Trunk Impairment Scale: What It Measures and Why

If you have read the cerebral palsy guide on this site, you have seen the Trunk Impairment Scale listed among the outcome measures in the completed clinical trial comparing DMI to the Bobath approach. This post explains what the TIS is, how it complements the GMFM-88, and why trunk control matters specifically when evaluating DMI.

What is the Trunk Impairment Scale?

The Trunk Impairment Scale (TIS) is a standardized clinical assessment of trunk motor control. It was developed by Geert Verheyden and colleagues at Katholieke Universiteit Leuven in Belgium and first published in 2004 in Clinical Rehabilitation. The original TIS was designed for adults who had experienced a stroke. A separate pediatric body of research has since established that the TIS is also valid and reliable for children with cerebral palsy.

The key insight behind the TIS is that trunk control is a distinct domain of motor function. A child may improve in mobility (as captured by the GMFM-88) without necessarily improving in trunk stability, or vice versa. Measuring trunk control directly gives a more complete picture than measuring gross motor function alone.

This is especially relevant for DMI. DMI targets automatic postural responses against gravity, and those responses depend heavily on trunk control. An assessment that isolates trunk function can capture changes that a general gross motor measure might miss or show only indirectly.

The three subscales

The TIS has 17 items grouped into three subscales, all assessed while the child sits on a treatment table or mat with their feet unsupported and no back support:

The total TIS score ranges from 0 to 23, with higher scores indicating better trunk control. Items are not all scored on the same range. Some are scored 0 or 1, others 0 to 2 or 0 to 3, which is why the three subscales have maximum scores of 7, 10 and 6 rather than simply twice the number of items. The assessor scores what the child actually does, not what they believe the child could do with encouragement.

What does the TIS tell you that the GMFM-88 does not?

The GMFM-88 measures gross motor function across five dimensions. Its sitting dimension (Dimension B) captures whether a child can sit independently, reach while sitting, and sit up from lying down. But it does not isolate trunk control. A child who sits independently but with poor stability may score the same as a child with good trunk control on the GMFM-88 sitting items, because the GMFM-88 scores completion of the movement rather than quality or stability of the posture.

The TIS captures that difference. Two children may both achieve a 3 (full completion) on a GMFM-88 sitting item such as "sits on mat, arms free, for 3 minutes," but one of them is wobbling, bracing, or using compensatory trunk strategies while the other is stable and efficient. The TIS tells you which is which.

In the DMI trial, the GMFM-88 and the TIS together give a more complete picture than either alone. The GMFM-88 shows whether the child progressed through broad motor categories (sitting, crawling, standing, walking). The TIS shows whether the underlying trunk control improved enough to support that progression.

Psychometric properties in children with cerebral palsy

A 2022 study by Jung and Choi, published in Children, used Rasch analysis to examine the construct validity of the TIS in 60 children with cerebral palsy. The analysis supported the scale measuring a single underlying construct, but it also identified five items that did not fit the model well: two static sitting balance items, two dynamic sitting balance items,and one coordination item. Of the three subscales, only static sitting balance failed to meet the appropriate rating scale criteria.

That is a more mixed picture than a simple endorsement. It supports the TIS as a coherent measure of trunk control in this population while indicating that some individual items perform less well than others.

However, this study did not examine whether the TIS is sensitive to change over time in children receiving therapy. That question remains open, and it is directly relevant to the DMI trial. If the TIS proves sensitive to changes from DMI, it would provide evidence that DMI affects trunk control specifically, rather than motor function generally. Until the trial results are published, that is a hypothesis rather than a finding.

What the TIS does not tell you

The TIS measures trunk control in sitting only, in a controlled clinical environment with feet unsupported. It does not measure trunk control during movement, during standing, or in real-life situations such as sitting in a classroom chair, on a car seat, or on the floor during play. It also does not measure how much effort the child expends to maintain trunk stability. A child who scores well on the TIS but uses visible compensatory tension or fatigue quickly may have different therapy needs from a child who achieves the same score with ease.

Like all standardized assessments, the TIS captures what a child does on demand in a testing situation, not what they do spontaneously at home. Video taken by parents in familiar settings can complement the clinical picture.

And as noted above, the TIS has not yet been clearly established as a measure of change (responsiveness) in children receiving therapy, so its ability to detect improvement after DMI is not yet proven, even in a population where it is valid for classification.

Why it matters for the DMI clinical trial

The completed trial comparing DMI to the Bobath approach (NCT07238634) listed three primary outcome measures: the GMFM-88, the Trunk Impairment Scale, and the Shoaib Sensorimotor Development Tool. The inclusion of the TIS tells us the researchers considered trunk control a relevant and separable domain of motor function worth measuring independently.

This makes clinical sense. DMI targets antigravity postural responses, and those responses depend on trunk control. If the trial finds improvement on the TIS but not on the GMFM-88, that would suggest DMI affects trunk stability without necessarily producing broad functional motor gains in the study period. If both improve, that is stronger evidence. If neither improves, that is also informative.

When the trial results are published, looking at the TIS scores alongside the GMFM-88 scores will give you a more specific picture of what changed and for whom.

What you can do with this information

If your child has cerebral palsy and you are considering DMI, you can ask the therapist whether they assess trunk control and what they use. Not every clinic uses the TIS, and that is not necessarily a problem — some use alternative trunk assessments or rely on clinical observation. But a therapist who can describe how they measure trunk control, or who is willing to use the TIS, is demonstrating a systematic approach to evaluation.

You can also ask: what specifically about your child's trunk control makes DMI a good fit? A therapist who can point to sagging in sitting, poor lateral weight shift, or inability to rotate the trunk is telling you something specific. A therapist who says only that your child needs "better core strength" is being less specific than the evidence warrants.

Where it appears on this site

The Trunk Impairment Scale is listed as a primary outcome measure on our cerebral palsy guide, alongside the GMFM-88 and the Shoaib Sensorimotor Development Tool. It is also relevant to our GMFM-88 explainer, which covers the other main outcome measure from the same trial.

Sources

• Verheyden G, Nieuwboer A, Mertin J, Preger R, Kiekens C, De Weerdt W. The Trunk Impairment Scale: a new tool to measure motor impairment of the trunk after stroke. Clinical Rehabilitation. 2004;18(3):326-334. Sage Journals PubMed
• Jung H, Choi YE. The Psychometric Properties of the Trunk Impairment Scale in Children with Cerebral Palsy. Children. 2022;9(3):435. PMC PubMed
• ClinicalTrials.gov. Effects of DMI vs Bobath on Neuromuscular Development in CP (NCT07238634). ClinicalTrials.gov