Altered spinal motion in low back pain associated with lumbar strain and spondylosis.

Study Design We present a patient-specific computer model created to translate two-dimensional (2D) fluoroscopic motion data into three-dimensional (3D) in vivo biomechanical motion data. Objective The aim of this study is to determine the in vivo biomechanical differences in patients with and without acute low back pain. Current dynamic imaging of the lumbar spine consists of flexion-extension static radiographs, which lack sensitivity to out-of-plane motion and provide incomplete information on the overall spinal motion. Using a novel technique, in-plane and coupled out-of-plane rotational motions are quantified in the lumbar spine. Methods A total of 30 participants-10 healthy asymptomatic subjects, 10 patients with low back pain without spondylosis radiologically, and 10 patients with low back pain with radiological spondylosis-underwent dynamic fluoroscopy with a 3D-to-2D image registration technique to create a 3D, patient-specific bone model to analyze in vivo kinematics using the maximal absolute rotational magnitude and the path of rotation. Results Average overall in-plane rotations (L1-L5) in patients with low back pain were less than those asymptomatic, with the dominant loss of motion during extension. Those with low back pain also had significantly greater out-of-plane rotations, with 5.5 degrees (without spondylosis) and 7.1 degrees (with spondylosis) more out-of-plane rotational motion per level compared with asymptomatic subjects. Conclusions Subjects with low back pain exhibited greater out-of-plane intersegmental motion in their lumbar spine than healthy asymptomatic subjects. Conventional flexion-extension radiographs are inadequate for evaluating motion patterns of lumbar strain, and assessment of 3D in vivo spinal motion may elucidate the association of abnormal vertebral motions and clinically significant low back pain.

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:

Group 1 was of asymptomatic subjects, never treated for low back pain.

Group 2 was of acute low back pain, with a normal spine on radiology studies.

Group 3 was of acute low back pain, with radiological findings of lumbar degeneration and spondylosis.

○ Modic changes

○ Degenerative disc disease with Schmorl nodes or disc bulging

○ Spinal canal or foraminal stenosis

○ Disc osteophyte complexes

○ Facet spondyloarthropathy

Exclusion Criteria:

Nondegenerative diseases

Chronic low back pain

Sensory loss

Motor weakness

Prior lumbar spine surgery

Patient Selection:

This study recruited a convenience sample of 30 subjects, 10 subjects in each group with an equal distribution of males and females except for Group 3 (Fig. 1, Table 1).

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

	N = 30
Age, years median (range)	41.7 (23–65)
Group 1: Asymptomatic subjects, never treated for low back pain
Male, n (%)	5 (50)
Spondylosis, n (%)	0 (0)
Group 2: Acute low back pain with a normal spinal radiology studies
Male, n (%)	5 (50)
Spondylosis, n (%)	0 (0)
Group 3: Acute low back pain, with lumbar degeneration and spondylosis
Male, n (%)	6 (60)
Spondylosis, n (%)	10 (100)

○ Healthy, asymptomatic subjects never treated for low back pain.

○ Acute low back pain without radiological evidence of degeneration.

○ Acute low back pain with radiological findings of lumbar degeneration and spondylosis.

Translational Biomechanical Model:

Patient-specific spiral computed tomography scan was used to create 3D models of the L1 through L5 vertebrae.

Model was overlaid with a local coordinate system assigned based on the Standardization and Terminology Committee of the International Society of Biomechanics6 (Fig. 2).

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.

Fluoroscopic video of flexion plus extension motion captured using a pulsed x-ray output at 30 frames per second.

A 3D-to-2D intensity-based image registration method was used to fit the 3D model to the fluoroscopic motion video capture7,8 (Fig. 3).

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).

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.

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).

Table 2

Average in-plane range of motion for the lumbar spine from maximum flexion to maximum extension

Flexion plus extension (degrees)
Type of spine	Mean ± SD	Range of values
Healthy	46.6 ± 10.8	31.0–67.0
Low back pain	44.8 ± 13.6	20.0–62.0
Degenerative	42.5 ± 10.3	28.0–57.0

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

Spine level	Flexion plus extension (degrees)
	Type of spine			Previous literature (author, yr)
	Healthy	Low back pain	Degenerative	Pearcy et al (1984)9	Dvorák (1991)3	White and Panjabi (1990)10
L1–L2	11.8 ± 3.2	11.0 ± 2.1	10.8 ± 2.6	13.0 ± 5.0	11.9	12.0
L2–L3	9.6 ± 3.0	9.7 ± 4.1	9.9 ± 4.2	14.0 ± 2.0	14.5	14.0
L3–L4	12.2 ± 4.5	9.9 ± 4.6	11.1 ± 3.9	13.0 ± 2.0	15.3	15.0
L4–L5	13.1 ± 3.8	14.4 ± 5.7	10.7 ± 3.6	16.0 ± 4.0	18.2	17.0

Note: Pearcy, Dvorák, and White/Panjabi motion values derived from normal asymptomatic volunteers.

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).

Table 4

Average out-of-plane rotations from L1 to L5 derived using the MARM and POR methods

Type of spine	Coupled out-of-plane rotations (degrees)
	MARM			POR
	AR	LB	Summation (AR + LB)	AR	LB	Summation (AR + LB)
Healthy	2.5 ± 1.1	2.9 ± 0.9	5.5 ± 1.9	3.9 ± 1.9	4.9 ± 1.4	8.8 ± 2.9
Low back pain	10.6 ± 2.3	10.6 ± 3.2	21.2 ± 4.8	15.6 ± 4.0	16.1 ± 5.3	31.6 ± 8.2
Degenerative	12.2 ± 5.1	12.6 ± 2.4	24.7 ± 6.7	19.2 ± 7.0	18.3 ± 3.7	37.5 ± 8.6

Abbreviations: AR, axial rotation; LB, lateral bending; MARM, maximum absolute rotational magnitude; POR, path of rotation.

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.

Surgically relevant low back pain has a biomechanical etiology, originating when a loading stress is applied and exacerbated by abnormal motion or balance.

Current radiological studies do not assess abnormal loading stress or motion.

“Dynamic” flexion–extension radiographs are only static images obtained at end-ranges of a 2D sagittal plane.

An in vivo fluoroscopic 3D lumbar model can be used to evaluate abnormal motion patterns in patients.

Our study showed the differences in lumbar spinal motion in healthy asymptomatic subjects, patients with acute low back pain but without spondylosis, and patients with acute low back pain with radiological findings of spondylosis.

Further work is needed to determine the utility of this advanced imaging technique to elucidate patterns of acute and chronic low back pain.

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.