Limb-specific mediolateral ground reaction force impulses during cross-slope walking in unilateral lower-limb prosthesis users

Walking on coronally inclined (cross-slope) surfaces imposes downhill-directed gravitational impulses that must be countered by uphill-directed mediolateral (ML) ground reaction force (GRF) impulses to sustain steady-state straight-ahead walking. We investigated how transfemoral (TFPUs) and transtibial (TTPUs) prosthesis users regulate limb-specific ML GRF impulses when walking on cross-slope. Participants included 12 TFPUs (12 males), 12 TTPUs (11 males, 1 female), and 14 able-bodied controls (6 males, 8 females) who walked at a self-selected speed on an instrumented inclined walkway. The GRFs were recorded and expressed in a surface-aligned coordinate system. The uphill-directed ML GRF impulse for each limb was computed over stance, and the total uphill ML impulse per stride was compared with the theoretical downhill gravitational impulse. We further compared downhill versus uphill limb distributions across groups and examined temporal ML GRF profiles using one-dimensional statistical parametric mapping. The strategies to achieve this balance depended on amputation level and limb position. With the intact limb downhill, both TFPUs and TTPUs relied heavily on the intact limb, generating greater uphill impulse than controls, whereas the uphill prosthetic limb contributed less. With the prosthetic limb downhill, TTPUs behaved like controls, but TFPUs increased prosthetic uphill impulse during mid-stance to exceed controls. These asymmetric strategies were achieved through the modulation of average ML GRF rather than stance time, and were accompanied by wider steps. Improving prosthetic inversion-eversion compliance and residual hip abductor-adductor strength may reduce sound-side overload and enhance safety on cross-slopes.