Paralysis of the Femoral (Crural) Nerve.

Anatomy.—­The femoral nerve (crural) is derived chiefly from the fourth and fifth lumbar nerves.  It runs ventrally and backward, at first between the psoas major and minor, then crosses the deep face of the tendon of the latter and descends under cover of the sartorious over the terminal part of the iliopsoas.  It innervates the psoas major (magnus), psoas minor (parvus), sartorious, rectus femoris, vastus lateralis (interims).  Branches supply the stifle and the adductor and pectineus muscles.

Etiology and Occurrence.—­While paralysis of the femoral nerve, also known as “dropped stifle” occurs as a result of local injuries and melanotic tumors in gray horses, most cases are due to azoturia.  So-called crural paralysis or “hip swinney” is occasionally observed but this is not a condition wherein the nerve is affected in the manner that characterizes the marked atrophy of quadriceps femoris (crural) muscles in some cases of hemaglobinuria.  This form of paralysis according to Hutyra and Marek is due primarily to diffuse degeneration of the muscles.

Symptomatology.—­When muscular atrophy is not extensive no particular evidence of this condition may be manifested while the subject is at rest, but where muscular waste has occurred, the nature of the ailment is at once recognized.  Since the femoral nerve supplies the quadriceps femoris muscles, it follows that when the psoic portion of this nerve becomes diseased, the stifle loses its support, and in a unilateral involvement when the subject attempts to walk on the affected member, the stifle sinks down for want of support and the leg collapses unless weight is caught up with the other leg.  Often, following azoturia, a bilateral affection is to be observed.

Treatment.—­Horses may be restrained in the standing position, and in the average instance, a twitch and hood are all the restraining appliances necessary.

In cases where the disease is unilateral and atrophy is not of too long standing, recovery is possible in vigorous subjects.  All affections, however, wherein degenerative changes involve the nerve trunk, whether due to diffuse myositis or pressure from malignant tumors, will not yield to treatment.

The same general plan of treatment is indicated that is described on page 74 in the consideration of atrophy of the scapular muscles.  It is especially important to provide for the subject to be exercised when there is atrophy of the quadriceps muscles following azoturia.

In addition to the foregoing, good results have attended the use of intramuscular injections of oxygen.  The technic of the operation consists in preparing the area of skin which covers the atrophied muscles as for any operation.  The hair is clipped over five or six or more circular areas of about an inch in diameter; the skin is cleansed and then painted with tincture of iodin.