Central neuromuscular dysfunction of the deltoid muscle in patients with chronic rotator cuff tears.
BACKGROUND
Previous surface electromyogram (EMG) studies have shown that chronic rotator cuff tears (RCT) may be associated with a altered activation of adjacent shoulder muscles. The effect of RCT on central neuromuscular control mechanisms of the shoulder girdle muscles such as the deltoideus muscle (DM), a key muscle of shoulder function, has as not yet been studied in detail.


METHODS
This study investigated the corticospinal excitability of the DM to assess the effects of RCT on the central neuromuscular function of proximal upper limb muscles. The motor-evoked potentials (MEP) in response to transcranial magnetic stimulation of DM on both sides were obtained from patients with unilateral RCT and compared with healthy control subjects.


RESULTS
In patients, stimulus response curves of DM demonstrated a bilateral hyperexcitability at rest and a hypoexcitability during voluntary activation (F = 3.82, P = 0.007).


CONCLUSIONS
The DM hyperexcitability may be related to alterations in the sensory output from the shoulder. The insufficient facilitation of the DM points toward a bilateral central activation deficit. These findings seem to be assigned to adaptive changes in the motor cortex as a consequence of chronic RCT, and the neuromuscular alteration of the DM should be considered when treating patients with RCT.
Berth
Alexander
A
Department of Orthopaedics, Otto-von-Guericke-University, Magdeburg, Germany. alexander.berth@med.ovgu.de
Pap
Géza
G
Neuman
Wolfram
W
Awiszus
Friedemann
F
D000222:Adaptation, Physiological; D000328:Adult; D002908:Chronic Disease; D005071:Evoked Potentials; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000503:physiopathology*; D020511:Neuromuscular Junction Diseases / Q000175:diagnosis / Q000209:etiology / Q000503:physiopathology*; D017006:Rotator Cuff / Q000503:physiopathology; D000070636:Rotator Cuff Injuries; D012782:Shoulder / Q000503:physiopathology; D013708:Tendon Injuries / Q000150:complications / Q000175:diagnosis / Q000503:physiopathology*; D050781:Transcranial Magnetic Stimulation; D055815:Young Adult
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