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Shoulder Internal Rotation Contracture Formation in Surgically Managed C5, C6 Brachial Plexus Birth Injuries

Background: A typical feature in infants with severe C5-C6 brachial plexus birth injury (BPBI) requiring nerve repair is the formation of shoulder internal rotation contracture (IRC). The underlying pathophysiological mechanism is unknown, and the sequelae can be difficult to treat. The severity of the IRC differs among children. C5-C6 lesions are heterogeneous at the root level. Our null hypothesis was that the type of root-level lesion (axonotmesis or neurotmesis versus avulsion) was not associated with the extent of IRC formation over time in children with upper-trunk BPBI. Methods: We performed a retrospective analysis of all patients with upper-trunk BPBI who underwent primary surgery of the C5 and/or C6 spinal nerves between 1990 and 2020 and had follow-up of at least 2 years. The primary outcome was passive shoulder external rotation (ER) in adduction at 1, 3, 5, 7, and 15 years of age. The secondary outcome was whether additional shoulder surgery was performed. The relationship between the nature of the C5-C6 lesion and IRC formation was analyzed using linear mixed models. The Kaplan-Meier method was used to estimate the cumulative risk of secondary shoulder procedures. Results: In total, 322 patients were analyzed; mean follow-up was 7.2 ± 4.6 years. The C5-C6 root lesion type was significantly related to the passive range of ER (overall test in linear mixed model, p = 0.007). Children with avulsion of C5 and C6 (n = 21) had, on average, 18° (95% confidence interval [CI], 6.3° to 30°) less IRC formation than those with neurotmesis of C5 and C6 (n = 175) and 17° (2.9° to 31°) less than those with neurotmesis of C5 and avulsion of C6 (n = 34). IRC formation did not differ between the neurotmesis C5-C6 and neurotmesis C5-avulsion C6 groups. Secondary shoulder procedures were performed in 77 patients (10-year risk, 28% [95%CI, 23% to 34%]). Conclusions: Shoulder IRC formation in infants with BPBI with surgically treated C5-C6 lesions occurs to a lesser degree if the C5 root is avulsed than when C5 is neurotmetic. This finding provides insight into the possible causative pathoanatomy and may ultimately lead to strategies to mitigate IRC. Level of Evidence: Prognostic Level III. See Instructions for Authors for a complete description of levels of evidence.