Amputation of the Forelimb

This topic is written based on the available literature through 2010 and does not cover the most current literature on this topic.

Introduction

Amputation of the forelimb is occasionally indicated as a primary treatment for severe traumatic injuries resulting in irreparable fracture or soft tissue injury. Other indications are severe neurological lesions such as brachial plexus avulsion, irreparable vascular occlusion, and severe congenital or acquired deformities. Amputation may also be considered as an adjunct to the treatment of neoplasia or severe infections involving the limb. With the possible exception of neoplasia, amputation should be considered a last resort “salvage” procedure, indicated only when no alternative exists that would allow the retention of a useful limb. Unfortunately, with the development of more sophisticated and expensive procedures which allow saving a limb with severe fractures or soft tissue injuries, amputation may be requested solely based on economic considerations. Because almost all animals will do extremely well with a forelimb amputation, it is better to offer amputation than resort to euthanasia because the animal owners are unable to afford the more sophisticated procedures.

Preoperative Considerations

Amputation performed at the shoulder level or above is generally preferable because a residual limb below this level serves no useful purpose and is prone to abrasions and infections from frequent trauma if the animal attempts to walk on the limb. Small dogs and cats invariably adapt well to forelimb amputation; however, some giant breed dogs may have some difficulty. If the patient is able to ambulate while carrying the affected limb, it will usually do well following forelimb amputation. It is difficult for some owners to accept the option of amputation. However, for most large breed dogs with otherwise normal bone and muscle structure, amputation is not as limiting as it would seem. Most owners and pets acclimate to amputation within a few days to two weeks. Surveys of owners who wanted to avoid amputation, but ultimately accepted that option, have revealed that 90% felt the amputation resulted in fair, good or excellent quality of life.

Forelimb amputation can be performed through or directly below the scapulohumeral joint, or the scapula may be removed with the limb. Forequarter amputation with the removal of the scapula is advantageous because major vessels and nerves are easily visualized, bone cutting instruments (oscillating saw, osteotome, or Gigli wire) are not required, and no prominent scapular spine remains behind. The procedure of choice, however, is the one that works best for each individual surgeon.

Forelimb amputation is a major procedure that should be performed only with a thorough knowledge of the patient’s physical status. Because blood loss is likely to be greater than in most major surgical procedures, the surgeon must evaluate both the hematocrit and plasma proteins pre-operatively. Anemic or hypoproteinemic patients should be treated medically, if time allows, or provisions should be made for transfusions of whole blood or plasma as the situation dictates. Balanced electrolyte solutions should be given intravenously continuously during the surgical procedure and post-operatively until the patient has recovered from anesthesia. The intravenous catheter should be large enough to allow whole blood transfusion should the need arise. In cases of amputation because of neoplasia or infection, a tourniquet may be used between the disease site and the amputation site to limit metastasis of infection or neoplasia to the general circulation.

Amputation of a limb is by necessity a painful procedure and careful consideration should be given to managing pain preand post-operatively. Preemptive analgesia is provided with parenterally administered narcotics and a bupivacaine brachial plexus block. If transdermal Fentanyl is used it must be applied the day before the surgery. Post-operative pain management can include narcotics, NSAIDS, and local anesthetics delivered through a “soaker catheter” placed at the time of surgery.

Regardless of the amputation method used, preliminary preparations for the surgical procedure are identical. The affected limb is clipped with a number 40 clipper blade from the carpus to the dorsal and ventral midlines. Clipping should also extend well cranially and caudally to allow adequate draping. The paw is usually covered with a gauze wrap, plastic bag or latex glove before the patient is transported to the operating room where final skin preparation is done.

Forequarter Amputation

The objective of forequarter amputation is to remove the entire pectoral limb, including the scapula, from the thorax. This procedure involves the division of all muscles, nerves and vessels that normally join the two parts. The muscles are the trapezius, rhomboideus, omotransversarius, serratus ventralis, brachiocephalicus, superficial and deep pectorals, and the latissimus dorsi.

After adequate pre-operative evaluation and preparation including the administration of pre-operative analgesics, the patient is anesthetized and is placed in lateral recumbency with the affected limb uppermost. After draping, a skin incision is made over the scapular spine beginning at the dorsal rim of the scapula and proceeding downward to the acromion. At the acromion, the incision curved cranially to cross the cranial aspect of the forelimb at the level of the greater tubercle. This incision is eventually extended to cross the medial surface of the forelimb in the axilla and to curve around the caudal aspect of the limb at the axillary fold, finally to join the lateral incision at the level of the acromion. (Figure 59-1A). The entire skin incision does not need to be completed at the beginning of the operation. The lateral incision alone allows sufficient exposure to remove all muscle insertions, and the remainder of the incision can be delayed as the final act in amputation of the limb.

After the lateral incision to the level of the greater tubercle is completed, subcutaneous dissection exposes the omotransversarius and trapezius muscles. An incision is made in these muscles to sever their attachments to the scapular spine. (See Figure 59-1A) Retraction of the trapezius muscle reveals the rhomboideus muscle which is severed as close to its attachment to the scapula as possible (Figure 59-1B). Several blood vessels that require ligation are generally encountered in the muscle bellies as they are cut. Smaller vessels may be cauterized, but vessels larger than about 1 mm diameter should be ligated with fine monofilament absorbable suture. Further lateral retraction of the scapula reveals the insertion of the serratus ventralis on the medial face of the scapula. The insertion is easily elevated with a sharp periosteal elevator, and thus the detachment of all muscles connecting the scapula to the trunk is completed (See Figure 59-1B).

At this point the vessels and nerves of the brachial plexus are easily visualized and are transected. The axillary artery and vein should be doubly ligated using a three clamp technique. Use of a transfixation suture is recommended in the axillary artery (Figure 59-1C). Nerves may be divided with either a scalpel or scissors without special treatment of the proximal severed ends. Neuroma formation is not a common problem in dogs or cats.

After division of the brachial plexus, attention is turned to the cranial portion of the limb. The brachiocephalicus muscle is transected near the greater tubercle. This is the only muscle in this procedure that is necessary to divide in mid belly, the remainder being severed at their insertions. The omocervical artery and vein are encountered near the greater tubercle and both should be ligated. The superficial and deep pectoral muscles are transected near their insertions on the greater and lesser tubercles respectively (Figure 59-1D). The cephalic vein can also be ligated and divided at this point. The last remaining muscular attachment, the latissimus dorsi, is severed from its insertion on the teres tuberosity and the medial brachial fascia. The axillary lymph node and the accessory axillary lymph node are located just under the latissimus dorsi muscle near its attachment to the humerus and can be conveniently removed, if indicated as in neoplastic disease) once this muscle has been cut (Figure 59-1E).

The amputation is completed by incising the skin of the medial surface of the brachium. A flap must be made that is sufficiently large to cover the defect caused by removal of the limb. The base of the flap must be in the axillary space and as much skin as possible is taken from the medial brachium. It is always desirable to take extra skin to allow trimming as necessary.

Once the limb has been removed, the muscle bellies are pulled together over the ends of the severed vessels and nerves of the brachial plexus. This maneuver is accomplished by inverting the severed ends of the omotransversarius, trapezius, rhomboideus and latissimus dorsi muscles over the surface of the serratus ventralis muscle with a continuous Lembert suture pattern (Figure 59-1F). The superficial and deep pectorals are then similarly inverted by suturing them to the ventral margins of the more dorsal muscles. If a “soaker” catheter is to be used for post-operative administration of local anesthetics to the surgical site, it can be placed just prior to closure of the muscle bellies. Closure of the subcutaneous muscles and skin is routine (See Figure 59-1F). If excessive skin is present, trimming should be done on the medial skin flap in order to preserve the thicker skin and hair coat present on the lateral surface of the limb.

Some veterinary surgeons place several Penrose drains into the wound before beginning closure. If placed, the drains should penetrate the skin as far ventrally as possible. If adequate attention is paid to hemostasis and atraumatic operative technique, drains are not required. In cases that will require surgical drainage, an active suction drain is a better option than the passive Penrose drains. In all cases, a light pressure bandage is used for 2 to 3 days to help prevent swelling, hematoma, and seroma formation. Post-operative pain management will be required. Most patients respond well to morphine at a dosage of 0.25 to 0.5 mg/kg SC or IM q2-6h as needed.
 

Forelimb Amputation by Scapulohumeral Disarticulation

Scapulohumeral disarticulation is preferred by some surgeons for forelimb amputation. Pre-operative evaluation, preparation, pain management and positioning are identical to that described for forequarter amputation.

In this procedure, the initial incision is made as a semilunar incision that begins at the point of the shoulder, extends across the mid-diaphysis of the humerus, and curves back into the axillary fold. This incision produces a large flap that is later used to cover the wound. A similar flap is then made on the medial side of the limb to ensure adequate surgical exposure for the procedure and a generous supply of skin for closure (Figure 59-2A).

The brachiocephalicus muscle is transected first just below the clavicular tendon. The cephalic vein lies in this region and must be ligated and divided. External rotation of the limb exposes the superficial and deep pectoral muscles which are divided close to their insertions on the humerus (See Figure 59-2A). Retraction of these muscles exposes the nerves and vessels of the brachial plexus, which are separated and ligated as necessary. The nerves may be cut with a scalpel or scissors. The axillary artery and vein should be doubly ligated. The axillary artery is divided distal to the point of origin of the external thoracic and lateral thoracic arteries, which arise close to the first rib.

After division of the brachial plexus, the acromial head of the deltoideus muscle is removed from its origin on the acromion process (Figure 59-2B). Distal retraction of this muscle exposes the insertions of the supraspinatus, infraspinatus and teres minor muscles, which should be transected (Figure 59-2C). The insertions of the latissimus dorsi, teres major, and cutaneous trunci muscles are next divided close to the humerus. The scapulohumeral joint capsule is then opened; total dislocation of the joint is easily accomplished once the tendons of the biceps brachii, coracobrachialis, and subscapularis muscles are severed over the joint space (Figure 59-2D). The spinous head of the deltoideus muscle is elevated from its insertion on the humerus (See Figure 59-2D). The long head of the triceps brachii muscle is then divided as distally as possible to complete the amputation. (Figure 59-2E).

The infraspinatus and supraspinatus muscles soon atrophy from disuse and loss of their nerve supply, exposing the acromion and spine of the scapula. A better cosmetic effect is obtained if an osteotome is used to remove the scapular spine, or at least the prominent acromion (See Figure 59-2E, inset). 

Closure of the wound involves suturing the superficial and deep pectoral muscles to the latissimus dorsi , teres major, infraspinatus, supraspinatus, and brachiocephalicus muscles. During closure of the subcutaneous muscles and skin, an attempt is made to preserve as much of the lateral skin flap as possible because this skin is thicker and has a denser hair coat that produces a more cosmetic final result. Post-operative bandaging for 2 to 3 days is desirable to prevent seroma formation. Post-operative pain management is identical to that described for forequarter amputation.
 

Suggested Readings

Evans, H.E., Miller’s Anatomy of the Dog. 3rd ed. Philadelphia: WB Saunders, 1993.

Johnson, A.L., Hulse, D.A. Other Diseases of Bones and Joints. In Fossum, T.W. ed. Small Animal Surgery. 2nd ed. St.Louis, MO, Mosby, 2002, p 1173.