The Coflex® vs. Fusion U.S. FDA I.D.E. Trial –
An in vivo Biomechanical Study of Adjacent Segment Motion Following Fusion
Podium presentation at North American Spine Society
27th Annual Scientific Meeting
Dallas, October 2012
27th Annual Scientific Meeting
Dallas, October 2012
Abstract
Background Context:
Numerous in vitro biomechanical studies have reported increased motion and stresses at segments adjacent to a simulated lumbar spinal fusion. However, some authors have questioned the methodology & hence, the findings of these cadaveric studies. Questions remain regarding the optimal methodology to replicate in vivo conditions; in particular, should in vitro models use displacement, load or hybrid control? The recent FDA trial, which examined the Coflex® interlaminar device, included an examination of overall lumbar spinal and segmental motion using digital quantitative motion analysis (QMA™). QMA™ has been found to be accurate to within 0.5-1°.
Purpose:
To prospectively examine in vivo lumbar segmental motion before and after fusion to help resolve questions regarding: firstly, the affects of fusion on adjacent segment motion and secondly, the optimization of in vitro methodology.
Study Design/Setting:
In vivo biomechanical study of patients participating in a multicenter, prospective, randomized FDA IDE trial.
Patient Sample:
190 patients randomized 2:1 to the investigational (decompression + Coflex® interlaminar device) or control (decompression + instrumented, posterolateral fusion) arms. Inclusion criteria: back pain (VAS>50) with neurogenic claudication. ODI>40. Moderate or severe canal stenosis and up to Grade 1 degenerative spondylolisthesis. Mean age: 62.5 years ±9(StDev).
Outcome Measures:
Individual lumbar segmental and overall (L1-S1) range-of-motion (ROM) in degrees.
Methods:
Dynamic x-rays were examined pre-operatively and at regular time-intervals for a minimum 24-months using QMA™. Total lumbar (L1-S1) range-of-motion (ROM°), motion at the index level(s) and motion at one level above, two levels above and one level below are reported in this study. Non-parametric statistics were used with significance set at p<0.05. Results are shown as means (± Standard Deviation)
Results:
In the 45 patients who underwent 1-level and 24 patients who underwent 2-level fusions, a trend toward increased ROM was evident at the segments immediately above the fused segments at 12-months: pre-operative ROM measured 3.4°(±3.3°) and 3.8°(±2.8°) in the 1- and 2-level fusions, respectively and measured 4.6°(±4.6°, p=0.08) and 5.2°(±4.3°, p=0.18) at 12-months. By 24-months, ROM at these segments had increased further & significantly to: 4.9°(±4.5°, p=0.035) above 1-level and 7.6°(±4.8°, p=0.0005) above 2-level fusions. The mean increase in ROM above 2-level fusions at 24-months was 3.7°(95%CI:1.8°-5.6°). A small but apparently significant increase in ROM was seen at 24-months at the level immediately below 1-level fusions (1.6°, p=0.02). Otherwise, no significant changes in ROM were observed at segments two-levels above or one-level below the fusions. In the 1-level fusion patients, ROM at the fused levels decreased by 2.8° at both 12- and 24-months. In the 2-level fusion patients, mean ROM at the fused segments reduced by 4.0° and 3.6° at 12 & 24-months, respectively (p<0.0001). Despite the reduction in motion at the fused segments, total (L1-S1) ROM did not change over the pre-, 12- and 24-month time-points: 20.4°(±13.1°), 19.8°(±13.2°, p=0.62), 22.2°(±13.3°, p=0.33), respectively. No significant changes were observed in any motion parameters in patients implanted with the Coflex® device.
Conclusions:
The current in vivo study has shown a trend, both over time and with more fused levels, towards increasing ROM at levels immediately above a spinal fusion – most apparent at 24-months, above 2-level fusions, where a two-fold increase in mean ROM was evident. While inter- and intra-patient variations were observed, likely related to factors such as patient effort or pain, analysis of mean values over 12 & 24-months showed no significant change in L1-S1 ROM, despite significant reductions in motion associated with fused segments. This would appear to indicate that the presence of a fusion does not naturally lead to a reduction in patients’ subsequent L1-S1 ROM and that displacement or hybrid control in vitro methodology may be appropriate. Examination of x-rays at additional post-operative time points may confirm the apparent trend towards increasing motion, evident at segments above fusions, over time. If so, this finding may also require attention in in vitro experimental methodology.
Background Context:
Numerous in vitro biomechanical studies have reported increased motion and stresses at segments adjacent to a simulated lumbar spinal fusion. However, some authors have questioned the methodology & hence, the findings of these cadaveric studies. Questions remain regarding the optimal methodology to replicate in vivo conditions; in particular, should in vitro models use displacement, load or hybrid control? The recent FDA trial, which examined the Coflex® interlaminar device, included an examination of overall lumbar spinal and segmental motion using digital quantitative motion analysis (QMA™). QMA™ has been found to be accurate to within 0.5-1°.
Purpose:
To prospectively examine in vivo lumbar segmental motion before and after fusion to help resolve questions regarding: firstly, the affects of fusion on adjacent segment motion and secondly, the optimization of in vitro methodology.
Study Design/Setting:
In vivo biomechanical study of patients participating in a multicenter, prospective, randomized FDA IDE trial.
Patient Sample:
190 patients randomized 2:1 to the investigational (decompression + Coflex® interlaminar device) or control (decompression + instrumented, posterolateral fusion) arms. Inclusion criteria: back pain (VAS>50) with neurogenic claudication. ODI>40. Moderate or severe canal stenosis and up to Grade 1 degenerative spondylolisthesis. Mean age: 62.5 years ±9(StDev).
Outcome Measures:
Individual lumbar segmental and overall (L1-S1) range-of-motion (ROM) in degrees.
Methods:
Dynamic x-rays were examined pre-operatively and at regular time-intervals for a minimum 24-months using QMA™. Total lumbar (L1-S1) range-of-motion (ROM°), motion at the index level(s) and motion at one level above, two levels above and one level below are reported in this study. Non-parametric statistics were used with significance set at p<0.05. Results are shown as means (± Standard Deviation)
Results:
In the 45 patients who underwent 1-level and 24 patients who underwent 2-level fusions, a trend toward increased ROM was evident at the segments immediately above the fused segments at 12-months: pre-operative ROM measured 3.4°(±3.3°) and 3.8°(±2.8°) in the 1- and 2-level fusions, respectively and measured 4.6°(±4.6°, p=0.08) and 5.2°(±4.3°, p=0.18) at 12-months. By 24-months, ROM at these segments had increased further & significantly to: 4.9°(±4.5°, p=0.035) above 1-level and 7.6°(±4.8°, p=0.0005) above 2-level fusions. The mean increase in ROM above 2-level fusions at 24-months was 3.7°(95%CI:1.8°-5.6°). A small but apparently significant increase in ROM was seen at 24-months at the level immediately below 1-level fusions (1.6°, p=0.02). Otherwise, no significant changes in ROM were observed at segments two-levels above or one-level below the fusions. In the 1-level fusion patients, ROM at the fused levels decreased by 2.8° at both 12- and 24-months. In the 2-level fusion patients, mean ROM at the fused segments reduced by 4.0° and 3.6° at 12 & 24-months, respectively (p<0.0001). Despite the reduction in motion at the fused segments, total (L1-S1) ROM did not change over the pre-, 12- and 24-month time-points: 20.4°(±13.1°), 19.8°(±13.2°, p=0.62), 22.2°(±13.3°, p=0.33), respectively. No significant changes were observed in any motion parameters in patients implanted with the Coflex® device.
Conclusions:
The current in vivo study has shown a trend, both over time and with more fused levels, towards increasing ROM at levels immediately above a spinal fusion – most apparent at 24-months, above 2-level fusions, where a two-fold increase in mean ROM was evident. While inter- and intra-patient variations were observed, likely related to factors such as patient effort or pain, analysis of mean values over 12 & 24-months showed no significant change in L1-S1 ROM, despite significant reductions in motion associated with fused segments. This would appear to indicate that the presence of a fusion does not naturally lead to a reduction in patients’ subsequent L1-S1 ROM and that displacement or hybrid control in vitro methodology may be appropriate. Examination of x-rays at additional post-operative time points may confirm the apparent trend towards increasing motion, evident at segments above fusions, over time. If so, this finding may also require attention in in vitro experimental methodology.
