2015 ISAKOS Biennial Congress ePoster #1411

Intramedullary Guide Rod Control for Restoring Accurate Knee Flexion Axis in Total Knee Arthroplasty

Akihiro Ariumi, MD, PhD, Nagaoka, Niigata JAPAN
Satoshi Watanabe, MD, Niigata City JAPAN
Osamu Tanifuji, MD, Niigata City JAPAN
Takashi Sato, MD, Niigata City JAPAN
Nagaoka Central General Hospital, Nagaoka, Niigata, JAPAN

FDA Status Not Applicable

Summary: To provide ideal femoral implant alignment and avoiding anterior femoral cortex notching, intramedullary guide rod simulation was performed in 60 females of total knee arthroplasty candidate. The distance between the anterior femoral cortex and the rod entry point was 18.7mm, and the varus-valgus angle to the femur was 5.1 degrees. The average depth of the rod from the entry point was 184.4mm.

Abstract:

Introduction

For femoral resection in total knee arthroplasty (TKA), intramedullary guiding rod (IM rod) is commonly used. We have used three-dimensional (3D) preoperative planning computer software and special surgical supporting jigs for accurate positioning of TKA implants. The aim of this study is to evaluate the position of the IM rod three-dimensionally for restoring knee flexion axis accurately and avoiding anterior femoral cortex notching.

Materials And Methods

Computed tomography (CT) of the femur was obtained from 60 Japanese females of TKA candidate (Average age 74.0). The preoperative diagnosis was medial knee osteoarthritis in all cases.
After 3D bone model was established, surgical transepicondylar axis (SEA) and the axis of distal femur (ADF) were defined. Appropriate size of femoral implant was chosen and the implant was placed parallel to the SEA and 1-3 degree more flex than ADF. IM rod CAD model was set into the femoral bone model to provide predetermined distal cut plane. For reproducing accurate position and stability of the IM rod in actual surgery, the IM rod model was adjusted anterior-posterior and varus-valgus direction to contact two point (anterior and posterior) of intramedullary side cortex bone without changing planned distal cut. The entry point, the varus-valgus angle to the distal end plane of the femur and the depth of the tip of IM rod were calculated. Actual surgery was performed with surgical supporting jigs for reproducing the result of this computer simulation.

Results

The mean values of the distance between the anterior femoral cortex and the IM rod entry point was 18.7mm, and the varus-valgus angle to the femur was 5.1 degrees. The average depth of IM rod from the entry point was 184.4mm. All of operations had been done successfully without anterior notching, severe malalignment or instability.

Discussion

This 3D computer simulation and surgical supporting system enable us detailed preoperative planning and accurate osteotomy to restore the postoperative knee flexion axis close to SEA which is recognized as consistent knee flexion axis, without decreasing the safety of conventional intramedullary guiding system. Certain amount of individual variability of the IM rod position was observed, that is coming from the individuality of femoral bone shape and the thickness of cortex bone. The result of present study can help the surgeons to make the postoperative knee flexion axis close to SEA without breaking anterior cortex.