Acute Mechanical and Functional Effects of Lumbar Mechanical Traction in Healthy Adults: A Randomized Placebo-Controlled Trial

Introduction & Purpose Although mechanical traction (MT) has been used for years to treat people with lower back pain (LBP) (Cavagnaro, 2014; Werners et al., 1999), its possible acute effects are not yet well understood. Mechanical tension is supposed to decrease muscle stiffness and tonus of the muscle and should therefore decrease LBP. However, while Cheng et al. (2020) were able to measure an acute positive effect, Wegner et al. (2013) reported that MT alone or in combination with other interventions has little to no effect on pain of patients with LBP. A reason for these mixed results could be the complex nature of LBP and the missing understanding of the exact mechanical mechanism of MT. Given that the clinical efficacy of MT remains uncertain, understanding its immediate mechanical effects is particularly relevant. Therefore, the aim of this study was to investigate the acute mechanical and functional effects of MT in healthy individuals as a first-step mechanistic assessment. Methods 22 healthy physically active participants (27,8 ± 6,79 years, recruited via personal contact) volunteered for the study and were randomized into two groups: intervention (IG, n=12) and placebo (PG, n=10). Prior to the warm-up and intervention (and following the intervention), participants were asked about current level of LBP through VAS (Bijur et al., 2001). Subsequently, the participants started with a five-minute warm-up on an ergometer with 100 Watts resistance. After the warm-up and following the intervention, we measured muscle stiffness on four measurement points of the M. erector spinae with the MyotonPRO device, maximum isometric force of the M. erector spinae with a handheld dynamometer, pain threshold with an algometer, the flexibility of the posterior chain using a sit-and-reach box, the distance between the spinous processes L4 and L5 with b-mode ultrasound (Aixplorer, Supersonic), and the elasticity of the M. erector spinae with ultrasound (US) shear wave elastography (Aixplorer Supersonic). For the intervention, the participants lay supine on a DORSI traction system (https://dorsi.at/). The intervention for the IG consisted of 10% bodyweight (BW) traction force for the first seven minutes, then one minute break following 13 minutes of 20% BW traction force. For the PG we used 5% BW traction force throughout the whole 20 minutes with a one-minute break after seven minutes. We analyzed the results using paired t-tests to identify within group changes and t-tests between groups’ changes (PRE to POST). Results All participants tolerated the MT very well. Both the IG (Pre: 34,99 ± 5,84 cm; Post: 37,05 ± 5,75 cm, p=0,01) and the PG (Pre: 30,73 ± 10,67 cm; Post: 32,11 ± 9,78 cm, p=0,03) significantly increased the flexibility of the posterior chain without any difference between the groups. The distance between the spinous processes significantly increased from Pre (2,89 ± 0,29 cm) to Post (3,06 ± 0,29 cm, p=0,01) in the IG but remained unchanged in the PG (Pre: 3,18 ± 0,25 cm; Post: 3,11 ± 0,24 cm, p=0,55). This was accompanied with a trend (p=0.07) in the comparison of group’s changes. In contrast, muscle stiffness assessed by elastography decreased in the PG (Pre: 129,31 ± 73,93 kPa; Post: 105,18 ± 58,46 kPa, p=0,01) but not in the IG (Pre: 107,72 ± 71,85 kPa; Post: 80,47 ± 52,67 kPa, p=0,08) without any difference between the groups. There was a significant difference in the group’s changes of pain threshold (p=0,04), however, this changes were not significant in either group (IG: Pre: 69,79 ± 33,91 N; Post: 74,69 ± 43,71 N, p=0,3; PG: Pre: 72,88 ± 20,77 N; Post: 63,29 ± 11,9 N, p=0,07). Muscle stiffness did not change significantly on either of the four measurement points from pre to post. Similarly, the maximum isometric force did not change significantly for the IG (Pre: 32,69 ± 6,8 N; Post: 33,61 ± 11,94 N, p=0,73) or the PG (Pre: 30,53 ± 9,41 N; Post: 29,89 ± 8,61 N, p=0,47). The acute sensation of pain did not change for the IG (Pre: 9,02 ± 18,67%; Post: 3,52 ± 6,90%, p=0,33) or the PG (Pre: 11,75 ± 13,70%; Post: 7,01 ± 10,70%, p=0,34). Neither of these results showed a difference between the groups (p>0.05). Discussion We were able to show that a MT with 20% BW traction force is well tolerated by healthy individuals. The MT significantly increased the distance between the spinous processes (p=0,01), indicating a real stretching effect of the vertebra in the IG. However, muscle stiffness measured with the MyotonPRO did not change. As expected in a healthy sample, baseline pain was minimal and did not change, confirming a floor effect. A particular strength of this study is the comprehensive set of mechanical and functional measures, which allowed a differentiated characterization of the acute effects of MT. However, as the study was conducted in healthy individuals, extrapolation to patients with low back pain is limited; factors such as pain, muscle guarding, and altered tissue properties may substantially modify the response to traction.Moreover, only immediate post-intervention effects were assessed, so neither the duration nor the clinical relevance of the observed changes can be determined. Conclusion The device was well tolerated in this sample of healthy individuals and produced an immediate increase in interspinous distance. As the study addresses only acute mechanical responses, further research in patients with LBP is needed to evaluate any clinical effects. References Bijur, P. E., Silver, W. & Gallagher, E. J. (2001). Reliability of the visual analog scale for measurement of acute pain. Academic emergency medicine: official journal of the Society for Academic Emergency Medicine, 8(12), 1153–1157.     https://doi.org/10.1111/j.1553-2712.2001.tb01132.x Cavagnaro, L. (2014). Lumbar Traction in the Management of Low Back Pain: A Survey of Latest Results. Journal of Novel Physiotherapies, 04(05). https://doi.org/10.4172/2165-7025.1000231 Cheng, Y.‑H., Hsu, C.‑Y. & Lin, Y.‑N. (2020). The effect of mechanical traction on low back pain in patients with herniated intervertebral disks: a systemic review and meta- analysis. 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