To the Editor:

I thank Dr. Anderson for his interest in our article, "Soft Tissue Balancing of the Hip. The Role of Femoral Offset Restoration". The purpose of our article was to re-emphasize the importance of considering femoral head offset restoration as well as leg length equalization during total hip replacement. Hopefully, we have properly addressed the advantages of getting both leg length and offset restoration just right during total hip replacement.

We both seem to agree that use of a femoral component with a single neck shaft angle and with the option to use a standard or medialized neck can improve femoral head offset without adversely affecting leg length. The use of lateralized acetabular liners is indeed a little more controversial.

I would agree that use of a lateralized liner increases not only leg length but also has the potential to lateralize the center of the hip joint. We actually only use lateralized liners in situations where the center of the hip joint is medialized (i.e. protrusio acetabular deformities) in an effort to place the center of rotation in the proper location.

Thank you once again for your interest in our article and for your insightful comments.

Sincerely, R. B. Bourne, MD, FRCSC

To the Editor:

A casual review of this Instructional Course Lecture may lead the reader to believe that using an offset liner is mechanically equivalent to using a high offset stem. Figure 8 incorrectly states "that a modular ‘offset’ or ‘lateralized’ liner increases the offset while preserving limb length".

But from a biomechanical standpoint, these liners only translate the hip center laterally. They do not increase the offset (defined as the distance from the hip center to the long axis of the femur) as shown in Figure 1. While both techniques( increasing femoral offset or lateralizing the hip center) increase the tension in the soft-tissues, they have opposite effects on the forces across the articulation and on abductor tension. As pointed out in the text of the article, lateralizing the hip center with these liners actually produces the detrimental mechanical effects of increased joint reaction force and higher abductor tension.