［Purpose］This study aimed to evaluate the differences in the immediate postoperative muscle strength around the hip and knee joints, joint range of motion, pain, and mobility between the anterolateral-supine (AL-S) approach, as a form of minimally invasive total hip arthroplasty (THA), and the posterior approach (PA), as a form of small-incision THA.

［Methods］The subjects were 68 patients with hip osteoarthritis who underwent unilateral THA for the first time. Maximal isometric muscle strength around the hip and knee joints, joint range of motion, walking ability, and pain were measured before surgery, and on Day 10, Day 21, and 2 months after surgery.

［Results］Significant interactions were found between the time and the type of surgery for hip abduction, external rotation, and extension strength. Interaction was also found between the surgical approach and the time required to achieve optimal hip extension range of motion.

［Conclusion］The differences in the functional recovery after AL-S approach and PA were most likely caused by differences in muscle damage. Therefore, it is necessary to customize rehabilitation programs according to the characteristics of each approach.