Abstract: BACKGROUND: Open wedge high tibial osteotomy is one of the most effective surgical methods for the treatment of medial compartment knee osteoarthritis. Clinically, the distraction angle is routinely adjusted by force bar and fluoroscopy during the operation, but there is a risk of over-correction. Through the preoperative planning of the Picture Archiving and Communication Systems, can a better line of force of the lower extremities be obtained without fluoroscopy during the operation?  
OBJECTIVE: To clarify the feasibility and reliability of the gap width reference method by comparing the accuracy of the two reference methods of force line correction in open wedge high tibial osteotomy.
METHODS:  The patients with knee osteoarthritis who underwent open wedge high tibial osteotomy in Wuxi People’s Hospital Affiliated to Nanjing Medical University from August 2018 to August 2020 were reviewed. According to different reference methods of osteotomy, they were divided into two groups. In the conventional group (n=16), the correction angle was calculated by the whole length film of the lower limb before operation, and the osteotomy distraction height was calculated by the conversion table according to the angle. During the operation, the distraction angle was adjusted by force pole and X-ray perspective, so that the force bar passed through the target force line. In the planning group (n=12), the height of osteotomy needed to be distracted was directly calculated by Picture Archiving and Communication Systems before operation, and it was directly stretched to the height measured before operation after osteotomy, which was not adjusted by force bar X-ray during operation. The operation time of the two groups was compared; the difference between the postoperative force line and the target force line (converted into an angle) was evaluated. The tilt angle of tibial plateau was compared between the two groups after operation. American knee society score was calculated at 1 and 3 months after operation.  
RESULTS AND CONCLUSION: (1) The operation time in the planning group was shorter than that in conventional group, and the difference was significant (P < 0.05). (2) There was a significant difference between the postoperative lower limb force line and the target force line between the two groups (P < 0.05). The deviation between the force line and the target force line obtained after operation in planning group was smaller than that in conventional group. There was no significant difference in the absolute value of the difference between the postoperative force line and the target force line between the two groups (P > 0.05). There was no significant difference in the increase of tibial plateau posterior inclination angle between the two groups (P > 0.05). (3) There were 0 cases of hinge point fracture in both conventional group and planning group during the perioperative period. (4) American knee society score of planning group was higher than that of conventional group at 1 and 3 months after operation. The difference was significant (P < 0.05). (5) The results show that through the reference of osteotomy and correction of open wedge high tibial osteotomy by Picture Archiving and Communication Systems, there is little difference between the postoperative force line and the target force line, and the incidence of excessive valgus can be reduced. It can achieve a good early clinical effect, shorten the operation time and reduce unnecessary fluoroscopy during the operation, but the follow-up time is insufficient, and the medium- and long-term effect remains to be further observed.

Key words: osteoarthritis of knee, open wedge high tibial osteotomy, digital, image, lower limb force line, American knee society score