Partial Hand Amputation: Prosthetic Management

Jack E. Uellendahl CPO

Matthew J. Mikosz CP, LP

Jack E. Uellendahl or an immediate family member serves as a paid consultant to or is an employee of Hanger Clinic and has stock or stock options held in Hanger Clinic. Neither Matthew J. Mikosz nor any immediate family member has received anything of value from or has stock or stock options held in a commercial company or institution related directly or indirectly to the subject of this chapter.

ABSTRACT

Partial hand amputation is reported to be the most common upper limb amputation level in the United States. The hand has 29 joints, and approximately 25% of the motor cortex controls the 34 muscles that move the hand. Because these joints allow the hand to assume many postures and produce various grasping patterns, replacement with a prosthesis is challenging. Sensory feedback provides information about objects being grasped; loss or compromise of this feedback results in further disability. Trauma is the most common cause of partial hand amputation and often damages the remaining parts of the hand. Limited joint range of motion, malalignment of the remaining fingers, hypersensitivity or insensitivity, scarring, and a lack of strength in the remaining portions of the hand can be complicating factors. Prosthetic options for managing partial hand amputations have increased substantially in recent years.

Introduction

Partial hand amputation is the most common upper limb amputation level in the United States. In a review of hospital discharge records between 1988 and 1996, Dillingham et al¹ found that a mean of 18,496 individuals annually were reported to undergo upper limb amputations or have congenital limb deficiencies; 92% of these were below the wrist. Partial hand amputations have many possible presentations based on the large number of possible hand configurations that result from traumatic injury (Figure 1).

The hand is a marvelous tool. It has 29 joints, and approximately 25% of the motor cortex controls the 34 muscles of the hand. These joints allow the hand to assume many postures and produce a variety of grasping patterns. Therefore, prosthetic replacement is challenging. Sensory feedback provides information about objects being grasped; loss or compromise of this feedback results in further disability. Trauma is the most common cause of partial hand amputation and often damages the parts of the hand that remain. Limited joint range of motion, malalignment of the remaining fingers, hypersensitivity or insensitivity, scarring, and a lack of strength in the remaining portions of the hand may be complicating factors.² Prosthetic options for managing partial hand amputations have increased substantially in recent years. The current prosthetic options and indications for their use are reviewed.

Clinical Considerations: Prosthetic Options

Prosthetic options can be divided into five categories: aesthetic, oppositional, activity-specific, body-powered, and externally powered. Not all options are available for all levels of partial hand absence. However, when evaluating a partial hand amputation, all options relevant to the amputation level should be reviewed. When deciding on the type of prosthesis to be used, considerations should include age, sex, occupation, degree of physical activity, gadget tolerance, type of amputation, functional goals, and unilateral versus bilateral involvement.²

Because the thumb is the most important finger, representing 40% of hand function, its presence and condition should be carefully evaluated.³ Optimal management of the thumb should account for sensibility, stability, opposition, and length.⁴ With partial thumb amputation, it is sometimes advantageous to restore length with a customized silicone finger prosthesis. However, this type of prosthesis will cover sensate skin and can impede function in instances in which comorbid missing fingers have been treated with a prosthetic replacement, which also provides no sensation (Figure 2). In this case, a short, sensate thumb may be more functional than a normallength prosthetic thumb without normal sensation.

Additional options include surgical solutions. A partially amputated
thumb may be treated surgically with lengthening, web space deepening, toe transfer, pollicization, or osteointegration⁵^,⁶ (Figure 3). Such cases highlight the importance of early interaction among the patient, prosthetist, surgeon, and therapist in developing a treatment plan that optimizes a patient’s outcome.

FIGURE 1 Photographs showing a variety of partial hand amputations.

Component Considerations

Aesthetic Restoration

High-definition custom silicone prostheses are the best option to reproduce the natural appearance of the hand.⁷ These prostheses are appropriate for all levels of partial hand amputation from fingertip to complete hand prostheses. The prosthesis is carefully matched in size, shape, surface detail, and color to the sound hand, which allows differences between the normal and prosthetic hand to go unnoticed by the casual observer (Figure 4). Silicone prostheses provide an extremely important psychological benefit in restoring body image.⁷ The prostheses have a long history of use and are generally well accepted by patients.⁷^,⁸ They do not provide finger movement and are often referred to as passive prostheses. However, a study by Fraser⁹ showed that, despite the lack of movement, these prostheses are used functionally when performing daily tasks. Passive silicone prostheses can provide opposition when some fingers remain and broaden the surface available for gripping stability. In addition, silicone prostheses protect sensitive or painful areas of the hand, with attendant improvements to manual function. Although silicone has good stain resistance, the material can be damaged if used for manual labor. Many individuals with partial hand amputations benefit from the use of an aesthetic prosthesis in addition to another type of prosthesis.

FIGURE 2 Photograph of a thumb that was left uncovered to preserve sensation while opposing three powered fingers. The little finger was also partially amputated and left uncovered.

FIGURE 3 Preoperative (A) and postoperative (B) photographs of a thumb amputation that underwent bone lengthening and web space deepening to provide sufficient length for functional grasp.

Opposition Prostheses

The primary goal of an opposition prosthesis is to provide opposition for intact fingers or the palm of the hand. These prostheses can be made of many materials but are usually strong, robust, and well suited for manual tasks (Figures 4, 5 and 6). Most opposition prostheses are static, but some have joints that can be prepositioned on a task-specific basis, such as the CAPP Multi-Position Post (Hosmer), APRL thumb (Hosmer), and Vincent Finger Joint (Vincent Systems GmhH).

Activity-Specific Prostheses

In some cases, a prosthesis is needed to accomplish a specific function. The prosthesis may be constructed to hold and support a specific tool, with or without the contribution of any remaining digits (Figure 7). Alternatively, a
quick-disconnect mechanism can be fixed onto the palm of the remnant hand that allows attachment to a variety of commercially available tools and implements. At the partial finger amputation level, simple fingertip caps can extend the functional length of the residual finger to enable enhanced function (Figure 8). Collectively, these prostheses may allow participation in hobbies and sports and can be critical to performing job duties.

FIGURE 4 Photograph of a hybrid silicone and composite thumb prosthesis that provides good appearance and stability for functional opposition to the remaining fingers.

Body-Powered Prostheses

Body power refers to the use of force and excursion produced by more proximal joints to control a prosthesis. Because of the link between the controlled component and the proximal physiologic joints, body-powered control has the inherent advantage of providing proprioceptive feedback to the user regarding force, position, and speed of movement.¹⁰ However, a possible disadvantage is that the required movements of the proximal joint segments may appear unnatural.² Body-powered prosthetic options are now available for nearly all levels of partial hand absences. Control is accomplished either through rigid linkages or through cables connecting the prosthetic joint(s) to a proximal intact joint. Examples of linkage-driven fingers are the Naked Prosthetic Finger (Naked Prosthetics; Figure 9) and the X-Finger (Didrick Medical; Figure 10).

FIGURE 5 Photographs of a thumb amputated at the metacarpophalangeal joint (A) that was fitted with a rigid thumb opposition post (B).

Alternatively, the M-Fingers and Partial M-Fingers (Partial Hand Solutions) are cable driven. Partial M-Fingers use metacarpophalangeal (MCP) joint flexion to drive proximal interphalangeal joint flexion, whereas the distal interphalangeal joint is fixed (Figures 11, 12 and 13). M-Fingers are designed for complete finger absence at or proximal to the MCP joints. Flexion at the MCP and proximal interphalangeal joints is actuated by wrist flexion; internal spring mechanisms return the joints to their extended positions with wrist extension¹¹ (Figure 14). Another body-powered option is a handihook-type device (Figure 15) in which a conventional hook terminal device, either voluntary opening or voluntary closing, is attached to a prosthetic socket in the palm of the partial hand prosthesis. The handihook is generally activated using a cable attached to a shoulder harness.²^,¹²

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