SHOCKWAVE
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essentially a pressure disturbance that propagates through a medium.
an acoustic wave that transmits energy
SHockwave therapy is effectively a controlled explosion that enters tx, it will be reflected, refracted, transmitted and displaced like other forms of energy
Definition: A large amplitude compression wave, as produced by an explosion of supersonic motion of a body in a medium
1) HISTORY
Animal experiments leading to adverse effects on bone prompted experimental investigation on cartilage and associated soft tx (ligaments, tendons, fascia)
Clinical uses expanded to wound management and treatment of non-union fractures
Initially used as non invasive treatment for kidney stones
the use of shockwave to treat fractures was researched in 1980's with earliest clinical work being used on delayed and non-union fractures
2) PRINCIPLES OF PRODUCTION
When shockwaves enter living tx it will be reflected, refracted, transmitted or dissipated, just like any other waves
Shockwaves pass nearly unchanged through liquids and hence soft tissue, exerting their effects where there is a
change of acoustic impedance along their path
Shockwave energy is released at these interfaces of different impedance values
Extracorporeal shockwaves are pressure waves generated acoustically (thunder after a flash of lightening)
The rapid interaction between the compression and shear force results in what is known as cavitation
where there is a change in structure, part of the shockwave energy will be released and create a compression and shear loads on the surface of the material with the greater impedence
Microscopic gas bubbles are built up on the surface of the material and the collapse of these bubbles create a small get of liquid that causes high local stress
3) TYPES OF SHOCKWAVE
NON-FOCUSED/RADIAL SHOCKWAVE (SOFT SHOCKWAVE)
FOCUSED (HARD SHOCKWAVE A.K.A LITHOTRIPSY)
Created by mechanical concussion that creates expanding wave fronts away from the concussion plate (end of machine) which travels into the body
waves rapidly attenuate (decrease in force) after generation
GENERATED IN 2 WAYS
Air compressed system
Electromagnetic
bullet in a barrel is accelerated using compressed air to strike an end plate generating the shockwave.
machines are characterised by requiring an air compressor and their shockwave generation is normally referred to in terms of pressure
bullet in barrel accelerated using alternating magnetic fields causing the bullet to strike an end plate creating the shockwave
machines are characterised by their shockwave energy being described in terms of actual energy in millijoules
4) DOSAGE
LOW – UP TO 0.09 mJ/mm2
HIGH – OVER 0.6mJ/mm2
MEDIUM – UP TO 0.28 mJ/mm2
Radial shockwave = non-focused shockwave because it is not reflected or redirected towards a focal point in the pts body
radial shockwave energy declines rapidly in proportion to the distance from the site of generation; radial shockwaves loose power the deeper they go into the body
E.G. convex 15mm head delivers its energy across the head radially. at 3.0 bar the axial penetration is 3.9cm
treatment depth or effective distance for therapeutic purposes could be said to be the Rayleigh wave distance (mid distance from the treatment head)
further than the mid distance the waves loose so much energy they are no longer effective
using a hand held applicator these waves are transmitted up to 35mm into pts body
Depth of shockwave depends on the force with which it was produced; higher input of energy = deeper shock will travel = more energy will be transmitted into the tissue
shockwaves produced are generally believed to travel out from the head of the machine in a cylindrical shape with very little energy outside the physical size of the head.
i.e. 15mm round head will produce a 15mm round shockwave which will stay the shape of the head as it enters another medium
5) HEAD SIZE AND SHAPE
Radial shockwaves are produced cross the face of the shockwave head; these heads vary in shape and size
most commonly used head is 15mm across and described as convex (head reaches a peak in the center which is higher than the edges)
smaller diameter heads give more energy at the same power setting than a head with bigger area.
6) FREQUENCIES IN SHOCKWAVE TREATMENT
pulse rate frequency (PRF)
higher frequencies (14-15Hz) easier / more comfortable to experience
lower frequencies (8-12Hz) more painful
recommended to start at a high frequency when starting treatment to acclimatise the patient to the sensation then work down to the desired frequency. e.g. 200 @ 16Hz then 200 @ 14Hz then 200 @ 12Hz aiming for 10Hz at the end of 2000 shocks
higher frequencies ( above 5Hz) cause many more cavitation which increase in number with increasing speed/frequency. Although increasing frequency increased the number of cavitations it did not increase the size of those cavitations; only pressure (energy delivery per mm) can do that
low frequencies (0.5Hz -5Hz) cause much less cavitation during treatment ( there is little effect on cavitation bubble lifespan/size)
Increasing frequency affects the depth of wave penetration (lower frequency waves travel further than higher frequency waves)
high frequency waves travel less distance
thus increasing frequency can be used to decrease treatment depth whilst maintaining shock energy
7) OVERALL ENERGY
total energy density = shock head size and amount of E given to the shock and add the total number of shocks given
SHOCKWAVE
8) EFFECTS OF SHOCKWAVES
HEALING (INCREASED)
DECREASE PAIN
DESTRUCTION OF TISSUE
TB treatments over view
HEAD= 15mm
POWER= 2.5 bar
FREQUENCY 4-5Hz
SHOCKS= 1000-4000
HOW OFTEN= every 5 days
No. OF SESSIONS= 1-3 more likely 6+
HEAD= 15-35mm
POWER= 1-2 bar
FREQUENCY= 10-16Hz
SHOCKS 1000 to 1 spot 4000 larger area
HOW OFTEN= every 7-10 days
No. OF SESSIONS 4-6
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HEAD= 6-35mm
POWER= 1-2 bar
FREQUENCY= 15-30Hz
SHOCKS= 1500 one spot 4000 larger area
HOW OFTEN= every 7-10 days
No. OF SESSIONS= 3
the destruction of cells through spalling, spall crack formation or tension; normally requires higher shock pressure and slower speeds. Although for the effect of cavitation higher speeds are most definitely favorable
HOW OFTEN: damage occurs almost instantly, perform the next session before any repair can occur, critical window for healing is 6-12 days, thus treatment for destruction should be performed every 5 days
NUMBER OF SHOCKS: 1000 shocks upwards; 2000 conventional number; figures as high as 4000 have been demonstrated
FREQUENCY: as low as 4Hz up; normal convention= 10Hz; desired result is mainly cavitation then any frequency from 5Hz will do but from 15Hz cavitation will be much better. NB increasing frequency will decrease depth
SESSIONS: 1-3 but may not lead to full resolution, average is 6 though some prominent bone spur don't go in 6
POWER: higher the pressure setting usually the better though post pt can't tolerate high settings initially. (increase for 200 shocks @ a time) anything 2.5 bar or more should have the desired effect
HEAD: 15mm head convex/concave as most structures needing destruction or not that deep. small heads can give far too much energy density to be used for this purpose and they can easily cause skin damage at high pressure.