In Vitro Biomechanical Evaluation of Single Impulse and Repetitive Mechanical Shockwave Devices Utilized for Spinal Manipulative Therapy

Abstract

Mechanical shockwave therapy devices have been in clinical use for almost 40 years. While most often used to treat back pain, our understanding of their biomechanical performance is very limited. From biomechanical studies we know that biological tissue is viscoelastic and preferably excited around its resonance frequency. Targeting these frequencies has been the focus in extracorporeal shock wave lithotripsy, but these concepts are relatively new in orthopedic and rehabilitation therapies. The exact mechanism by which shockwave therapy acts is not known. Knowledge of the performance characteristics of these devices, correlated with clinical outcome studies, may lead to better patient selection, improvement of device functionality, and knowledge of the underlying working principals of therapy. The objectives of this study were to determine the ability of several commercial shockwave devices to achieve a desired thrust profile in a benchtop setting, determine the thrust profile in a clinical analog, and determine the influence of operator experience level on device performance. We conducted two different types of testing: (1) bench testing to evaluate the devices themselves, and (2) clinical equivalent testing to determine the influence of the operator. The results indicated a significant dependence of thrust output on the compliance of the test media. The Activator V-E device matched the ideal half-sine thrust profile to 94%, followed by the Impulse device (84%), the Activator IV/FS (74%), and the Activator II (48%). While most devices deviated from the ideal profile on the return path, the Impulse device exhibited a secondary peak. Moreover, the Activator V-E device provided evidence that the device performs consistently despite operator experience level. This has been a major concern in manual spinal manipulation. Based on our results, a hyper-flexible spine would receive a lower peak thrust force than a hypo-flexible spine at the same power setting. Furthermore, a hand-held operation further reduced the peak thrust force as it increased the system compliance. However, that influence was dissimilar for the different devices. Although controlled clinical trials are needed to determine the correlation between thrust profile and clinical outcome, already ongoing clinical studies indicate an improved patient satisfaction due to reduced treatment pain when devices are used with a thrust characteristic closer to an ideal sine wave.

Forces of Commonly Used Chiropractic Techniques for Children: A Review of the Literature

“…This search identified 2 articles by Marchand,15,16 which when references were hand searched yielded 3 more articles, by Koch et al 17,18 and Snodgrass et al 19 Searching of the literature using technique-specific search terms resulted in the inclusion of a further 4 studies 16,20-22 and 1 textbook source, 23 with an additional in-press journal article yielding direct contact with the author 24 (Table 1).…”

“…According to Colloca et al, 22 the mean minimum force applied by an Activator I is 61.5 N (Table 2), whereas the Activators II and III apply approximately 137.8 N and 128.2 N, respectively, and the Activator IV applies 123.1 N. 22 These values were measured by fixing the instruments to a stable surface and applying the tip directly to a metal force plate (Fig 2a). However, Liebschner et al 24 argue that the approach to applying and measuring force needs to be analogous to the way in which it is delivered to a human patient and so incorporated a range of polymorphous structures to replicate different levels of tissue stiffness in the human spine (Fig 2b). This use of a spinal analog resulted in notably lower-force recordings ( Table 2).…”

“…Liebschner et al 24 Measurement of peak forces at the minimum and maximum setting on the Activator instruments II, IV, and V and the NMI. Instruments were applied to polymorphous substances (analogous to the spine and surrounding tissue) attached to a force plate.…”

“…The minimum force applied with this instrument was measured with a soft polymorphous substance analogous to a flexible child spine at approximately 40 N. 24 …”

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“…The output of the activator device does not generate enough energy to injure intracranial blood vessels of normal strength and integrity, but more importantly, the type of mechanical output such devices generate is not consistent with the mechanism of blood vessel injury. 1 Activator devices used in chiropractic treatments employ an energy level designed merely for neuromodulation and sensory fiber stimulation. An engineering analysis is required to determine the existence of a mechanism to cause this tissue injury, in addition to the author's temporal analysis, which seems to implicate the device.…”