Using Clinical Balance Tests to Assess Fall Risk among Established Unilateral Lower Limb Prosthesis Users: Cutoff Scores and Associated Validity Indices.

BACKGROUND

Clinicians are routinely required to make decisions about fall risk among lower limb prosthesis (LLP) users. These decisions can be guided by standardized clinical balance tests but require population- and test-specific cutoff scores and validity indices to categorize individuals as probable fallers or nonfallers on the basis of test performance. Despite the importance of cutoff scores and validity indices to clinical interpretation of clinical balance test scores, they are rarely reported for LLP users. In their absence, clinicians cannot use results from clinical balance tests to assess the likelihood of a fall by any one patient.

OBJECTIVE

Derive cutoff scores, and associated validity indices, for clinical balance tests administered to established unilateral LLP users.

DESIGN

Cross-sectional study.

SETTING

Outpatient clinic and research laboratory.

PARTICIPANTS

Established ambulatory unilateral transtibial and transfemoral prosthesis users (n = 40).

INTERVENTION

Not applicable.

MAIN OUTCOME MEASURE(S): Optimal cutoff scores and related validity indices (ie, area under the curve, sensitivity, specificity, likelihood ratios) were computed for five balance tests, the activities-specific balance confidence scale (ABC), timed up and go (TUG), four square step test (FSST), Berg balance scale (BBS), and narrowing-beam walking test (NBWT).

RESULTS

Cutoff scores were identified for the NBWT (≤.43/1.0), TUG (≥8.17 seconds], FSST (≥8.49 seconds), BBS (≤50.5/56), and ABC (≤80.2/100). Validity indices (ie, area under the curve, sensitivity, specificity, and likelihood ratios) for the NBWT, TUG, and FSST had greater diagnostic accuracy and provided more information about the probability of a fall than those for the BBS or ABC.

CONCLUSION

Performance above or below identified cutoff scores for the NBWT, FSST, and TUG provides information about potentially important shifts in the probability of falling among established unilateral LLP users. These results can serve as initial benchmarks to reduce uncertainty surrounding fall risk assessment in established unilateral LLP users but require future prospective evaluation.

LEVEL OF EVIDENCE

III.