Effect of alignment perturbations in a trans-tibial prosthesis user: a pilot study

A recurring complication voiced by trans-tibial prosthetic limb users is ‘poor socket fit’ with painful residuum-socket interfaces, a consequence of excess pressure. This is attributable to both poor socket fit and poor socket alignment, however, their interaction has not been quantified. Through evaluation of kinetic data this study aimed to articulate an interaction uniting socket design, alignment and interface pressures (IPs). Results will help refine future studies, which will help determine if sockets can be designed, fitted and aligned to maximise mobility whilst minimising injurious forces. IPs were recorded throughout ambulation in one user with ‘optimal (reference) alignment’ followed by five malalignments in a patellar tendon-bearing (PTB) and a hydrocast socket. Marked differences in pressure distribution were discovered when equating the PTB against the hydrocast socket and when comparing IPs from reference to offset alignment. PTB sockets were established more sensitive to alignment perturbations than hydrocast sockets. A complex interaction was found, with the most prominent finding demonstrating the requisite for attainment of optimal alignment: a translational alignment error of 10mm can increase maximum peak pressures by 227 percent (x̄=17.5%). Refinements for future trials have been established, as has the necessity for future research regarding socket design, alignment and IPs.