European Spine Journal. Volume 18, Number 5 / May, 2009, pp. 696-703

Effect of a novel interspinous implant on lumbar spinal range of motion

Robert Gunzburg1, 10 , Marek Szpalski2, Stuart A. Callary3, Christopher J. Colloca4, Victor Kosmopoulos5, 6, Deed Harrison7, 8 and Robert J. Moore9

(1) Department of Orthopaedic Surgery, Eeuwfeestkliniek Hospital, Antwerp, Belgium
(2) Department of Orthopedics, Hôpitaux Iris Sud/IRIS South Teaching Hospitals, Brussels, Belgium
(3) Department of Orthopaedics and Trauma, Royal Adelaide Hospital, Adelaide, SA, Australia
(4) Biomechanics Laboratory, Department of Kinesiology, Arizona State University, Tempe, AZ, USA
(5) Bone and Joint Research Center, Department of Orthopaedic Surgery, University of North Texas Health Science Center, Fort Worth, TX, USA
(6) Department of Orthopaedic Surgery, John Peter Smith Hospital, Fort Worth, TX, USA
(7) CBP Non-Profit, Inc., Evanston, WY, USA
(8) Private Practice, Elko, NV, USA
(9) The Adelaide Center for Spinal Research, Adelaide, SA, Australia
(10) Spine Surgery, Niellonstraat 14, 2600 Berchem, Belgium

Abstract Interspinous devices have been introduced to provide a minimally invasive surgical alternative for patients with lumbar spinal stenosis or foraminal stenosis. Little is known however, of the effect of interspinous devices on intersegmental range of motion (ROM). The aim of this in vivo study was to investigate the effect of a novel minimally invasive interspinous implant, InSwing®, on sagittal plane ROM of the lumbar spine using an ovine model. Ten adolescent Merino lambs underwent a destabilization procedure at the L1–L2 level simulating a stenotic degenerative spondylolisthesis (as described in our earlier work; Spine 15:571–576, 1990). All animals were placed in a side-lying posture and lateral radiographs were taken in full flexion and extension of the trunk in a standardized manner. Radiographs were repeated following the insertion of an 8-mm InSwing® interspinous device at L1–L2, and again with the implant secured by means of a tension band tightened to 1 N/m around the L1 and L2 spinous processes. ROM was assessed in each of the three conditions and compared using Cobb’s method. A paired t-test compared ROM for each of the experimental conditions (P < 0.05). After instrumentation with the InSwing® interspinous implant, the mean total sagittal ROM (from full extension to full flexion) was reduced by 16% from 6.3° to 5.3 ± 2.7°. The addition of the tension band resulted in a 43% reduction in total sagittal ROM to 3.6 ± 1.9° which approached significance. When looking at flexion only, the addition of the interspinous implant without the tension band did not significantly reduce lumbar flexion, however, a statistically significant 15% reduction in lumbar flexion was observed with the addition of the tension band (P = 0.01). To our knowledge, this is the first in vivo study radiographically showing the advantage of using an interspinous device to stabilize the spine in flexion. These results are important findings particularly for patients with clinical symptoms related to instable degenerative spondylolisthesis.