Page 178 - Canine Lameness

150 12 Distal Limb Region

with lateral and medial movement restrained by the joint morphology, the bilateral collateral ligaments,
DISTAL LIMB REGION and the proximal palmar surface of the first phalanges). The paired sesamoids are connected to each
and the lateral and medial collateral sesamoidean ligaments. Extension is limited by the short sesa-
moidean ligaments and the cruciate ligaments (located between the distal pole of the sesamoid bones

other by short palmar ligaments, and the four bones of each joint share a single joint capsule.
The powerful interosseous muscles originate from the palmar side of the bases of metacarpals
II–V. They split into two tendons which each receive a sesamoid bone before inserting on the bases
of the adjacent first phalanx. The muscle bellies run between the bifurcating tendons of the deep
and superficial digital flexors and flex the metacarpophalangeal joints. The flexor carpi radialis
muscle inserts on the proximal palmar surfaces of metacarpals II and III body. The two heads of
the flexor carpi ulnaris muscle both insert on the accessory carpal bone. The two accessory carpal
ligaments anchor the accessory carpal bone to the base of metacarpals IV and V. Together, they
serve to flex the carpus and may also provide antigravity support in dogs. There are numerous
small muscles which lie deep to the deep digital flexor in this area. The extensor carpi radialis
muscles insert on the dorsal surface of the base of metacarpals II and III.
There are three phalanges for each of digits II–V, whereas the underdeveloped digit I has no
second phalanx (Figure 12.3). The first phalanx is a short cylinder with a concave proximal joint
and a distal joint which is sagittally convex, is transversely concave, and extends further on the
palmar than the dorsal surface. This arrangement provides for more flexion than extension and
limited lateral movement. The second phalanx, similarly cylindrical but shorter, forms a flexion
angle of 135° with first phalanx. The four tendons of the superficial digital flexor, which bifurcate
from the primary tendon at the proximal third of the metacarpus and are surrounded by a long
synovial sheath, insert on their proximal bases. They serve to flex both the metacarpophalangeal

(A) (B) (C) (D)

Figure 12.3 Normal radiographs of the forepaw: (A) lateral; (B) dorsopalmar; (C) dorsolateral palmaro-
medial oblique (DLPMO); and (D) dorsomedial palmaro-lateral oblique (DMPLO) view: (a) dorsal sesamoid;
(b) sesamoid 2; and (c) sesamoid 7 (these are the sesamoids most commonly affected by “sesamoid
disease”); metacarpals 1–5 are labeled with roman numerals (I–V).