Fig. 4

Schematic diagram of ischial osteotomy. A Expose the posterolateral assisted incision, and only the quadratus femoris, the inferior gemellus, and the obturator external muscles need to be exposed. B Enter into the intermuscular space of the upper margin of quadratus femoris, revealing the site of ischial branch osteotomy, that is the inferior acetabular sulcus (marked as “a”), then one Hoffman hooks (b) was placed into the obturator foramen along the front edge of the inferior acetabular sulcus, and another pointed Hoffman hooks (c) was hit into bone at 1.5 cm away from the edge of the posterior column, the sciatic nerve (black arrow) was protected by “S” hook and extending the affected lower limbs simultaneously. C 1–1, 1–2, and 1–3 represent the cortex of the inferior acetabular sulcus, lateral and medial cortex of the lower edge of the acetabulum, respectively