Amputations

Chapter 65


Amputations



Amputation of a limb is performed relatively commonly in small animals. It is performed for a number of reasons: (1) tumor of the soft tissues or bone located in a limb that is unresectable without amputation. Amputation remains the standard of care to address the local tumor for osteosarcoma in dogs; (2) severe trauma to the bones, joints, or soft tissues of a limb that is not treatable or that would be otherwise cost-prohibitive for the owners to treat; (3) peripheral nerve problems (such as neoplasia or trauma leading to avulsion of a nerve root) that render the limb nonfunctional, which can lead to self-trauma of the limb; (4) ischemic necrosis of the limb following trauma or formation of a thrombus or thrombi, compromising the vascular supply to the limb; (5) intractable orthopedic or soft tissue infection of the limb; and (6) severe disability due to unmanageable osteoarthrosis or arthritis or congenital deformity.15


The animal should be carefully evaluated before performing the amputation to determine the appropriateness of the amputation for this particular animal and the suitability of the animal for surgery. The other limbs are assessed orthopedically and neurologically. It has been proposed that for animals for which the veterinary surgeon has concerns regarding how the animal might perform with an amputation (e.g., animals that are obese, animals that have advanced degenerative osteoarthritis in the other limbs), the animal can be evaluated by temporarily slinging the affected limb and observing the animal’s response. This test can be misleading in some dogs, for instance, when the dog’s response to having its limb in a sling is poor and yet the dog can perform very well after the amputation. This probably occurs because the dog needs to carry the weight of the limb in an uncomfortable and maybe even painful position. Contraindications to performing an amputation include severe orthopedic or neurologic disease affecting the other limbs and/or extreme obesity.9


The animal needs to be evaluated preoperatively for suitability to undergo this type of surgery. Although morbidity and mortality are very low with this procedure, it still remains an invasive procedure, leading to significant fluid, electrolytes, and red blood cell loss trapped in the limb. A complete blood count (CBC), chemistry panel, and urinalysis are advisable. If the amputation is performed to remove a malignant neoplasm, the animal also needs to be properly staged.


Educating the owners before the surgery is very important in helping them making the right decision. The goal is not to persuade them to have the amputation performed even when medically indicated, but rather to make sure they have all the relevant information needed to make a rational decision rather than an emotional one. One study showed that owners were more satisfied with their decision and the outcome of the surgery when amputation was considered properly in advance.9 In helping owners make the decision, providing clear information about the need for the amputation and about its prognosis is essential (see outcome and complications section). For this purpose, slides, pictures, and videos of dogs with an amputated limb can be very helpful.9 However, no matter what decision is ultimately made by the owners, it must be respected by the veterinary health team.



Surgical Techniques



General Principles and Considerations


The surgical techniques presented in this chapter have many variations. The specific order of what steps are to be performed is not always important, so long as the goals of the amputation are met. These goals are to remove the limb while providing appropriate and secure hemostasis. This should be accomplished with the least morbidity, which implies proper analgesia, proper tissue handling, and proper wound closure at the end.


For the purposes of this chapter, full limb amputations are discussed. Partial limb amputations are possible; with these procedures, more length of the limb is preserved, so that the amputation is performed at a level distal to what is described in this chapter. Partial limb amputations, other than digit amputations, are discouraged. Partial limb amputations should be reserved for rare cases in which a prosthesis is going to be used.7 Otherwise, even when the lesion is very distal on the limb, a full limb amputation is performed. Leaving excessive length to the limb can lead to pressure sores and adds unnecessary weight that the animal must carry without any purpose or benefit to the animal.


The skin incision used to perform the amputation might have to vary for lesions (particularly tumors) that are more proximal on the limb and closer to the scapulohumeral or coxofemoral joint. When the location of the lesion prompting the amputation is on the distal aspect or is irrelevant, such as with plexus avulsion, the skin incision goes around the limb without being affected by the lesion. For the thoracic limb, it is made at the level of the scapulohumeral joint. For the pelvic limb, it is at about mid-femur laterally and slightly more proximal medially to allow better access to the femoral artery and vein. With a lesion that is located more proximally, the skin incision has to accommodate for the excision of the lesion. If the lesion is located on the lateral aspect of the limb, the skin incision is more proximal laterally, but then the skin incision becomes more distal than typical on the medial aspect to allow closure of the defect once the limb is removed. If the lesion is located on the medial aspect of the limb, the skin incision is more proximal on the medial side of the limb but becomes more distal than typical on the lateral aspect, again to allow closure of the skin.


Major arteries and veins are divided and ligated individually to prevent the formation of arteriovenous fistulas and to ensure that the ligation of each vessel is more secure. Major arteries are doubly ligated. In giant-breed dogs, the second ligature can be a transfixation ligature for added security instead of a simple encircling ligature. Although double ligation is traditionally reserved for arteries, some surgeons also doubly ligate large veins. Albeit veins are the low-pressure system, the muscularis layer of the veins is considerably weaker than that of the arteries, and slippage of a ligature can occur owing to the flimsy venous wall. It has been proposed that arteries should be ligated first to prevent pooling and loss of blood in the tissues of the limb, as would occur if the veins are ligated first. In cases of malignant neoplasms, it has been suggested to ligate the vein first to limit the possibility of allowing metastasis to occur during surgical manipulation (although this is controversial even in cases of malignant neoplasm).13,15,16 Because of the significant collateral circulation on both the arterial and venous sides in dogs and cats, the benefit of following these recommendations in dogs and cats is unclear.


Traditionally, silk has been advocated to ligate larger arteries and veins. Although nonabsorbable suture materials have been recommended to ligate major arteries, long-lasting absorbable suture materials such as polydioxanone and polyglyconate are also suitable. Smaller vessels can be cauterized when available. Cautery is also helpful in performing midbelly myotomies where indicated.


With the surgical techniques described in this chapter, whenever it is instructed to transect a tendon of origin or insertion from the bone, it should be remembered that if the tendon is close to necrotic tissue or a tumor in the bone, the muscle should be transected away from the lesion. This can necessitate transection through the muscle belly itself.


With the goal to provide multimodal analgesia, when nerves are isolated during surgery, they can be injected with 0.5% bupivacaine before they are transected. A 25-gauge needle is used to inject the local anesthetic. The needle is inserted into the nerve and bupivacaine is injected until a bleb develops into the nerve. The nerve is then transected distal to the injection site. Also, wound soaker catheters can be placed in the surgical bed after the limb is removed but before the surgical wound is closed. Soaker catheters are flexible indwelling catheters embedded near or in surgical sites that can be used to deliver continuous infusion of local anesthetics.1 Bupivacaine or lidocaine can be used.1



Thoracic Limb


Two main surgical techniques can be used for the thoracic limb: (1) removal of the scapula along with the limb, and (2) disarticulation of the limb at the scapulohumeral joint. Removal of the scapula is faster and easier and is the preferred technique of the authors. It has been postulated that removing the scapula may render the chest wall more susceptible to blunt trauma. This is a weak argument to leave the scapula, given that no scientific data support that recommendation. Furthermore, if the scapula is not removed, after surgery the remaining muscles of the limb will atrophy, and this can allow bony protuberances of the scapula, particularly the acromion to become particularly prominent, possibly leading to pressure sores. Amputations performed to treat osteosarcoma of the proximal region of the humerus in dogs should to be performed by removing the scapula to provide better soft tissue margins.



Amputation by Disarticulation at the Scapulohumeral Joint11,15


A skin incision is made circumferentially around the limb. The incision is started at the level of the greater tubercle of the humerus, staying lateral to the limb; it curves distally to the midlevel of the brachium and is directed caudoproximally to end in the caudal point of the axillary space. A straight medial incision is made to connect the cranial and caudal points of the lateral incision. The skin distal to the incision is dissected free from the subcutaneous tissue to the level of the elbow joint circumferentially. The cephalic vein is ligated and divided as it passes cranially under the cleidobrachialis muscle. The axillobrachial vein is ligated and divided as it branches from the cephalic vein. The cleidobrachialis muscle is transected at its insertion on the distal aspect of the humeral crest. The acromion portion of the deltoideus muscle is transected at its insertion on the deltoid tuberosity of the humerus and is reflected proximally. The brachial fascia is incised distally along the cranial border of the lateral head of the triceps muscle to the level of the olecranon. The tendon of the triceps brachii muscle is completely isolated and transected just proximal to the olecranon (Figure 65-1).



The leg is then abducted to allow access to the medial aspect of the limb. The superficial pectoral muscles are transected at their insertion on the crest of the major tubercle. The deep pectoral muscle can then be viewed and is transected at its insertion on the minor and major tubercles of the humerus and the medial fascia of the brachium. The cutaneous trunci muscle, which passes lateral to the vasculature and nerves, is transected and reflected to expose the main neurovascular structures. The brachial artery is isolated, doubly ligated, and divided between its deep brachial branch and bicipital branch. The brachial vein is separately ligated and transected at the same level. The median and ulnar nerves, caudal to the brachial artery, are infused with bupivacaine and sharply transected. The radial nerve is transected as it passes lateral to the brachial artery and into the accessory and medial heads of the triceps brachii muscle. The musculocutaneous nerve is transected as it passes cranial to the nerves and vessels just described. The cranial circumflex humeral artery is divided as it branches from the proximal portion of the brachial artery. The severed vessels and nerves are retracted so that the combined insertion of the latissimus dorsi, teres major, and cutaneous trunci muscles can be transected from the teres tuberosity of the humerus. The fascia along the cranial border of the tensor fasciae antebrachii muscle is incised distally and retracted caudally. The division between the medial and accessory heads and the lateral and long heads of the triceps brachii muscle is exposed. The triceps brachii muscle is bluntly separated so that the medial and accessory heads are left with the amputated limb. The medial and accessory heads are transected distally from the common tricipital tendon.


The branches of the collateral ulnar artery, which supply the distal portion of the triceps brachii muscle, are severed as they enter the long head of the triceps brachii muscle. Branches of the distal radial nerve to the lateral and long heads are transected. The deep brachial artery is still intact and supplies the lateral and long heads of the triceps brachii muscle. The axillobrachial vein is ligated and divided again as it terminates in the axillary vein (Figure 65-2).



The final step is division of the muscles close to the joint. This dissection is started by transecting the insertion of the supraspinatus muscle from the major tubercle of the humerus. The joint capsule is incised along with the muscle. The insertions of the infraspinatus and teres minor muscles are transected from the humerus. After the aponeurosis of the lateral head of the triceps brachii muscle is elevated or transected from the humeral crest, the incision in the lateral joint capsule is continued caudally and around the joint to the medial side, where the subscapularis muscle is transected from its insertion on the minor tubercle of the humerus. The incision is continued cranially and transects the tendon of origin of the coracobrachialis muscle and finally the tendon of origin of the biceps brachii muscle (Figure 65-3).


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Jul 18, 2016 | Posted by in PHARMACOLOGY, TOXICOLOGY & THERAPEUTICS | Comments Off on Amputations
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