
± ± ± ± ± ±
0.44 0.38 0.83 5800.17 5813.59 7402.77
Left leg balance test
TABLE 3 Sway Area and Superficial Ellipse Values for the Healthy and the ACL Reconstructed Group during the Three Different Balance Tests. Units of Measured Variables are as Follows: Superficial Ellipse (cm2) Sway Area (mm2)
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Sway Ellipse
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The Sway Ellipse mean values ranged from 0.37 ± 0.51 (double leg balance test) to 2.19 ± 1.17 cm2 (left leg balance test) (Table 3) for the healthy group. The ICC values ranged from 0.83 (left leg balance test) to 0.92 (double leg balance test) (Table 1). The mean values of the Sway Ellipse for the ACL group ranged from 0.24 ± 0.25 (double leg balance test) to 1.74 ± 0.93 cm2 (right leg balance test) and the ICC values ranged from 0.53 (left leg balance test) to 0.88 (double leg balance test) (Table 1).
DISCUSSION The results of this study indicated that double and single leg balance tests display moderate to high reliability in individuals with ACL reconstruction and controls. To our knowledge, no study examined the test–retest reliability of postural stability measures using computerized pressure plates in ACL reconstructed individuals. Nevertheless, our results are in agreement with those reported by Harrison, Duenkel, Dunlop, and Russell (1994) on single-leg standing balance measurements using simple ordinal scale in ACL reconstructed individuals. Further, studies on reliability of posture balance tests in ACL injured individuals also confirm our findings. In particular, Hadian et al. (2008), found low to moderate correlation coefficients (0.81 to 0.89) during single and double stance tests in ACL injured individuals while Salavatti et al. (2009) reported low to moderate reliability of posture balance measurements in a group of patients of diverse pathologies, including ACL injury. It has been suggested that reliability may be a population-specific property (Hadian et al., 2008). Consequently, it is difficult to make comparisons between different studies due to the differences in the population, the measured variables, the experimental setup and the duration or the number of trials. Nevertheless, our results indicate that evaluation of postural balance using computerized pressure plates in patients who underwent ACL reconstruction displays acceptable reliability. In the present study, some variables (total cop path, cop velocity and sway area) were more reliable for the ACL reconstructed group compared with the healthy group during the single limb balance tests. This is an interesting finding as one might expect a higher variability in balance parameters in the patient group due to ACL injury and subsequent ACL reconstruction surgery. There are various factors that might have contributed to these findings. First, the ACL reconstruction group included individuals who underwent surgery two years prior to the measurement session. They also underwent standard physical therapy treatment post surgery for an average period of 6 months and they were all physically active at the time of testing.
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Since ACL rehabilitation includes both muscle strengthening and balance training, one might suggest that they were trained in performing balance exercises (Ageberg, 2003). In contrast, the control group consisted of matched-paired individuals based on age and level of physical activity, who did not systematically take part in a balance or proprioception training program. This is further supported by the observation that reliability coefficients were higher in the ACL reconstruction group mainly during the right (injured) limb single balance test while differences in ICCs were smaller for the left leg single balance test and even smaller for the double leg test (Table 1). This leads us to suggest that the ACL reconstruction surgery and rehabilitation program followed by this particular group of patients aimed to restore postural stability of the ACL injured leg and less on the uninjured leg and, hence, they were more familiar and trained in balancing on their injured leg rather than performing exercises on the healthy limb or both legs. One might expect that reliability would be higher in the double leg support test. This is because during the single leg balance test, body mass is transmitted through only one leg, which involves a higher activity of fewer muscle groups to counteract any shifts in the centre of mass that may occur during the test. The continuous adjustments in muscle contraction coupled with a smaller base of support may increase postural sway and increase performance variability (O’Connell, George, & Stock, 1998). It was interesting that the ICC values were higher for double-leg balance tests compared with single-leg balance tests for the control group but not for the ACL reconstruction group (Table 1). As already mentioned, this may be a result of postsurgery rehabilitation followed by ACL reconstruction individuals with a focus on single leg, rather than double leg, balance exercises. Further research is necessary to examine variability during single and double leg balance tests after ACL surgery. It is not clear why differences in reliability coefficients between groups depend on the parameters used to assess balance (Table 1). As far as the right limb stance test is concerned, it appears that only the sway ellipse showed less reliability in the ACL group than the healthy group. This may be related to the nature of the ellipse, which is the outcome of fitting the COP path with a known geometrical measure without taking into consideration the total COP path, the speed of the COP or its full deviations relative to the mean value (Tropp et al., 1984). However, it our opinion that the implications of this finding for testing ACL reconstruction for single balance stability are rather limited. This is based on two factors: first, despite the aforementioned differences, all estimated parameters displayed moderate to high reliability. Second, variability in COP-related measures is common and may be non-systematic. Even when considering the data from both groups, reliability was higher for some postural stability variables as opposed to others (Table 1). In particular, we noticed that measurements in sway area, COP
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velocity, total COP path and superficial ellipse were more reliable and sensitive than the SDx and SDy (Table 1). As mentioned before, COP SDx and SDy are the standard deviations of the mean value of COP in anteroposterior and mediolateral axes respectively. This high variability of the SDx and SDy values leads to low ICC values. Even the smaller perturbation or change in subject position during testing has a pronounced effect on SD but a smaller effect on other variables. This has an implication for testing balance posture using posturography. In particular, the decision on which parameters should be based on the clinical or experimental use of the test as well as its reliability. The use of SD serves as a measure of the shifts of the COP during the whole test. For example, two individuals may show a very similar COP path and COP speed, but one may show a steady position of COP throughout the test while the other individual displays continuous small shifts relative to the baseline. If this information is essential for the clinician, evaluation may include multiple trials to reduce a potential reliability issue, as seen in this study. In contrast, evaluation of other variables, such as COP path or Speed is generally less prone to variability and, therefore, they can be used with more confidence. The results of this study showed large differences in COP path and COP speed between limbs for both groups. This is not in line with previous studies for both healthy individuals and individuals who underwent ACL reconstruction (Harrison et al., 1994; Henriksson, Ledin, & Good 2001; Hoffman, Schrader, & Koceja, 1999; Mattacola et al., 2002). The factors that might have contributed to this observation are not clear. The participants in the present study were systematically trained players. It is not clear whether training might have caused less balance ability on one leg over the other. There are suggestions in the literature that one leg is tuned for mobilizing features and the other leg for postural stability (Grouios et al., 2009), while others argue that one leg is predominantly used for the most difficult aspect of a task (Hart & Gabbard, 1997). If we take into consideration that the bilateral leg differences reported in this study were reproduced in three (for ACL group) or two (control group) consecutive testing sessions, then this deserves further consideration. Even in this case, however, the variability that characterizes balance ability precludes generalization of the present findings. Further research on bilateral leg differences in balance ability is guaranteed. As we mentioned previously it is rather difficult to make specific and direct comparisons across studies on the test–retest reliability of postural control measures. This is due to differences in the experimental set-up, the instructions given to subjects, the duration or the number of trials and the different measured variables. Previous studies that measured test–retest reliability examined only a few specific COP variables during single or double leg balance tests, but not during both conditions, and without examining the variability of the measures in healthy and ACL reconstructed groups. In the
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present study, we measured five COP variables during two different balance tests, single leg balance test and double leg balance test, between healthy and ACL reconstructed groups.
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CONCLUSIONS The results indicated a moderate to high reliability of single and double leg balance tests in patients who underwent ACL reconstruction. However, reliability was higher for the double-leg balance test compared with single-leg balance tests while the use of COP variability measures (SDx and SDy) was the least reliable and should be used with caution.
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