The Relative Contribution of Trunk Movements to Modified Mallet Scores in Children with Brachial Plexus Birth Injury.

Abstract

Children with Brachial Plexus Birth Injury (BPBI) often rely on compensatory movements due to limited shoulder mobility. In clinical practice, the Modified Mallet Scale (MMS) is frequently used to assess shoulder movements. However, MMS scores can be influenced by trunk contributions, preventing an accurate evaluation of pure shoulder complex motion. This study aimed to quantify the relative contributions of the extremity and trunk during MMS movements using wearable inertial sensors. The study included twenty-four children (7.20 ± 1.41 years; range 4-10 years), and three-dimensional kinematic data of upper extremity and trunk movements during MMS tasks were collected from both the affected and unaffected sides using Movella DOT inertial measurement unit sensors. Relative contributions of the extremity and trunk were calculated for each movement, and differences between affected and unaffected sides were analyzed using the Wilcoxon signed-rank test. On the affected side, extremity contribution was significantly lower, while trunk contribution was higher compared to the unaffected side for "Global Abduction," "Global External Rotation," "Hand to Neck," "Hand to Back," and "Hand to Mouth" movements (p<0.05). "Hand to Belly/Internal Rotation" movement showed no significant difference (p>0.05). These findings show that trunk movements are increased on the affected side during MMS tasks in children with BPBI, highlighting the potential for trunk motion to influence observed shoulder performance. Accounting for trunk contributions is essential for accurate interpretation of functional performance, informs therapy planning and outcome evaluation, and underscores the limitations of purely observational MMS scoring.