Purpose <p>Adult traumatic brachial plexus injuries result in partial to complete loss of upper extremity function. Outcome measures to assess function after brachial plexus reconstruction have traditionally been obtained in the clinic or via a survey. An objective outcome measure representing a longer time duration in the patient’s life obtained in the patient’s normal living environment is necessary to assess the outcomes of surgical reconstruction adequately.</p> Methods <p>A novel method was developed to measure the affected arm’s activity in the patient’s living environment and compare it to the unimpaired contralateral arm. A secondary analysis of activity monitoring data was used to create an asymmetry index comparing the injured arm to the contralateral extremity. Activity data from healthy individuals was used to create a normative range. The graphical representation visually assessed bilateral arm function for surgeons and patients to understand.</p> Results <p>While the postoperative dynamic asymmetry index (DASI) was statistically different from the controls, there was no significant relationship with the disabilities of the arm, shoulder and hand (DASH) outcome measure or the manual muscle testing grade (MMT). This demonstrates the inadequacies of traditional non real-world outcome measures. The DASI provided an independent, comprehensive view of the patient’s volitional choice to use their injured limb during daily living.</p> Conclusions <p>The DASI is an objective outcome measure that can measure recovery and improvement of patient function in a real-world setting over a longer duration and allows for a more realistic assessment of outcomes than traditional measures.</p>