A Treatise on Fractures, Luxations, and Other Affections of the Bones

by P.-J. Desault

16. The illustrious Petit, and with him Duverney, in acknowledging this cause of displacement, have added to it as another the action of the deltoid muscle on the external end of the bone; in this action, the end of the clavicle is the moveable point, while the humerus affords the fixed point. But how can we admit this cause, when the humeral fragment, in passing under the sternal, moves in a backward direction? So far is the deltoid muscle from drawing the bone downward, that here the bone rather draws the muscle in part backward, and yet, in such a case, the displacement is as perceptible as in any other. Besides, when the sternal fragment, broken obliquely upwards, supports the humeral and prevents a displacement, why does not the deltoid produce this displacement?

It is then in the weight of the arm and shoulder alone, that we must look for the passive power, which depresses them, and which produces a displacement in the direction of the transverse diameter or thickness of the clavicle.

17. A second power, highly active, co-operates with this. I allude to the permanent contraction of the muscles, that extend from the breast to the clavicle and shoulder: from this cause arises the displacement in the longitudinal direction of the bone.

The pectoralis major, the pectoralis minor, the subclavius, the serratus major, and the trapezius, unite their efforts in producing this displacement. These muscles are, in certain respects, antagonists to each other, but they all unite in drawing the shoulder forward and inward. None of them appears to act with more effect than the pectoralis major. To this, in particular, is to be attributed the displacement in a forward direction.

Except in the instances stated above, the action of the muscles is not immediate. They act only secondarily on the external fragment, which, being stedfastly attached to the scapula and humerus, is obedient to the motions impressed by the muscles on these two bones; motions which, in a sound state, the clavicle has a power of controlling.

18. To the weight of the lower extremity (15 and 16), and the spontaneous action of the muscles (17) must be added, as another cause of displacement, the motions which are communicated to the arm by external bodies, and which, being imparted ultimately to the clavicle, derange the fragments, by separating them, approximating them, or making them overlap each other, according to the direction in which they act.

19. When a fracture occurs at the extremity next the shoulder, no displacement of the fragments in general takes place. This circumstance is attributed to the action of the trapezius, which draws each fragment upwards with equal force. However this may be, it is doubtless to such cases that we must refer the complete cures, obtained without any retentive apparatus, by Gasparetti, Brown, and other writers. Hence also, without doubt, arise the difficulties experienced by certain practitioners, such as Duverney, with respect to the diagnosis of this disease. These fractures may be mistaken for fractures of the acromion, being situated so immediately in its vicinity.

§ VI.