A new special femoral neck osteotomy method for application in the surgical treatment of patients with ankylosing spondylitis and severe thoracolumbar kyphosis combined with hip flexion contracture

Abstract Background Surgeons often experience difficulty operating on patients with ankylosing spondylitis who have thoracolumbar kyphosis combined with hip fusion. Femoral osteotomy is used when performing pedicle subtraction osteotomy (PSO) and total hip arthroplasty (THA). We evaluate the effect of a new special femoral neck osteotomy (FNO) method in the surgical treatment of patients with ankylosing spondylitis and severe thoracolumbar kyphosis combined with hip flexion contracture. Methods We included 5 male patients with 9 bone-fused hips who underwent the new femoral neck osteotomy from October 2021 to March 2022. We designed the saw blade to be manipulated from the lateral femoral neck base to the inferior part of the femoral head, keeping Pauwels’ angle less than 30° on the coronal plane. On the transverse plane, the angle between the saw blade and the coronal plane was more than 15°. On the sagittal plane, the saw blade cut through the femoral neck. Results The average operation time and blood loss of FNO, the average interval between FNO and THA were showed. The average angle of the trunk and lower limb (ATL) was 36.33 ± 16.36° pre-FNO, 82.89 ± 13.51° post-FNO and 175.22 ± 3.42° post-THA. The average visual analogue scale (VAS) scores was 0 pre-FNO, 5 ± 1.58 post-FNO and 2.6 ± 0.55 post-THA. The average Harris hip score (HHS) was 43.56 ± 1.59 preoperatively and 83.89 ± 2.21 postoperatively. The average hip extension range of motion (ROM) was 23.89 ± 12.69° pre-FNO, -22.67 ± 14.18° post-FNO and − 3.33 ± 2.50 post-THA°. The average hip flexion ROM was 23.89 ± 12.69° pre-FNO, 35.56 ± 12.11° post-FNO and 104.44 ± 5.27° post-THA. The differences among them were significant (P < 0.05). Only one hip (11.11%) was dislocated after FNO. Conclusions We developed a new special FNO, which can provide osteotomy with a certain degree of stability and greater ease for performing PSO and THA.