fem varus derotational osteotomy rehabilitation after hip preservation fem varising derotation osteotomy fem osteotomy anteversion proximal fem varus fem derotational osteotomy st proximal fem osteotomy bone and spine intertrochanteric osteotomy and distal fem osteotomy valgus knee proximal fem osteotomies distal fem opening wedge osteotomy fem head reduction osteotomy fhro fem derotational osteotomy level