Abstract
Introduction
Numerous studies have been conducted to investigate the kinematics of the lumbar spine, and while many have documented its intricacies, few have analyzed the complex coupled out-of-plane rotations inherent in the low back. Some studies have suggested a possible relationship between patients having low back pain (LBP) or degenerative conditions in the lumbar region and various degrees of restricted, excessive, or poorly-controlled lumbar motion. Conversely, others in the orthopedic community maintain there has been no distinct correlation found between spinal mobility and clinical symptoms. The objective of this study was to evaluate both the in-plane and coupled out-of-plane rotational magnitudes about all three motion axes in both symptomatic and asymptomatic patients.
Methods
Ten healthy, 10 LBP, and 10 degenerative patients were CT scanned and evaluated under fluoroscopic surveillance while performing flexion/extension of the lumbar spine. Three-dimensional, patient-specific bone models were created and registered to fluoroscopic images using a 3D-to-2D model fitting algorithm. In vivo kinematics were derived at specified increments and the overall in-plane flexion/extension and coupled out-of-plane rotations were analyzed using two techniques. The first method derived the maximal absolute rotational magnitude (MARM) at each level by subtracting the rotational motion in the increment exhibiting the most negative or least amount of rotation from the increment having the greatest amount of rotation. The second method was designed to isolate the path of rotation (POR) of the vertebrae at each level while performing the prescribed flexion/extension activity. By tracking the rotational path of the cephaled vertebrae as it articulated upon the more caudal vertebrae and summing the absolute rotation between each increment about each axis the POR was calculated over the entire flexion/extension activity.
Results
Using both the MARM and POR methods, the average overall in-plane rotations between L1 and L5 were not significantly different among any of the groups, although the degenerative group did exhibit less in-plane range-of-motion compared to the healthy and LBP patients. At the L4–L5 level, patients in the healthy and LBP groups achieved 13.1° and 14.4° of rotation, respectively, compared to only 10.7° in the degenerative group. In addition, both of the symptomatic patient groups experienced less rotation during the extension phase of the activity. The coupled out-of-plane motions in both the LBP and degenerative subjects were significantly greater than those observed in healthy subjects (p=0.0199 and p<0.001, respectively). On average, LBP and degenerative patients achieved 5.5° and 7.1° more out-of plane rotational motion per level, respectively, compared to healthy subjects.
Conclusions
These findings correlate with previous studies documenting paradoxical motions in the lumbar spine during an overall gross motion and support the idea of pain being a biological response to tissue injury which may result from excessive kinetic energy introduced into the biological system. Identification of these aberrant motion path magnitudes may aid in recognizing possible causes of pain in patients suffering from non-specific low back problems. Increased magnitudes of out-of-plane rotational paths observed in symptomatic patients may also be an indicator for progressive pathologies requiring surgical intervention in the lumbar spine region.
