This case is one of the more difficult cases I have encountered in the clinic. Difficulties: 1. left congenital hip dislocation (shallow acetabulum, abnormal development of femoral anteversion angle), osteoarthropathy with knee flexion deformity (45 degrees) on the affected side; 2. severe osteoporosis of the left (L) femur, thin cortical bone, highly susceptible to intraoperative and postoperative fractures; 3. post-polio sequelae of the affected lower extremity, thin femoral stem, and weak muscle strength of the lower extremity. The patient was a 63-year-old female with congenital acetabular dysplasia of both hips, osteoarthropathy of the left knee, deformity of knee flexion, and sequelae of poliomyelitis of the left lower extremity. He underwent total hip replacement on the right side one year ago. He came to the clinic with pain in the left hip joint. On examination, he saw a 30 degree deformity of left hip flexion and a 45 degree deformity of left knee flexion, with obvious pressure pain in the inguinal region of the hip joint and limitation of hip flexion, extension, extension and internal and external rotation. The left knee joint had no pressure pain, a 45 degree deformity in flexion and 45 to 110 degrees in flexion and extension. The muscle strength of the left lower limb was grade 4 in the gluteus medius, grade 4 in the quadriceps, grade 3 in the tibialis anterior group and grade 4 in the tibialis posterior group. The left acetabulum was shallow on X-ray, the femoral stem was thin, the anterior femoral tilt was abnormally large, the femoral medullary cavity was narrow, and the cortical bone was thin. Since the patient had significant hip pain and a strong desire for surgery, it was decided that total hip arthroplasty would be performed first. In order to determine the size of the femoral medullary cavity and to facilitate the selection of the prosthesis, a CT reconstruction of the femoral medullary cavity was performed before surgery, and the diameter of the narrowest part of the cavity was measured to be 9 mm. This prosthesis has the feature of aligning the proximal elliptical long axis of the stem with the maximum elliptical long axis of the patient’s proximal femur according to the size of the patient’s anterior tilt, and implanting the largest prosthesis possible to maintain the initial stability of the prosthesis. At the same time, use the combined neck piece to adjust the neck to the normal femoral anteversion angle to avoid the patient’s postoperative internal rotation of the foot and dislocation of the prosthesis due to excessive anteversion angle. 2. In order to avoid fractures during and after surgery, we used two allograft bone plates placed on the inside and outside of the femur (12 CM) to facilitate the prevention of fractures while implanting the femoral prosthesis. At the same time, the bending and torsional moments of inertia of the femur were strengthened to prevent postoperative fractures. 3.The acetabular part adopts a small cup to fix the femoral head above the external acetabulum after correction and shaping, increasing the coverage of the acetabular cup and improving the immediate stability of the prosthesis. 4.Because the patient was severely osteoporotic, thus non-cemented fixation of the femur and acetabular prosthesis was used. Preservation of bone volume. The tuning fork grooving at the distal end of the prosthesis helps to reduce the stress concentration at the distal end of the prosthesis.