Acta chirurgiae orthopaedicae
et traumatologiae Čechoslovaca

Acta Chir Orthop Traumatol Cech. 2009; 76(6):456-461 | DOI: 10.55095/achot2009/085

Central Motor Deficits of the Deltoid Muscle in Patients with Chronic Rotator Cuff TearsOriginal papers

A. BERTH^1,*, G. PAP², F. AWISZUS¹, W. NEUMANN¹

¹ Department of Orthopaedic Surgery, Otto-von-Guericke-University, Magdeburg, Germany

² Centre of Orthopaedics and Traumatology, Park-Hospital Leipzig, Leipzig, Germany

PURPOSE OF THE STUDY:
Previous surface 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 (MD), a key muscle of shoulder function, has as yet not been studied in detail. This study investigated the cortico-spinal excitability of the MD to assess the effects of RCT on the central neuromuscular function of upper limb muscles.

MATERIAL AND METHODS:
The motor evoked potentials (MEP) in response to transcranial magnetic stimulation of MD and first dorsal interosseus muscle (FDI) on both sides were obtained of six right-handed men with chronic, symptomatic, full-thickness RCT on the dominant sides. Stimulus response curves at four different levels were measured at two tasks (MD at rest and during activity).

RESULTS:
Different interactions were found between stimulus intensity, task and side for MEP of the MD (F = 3.9, P = 0.03), indicating that MD excitability on the affected side were lower when compared with the non-affected side. No correlation was found between the correspondent MEP amplitudes of MD and FDI at rest (r = 0.1, P = 0.44) and MD activation (r = 0.3, P = 0.05) on the affected side whereas a correlation existed on the non-affected side at rest (r = 0.5, P = 0.007) and during activation (r = 0.8, P < 0.001).

CONCLUSIONS:
These decreased cortico-motoneuronal excitability of the MD on the affected side seems to related to adaptive changes in motor cortex as a consequence of chronic RCT. The data suggest an involvement of central mechanisms and seem to precede severe changes of osteoarthritis of the shoulder.

Keywords: transcranial magnetic stimulation, motor evoked potentials, deltoid, rotator cuff tear, shoulder

Published: December 1, 2009  Show citation