Association Of Protective Stepping With Fall History

Falls in older adults represents an urgent and major global public health concern as they are the leading cause of injury-related mortality and morbidity among the ever growing number of American adults over 65 years of age and older [1].

Diminished postural control in the anterior-posterior direction is associated with an increased risk for injurious fall [2].  Future falls are strongly associated with failure to recover from external perturbations  and reactive stepping behavior in response to forward loss of balance.[3,4,5]  Mechanical perturbation testing employing sufficient perturbation force often results in a protective stepping response initiated well before the base of support provided limits of stability are reached. [3-6]

Recent attention has been given to the characteristics of critical stepping adaptations involving, protective stepping and the ability to withstand perturbation forces which are significantly related to effective balance control and fall risk. (4-14)

Repeated perturbation step training improves compensatory stepping responses, decreases time to stabilization, reducing fall risk. [3,4,5,15,17]

Evidence suggests that repeated exposure to loss of balance can result in rapid improvements in balance recovery [4,16] findings which are consistent with principles of training specificity.

Reactive balance is not routinely assessed, [5,11,17]  as many clinical balance assessment tools do not contain elements of reactive balance, predicated on voluntary or static movement-based balance assessments which may provide misleading information regarding balance abilities requiring perturbation- evoked balance responses. [11]  The need exists for development of alternate methods of perturbation with specific and standardized clinical assessments of reactive balance, employing the most appropriate and clinically meaningful measures associated with fall risk [11.]

The Spring Scale Test (SST)  PROTOCOL (appendix A) is a clinical first trial [22], tether-release, repeated, incremental,  “predictable” perturbation, reactive stepping (RIPPS),  fall assessment and intervention tool which measures protective reactive stepping responses as a percent of total body weight (% TBW) force.  DePasquale and Toscano [12] demonstrated the reliability (ICC .94) and validity of the SST in active, independent, community-living older adults.  The Spring Scale Test employs repeated incremental “predictable “perturbations (RIPPS) in standing.  Rear stepping direction testing precedes forward stepping direction testing. Individuals are repeatedly instructed to withstand repeated, 1- pound incremental, predictable loading and quasi-random unloading perturbations (RIPPS) to maximal force limits of foot flat loading or within a 3 step limit in response to quasi-random (5 second window) unloading  SST /RIPPS performance criteria.  Forward and rear direction stepping frequency and % TBW force data are obtained at threshold, 10% and limit % TBW force SST milestones.  Spring scale test 10% TBW force highly discriminated fall history among active older adults with sensitivity 93.1 and specificity 96.6. Individuals unable to withstand SST 10% TBW force within SST loading and unloading performance criteria in either stepping direction, are at increased risk for future fall (positive predictive validity 96.4 and negative predictive validity 93.3). [12]

Whether  predictable perturbations are useful for providing appropriate and clinically meaningful protective recovery stepping response measures discriminant to fall history in older adults, has not been established [11.] This paper has undertaken to investigate this issue.

PURPOSE

The purpose of this paper is to describe the ability of the SST/RIPPS method to obtain protective stepping response correlations associated with fall history and to compare the stepping response data obtained using the SST/RIPPS method with lab based methods reported in the literature.

Method

This retrospective descriptive paper involves secondary analysis of data from a study of The Spring Scale Test [12] Initially approved by the IRB of the Visiting Nurse Service of New York Center for Home CarePolicy and ResearchBasic descriptive statistical analysis supported with Pearspn correlation coefficients.

Subjects

All subjects were independently ambulatory and community-living older adults who provided written consent prior to participation, 19 were men and 39 were women. The age range was from 65 to 94 years; mean age 80.8 (SD=7.23), thirty participants were 80 to 89 years of age. By self – report, 29 of the 58 subjects had fallen at least once over the previous 2 years.

Data Analysis

For the purposes of this paper, the value of the measures for distinguishing between fallers and nonfallers was examined using Pearson correlations.

RESULTS

Protective recovery stepping measures obtained in response to repeated incremental, “predictable” waist-pull perturbations (RIPPS), are associated with fall history in older adults.

Fall history was highly correlated with protective stepping frequency at SST/RIPPS 10 % TBW force,  (TABLE 1), (.788 rear stepping, .753 forward stepping) and the maximal amount of SST/RIPPS force sustained within an effective protective stepping response limit of 3 steps, (.786 rear direction, .743 forward direction). At SST/RIPPS 10 TBW force, 67% of the nonfallers displayed a 1 step response compared to 0.09 % fallers.

Threshold and Limit % TBW stepping frequency measures were poorly associated with fall history,  with correlations ranging from (.258 ) threshold rear step frequency,  to (.418) limit force, forward stepping direction).

Threshold rear stepping force was moderately correlated with fall history (.557), compared to (.301) forward step direction.

Rear direction measures displayed slightly higher correlations with fall history compared to forward direction measures.

 DISCUSSION

Existing relationships between fall history in older adults and reactive protective stepping responses obtained using repeated, incremental, “predictable” waist-pull perturbations, were identified supported by Pearson Correlations.

Findings of this study suggest that fall history in older adults is strongly associated with the number (frequency) of recovery steps (0 to 3) required to regain balance in response to 10 % TBW predictable waist pull perturbation force. In 96% of all 10 % TBW force trials, nonfallers exhibited a 1step (67%) or a 2 step (29%) effective stepping strategy indicating as others have [4,9,11,15,16]  that a single step recovery strategy could further discriminate fall risk, representative of a more effective and efficient response [9,15,16] associated with a lower risk for a future fall [8.]

Regarding directional correlation measures obtained in this study, no significant between- group differences were found, nonetheless, several posterior direction step measures examined, best discriminated known fallers from known nonfallers, consistent with experimental, unpredictable perturbation-based method findings . [13]

Fallers exhibited lower threshold force for stepping (4.5%) compared to nonfallers (6.5%) (TABLE 2) as others have reported [13], however, only rear direction threshold stepping force was moderately correlated at best with fall history providing limited information about fall risk (.557).

Nonfallers exhibited multiple stepping responses at both threshold and limit SST/RIPPS stepping milestones, with threshold force frequency (44 % rear , 30% forward) and  limit stepping force trials, (69% rear, 38% forward), perhaps possessing limited clinical utility for fall risk assessment.

The 10 % TBW stepping frequency step measures reported in this study supports those indicating, as the ability to withstand and adapt to displacing postural perturbations is associated with fall risk [6,10,12,13] utilizing effective and efficient stepping responses, [4,7,8,9,14] the adequacy of such measures for identifying older adults at risk of fall is critical.

This study includes several potential limitations. First, is the extent to which the results of this study may be generalized to all older adult sub – groups. Independent, community-living older adults were relatively healthy and functionally independent, thus older frail adult sub-groups with multiple co-morbidities affecting balance and function may be more vulnerable to loss of balance and falls, possessing limited stepping ability. Second, the findings reported in this study based upon waist-pull perturbations may not be generalized to other forms of fall-provoking circumstances, such as slips and trips or self-induced balance loss associated with intended movement. Third, the present study restricted its analyses to observational measures, void of technology-based measurements  such as  first step characteristics including floor clearance, recovery kinematics and  step initiation time which could influence successful reactive stepping responses.

Summary and Conclusions

A strength of this study was the ability of predictable perturbations to characterize protective recovery stepping performance in active older adult faller and nonfallers, providing insight regarding an alternative clinical perturbation method compared to existing unpredictable methods. The repeated, incremental, “predictable” waist-pull perturbation method (RIPPS)described in this study appears capable of providing appropriate, quantifiable, clinically meaningful protective stepping measures highly associated with fall history in older adults.
Stepping and reactive postural responses associated with falls in active older adults are described and identified in this paper supported by Pearson correlation coefficient analysis.

Clinically meaningful stepping responses identified in this paper, namely stepping frequency at 10 % TBW and % TBW maximal force limit measures, were obtained using a clinically reliable and valid tether release method employing RIPPS, employing  % TBW and stepping frequency performance measures.

The SST/RIPPS method described in this paper incorporates elements of experimental, lab based lean-release methods. [3,20,21]

Reactive stepping is associated with falls after stroke[20] and is predictive of falls¹ in the community [12,21]

Findings of this paper supports those who suggest that future research should explore the feasibility of implementing more specific and standardized assessments of reactive balance control into clinical practice. [11]

Results of this study supports the clinical feasibility of RIPPS for obtaining meaningful reactive postural and stepping responses associated with fall risk in active older adults.

The use of RIPPS as an intervention to train reactive protective stepping responses seems plausible, consistent with tenets of specificity. Further prospective research is urgently warranted to validate skill retention which seems plausable [23] and reduction in fall risk associated with repeated incremental predictable perturbation training. [24]

 

Table 1
Pearson Comparisons
Direction % TBW (T) Steps(T) 10% TBW steps % TBW (L)  Steps (L)
Rear .557 .258 .788 .786 .283
Forward .301 .245 .753 .743 .418

T  Threshold   L Limit 

Table 2
                                 Threshold 

    Fallers                Rear Direction         Non Fallers                                                        

4.5% TBW               Mean% TBW         6.5% TBW

1 step 35 %                                               1 step 55 %

2 step 52 %                                               2 step 31 %

3 step 13 %                                               3 step 13 %

Forward Direction 

1 step 55 %                                               1 step 72 %

2 step 31 %                                               2 step 26 %

3 step 13 %                                               3 step 04  %

Limit

Rear Direction

7.5 % TBW             Mean % TBW           12.3 %TBW

1 step 10 %                                                1 step 31 %

2 step 42 %                                                2 step 45 %

3 step 48 %                                                3 step 24 %

Forward Direction

1 step 17 %                                                1 step 62 %

2 step 59 %                                                2 step 31 %

3 step 24 %                                                3 step 07 %

                                    10% TBW

1 step  .09%                                               1 step 67 %

2 step  1.2 %                                              2 step 29 %

 

Frequency % TBW

    Fallers                        SST (%)                Non Fallers

N   %TBW (%)                                            N   %TBW (%)

3       5       (10)                                            1          9       (3.5)

7       6       (24)                                            3    9.7-10.5  (10)

5       7       (17)                                            7          11      (24)

10     8       (35)                                            6          12      (21)

2       9       (07)                                            8          13      (28)

2       10     (07)                                            4          14   (13.5)

 

 Table 2

SST acquired DL stepping data compares favorably to random testing, lab-based stepping data reported by (Shulz) at 5 % TBW forces in balance impaired and unimpaired older adults.

Schultz: 5 % TBW average number steps;

balance unimpaired 1.14 forward           1.60 rear

balance impaired     1.63 forward (43)   2.11rear (32)   ___________________________________________________________________________

SST study: Directional limit mean steps:

non-fallers                1.45 forward            1.43 rear

fallers                        2.17 forward(50)     2.41 rear(69)

 

Appendix A

                            RIPPS SST PROTOCOL

 

Component Method Purpose SST End Point Performance Criteria
ANTERIOR

 

Facing subject

Loading

 

Continuous 1 lb incremental loading forces applied in a gentle / accommodative fashion Assess non-stepping effective accommodation foot flat limits.

 

No stepping to x% total body weight or %TBW where loss of foot flat contact or stepping response occurs.

 

ANTERIOR

 

Facing subject

 

Loading/unloading

Cyclic 1 lb incremental loading/unloading To assess effective back stepping limits expressed as percent of total body weight. % TBW >3 steps observed or contact with support surface.  % TBW at highest successful  trial observed.

 

POSTERIOR

Subject’s back to examiner

Loading

 

 

Continuous 1 lb incremental loading forces applied in a gentle/accommodative

fashion

Assess non-stepping effective accommodation foot-flat limits No stepping to x%   TBW at point of stepping or loss of foot flat contact.
POSTERIOR

 

Subject’s back to examiner

Loading/unloading

 

Cyclic 1 lb incremental loading /unloading To assess effective forward stepping limits expressed as percent of total body weight. % TBW > 3 steps or support surface contact % TBW at highest successful trial observed.

 

Glossary:

SST % TBW Performance Measure:  Highest waist pull force tolerated achieving SST RIPP effective loading and unloading limit criteria .

Accommodation: Maintained heel to metatarsal head (toes excluded) foot to floor contact during loading waist pull force application.

Step: Complete loss of foot contact with floor

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Louis DePasquale PT, MA

Louis DePasquale PT, MA

Master of Arts Kinesiology, New York University
Physical Therapy Certificate, Columbia University
B.S. Physical Education, Manhattan College

Affiliations:
Bon Secours Health System, Francis Schervier Long Term Home Health Program
Hebrew Home at Riverdale, Long Term Home Health Program

Practice:
30+ years geriatric home care setting

Publications:
• DePasquale L, Toscano L. ”The Spring Scale Test (SST): A Reliable and valid Tool for Explaining Fall History.” JGPT 2009; 32:(4).
• Bohannon R, DePasquale L. ”Physical Functioning Scale of the Short-Form (SF) 36: Internal Consistency and Validity with Older Adults.” JGPT 2010; 33(1).
• DePasquale L, ”Perturbation Neurophysiology.” Advance: for Physical Therapy and Rehab Medicine 2011: October 17.
• DePasquale L, ”Safety in the Balance.” Physical Therapy Products. November 2011.

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