Secondary Logo

Journal Logo


Case Report: Using the Activities-Specific Balance Confidence Scale to Quantify the Impact of Prosthetic Knee Choice on Balance Confidence

Stevens, Phillip M. MEd, CPO; Carson, Randy PT

Author Information
JPO Journal of Prosthetics and Orthotics: October 2007 - Volume 19 - Issue 4 - p 114-116
doi: 10.1097/JPO.0b013e31815711a3
  • Free

For many years, investigations regarding the balance of persons with lower extremity amputations were conducted in static conditions in controlled laboratory environments.1–4 More recently, researchers have investigated the notion of daily balance confidence among this population.5–7 This has largely been accomplished through the use of the Activities-specific Balance Confidence Scale (ABC).6–8 Although this survey instrument was initially developed for use among the elderly, research has been done to validate its use among the amputee population as well.7–9

One of the results of this area of research has been the challenge to clinicians and researchers to “determine whether there are specific interventions that assist in improving the balance confidence among the amputee population.9(p880)” Although various instructional strategies, including postural training,10 resistance and agility training,11 and tai chi exercises,12 have been attempted to improve ABC scores among the elderly, the field of prosthetics is characterized by the ability exchange prosthetic component choices in attempts to improve functional outcomes. In the current endeavor, the ABC was administered immediately before and shortly after a patient with a transfemoral amputation was switched from a rotary hydraulic knee mechanism to a microprocessor controlled knee unit to isolate the potential effect of prosthetic knee choice on the subject’s reported balance confidence.


Our case subject was a 30-year-old man who had suffered a traumatic amputation at the transfemoral level. The patient was 3 months postamputation, and had walked with his existing prosthesis for 6 weeks. He was an accomplished walker at the time, participating in such demanding activities such as running and cycling. His existing prosthesis consisted of an ischial containment socket with a flexible inner liner, a rotary swing and stance phase hydraulic knee joint (3R-80; Otto Bock, Duderstadt, Germany), and a dynamic pylon/foot (Renegade, Freedom Innovations, Irvine, CA).

The 16-item ABC was used to determine the subject’s baseline balance confidence when using the existing prosthetic components.13 The subject was asked to rate his level of confidence on a scale between 0% (no confidence) and 100% (total confidence) when performing a variety of specific activities such as walking around the house, reaching above his head, and walking on different surfaces or in a crowded environment. A total score was derived for each iteration of the scale by summing the items and dividing by 16. Thus, any increases in the ABC score would represent the presence of improved balance confidence. The ABC has been found to be both valid and internally consistent within the amputee population.8,9

Two days after the initial administration of the ABC, the subject’s prosthetic knee unit was replaced with a microprocessor swing and stance controlled knee unit (C-leg, Otto Bock) and a dynamic foot (Axion, Otto Bock). The subject was given 9 days to adjust to the change in prosthetic component choices, at which time the ABC was readministered.

At the first administration of the ABC, the subject scored 69 points. After the changes to the prosthetic foot and knee, the subjects score increased to 89 points (Fig. 1). Using the formula described by Myers et al.,14 this change represented a 30% increase in the subjects reported balance efficacy. Following an additional 6 months of daily use of the microprocessor controlled knee unit, the ABC was administered a third time. The patient’s reported balance confidence was comparatively unchanged, reported at 87 points.

Figure 1.
Figure 1.:
Study subject’s reported values for the Activities-specific Balance Confidence Scale with both prosthetic knee mechanisms. The reported mean for lower extremity amputees and the minimum value for “highly functional” elderly adults are included for comparison. *As reported by Miller et al.6; †as reported by Myers et al.14


Early research on fall and fall prevention was focused on the elderly and was limited to inquiries about fall frequency and fear of falling. A paradigm shift in this research occurred when researchers applied Bandura’s concept of self-efficacy to the questions of balance. More specifically, researchers asked subjects to rate their perceptions of their own capabilities within a particular domain of activities.15 Beyond the intended implications with respect to risk of falling, early results found such reports to correlate quite strongly with a given individual’s ability to perform activities of daily living and engage in both physical and social events.15 Repeated investigations with the more sensitive ABC survey tool found similar results.13

Speculating that the unique challenges faced by those persons with amputations might likewise result in daily experiences of compromised balance, Miller et al.5,6 began to explore the question of fall frequency, balance and balance efficacy among the amputee population. Preliminary investigations found that over half of the surveyed lower extremity amputees, and two-thirds of those with amputations at the transfemoral level, reported having fallen in the past year.5 In contrast, fall rates among the community-living elderly are reported between 30% and 40%.16,17

Among a cohort of amputees who reported daily use of a prosthesis, a mean ABC score of 62.8 was reported.6 To better appreciate the significance of this mean score, Myers et al.14 reported on a large sampling of older adults, ranging from home care clients to highly functioning individuals in community exercise programs. They found ABC scores lower than 50 to be associated with a low level of physical functioning characteristic of home care clients. ABC scores above 50 and lower than 80 indicated a moderate level of functioning characteristic of elders in retirement homes and persons with chronic health conditions. ABC scores above 80 are indicative of highly functioning, usually physically active older adults.14

Miller et al.7 found that 65% of surveyed amputees (81% of amputees secondary to vascular causes and 46% of amputees with nonvascular causes) scored below 80 on the ABC, indicating that they have a balance confidence comparable to those of the elderly in retirement homes and persons with chronic health conditions and may be candidates for corrective interventions.14 Approximately 25% of surveyed amputees reported an ABC score below 50,9 indicating a very low level of physical functioning and a balance confidence comparable to elderly home care clients.14

The relevance of reported ABC scores with respect to quality of life was established by the continued work of Miller et al.,6 who found that these scores correlated strongly to prosthetic performance (what people do), prosthetic capability (what people can do), and social activity participation.

Up to 76% of those individuals with lower limb amputation report that they avoid many activities as a result of loss of confidence.5 Such restrictions can lead to a debilitating cycle, suggested by Miller and Deathe,9 in which deterioration in muscle, endurance, strength, flexibility, and coordination contribute to further deterioration of balance and balance confidence.18,19

In the case of our study subject, his initial ABC score of 69, although slightly higher than the reported mean value for lower extremity amputees, still placed his balance confidence within the range wherein corrective interventions have been suggested. Given that he was a young, active otherwise healthy individual, a higher balance confidence seemed an appropriate objective. After a brief acclimation period in which the socket remained unchanged and no formal physical training was received, his ABC score improved to 89. This second score was within a single point of the mean reported score among the physically active elderly in good health (88).14 The standard error of measurement for the ABC among surveyed amputees was ±6 points.8 This suggests that any change in reported scores greater than 6 points would indicate that a real change has occurred. Thus, the replacement of his prosthetic components, most notably, the use of a microprocessor controlled knee unit, produced a rather immediate improvement to his overall balance confidence. Importantly, these improvements in balance confidence proved to be enduring as a similar confidence was reported following a 6 month acclimation period. The ABC, which required approximately 5 minutes to administer on each occasion, allowed us to quantify these improvements and compare his balance efficacy against the mean values of various patient populations.


Given the importance of balance confidence to overall function, societal involvement, and general health, there is great value in the ability to quantify this confidence and those changes that might occur to it in the presence of clinical interventions. The limitations to a single case study are obvious. However, our case suggests the ABC as a simple but efficient means to quantify the value of various interventions in augmenting balance confidence within the lower extremity amputee population. Further studies of larger cohorts are needed to determine the impact of various interventions upon balance confidence within this population.


1. Guerts AC, Mulder TW, Nienhuis B, Rijken RA. Dual-task assessment of reorganization of postural control in persons with lower limb amputation. Arch Phys Med Rehabil 1991;72:1059–1064.
2. Isakov E, Mizrahi J, Ring H, Susak Z, Hakim N. Standing sway and weight-bearing distribution in people with below-knee amputations. Arch Phys Med Rehabil 1992;73:174–178.
3. Guerts AC, Mulder TW, Nienhuis B, Rijken RA. Postural reorganization following lower limb amputation. Scand J Rehab Med 1992;24:83–90.
4. Hermodsson Y, Ekdahl C, Persson BM, Roxendal G. Standing balance in trans-tibial amputees following vascular disease or trauma: a comparative study with health subjects. Prosthet Orthot Int 1994;18:150–158.
5. Miller WC, Speechley M, Deathe B. The prevalence and risk factors of falling and fear of falling among lower extremity amputees. Arch Phys Med Rehabil 2001;82:1031–1037.
6. Miller WC, Deathe AB, Speechley M, Koval J. The influence of falling, fear of falling, and balance confidence on prosthetic mobility and social activity among individuals with lower extremity amputation. Arch Phys Med Rehabil 2001;82:1238–1244.
7. Miller WC, Speechley M, Deathe AB. Balance confidence among people with lower-limb amputation. Phys Ther 2002;82:856–865.
8. Miller WC, Deathe AB, Speechley M. Psychometric properties of the Activities-Specific Balance Confidence Scale among individuals with a lower-limb amputation. Arch Phys Med Rehabil 2003;84:656–661.
9. Miller WC, Deathe AB. A prospective study examining balance confidence among individuals with lower limb amputation. Dis Rehabil 2004;26:875–881.
10. Lajoie Y. Effect of computerized feedback postural training on posture and attentional demands in older adults. Aging Clin Exp Res 2004;16:363–368.
11. Liu-Ambrose T, Khan KM, Eng JJ, et al. Balance confidence improves with resistance or agility training. Increase is not correlated with objective changes in fall risk and physical abilities. Gerontology 2004;50:373–382.
12. Sattin RW, Easley KA, Wolf SL, et al. Reduction in fear of falling through intense tai chi exercise training in older, transitionally frail adults. J Am Geriatr Soc 2005;53:1168–1178.
13. Powell LE, Myers AM. The Activities-specific Balance Confidence (ABC) Scale. J Gerontol Med Sci 1995;50:M28–M34.
14. Myers AM, Fletcher PC, Myers AH, Sherk W. Discriminative and evaluative properties of the Activities-specific Balance Confidence (ABC) Scale. J Gerontol Med Sci 1998;53A:M287–M294.
15. Tinetti ME, Mendes de Leon CM, Doucette JT, Baker DI. Fear of falling and fall-related efficacy in relationship to functioning among community-living elders. J Gerontol Med Sci 1994;49:M140–M147.
16. Campbell AJ, Reinken J, Allan MC, Martinez GS. Falls in old age: a study of frequency and related clinical factors. Age Ageing 1981;10:264–270.
17. Prudham D, Evans JG. Factors associated with falls in the elderly: a community study. Age Ageing 1981;10:141–146.
18. Maki ME, Holliday PJ, Topper AK. Fear of falling and postural performance in the elderly. J Gerontol Med Sci 1991;46:M123–M131.
19. Myers A, Gonda G. Research on physical activity in the elderly: practical implications for program planning. Can J Aging 1991;5:175–187.

amputee; balance; confidence; prosthetic knee

© 2007 American Academy of Orthotists & Prosthetists