Interspinous process stabilization with Rocker via unilateral approach versus X-Stop via bilateral approach for lumbar spinal stenosis: a comparative study

Abstract

Background: Rocker is a novel interspinous process stabilization (IPS) that can be installed via unilateral approach by virtue of its unique design. This controlled study compared the clinical outcome of Rocker versus X-Stop to access the feasibility and validity of the novel IPS.

Methods: From March 2011 to September 2012, 32 patients treated with Rocker and 30 patients treated with X-Stop were enrolled in this study. The primary clinical outcome measure was Oswestry Disability Index (ODI) score. The secondary clinical outcome measure was Japanese orthopaedics association (JOA) score. Disc height index (DHI) and foraminal height index (FHI) were measured for postoperative radiographic evaluation. Implant failures were also recorded.

Results: There were 55 patients with complete data during 24 months follow-up. Among the 55 patients, 38 patients underwent IPS in combination with microdecompression. At the final follow-up, 49 patients achieved a minimal clinical important difference (≥ 8 points ODI improvement). The mean operative time was 53.6 min (range, 30 to 90 min) in Rocker group and 63.1 min (range, 30 to 100 min) in X-Stop group. The average blood loss was 111 ml (range, 50 to 400 ml) in Rocker group and 138 ml (range, 50 to 350 ml) in X-Stop group. ODI score were significantly improved from preoperative 46.8 ± 9.2 to 12.2 ± 2.6 at 24 months follow-up in the Rocker group and from preoperative 45.8 ± 9.8 to 11.8 ± 2.4 at 24 months follow-up in the X-Stop group. JOA score also improved significantly in both groups. The radiographic parameters of DHI and FHI in both groups increased immediately postoperatively, however, the improvements seemed to revert toward initial value during follow-up. Two patients in Rocker group demonstrated implant dislocation within one week postoperatively and one patient in X-Stop group demonstrated implant migration at two months postoperatively.

Conclusions: Preliminary clinical and radiographic outcome was similar between Rocker and X-Stop group. For patients of lumbar spinal stenosis with unilateral nerve root involved or mild-to-moderate central canal stenosis, Rocker offers a new alternative with less damage.

Fig. 1

Schematic illustrations demonstrate the surgical procedure to install Rocker. A customized detacher is used to partially dissect the paraspinous muscles of asymptomatic side (a). Properly sized pilot is inserted to ensure that the optimal distraction were achieved (b). Unlocked Rocker is folded to facilitate installation (c). When inserting between spinous processes, folded Rocker deploys and locks by itself (d)

Fig. 2

DHI (disc height index) is measured by ab/bc and FHI (foraminal height index) is measured by de/bc. Ab indicates the disc height, bc indicates the vertebrae height and de indicates the longest distance between the upper and lower vertebral pedicle. Ac represents the line labeling the centers. The center of the vertebral body is marked by the crossing point of two diagonal lines

Fig. 3

Flow diagram with study enrolment and follow-up

Fig. 4

Intraoperative photographs displays that Rocker has been fixed between spinous process (a). Anterior to posterior radiographic image shows a properly placed Rocker (b). Anterior and posterior radiographic image demonstrates that Rocker dislocated to the paraspinous site (c)

Fig. 5

Clinical outcome measured by ODI (Oswestry disability index) score and JOA (Japanese orthopaedics association) score in both groups

Fig. 6

Radiographic outcome of DHI (disc height index) and FHI (foraminal height index) in both groups