“Popeye muscle” morphology in OBPI elbow flexion contracture

Abstract

Background: The pathophysiology of elbow flexion contracture (EFC) in obstetrical brachial plexus injury (OBPI) is not established. In basic science models, neonatal denervation leads to impaired muscle growth. In clinical studies, diminished growth is correlated with extent of denervation, and improved with surgical repair. In EFC, the biceps are clinically short and round vs the contralateral size, termed the “Popeye muscle”. The objective of this study was to determine if the biceps morphology (muscle belly and tendon length) in arms with EFC secondary to OBPI is different vs the contralateral. Methods: This is a retrospective matched-cohort study. Patients with unilateral EFC (>20°) secondary to OBPI were identified (median = 6.6 years, range = 4.7–16.8). A blinded radiologist used computed tomography to measure length of the biceps short head muscle belly, and tendon bilaterally using standardised anatomical landmarks. Results: Twelve patients were analyzed. The biceps muscle belly in the injured arm was shorter in all patients vs contralateral, mean difference = 3.6 cm (80%), p < 0.001. The biceps tendon in the injured arm was longer in all patients vs contralateral, mean difference = 1.13 cm (127%), p < 0.001. The total biceps length in the injured arm was shorter in all patients vs contralateral, mean difference = 2.5 cm (89%), p < 0.001. Conclusions: This is the first human study confirming growth discrepancy of an elbow flexor in EFC. Distinct biceps morphology is demonstrated, with a significantly shorter muscle belly and overall length, but longer tendon vs normal. This is termed the “Popeye muscle” for its irregular morphology. Findings are consistent with impaired limb growth in denervation.

Key Words:

• Arm/growth & development
• birth injuries/physiopathology
• brachial plexus/injuries
• child
• infant
• newborn

Acknowledgements

This study was presented at Neonatal Brachial Plexus Palsy: Moving the Science Forward. National Institutes of Child Health and Human Development, NIH, Wayne State University, Detroit, MI, May 2014. This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors. Dr Christopher Coroneos has formal statistics training and an MSc in clinical epidemiology. He is responsible for all analyses.

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.