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

Objective: A recurring complication in trans-tibial prosthetic limb users is "poor socket fit" with painful residuum-socket interfaces, a consequence of excess pressure. This is due to both poor socket fit and poor socket alignment; however, the interaction of these factors has not been quantified. Through evaluation of kinetic data this study aimed to articulate an interaction uniting socket design, alignment and interface pressures. The results will help to refine future studies and will hopefully help determine whether sockets can be designed, fitted and aligned to maximize mobility whilst minimizing injurious forces.

Methods: Interface pressures were recorded throughout ambulation in one user with "optimal (reference) alignment" followed by 5 malalignments in a patellar tendon-bearing and a hydrocast socket.

Results: Marked differences in pressure distribution were discovered when equating the patellar tendon-bearing against the hydrocast socket and when comparing interface pressures from reference with offset alignment. Patellar tendon-bearing sockets were found to be 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 10 mm can increase maximum peak pressures by 227% (mean 17.5%).

Conclusion: Refinements for future trials are described and the necessity for future research into socket design, alignment and interface pressures has been estabilished.