Abstract: BACKGROUND: Anterior cruciate ligament rupture is one of the common sports injuries, which is generally treated by anterior cruciate ligament reconstruction. Balance and walking abilities are often decreased after surgery, and there is a lack of comprehensive comparative study.  
OBJECTIVE: To explore the balance and gait characteristics of patients after anterior cruciate ligament reconstruction during static standing and walking, and make a comprehensive comparative analysis with the healthy group to provide scientific guidance for rehabilitation treatment.
METHODS: Totally 23 patients 6-8 weeks after anterior cruciate ligament reconstruction and 23 healthy controls were selected. The plantar pressure plate was used to collect 95% confidence elliptical area, path length, average velocity and major and minor axis length of the plantar center of pressure during static standing. Simultaneously, the center of pressure displacement, gait line length, maximum velocity, gait phase ratio and maximum pressure in the tripod area were collected.  
RESULTS AND CONCLUSION: (1) Static standing balance: The center of pressure 95% confidence ellipse area, path length, average moving speed and length of major and minor axes in the anterior cruciate ligament reconstruction group were significantly higher than those in the healthy control group (P < 0.05). Simultaneously, the weight-bearing of the forefoot in the anterior cruciate ligament reconstruction group was higher than that in the healthy control group (P < 0.05). (2) Characteristics of walking balance: Compared with the healthy control group, the medial and lateral displacement of the center of pressure in the anterior cruciate ligament reconstruction group was significantly larger (P < 0.05), and there was no significant difference in anterior and posterior displacement and maximum movement speed. Compared with the affected side and the healthy side in the anterior cruciate ligament reconstruction group, the affected side and the healthy control group, and the healthy side and the healthy control group, the gait line and single support line length of the former in the three groups were smaller than those of the latter (P < 0.05). (3) Gait cycle characteristics: The stride width and double support period of the anterior cruciate ligament reconstruction group were larger than those of the healthy control group (P < 0.05). Stride length was smaller in the anterior cruciate ligament reconstruction group than that in the healthy control group (P < 0.05). Compared with the healthy side, the standing phase, single leg support period, pre-swing period and heel to the forefoot time on the affected side of the anterior cruciate ligament reconstruction group decreased (P < 0.05), while the load-bearing response period and swing period increased (P < 0.05). Compared with the healthy control group, the foot deviation angle, load-bearing response period and pre-swing period increased, and the single leg support period decreased on the affected side (P < 0.05). Compared with the healthy control group, the standing phase, load-bearing response period, pre-swing period and the time from heel to the forefoot were significantly increased, and the swing period decreased on the healthy side (P < 0.05). (4) The maximum pressure of the tripod area: Compared with the healthy side, the maximum pressure of the forefoot, arch and heel of the affected side decreased significantly (P < 0.05). Compared with the healthy control group, the maximum pressure of the tripod area of the affected side also decreased significantly (P < 0.05). Compared with the healthy control group, the maximum pressure of the forefoot of the healthy side decreased significantly (P < 0.05), but there was no significant difference between the arch and the heel. (5) The results showed that the static and dynamic balance ability of the patients 6-8 weeks after anterior cruciate ligament reconstruction was significantly lower than that of the healthy subjects, and the balance function of the healthy side also decreased significantly. During walking, the patients had gait problems such as a shortening of stride length, an increase of stride width, a decrease of support period and increase of swing period. It is suggested that attention should be paid to bilateral balance and gait training during postoperative rehabilitation.

Key words: anterior cruciate ligament reconstruction, static balance, gait cycle, center of pressure, length of gait line, forward and backward displacement, medial and lateral displacement,  maximum velocity,  plantar pressure