Chapter 10A - Atlas of Limb Prosthetics: Surgical, Prosthetic, and Rehabilitation Principles
Shoulder Disarticulation and Forequarter Amputation: Surgical Principles
John A. McAuliffe, M.D.
Amputations through the glenohumeral and scapulotho-racic articulations are uncommon. Tumor control remains the primary indication for amputation at this level despite efforts at limb salvage made possible by more accurate methods of preoperative localization, modern adjuvant therapy, and advances in tissue banking. Serious injury is the next most common cause for limb loss about the shoulder, although fewer than 3% of traumatic amputations of the upper limb occur at these proximal levels. All other causative factors are decidedly rare. Congenital limb deficiencies do occur this far proximally, but as at other levels, the need for surgical revision is rare and usually best avoided.
Advances in vascular surgery have made re-establishment of blood flow to severely traumatized limbs commonplace, safe, and effective. Replantation of a limb amputated through the shoulder girdle is, however, seldom feasible or indicated. The vast majority of traumatic amputations about the shoulder are due to avulsion forces, and the re-establishment of structural con-, tinuity is severely limited by the fact that most of these injuries occur through the scapulothoracic articulation rather than through the glenohumeral joint with its greater ligamentous integrity. Replantation may occasionally be considered when the skeletal and neural injuries allow repair or reconstruction, and probably then only in the very young patient in whom some useful neurologic and functional recovery is possible. All of the caveats of major limb replantation concerning the patients overall injury status, duration of ischemia, and the possibility of metabolic replantation toxemia must be carefully borne in mind when such a decision is made.
The cosmetic deformity of forequarter amputation is significant (Fig 10A-1.). When sound surgical judgement permits, retention of the scapula is far less disfiguring (Fig 10A-2.) and of considerable psychological benefit to the patient. Although amputation through the surgical neck of the humerus is functionally equivalent to shoulder disarticulation, maintenance of shoulder width and axillary contour by the former procedure is a distinct cosmetic advantage. This is particularly true for the female patient in whom sacrifice of the pec-toralis major insertion disrupts breast contour and symmetry. Preservation of the deltoid musculature also facilitates myoelectric control of a prosthesis.
The amputation stump itself is of no inherent functional value at these levels because even the ability to grasp or stabilize large objects between the residual limb and thorax will be eliminated. The available function from a prosthetic replacement decreases as the level of amputation progresses more proximally. Acceptance rates of conventional body-powered prostheses therefore fall considerably for shoulder-level amputees. Electrically powered prostheses, however, can provide important function and increase levels of acceptance, albeit at higher cost. Rigid dressings are unnecessarily cumbersome and do not provide the same beneficial effects on wound management and pain control as in amputees with longer stumps. Nonetheless, early prosthetic fitting does encourage the retention of two-handed patterns of activity and may result in significantly higher rates of long-term prosthetic use even at these levels.
It is imperative that any amputation be performed not as an end-stage surgical procedure but as a reconstructive undertaking that is viewed as the first step in the patient's rehabilitation. With this in mind, the surgeons goal should be a mobile, strong, and painless but shortened limb ready for early prosthetic prescription.
Sufficient sensate skin with adequate subcutaneous tissue for padding and normal vascularity is seldom a problem at this level, save in the traumatic amputee. In cases of trauma, the lessons of military surgery must be well remembered and primary wound closure performed rarely, if at all. Despite the superficial osseous structures of the shoulder girdle and chest wall, split-thickness skin grafting of these areas can often be tolerated beneath a prosthetic socket. Excision of previous biopsy scars or skin involved with tumor can usually be accomplished by the design of unconventional flaps, the ultimate location of the scar being of little consequence with modern socket construction. Microsurgical techniques enable the surgeon to make use of distal portions of the limb uninvolved with the disease process necessitating amputation to provide skin or muscle flaps to aid in reconstruction of the amputation site. Such nonconventional use of otherwise discarded portions of the amputated limb should always be considered.
Muscle and Tendon
In the case of forequarter amputation, any remaining musculature, such as the pectoralis major, latissimus dorsi, and trapezius, should be sutured together to form additional padding and contour over the chest wall. Conventional technique for shoulder disarticulation suggests that the rotator cuff tendons be sutured together over the glenoid, following which the deltoid is attached to the inferior glenoid and lateral scapular border to fill the subacromial space. Myodesis ensures consistent electromyographic localization that may improve functional control and particularly proportional grasp for wearers of electric prostheses.
Literally dozens of methods have been described in attempts to alleviate the problems of amputation neuromas. As is usually the case when a plethora of techniques exist, none of them are uniformly successful. All severed nerves form neuromas, and the prime objective is to locate this normal neural reaction in an area where it will not be symptomatic. None of the various physical and chemical methods of treating the nerve stump seems to have an advantage over simple distal traction on the nerve, sharp division, and its retraction under proximal cover away from the end of the residual limb and the cutaneous scar. Overzealous distal traction may produce interstitial failure of the neural elements and formation of a more proximal symptomatic neuroma in continuity. Vasa nervorum that are large enough to be evident are best controlled by gentle dissection from the surface of the nerve and bipolar electrocoagulation.
Major arteries and veins should be dissected separately and doubly ligated proximally. This includes collateral vessels, which in this region may be quite large. Cautery should not be relied upon for their control. Skin and muscle flaps are large, and wound drainage should be used routinely. A postoperative compression dressing is carefully applied to stabilize the flaps and control shear without strangulation.
Bone and Joints
During forequarter amputation, osteotomy of the clavicle should be performed at the lateral margin of the sternocleidomastoid insertion whenever possible in order to preserve contour of the neck. In shoulder disarticulation the articular cartilage on the face of the glenoid is left undisturbed. Removal of acromial and cora-coid prominences is unnecessary and will further disrupt form as well as reduce leverage for body-powered prostheses.
The details of surgical technique are well delineated in the standard textbooks and monographs on amputation. There are two major techniques for performance of the forequarter amputation. Suggested skin incisions are depicted in Fig 10A-3. and Fig 10A-4.. In the anterior technique of Berger (Fig 10A-3.), clavicular osteotomy is performed at the outset, and the lateral portion of the clavicle may be removed from the field by disarticulating the acromioclavicular joint. Following release of the pectoralis major from the humerus and the pectoralis minor from the coracoid process, the major neurovascular structures are exposed and controlled. Anterior dissection is completed by release of the latissimus dorsi from its humeral insertion. The limb is then allowed to fall posteriorly and dissection completed by release of the periscapular musculature from the superior and medial borders of the bone, including the trapezius, omohyoid, levator scapulae, rhomboids, and serratus anterior.
Littlewood's posterior approach is found by many to be technically easier and to involve less blood loss (Fig 10A-4.). Dissection begins posteriorly with transection of the trapezius and latissimus dorsi muscles in line with the medial border of the scapula. The superior and medial borders of the scapula are then freed by division of the levator scapulae, rhomboids, and serratus anterior. The clavicle is exposed subperiosteally and divided. The scapula and upper limb are rotated laterally and displaced anteriorly to allow for identification and control of the neurovascular structures, which are thus placed under tension. Division of the pectoralis major and minor muscles anteriorly then allows the limb to fall free.
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