Stepping responses for reactive balance for individuals with incomplete spinal cord injury

Incomplete spinal cord injury (iSCI) causes impairment of reactive balance control, leading to higher fall risk. In our previous work, we found that individuals with iSCI were more likely to exhibit multiple-step response during the lean-and-release (LR) test, where the participant leaned forward while a tether supported 8-12% of the body weight and received a sudden release, inducing reactive steps. Here we investigated the foot placement of people with iSCI during the LR test using margin-of-stability (MOS). Twenty-one individuals with iSCI (age: 56.1 ± 16.1 years old; mass: 72.5 ± 19.0 kg; height: 166 ± 12 cm), and fifteen age- and sex-matched able-bodied (AB) individuals (age: 56.1 ± 12.9 years old; mass: 57.4 ± 10.9 kg; height: 164 ± 8 cm) participated in the study. The participants performed ten trials of the LR test and also completed clinical assessment of balance and strengths, including the Mini-Balance Evaluations Systems Test, the Community Balance and Mobility Scale, gait speed, and lower extremity manual muscle testing. MOS was significantly smaller during multiple-step responses than during single-step responses for both individuals with iSCI and AB counterparts. Using binary logistic regression and receiver operating characteristic analyses, we demonstrated that MOS can distinguish single- and multiple-step responses. In addition, individuals with iSCI demonstrated significantly larger intra-subject variability of MOS compared to AB individuals at first foot contact. Further, we found that MOS correlated with clinical measures of balance including one for reactive balance. We conclude that individuals with iSCI were less likely to demonstrate foot placement with sufficiently large MOS, which may increase the tendency to exhibit multiple-step responses.