Sandra Saavedra

The development of trunk control and its relation to reaching in infancy: a longitudinal study

The development of reaching is crucially dependent on the progressive control of the trunk, yet their interrelation has not been addressed in detail. Previous studies on seated reaching evaluated infants during fully supported or unsupported conditions; however, trunk control is progressively developed, starting from the cervical/thoracic followed by the lumbar/pelvic regions for the acquisition of independent sitting. Providing external trunk support at different levels to test the effects of controlling the upper and lower regions of the trunk on reaching provides insight into the mechanisms by which trunk control impacts reaching in infants. Ten healthy infants were recruited at 2.5 months of age and tested longitudinally, until 8 months. During the reaching test, infants were placed in an upright seated position and an adjustable support device provided trunk fixation at pelvic and thoracic levels. Kinematic and electromyographic data were collected. Results showed that prior to independent sitting, postural instability was higher when infants were provided with pelvic compared to thoracic support. Associated reaches were more circuitous, less smooth and less efficient. In response to the instability, there was increased postural muscle activity and arm muscle co-activation. Differences between levels of support were not observed once infants acquired independent sitting. These results suggest that trunk control is acquired in a segmental sequence across the development of upright sitting, and it is tightly correlated with reaching performance.

Effect of Segmental Trunk Support on Posture and Reaching in Children With Cerebral Palsy.

Purpose: To test the effects of segmental trunk support on seated postural and reaching control in children with cerebral palsy. Methods: Seventeen children (age range 2-15 y, Gross Motor Function Classification System levels III-V) were classified with the Segmental Assessment of Trunk Control into mild (complete trunk control/lower lumbar deficits), moderate (thoracic/upper lumbar deficits), and severe (cervical/upper thoracic deficits). Postural and arm kinematics were measured while reaching with trunk support at axillae, mid-ribs, or pelvis. Results: Children in the mild group did not display changes in posture or reaching across conditions. The moderately involved group showed decrements in postural and reaching performance with pelvic compared with higher supports (P < .01). Children in the severe group were unable to maintain posture with pelvic support and showed postural deficiencies with mid-ribs compared with axillae support (P < .01). Conclusions: Children with cerebral palsy and trunk dysfunction demonstrate improved motor performance when the external assistance matches their intrinsic level of trunk control.

Effect of Biomechanical Constraints on Neural Control of Head Stability in Children With Moderate to Severe Cerebral Palsy

Background External support has been viewed as an important biomechanical constraint for children with deficits in postural control. Nonlinear analysis of head stability is necessary to confirm benefits of interaction between external trunk support and level of trunk control. Objective To compare the effect of biomechanical constraints (trunk support) on neural control of head stability during development of trunk control. Design Quasi-experimental repeated measure study. Methods Fifteen children (4-16 years) with moderate (Gross Motor Function Classification System (GMFCS) IV; n=8; 4 males) or severe (GMFCS V; n=7; 4 males) CP were compared to previous longitudinal data from TD infants (3-9 months of age). Kinematic data were used to document head sway with external support at four levels (axillae, mid-rib, waist, and hip). Complexity, predictability and active degrees of freedom (DOF) for both AP and ML directions were assessed. Results Irrespective of level of support, CP groups had lower complexity, increased predictability and greater DOF (p<0.001). The effect of support differed based on the childs segmental level of control. GMFCS V and youngest TD groups demonstrated better head control with increased complexity and decreased predictability with higher levels of support. GMFCS IV group had the opposite effect, showing decreased predictability, increased complexity and DOF with lower levels of support. Conclusions The effect of external support varies depending on the childs level of control and diagnostic status. Children with GMFCS V and young TD infants had better outcomes with external support, but external support was not enough to completely correct for influence of CP. Children with GMFCS IV performed worse with support at axillae or midribs suggesting that too much support can interfere with postural sway quality.

Segmental trunk and head dynamics during frontal plane tilt stimuli in healthy sitting adults

A more detailed understanding of trunk behavior during upright sitting is needed to create a foundation to address functional posture impairments. Therefore, we characterized the dynamics of the trunk and head during perturbed sitting. A three-link inverted pendulum model of head and trunk segments was used to analyze kinematics of eight healthy sitting adults. Magnetic sensors were placed at the head and two locations of the trunk (C7 and T7). Six surface tilt stimuli (two spontaneous sway tests [no surface stimulus; eyes open, EO/eyes closed, EC] and four tests with continuous pseudorandom surface tilts [2 peak-to peak amplitudes of 2° or 8°; EO/EC]) were applied in the frontal plane. We used frequency-response functions (FRFs) to analyze sway across ~0.045-3Hz and found systematic differences in sway dynamics across segments. Superior segments exhibited larger fluctuations in gain and phase values across frequencies. FRF gains in superior segments were attenuated compared to other segments only at low frequencies but were larger at the higher frequencies. We also tested the influence of stimulus amplitude and visual availability on FRFs. Across all segments, increasing stimulus amplitude and visual availability (EO) resulted in lower gains, however, these effects were most prominent in superior segments. These changes in gain were likely influenced by changes in sensory reliance across test conditions. In conclusion, these results provide a benchmark for future comparisons to segmental responses from individuals with impaired trunk control. We suggest that a frequency-based approach provides detail needed to characterize multi-segment dynamics related to sensorimotor control.

Trunk control in cerebral palsy: are we ready to address the elephant in the room?

From the earliest definitions onwards, deficits in postural control have been a hallmark of cerebral palsy (CP). Trunk control creates the foundation of postural control and has long been recognized as a primary factor in predicting ambulatory status of children with CP. Historically, evaluating the contribution of trunk control to function in children with CP has been difficult to address. Thus, focus on assessment and treatment of trunk control in children with CP has been scattered and sparse in comparison to the focus on upper and lower extremity research and treatment. Like the proverbial ‘elephant in the room’ the issue of trunk control in this population cannot continue to be ignored. The article by Sæther et al. offers concrete clinical options for beginning to explore and discuss the potentially crucial contribution of trunk control to gait deviations in children with CP. There have been a number of recent advances with development of specific assessment techniques for trunk control in children with CP. Sæther et al. take advantage of the increased specificity of two of these evaluations, the Trunk Impairment Scale (TIS) and the Trunk Control Measurement Scale (TCMS), in order to examine the relation between trunk control and gait deviations in ambulatory children with CP. The focus of their research is to provide busy clinicians with a screening tool for selecting those children in whom trunk control may play a critical role in the success of gait interventions. It is important to note that these are preliminary steps toward further examination and exploration of the contribution of trunk control to functional skills in children with CP. We do not yet know if treatment of trunk control in sitting can generalize to improvements during gait or if specific training of the trunk during gait may be warranted. While a number of treatment regimes have claimed to contribute to improved postural control in children with CP, these must be interpreted with caution until more rigorous testing for reliability and responsiveness of clinical balance tools is completed. At the very least, the results reported by Sæther et al. support a more comprehensive evaluation of trunk control for this group of children prior to major decisions regarding interventions for gait. From a research perspective, the suggested subscales also provide amethod for selecting the population of children with greatest potential to showmeasureable functional gait changes in relation to intervention. Sæther et al.’s results also serve as guideposts toward future empirical studies aimed at isolating the most critical components of trunk control with respect to specific gait deviations. The subscales with the strongest correlation to gait deviations in this article examined different aspects of trunk control. The TIS dynamic sitting balance (DSB) items have been referred to as a test of selective movement control within the base of support, while the TCMS dynamic sitting balance reaching (DSB-R) is a test of trunk control outside the base of support. Interestingly, the TIS (DSB) components are all present in the TCMS dynamic sitting balance selective movement control subscale (DSBS), yet the TIS (DSB) was highly correlated with trunk control during gait and the TCMS (DSB-S) was poorly correlated. The difference in the two subscales is that the TCMS (DSB-S) includes additional items that examine selective control of trunk movements in the sagittal plane. These results in conjunction with recent work of Heyrman et al. suggest that selective control of trunk movements in the lateral and transverse planes may be most critical to trunk control during gait. The specificity of new interventions could be further improved by analysis with the Segmental Assessment of Trunk Control (SATCo). The combination of SATCo to isolate contributions of different trunk segments along with the TCMS to determine specific aspects of selective control could increase the specificity and efficiency of new interventions.

Hippotherapy simulator for children with cerebral palsy.

We have developed a mechanical horseback riding simulator for the rehabilitation of children with neurological and musculoskeletal disabilities, focused on improving trunk control in this population. While overseen by a physical or occupational therapist, the movement of a horse is often used as therapy for these patients (hippotherapy). However, many children never have the chance to experience hippotherapy due to geographical and financial constraints. We therefore developed a horseback riding simulator that could be used in the office setting to make hippotherapy more accessible for our patient population. The system includes a motion platform, carousel horse, and tracking system. We developed a virtual reality display which simulates a horse moving along a pier. As the horse moves forward, other horses come toward it, and the patient must lean left or right to move out of the way. The tracking system provides the position of tracking markers which are placed on the patient’s back, and this information is used to control the motion of the horse. Under an Institutional Review Board (IRB) approved trial, we have enrolled two patients with cerebral palsy to date. This was after completing testing on five healthy pediatric volunteers as required by the IRB. Early results show the feasibility of the system.

Sensorimotor control of the trunk in sitting sway referencing

We developed a sway-referenced system for sitting to highlight the role of vestibular and visual contributions to trunk control. Motor control was investigated by measuring trunk kinematics in the frontal plane while manipulating visual availability and introducing a concurrent cognitive task. We examined motor learning on three timescales (within the same trial, minutes), within the same test session (1 h), and between sessions (1 wk). Posture sway was analyzed through time-based measures [root mean square (RMS) sway and RMS velocity], frequency-based measures (amplitude spectra), and parameterized feedback modeling. We found that posture differed in both magnitude and frequency distribution during sway referencing compared with quiet sitting. Modeling indicated that sway referencing caused greater uncertainty/noise in sensory feedback and motor outputs. Sway referencing was also associated with lower active stiffness and damping model parameters. The influence of vision and a cognitive task was more apparent during sway referencing compared with quiet sitting. Short-term learning was reflected by reduced RMS velocity in quiet sitting immediately following sway referencing. Longer term learning was evident from one week to the next, with a 23% decrease in RMS sway and 9% decrease in RMS velocity. These changes occurred predominantly during cognitive tests at lower frequencies and were associated with lower sensory noise and higher stiffness and integral gains in the model. With the findings taken together, the sitting sway-referenced test elicited neural changes consistent with optimal integration and sensory reweighting, similar to standing, and should be a valuable tool to closely examine sensorimotor control of the trunk. NEW & NOTEWORTHY We developed the first sway-referenced system for sitting to highlight the role of vestibular and visual contributions to trunk control. A parametric feedback model explained sensorimotor control and motor learning in the task with and between two test sessions. The sitting sway-referenced test elicited neural changes consistent with optimal integration and sensory reweighting, similar to standing, and should be a valuable tool to closely examine sensorimotor control of the trunk.

The Impact of Segmental Trunk Support on Posture and Reaching While Sitting in Healthy Adults

ABSTRACT The authors investigated postural and arm control in seated reaches while providing trunk support at midribs and pelvic levels in adults. Kinematics and electromyography of the arm and ipsiliateral and contralateral paraspinal muscles were examined before and during reaching. Kinematics remained constant across conditions, but changes were observed in neuromuscular control. With midribs support, the ipsilateral cervical muscle showed either increased anticipatory activity or earlier compensatory muscle responses, suggesting its major role in head stabilization. The baseline activity of bilateral lumbar muscles was enhanced with midribs support, whereas with pelvic support, the activation frequency of paraspinal muscles increased during reaching. The results suggest that segmental trunk support in healthy adults modulates ipsilateral or contralateral paraspinal activity while overall kinematic outputs remain invariant.

Measuring trunk control in cerebral palsy: what's next?

Definitions of cerebral palsy (CP) have for many years described it as a ‘disorder of movement and posture’. It is thus surprising that so little attention has been paid historically to the foundational role that trunk control might play in the motor deficits exhibited by these children. This is now changing. Over the past decade a battery of new assessment tools specifically designed to measure trunk control in children with CP have been developed. In the past 5 years, a number of published studies using these new assessments have reflected the central role played by trunk control on functional skills in ambulatory and non-ambulatory children with CP. The paper by Marsico et al. contributes to this growing body of evidence. By expanding the population to include children aged 5 to 8 years of age with a range of neuromotor deficits, these authors have provided data for the Trunk Control Measurement Scale (TCMS) that supports its use for the heterogeneous populations seen in most clinical settings. Cut points with respect to independence in self-care or mobility and scores on the TCMS will appeal to clinicians; however, this information should be used with caution. We do not yet adequately understand the relationship between these cut points and clinical outcomes. More information is needed to understand why there were children with scores above the cut point (eight children for self-care, nine children for mobility) who were not independent. Are factors other than trunk control limiting that subgroup of children? Does this type of cut point require a combination of trunk and extremity measures? Likewise, what is unique about the five children (three children for self-care, two children for mobility) who were independent in spite of scores below the cut points? Logically, training trunk control would help a child gain independence but we do not yet have data that demonstrates a causative relation between changes in trunk control and functional skills or independence. In order to understand causation we need to measure change in trunk control and its relationship to control of the head, eyes, and extremities over time. The next critical step is for researchers and clinicians to embrace the task of testing responsiveness for this new battery of assessments. At the heart of the dilemma for studying responsiveness is the selection of a population and an intervention that is likely to exhibit consistent change in trunk posture control. Not only is there scarce data regarding the responsiveness of these trunk assessment tools, there is limited data regarding the plasticity of trunk control, especially in children with CP. Although it may sound counterintuitive, the first tests of responsiveness may need to be completed in typically developing children below 2 years of age because this is the critical period during which trunk control usually develops. Once responsiveness and trajectories of trunk control have been established and validated in typically developing children, we will be able to address constraints on development of trunk control in children with CP. From this perspective it would be valuable to adapt and test the TCMS for reliability and validity in young, typically developing children even though it was originally created for older children with CP. Progress over the past decade provides ample evidence that trunk control can be studied with higher specificity in a clinically meaningful way. We are poised to take the next essential steps for understanding current treatments and creating strategies to improve outcomes. The children and families who face daily struggles with the consequences of trunk control deficits have been waiting a long time for the attention of researchers and clinicians. Let’s start now.

Corrigendum: The development of trunk control and its relation to reaching in infancy: a longitudinal study.

[This corrects the article on p. 94 in vol. 9, PMID: 25759646.].