Published by : PROFESSIONAL MEDICAL PUBLICATIONS
April - June 2008 (Part-II)
Evaluation of postural balance using the
biodex balance system in subjects
with and without low back pain
Noureddin Karimi1, Ismaeil Ebrahimi2, Sedigheh Kahrizi3, Giti Torkaman4
Objective: To evaluate the reliability of dynamic standing balance in individuals with and without low back pain (LBP) using Biodex Balance System (BBS) and to compare the balance indices between two groups.
Design: A cross-sectional non-experimental design.
Setting: Biomechanics laboratory and Saba spine specific physical therapy clinic, University of social welfare and rehabilitation sciences, Tehran, Iran.
Methodology: Twenty three male patients with LBP (mean age: 30.4 ± 6.5 years) and twenty age-matched healthy male subjects (mean age: 29.8 ± 6.4 years) participated in this study. Medial–lateral stability index (MLSI), Anterior–posterior stability index (APSI) and an Overall stability index (OSI) were measured in two measurement sessions using the BBS. Balance was measured in four conditions; bilateral and unilateral stance with eyes open and eyes closed; over a period of 20s.
Results: The results showed that ICC in healthy subjects and those with LBP was between (0.91-0.95) and (0.88-0.96) respectively. The Bland-Altman plot of agreement in balance scores between tests and retests demonstrated good agreement. A significant difference was found in MLSI and OSI between subjects with and without LBP. However, no significant difference was detected in APSI between two groups.
Conclusions: The findings of this study showed high reliability for BBS to evaluate dynamic postural balance in subjects with and without LBP. It seems that MLSI and OSI significantly differ between subjects with and without LBP.
KEY WORDS: Biodex Balance System, Low Back Pain, Balance.
Pak J Med Sci April - June 2008 (Part-II) Vol. 24 No. 3 372-377
How to cite this article:
Karimi N, Ebrahimi I, Kahrizi S, Torkaman G. Evaluation of postural balance using the biodex balance system in subjects with and without low back pain. Pak J Med Sci 2008;24(3):372-7.
1. Nooreddin Karimi, PT, M.Sc, PhD
Tarbiat Modares University,
Tehran, Iran. Address all correspondence to N Karimi.
2. I Ebrahimi, PT, PhD,
Professor, Faculty of Rehabilitation,
Iran University of Medical Sciences,
3. S Kahrizi PT, PhD,
Tarbiat Modares University,
4. G Torkaman PT, PhD,
Tarbiat Modares University,
Noureddin Karimi, PT., M.Sc, Ph.D candidate.
Department of Physical Therapy,
Tarbiat Modares University, Tehran, Iran.
Faculty member at University of Social Welfare
& Rehabilitation Sciences.
* Received for Publication: April 17, 2008
* Revision Received: April 21, 2008
* 2nd Revision Received: April 28, 2008
* Final Revision accepted: May 10, 2008
Low back pain (LBP) is one of the most common and costly musculoskeletal complaints in today’s societies, affecting up to 70-80% of the population at least one episode during their lifetime.1 Several factors such as lumbar spine stiffness, muscle shortness and weakness, decreased muscle endurance have been associated with the LBP.2,3 Several recent studies have also indicated that patients with LBP show reduced postural control commonly manifested in balance problem.4-7 The maintenance and control of balance, whether under static or dynamic conditions, is considered as an essential requirement for physical and daily activities.8 Thus postural control variables have often been used to evaluate patients with various musculoskeletal or neuromuscular disorders.9,10 Balance is a complex function involving numerous neuromuscular processes.11,12 Balance is controlled by sensory input, central processing, and neuromuscular responses. The sensory components include the vestibular, visual and proprioceptive systems.13-16 An appropriate motor response requires an intact neuromuscular system and sufficient muscle strength to return the center of mass within the base of support when balance is disturbed.17 Proprioceptive impairment has also been suspected as one of the possible causes for balance impairments in LBP. LBP has been associated with decreased muscle strength and proprioception.2,3 This may affect the quality of sensory information and disrupt the relation between postural responses and sensory information. The Biodex Balance System (BBS; Biodex Inc.) has been used to evaluate postural balance in recent years.18,19 The BBS is a multi-axial device that objectively measures and records an individual’s ability to stabilize the involved joint under dynamic stress. It uses a circular platform that is free to move in the anterior–posterior and medial–lateral axes simultaneously.19 The BBS allows up to 20° of foot platform tilt, which permits the ankle joint mechanoreceptors to be stimulated maximally. The BBS measures, in degrees, the tilt about each axis during dynamic conditions and calculates a medial–lateral stability index (MLSI), anterior–posterior stability index (APSI), and an overall stability index (OSI). These indexes represent fluctuations around a zero point established prior to testing when the platform is stable.19 For example, an OSI of 5° would be interpreted to mean that on average, the displacement from center is 5°.
Previous studies have shown that BBS is reliable for evaluating dynamic postural balance in healthy subjects.19,20 It has been assumed that in normal subjects, balance and postural adjustments during standing are generally achieved using "ankle strategy", while patients with LBP use different strategies to maintain balance.8,21,22 Furthermore some attributed changes in postural control in LBP patients to pain and disability. This interference is likely to contribute to different adaptive changes in postural control and balance in individuals with LBP.
The purpose of this study was to evaluate the reliability of dynamic standing balance in individuals with and without LBP using BBS and to compare the balance indices between two groups.
Subjects: Twenty three LBP male patients (age: 30.4±6.5 years, height: 174.5±7.3cm, weight: 76.6±10.8kg) and twenty age-matched healthy subjects (age: 29.8±6.4 years, height: 174.9±6.4cm, weight: 76.1±10.1kg) participated in this study. All the individuals who were participated in the study filled out a simple health questionnaire. Those who met the selection criteria were included in the study. All the subjects signed an informed consent form approved by the human subjects committee at the Tarbiat Modares University before participating in the study. LBP patients were included if they had a history of LBP for more than six weeks before the study or had on and off back pain and had experienced at least three episodes of LBP, each lasting more than one week, during the year before the study. Asymptomatic subjects were evaluated and found to have no complaint of any pain or dysfunction in their low back, thoracic and neck area and lower extremities. Subjects with history of spinal surgery, fracture of the spine, pelvis and lower extremities, hospitalization for severe trauma or car accident, leg length difference, hip/knee dysfunctions, any systemic disease such as arthritis or tuberculosis and liver and/or kidney failure were also excluded.
Instruments and procedure: The BBS was used to measure balance and postural stability under dynamic stress (BBS; Biodex Inc., Shirley, NY). As noted, the BBS uses a circular platform that is free to move in the anterior–posterior and medial - lateral axes simultaneously. The BBS allows up to 20° of foot platform tilt and calculates three separate measures: MLSI, APSI and OSI. A high score in the for example, OSI, indicates poor balance. The OSI score is believed to be the best indicator of the overall ability of the patient to balance the platform. The stability of the platform can be varied by adjusting the level of resistance given by the springs under the platform. The platform stability ranges from 1–8, with 1 representing the greatest instability. The lower the resistance level the less stable the platform.22-24 In this study, we assessed bilateral and unilateral stance both with eyes open and eyes closed with the BBS over a period of 20s. Stability levels were changed from level 6 to level 3 and from level 8 to level 4 for bilateral and unilateral stance assessment respectively, and subjects were instructed to maintain their center of pressure in the smallest concentric rings (balance zones) of the BBS monitor, named A zone. All subjects in two groups were right leg dominant and right leg was used for stability scores in unilateral stance. To begin, participants stood on the BBS’s locked platform. To assess the foot position coordinates and establish the subjects’ ideal foot positioning for testing, the stability platform was unlocked to allow motion. Participants were instructed to adjust the position of the foot until they found a position at which they could maintain platform stability. The platform was then locked. Foot position coordinates were constant throughout the test session. Next, testing began as the platform was released for a 20s trial and participants were asked to maintain an upright standing position on their limb/limbs. For the trial to be complete, balance needed to be maintained for 20 sec.23-25 All participants were trained 1 min for adaptation to the machine, following which three practice trials, to reduce any learning effects, and three test evaluations were performed in each measurement session. A mean score was calculated from the three trials. As noted, balance was measured in four conditions: bilateral and unilateral stance with eyes open and eyes closed. The tester undertook the balance test in each condition in random order and not in specified in subjects.
The subjects were assigned to two groups (with and without LBP) by an independent observer. The tester was unaware of the group assignment and completed balance test using BBS. Two days after the first measurement session, the tester retested the subjects in the second measurement session in a random order, different from the first measurement session.
Data Analysis:The intra-class correlation coefficient (ICC), two way mixed effect model, was used to assess intra-tester reliability of the measurement for dynamic standing balance in patients with LBP and control group. We calculated the ICC (3,1), because only one judge evaluated the same population of subjects. The 95% limits of agreements method of reliability assessment providing upper and lower limits for variation with a confidence level of 95% was measured by plotting a Bland-Altman plot to assess absolute reliability. Independent t–test was also used to determine any difference in balance scores between LBP patients and control group.
Twenty three male patients with LBP (age: 30.4±6.5 years, height: 174.5±7.3cm, weight: 76.6±10.8kg) and twenty age-matched healthy male subjects (age: 29.8±6.4 years, height: 174.9±6.4cm, weight: 76.1±10.1kg) participated in this study. Statistical analysis (independent t-test) revealed no significant difference in age (P = 0.87), weight (P = 0.83) and height (P = 0.83) between two groups.
Table-I presents the ICC for each index in different test position. All ICC values were greater than 0.90 and 0.85 in healthy subjects and those with LBP, respectively. (Table-I). The Bland-Altman plot of agreement in balance scores between tests and retests demonstrated good agreement between test and retest. The Bland-Altman plot for OSI in double leg eyes open condition is shown in Fig-1 as an example.
Independent t-test showed significant difference in the OSI (P < 0.001) and MLSI (P< 0.001 = 0.25) in four test conditions between subjects with and without LPB. Our data, however, showed no significant difference in APSI between two groups (Table-II).
Our data indicate a high reliability in balance test indices measured by using BBS (OSI, APSI, MLSI) both in subjects with and without LBP (Table-I, Fig-1). This finding is in accordance with other studies showing good reliability for using BBS to assess postural balance in healthy subjects.19,20 The BBS was shown to be reliable in several previous studies. Pincivero et al. found the BBS to be a reliable assessment device across multiple test trials (20 sec) in healthy college students (N = 20). At Level 2 resistance (out of 8 possible), the ICC for the OSI measures was 0.60 for testing on the dominant and the non-dominant limb.26 At Level 8, the ICC was 0.95 for the dominant limb, and 0.87 for the nondominant limb. Pincivero et al. recommended two practice trials.26 With respect to the other two indexes available when using the BBS (MLSI and APSI), Schmitz and Arnold found with a decreasing stability protocol (from Level 8 to Level 1 over 30 sec; N = 19), intra-tester reliability of 0.80 for the APSI and 0.43 for the MLSI.21 The intra-tester reliability was reported as 0.82 for the OSI. Schmitz and Arnold concluded that the overall stability index measures were the most reliable. Reliability estimates obtained in this study for the OSI measures were higher than those reported by Pincivero et al.26 The high reliability estimates of the OSI measures was found in this study, supports the conclusion drawn by Schmitz and Arnold21 that the overall stability index measures may be more reliable than the other two indexes. The more important observation, however, was that for the protocol of two test trials, all of the measures provided by the BBS had similar and good, reliability estimates. However, the significance of this study was assessing the reliability of BBS to assess postural control both in subjects with and without LBP. We found that BBS is reliable for postural balance assessment is LBP patients and could be used in studies assess balance in these patients. The results of this study showed a significant difference in the OSI and MLSI between subjects with and without LPB. Our data, however, showed no significant difference in APSI between two groups (Table-II).
Similar findings have been reported by others.4-7 An appropriate motor response for postural balance control requires an intact neuromuscular system and sufficient muscle strength to return the center of mass within the base of support when balance is disturbed. Decreased muscle strength and proprioception in LBP patients compared to those without LBB have been shown in several studies. Muscle weakness and proprioceptive impairment has been suspected as one of the possible causes for balance impairments in patients LBP.2,3,6,7 This may affect the quality of sensory information and disrupt the relation between postural responses and sensory information.27-30 Nadler et al found that muscle imbalance in hip abductors is highly associated with LBP occurrence in female athletes.31 The fact that in this study there was significant difference in MLSI and no significant difference in APSI between healthy group and LBP patients may be because of hip abductor weakness and imbalance in patients with LBP.
The findings of this study showed high reliability for BBS to evaluate dynamic postural balance in subjects with and without LBP. It seems that MLSI and OSI significantly differ between subjects with and without LBP. However, there is no significant difference in APSI between the LBP patients and those without LBP.
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