Incidence and risk factors of adjacent segment disease following posterior decompression and instrumented fusion for degenerative lumbar disorders

Abstract

The purpose of this study was to explore incidence and risk factors of adjacent segment disease (ASD) following posterior decompression and instrumented fusion for degenerative lumbar disorders, and hope to provide references in decision making and surgical planning for both spinal surgeon and surgically treated patients.By retrieving the medical records from January 2011 to December 2013 in our hospital, 237 patients were retrospectively reviewed. According to the occurrence of ASD at follow up, patients were divided into 2 groups: ASD and N-ASD group. To investigate risk values for the occurrence of ASD, 3 categorized factors were analyzed statistically: Patient characteristics: age, sex, body mass index (BMI), bone mineral density (BMD), duration. Surgical variables: surgical strategy, number of fusion level, surgery segment, surgery time, blood loss, intraoperative superior facet joint violation. Radiographic parameters: preoperative lumbar lordosis, preoperative angular motion at adjacent segment, preoperative adjacent segment disc degeneration, preoperative paraspinal muscle degeneration.Postoperative ASD was developed in 15 of 237 patients (6.3%) at final follow up. There was no statistically significant difference between the 2 groups in patient characteristics of age, sex composition, BMD, duration, while the BMI was higher in ASD group than that in N-ASD group. There was no difference in surgical variables of surgical strategy, number of fusion level, surgery segment, surgery time, blood loss, while intraoperative superior facet joint violation was more common in ASD group than that in N-ASD group. There was no difference in radiographic parameters of preoperative lumbar lordosis, preoperative paraspinal muscle degeneration, while preoperative adjacent segment disc degeneration were more severe in ASD group than that in N-ASD group. The Logistic regression analysis revealed that, BMI >25 kg/m, preoperative disc degeneration, and superior facet joint violation were independently associated with ASD.In conclusion, higher BMI, preoperative disc degeneration at adjacent segment and intraoperative superior facet joint violation are risk factors for ASD. Patients who are overweight or obesity and with preoperative disc degeneration at adjacent segment should be fully informed the risk of ASD. For surgeons, it is essential to prevent superior facet joint violation in pedicle screw insertion procedure.

Figure 1

Lumbar lordosis was measured from T12 inferior endplate to S1 superior endplate by the Cobb method.

Figure 2

Angular motion was measured between the inferior end plate line of the upper vertebral body and superior end plate line of the lower vertebral body on flexion and extension lateral radiographs.

Figure 3

Pfirrmann Grade I: the structure of the disc is homogeneous, with bright hyperintense white signal intensity any normal disc height. Grade II: the structure of the disc is inhomogeneous, with the hyperintense white signal. Grade III: the structure of the disc is inhomogeneous, with an intermittent gray signal intensity. Grade IV: the structure of the disc is inhomogeneous, with a hypointense dark gray signal intensity. Grade V: the structure of the disc is inhomogeneous, with a hypointense black signal intensity.

Figure 4

Fatty infiltration rate (FIR) of paraspinal muscles (multifidus and erector spinae) was calculated by subtracting the muscle without the fat value from the total muscle value. Left is the original image, middle is the image of fat left, and right is the calculation of fat area by software.

Figure 5

(A–D) Preoperative L_4–5 disc herniation, and L_3–4 disc degeneration of Pfirrmann Grade III on MRI. (E and F) L_4–5 instrumented fusion without intervention to the L_3–4 disc. (G and H) Bony fusion between cage and endplate in L_4–5 disc space at 1 year follow up. (I and J) Intervertebral disc prolapse on L_3–4 27 months after spinal fusion of L_4–5. (K and L) Revision surgery of L₅ pedicle screws taken off and L_3–4 instrumented fusion was performed.

Figure 6

Intraoperative view of the complete reservation of facet joint, without superior facet joint violation.