In vivo range of motion of the lumbar spinous processes

Abstract

The study design included an in vivo laboratory study. The objective of the study is to quantify the kinematics of the lumbar spinous processes in asymptomatic patients during un-restricted functional body movements with physiological weight bearing. Limited data has been reported on the motion patterns of the posterior spine elements. This information is necessary for the evaluation of traumatic injuries and degenerative changes in the posterior elements, as well as for improving the surgical treatment of spinal diseases using posterior procedures. Eight asymptomatic subjects with an age ranging from 50 to 60 years underwent MRI scans of their lumbar segments in a supine position and 3D models of L2–5 were constructed. Next, each subject was asked to stand and was positioned in the following sequence: standing, 45° flexion, maximal extension, maximal left and right twisting, while two orthogonal fluoroscopic images were taken simultaneously at each of the positions. The MRI models were matched to the osseous outlines of the images from the two orthogonal views to quantify the position of the vertebrae in 3D at each position. The data revealed that interspinous process (ISP) distance decreased from L2 to L3 to L4 to L5 when measured in the supine position; with significantly higher values at L2–3 and L3–4 compared with L4–5. These differences were not seen with weight-bearing conditions. During the maximal extension, the ISP distance at the L2–3 motion segment was significantly reduced, but no significant changes were detected at L3–4 and L4–5. During flexion the ISP distances were not significantly different than those measured in the MRI position at all segments. Going from the left to right twist positions, the L4–5 segment had greater amounts of ISP rotation, while all segments had similar ranges of translation in the transverse plane. The interspinous process distances were dependent on body posture and vertebral level.

Appendix

In addition to the shortest ISP distances, we also measured and compared the ISP distances at the approximated ISPD locations. Using a geometric technique, smooth tangential curves were drawn through the outermost tips of the spinous processes of L2–5 from the sagittal MRI images. The curve was offset 1 cm towards the vertebral body to replicate the location of ISPDs [3]. The ISP distance between “a” and “b” was measured at each level (Fig. 6). When measuring this distance, we anticipated that we would find similar trends and statistical differences with larger numerical values when compared with our initial technique of measuring the shortest distances.

Fig. 6

Tangential curve through the outmost tips of processes was offset by 1 cm. Distance was measured between intersection points A and B. Shortest ISP distance was also shown for reference

The ISP distances between “a” and “b” were determined at the L2–3, L3–4 and L4–5 segments for the MRI, standing, extension and flexion positions (Table 3). During movement activities, the distances between the motion segments decreased from the supine position at the time of the MRI scan to the standing position during the fluoroscopic imaging. Statistical significance was found for the L2–3 (P = 0.017) and L3–4 (P = 0.021) motion segments, but not for L4–5 (P = 0.742). They also slightly decreased when going from standing to maximal extension, but no statistical difference was determined (P > 0.05). Predictably, they increased significantly when going from standing to maximal flexion for L2–3 (P = 0.016) and L3–4 (P = 0.002), but not significantly for L4–5 (P = 0.216). They also increased when going from the extension to the flexion position, but no significance was found for any of the three segments that were tested (P > 0.05) (Fig. 7).

Table 3 Distance at the location between “a” and “b”

Fig. 7

Distance between processes measured between “a” and “b” at various postures and different levels (*P < 0.05)

Using this technique, the ISP distances were also compared between different vertebral levels. The only significant difference was noticed in the MRI (supine) position. The L4–5 distance was found to be significantly smaller than the L2–3 (P = 0.002) and L3–4 (P = 0.016) distances. The distance changes that occurred while going from the flexion to the extension positions were also determined and were as follows: L2–3 = 4.4 ± 4.5 mm, L3–4 = 5.1 ± 4.5 mm and L4–5 = 2.5 ± 2.7 mm. No significance was seen between the different levels during this positional change (Fig. 8). Overall, the values were on average 0.5–1.5 mm larger than those obtained when measuring the shortest ISP distances. However, similar trends and statistical differences were noticed as was anticipated. It is, therefore, conceivable that either set of values can be used as a reference for future studies.

Fig. 8

Distance change between processes during flexion and extension at different levels, measured between “a” and “b”