Does transverse plane mechanical compliance affect amputee gait and in-socket forces?

Transverse plane rotation in an amputee's residual-limb appears to be lessthan in non-amputees [1,2]. However, it remains unclear firstly, to what extentthis is driven by the properties of the prosthesis, and secondly, whether thishas detrimental effects on the residual-limb. In trans-tibial prostheses, thesocket and foot are commonly connected via a rigid adapter, which restrictsthe residual-limb's transverse rotation while inside the socket and can increasethe forces exerted onto the residual-limb. This can subsequently trigger tissuedamage. Instead of a rigid connection, an adapter with a compliant elementcan be fitted to prostheses to allow some transverse rotation. This novel studyquantified in-socket forces and amputated side kinetics and kinematics toinvestigate the mechanisms by which the adapter reduces in-socket forces.Gait tests were conducted with ten unilateral trans-tibial amputees who walkedon a prosthesis that had an adapter with (A) and without (B) a compliantelement. Comparing (A) with (B) showed that, at early stance, whilst the socketrotated internally due to adapter compliance, the pelvis was therefore likelyto internally rotate and move forward more relative to the prosthesis. Thisforward motion is associated with greater elevation of the centre of mass, whichcan be compensated for by increasing and delaying the peak in knee flexionduring stance. Peak knee flexion magnitude was not significantly increasedwith the adapter (approximately 0.6 °, p = 0.976). However, peak knee flexionwas significantly delayed with the adapter (approximately 3.28% of stance,p=0.010). Knee flexion is a common shock absorption mechanism, whichsignificantly reduced the peak vertical ground reaction force (approximately0.2N/kg, p=0.050) and delayed it, although not significantly (approximately1.41% of stance, p=0.141), thus overall reducing the vertical loading rate.Reduced in-socket forces supported these findings. In conclusion, adaptercompliance has therefore beneficial effects on residual-limb forces