The joints, by virtue of their function and anatomical relations, are liable to a variety of injuries and affections, most of which are essentially surgical. The joints most subject to traumatism belong to the extremities. On the other hand, the deeper joints (e. g., of the spine) are quite prone to toxic and infectious diseases and less liable to serious injury. The surgeon cannot disregard the structure of the joint when considering the pathology of its surgical affections. More or less completely protected externally, though sometimes with but a thin coating of integument and fibrous textures, it is composed largely of resistant, white, fibrous tissue, seen in its ligaments, of spongy bone in the expanded bone ends, covered with cartilage of incrustation, the articular termination of the bone shaft not being firmly affixed until a certain age has been reached, while the interior is lined with a serous membrane whose lymphatic connections are most abundant, portions of which are often loaded with fat. In certain joints—particularly the knee-there enter separate considerations in the shape of interarticular cartilages which are not so firmly attached but that they may be sometimes displaced.
Lymphatic connection between the exterior and the interior is often free, and after trifling abrasions or infections of the overlying skin the joint beneath may suffer seriously or even fatally. Many of the surgical diseases of the joints begin within the joint membranes proper, i. e., the synovia. Numerous other expressions, particularly of tuberculosis, have their origin in the bony structure contiguous to the joint cavity.
In any destructive affection of the joint in childhood the corresponding epiphyses are often involved. This is also true of fractures extending into joints or occurring near them in the young. Below will be found a table of the time when the epiphyses are usually consolidated with the main portion of the bone. In general, they unite earlier in the upper limb than in the lower, or, as Sappey puts it, the upper limb first arrives at maturity. The following table represents simply the average, there being considerable variance on either side of it in different individuals:
| UPPER EXTREMITIES. | ||
| Clavicle | 23d | year. |
| Humerus, upper | 20th | year. |
| Humerus, lower | 17th | year. |
| Radius, upper | 16th | year. |
| Radius, lower | 20th | year. |
| Ulna, upper | 16th | year. |
| Ulna, lower | 19th | year. |
| Phalanges | 18th to 20th | year. |
| LOWER EXTREMITIES. | ||
| Femur, head and great trochanter | 19th | year. |
| Femur, lower epiphysis | 21st | year. |
| Tibia, upper | 21st | year. |
| Tibia, lower | 18th | year. |
| Fibula, upper | 21st | year. |
| Fibula, lower | 20th | year. |
| Phalanges | 18th | year. |
These dates should be remembered, as an ununited epiphysis may be involved in a necrotic or suppurative process and thus break down and require removal. Moreover, these facts will also be of value in considering fractures, for up to these dates epiphyseal separations will often be met.
INJURIES TO JOINTS
Sprains.
—A sprain is either the result of a momentary dislocation of a joint, the parts returning immediately to their proper position, or else is produced when a joint has been strained beyond its probable physiological limit without any true displacement. It may be the consequence of direct or indirect violence, or even of incessant muscular action. It always implies a certain degree of tissue injury, which may vary from minute lacerations of ligaments, fasciæ, aponeuroses and periosteum, up to a degree where ligaments are violently sundered or torn out of their bony attachments.
A sprain is generally followed by hyperemia, with its attendant phenomena, as described in a previous chapter, and as long as possibility of infection can be excluded the resulting outpour which produces the extreme joint swelling will more or less quickly disappear.
In fact, as insisted throughout this work, the differences between hyperemia and its consequences, and true inflammation with its results, can nowhere be more perfectly demonstrated than in such a case as this. Even with great damage and effusion there can be complete repair, so long as infection is excluded. Once the germ element enter, the whole aspect is altered and a serious feature is then introduced.