Reliability, validity, and effectiveness of center of pressure parameters in assessing stabilometric platform in subjects with incomplete spinal cord injury: a serial cross-sectional study

Journal of NeuroEngineering and Rehabilitation Reliability, validity, and effectiveness of center of pressure parameters in assessing stabilometric platform in subjects with incomplete spinal cord injury: a serial cross-sectional study Federica Tamburella 0 Giorgio Scivoletto 0 Marco Iosa 1 Marco Molinari 0 0 Clinical and Movement Analysis Research Laboratory- CaRMA Lab, Spinal Cord Unit, IRCCS Santa Lucia Foundation , Rome , Italy 1 Clinical Laboratory of Experimental Neurorehabilitation, IRCCS Santa Lucia Foundation , Rome , Italy Background: Spinal cord injury (SCI) can damage long tracts, affecting postural stability. Impairments in balance have recently been proposed to be highly predictive of functional recovery in patients with SCI and thus merit evaluation. In addition to common observational clinical scales, more objective evaluation methods of balance can be implemented by analyzing center of pressure (COP) parameters using stabilometric platforms (SPs). COP analysis has been used in various pathologies, but the COP parameters with regard to measurement vary, depending on the features of the target population, and have only been assessed in healthy subjects. Specifically, concerning subjects with SCI, few studies have reported COP parameters, and none has addressed the reliability, validity, or responsiveness of this measure. The objective of this serial cross-sectional study was to analyze the reliability, validity, and responsiveness of COP parameters under various conditions in incomplete SCI subjects to assess balance. Methods: Twenty-three patients with incomplete SCI were examined 111 times for 1 year. Each session comprised administration of the Berg Balance scale, Tinetti scale, and WISCI scale and evaluation of stabilometric platform use. Stabilometry was performed under various sensory conditions (OF: open feet; CF: closed feet; OE: open eyes; CE: closed eyes), wherein several COP parameters were analyzed (L: COP path length; V: mean COP velocity, VAP: anteroposterior COP velocity; VLL: laterolateral COP velocity, A: COP ellipse area, SA1: x-axis of COP ellipse area; SA2: y-axis of COP ellipse area). The reliability, validity, and responsiveness of COP parameters that were associated with visual/support area conditions were analyzed. Results: Of the COP parameters, V and arithmetically related measures had the highest reliability, validity, and effectiveness scores. Of all test conditions, OE-OF was the most valid, whereas CE-OF was the most responsive. Conclusion: The assessment of balance in SCI subjects can be reliable, valid, and effective in acquiring V data, based on OF-OE and OF-CE conditions and heel distance values. Spinal cord injury; Stabilometry; Center of pressure; Balance; Reliability; Validity - Background Balance is usually defined as preservation of the vertical projection of the bodys center of mass (COM) onto the support area that is formed by the feet [1]. Human balance is typically modeled as an inverted pendulum, in which the body is controlled as a single rigid segment that supports a single mass pointthe COMwhich rotates around the ankle joint [2]. The inverted pendulum is regulated through the development of ground-reaction forces, the vector sum of which is applied to a point that is defined as the vertical projection of the COM onto the ground [3]: the center of pressure (COP). The bodys equilibrium is maintained by the central nervous system, which fixes the COM around a specific pointa goal that is under constant challenge by continuous perturbations to the COM by factors, such as breathing, heart rate, and muscle activity [4]. To maintain postural stability, several afferent inputs, such as visual, vestibular, and somatosensory, are integrated and converted into efferent motor outputs, which in turn are transmitted down to the spinal cord along various motor tracts [5]. Postural sway, such as spontaneous shifts in the COP during quiet standing, represents the integrated output of complex interactions between systems [6]. Damage to any of these systems can result in postural instability, affecting static and dynamic balanceie, stance and gait [7]. Of the postural control systems, the spinal centers have a significant function, explaining the clinical relevance of postural control deficits in spinal cord injury (SCI) [8,9]. Despite the availability of many technical instruments to assess balance, the most common clinical tools remain observational scales, such as the Tinetti [10] and Berg balance scales [11]. Nevertheless, these scales are hampered by a lack of sensitivity and objectivity and are limited by floor-ceiling effects [11,12]. To overcome these drawbacks, stabilometric platforms (SPs), consisting of a rigid plate that is supported by force transducers, and COP analyses have been introduced in clinical settings [6]. Many studies have reported the use of various SPs to evaluate balance deficits in healthy subjects [13] and in several pathologies, including orthopedic diseases [14], neuropathic lesions [15], essential tremor [16], Parkinson disease [15], multiple sclerosis [17], muscular dystrophy [18], cerebral palsy [19], cerebellar ataxia [20], and stroke [21]. Two recent studies assessed balance in SCI, examining recoveries after visual biofeedback rehabilitation by COP analysis [8,9]. Impaired balance is a significant limitation to overground ambulation in patients with SCI [11], and impairments in balance are predictive of gait recovery [22], thus meriting evaluation [9]. Despite the growing interest in balance, the standardization of COP parameters with regard to measurements and the related quality domains [23,24] (ie, reliability, validity, and responsiveness) [25] is poor [26] and is absent from the SCI population. COP measurements have been examined in healthy elderly individuals [6,27] and in patients with Parkinson [28] and orthopedic diseases [29]. Data from healthy subjects can inflate the reliability estimates, because measurements can be made in them more easily than in patients [6]. Measurement errors, and hence the reliability of a measure, are not fixed but depend on the study population [30] and can vary between test conditions [6]. Thus, measurement properties must be specified for a study population and test conditions. No study has examined the properties of COP parameters by SP in subjects with SCI. Our serial cross-sectional study aimed to determine the reliability, validity, and responsiveness of COP parameters under various test conditions and define the protocol parameters that are suitable for specifically assessing balance in subjects with incomplete motor SCI. Methods Population This serial cross-sectional study included 23 subjects with incomplete motor SCI. The inclusion criteria comprised traumatic and nontraumatic etiology, subacute and chronic AIS D SCI, and the ability to maintain a standing position unsupported for at least 52 s. The exclusion criteria were the (...truncated)