L Wiesner, R Kothe, R Abel, KP Schulitz
Dep. of Orthopaedics, Heinrich-Heine-University, Duesseldorf, Germany
The exploration of different causes of low back pain is one of the most challenging problems in temporary spinal research. For many authors degenerative segmental instability is the main mechanical factor in the development of low back pain. In the External Fixation Test the identification of a possible instable segment is based on the subjective information on pain relief given by the patient, which may be influenced by many factors. The purpose of our study was to investigate the correlation between this subjective information on pain relief and 3D-segmental motion patterns measured by a new ultrasound method.
45 patients with low back pain and suspected segmental instability were temporarily fused using an external fixator device. In 35 patients 3 segments were fused (L3-S D, while l0 patients were fused in 4 levels (L2-S l).
External Fixation Test: 5 days after the operation the patients were encouraged to perform the daily activities usually provoking pain. Following a standardized protocol the different spinal segments were then repeatedly fixed and loosened. After each step the patients were asked to fill out a questionnaire about there comfort and pain relief.
3D-Motion Test: Before completely removing the external fixator a newly developed 3DUltrasonic Motion Analyzer (CMS 50/4, Zebris, Germany) was attached to the head of one pedicle screw in each segment. Every patient was examined in active flexion/extension, left/right lateral bending and left/right axial rotation in a standing and sitting position. An ultrasonic receiver allowed the continuos measurement of the ultrasonic signals.
With the External Fixation Test at least one painful segment could be clearly identified in 37 patients, while in 8 patients there was either no pain relief at all or the subjective statements were contradictory. In the 3D-Motion Test the continuos active motion was analyzed in a qualitative manner for each motion direction and each spinal segment separately. The abnormal segmental motion patterns included: 1. Abrupt ending of the main motion; 2. Increased coupled motions; 3 . A zigzag profile of the main motion curve. Based on these findings at least one abnormal motion segment was found in 38 patients. 80% of these abnormal segments were identified as painful in the external fixation test by the patient, while in 4 patients abnormal segmental motion patterns were found although they gave a negative response in the External Fixation Test.
The results of our study have shown that the External Fixation Test is an adequate diagnostic tool for the prediction of segmental instability in the lumbar spine, although its diagnostic value depends considerably on the subjective information given by the patient. Due to this fact the 3DMotion Test is a useful addition to gain objective data for the assessment of spinal instability. Because of the continous measurement not only the range of motion can be determined but also the quality of the segmental motion can be analyzed. Future studies based on this method will address the phenomenon of spinal instability, which may be insufficiently described by simple quantitative measurements like the range of motion.