Tendon sheaths have the same structure and function as the synovial membranes of joints, and are liable to the same diseases. Apart from the tendon sheaths displayed in anatomical dissections, there is a loose peritendinous and perimuscular cellular tissue which is subject to the same pathological conditions as the tendon sheaths proper.

Teno-synovitis.—The toxic or infective agent is conveyed to the tendon sheaths through the blood-stream, as in the gouty, gonorrhœal, and tuberculous varieties, or is introduced directly through a wound, as in the common pyogenic form of teno-synovitis.

Teno-synovitis Crepitans.—In the simple or traumatic form of teno-synovitis, although the most prominent etiological factor is a strain or over-use of the tendon, there would appear to be some other, probably a toxic, factor in its production, otherwise the affection would be much more common than it is: only a small proportion of those who strain or over-use their tendons become the subjects of teno-synovitis. The opposed surfaces of the tendon and its sheath are covered with fibrinous lymph, so that there is friction when they move on one another.

The clinical features are pain on movement, tenderness on pressure over the affected tendon, and a sensation of crepitation or friction when the tendon is moved in its sheath. The crepitation may be soft like the friction of snow, or may resemble the creaking of new leather—“saddle-back creaking.” There may be swelling in the long axis of the tendon, and redness and œdema of the skin. If there is an effusion of fluid into the sheath, the swelling is more marked and crepitation is absent. There is little tendency to the formation of adhesions.

In the upper extremity, the sheath of the long tendon of the biceps may be affected, but the condition is most common in the tendons about the wrist, particularly in the extensors of the thumb, and it is most frequently met with in those who follow occupations which involve prolonged use or excessive straining of these tendons—for example, washerwomen or riveters. It also occurs as a result of excessive piano-playing, fencing, or rowing.

At the ankle it affects the peronei, the extensor digitorum longus, or the tibialis anterior. It is most often met with in relation to the tendo-calcaneus—Achillo-dynia—and results from the pressure of ill-fitting boots or from the excessive use and strain of the tendon in cycling, walking, or dancing. There is pain in raising the heel from the ground, and creaking can be felt on palpation.

The treatment consists in putting the affected tendon at rest, and with this object a splint may be helpful; the usual remedies for inflammation are indicated: Bier's hyperæmia, lead and opium fomentations, and ichthyol and glycerine. The affection readily subsides under treatment, but is liable to relapse on a repetition of the exciting cause.

Gouty Teno-synovitis.—A deposit of urate of soda beneath the endothelial covering of tendons or of that lining their sheaths is commonly met with in gouty subjects. The accumulation of urates may result in the formation of visible nodular swellings, varying in size from a pea to a cherry, attached to the tendon and moving with it. They may be merely unsightly, or they may interfere with the use of the tendon. Recurrent attacks of inflammation are prone to occur. We have removed such gouty masses with satisfactory results.

Suppurative Teno-synovitis.—This form usually follows upon infected wounds of the fingers—especially of the thumb or little finger—and is a frequent sequel to whitlow; it may also follow amputation of a finger. Once the infection has gained access to the sheath, it tends to spread, and may reach the palm or even the forearm, being then associated with cellulitis. In moderately acute cases the tendon and its sheath become covered with granulations, which subsequently lead to the formation of adhesions; while in more acute cases the tendon sloughs. The pus may burst into the cellular tissue outside the sheath, and the suppuration is liable to spread to neighbouring sheaths or to adjacent bones or joints—for example, those of the wrist.

The treatment consists in inducing hyperæmia and making small incisions for the escape of pus. The site of incision is determined by the point of greatest tenderness on pressure. After the inflammation has subsided, active and passive movements are employed to prevent the formation of adhesions between the tendon and its sheath. If the tendon sloughs, the dead portion should be cut away, as its separation is extremely slow and is attended with prolonged suppuration.

Gonorrhœal Teno-synovitis.—This is met with especially in the tendon sheaths about the wrist and ankle. It may occur in a mild form, with pain, impairment of movement, and œdema, and sometimes an elongated, fluctuating swelling, the result of serous effusion into the sheath. This condition may alternate with a gonorrhœal affection of one of the larger joints. It may subside under rest and soothing applications, but is liable to relapse. In the more severe variety the skin is red, and the swelling partakes of the characters of a phlegmon with threatening suppuration; it may result in crippling from adhesions. Even if pus forms in the sheath, the tendon rarely sloughs. The treatment consists in inducing hyperæmia by Bier's method; and a vaccine may be employed with satisfactory results.

Tuberculous Disease of Tendon Sheaths.—This is a comparatively common affection, and is analogous to tuberculous disease of the synovial membrane of joints. It may originate in the sheath, or may spread to it from an adjacent bone.

The commonest form—hydrops—is that in which the synovial sheath is distended with a viscous fluid, and the fibrinous material on the free surface becomes detached and is moulded into melon-seed bodies by the movement of the tendon. The sheath itself is thickened by the growth of tuberculous granulation tissue. The bodies are smooth and of a dull-white colour, and vary greatly in size and shape. There may be an overgrowth of the fatty fringes of the synovial sheath, a condition described as “arborescent lipoma.”

The clinical features vary with the tendon sheath affected. In the common flexor sheath of the hand an hour-glass-shaped swelling is formed, bulging above and below the transverse carpal (anterior annular) ligament—formerly known as compound palmar ganglion. There is little or no pain, but the fingers tend to be stiff and weak, and to become flexed. On palpation, it is usually possible to displace the contents of the sheath from one compartment to the other, and this may yield fluctuation, and, what is more characteristic, a peculiar soft crepitant sensation from the movement of the melon-seed bodies. In the sheath of the peronei or other tendons about the ankle, the swelling is sausage-shaped, and is constricted opposite the annular ligament.

The onset and progress of the affection are most insidious, and the condition may remain stationary for long periods. It is aggravated by use or strain of the tendons involved. In exceptional cases the skin is thinned and gives way, resulting in the formation of a sinus.

Treatment.—In the common flexor sheath of the palm, an attempt may be made to cure the condition by removing the contents through a small incision and filling the cavity with iodoform glycerine, followed by the use of Bier's bandage. If this fails, the distended sheath is laid open, the contents removed, the wall scraped, and the wound closed.

A less common form of tuberculous disease is that in which the sheath becomes the seat of a diffuse tuberculous thickening, not unlike the white swelling met with in joints, and with a similar tendency to caseation. A painless swelling of an elastic character forms in relation to the tendon sheath. It is hour-glass-shaped in the common flexor sheath of the palm, elongated or sausage-shaped in the extensors of the wrist and in the tendons at the ankle. The tuberculous granulation tissue is liable to break down and lead to the formation of a cold abscess and sinuses, and in our experience is often associated with disease in an adjacent bone or joint. In the peronei tendons, for example, it may result from disease of the fibula or of the ankle-joint.

When conservative measures fail, excision of the affected sheath should be performed; the whole of the diseased area being exposed by free incision of the overlying soft parts, the sheath is carefully isolated from the surrounding tissues and is cut across above and below. Any tuberculous tissue on the tendon itself is removed with a sharp spoon. Associated bone or joint lesions are dealt with at the same time. In the after-treatment the functions of the tendons must be preserved by voluntary and passive movements.

Syphilitic Affections of Tendon Sheaths.—These closely resemble the syphilitic affections of the synovial membrane of joints. During the secondary period the lesion usually consists in effusion into the sheath; gummata are met with during the tertiary period.

Arborescent lipoma has been found in the sheaths of tendons about the wrist and ankle, sometimes in a multiple and symmetrical form, unattended by symptoms and disappearing under anti-syphilitic treatment.

Tumours of Tendon Sheaths.—Innocent tumours, such as lipoma, fibroma, and myxoma, are rare. Special mention should be made of the myeloma which is met with at the wrist or ankle as an elongated swelling of slow development, or over the phalanx of a finger as a small rounded swelling. The tumour tissue, when exposed by dissection, is of a chocolate or chamois-yellow colour, and consists almost entirely of giant cells. The treatment consists in dissecting the tumour tissue off the tendons, and this is usually successful in bringing about a permanent cure.

All varieties of sarcoma are met with, but their origin from tendon sheaths is not associated with special features.