Amputations in the shoulder region are relatively uncommon and are generally related to malignant lesions, trauma, and congenital etiologies.^1,2 The complete loss of an upper limb is a substantial loss. Replacing the natural limb with a mechanical limb presents many challenges, including short lever arms, multiple joint involvement, and diminished excursion capabilities.^3,4 In addition, proximal amputation levels can limit componentry selection and may require the use of externally powered components for improved functional outcomes.⁵ Individuals with shoulder-level amputations often reject the use of a prosthesis for a variety of reasons, including socket discomfort, lack of heat dissipation, the weight of the prosthesis, and displeasing appearance.^6,7,8 Based on the literature, the overall rejection rate for a high-level upper limb prosthesis ranges from 32% to 65%.^6,7,8,9,10 However, with advances in modern socket designs and materials, many of these rejection factors have been mitigated.

Amputations and deficiencies in the shoulder region present in a range of configurations; however, this chapter focuses on humeral neck amputation, glenohumeral (shoulder) disarticulation, and interscapulothoracic (forequarter) amputation. These levels of amputation differ in their clinical presentation but are managed prosthetically in a very similar fashion.³

Amputations and deficiencies about the shoulder region present differently and require different fitting considerations.¹¹ It is important to understand the unique clinical presentations and functional capabilities of each level of amputation when designing a prosthesis for the shoulder region.

Patients with an amputation at the level of the humeral neck have an intact glenohumeral joint and a considerably shortened residual humerus (Figure 1). Because the residual limb does not have the necessary length to be fitted with standard transhumeral socket designs, thoracic-style sockets are generally chosen. A glenohumeral disarticulation is an amputation through the glenohumeral joint or a disarticulation of the humeral head from the glenoid cavity (Figure 2). Individuals with an interscapulothoracic amputation have undergone complete removal of the shoulder girdle, including the scapula and the lateral two-thirds of the clavicle (Figure 3).

The initial stage in designing a prosthesis requires a comprehensive patient evaluation. This evaluation is essential to the development of the most
appropriate prosthetic prescription to meet an individual patient’s psychosocial and functional needs. Prosthetic components should be matched to the patient’s physical characteristics, customary activities of daily living, and vocational goals. The physical findings from the residual limb examination as well as any associated injuries must be considered.

The rehabilitation team should take great care in gathering the necessary information during the evaluation and design of the prosthesis.^12,13 Obtaining information on the amputation level, the characteristics of the residual limb, the location of scarring, preinjury hand dominance, the results of myoelectric and manual muscle testing, range of motion, and the presence of phantom pain or sensation can assist in designing the prosthesis, including component selection. Comorbidities, including diabetes, overuse symptoms, decreased functionality of the sound side, and any history of neck and back pain, provide further guidance in determining the most appropriate prosthetic approach.

A thorough understanding of the patient’s work-related tasks is necessary in designing the prosthesis. In some instances, a visit to the patient’s worksite may be necessary to better understand vocational requirements and to justify the components being provided. In other cases, the patient may be transitioning to a new occupation. Understanding the requirements of current and future vocational goals is an important consideration in prosthetic design.

The clinical evaluation lays the foundation for selecting the design and control of the prosthesis. During the patient evaluation process, the conceptual design of the prosthesis begins to develop. The size, shape, and features of the socket for the shoulder region become apparent based on the needs and abilities of the individual. For example, if a patient has an amputation at the humeral neck level, the use of the movable humeral head to activate force-sensitive resistors or switches is a consideration in the design of the prosthesis. Alternatively, strong, distinct muscle contractions allow for the consideration of myoelectric control strategies. Taking into account the individual’s unique capabilities to control the prosthesis helps in the creation of a device that more easily permits intuitive learning.

Socket designs for the shoulder region have substantially evolved from the original bucket-style sockets, which encompassed the entire shoulder proximally, extended 6 inches distally from the axilla, and wrapped around almost to the midline of the torso in their anterior and posterior dimensions. The contributions of many clinicians and researchers have reduced the bulk of these sockets, improved heat dissipation, enhanced suspension, incorporated advanced materials, and refined harnessing techniques.^14,15,16

The prosthetic socket can be evaluated in the following five critical support areas: anterior proximal, posterior proximal, lateral wall, anterior distal, and posterior distal. A critical evaluation of these five support areas with respect to suspension, soft-tissue loading, force couples during prosthesis use, comfort, and stability will collectively provide the framework for designing the shoulder socket.

During the molding process, it is necessary to provide anterior proximal compression over the pectoralis and infraspinatus muscles (Figure 4). This compression creates a wedge shape that assists with suspension, axial loading, rotational stability, and maintaining electrode contact in externally powered prosthetic designs. The anterior socket trim line is typically located inferior to the clavicle for improved comfort. The posterior proximal trim line is located over the supraspinatus and is responsible for load bearing as well as reducing distal migration of the socket. The lateral wall connects the proximal and distal sockets. This area assists with the transfer of forces to the inferior aspect of the socket. The lateral wall is generally 3 to 5 inches wide, assists with
soft-tissue containment, and broadens the surface area of the socket for force distribution.

Socket torque increases when the shoulder or elbow joint is flexed. The resultant torque produces force couples at the anterior distal and posterior proximal aspects of the socket interface (Figure 5). The anterior distal and posterior proximal socket regions assist with torque stabilization and should be dynamically simulated during diagnostic socket fitting to ensure that the necessary force couple support has been achieved. In contrast, because of the predominance of the force couple previously described, the posterior distal aspect of the socket can be reduced to a smaller area of support. This area of the socket generally assists with rotational stability and is useful in activities involving shoulder and elbow extension.

The selection of appropriate socket interface materials is a critical factor in the successful application of a prosthesis for the shoulder region. In general, socket interface materials with a higher coefficient of friction assist in maintaining the position of the socket on short residual limbs. Securing the position of the socket assists in maintaining the optimal mechanics of the prosthesis.

In the past, rigid, laminated hard sockets were commonly used; however, the low friction characteristics of the laminated surface created difficulties in maintaining socket position. With the development of frame-type sockets, the laminated sockets were largely replaced by flexible thermoplastic inner sockets. The flexible thermoplastic material provided greater stability and improved comfort compared with laminated sockets (Figure 6).

In recent years, there has been a shift from traditional thermoplastic socket interfaces to silicone rubber materials. A high-consistency rubber (HCR) silicone socket offers several advantages over thermoplastic materials. It can be manufactured to the desired thickness and stiffness (shore durometer), allowing the prosthetist to have localized control over the physical properties of the socket construction. The HCR silicone socket design for a shoulder disarticulation generally includes an over-the-shoulder strap that is integrated into the silicone (Figure 7). This strap, coupled with the high coefficient of friction of HCR silicone, helps prevent distal migration of the prosthesis. The strap fits the contour of the shoulder exactly and is soft and flexible so it moves with the patient to provide greater comfort than other strap materials used in this application. Because the HCR silicone is custom pigmented to approximate the general skin tone of the amputee and the strap is continuous with the inside surface of the socket, the cosmetic appearance is good. To provide greater comfort in the transition area from a rigid structure to a patient’s body, the HCR silicone socket is made to extend farther than the composite frame to which it is attached. If there are particularly sensitive areas that require additional cushioning, silicone gel pads can be integrated into the HCR silicone to provide excellent padding for improved comfort. This feature is especially useful when a hybrid or body-powered prosthesis is used, because high forces may be needed for activation of prosthesis components.