The most important finding in this study was that there were no significant differences with respect to flexion angle, anteroposterior movement of the femur, and rotation of the tibia, before and after correction by HCO. Accordingly, we found that the kinematics of post-HCO knee joints never recovered to healthy levels, because there were no significant differences between the pre- and post-operative kinematics, which was contrary to our hypothesis. Although several previous studies have analyzed gait patterns following HTO, there is no information on the surgical intervention for knee joint kinematics. This is, therefore, the first study that evaluated the effects of HCO on kinematics on the knee.
With respect to the knee OA, both posterior movement and rotation of the femur with respect to the tibia decreased, when compared to healthy knees [20, 22]. We observed that the preoperative femoral anteroposterior movements and rotation in this study were similar to those of normal knees [22]. We believe that this was due to the mild medial compartment deformations in our patients. There was also a tendency for the degree of rotation to decrease after HCO, compared with the preoperative value, but there were no significant differences between the preoperative and postoperative values of rotation and anteroposterior movement. This observation suggests that the HCO had no significant effect on the knee joint kinematics.
One of the reasons for this lack of significant difference may have been due to the HCO procedure not changing the length of the patellar tendon, because it involved osteotomy being performed below the tibial tuberosity. Meanwhile, the results of motion analysis using an electric goniometer in connection with closing-wedge osteotomy (CWO) which osteotomy being performed above the tibial tuberosity showed the loss of screw home movement following surgery leads to a reduced medial pivot motion [24]. Although we observed a tendency for the amount of rotation to decrease, there was no clear loss of the screw home movement, and therefore, there was no decrease in the medial pivot motion. The differences between the OWDTO and HTO procedures might have greatly affected this finding. In the future, it will be necessary to further accumulate 3-dimensional kinematic analysis data pertaining to various OWDTO operations.
Compared to HTO, no changes in patellar height or posterior inclination were observed in the sagittal plane with respect to the OWDTO procedures. However, since OWDTO other than HCO corrects all at once, tension in the medial soft tissue causes unintended internal axial rotation of the distal tibia and increased medial compartment contact pressure [5, 25]. Magyar et al. reported after HCO, the internal rotation of the distal tibia and the medial/lateral and distal translation of the proximal segment do not occur compared to CWO [26]. This observation indicates that excessive increases in joint pressure due to soft tissue tightness do not occur due to the restoration of the medial articular surface and fibrocartilage following HCO up to a correction angle of 18 degrees [27].
Long-term results for both CWO and HTO have improved in recent reports, but are gradually deteriorating with time [28–30]. OWDTO has not yet achieved long-term results, but HCO has already achieved good long-term results [18]. The reason for the good long-term results of HCO is that it has less effect on soft tissues and accurate correction. We believe that this technique has less impact on kinematics despite differences in leg length increases due to the medial expansion during the OWDTO. In addition, the HCO extension averaged at 8.3 mm [31].
A limitation of this study was the small sample size. As such, we recognize that the results of this study are supported by insufficient statistical power. Enrolling large numbers of subjects proved difficult owing to the necessity of performing CT and radiography.