Fall is just around the corner, and a dog's activity level often increases with the cooler weather. It is wise to take a few minutes to evaluate your pet's gate to make sure no subtle changes have occurred. That is an easy chore if you understand flexion and extension and how your dog should move.
The muscular system is divided into axial and appendicular parts that correspond to the axial and appendicular skeleton. Muscles of the head, neck, spine and trunk make up the axial muscles while the muscles of the pectoral girdle, front limb, pelvic girdle and hind limb compose the appendicular muscles. One should consider the action of muscles when evaluating the gait of a dog. This is especially true when considering which muscles may be compromised in a dog that is limping.
Skeletal muscles allow the dog to move by changing the angle of one bone to another at a joint. Freely movable joints, synovial joints, exhibit several types of movement including flexion and extension.
Flexion describes the movement of two bones in relation to one another in a manner that decreases the angle at their joint. If a dog bends or flexes his foreleg at the elbow or wrist or the hind limb at the stifle or hock, the angle of the two bones at their joint is decreased (Fig. 1a). The rule of thumb is that muscles that flex a joint are above the joint and on the side that the joint angle is decreased (Fig. 1b).
|Figure 1 – (a.) Sand flexes at the elbow (1), the wrist (2), the hock (3) and the knee (4) as handler, Debbie Coggin, moves him around the show ring. (b.) The muscles responsible for flexion are above or proximal to the joint on the side that the joint angle is decreased.|
On the other hand, extension increases the angle of two bones at their joint. Therefore, if the forelimb is flexed at the elbow and the dog extends or straightens the leg, the angle of the elbow joint will increase (Fig. 2a). Muscles that extend a joint are usually below the joint and on the side opposite of the joint angle increase (Fig. 2b).
|Figure 2 – (a) Continuing around the show ring, Sand extends his elbow to maintain an even smooth gait. (b) The extensor muscles that increase the angle of the elbow are located below or distal to the joint on the side opposite that the joint angle is increased.|
This information helps evaluate a dog with a limp. Watch him move to determine if he has difficulty flexing or extending a joint in the affected limb. Now you know which muscles may be strained or injured. You can palpate for tenderness to determine if rest or a visit to the veterinarian are indicated. The discomfort of sore achy muscles caused by overexerting or other neuromuscular problems can be soothed by appropriate massage. Regular massage also decreases the risk of injury.
It is not necessary to learn names of all the muscles in a dog's body. It is very helpful to know where muscles responsible for actions like flexion and extension of joints are located. This gives you a great advantage when assessing movement or aberrations of movement in a dog.
Note: This material is excerpted from Dr. C. Sue Furman's book, Canine Massage for the Athlete in Every Dog©.
C. Sue Furman, Ph.D.