A Femoral Neck Osteotomy for the Patients with Ankylosing Spondylitis and Thoracolumbar Kyphosis Combined with Hip Flexion Contracture

Objective. The surgical treatment of patients with ankylosing spondylitis and severe thoracolumbar kyphosis combined with hip flexion contracture is very difficult for all the surgeons. The femoral neck osteotomy (FNO) is the first step to break the ice. The evaluation of a new modified FNO method is very important to improve the curative effect.Methods. Five male patients with nine bone-fused hips who underwent the new femoral neck osteotomy were included from October 2021 to March 2022. The FNO was designed that the saw blade was manipulated from the lateral femoral neck base to the inferior part of the femoral head, keeping Pauwels' angle less than 30(degrees) on the coronal plane. On the transverse plane, the angle between the saw blade and the coronal plane was more than 15(degrees). On the sagittal plane, the saw blade cut through the femoral neck. They accepted pedicle subtraction osteotomy (PSO) after FNO according to the patient' recovery. Then, 2 weeks later, the patients underwent total hip arthroplasty (THA). The visual analogue scale (VAS), Harris hip score (HHS) and passive hip flexion-extension range of motion (ROM) were used to evaluate hip function. The data were analyzed by paired t-test.Results. The average operation time and blood loss of FNO, the average interval between FNO and THA were collected. The average angle of the trunk and lower limb (ATL) was 36.33 degrees +/- 16.36 degrees pre-FNO, 82.89 degrees +/- 13.51 degrees post-FNO and 175.22 degrees +/- 3.42 degrees post-THA. The average VAS scores were 0 pre-FNO, 5 +/- 1.58 post-FNO and 2.6 +/- 0.55 post-THA. The average HHS was 43.56 +/- 1.59 preoperatively and 83.89 +/- 2.21 postoperatively. The average hip extension ROM was 23.89 degrees +/- 12.69 degrees pre-FNO, -22.67 degrees +/- 14.18 degrees post-FNO and - 3.33 degrees +/- 2.50 post-THA degrees. The average hip flexion ROM was 23.89 degrees +/- 12.69 degrees pre-FNO, 35.56 degrees +/- 12.11 degrees post-FNO and 104.44 degrees +/- 5.27 degrees post-THA. The differences among them were significant (p < 0.05). Only one hip (11.11%) displaced completely after FNO.Conclusion. A new modified FNO was developed, which can provide osteotomy with a certain degree of stability and greater ease for performing PSO and THA.