P B de Witte1, J F Henseler2, E W van Zwet3, J Nagels4, R G H H Nelissen4, J H de Groot5. 1. 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. 2. 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. 3. Department of Medical Statistics and BioInformatics, LUMC, Postbus 9600, 2300 RC Leiden, the Netherlands. 4. Department of Orthopaedics, Leiden University Medical Center (LUMC), Postzone J11R, Postbus 9600, 2300 RC Leiden, the Netherlands. 5. Laboratory for Kinematics and Neuromechanics, Department of Orthopaedics & Rehabilitation, LUMC, Postzone B0-Q, Postbus 9600, 2300 RC Leiden, the Netherlands.
Abstract
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. FINDINGS: 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. INTERPRETATION: 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.
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. FINDINGS: 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. INTERPRETATION: 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.
Authors: Cathryn D Peltz; George Divine; Anne Drake; Nicole L Ramo; Roger Zauel; Vasilios Moutzouros; Michael J Bey Journal: J Biomech Date: 2015-07-06 Impact factor: 2.712