MRI of rotator cuff muscle atrophy in relation to glenohumeral joint incongruence in brachial plexus birth injury.
OBJECTIVE
To evaluate rotator cuff muscles and the glenohumeral (GH) joint in brachial plexus birth injury (BPBI) using MRI and to determine whether any correlation exists between muscular abnormality and the development of glenoid dysplasia and GH joint incongruity.


METHODS
Thirty-nine consecutive BPBI patients with internal rotation contracture or absent active external rotation of the shoulder joint were examined clinically and imaged with MRI. In the physical examination, passive external rotation was measured to evaluate internal rotation contracture. Both shoulders were imaged and the glenoscapular angle, percentage of humeral head anterior to the middle of the glenoid fossa (PHHA) and the greatest thickness of the subscapular, infraspinous and supraspinous muscles were measured. The muscle ratio between the affected side and the normal side was calculated to exclude age variation in the assessment of muscle atrophy.


RESULTS
All muscles of the rotator cuff were atrophic, with the subscapular and infraspinous muscles being most severely affected. A correlation was found between the percentage of humeral head anterior to the middle of the glenoid fossa (PHHA) and the extent of subscapular muscle atrophy (r(s)=0.45, P=0.01), as well as between its ratio (r(s)=0.5, P P=0.01). Severity of rotator cuff muscle atrophy correlated with increased glenoid retroversion and the degree of internal rotation contracture.


CONCLUSIONS
Glenoid retroversion and subluxation of the humeral head are common in patients with BPBI. All rotator cuff muscles are atrophic, especially the subscapular muscle. Muscle atrophy due to neurogenic damage apparently results in an imbalance of the shoulder muscles and progressive retroversion and subluxation of the GH joint, which in turn lead to internal rotation contracture and deformation of the joint.
Pöyhiä
Tiina H
TH
Department of Radiology, Hospital for Children and Adolescents, Helsinki University Central Hospital, PO Box 281, Helsinki, 00029 HUS, Finland. tiina.poyhia@hus.fi
Nietosvaara
Yrjänä A
YA
Remes
Ville M
VM
Kirjavainen
Mikko O
MO
Peltonen
Jari I
JI
Lamminen
Antti E
AE
D000293:Adolescent; D001720:Birth Injuries / Q000150:complications*; D001917:Brachial Plexus / Q000293:injuries*; D002648:Child; D002675:Child, Preschool; D003286:Contracture / Q000209:etiology; D005260:Female; D006801:Humans; D006811:Humerus / Q000473:pathology; D007592:Joint Diseases / Q000175:diagnosis* / Q000209:etiology / Q000503:physiopathology; D008279:Magnetic Resonance Imaging; D008297:Male; D009133:Muscular Atrophy / Q000175:diagnosis* / Q000209:etiology / Q000503:physiopathology; D010808:Physical Examination; D016059:Range of Motion, Articular / Q000502:physiology; D012399:Rotation; D017006:Rotator Cuff / Q000473:pathology*; D012540:Scapula / Q000473:pathology; D012783:Shoulder Dislocation / Q000175:diagnosis / Q000209:etiology; D012785:Shoulder Joint / Q000473:pathology* / Q000503:physiopathology