Abstract: BACKGROUND: In the selection of minimally invasive total hip arthroplasty approaches, there is considerable debate about whether direct anterior and posterior approaches differ in postoperative gait, limb balance, and hip motor capacity, and therefore further investigation is warranted.  
OBJECTIVE: To assess the gait and hip ambulation ability of direct anterior and posterior approaches for primary unilateral total hip arthroplasty with a prospective randomized controlled study. 
METHODS: A total of 61 patients with unilateral avascular necrosis of the femoral head in Qingdao Municipal Hospital from January 2019 to June 2020 were included in the study. There were 40 males and 21 females, at a mean age of (64.83±5.52) years. All the patients were randomly divided into a direct anterior approach group (n=28) and a posterior approach group (n=33), and received initial total hip arthroplasty by direct anterior approach and posterior approach, respectively. Gait analysis (gait time-space parameters such as stride length, stride frequency, single-leg support time, and plantar pressure difference) and hip ambulation ability (standing-walking timing test and 2-minute walking test) were performed before and 1, 3 and 6 months after operation. 
RESULTS AND CONCLUSION: (1) With the extension of postoperative time, gait time-space parameters in both groups were gradually improved. The stride length, stride frequency, single-leg support time, and plantar pressure difference in the direct anterior approach group were significantly better than those in the posterior approach group 1 month after surgery (P < 0.01). The stride frequency, single-leg support time, and plantar pressure difference in the direct anterior approach group were significantly better than those in the posterior approach group 3 months after surgery (P < 0.05). The plantar pressure difference in the direct anterior approach group was significantly better than that in the posterior approach group 6 months after surgery (P < 0.01). (2) With the extension of postoperative time, the results of the standing-walking timing test and 2-minute walking test were gradually improved in both groups. The results of the standing-walking timing test and 2-minute walking test 1 and 3 months after operation in the direct anterior approach group were better than those in the posterior approach group (P < 0.05). (3) The results have indicated that the recovery of postoperative gait and hip ambulation ability of the two groups is inconsistent. The direct anterior approach group has some advantages in the improvement of postoperative gait and hip ambulation ability compared with the posterior approach group in the early postoperative period. 

Key words: direct anterior approach, posterior approach, total hip arthroplasty, avascular necrosis of the femoral head, gait, hip ambulation ability