Cranial humerus translation, deltoid activation, adductor co-activation and rotator cuff disease - different patterns in rotator cuff tears, subacromial impingement and controls.
BACKGROUND
Arm adductor co-activation during abduction has been reported as a potential compensation mechanism for a narrow subacromial space in patients with rotator cuff dysfunction. We assessed differences in acromiohumeral distance at rest and the amount of humerus translation during active abduction and adduction in patients with rotator cuff tears (n=20) and impingement (n=30) and controls (n=10), controlled for deltoid, pectoralis major, latissimus dorsi and teres major activation (electromyography).


METHODS
During the acquirement of shoulder radiographs, subjects performed standardized isometric arm abduction and adduction tasks. EMG's were normalized between -1 and 1 using the "Activation Ratio", where low values express (pathologic) co-activation, e.g. adductor activation during abduction.


RESULTS
In patients with cuff tears mean rest acromiohumeral distance was 7.6mm (SD=1.6): 3.5mm narrower compared to patients with impingement (95%-CI: 2.4-4.5) and 1.3mm narrower compared to controls (95%-CI: -0.1-2.7). Both during abduction and adduction tasks, cranial translation was observed with equal magnitudes for patients and controls, with average values of 2.3 and 1.7mm, respectively. Where patients with cuff tears had lower adductor Activation Ratios (i.e. more adductor co-activation during abduction), no association between abductor/adductor muscle activation and acromiohumeral distance was found.


CONCLUSIONS
The subacromial space is narrower in patients with rotator cuff tears compared to patients with impingement and controls. We found additional subacromial narrowing during isometric abduction and, to a lesser amount, during adduction in all subjects and more adductor co-activation in patients with cuff tears. We found no association between subacromial space and activation of the deltoid and main adductors.
Department of Orthopaedics, Leiden University Medical Center (LUMC), Postzone J11R, Postbus 9600, 2300 RC Leiden, the Netherlands; Laboratory for Kinematics and Neuromechanics, Department of Orthopaedics & Rehabilitation, LUMC, Postzone B0-Q, Postbus 9600, 2300 RC Leiden, the Netherlands. Electronic address: p.b.de_witte@lumc.nl.
P B
PB
de Witte
Department of Orthopaedics, Leiden University Medical Center (LUMC), Postzone J11R, Postbus 9600, 2300 RC Leiden, the Netherlands; Laboratory for Kinematics and Neuromechanics, Department of Orthopaedics & Rehabilitation, LUMC, Postzone B0-Q, Postbus 9600, 2300 RC Leiden, the Netherlands.
J F
JF
Henseler
Department of Medical Statistics and BioInformatics, LUMC, Postbus 9600, 2300 RC Leiden, the Netherlands.
E W
EW
van Zwet
Department of Orthopaedics, Leiden University Medical Center (LUMC), Postzone J11R, Postbus 9600, 2300 RC Leiden, the Netherlands.
J
J
Nagels
Department of Orthopaedics, Leiden University Medical Center (LUMC), Postzone J11R, Postbus 9600, 2300 RC Leiden, the Netherlands.
R G H H
RG
Nelissen
Laboratory for Kinematics and Neuromechanics, Department of Orthopaedics & Rehabilitation, LUMC, Postzone B0-Q, Postbus 9600, 2300 RC Leiden, the Netherlands.
J H
JH
de Groot
D000368:Aged; D000704:Analysis of Variance; D016022:Case-Control Studies; D057645:Deltoid Muscle / Q000503:physiopathology*; D004576:Electromyography; D005260:Female; D006801:Humans; D006811:Humerus / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D010369:Pectoralis Muscles / Q000503:physiopathology*; D011859:Radiography; D016059:Range of Motion, Articular / Q000502:physiology; D017006:Rotator Cuff / Q000000981:diagnostic imaging / Q000503:physiopathology*; D019534:Shoulder Impingement Syndrome / Q000000981:diagnostic imaging / Q000503:physiopathology*
Adductor co-activation; Diagnostic techniques and procedures; Electromyography; Rotator cuff; Shoulder impingement syndrome