3D intersegmental knee loading in below-knee amputees across steady-state walking speeds.

BACKGROUND Unilateral below-knee amputees often develop comorbidities that include knee joint disorders (e.g., intact leg knee osteoarthritis), with the mechanisms leading to these comorbidities being poorly understood. Mechanical knee loading of non-amputees has been associated with joint disorders and shown to be influenced by walking speed. However, the relationships between amputee knee loading and speed have not been identified. This study examined three-dimensional mechanical knee loading of amputees across a wide range of steady-state walking speeds. METHODS Fourteen amputees and 10 non-amputee control subjects were analyzed at four overground walking speeds. At each speed, intersegmental joint moment and force impulses (i.e., time-integrals over the stance phase) were compared between the control, intact and residual knees using repeated-measures ANOVAs. FINDINGS There were no differences in joint force impulses between the intact and control knees. The intact knee abduction moment impulse was lower than the non-amputees at 0.6 and 0.9 m/s. The intact knee flexion moment impulses at 0.6, 1.2 and 1.5m/s and knee external rotation moment impulses at all speeds were greater than the residual knee. The residual knee extension moment and posterior force impulses were insensitive to speed increases, while these quantities increased in intact and control knees. INTERPRETATION These results suggest the intact knees of asymptomatic and relatively new amputees are not overloaded during walking compared to non-amputees. Increased knee loads may develop in response to prolonged prosthesis usage or joint disorder onset. Further study is needed to determine if the identified bilateral loading asymmetries across speeds lead to diminished knee joint health.