Introduction: The purpose of the current study is to evaluate the in vivo biomechanical performance profile of a motion-preserving Interlaminar Stabilization device compared with posterolateral fusion (PLF) by quantifying the relative segmental contribution to total lumbar ROM (TLROM) at each operative and adjacent level at baseline and 2 years.
Methods: Radiographic evaluation from a prospective, randomized, multicenter IDE trial comparing IS (n=204) with PLF (n=105) to treat stenosis or low-grade spondylolisthesis. Using previously validated methods, we defined TLROM as L1-S1 (i.e. 100%), and calculated the segmental contribution to each operative and adjacent level with IS or PLF at baseline and 2 years.
Results: Operative level contribution to TLROM in the coflex® cohort at baseline was 17.8% compared with 17.6% at 24 months (p=0.79). In contrast, operative level motion in the PLF group was 17.5% at baseline and was significantly less at 24months (7.3%, p=<0.0001). At
the first cranial adjacent level, the percent contribution to TLROM at 24 months was unchanged with coflex® (15.9-->16.7%, p=0.30) but was significantly elevated in the PLF group (14.7-->23.1%, p<0.0001). Similarly, there were non-significant elevations at the 2nd and 3rd cranial adjacent levels in PLF, with slight reductions in the coflex® group. In the 1st caudal adjacent level, the coflex® group experienced a trend towards increased contribution to TLROM (27.2-->30.2%, p=0.053), while PLFs experienced a significant elevation (28.9-->33.7%, p=0.045), with no differences seen in the 2nd caudal adjacent level.
Conclusions: Our results demonstrate that IS preserves not only physiologic contribution to TLROM at the operative level, but at superior adjacent levels as well, with a non-significant increase seen at the caudal adjacent level. In contrast, the relative loss of motion at the operative level in fusions is compensated for by significantly elevated relative motion at both the 1st superior and the 1st inferior adjacent levels.
Patient Care: A better understanding of the resultant spinal kinematics following interlaminar stabilization will allow an assessment of whether or not a motion-preserving stabilizing device, as an alternative to fusion, may positively impact on the ultimate fate of the adjacent levels.
Learning Objectives: By the conclusion of this session, participants should be to: 1) Describe the importance of segmental contribution to total range of motion that occurs as a result of either motion-preserving interlaminar stabilization, or fusion; 2) Discuss, in small groups, the potential impact that this motion-preserving device may have on the possibility of protecting the adjacent levels from breakdown; 3) Identify an effective treatment for stenosis and low-grade spondylolisthesis that allows for direct neural decompression, yet maintains physiologic distribution of lumbar segmental range of motion.