Scapular Rotation Research Articles

Electromyography in voluntary posterior instability of the shoulder

Electromyographic (EMG) activity of selected shoulder girdle muscles was analyzed during voluntary posterior subluxation of the glenohumeral joint in four subjects. Although there was a great deal of variation in the muscle activation patterns during subluxation, subjects either pushed the humeral head backwards with the anterior muscles (deltoid, biceps) or pulled the humeral head backwards with the infraspinatus and/or posterior deltoid. In all cases, inhibition of the scapular rotators and winging of the scapula accompanied this maneuver. The method used in this study is presented as an objective technique for quantifying EMG activity during subluxation and relocation phases of shoulder instability.

SPECIAL REVIEW POLIOMYELITIS

The dynamic pattern of scapulohumeral rhythm and the scapular instantaneous center of rotation were studied in 20 healthy young male subjects. The most common pattern of scapulohumeral rhythm was characterized by three separate phases, with the greatest relative amount of scapular rotation occurring between 80 and 140° of arm abduction. The scapular instantaneous center of rotation was observed to be located initially at, or near, the medial root of the scapular spine, and gradually migrated toward the region of the acromioclavicular joint as arm abduction progressed. A biomechanical model of the shoulder girdle was proposed by correlating the results from the present study with the electrical activity of the scapular rotators. This model is useful in demonstrating the true dynamic function of the muscles acting on the scapula as well as the mechanical efficiency of upward scapular rotation during arm abduction.

Fine wire electromyography analysis of muscles of the shoulder during swimming.

Fine wire EMG of the shoulder was performed on 11 swimmers; 5 performed during dry land studies and 7 during aquatic studies. One individual underwent both studies. A cinematographic analysis was synchronized with the EMG data to determine what muscles were firing at each phase of the swim stroke. Eight muscles were studied: biceps, subscapularis, latissimus dorsi, pectoralis major, supraspinatus, infraspinatus, serratus anterior, and deltoid. Three strokes were analyzed: freestyle, breaststroke, and butterfly. The freestyle and butterfly are frequently associated with impingement type syndromes in swimmers. It was determined that the supraspinatus, infraspinatus, middle deltoid, and serratus anterior were predominately recovery phase muscles. The latissimus dorsi and pectoralis major were predominately pull-through phase muscles. The biceps had mixed inconsistent activity during both phases. From dry land quantifications of the EMG signal it was determined that the serratus anterior functions near maximal muscle test during each stroke, and theoretically may fatigue with repetition. It is hoped that a training program aimed to strengthen the scapular rotators may help alleviate impingement syndrome in swimmers.

A Biomechanical Analysis of the Functions of the Deltoid during Abduction of the Arm

In this paper a method is presented for the analysis of the functions of the deltoid during abduction of the arm. The influence of several parameters such as the active and passive properties of the muscle, the length of the muscle fibres at certain positions of the arm, the kind of attachment of the deltoid to the scapula and the clavicula and the rotation of the scapula are discussed with respect to the behaviour of the muscle. The importance of the centre of rotation of the humerus in relation to the required equilibrium is shown.

An electromyographic study of serratus anterior in atelines and Alouatta: Implications for hominoid evolution

AbstractThe serratus anterior pars caudalis muscle of nonhuman primates displays anatomical differences among genera that can be attributed to differences in the mechanical demands placed on these genera by their diverse locomotor: behaviors. In primates that engage extensively in climbing and suspensory behaviors, the caudal digitations of this fan‐shaped muscle are aligned more nearly parallel to the long axis of the trunk. In order to clarify the selective factors promoting such a morphological change, we have conducted a telemetered electromyographic study of the caudal and middle digitations of the serratus anterior pars caudalis. During voluntary elevation of the forelimb, only the middle, more obliquely disposed digitations are powerfully recruited. The caudal digitations are either inactive or function just to initiate scapular rotation. During locomotion, the middle digitations act in the swing (recovery) phase, whereas the caudal digitations are predominatly active in the support (propulsive)These Pashe findings suggest that the caudal digitations are important in propelling the trunk past the scapula during locomotion. Evolution of a fiber orientation more parallel to the long axis of the trunk is suggested to have occurred in broad chested primates for the purpose of facilitating locomotor behaviors requiring caudal scapular retraction for propulsion, but which would be deleteriously affected if such retraction were linked to simultaneous ventral displacement of the shoulder girdle. In its current state, the human serratus anterior seems clearly adapted for arm‐raising functions and indicates descent from a small ape with a thoracic shape similar to atelines.

Morphology and distribution of muscle spindles in dorsal muscles of the cat neck

Silver-stained sections have been examined from the five dorsal neck muscles splenius, biventer, cervicis, complexus, rectus capitis major, and occipitoscapularis. Every serial section was examined for at least one muscle of each type so that a complete description of the spindle distribution and morphology could be made. With the exception of occipitoscapularis (whose prime function is probably in scapula rotation and not in head movement), neck muscles have a remarkably high spindle density. Occipitoscapularis has a spindle density similar to that of hindleg locomotor muscles (13-19 per gram), but splenius has a density of 46-66 per gram, biventer cervicis 74-96 per gram, complexus 71-107 per gram, and rectus capitis major 48-84 per gram. Such high densities have only previously been seen in small muscles whose total spindle population is not large. Because of the relatively large size of some neck muscles, individual muscles with a spindle content of up to 254 spindles have been found.

Biomechanics of the shoulder joint.

The functional anatomy of the shoulder is reviewed and the biomechanics presented. Deltoid force was maximal with the arm abducted 90°, and was calculated to be 8.2 times the weight of the extremity. At 60° of abduction, the downward (short rotator) force was maximal at 9.6 times limb weight. The mechanism whereby the deltoid and the downward-acting short rotators combine to effect abduction is known as a force-couple. The biceps mechanism provides weak abduction in deltoid paralysis. Scapular rotation normally occurs with glenohumeral abduction and is known as scapulohumeral rhythm. Scapular rotation permits the deltoid to maintain an optimum length-tension ratio during most of the abduction range. The acromioclavicular articulations and pathomechanics are also discussed.

Uncommon Dysfunction of Scapular Rotation in Chest Surgical Patients. H. B. DOPPELT AND J. GOLDBERG. Phys. Ther. Revs. August 1951. 31

Uncommon Dysfunction of Scapular Rotation in Chest Surgical Patients. H. B. DOPPELT AND J. GOLDBERG. Phys. Ther. Revs. August 1951. 31

Uncommon dysfunction of scapular rotation in chest surgical patients; a clinical study of five patients.

Uncommon dysfunction of scapular rotation in chest surgical patients; a clinical study of five patients.

THE MOTOFACIENT AND NONMOTOFACIENT CYCLES IN ELEVATION OF THE HUMERUS

The generally accepted view that in raising the humerus to a straight angle, the deltoid elevates the arm approximately to a right angle, after which elevation is completed by scapular rotation, is not supported by our investigation. The deltoid alone is unable to raise the humerus beyond 60 degrees while elevation from this to approximately 115 degrees involves scapular rotation, after which the deltoid again becomes active and completes the elevation. Inspection and palpation or electrical stimulation of the deltoid will verify the active role it plays in elevation of the arm from 115 degrees to a straight angle. The deltoid acts first as an abductor, abducting the arm approximately 60 degrees, and then after elevation to 115 degrees it becomes an adductor, thereby raising the arm through the final arc to 180 degrees. The origin and insertion of the deltoid are so placed that it may serve this dual