Prosthetic Disuse Leads to Lower Balance Confidence in a Long-Term User of a Transtibial Prosthesis

Abstract

Residual limb wounds or ulcers are one of the most frequent skin problems reported by lower extremity prosthesis users. Healing often requires prosthesis disuse, which can logically impair physical functioning. However, there are limited data available to support this idea. We report the impact of prosthesis disuse by presenting assessments of balance, gait, physical activity, and balance confidence obtained on a case subject before experiencing a wound and following reintroduction to a well-fit prosthesis after wound-related prosthesis disuse. The case subject was a 76-year-old male who suffered a unilateral, transtibial amputation due to synovial sarcoma 13 years before. After presenting with a history of pain in the area of a chronic skin plaque, he received a punch biopsy, which resulted in 4 weeks of prosthesis disuse followed by 12 weeks of limited use before a final well-fitting socket was received. The following data were collected 24 weeks before the biopsy and 4 weeks after receiving the final well-fitting socket: Berg Balance Scale, L-test of walking, quantitative gait analysis, Activity-specific Balance Confidence Scale, and 1 week of community-based activity. Balance confidence decreased nearly 19%, walking speed decreased by 12%, and steps/day decreased by 19% following ∼4 months of prosthesis disuse/limited use; functional measures were not impacted. Lower balance confidence is not trivial as it can lead to activity avoidance and increased fall risk. Interventions to target balance confidence changes following prosthesis disuses may be important to minimize the impact of disuse on physical and mental well-being.

Noah J. Rosenblatt, PhD

Introduction

Skin problems on the residual limb of the lower limb amputee are common, affecting up to 63% of prosthetic users.¹ Despite the broad etiology of skin problems for lower limb prosthetic users (LLPU), wounds/ulcers are consistently one of the most commonly reported. A 6-year retrospective chart review of cases presenting to an amputee clinic reported pressure ulcers were the most frequent cause of skin problems, accounting for 27% of cases.² In another study, 57% of surveyed individuals reported experiencing a pressure ulcer >1 month before completing a survey.¹

A systematic review on interventions to manage residual limb ulcers due to prosthetic use concluded that prosthetic discontinuance is a viable method to promote healing in severe acute ulcers, particularly in patients with specific comorbidities that can impact healing such as advanced dysvascular disease or a history of chronic ulceration.³ Indeed 53% of individuals with a history of skin problems self-report a reduction in prosthetic wear time as a result of skin problems.⁴ Logically, prosthetic discontinuance, or significant reduction in wear time, may compromise physical and mental functioning and lead to diminished community participation. In one study, 28% of persons with skin problems reported these problems negatively influenced their ability to perform household activities and 21% reported these problem negatively influenced their ability to engage in social activities.⁴ In a second study, dysvascular, transtibial amputees suffering from ulcers engaged in a 12-week rehabilitation program either after receiving a prosthesis that could be used while the ulcer healed, or after being assigned to prosthesis fitting only after healing.⁵ At the end of the rehabilitation program, a greater proportion of the former group could independently ambulate. However, these are the only studies we are aware of that have considered the impact of prosthesis disuse on functional outcome and activity.

Clinical Problem Adressed

In this study, we report on the impact of prosthesis disuse on balance, gait, physical activity (PA), and balance confidence of a single transtibial amputee, by presenting assessments obtained before disuse and following reintroduction to his prosthesis.

Methods

Participant

The case subject was a 76-year-old male (185.4 cm, 100 kg) who suffered a unilateral, transtibial amputation due to synovial sarcoma 13 years before. Information regarding his prosthetic setup and medical history is summarized in Table 1.

Table 1.

Prosthetic set-up and medical history

Variable	Description
Prosthetic socket	Total contact
Prosthetic suspension	Harmony vacuum suspension (Otto Bock)
	Proflex suspension sleeve (Otto Bock)
Liner	3 mm alpha gel
Prosthetic ankle	Empower Ankle (Otto Bock)
Prior medical conditions	History of vertigo (no recent bouts)
	Severe spinal stenosis (cervical, thoracic, and lumbar)
	Arthritic knee pain (contralateral limb)
	Phantom pain
	Neuropathy (contralateral limb)
History of falls in previous year	None

On July 26, 2018, the participant enrolled in our on-going 24-week randomized control trial (RCT) to evaluate the effects of different exercises on balance confidence. Twenty-three weeks later (on January 4, 2019), he presented to his dermatologist reporting a 6-month history of increased pain just posterior to the fibular head of the residual limb, in the area of a chronic (4 years) skin plaque. As a result of his medical history, a 4 mm punch biopsy of the lesion of the residual limb was taken and the patient was instructed to stop wearing his prosthesis. Approximately 4 weeks later (February 8, 2019), the wound healed enough that the dermatologist cleared the patient to be fit for a new prosthesis, intended to limit irritation posterior to the fibular head. Due to fit issues of the new socket, prosthesis use was limited for the next 9 weeks, at which point (April 11, 2019), the patient returned to the amputee clinic for an appointment and a new socket was ordered to address excess space between the residual limb and current socket. A well-fitting definitive socket was received 3 weeks later.

Protocol

The participant provided written informed consent to participate in the RCT and separate written consent to participate in the follow-up assessment, which fell outside of the time frame of the RCT. The Rosalind Franklin University IRB approved protocols for both the RCT and follow-up study. Only details of the RCT relevant to this case study are presented.

Upon enrolling in the RCT (baseline), the subject completed two performance-based measures of function: the Berg Balance scale (BBS) and L-test of walking. The BBS involves completing 14 balance tasks, graded on a scale of 0–4 (maximum score of 56). The L-test involves getting up from a chair, walking an 8-m path in the shape of an L, and then returning to the seat along the same path⁶ with the time to completion recorded. A quantitative gait analysis was also performed at baseline using standard motion capture methods from which the following gait parameters were calculated for each limb: step time, stride time, step length, and step width; walking speed was calculated for each pass across the walkway. The subject also completed the Activities-specific Balance confidence (ABC) scale, the primary outcome measure of the RCT. The ABC scale is a widely used survey, originally developed by Powell and Myers,⁷ which measures one's perceived ability to maintain balance, while performing 16 activities of daily living on a scale of 0–100%. The scale has previously been validated for lower limb amputees.⁸

After completing baseline measures, the participant was provided a StepWatch 3 activity monitor (modus health, Edmonds WA), which was worn around his prosthesis for 7 days to measure steps/day. He then returned to the laboratory and was randomized to engage in 8 weeks of at-home, seated exercises, not expected to improve balance or balance confidence. Sixteen weeks later (late December 2018), the participant was mailed an ABC scale and activity monitors to use. An additional 6 weeks later, we received the mailed materials with a note that said “As of 1-18-2019 Lost use of prosthetic, walker, crutches, wheelchair only.” Thereafter, we maintained contact until prosthesis use resumed, at which point, we invited him to the laboratory (follow-up) to complete the same tests performed at baseline. Follow-up occurred ∼4 weeks after receiving the final well-fit definitive socket (May 29, 2019).

For all gait measures and step counts, which included multiple steps or days of recording, average values and effect sizes (Cohen's d) were calculated.

Results

Performance-based measures of function were not meaningfully affected by prosthesis disuse. BBS at baseline was 55/56 and 54/56 at follow-up; L-test of walking required 20.2 s to complete at baseline and 20.7 s at follow-up. Although objective balance measures were unaffected by prosthesis disuse, the subjects' balance confidence score dropped from 79.4 at baseline to 60.9 at follow-up. In addition, several changes in gait were noted (Table 2). Finally, there was a medium-to-large effect of prosthesis disuse on PA with steps/day decreasing from 8258.8 ± 2092.8 to 6698.0 ± 2296.1 (d = 0.90).

Table 2.

Summary of gait measures

	Prosthetic Side			Intact Side
	Baseline	Follow-Up	Cohens' d	Baseline	Follow-Up	Cohens' d
Walking speed (m/s)a	1.19 ± 0.04	1.05 ± 0.04	3.5	—	—	—
Stride length (mm)	1389.2 ± 38.2	1310.5 ± 46.5	1.9	1379.4 ± 39.9	1315.7 ± 48.7	1.5
Step length (mm)	704.2 ± 29.4	666.8 ± 25.9	1.3	676.2 ± 25.2	645.8 ± 30.6	1.1
Stride time (s)	1.14 ± 0.03	1.23 ± 0.03	3.0	1.14 ± 0.02	1.22 ± 0.03	3.5
Step time (s)	0.56 ± 0.02	0.60 ± 0.02	2.7	0.58 ± 0.02	0.63 ± 0.02	2.2
Double support time (s)	0.20 ± 0.03	0.23 ± 0.03	1.1	0.17 ± 0.02	0.18 ± 0.02	1.0
Single support time (s)	0.75 ± 0.03	0.81 ± 0.03	2.4	0.75 ± 0.06	0.83 ± 0.04	1.2
Step width (mm)	168.1 ± 33.7	184.9 ± 41.2	0.5	164.2 ± 47.5	184.1 ± 54.6	0.4

^aSpeed is listed under prosthetic side only, but is calculated independent of side.

Discussion

Perhaps the most important change with disuses was the 19-point reduction in balance confidence. This change exceeds the minimum detectable change of 13 points established for patients with Parkinson's disease.⁹ Although a score of 60.9 at follow-up is consistent with the average of 63.8 reported for amputees,¹⁰ it may also indicate increased fall risk. For example, in a group of older adults, a score of <67 accurately classified fallers 84% of the time.¹¹ The lower level of confidence is concerning in light of the impact that low balance confidence can have on activity. An LLPU may avoid an activity if they lack balance confidence, regardless of whether or not they have the skill to safely complete the activity. Indeed, low balance confidence is a significant predictor of participation in social activities, even after accounting for mobility capability¹²; it is a strong predictor of whether an LLPU can attain a level of walking consistent with a community ambulator¹³; and it is significantly correlated with steps/day in patients with transtibial amputation.¹⁴

The fact that balance confidence and PA decreased, but not functional performance, is not entirely surprising. Balance confidence and BBS are only moderately correlated¹⁵ and the case subjects' baseline abilities were high (his BBS was nearly perfect and L-test time was considerably faster than the average of 32.6 ± 14.9 s reported for LLPU⁶). In addition, baseline PA was considerably higher than the average of 3,000 steps/day reported for LLPU,¹⁶ which may limit the impact of prosthesis disuse. Highly active amputees are able to perform activities without prostheses, although with reduced functional ability,¹⁷ and limiting sedentary behavior may promote better outcomes following reintroduction to the prosthesis.

Although functional measures were not impacted, several gait parameters appear to have changed. Specifically, we observed a reduction of 0.14 m/s in walking speed, which is not trivial. In older adults, the chances of mortality decrease by 12% for every 0.1 m/s increase in self-selected walking speed.¹⁸ Slower walking speed may also increase the amount of time required to complete daily activities, which may in turn limit the number of activities that are performed. Accordingly, a reduction in walking speed may reinforce any negative effect of lower balance confidence on PA.

The extent to which changes in balance confidence, gait, and/or PA would persist over time is unclear. At follow-up testing, the participant reported “getting tired quickly” (fatigue), which is a known barrier to activity.¹⁹ Presumably, through continued prosthesis use, this barrier would reduce and PA would increase. Nonetheless, any activity restriction for this participant could significantly impact his mental health and quality of life. At the start of the study the subject took pride in hobbies such as independently sailing across Lake Michigan (despite having to walk long ramps to get to the dock). It is hard to imagine that the process of being confined to a wheelchair and then having reduced confidence to safely engage in such hobbies would not promote feelings of depression and diminished quality of life. Future work should evaluate the impact of disuse on mental health. Even if mental health were not impacted, changes in PA are still concerning, given that inactivity may be the mediating factor between low balance confidence and increased fall risk.²⁰

Views on limiting and/or addressing impact of prosthesis disuse

Reducing the risk of wounds or ulcers can clearly prevent disuse, and reducing the time of prosthetic disuse, should wounds occur, can minimize its impact. More directly, therapies to address low balance confidence and activity avoidance may be prudent.

Prosthetic technologies allowing users to accommodate to diurnal fluctuations in residual limb volume that contribute to poor fit and abnormal intrasocket pressures may reduce the risk of ulceration. Elevated vacuum suspension (EVS) uses negative pressure to tightly anchor the prosthesis to the limb and has been shown to limit fluctuations in limb volume,²¹ reduce peak socket pressures,²² and improve socket fit and comfort.²³ However, not everyone responds well to EVS²⁴ and, despite using a socket with EVS, our case subject still faced issues. Commercially available adjustable prosthetic sockets offer another solution to address fit issues, allowing the user to directly tighten or loosen the socket as needed and may help reduce the risk of wounds. However, these devices have been studied considerably less than EVS.

In the event that wounds do occur, the negative pressure used in EVS may promote healing. Indeed, certain users with active wounds can continue prosthesis use and maintain activity levels even during healing,^5,25 minimizing time of disuse. The effects of disuse may also be minimized by reducing the time required to fabricate a well-fitting socket. The case subject waited 3 weeks to receive a socket that corrected for the fit issues, which contributed to his wound (after using an ill-fitting socket for 9 weeks). 3D printing is a technology with promise to provide rapid, inexpensive production of multiple sockets that can be easily and quickly adjusted throughout the fitting process. While initial safety of 3D printed sockets has been reported,²⁶ additional work is needed to understand its long-term usability.

With regard to rehabilitation methods to address balance confidence, it has been stated that, “Balance confidence is not directly addressed during prosthetic rehabilitation despite evidence that [it] is low. …Improvements in balance confidence may require [a more] specialized or targeted intervention.”¹² Based on studies from intact older adults (see review by Rand et al.²⁷), such interventions should be multifaceted and include exercises to target balance and gait, as well as components of balance self-efficacy (confidence) training. Indeed, this is the basis of the experimental intervention that is being tested in our RCT (see Bourque et al.²⁸ for details). We believe such an intervention (and variants thereof) may be particularly important, immediately following (and during) prosthetic disuse.

Summary

In conclusion, balance confidence decreased nearly 19%, walking speed decreased by 12%, and steps/day decreased by 19% for our case subject following ∼3 months of prosthesis disuse/limited use; functional measures were not impacted.

Take Home Message

• Interventions to target balance confidence changes following prosthesis disuses may be important to minimize the impact of disuse on physical and mental well-being.

Abbreviations and Acronyms

ABC

activity-specific balance confidence

BBS

Berg Balance Scale

EVS

elevated vacuum suspension

LLPU

lower limb prosthesis user

PA

physical activity

RCT

randomized control trial

Author Disclosure and Ghostwriting

No competing financial interests exist.

About the Authors

Noah J. Rosenblatt, PhD, earned his PhD in biomedical engineering and has been an Assistant Professor with the Center for Lower Extremity Ambulatory Research since 2015. He is the principle investigator for the RCT to improve balance confidence in LLPU and is focused on research to improve outcomes in this population. Aaron Stachowiak, MD, Physiatrist at the Captain James. A. Lovell Federal Health Care Center (FHCC), where he runs the weekly amputee clinic within the Department of Physical Medicine and Rehabilitation. Christopher Reddin, PhD, registered nurse as well as a recently retired Captain of the US Navy. His most recent appointment with the Navy was as a Staff Psychiatric Nurse Practitioner within the Department of Outpatient Mental Health at the FHCC. He is currently in private practice in the Chicago area.