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Defining the Relationship between Prosthetic Wrist Function and Its Use in Performing Work Tasks and Activities of Daily Living

Susan Kestner, BS, MSPO

ABSTRACT

Ninety-eight upper extremity amputees were surveyed to determine the impact of prosthetic wrist units in task completion. Data regarding amputation level, prosthesis type, wrist unit functions, daily duration of wear, work experience, and prosthetic training were collected to assess statistically significant relationships among the user characteristics and their impact on wrist utilization. Responses also were recorded addressing prosthesis use, wrist unit functions, wrist unit utilization, and ease of task completion for specific tasks. Respondents were surveyed by mail, phone, and the Internet. Results indicated no clear correlations between most user characteristics and the ease of task completion with a wrist unit. However, analysis between prosthetic training and wrist use did reveal some relationships. Only 29% of unilateral prosthesis users received training from a therapist, and only 22% of the unilateral amputees received more than 10 hours of training from a therapist or prosthetist. Approximately 62% of unilateral and 70% of bilateral users wore their prostheses 10 or more hours a day. However, less than 50% of unilateral users reported using their prosthesis for the majority of tasks evaluated. Unilateral users used their prosthesis more than half the time to stuff envelopes and drive, indicating that unilateral users primarily use their prosthesis for bimanual tasks. Statistically significant improvement was seen in the use of the wrist unit for writing, eating with utensils, chopping vegetables, and hammering. More tasks performed using a wrist unit need to be evaluated. Future studies should focus on measuring tasks that individuals report using their wrist units to perform to more definitively assess the overall benefit of the wrist unit to upper extremity prosthesis users. (J Prosthet Orthot. 2006;18:80–86.)

Wrist motion is essential to the optimal positioning of the human hand for prehension. ^1–3 The human wrist has been measured to have 3° of freedom to facilitate such hand placement: flexion/extension, radioulnar deviation, and rotation. ² The loss of the wrist greatly reduces the functional range of the hand. Prosthetic wrist units were developed to help restore some of this lost functional range to individuals who do not have a wrist as a result of upper limb amputation or congenital absence. Unfortunately, the best prosthetic wrists are still poor substitutes for the human anatomy. Motion of the human wrist is fluid, allowing for constant repositioning of the hand throughout the duration of a task. Studies have shown that most individuals use the fluid positioning of the wrist in flexion/extension, radioulnar deviation, and rotation to complete most activities of daily living (ADLs). ² The majority of prosthetic wrists offer only static repositioning of a prosthetic terminal device into one of an allotted set of fixed positions.

The deficit in function provided by prosthetic wrists was highlighted in a national study by Atkins et al., ⁴ who surveyed 1,575 individuals with upper extremity limb loss to determine where improvements were desired by prosthesis users. Both body-powered and externally powered upper extremity prosthesis users reported a strong desire for prostheses with additional wrist movement. Explicitly mentioned were desired improvements in wrist motion to rotate the terminal device, wrist motion to move the terminal device from side to side, and wrist motion to move the terminal device up and down. Upper extremity prosthesis users also desired improvements that would require less visual attention to complete tasks with the prosthesis and provide the ability to make coordinated motions of two joints. More specifically, both body-powered and externally powered users expressed interest in the ability to position their prostheses to complete tasks such as opening a door with a knob, using a spoon and fork, and tying shoe laces.

Numerous studies have been conducted to evaluate the success of various types of prostheses as a whole, including externally powered, conventional, and passive. In one study, Stein and Walley ⁵ evaluated the influence of task completion speed on frequency of prosthetic use. It was found that subjects used their conventional prosthesis more when they were able to complete tasks as quickly with their hook as with their unimpaired hand. ⁵ Another study ⁶ looked at how prosthetic use was influenced by level of limb loss and rehabilitation training received, determining that the level of limb loss did affect the frequency of prosthetic use. However, the study found, as did that of Burger and Marincek, ⁷ that rehabilitation training did not increase prosthesis use. Comparisons have also been made between the use of different types of prostheses and their use in different environments. ⁸ In addition, studies have analyzed how individuals use different types of prostheses to perform different categories of tasks, including ADLs and occupational activities. ^7,9

However, only one study has evaluated how the wrist unit component of a prosthesis influences prosthetic use or enables tasks. That study by Sears and Shaperman ¹⁰ evaluated the functional usage of electric wrist rotation and assessed its value to upper extremity prosthesis wearers. The study found that 47% of respondents used the electrically powered wrist rotation regularly to assist in completing ADLs. The study also showed that bilateral users identified more tasks for which they used the electrically powered wrist rotator than did unilateral amputees. ¹⁰ No study has examined or attempted to calculate the increased function that manually powered wrist units provide to individuals with upper limb loss.

The goal of this study was to attain a greater understanding of how manually powered and electrically powered wrist units improve task performance of work and daily living activities for upper extremity prostheses users. A survey instrument was developed to evaluate: 1) the user characteristics that influence the use of prostheses and wrist units and 2) how upper extremity amputees use their wrist units to complete specific tasks. Analysis of user characteristics included assessment of how amputation level, prosthesis type, wrist unit function, daily duration of wear, work experience, and prosthetic training influenced a prosthesis user's use of his or her prosthetic wrist unit. The study then evaluated specific tasks to determine if upper limb prosthesis users: used their prosthesis to complete these tasks; manipulated their wrist unit during these tasks; employed certain wrist functions (flexion, extension, rotation) for tasks; and recorded any significant benefit of wrist function in completing specified tasks. The hope is that these findings will help prosthetists determine which users might be appropriate candidates for prosthetic wrists and which prosthetic wrist functions would be most beneficial for the daily tasks the user performs.

METHODS

RECRUITMENT

Individuals who had sustained an upper extremity amputation or were born with a congenital limb absence and who were recommended for an upper extremity prosthesis with a wrist unit were recruited for this study. Subjects were recruited from a national chain of private clinics and a public access listserv. No preference was given to gender, ethnicity, or socioeconomic status of the participants. Institutional Review Board approval was obtained before data collection.

The first group of subjects was recruited through the upper extremity prosthetics division of a nationwide patient care company (Hanger Orthopedic Group, Inc.). Recruitment letters were sent to a central office and then were distributed to individuals who had been recommended for prostheses with manually or electrically powered wrist units between January 1999 and January 2005. Interested participants were given the option to answer the survey via mail, phone, or Internet. Participants choosing the written option were mailed the survey, which they completed and mailed back to the researchers. Subjects who chose a phone interview were called at a time they had designated as convenient. The survey was read to the subject over the phone, and the responses were recorded. Participants interested in the web-based survey were given a web address where they could access the survey and consent form. All participants gave their consent before completing the survey.

The second group of subjects was recruited through an upper extremity amputee listserv. Participants contacted through the listserv were able to complete only the web-based survey. A recruitment letter describing the research protocol was posted on the listserv with a link to the consent disclosure and survey.

Two thousand recruitment letters were mailed to individuals who met the qualification criteria for subjects. Three hundred eighty-eight of these recruitment letters were returned as undeliverable. Among those who expressed interest in the survey, 49 completed written surveys, five completed phone interviews, and 47 completed web-based surveys. Written surveys were mailed to individuals who requested phone interviews but could not be reached. Respondents were not financially compensated for their participation.

SURVEY STRUCTURE

The wrist survey consisted of four sections. The survey collected each individual's demographic information. Next, date of amputation, level of amputation, hand dominance, work history, and the impact of the amputation on work history were documented. Specifics on the type of prosthesis and components, as well as training received for the use of the prosthesis were recorded by respondents. Finally, the survey documented the frequency of prosthesis use, the position of the prosthetic wrist during the completion of specific ADLs and work tasks, and the benefit(s) upper extremity prosthesis users felt the wrist unit provided in completing the specific tasks.

A section of the survey included a list of occupational and ADL tasks selected from a list of activities identified as important to be considered in prosthetic use and design. ¹¹ The selection of tasks from the list was made with advisement from an upper extremity amputee who designs and manufactures wrist units (personal communication, Ron Farquharson, Texas Assistive Devices, LLC, Brazoria, TX, November 2004). The following activities were selected: writing, typing, carrying a glass of water, stuffing an envelope, holding a telephone, turning the pages of a book, turning the steering wheel when driving, chopping food, pouring liquids from a pitcher, turning a door knob, eating with utensils, and hammering a nail. These tasks were also chosen because they had been shown to require wrist flexion and extension and forearm rotation in individuals without upper limb impairment. ^1–3 Previous studies of individuals without a disability found that 100° of forearm rotation, 35° of wrist flexion/ extension, and 25° of wrist radioulnar deviation were needed to eat with utensils and drink from a glass. ³ Additional studies have presented the similar ranges of motion at the wrist and forearm as those necessary to complete an assortment of ADLs. ^1,2 In our survey, prosthesis wearers were asked to evaluate how often they used their prosthesis and theposition of their wrist when they used their prosthesis to complete the same and similar tasks.

All of the survey results were self-reported by the prosthesis users. In two cases, follow-up phone calls were used for clarification of reported responses.

STATISTICAL ANALYSIS

Data were analyzed using SPSS software. Frequencies, means and standard deviations were generated for much of the demographic data. Age, gender, level of amputation, bilateral or unilateral involvement, types of prostheses, and types of wrist units were summarized for review. Bivariate correlations and crosstab procedures were used to evaluate relationships among variables. Chi-square tests were performed on the crosstab tables to evaluate for significant relationships among variables in the table (p < 0.05). Paired-samples t-tests were run to compare the means of difficulty scores reported by prosthesis users on tasks performed with and without a wrist unit.

RESULTS

USER CHARACTERISTICS

The number of surveys completed by paper, phone, and web totaled 101. Of these, 3 had to be excluded from calculations because the patients did not meet the required age criteria of 18 years. The participants included 80 men and 18 women. Ages ranged from 25 to 85 years, with a mean age of 54 (s = 14.17). Only 2 of 40 individuals with unilateral limb loss who lost their dominant hand did not change hand dominance to their unaffected side.

LIMB LOSS LEVEL

The most common level of amputation was transradial. The breakdown of side and level of amputation is shown in Table 1 .

PROSTHESIS TYPE

The total number and types of prosthetic devices used by respondents are reported in Table 2 . Many wearers reported the use of more than one type of prosthesis. Most respondents used either myoelectric or body-powered devices as their primary prosthesis. Thirteen bilateral users were fit bilaterally with body-powered prostheses, 3 bilateral users were fit unilaterally with body-powered prostheses, and the remaining bilateral user did not wear a body-powered prosthesis. Three bilateral users were also fit bilaterally with myoelectric prostheses, and four were fit unilaterally with a myoelectric device. Two unilateral users wore a passive prosthesis as their primary prosthesis, and the other users of passive prostheses wore them as secondary prostheses. One bilateral user wore a hybrid prosthesis on one side and a body-powered prosthesis on the other. The other bilateral hybrid prosthesis user used only that device unilaterally and wore nothing on his contralateral arm.

WRIST FUNCTIONS

Prosthesis users recorded the function provided by their prosthetic wrist. Bilateral users recorded function for two wrists if they wore a wrist on each prosthesis. Wrist function could not be clearly determined for all wrist users because some of the information respondents provided was insufficient or conflicting, making a definitive determination of their wrist function difficult. Of those whose wrist function could be determined, 25% of respondents used electrically rotated wrists. The most commonly provided wrist function was passive rotation, comprising 46% of respondents. All of the wrists with flexion/ extension or radioulnar deviation contained passive rotation as well. Wrists with flexion/extension or radioulnar deviation comprised a total of 14% of the wrist units. Of the respondents, 8% reported wearing no wrist unit on their prosthesis. These individuals were counted as having no wrist function. Wrist function could not be definitively determined for 6% of respondents.

WEAR TIME

Prosthesis users were asked to evaluate the average number of hours a day they wore their prosthesis. Responses showed 62% of unilateral users and 71% of bilateral users wear their prostheses 10 or more hours a day. Two respondents interviewed by phone and living in northern states reported that on average they wear their prostheses more in the summer because there are more outdoor tasks that require the use of their prosthesis. In general, after completion of a crosstab analysis, no clear relationships were observed between the level of amputation and the average number of hours a day an individual wore his/her prosthesis. However, it was found that prosthetic wear times for individuals who worked were slightly higher than for those who were unemployed or retired.

WORK EXPERIENCE

According to the survey responses, 71% of working age individuals (18–60 years old) are currently working. Thirtysix percent of individuals older than 60 years reported they were still working. Including individuals of all ages who were working, 41 were traumatic amputees, 11 had congenital limb absence, and 5 did not specify the cause of limb loss (n = 57). Of individuals with congenital limb loss, 92% were employed, whereas 72% of traumatic amputees returned to work after their amputation.

TRAINING

Respondents' results showed that unilateral amputees did not receive the same level of training as did bilateral amputees. Approximately 35% of unilateral respondents reported not receiving training of any kind in the use of their prosthesis. About 36% of unilateral patients received training only from their prosthetist, and only 27% of unilateral respondents were trained by a physical or occupational therapist. The remaining 2% did not specify the type of training they received. Only 22% of unilateral individuals received more than 10 hours of training. In contrast, 71% of bilateral patients were trained by a physical or occupational therapist; only one individual did not receive any training; 65% of these individuals received more than 15 hours of training. Some respondents reported having received training from multiple sources. Those who reported receiving training from both a therapist and a prosthetist were counted as therapist trained.

TASK EVALUATION

All prosthesis users were asked to evaluate the frequency with which they used their prosthesis to complete 12 ADL and work-related tasks. Bilateral respondents reported a greater prosthesis usage rate on all tasks. Unilateral users reported using their prosthesis less than half of the time for all tasks except stuffing envelopes and turning the steering wheel ( Figure 1 ). Some respondents did not record a prosthesis usage percent for each task. In addition, because of data collection complications, not all respondents were able to record responses for hammering a nail. Many unilateral users commented that they did not use their prosthesis often because they found they could complete most tasks with one hand. Others commented that they used their prosthesis primarily for assistance and stabilizing but not for prehensile functions. Both stuffing envelopes and turning a steering wheel could be considered bimanual activities in which there is not a clear dominant hand. Turning a steering wheel was the most frequently reported task for which the prosthesis was used.

Wrist positions used for completing tasks varied among respondents. For all tasks, fewer than one-third of respondents reported they prepositioned the terminal device using rotation, flexion/extension, or radioulnar deviation. More individuals reported using the terminal device in a neutral position or not using the wrist unit. There were no apparent trends of specific wrist functions being used for specific tasks. When the wrist unit was used, the use of rotation to preposition the terminal device was the most frequently used wrist function for all tasks. Some users did not find it necessary to adjust the position of their terminal device, choosing neutral as their optimal position for tasks. Few wrists used contained the functions of wrist flexion/extension or radioulnar deviation, making their influence difficult to assess. Nine people with wrist flexion/extension reported using the function for eating with utensils. This task exhibited the greatest reported use of the flexion/extension function. One individual reported that he did not use his wrist unit to preposition his prosthesis for hammering. Instead, he used his prosthesis as the hammer, eliminating the need for a wrist unit.

Paired-samples t-tests were used to evaluate the added benefit of a wrist unit in completing the evaluated tasks. Upper limb prosthesis users were asked to rate the difficulty of completing each task without the use of their wrist unit on a scale from 1 to 5. Users were then asked to use the same scale to rate the difficulty of the same task when they used their wrist unit to preposition their terminal device. A comparison was made between the mean scores for completing the task with and without the wrist unit. A statistically significant difference was found showing increased ease with the wrist unit for unilateral prosthesis users when writing (t(10) = 2.67, p < 0.05), hammering a nail (t(23) = 3.32, p < 0.05), eating with utensils (t(21) = 2.67, p < 0.05), and chopping vegetables (t(10) = 2.12, p < 0.05). Statistical significance was not detected in any of the remaining evaluated tasks. In addition, the difference in mean scores indicated that a larger number of individuals with unilateral limb loss found all the tasks to be less difficult when they used their wrist unit.

Crosstab two-way tables were analyzed to assess the relationship between user characteristics and a prosthesis user's utilization of his or her wrist unit. Comparisons were made among the ease of task completion and unilateral or bilateral limb absence, level of limb absence, wrist unit functions, daily wear duration, and prosthetic training. Chi-square calculations found no statistically significant relationships between wrist uses and the evaluated characteristics. The absence of statistical significance was affected by the small sample size of respondents.

DISCUSSION

Studies have shown that wrist function is a high priority for both body-powered and externally powered prosthesis users. However, no studies have attempted to measure the benefit the wrist unit provides to prosthetic users. There were two primary goals of this study. The first goal was to analyze the user characteristics of prosthetic wrist unit users and determine if there were any definitive correlations among the attributes of individuals who use the wrist units, the type of wrist unit, and the success in using the wrist unit. The second goal was to evaluate specific tasks and determine if individuals were using their wrist units to complete these tasks and how effective they found the wrist unit to be.

USER CHARACTERISTICS: INFLUENCE ON PROSTHESIS UTILIZATION

Analysis of the relationship of an individual's amputation level, prosthesis type, wrist unit functions, daily duration of wear, work experience, prosthetic training, and a prosthesis user's use of the prosthetic wrist unit showed few statistically significant results. The strongest relationships were seen in analysis of work experience, wear time, and training.

WORK EXPERIENCE AND WEAR TIME

Slight increases in prosthetic wear time were observed for individuals who were employed. ¹² The reason for the increased wear at work is unclear. The prosthesis may provide increased function, particularly if the user is performing a large number of bimanual tasks. However, the increased wear at work may also be related to a desire for improved cosmesis in a public setting. A Slovenian study ⁷ reported that 70% of upper limb amputees wore their prosthesis only for cosmesis, and another study⁶ found that cosmesis was the most frequently cited reason for myoelectric prosthesis use. Several male respondents to this survey made the unsolicited comment that they wore myoelectric prostheses for the increased cosmetic benefit.

TRAINING

Of great interest is how few unilateral prosthesis users received prosthetic training from a therapist. Several researchers have commented that prosthetic training is central to successful prosthetic rehabilitation. ^5,13 One study ¹⁴ showed that individuals with conventional prostheses who received training improved efficiency and skill in task performance. The study also illustrated that the training in how to preposition the terminal device was an important aspect of developing efficiency in task completion. ¹⁴ Supporting the impact of efficiency in prosthetic task completion, another study showed that users would utilize their conventional prosthesis more if they could complete tasks rapidly and efficiently. ⁵ Analysis of these two studies suggests that providing individuals with the training to use their prosthetic wrists proficiently may increase their prosthesis use and overall ability, supporting the finding that prosthetic rehabilitation may be as important as a well-fitting prosthesis. ¹⁴ Another study mentioned a lack of occupational therapy as a limitation that might prevent a patient from fully using his or her prosthesis. ⁵ Several anecdotal comments made by respondents in this study indicated they also felt training provided a benefit. One individual commented that the lack of proper training had resulted in abandonment of his prostheses.

In contrast, two studies have shown that rehabilitation is not a factor in increasing the frequency of prosthetic use. ^6,7 Our study also could not find a statistically significant relationship between the number of hours of training and prosthesis wear time. However, neither the two previous studies nor our study considered the methods or regimen used to train upper extremity prosthesis users. They also did not evaluate whether training had helped increase the speed at which individuals could complete tasks with their prosthesis. ^6,7 Because of the great variation in training techniques and therapists' experience with prostheses, it is difficult to fully assess the effect of prosthetic training from any of the current research. The full effect of prosthetic training by an experienced therapist is not clearly documented. Training should focus on teaching the user to take advantage of all features of the prosthesis to optimize performance. More definitive studies are needed to analyze the quantity of therapy and therapeutic training techniques most beneficial in effectively training users of all types of prostheses.

TASK EVALUATION: PROSTHESIS AND WRIST USE

Little research has been done on the added benefit a prosthetic wrist unit provides to the user. This study looked at both the time individuals wore a prosthesis and the effect their wrist unit had on their ability to complete certain tasks with the prosthesis. It also assessed the wrist functions most frequently used for each task. Analysis was performed in an attempt to determine the overall benefit the wrist unit provided in completing specified tasks.

PROSTHESIS USE FOR TASK COMPLETION

Although most individuals with unilateral limb loss reported wearing their prosthesis more than half the day, unilateral users showed a general absence of prosthetic use for task completion. It is likely that many of these individuals found they were more efficient when completing these activities with their unimpaired hand. In fact, the unimpaired hand was found to be so much more effective that 95% of individuals who lost their dominant hand switched hand dominance after their limb loss. Experts in upper extremity prosthetic rehabilitation report the sound arm always takes on a dominant role for a unilateral amputee. ¹⁵ Ten of the 12 activities evaluated in this survey could be adequately completed with one hand. However, two activities, turning a steering wheel and stuffing an envelope, are bimanual tasks. More than half of unilateral respondents reported using their prosthesis to stuff envelopes and turn a steering wheel, indicating that unilateral users will use their prosthesis for bimanual tasks. In addition, a number of unilateral users commented that they use their prosthesis frequently for stabilizing and supporting. These findings indicate that individuals with unilateral limb loss who frequently perform bimanual tasks may be good candidates for wrist units.

WRIST UNIT UTILIZATION

Some individuals stated that although they did not use their wrist unit for the 12 specific tasks in the survey, their wrist was critical in their completion of other tasks that were not evaluated. Three bilateral users reported using the wrist flexion function for shaving, toileting, and combing hair. A unilateral user reported the benefit of her wrist was in holding plates and cups, folding laundry, and washing dishes. Another unilateral user said his wrist allowed him to ride his motorcycle and use his tools. Both unilateral and bilateral users expressed a benefit in using wrist functions for dressing. Because of the numerous uses individuals find for their wrist units, it is difficult to definitively conclude the full effect of the wrist unit based on the 12 tasks assessed. It was learned that many individuals do not require a wrist unit for the completion of these tasks. In the future, it may be beneficial to first inquire which tasks prosthesis users most frequently use their wrist unit to complete, then conduct the evaluation of the wrist units benefit based on those tasks.

The benefits of independent wrist functions of flexion and extension were difficult to evaluate because of the small number of respondents who reported wearing wrists with these functions. A few respondents commented that they were confused by the wrist function terms flexion and extension although pictures and definitions were provided. This confusion may have resulted in some inaccurate reporting of wrist functions used. It may also be that current designs are inefficient or ineffective in assisting with desired activities.

Future research should assess how wrist designs might be improved to better enable individuals in tasks they currently find difficult. Two respondents to this survey indicated that they would be interested in wrist function that provided some flexibility and shock absorption. Studies have shown that the functional range of motion for the human hand is 5° of flexion, 30° of extension, 10° of radial deviation, and 15° of ulnar deviation. ² None of the current wrist units offer flexion/extension and radioulnar deviation in combination.

BENEFIT OF WRIST FUNCTION IN TASK COMPLETION

In evaluating the paired t-tests for tasks with and without use of the prosthetic wrist unit, the difference in means was small. A minimal improvement in ease when using the wrist unit was calculated; however, the difference was so small the improved ease may not be readily evident when the wrist is used by an upper extremity amputee in a clinical setting. It should be noted that the sample size of respondents for all tasks was small, likely influencing the absence of significance seen in many of the tasks. It is possible that greater significance may be observed with a larger sample population. The results of this survey were also limited by the great diversity of the sample. Because of the large number of unilateral prosthesis wearers who did not use their prosthetic wrists for the specified tasks, a statistically significant analysis of the influence of different variables on the ease of task completion with a wrist unit was not possible.

Little has been done to improve the function of the prosthetic wrist unit during the last 20 years. Texas Assistive Devices has developed a new wrist, which includes passive rotation and wrist flexion/extension, but there are still only a small number of users. No prosthetic wrist has been able to duplicate the human anatomy with triplanar motions of rotation, flexion/extension, and radioulnar deviation. One survey respondent who was bilateral with a partial hand said he still completed most tasks with his partial hand because his partial hand had more functional wrist motion than did his prosthesis. Prosthetic wrist units may not be indicated for every person with an upper limb loss; however, training individuals to use the wrist unit and selecting a design appropriate to the user's needs could produce yet unrecognized benefits for the prosthesis user.

ACKNOWLEDGMENTS

This research was supported by a grant for Rehabilitation Engineering Research Center on Workplace Accommodations from the U.S. Department of Education. The author thanks the Hanger Orthopedic Group, Inc., Upper Extremity Division for assistance in distributing surveys to patients. The author would also like to thank Karen Mikhus, Jon Sanford, and Michael Williams, PhD, at the Center for Assistive Technology and Environmental Access for their research guidance and statistical analysis assistance.

Correspondence to: Susan Kestner, 60 Jamaica Road, Brookline, MA 02445; e-mail: .

SUSAN KESTNER, BS, MSPO, at the time of this study was affiliated with the Center for Assistive Technology and Environmental Access at Georgia Institute of Technology, Atlanta, Georgia.

References:

1. Morrey BF, Askew LJ, An KN, Chao EY. A biomechanical study of normal functional elbow motion. J Bone Joint Surg Am 1981;63:872–877.
2. Palmer AK, Werner FW, Murphy D, Glisson R. Functional wrist motion: a biomechanical study. J Hand Surg [Am] 1985;10: 39–46.
3. Safaee-Rad R, Shwedyk E, Quanbury AO, Cooper JE. Normal functional range of motion of upper limb joints during performance of three feeding activities. Arch Phys Med Rehabil 1990; 71:505–509.
4. Atkins DJ, Heard DCY, Donovan WH. Epidemiologic overview of individuals with upper-limb loss and their reported research priorities. J Prosthet Orthot 1996;8:2–11.
5. Stein RB, Walley M. Functional comparison of upper extremity amputees using myoelectric and conventional prostheses. Arch Phys Med Rehabil 1983;64:243–248.
6. Silcox DH III, Rooks MD, Vogel RR, Fleming LL. Myoelectric prostheses. A long-term follow-up and a study of the use of alternate prostheses. J Bone Joint Surg Am 1993;75:1781–1789.
7. Burger H, Marincek C. Upper limb prosthetic use in Slovenia. Prosthet Orthot Int 1994;18:25–33.
8. Northmore-Ball MD, Heger H, Hunter GA. The below-elbow myo-electric prosthesis. A comparison of the Otto Bock myoelectric prosthesis with the hook and functional hand. J Bone Joint Surg Br 1980;62:363–367.
9. Fraser CM. An evaluation of the use made of cosmetic and functional prostheses by unilateral upper limb amputees. Prosthet Orthot Int 1998;22:216–223.
10. Sears HH, Shaperman J. Electric wrist rotation in proportionalcontrolled systems. J Prosthet Orthot 1998;10:92–98.
11. McWilliam RP. A list of everyday tasks for use in prosthesis design and development. Bull Prosthet Res 1970;10:135–164.
12. U.S. Census Bureau. American Fact Finder. 2002 http://factfinder.census.gov/home/saff/main.html?_lang.en .
13. Atkins DJ. Prosthetic training. In: Smith DG, Michael JW, Bowker JH, eds. Atlas of Amputations and Limb Deficiencies: Surgical, Prosthetic, and Rehabilitation Principles. Rosemont, IL: American Academy of Orthopaedic Surgeons; 2004:275–284.
14. Lake C. Effects of prosthetic training on upper-extremity prosthesis use. J Prosthet Orthot 1997;9:3–9.
15. Atkins DJ. Functional skills training with body-powered and externally powered prostheses. In: Atkins DJ, Meier RH, eds. Functional Restoration of Adults and Children With Upper Extremity Amputation. New York: Demos Medical Publishing, Inc.; 2004:139–158.