Lameness of the Horse Part 19

[Footnote 25: Traite De Therapeutique Chirurgicale Des Animaux Domestique, par P.J. Cadiot et J. Almy, Tome Second, page 547.]

[Footnote 26: Anatomie Regionale Des Animaux Domestique, page 695.]

[Footnote 27: Manual of Veterinary Physiology, by Major-General F.

Smith, C.B., C.M.G., page 678.]

[Footnote 28: Moller's Regional Veterinary Surgery, by Dollar, page 630.]

[Footnote 29: Edinburgh Veterinary Review, Vol. VI, page 616.]

[Footnote 30: Equine Laminitis or Pododermat.i.tis, by R.C. Moore, D.V.S., American Journal of Veterinary Medicine, Vol. XI, page 284.]

[Footnote 31: American Journal of Veterinary Medicine, Vol. XI, page 318.]

[Footnote 32: The Shoeing of a Dropped Sole Foot by Dr. David W.

Cochran, New York City, The Horse Sh.o.e.rs Journal, March, 1915.]

[Footnote 33: Quittor and Its Treatment by the Hughes Method, J.T.

Seeley, M.D.C., Seattle, Was.h.i.+ngton, Chicago Veterinary College Quarterly Bulletin, Vol. 9, page 27.]

SECTION IV.

LAMENESS IN THE HIND LEG.

Anatomo-Physiological Consideration of the Pelvic Limbs.

The pelvic bones as a whole const.i.tute the a.n.a.logue of the scapulae with respect to their function as a part of the mechanism of locomotive and supportive apparatus of the horse. The manner of attachment or connection between the ilia and the trunk is materially different from that of the scapulae, however, and the angles as formed by the long axes of the ilia in relation to the spinal column are maintained by two functionally antagonistic structures--the sacrosciatic ligaments, and the abdominal muscles by means of the prepubian tendon. The sacro-iliac articulations are such that a very limited amount of movement is possible; free movement, however, is unnecessary because of the enarthrodial (ball and socket) femeropelvic joint.

The various muscles which exert their effect upon the pelvis in changing their relations.h.i.+p between the long axes of the ilia and spinal column, are concerned but little more in propulsion and weight bearing than are the pectoral muscles. A general treatise on the subject of lameness does not properly include such structures any more than it does the various affections of the dorsal, lumbar and sacral vertebrae or inflammation of the abdominal parietes. Involvement of such parts cause manifestations of lameness but the matter of establis.h.i.+ng a diagnosis is difficult in many instances and in some cases impossible.

The femeropelvic articulation is formed by the hemispherical head of the femur and the acetabulum; the latter const.i.tuting a cotyloid cavity which is deepened by the cotyloid ligament.

The round ligament (ligamentum teres) is the princ.i.p.al binding structure of the hip joint and it arises in a notch in the head of the femur and is attached in the subpubic groove close to the acetabular notch.

Another ligament, peculiar to Equidae--the accessory (pubiofemoral)--is attached to the head of the femur near the round ligament and pa.s.ses through the cotyloid notch and along the under side of the pubis. It is inserted or blends with the prepubic tendon. This ligament prevents extreme abduction of the leg. The joint capsule encompa.s.ses the articulation and is attached to the brim of the acetabulum and the edge of the head of the femur.

[Ill.u.s.tration: Fig. 40--Sagital section of right hock. The section pa.s.ses through the middle of the groove of the trochlea of the tibial tarsal bone. 1 and 2. Proximal ends of cavity of hock joint. 3. Thick part of joint capsule over which deep flexor tendon plays. 4. Fibular tarsal bone (sustentaculum). A large vein crosses the upper part of the joint capsule (in front of 1). (From Sisson's "Anatomy of the Domestic Animals.")]

[Ill.u.s.tration: Fig. 41--Muscles of right leg; front view. The greater part of the long extensor has been removed. 1, 2, 3. Stumps of patellar ligaments. 4. Tuberosity of tibia. (From Sisson's "Anatomy of the Domestic Animals.")]

The stifle joint is a.n.a.lagous to the knee joint of man and is to be considered an atypical ginglymus (hinge) articulation formed by the femur, tibia and patella. The ligaments are femerotibial, femeropatellar and capsular.

In addition to the usual provision for articulation of bones there are situated cartilaginous _menisci_ between the condyles of the femur and the head of the tibia. These discs surround the tibial spine and are otherwise shaped to fit perfectly between the articular portions of the femur and tibia.

Collateral ligaments (internal and external lateral) pa.s.s from the distal end of the femur to the proximal portion of the tibia. The mesial (internal) arises from the internal condyle of the femur and is attached to a rough area below the margin of the medial (internal) condyle of the tibia. The lateral (external), shorter and thicker, arises from the depression on the lateral epicondyle and inserts to the head of the fibula.

The crucial or interosseus, anterior and posterior, are situated between the femur and tibia, and according to Smith,[34] the crucial ligaments are necessary to properly join the two bones, because of the character of the structure of the articular ends of the femur and tibia.

The femeropatella ligaments are two thin bands which reinforce the capsular ligament. They arise from the lateral aspects of the femur, just above the condyles and are inserted to the corresponding surfaces of the patella.

The patellar ligaments are three strong bands which arise from the antero-inferior surface of the patella, and are inserted to the anterior aspect of the tuberosity of the tibia.

Taken as a whole, the tarsal bones, interarticulating and articulating with the tibia and metatarsal bones form the hock joint and this articulation is a.n.a.lagous to the carpus. As with the carpus, there is less movement in the inferior portion of the joint than in the superior part of the articulation. The chief articulating parts are the tibia with the tibial tarsal bone (astragulus).

[Ill.u.s.tration: Fig. 42--Muscles of lower part of thigh, leg and foot; lateral view, o', Fascia lata; q, q', q", biceps femoris; r, semitendinosus; 21', lateral condyle of tibia. The extensor brevis is visible in the angle between the long and lateral extensor tendons.

(After Ellenberger-Baum, Anat. fur Kunstler.) (From Sisson's "Anatomy of the Domestic Animals.")]

The capsular ligament is attached around the margin of the articular surfaces of the tibia, to the tarsal bones, the collateral ligaments (internal and external lateral) and to the metatarsus.

[Ill.u.s.tration: Fig. 43--Right stifle joint; lateral view. The femoro-patellar capsule was filled with plaster-of-Paris and then removed after the cast was set. The femoro-tibial capsule and most of the lateral patellar ligament are removed. M. Lateral meniscus. (From Sisson's "Anatomy of the Domestic Animals.")]

The common ligaments of the tarsal joint are the collateral, the plantar (calcaneo-metatarsal and c. cuboid) and dorsal ligaments (oblique).

The medial (internal lateral) ligament serves to join the medial (internal) tibial malleolus with tibial tarsal (astragalus) and other tarsal bones.

The lateral (external lateral) ligament is inserted to the lateral (external) tibial malleolus and its distal portions are attached to the tibial tarsal (astragalus), fibular tarsal (calcaneum) bone, fourth tarsal (cuboid) and metatarsus bones.

[Ill.u.s.tration: Fig. 44--Left stifle joint; medial view. The capsules are removed. (From Sisson's "Anatomy of the Domestic Animals.")]

The plantar ligament (calcaneo-cuboid) is a strong flat band which is attached to the plantar surface of the fibular and fourth tarsal bones (calcaneum and cuboid) and the head of the lateral metatarsal (external small) bone.

The dorsal (oblique) ligament is attached above to the distal tuberosity on the inner side of the tibia. It is inserted below to the central (cuneiform magnum) and third (c. medium) tarsal bones, to the proximal ends of the large and outer small metatarsal bones.

The tarsus is a true hinge joint and because of the great strain which it sustains, is subject to frequent injury. About seventy-five percent of cases of lameness affecting the hind leg may be said to arise from disease of the hock.

As members of locomotion the legs receive strains of two kinds: those of concussion and weight-bearing and strains of propulsion; the latter are the greater. In the horse as a work animal, the hind legs are probably subjected to greater strains than are the front but the manner of construction of the various parts of the pelvic limbs with the possible exception (according to some authorities) of the tibial tarsal joint, offsets this condition.

The femur may be considered a.n.a.lagous to the humerus in that it bears a similar relations.h.i.+p to the ilium, that exist between the humerus and scapula. Further flexion during repose is prevented chiefly by the glutens medius (maximus) muscle and its tendons. The larger tendon inserts to the summit of the trochanter major of the femur and corresponds to the biceps brachii in the action of the latter on the scapulohumeral joint, except that the gluteus medius, in attaching to the femoral trochanter, exerts its effect as a lever of the first cla.s.s.

Because of the relations.h.i.+p between the long axes of the femur and iliac shaft it is evident that the angle formed by these two bones is maintained chiefly by the gluteus muscles during weight bearing.

Contraction of muscular fibers of the gluteus medius causes extension of the femur and muscular strain is prevented to a great degree by the inelastic portion of this muscle. The chief physiological antagonistics of the glutei are the quadriceps femoris and tensor fascia lata.

While the leg is supporting weight the stifle joint is fixed in position mainly by the quadriceps femoris group of muscles which are attached to the patella. Tendinous fibres intersect this muscular ma.s.s and relieve muscular strain during weight bearing. Because of the manner in which the patella functionates with the trochlea of the femur, comparatively little energy is required to prevent further flexion of the stifle joint. The patella, according to Strangeways, may be considered a sesamoid bone.

[Ill.u.s.tration: Fig. 45--Left stifle joint; front view. The capsules are removed. 1. Middle patellar ligament. 2. Stump of fascia lata. 3. Stump of common tendon of extensor longus and peroneus tertius. (From Sisson's "Anatomy of Domestic Animals.")]

The quadriceps group of muscles is a.s.sisted by the anterior digital extensor (extensor pedis) peroneus tertius and tibialis anticus (flexor metatarsi) muscles. The latter pair (flexor metatarsi, muscular and tendinous portions, because of their attachment to the external condyle of the femur and to the metatarsal bone) are enabled to automatically flex the tarsal joint when the stifle is flexed.

The hock is kept fixed in position by the gastrocnemius and the superficial digital flexor (perforatus). The latter structure, which is chiefly tendinous, originates in the supracondyloid fossa of the femur and has an insertion to the summit of the fibular tarsal (calcis) bone.

It relieves the gastrocnemius of muscular strain during weight bearing.

Smith[35] styles the function of the stifle and hock joints a reciprocating action, and we quote from this authority the following:

From what has been said, it is evident that flexion and extension of stifle and hock are identical in their action. When the stifle is extended, the hock is automatically extended, nor can it under any circ.u.mstances flex without the previous flexion of the stifle.

There is no parallel to this in the body. The two joints, though far apart, act as one, and they are locked by the drawing up of the patella, and in no other way. The so-called dislocation of the stifle in the horse is a misnomer. That the patella is capable of being dislocated is beyond doubt, but the ordinary condition described under that term, when the stifle and hock are rigid while the foot is turned back with its wall on the ground, is nothing more than spasm of the muscles which keeps the patella drawn up.

The moment they relax the previously immovable limb and useless foot have their function restored as if by magic, but are immediately thrown out of gear in the course of a few minutes as a recurrence of the teta.n.u.s of the petallar muscle takes place. The fascia of the thigh, like that of the arm, is a most potent factor in giving a.s.sistance to the constant strain imposed on the muscles of the limbs during standing.