Detailed Study of Graft Sinking and Worsening of the Fused Segment Angle in Patients With Cervical Disease Treated With the Williams-Isu Method

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Detailed changes involved in the worsening of the fused segment angle were assessed after application of the Williams-Isu method using autologous bone grafts from cervical vertebral bodies in 30 patients with cervical disease treated by single-level anterior fusion. The mean follow-up duration was 25.4 months. The fused segment angle was measured on serial radiographs. Whole cervical spine alignment changed from 12.8° to 9.9°. The alignment of the fused segment worsened by mean 3.3°. To elucidate the characteristics of worsening of the fused segment, the 30 patients were divided into 2 groups: Group I (n = 20) without and Group II (n = 10) with postoperative worsening of the fused segment. The loss in the fused segment angle was significantly greater in Group II (8.0°) than Group I (0.9°). Preoperative range of motion and disc height were significantly greater in Group II than Group I. Worsening of the fused segment angle occurred within 1 month in Group I, whereas stabilization was observed after 3 months in Group II. Graft subsidence was primarily posterior and inferior. Our results indicate that the preoperative range of motion and disc height of the fused segment must be considered to prevent worsening in that segment after anterior fusion. Such detailed information is useful for the selection and postoperative monitoring of patients eligible for treatment by the Williams-Isu method.