Abstract
While femoral intramedullary alignment has been found to be the most accurate and
reproducible method for proper femoral component orientation in total knee arthroplasty,
certain situations preclude the use of intramedullary alignment, such as ipsilateral
long-stem total hip arthroplasty, femoral shaft deformity (congenital or post-traumatic),
capacious femoral canal, and retained hardware. These cases require alternative alignment
guides, that is, extramedullary alignment. The purpose of this study was to determine
the accuracy of intramedullary alignment in reproducing the femoral anatomic axis.
Using 35 adult cadaveric femora without obvious clinical deformity, and 7 with proximal
prosthetic devices blocking the passage of an intramedullary guide, the accuracy of
the guide rod was assessed both anatomically and radiographically. In the seven femora
with proximal femoral devices, the guide rod could not be completely seated, resulting
in a greater degree of flexion of the guide rod compared with the mechanical axis
of the femur, and a greater degree of varus compared with the anatomical axis, as
compared with 35 femora without obvious deformity. In cases where seating of the intramedullary
guide rod is either incomplete or impossible, extramedullary femoral guides allow
more accurate determination of the distal femoral cut by referencing directly from
the mechanical axis, that is, the center of the femoral head. We present case studies
as examples of indications for use of an extramedullary femoral guide. In addition,
we demonstrate two different techniques for extramedullary femoral alignment using
fluoroscopic guidance in cases incompatible with intramedullary alignment.
Keywords
total knee arthroplasty - femoral intramedullary alignment - extramedullary alignment
- techniques
