INJURIES OF JOINTS.
General Considerations.—A dislocation is the forcible separation of the surfaces of two or more bones forming a joint—the more or less complete displacement from one another of the articulating surfaces of bones.
Its causes are Predisposing and Exciting.
Predisposing Causes.—The muscles and tendons are very important agents in keeping the bones together. Anything which weakens or relaxes them will cause liability to disloca tion, such as constitutional weakness and re laxation owing to previous disease, dropsy of the joint, for example.
The Exciting Causes are—(1) External vio lence and (2) Muscular contraction. (1) The violence may be applied directly, as when a person falls on the shoulder and displaces the humerus; or indirectly, as when the person falls, not on the shoulder, but on the hand, which has been stretched out to save the per son. In the latter case the force acts on the shoulder-joint by means of the leverage supplied by the aim. (2) Muscular contraction during trials of strength, wrestling, or during fits, may cause displacement. The jaw is generally dis located by muscular action.
Kinds.—Dislocations are simple when there is no further injury than the separation of the opposed surfaces of bone, and compound when a wound leads into the joint. They are complete when no parts of the articulating surfaces of the two bones remain in contact with one another, and partial when some portions of the opposed surfaces are in contact, but not the proper parts. Again, according to their period or cause of production, dislocations are said to be congenital, that is, born with the child, pathological, when the dislocation is due to disease, and accidental or traumatic, when force is the agent.
Results.—Besides the bones being forcibly removed from their natural a consider able amount of injury is done to the surrounding parts. The ligaments of the joint are torn ; muscles are stretched and often torn also ; nerves are frequently compressed, causing severe pain at the time of the accident and paralysis afterwards. Blood-vessels are seldom seriously hurt unless in complicated cases, though they too may be compressed and the circulation in the part interfered with. When the bones are
restored to their proper position all these breaches are in time repaired ; even paralysed nerves may regain their power. But when no reduction has taken place, and the hone has been left in its unusual position, it proceeds to accommodate itself to the new situation. By constantly playing and moving in the unusual place it gradually forms there a new joint. The bone on which it moves gets hollowed out to fit it, and even becomes lined with a substance like gristle. Bands of adhesion are formed to secure the bone, and a joint capsule by and by surrounds the joint, while the old cavity gets filled up with deposited matter. The result of this reparative process is that after the lapse of a certain time from the date of the accident it would be rash and dangerous to attempt to restore the bone to its old socket. It is not merely on account of the fibrous adhesions and capsules that have been formed, but because blood-vessels and nerves may be implicated in the changes that have occurred since the dis location. Sometimes, especially in the case of small bones, bony union, instead of the forma tion of a new joint, takes place. At what time it becomes unsafe to reduce an old dislocation it is difficult to say. Sir Astley Cooper said that the thigh could not be reduced after eight weeks, and the arm after three months. But a shoulder displacement has been reduced more than a year after the injury, and without chloroform. In St. George's Hospital Reports two cases are related, one of reduction of die location of the shoulder on the one hundred and seventy-fifth day, and the other a reduction of dislocation of the wrist six years after the accident. The possibility or impossibility of reducing an old dislocation depends very much on the patient. If he is an old feeble man the changes that have been referred to are likely to occur slowly and imperfectly, and adhesions in the new unnatural position are probably corre spondingly few and feeble ; while if the person be young and vigorous, and especially if inflam mation has occurred, the new connections are probably strong, and quickly developed.