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. 2009 Sep;10(3):135-41.
doi: 10.1007/s10195-009-0061-7. Epub 2009 Aug 19.

Central neuromuscular dysfunction of the deltoid muscle in patients with chronic rotator cuff tears

Alexander Berth  1 , Géza Pap, Wolfram Neuman, Friedemann Awiszus
Affiliations

Central neuromuscular dysfunction of the deltoid muscle in patients with chronic rotator cuff tears

Alexander Berth et al. J Orthop Traumatol. 2009 Sep.

Abstract

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.

Materials and 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.

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Figures

Fig. 1
Fig. 1
Experimental setup of the study (investigation of the right side). The motor-evoked potentials (MEP) of the deltoid muscle (DM) and first dorsal interosseus muscle (FDI) were recorded after transcranial magnetic stimulation (TMS) over the scalp during rest and slight voluntary activation of the DM. Voluntary effort of the DM was exerted with a constant abduction of the arm against resistance (strap) at an angle of 40°
Fig. 2
Fig. 2
Motor-evoked potential (MEP) recruitment curves of the deltoideus muscle (DM), both sides averaged, at rest (a) and low-level muscular activity of the DM in slight voluntary abduction of the shoulder against resistance (b) in patients (filled circles) and control subjects (open circles) after transcranial magnetic stimulation (TMS) at five different stimulus levels. T individual resting motor threshold for first dorsal interosseus muscle (FDI); T+ increasing stimulus intensities given in percentage of the magnetic stimulator output (MSO)
See this image and copyright information in PMC

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