[MR-based 3D-analysis of the pathomechanics of traumatic and atraumatic shoulder instability].
OBJECTIVE
Until now it is unknown to what extent malpositioning of the scapula is a relevant factor in shoulder instability that should be considered in therapy. The objective was to analyse 3D-scapular kinematics and humeral head (de-)centering in patients with atraumatic and/or traumatic shoulder instability and to investigate the correlation between the two factors.


METHODS
The shoulders of 28 healthy volunteers and of 14 patients each with atraumatic or traumatic instability were examined in various arm positions - with and without muscle activity - using open MR imaging. After 3D reconstruction, analyses of scapular kinematics and glenohumeral translation were performed.


RESULTS
In atraumatic unstable shoulders, the scapular position [30 degrees of abduction: scapulo-humeral rhythm: 3.5 +/- 2.6 : 1 vs. healthy 2.4 +/- 1.3 : 1; internal rotation: 59 +/- 9 degrees vs. healthy 49 +/- 3 degrees (p < 0.05)] and humeral head position was significantly decentered in both planes (p < 0.05). While the correlation between the two factors was high during passive elevation (r = 0.60-0.87), it was low during muscular activity (r = 0.25-0.62). In patients with traumatic instability no alterations of the scapula kinematics were observed. Significant humeral head decentering (p < 0.05) occurred only during abduction and external rotation.


CONCLUSIONS
Patients with atraumatic instability demonstrated significant alterations of scapular kinematics and decentering of the humeral head. In traumatic instability a decentering occurred only in specific arm positions with no changes in scapula position. Because of the high correlation between the two factors, physiotherapeutic strategies for the scapula-stabilising muscles should be adapted to the direction of instability.
von Eisenhart-Rothe
R
R
Forschungsgruppe Kinematik und Biomechanik, Orthopädische Universitätsklinik Stiftung Friedrichsheim, Frankfurt. r_veisenhart@yahoo.de
Hinterwimmer
S
S
Braune
C
C
Jäger
A
A
Mayr
H
H
Vogl
T
T
Englmeier
K-H
KH
Graichen
H
H
D000293:Adolescent; D000328:Adult; D001696:Biomechanical Phenomena; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D021621:Imaging, Three-Dimensional; D007593:Joint Instability / Q000175:diagnosis / Q000503:physiopathology* / Q000601:surgery; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D011183:Postoperative Complications / Q000175:diagnosis / Q000503:physiopathology; D016059:Range of Motion, Articular / Q000502:physiology; D012008:Recurrence; D012540:Scapula / Q000503:physiopathology; D012783:Shoulder Dislocation / Q000175:diagnosis / Q000503:physiopathology* / Q000601:surgery; D000070599:Shoulder Injuries; D012785:Shoulder Joint / Q000503:physiopathology; D013223:Statistics as Topic