Rotational Changes in the Distal Tibial Fragment Relative to the Proximal Tibial Fragment at the Osteotomy Site after Open-Wedge High-Tibial Osteotomy

Abstract

The present study is aimed at assessing the changes in tibial rotation at the osteotomy site after an open-wedge, high-tibial osteotomy (OWHTO) and analysing the factors that affect rotational changes in the distal tibial fragment relative to the proximal tibial fragment at the same site. This study involved 53 patients (60 knees; 16 males and 37 females) with medial osteoarthritis (OA) who underwent OWHTO and preoperative and 3-month postoperative computed tomography (CT) scans. Rotational angles of the distal tibia were measured using Stryker OrthoMap 3D by comparing preoperative and postoperative CTs. The mean rotational angle yielded an external rotation of 2.9° ± 4.8°. There were 17 knees with internal rotations, 37 knees with external rotations, and one knee with no rotation. The rotational angle significantly correlated with the resultant change in the femorotibial angle (correction angle) and the angle between the ascending and transverse osteotomy lines on the anterior osteotomised surface on which a flange was formed with the distal tibial osteotomised surface (flange angle). The flange angle affected the rotation, but it may have been affected by our surgical technique. The rotational angle did not significantly correlate with the change in the angle of the posterior tibial slope or body mass index. There were significant correlations between the rotational angle and correction angle (r = 0.42, p < 0.05). Additionally, the rotational angle correlated with the flange angle (r = -0.41, p < 0.05).

Figure 1

Measurement of the femorotibial angle and the posterior tibial slope angle. The femorotibial angle (FTA) was defined as the lateral angle between the femoral anatomical shaft axis and the tibial anatomical shaft axis on the long leg radiograph at the coronal plane. The posterior tibial slope (PTS) was defined as the posterior angle between the tibial anatomical shaft axis and tibial plateau on the long leg radiograph at the sagittal plane.

Figure 2

Determination of the tibial axis. On the tibial image of the axial plane, we determined the line that connects the middle of the posterior cruciate ligament and the medial edge of the patellar tendon attachment to be the Akagi line. As noted, #1 and #2 are the points where the vertical line to the Akagi line crosses the medial and lateral cortical bone. In addition, points #3 and #4 are the points where the Akagi line crosses the anterior and posterior cortical bone (a). Determining the ankle centre on the axial plane required identifying the talar dome weight-bearing area of the distal tibial articular surface. Firstly, we drew a long axis on the long axis of the talar dome on the image of the distal tibial joint (b). On the sagittal plane, we drew the long axis on the talar dome (c and d) with the point of the intersection being #5 (the ankle centre). The reference coronal plane is shown (the green plane passing through #1, #2, and #5) (e). The reference sagittal plane is shown (the red plane passes through #3, #4, and #5) (f). These two planes are defined as the AP planes. The intersecting line of the two planes is defined as the tibial axis (g).

Figure 3

Positioning of matched images. (1) proximal fibula, (2) distal fibula, and (3) medial malleolus before and after the operation are shown. The rotational angle in this case was 4.6° (internal rotation).

Figure 4

Measurement of the flange angle. We measured the angle between the ascending and transverse osteotomy lines on the anterior osteotomised surface where the flange was formed with the distal tibial osteotomised fragment (this study defined it so that sagittal plane on the CT could pass through the most anterior point of the tibial tuberosity).

Figure 5

We found both external (n = 40) and internal (n = 19) rotations in the knees and no rotations in one knee. The “+” sign denotes external rotation.

Figure 6

Factors affecting the rotational angle. There is a significant correlation between the rotational and correction angles (r = 0.42, p < 0.05).

Figure 7

Factors affecting the rotational angle (flange angle). There was a significant correlation between the rotational and the flange angles (r = −0.41, p < 0.05).

Figure 8

Rotational change per flange angle. A right tibial model is used to show the rotational change per flange angle. The model compared the flange angles of 100° and 120°.