Concordance and Discordance of Intraoperative Nerve Root Findings in Brachial Plexus Birth Injury.

BACKGROUND: Accurate preoperative characterization of brachial plexus birth injury (BPBI) is important for counseling and surgical planning, but the prediction of root-level injury remains challenging. We evaluated the agreement between preoperative injury classification and intraoperative nerve root findings, patterns of discordance, and the influence of Horner syndrome (HS). METHODS: A retrospective review identified 162 infants who underwent primary brachial plexus exploration and reconstruction at a single institution between 2004 and 2023. Preoperative injury classification was assigned from clinical examination and Active Movement Scale (AMS) scores using a root level classification (2025): Injury A (C5-6), B (C5-7), C (C5-8), and D (C5-T1). Intraoperative class was assigned from operative findings, including nerve stimulation and direct assessment of root integrity. RESULTS: Preoperative and intraoperative classifications were concordant in 135 of 162 patients (83.3%) and discordant in 27 (16.7%), with substantial overall agreement (Cohen kappa=0.700). Concordance was highest for Injury D (C5-T1) and poorest for Injury C (C5-C8). Preoperative classification was least accurate for Injury C, with only 1 of 14 cases correctly identified. Among the 27 discordant cases, undercalls were more common than overcalls (19 [70.4%] vs. 8 [29.6%]), most frequently involving B-to-C and A-to-B misclassification. C7 and C8 were the roots most often misidentified. Concordance did not differ significantly before versus after adoption of differential nerve stimulation (86.9% vs. 81.2%, P=0.070). All undercalls occurred without HS. All 5 overcall events in which preoperative Injury D was downgraded intraoperatively to Injury B or C occurred in patients with HS, injuries of which had higher preoperative AMS scores than concordant D-D injuries. CONCLUSION: This intraoperative BPBI classification provides reliable broad categorization preoperatively with substantial agreement but is vulnerable at the C7-C8 transition. Focused assessment of the C8 nerve root is important because this injury pattern is commonly misidentified and may affect diagnosis and treatment. Viewing HS as a marker of severity rather than a standalone sign of global injury may improve preoperative assessment. LEVEL OF EVIDENCE: Level IV-retrospective case series.