Dynamic Balance

Dynamic balance is affected by medial compartment knee OA and in this study, we have determined that the modified SEBT is both a reliable and more functional test of dynamic balance than the commonly used ST. Both raw and normalised excursiondistance demonstrated high reliability for both sides with the anterior/medial directions with ICCs ranging from 0.92 to 0.98. However, the ST was less reliable for the affected side (knee OA) and contralateral side in individuals with medial knee OA, with ICC ranging from 0.57 to 0.46. So far, no studies have investigated the reliability of the SEBT and ST in individuals with medial knee OA, therefore this study is the first study that has compared both tests in measuring dynamic balance and evaluated the between-session reliability. However, the test-retest reliability of the original SEBT has been investigated in many studies in healthy subjects (Kinzey and Armstrong, 1998; Munro and Herrington, 2010).

The findings of this study support those of Kinzey and Armstrong (1998) who found that the test- retest reliability ranged from 0.67 to 0.87 in young healthy subjects. The participants performed five trials in four different diagonal directions; antero-medial, antero-lateral, postero-medial, and postero-lateral with wearing shoes. This procedure could reduce the consistency of the results because a variety of footwear may affect the reliability values by changing the balance base. Fatigue

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is another potential reason that could occur during the trials, therefore the reach distance may be influenced significantly (Gribble et al., 2004) leading to reduce the reliability. In addition, The findings of this study support those of Plisky et al., (2006) who found that the test-retest reliability (between sessions) of the SEBT with normalised distances (to leg length) was excellent, with ICCs ranging from 0.89 to 0.93; however, only three directions (A, PM, PL) were tested with athletes subjects (Plisky et al., 2006).

Most recently, Munro and Herrington (2010) demonstrated that the between-session reliability of the SEBT was high in all eight directions. ICCs were 0.84 and 0.86 for normalised excursion in anterior and medial directions, respectively. Whereas, for the raw excursion, ICCs were 0.88 and 0.90 for the anterior and medial directions, respectively. Their findings were lower compared to the current study, and this may be explained by the current study as this used modified SEBT where very accurate lines are on the platform determining foot position accurately throughout the tests in two sessions with the block denoting the distance reached. The participants in Munro and Herrington’s (2010) study were younger and healthy, therefore the different age groups and diseases may play a role as psychological reasons and may be the standard test ordering which was followed in the current study allowed for a highly consistent performance. Additionally, it may also be because the healthy individuals are reaching very far and the OA subjects are limited so the actual distance is probably lower and therefore some of the variability is reduced. However, there are slight differences in the ICC values in all the reliability studies of the SEBT (Kinzey and Armstrong, 1998; Hertel et al., 2000; Plisky et al., 2006; Munro and Herrington, 2010) including the current study, SEBT has shown excellent reliability to measure the dynamic balance in healthy subjects and in individuals with medial knee OA.

To our knowledge, this study is the first study that has investigated the reliability of ST to measure dynamic balance in individuals with medial knee OA. The current study shows that the ST has fair reliability to measure dynamic balance for both sides (ICC>0.47-0.57). Two previous studies investigated the reliability of step test to measure dynamic standing balance in stroke patients (Hill, 1996; Hong et al., 2012). Hill (1996) investigated the reliability of the ST to measure dynamic standing balance in stroke patients. Test-retest reliability was high with ICC>0.88 in stroke patients. The participants in Hill’s (1996) study were stroke patients while individuals with medial knee OA were recruited in the current study, therefore the different groups could be the reason for the different ICC values. Thus, this test could be suitable for individuals with cardiovascular diseases or upper motor neuron lesion. In the majority of the knee OA studies (Hinman et al., 2002; Bennell et al., 2010), they have used the ST with a 15 cm step height (as with this study) whereas the step height

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was 7.5 cm in Hill’s study (1996), therefore increasing step height could reduce the reliability of the ST because the participants need stronger muscle to lift their leg higher and may lead to muscle fatigue with repetition (less muscle performance with lower height). The same reason (variability of step height and different population) could be behind the reduction in the ICC value (ICC=0.47- 0.57) in the current study compared to a recent study (Hong et al., 2012). They used videotapes to record the trials (three trials) and from data of the second and third trials, ICCs were calculated (ICC=0.981-0.993) in Chinese population with stroke. Therefore, by using the data of the second and third trials, the learning effect could be reduced and thereby the ICC improved significantly.

As with any study, there are limitations to these results that include the relatively short time between tests which may have created some familiarisation effect although this should be controlled with the four practice trials for SEBT. The small sample size could be criticised although significant correlations have been found with small SEMs. Finally, the population sample were all individuals with mild knee OA and future studies should determine whether the results are applicable to greater severities of knee OA.