Page 32 - ISAKOS 2019 Newsletter Vol II

CURRENT CONCEPTS
Medial Stabilizing Gap Technique with
Tibia First Cut in Total Knee Arthroplasty for Varus Knees
In order to control the resection thickness, the surgeon should note the effect of the rotational center of the femoral sizing guide on the posterior part of the medial femoral condyle. Minoda et al. pointed out that posterior femoral condylar bone resection thickness differed depending on the location of the rotation center of the sizing guide, even if a posterior reference guide is used5. With most sizing guides, the rotation center is located at the center of the guide. When such guides are used, 3° of external rotation provides a 1–2-mm-thicker resection of the posterior part of the medial condyle and a 1 – 2-mm-thinner resection of the posterior part of the lateral condyle. As the rotation angle increases, the difference increases. In contrast, when the procedure is performed with use of a posterior reference guide in which the rotation center is located on the medial side, the amount of resection from the posterior part of the medial femoral condyle is consistent with the thickness of the implant no matter what degree of external rotation is adopted (Figs. 4-A through 5-C). When a posterior reference guide is used, the adjustment of the anterior-posterior position of the guide directly affects the size of the medial posterior gap.
04 A posterior reference guide in which the rotation center is located at the center. The double-ended arrows indicate the resection thickness of the posterior parts of the condyles.
05 A posterior reference guide in which the rotation center is located on the medial side. The double-ended arrows indicate the resection thickness of the posterior parts of the condyles.
05A Photograph showing the guide set to 3° of external rotation from the posterior condylar line.
05B Photograph showing the guide set to 6° of external rotation from the posterior condylar line.
04A Photograph showing the guide set to 3° of external rotation from the posterior condylar line.
04B Photograph showing the guide set to 6° of external rotation from the posterior condylar line.
05C Left: Illustration depicting the anterior and posterior resection levels (horizontal red lines) as determined with the posterior reference guide. TEA = transepicondylar axis and PCA = posterior condylar axis. Right: After the femoral implant was placed at the resection revel, the amount of resection from the posterior part of the medial femoral condyle is consistent with the thickness of the implant.
It is very important to know the characteristics of the femoral rotation or sizing guide in order to control the resection thickness from the posterior part of the medial femoral condyle and to control the medial flexion gap The goal of the procedure is to balance the medial gap between extension and flexion and to provide medial stability throughout the range of motion.
Results of Our Technique
We assessed 77 knees in 71 patients who underwent TKA with this technique. The mean age of the patients at the time of surgery was 73.3 years (range, 53 – 86 years). The component gap was measured on the medial and lateral sides in both extension and flexion with use of the tensor device with the femoral trial component in place just before the final implantation. The component gap was defined as the difference between the thickness of the tibial component and insert (in millimeters) and the extension or flexion gap (in millimeters) with the trial femoral component in place. If the thickness of the tibial component and insert was thinner than the medial or lateral gap, the component gap had a positive value. If the component gap in flexion was larger than that in extension, the component gap had a positive value.
04C Left: Illustration depicting the anterior and posterior resection levels (horizontal red lines) as determined with the posterior reference guide. TEA = transepicondylar axis and PCA = posterior condylar axis. Right: After the femoral implant was placed to the resection level, there was a difference between the femoral component and the posterior part of the medial femoral condyle (red zone).
30 ISAKOS NEWSLETTER 2019: VOLUME II