"Determining the Reliability of an Axial Rotation Measure for Children" by Quimby Wechter

Updated: Dec 2, 2020

Determining the Reliability of an Axial Rotation Measure for Children with Cerebral Palsy: Empowering Greater Activity, a Proof of Concept Study

by Quimby Wechter, University of Hartford

Abstract: Children with cerebral palsy (CP) tend to hold their body stiffly and lack normal axial rotation, limiting their movement and interfering with full participation in activities with their peers. A valid and reliable method for quantifying axial rotation is necessary to systematically address this deficit. The goal of the current study was to determine if a device originally created to measure functional axial rotation in adults could be modified for a child-friendly, reliable measure of axial rotation in typically developing (TD) children and children with CP. Child-friendly modifications to a published adult functional rotation measure were completed. Four TD children (TD, 5-7 years old) and three children with severe CP, (3-7 years old) were tested by two different raters. The raters rescored all video recorded evaluations along with two additional raters. Inter-rater reliability for video data and intra-rater reliability for in-person versus video data were excellent. Inter-rater reliability during live testing was moderate to good. External trunk support reduced degrees of rotation for TD children, however it allowed children with severe CP to participate in the study. Significant differences in degree of axial rotation were noted when comparing TD children to children with CP. This method of quantifying degrees of rotation was reliable across testers and well tolerated by children. With a better understanding of axial rotation, further studies can be completed, and new interventions can be developed to help children with disabilities participate more fully in physical activities.


Limited axial rotation is a clinically recognized issue for children with cerebral palsy (CP); however, little research has been completed on this topic. Cerebral palsy is a disorder that causes children to have slow motor development, abnormal muscle tone, and unusual posture as a result of a lack of trunk control (Krigger 91). This neurological condition affects about 0.002% of children born in the United States due to a brain injury before complete development of the brain (Krigger 91). The severity of CP varies for each child and different symptoms and developmental delays manifest. Increases in the severity of CP are associated with limited range of motion, spinal misalignment, and pain (Bartlett et al.155). While there are a number of tests that evaluate trunk postural control in children with CP, there are currently no tests that quantify functional axial rotation for this population (Butler et al. 246; Heyrman et al. “Clinical Tool” 2624; McCoy et al. 375).

Axial rotation is the ability to rotate the spine around its axis, allowing people to twist to the left or right while remaining upright. Many everyday activities require axial rotation. For example, turning and looking back while reversing a car or turning to look back as someone approaches both require axial rotation. Experiencing a stiff neck or back often lead to people turning their whole body to see something because they cannot rotate. This is the perfect example of the importance of axial rotation. Children with CP tend to hold their body more stiffly, which in theory leads to deficits in axial rotation. These deficits in axial rotation can make it more challenging for children with CP to participate in physical activities such as dance. In order to eventually explore the relationship between axial rotation, functional activities, and children’s ability to participate in recreational activities, a reliable device is needed.

Currently, there are several options for measuring cervical rotation including clinical evaluation, X-ray, CT and MRI, goniometers, inclinometers, Cybex, and 3D kinematic analysis (Antonaci et al. 46-52). However, these measures are used for measuring cervical rotation, not axial rotation. Axial rotation is rotation of the trunk, whereas cervical rotation is rotation of the neck and head. Some measures of trunk control include a basic rotational measure. Both the Trunk Control Measurement Scale and Trunk Mobility Scale evaluate axial rotation on a basic three and four number scale, respectively (Heyrman et al. “Clinical Characteristics” 329; Franco et al. 637). When graded via the Trunk Control Measurement Scale, most children with CP showed deficits in axial rotation (Heyrman et al. “Clinical Characteristics” 332). However, this scale does not give a clear degree of axial rotation which would be useful in a clinical setting, such as a physical therapy clinic or medical treatment facility. These assessments also require that the child be able to sit independently with adequate stability for movement thus they are only possible for children with mild to moderate CP and cannot be used for children with severe CP who are in greatest need for quantification and improved interventions for trunk posture control.

Within the medical field, it is recognized that limited rotation interferes with daily activities across a variety of diagnoses. Thus, devices have been created to measure axial rotation primarily in adult populations, to determine if changes in rotation lead to increased performance in daily tasks. A Functional Rotation Test has been tested on patients with and without Parkinson’s Disease (PD) (Batavia and Gianutsos “Healthy Adults” 185; Batavia and Gianutsos “Parkinson’s Disease” 259). This test was deemed reliable for healthy adults and adults with PD, although patients with PD achieved less rotation than healthy adults and were only tested in a seated position (Batavia and Gianutsos “Healthy Adults” 185,192; Batavia and Gianutsos “Parkinson’s Disease” 259,266). However, this device is not conducive to a clinical measure for patients with CP. The test must be performed in a circular room and the degree of rotation is measured using an angular ruler, which would be difficult in a clinical setting (Batavia and Gianutsos “Healthy Adults” 188). In addition, this test is not appropriate for participants who cannot maintain upright posture without external support, thus eliminating the possibility for it to be used with children with severe CP (Batavia and Gianutsos “Healthy Adults” 194). The test is meant to assess neck rotation, chest rotation, and rotation including the upper extremity through a seated and standing assessment in healthy adults (Batavia and Gianutsos “Healthy Adults” 187).

Another research study developed a Functional Axial Rotation (FAR) measure and tested it on community-dwelling adults and adults with PD (Schenkman et al. “Clinical Tool” 151; Schenkman et al. “Spinal Flexibility” 441). The FAR device was deemed reliable and valid for both populations (Schenkman et al. “Clinical Tool” 151; Schenkman et al. “Spinal Flexibility” 441). The average degree of rotation for participants with PD was 180.3 degrees compared to 208.7 degrees for adults without PD (Schenkman et al. “Spinal Flexibility” 443). The axial rotation device referenced in the current study is a modified variant of the FAR device developed by Schenkman and colleagues (“Clinical Tool” 152-153). The FAR device was also used as a measure of functional limitation in patients who had cervical spine disorders (Hermann and Reese 906). Researchers found a correlation between level of impairment due to cervical spine disorder and limited ROM and decreased axial rotation (Hermann and Reese 903).

The FAR device appears to have greater clinical utility than the Functional Rotation Test in adults and may be feasible for testing functional axial rotation in children. The goal of the current study was to determine if adaptations to the FAR device would allow functional axial rotation to be measured in TD children and children with CP. For this purpose, we created a child-friendly version of the device and completed testing with a small group of children. Our research questions were: 1) Can children with and without CP follow the directions and be patient enough to complete the test? 2) Does external trunk support influence axial rotation range? 3) Are measurements of axial rotation in children reliable during test-retest with the same and different testers? and finally, 4) Is accuracy of clinical observation for this measure improved through video recording and coding?


Human Ethics: IRB approval for this project was obtained from the University of Hartford IRB. The procedure was explained to children and their parents and informed consents were signed by at least one parent and verbal assent was given by the child prior to participation in the study.

Participants: A control group of four typically developing (TD) children (3 males ages 5,5,7 years and one female age 7 years) were tested first. Then, three children with CP (3 males ages 3,5,7 years) were recruited through word of mouth and the University of Hartford Pediatric Balance Lab (PBL) data base. The demographics of the children with CP can be found in Table 1. Non-ambulatory children with CP who would likely be more challenged by the task were purposefully selected. This allowed us to create the modifications necessary to make this protocol possible for all children with CP regardless of their level of trunk control or severity of CP. Participants were excluded if they were younger than three years or older than ten years. They were also excluded if they had been diagnosed with fixed scoliosis or had any previous history of spinal surgeries or any other surgeries within the past year. All children were tested on one occasion at the University of Hartford.

Device and Set up: The device used in this research study was created based on a previous publication showing a similar device for testing functional axial rotation in adults with and without Parkinson’s disease (Schenkman et al. “Clinical Tool” 152-153; Schenkman et al. “Spinal Flexibility” 441). We made three primary modifications to this testing device to make it more child friendly. First, a 180-degree structure was used instead of 360-degree to allow researchers to strap the children to the bench more easily, to access the children more efficiently, and to speak to the child more directly during the study. Second, colorful, clipart animal images were used to label the 180-degree structure and served as enticement for the children. Each animal correlated to 5 degrees, but each degree was indicated by a tick mark to increase precision. The animals were used to entice children to turn to their maximum potential. The study was presented as a “safari” for the children and researchers asked them to turn to different animals to determine their maximal degree of rotation. Finally, a laser headpiece was used to determine the degree of rotation for the child. The laser headpiece was also a modification that made it more fun for the children. The headpiece was strapped on the child’s head, with the laser placed on the middle of their forehead. The laser is less constraining and was theorized to track the movements more clearly than the head pointer device used in the FAR. The laser allows quick movements to be tracked so that when a child briefly illuminates the animal marker, the degree of rotation can still be recorded.

In order to evaluate the device for use in children with moderate to severe cerebral palsy who have partial trunk control, an additional trunk support was required. An additional device

(Meerkat stander base with one chest band) was used to give additional support for children with CP based on their level of trunk control during the trials (see fig 1A).[1] The Meerkat chest band was raised or lowered to the level of additional trunk support required. The stander was positioned behind the bench with the chest band extended to wrap around the child keeping the torso vertically aligned over the pelvis.

Figure 1: Children being tested in the device. Two seven-year-old children, one child with CP (left image) and one TD child (right). Pelvic strapping was achieved with the Leckey SATCo bench and pelvic cradle and trunk support was created using the chest band of a Meerkat stander.

Four cameras were used during the axial rotation test. One camera was directly in front of the children at 0 degrees, while another camera was directly behind the child at 180 degrees. The camera at 180 degrees was raised up on a table to ensure the entire setup was visible. The camera height at 0 degrees was adjusted for the child to ensure the entire body was visible. Two other cameras were positioned at 45 degrees, to the right and left of the child. The cameras at 45 degrees to the right and left were adjusted based on the child to ensure the child’s trunk and the device were visible (see fig 2).

Figure 2: Camera setup and degree measurements. The Xs mark cameras. The degree measurements are shown as what is noted on the animal marker of the device, the degree of L and R rotation for TD children when the device is behind them, and the degree of rotation for children with CP when the device is in front of them.

The children were positioned so that 0 degrees was in front of them and the device was behind them (Fig 1B). The degrees were positive to the right and left. The children began the test once they had turned 90 degrees. The maximum degree of rotation that could be obtained was 270 degrees total. If the child was unable to achieve 90 degrees of rotation, he was turned so that the device was in front of him (Fig 1A). They were positioned so that the marker in front of them was noted as 90 degrees but represented 0 degrees of rotation. Technically, the degrees declined as they turned, but the number of degrees turned counted as their positive rotation. The maximum amount of rotation that can be recorded in this position was 90 degrees in each direction.

Protocol: Children were introduced to pelvic stability strapping and a Segmental

Assessment of Trunk Control (SATCo) evaluation was completed to determine the child’s level of trunk control. The SATCo is a clinical test used to differentiate between seven levels of trunk control. The test measures static, active, and reactive control.

Following SATCo, the children were taken to the axial rotation set up, seated on the bench and the footrest and other straps were applied. Then children were introduced to the laser head piece and given a few minutes to explore how it could light up the various animals.

Once the children were seated on the Leckey SATCo bench and their hips and knees were in a 90-degree alignment, neoprene straps were attached to help them keep their feet in place.[2] Pelvic position for all children was secured using the Leckey pelvic cradle strapping system (fig 1).[3] The children with CP were offered mid-thoracic support unless they required a higher level of support to sit upright and rotate (as determined by their SATCo score (see table 1)). The children with CP completed all trials with external trunk support and pelvic support. The TD children completed 2 sets of trials, one set with only pelvic support and one set with trunk support at the mid-thoracic level and pelvic support.

Children were asked to rotate as far as they could to each side while pointing to animals using the head laser. The test was completed three times in each direction. The children were instructed to keep their hands on their lap and their feet in place. If the tester noted that the child’s hands or feet were not correctly placed, they reminded the child to keep them in place and asked the child to repeat the rotation. The children were allowed to rotate their head as long as their trunk remained upright. Live scorers noted the maximum degree of axial rotation for each turn (indicated by tick marks at each degree). Only turns where the restrictions were abided by and the laser made contact with the animal markers were scored. Then, all data was video behavior coded by four researchers (two who had also scored it live and two who had not scored live). Statistics were run on the data to determine reliability of scoring and the difference in axial rotation between the groups (CP, TD with thoracic support, TD without thoracic support).

Data Analysis: The primary outcome measure was degrees of rotation. The degree of rotation was recorded live by the scorer and via video analysis. It was based on the light from the laser touching the degree mark on the animal marker. Observation was used to determine if children with and without CP could follow directions and be patient enough to complete the test. Next, to determine if external trunk support influences axial rotation range, an Analysis of Variance (ANOVA) was used. An ANOVA is primarily for determining if there is a significant difference in means for two or more groups of data. Thus, we compared the TD children’s rotation when they had pelvic support to when they had additional thoracic support. In addition, we used an ANOVA to compare rotation for TD children (with pelvic and thoracic support) to the rotation for children with CP.

Intraclass Correlation Coefficient (ICC) was used to determine inter-rater reliability between scorers and intra-rater reliability between live and video scoring for the same scorer (see Figure 3). ICC is a statistic used to compare quantitative measurements that are arranged in groups. It determines the agreement within the group. We calculated the inter-rater reliability using ICC to determine if measurements of axial rotation in children were reliable during test-retest with different live scorers, and to determine if measures of axial rotation were reliable across raters when scored from video recordings. We hypothesized that the video recordings might be more reliable because children moved quickly during the live sessions. To answer the question, “Is accuracy of clinical observation for this measure improved by video recording and coding?” we used an ICC to calculate intra-rater reliability by comparing the live and video scoring results. Figure 3 shows a schematic of the ICC calculation plan. The results were interpreted as: poor (<0.5), moderate (0.5 to 0.75), good (>0.75 to 0.9), and excellent (>0.9) (Koo and Li 155-163).

Figure 3: Three reliability comparisons. Interrater reliability with 4 raters (video, green blocks and arrows) and with 2 raters (live, orange blocks and arrow), and Intra-rater reliability (Live vs. video rescore, blue blocks and blue arrows).


Viability of Test: Our first question was, “can TD children with and children with CP follow the directions and be patient enough to complete the test?” All children were able to complete 3 rotations in each direction during each set of trials for two different testers. The complete axial rotation test, not including the SATCo portion, took roughly 30 minutes for each participant to complete. Viable data was recorded from all participants.

Modifications for children with CP: Given the device modifications, TD children were able to complete the test per the protocol. However, some modifications were made for the children with CP. These children have GMFCS scores of 4 and 5 meaning they are the most severe (table 1) (Palisano et al. 424-428). All three children with CP were non-ambulatory and unable to remain upright and stable for the axial rotation testing with just pelvic support. Thus, they were tested with thoracic support adjusted at the height needed to accommodate their level of trunk control, based on their SATCo level (table 1). Children with CP were unable to keep their hands and feet planted throughout the duration of the testing. Most children with CP had difficulty controlling hand movements; however, one child with CP struggled with controlling his feet movements. Thus, the hand and foot movement restriction was alleviated for children with CP and the trials were still scored. In addition, none of the children with CP could obtain greater than 90 degrees of rotation. Thus, unlike the TD children, all the children with CP needed the device flipped in front of them (see fig 1 A & B).

Differences between populations: Children with CP displayed significantly less degrees of rotation compared to TD children with thoracic support (ANOVA, F(1,81)=952.5, p< 0.001). As seen in Table 2 and Figure 4, there is a 98-degree difference between children with CP and TD children without support. There was an 80-degree difference between children with CP and TD children, both with thoracic support. Although it was easy to differentiate between the scores of children with CP and TD children in our small cohort, it is undetermined if this would hold true for a larger cohort.

Figure 4: Box Plot showing range of axial rotation. CP= children with CP with trunk support, TDN = TD children with only pelvic support, TDY = TD children with trunk support

External Trunk Support: The next question was, “does external trunk support influence rotation?” To determine if trunk support influenced rotation, the TD children were also tested with mid-thoracic support. To avoid order bias, the children were tested once with support and once without, in no particular order. This was completed with two different scorers. The difference between the degree of rotation for TD children with and without thoracic support was significant, as determined by the ANOVA (F(1,94)=49, p< 0.001). On average, an 18 degree decrease in rotation was observed when TD children were given thoracic support (see table 2 and fig 4).

Reliability: Then we asked, “are the measurements of rotation reliable during test-retest with the same and different testers?” The ICC reliability output data can be found in Table 3. While the ICCs vary for left and right rotation, the cohort is too small to make a distinction regarding etiology. The inter-rater reliability between testers was determined via video behavior coding. The video inter-rater reliability was excellent (ICC= 0.98) The reliability from live to video was determined using an intra-rater evaluation of live scores versus video scores for each child. The intra-rater reliability was also excellent (ICC= 0.94-0.98). The live inter-rater reliability was moderate to excellent (ICC= 0.63-0.86). Thus, the test is reliable during test-retest with the same and different testers. In addition, the reliability of the test indicates that the test can be scored live, without the need for additional video analysis because of the excellent intra-rater reliability.


Viability of Test: Overall, the protocol was possible for both groups of children, while some modifications were necessary for children with CP. The protocol was successful with regards to ability to distinguish the degree of rotation reliably between testers, scorers and live versus video. Children expressed enthusiasm for the task and remained engaged in the process for more than thirty minutes. Modifications are needed for the angular surround system to accommodate the full range of rotation possible in children with CP as well as those who are TD. The clinical outcomes were as accurate as the video, eliminating the need for the video during further testing.