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Orthopaedic Proceedings
Vol. 95-B, Issue SUPP_15 | Pages 197 - 197
1 Mar 2013
Hirakawa M Kondo M Tomari K Higuma Y Ikeda S Noguchi T Tsumura H
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Introduction

In total knee arthroplasty, patients sometimes have pain in the posterolateral part of the knee. One possible cause is the impingement of the popliteus tendon against femoral components. In the literature, the incidence has been reported to be 1–4%. The purpose of this study is to quantify the amount of posterolateral overhang of the femoral component using 3-D templating software.

Methods

We investigated 40 knees with varus osteoarthritic knees (Male 6 knees and Female 34 knees), all cases were grade 2 or lower in Kellgren Lawrence classification. Three-dimensional preoperative planning software was used to simulate the replacement of femoral component. The distal femur was simulated to cut 9 mm thickness on the lowest point of the medial condyles with 6 degrees valgus. The femoral mediolateral axis was simulated to be parallel to the surgical epicondylar axis. The size of femoral components was decided by anteroposteriol dimension of distal femur. Mediolateral location of the femoral component was that the lateral edge of the femoral components is just on the lateral cortex of the femur. In coronal plane, amount of M-L overhang of the femoral component was measured in 3 Zones (distal, proximal, center) on the surface of the posterior condyle cut (Figure 1).


Orthopaedic Proceedings
Vol. 93-B, Issue SUPP_IV | Pages 408 - 408
1 Nov 2011
Itokawa T Kondo M Tomari K Sato M Hirakawa M Hara K Kaku N Higuma Y Noguchi T Tsumura H
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Introduction: Appropriate femoral component alignment is important for long-term survival of total knee arthroplasty (TKA). Valgus angle of femoral component is recommended as the angle between mechanical axis and anatomical axis of the femur. Intramedullary guide system is widely used for determining the valgus positioning of femoral component. Entry point of intramedullary guide is one of the key factors for determining valgus angle of femoral component. Some investigators have shown appropriate entry points of intramedullary guide, however, it is still unclear. In this study, appropriate entry point of intramedullary guide system was calculated using three-dimensional digital templating software “Athena” (Soft Cube, Osaka, Japan).

Method: Forty-one knees in 34 osteoarthritis patients except valgus deformity (30 females and 4 males, mean age 75.1 years) received TKA and were simulated using “Athena” from January 2009 to March 2009. All cases were grade III or IV in Kellgren-Lawrence index. Radiograph and CT scan image were used for determination of appropriate entry point of femur using “Athena”. The anatomical axis of femur was defined as a line connecting the midpoints of femoral AP and lateral diameter, at 60 mm and 110 mm proximal to the center of intercondylar notch. Two coordinate systems were configured as representation of entry points. One was at the center of intercondylar notch defined as the point of origin in axial view of CT image and the line parallel to the clinical epicondylar axis (cTEA) defined as X-axis. Another coordinate system was the same point of origin but parallel to the line between trochlear groove and the center of intercondylar notch (AP line) defined as Y-axis.

Result: In the coordinate system that defined the cTEA as the X-axis, the average of entry point was 0.3± 0.30 mm medial (range, −4.8~ 4.7mm) and 11.6 ± 0.52mm anterior (range, 3.1~ 16.5mm) to the center of intecondylar notch. In the other coordinate system that defined AP line as the Y-axis, the average of entry point was 2.6± 0.29 mm medial (range, −1.5~ 6.3mm) and 11.2±0.52 mm anterior (range, 2.8~ 16.0mm) to the center of intercondylar notch.

Discussion: In this study, the appropriate entry point of intramdullary guide was slightly medial and about 11mm anterior to the center of intercondylar notch on average. However, individual entry point varied considerably in distance. These data indicates that it is important to simulate the appropriate entry point of intramedullary guide in preoperative planning.