These adventitious bursæ are the following:—
In the first place certain normal bursæ in important situations are frequently so much enlarged by the constant irritation of pressure and friction that they become considerably enlarged. This enlargement may go on to definite pathological changes and thus come under the care of surgeons.
They are Prepatellar bursæ—“housemaid’s knee.”
Olecranon bursæ—“student’s elbow” and “miner’s elbow.”
Tuber ischii bursæ—“weaver’s bottom.”
These may be called “occupation-bursæ” and may be classed with three other well-known adventitious bursæ which are formed on the shoulder in “deal runners,” on the scalp in “fish porters” and in the back of the neck in Covent Garden porters, known as a “hummy.” Entirely new bursæ are formed also over the cuboid bone in talipes equino-varus, over the internal condyles of the femur in bad cases of knock-knee from friction of one joint against the other, over the prominent vertebrae in a humpback. A structure closely resembling a bursa and arising from similar causes to those producing adventitious bursæ is found in unreduced dislocations or ununited fractures.
A small example of an adventitious bursa came under my notice. A woman, E. L., aged 49, had remarkable enlargement of the metatarso-phalangeal joint of her great toe of the left foot, and over this joint was formed a well-marked bursa on the dorsal surface. The right foot showed a much less prominent joint and only a very slight development of the corresponding bursa.
This instance of a bursa-like structure being produced in unreduced dislocations and ununited fractures suggests the conception which I here propose, but do not attempt to verify that all joints in all animal forms from the lowest up to man have been evolved in a manner to which this pathological experiment may give a clue.
A remarkable case reported by Sir William MacEwen in the Royal Society’s Phil. Transactions, Series B, Vol. 199, pp. 253, 279, is worth referring to in this connection. It was a case of a growth of bone in muscle connected with an old injury to the thigh of a man 38 years old, and healthy. At the operation performed by the author of the paper the tumour was found to be movable, partly attached to the fascia lata of the thigh, and the upper part of the tumour moved on the lower. It was found that the tumour consisted of two parts, the upper three-and-a-half and the lower seven inches long, altogether a mass about ten inches in length. Muscular bundles of the vastus externus were included in this ossific formation, one passed through a tunnel in the bone through which it worked, and the sides of it were polished. At the point where the newly formed bone came in contact the surfaces fitted each other and were polished as if they were covered with cartilage, and were here surrounded by a capsule. (Italics not in original.) This fibrous covering when opened was seen to contain a thin serum, which, though not of the consistence of synovial fluid, still aided in lubricating the polished surfaces as they played over one another.
A similar case was reported also by Dr. C. Paterson, surgeon to the Glasgow Royal Infirmary.