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Guest Post: The Spring Scale Test (SST): Valid, Reliable, Discriminant Balance and Fall Risk Assessment Tool for Active Older Adults; evidence-based, innovative clinical perspective

Louis Depasquale

By Louis DePasquale, PT, MA

Louis obtained his Physical Therapy degree from Columbia University and has been practicing for 30+ years in the geriatric, home-care setting.  He has published numerous articles related to the assessment of balance and fall-risk in older adults and has taught multiple CEU courses. 
Introduction
Fall risk in the rapidly shifting, active community living older adult demographic has been identified as an urgent public health problem.1 Annual screening for fall risk in adults aged 65 years and older is required by the Center for Medicare Services and recommended by the American Geriatric Society.

Evidence for the development of new and more challenging balance measures capable of early identification of fall risk in the active older adult is overwhelming.2 Preliminary findings suggest a possible link between adaptability to externally imposed perturbations and future fall risk in community-living older adults.3 A valid, reliable, practical, safe and clinically feasible, evidence-based predictable perturbation fall risk assessment method, The Spring Scale Test (SST) (ICC = 0.94), has been described.4 Validated on active, independent, community-living older adults, the SST 10% value was determined to be most discriminant to fall status, ROC AUC = 0.992, sensitivity = 93%, specificity = 96.6%) compared to gait speed, single limb stance time, tandem stand time and timed get up and go performance measures.4

Overview
The Spring Scale Test (SST), predicated on repeated incremental predictable perturbations (RIPPS), is a first attempt, single-failure protocol to quantify forward and rear direction stepping limits. Beginning at 1-pound waist pull force, rounds of cyclic loading and unloading are administered in 1 pound increments to the limits of postural stability as determined by SST performance criteria, identifying forward and rear directional stepping limits, quantified as percent of total body weight (TBW %).

Instrumentation and Setup
Perturbation forces are quantified by a pocket-sized linear spring scale strain gauge calibrated in 1-pound increments, is affixed to a 5-inch wide padded waist belt secured around the client’s waist and connected to the examiner via a 4-foot length safety tether strap. Perturbations are administered with the examiner positioned in close proximity to the client, standing approximately 3 feet from a compliant support surface. Anterior direction limit testing (rear stepping) is performed with the examiner facing the client, while posterior direction limit testing (forward stepping) is performed with the client’s back toward the examiner.

SST Perturbation Method
Loading waist pull forces are administered in a predictable, gradual, accommodative fashion. Clients are continuously instructed to resist loading forces to their maximum limit and are reminded of the SST performance criteria.

Unloading occurs at each round of progressive 1-pound incremental accommodated loading force. Unloading is administered in a quasi-random fashion within a 5-count window, at the discretion of the examiner. Clients are continuously reminded of the SST unloading performance criteria.

SST Performance Criteria
SST loading forces must be accompanied by a foot-flat or heel – sole contact with floor postural response, defined as accommodation. Unloading postural responses must not exceed a 3-step response.

SST End Points
A SST end point occurs when either a loading or unloading RIPPS performance criteria is not achieved at a given round of waist pull force value.

SST Directional Limit Score
The SST TBW % directional limit score represents the highest waist pull force achieving the SST loading and unloading performance criteria. A directional limit force value is the directional end point (failure) force minus1. SST directional limits scores are obtained for both the anterior and posterior directions. The directional limit TBW % score is calculated by dividing the spring scale measured force in pounds by client’s body weight.

SST TBW % Performance Measure
The lower directional limit TBW % score determines the SST TBW % performance measure of clinical significance.

SST Clinical Applications

Assessment

The SST 10% TBW performance value is highly discriminant to fall status providing clinicians with a highly sensitive and specific fall risk screening tool capable of ID deficits that otherwise would go undetected in the active community living older adult. The SST 10% TBW value should be considered a minimal threshold performance value consistent with known non-fallers over the age of 65 (mean 12.3% TBW), suggesting a functional stepping ‘reserve’ exists and could be attainable and should be a clinical treatment outcome particularly in the 80 to 89 age group which represented the largest sample sub group in the SST study.

Despite the SST predictable design, reactive postural responses are typical, dominating anticipatory postural responses in those individuals with compromised balance evidenced by apprehension, excessive loading hip strategy, multiple steps in response to unloading and excessive upper extremity responses. Ceiling effects rarely occur utilizing the SST method of assessment.

Induced Stepping Treatment Paradigm
Induced stepping has been associated with greater skill retention.14
The SST method offers a safe option for induced step training for individuals 65 years of age and older.

Manipulation of anticipatory and reactive responses is possible by variations in perturbation loading/unloading force intervals. SST intervention options include step minimization, non-stepping training as well as lateral perturbations.

Summary
The SST evidence supports the use of RIPPS (repeated incremental predictable perturbations) method as an efficient, highly discriminant fall risk assessment tool for the active, independent, community- living older adult. The RIPPS goal is to introduce percent of total body weight (TBW %), as a practical clinical balance measure for fall risk assessment and treatment purposes. Research supports the reliability and discriminant validity of the (SST) RIPPS 10% TBW performance value for explaining fall history in active independent community living older adults.

References

Renfro MO, Fehrer S. Multifactorial screening for fall risk in community-dwelling older Adults in the primary care office: development of the fall risk & screening tool. JGPT. 2011; 34: 1-10

Pardasaney PK, Latham NK, Jette AM, et al. Sensitivity to change and responsiveness of four balance measures for community-dwelling older adults. Phys Ther. 2012; 92: 1 – 10.

Pai YC, Bhatt TS. Repeated-slip training: an emerging paradigm for prevention of slip-related falls among older adults. Phys Ther. 2007; 87:1 – 13.

DePasquale L, Toscano L. The spring scale test (sst): a reliable and valid tool for explaining fall history JGPT. 2009; 32(4):159 – 67.

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