Keywords
low back pain - lumbar strain - spondylosis - biomechanics - kinematics
Study Rationale
Lumbar flexion–extension radiographs are commonly used to evaluate for abnormal motion and “dynamic” instability, but are of limited value due to the nature of two-dimensional (2D) static images at the end-ranges of sagittal plane motion.[1]
[2]
[3]
[4]
[5]
Objective
We used an in vivo fluoroscopic three-dimensional (3D) lumbar model to assess spinal motion in asymptomatic and symptomatic patients to determine the altered kinematics of lumbar strain associated with low back pain in patients with and without radiological evidence of spondylosis.
Methods
Study Design: We present translational biomechanical study of a patient-specific 3D spinal motion model to determine differences in patients with and without acute low back pain.
Inclusion Criteria:
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Group 1 was of asymptomatic subjects, never treated for low back pain.
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Group 2 was of acute low back pain, with a normal spine on radiology studies.
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Group 3 was of acute low back pain, with radiological findings of lumbar degeneration and spondylosis.
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○ Modic changes
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○ Degenerative disc disease with Schmorl nodes or disc bulging
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○ Spinal canal or foraminal stenosis
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○ Disc osteophyte complexes
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○ Facet spondyloarthropathy
Exclusion Criteria:
Patient Selection:
Fig. 1 Patient selection diagram. Convenience sample of 30 subjects was recruited with 10 subjects in each group based on the inclusion criteria. LBP, low back pain; MARM, maximal absolute rotational magnitude; POR, path of rotation.
Table 1
Patient characteristics
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N = 30
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Age, years median (range)
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41.7 (23–65)
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Group 1: Asymptomatic subjects, never treated for low back pain
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Male, n (%)
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5 (50)
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Spondylosis, n (%)
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0 (0)
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|
Group 2: Acute low back pain with a normal spinal radiology studies
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Male, n (%)
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5 (50)
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|
Spondylosis, n (%)
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0 (0)
|
|
Group 3: Acute low back pain, with lumbar degeneration and spondylosis
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Male, n (%)
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6 (60)
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Spondylosis, n (%)
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10 (100)
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Translational Biomechanical Model:
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Patient-specific spiral computed tomography scan was used to create 3D models of the L1 through L5 vertebrae.
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Model was overlaid with a local coordinate system assigned based on the Standardization and Terminology Committee of the International Society of Biomechanics[6] ([Fig. 2]).
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Fluoroscopic video of flexion plus extension motion captured using a pulsed x-ray output at 30 frames per second.
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A 3D-to-2D intensity-based image registration method was used to fit the 3D model to the fluoroscopic motion video capture[7]
[8] ([Fig. 3]).
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3D rotational magnitudes were analyzed using maximum absolute rotational magnitude, calculated by finding the difference between any two increments representing the minimum and maximum motion observed, and the path of rotation of each functional spinal, tracked as it articulated upon the more caudal vertebrae.
Fig. 2 Data window illustrating the 3D-to-2D image registration process. The vertebra contained in the box is placed over the appropriate vertebral silhouette and the “best fit” is achieved by initializing the global optimization simulated annealing algorithm.
Fig. 3 Sample subject under fluoroscopic surveillance with image frames captured at full extension, 33% of ROM, 66% of ROM, and full forward flexion (top) with completed 3D-to-2D registration of image sequence (bottom).
Results
Patients with clinical and radiological findings achieved less overall in-plane rotation between L1 and L5 ([Table 2]). Intersegmental in-plane rotations were not statistically different among groups, but motion about the flexion–extension axis at L3–L4 and L4–L5 levels were altered in those with acute low back pain ([Table 3]). In comparison with the asymptomatic group, those with acute low back pain had decreased values during extension with an overall loss of in-plane range of motion moving from full flexion to extension. Intersegmental lumbar spine rotation had similar rotational magnitudes but different patterns of rotation among the three groups ([Fig. 4]). Analyses of the out-of-plane rotational motions indicate significantly more motion in those with low back pain compared with asymptomatic subjects ([Table 4], [Fig. 5]). These out-of-plane movements were also indicated when viewing the flexion plus extension activity in the coronal plane ([Fig. 6]).
Fig. 4 Comparison of the intersegmental in-plane rotations relative to the average flexion plus extension of the lumbar spine at four levels (A, L1–L2; B, L2–L3; C, L3–L4; D, L4–L5).
Fig. 5 The combined coupled axial rotation and lateral bending motions representing the average overall intersegmental out-of-plane rotations in three patient spine types derived using both the maximal absolute rotational magnitude (MARM) and path of rotation (POR) techniques.
Fig. 6 A healthy spine, a spine with low back pain, and a degenerative lumbar spine moving from maximum flexion to maximum extension. The line bisecting the stationary L5 vertebrae helps visualize the increased out-of-plane movements in both low back pain and degenerative patients.
Table 2
Average in-plane range of motion for the lumbar spine from maximum flexion to maximum extension
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Flexion plus extension (degrees)
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Type of spine
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Mean ± SD
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Range of values
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Healthy
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46.6 ± 10.8
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31.0–67.0
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Low back pain
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44.8 ± 13.6
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20.0–62.0
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Degenerative
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42.5 ± 10.3
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28.0–57.0
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Abbreviation: SD, standard deviation.
Table 3
Average primary intersegmental in-plane rotation for all groups in the present study compared with data from previous literature
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Spine level
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Flexion plus extension (degrees)
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Type of spine
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Previous literature (author, yr)
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Healthy
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Low back pain
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Degenerative
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Pearcy et al (1984)[9]
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Dvorák (1991)[3]
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White and Panjabi (1990)[10]
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L1–L2
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11.8 ± 3.2
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11.0 ± 2.1
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10.8 ± 2.6
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13.0 ± 5.0
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11.9
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12.0
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L2–L3
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9.6 ± 3.0
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9.7 ± 4.1
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9.9 ± 4.2
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14.0 ± 2.0
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14.5
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14.0
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L3–L4
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12.2 ± 4.5
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9.9 ± 4.6
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11.1 ± 3.9
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13.0 ± 2.0
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15.3
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15.0
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|
L4–L5
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13.1 ± 3.8
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14.4 ± 5.7
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10.7 ± 3.6
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16.0 ± 4.0
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18.2
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17.0
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Note: Pearcy, Dvorák, and White/Panjabi motion values derived from normal asymptomatic volunteers.
Table 4
Average out-of-plane rotations from L1 to L5 derived using the MARM and POR methods
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Type of spine
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Coupled out-of-plane rotations (degrees)
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MARM
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POR
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AR
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LB
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Summation (AR + LB)
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AR
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LB
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Summation (AR + LB)
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Healthy
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2.5 ± 1.1
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2.9 ± 0.9
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5.5 ± 1.9
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3.9 ± 1.9
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4.9 ± 1.4
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8.8 ± 2.9
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Low back pain
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10.6 ± 2.3
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10.6 ± 3.2
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21.2 ± 4.8
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15.6 ± 4.0
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16.1 ± 5.3
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31.6 ± 8.2
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Degenerative
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12.2 ± 5.1
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12.6 ± 2.4
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24.7 ± 6.7
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19.2 ± 7.0
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18.3 ± 3.7
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37.5 ± 8.6
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Abbreviations: AR, axial rotation; LB, lateral bending; MARM, maximum absolute rotational magnitude; POR, path of rotation.
Conclusions
Using a technique involving video fluoroscopy and 3D-to-2D image registration, we were able to measure out-of-plane motions in the lumbar spine that are not detected with conventional lumbar flexion–extension radiographs. This will facilitate the understanding, assessment, and interpretation of clinically significant abnormal vertebral motions.
