Vertical alignment axis for transtibial prostheses: a simplified alignment method

Abstract

Background and purpose: To evaluate a simplified method of alignment for fitting a transtibial prosthesis known as the vertical alignment axis method.

Methods: We measured the relationship between the vertical projection of the prosthetic socket center (geometric center of the cross section of the transtibial prosthetic socket at the level of the patella tendon bar) and the alignment reference center (junction of the middle and posterior thirds of the longitudinal axis of the shoe) in 36 dynamically aligned transtibial prostheses. The prostheses were fabricated by students, and the fit (proper vs improper) was assessed by the faculty.

Results: The faculty members found 26 of the 36 prostheses to be properly fitted. The vertical projections of the socket centers of the properly-fitted prostheses were concentrated within a small area of the shoe tracing (a mean value of 1.3 mm medially and 6.4 mm anteriorly from the alignment reference center). Conversely, in the improperly-fitted prostheses, the vertical projections of the socket center were scattered well away from the alignment reference center; the mediolateral deviation was significantly greater for improperly-fitted prostheses than for those that were properly fitted (p < 0.001).

Conclusions: These results demonstrate the usefulness of the vertical alignment axis procedure. This procedure may help clinicians to better understand the alignment of transtibial prostheses and gait deviations associated with improper prosthesis fit.