title: "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.
authors.affiliation: a 1 Division of Plastic Surgery, Department of Surgery.
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Coroneos
authors.affiliation: b 2 Department of Diagnostic Imaging.
authors.forename: Zeev V
authors.initials: ZV
authors.lastname: Maizlin
authors.affiliation: c 3 School of Rehabilitation Science.
authors.forename: Carol
authors.initials: C
authors.lastname: DeMatteo
authors.affiliation: d 4 McMaster Children's Hospital, McMaster University , Hamilton, ON, Canada.
authors.forename: Deborah
authors.initials: D
authors.lastname: Gjertsen
authors.affiliation: a 1 Division of Plastic Surgery, Department of Surgery.
authors.forename: James R
authors.initials: JR
authors.lastname: Bain
mesh_terms: D000293:Adolescent; D001720:Birth Injuries / Q000150:complications*; D020516:Brachial Plexus Neuropathies / Q000150:complications* / Q000000981:diagnostic imaging; D016022:Case-Control Studies; D002648:Child; D002657:Child Development / Q000502:physiology; D002675:Child, Preschool; D003286:Contracture / Q000000981:diagnostic imaging* / Q000209:etiology; D004551:Elbow Joint / Q000000981:diagnostic imaging / Q000503:physiopathology*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D018482:Muscle, Skeletal / Q000254:growth & development* / Q000503:physiopathology; D012189:Retrospective Studies; D018570:Risk Assessment; D013710:Tendons / Q000000981:diagnostic imaging / Q000503:physiopathology*; D014057:Tomography, X-Ray Computed / Q000379:methods
keywords: Arm/growth & development; birth injuries/physiopathology; brachial plexus/injuries; child; infant; newborn