Applications in Musculoskeletal Disorders - part 2 docx

A shock wave is defined as an acoustic wave, at the front of which pressure rises from the ambi-ent value to its maximum within a few nanosec-onds Krause 1997, Ogden et al.. According to

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Contents

1 Physical Characteristics of Shock

Waves 1

Physics 1

Acoustic Properties of Media 2

Cavitation 3

Shock Wave Generation 4

2 Dose-Dependent Effects of Extra-corporeal Shock Waves on Rabbit Achilles Tendon 7

Introduction 7

Material s and Methods 8

Resul ts 10

Sonography 10

Histopathology 11

Discussion 14

3Dose-Dependent Effects of Extra-corporeal Shock Waves on Rabbit Sciatic Nerve 17

Introduction 17

Resul ts 18

Discussion 21

4 Dose-Dependent Effects of Extra-corporeal Shock Waves in a Fibular-Defect Model in Rabbits 23

Introduction 23

Resul ts 27

Discussion 29

5 Extracorporeal Shock Wave Application in the Treatment of Chronic Plantar Fasciitis 33

Introduction 33

Inclusion Criteria 33

Exclusion Criteria 33

Randomization 33

Group I 33

Group II 33

Method of Treatment 35

Method of Eval uation 36

Primary Outcome Measure 36

Secondary Outcome Measures 36

Statistics 36

Resul ts 36

Follow-up 36

Primary Outcome Measure 36

Secondary Outcome Measures 36

Pressure Pain 36

Night Pain and Resting Pain 36

Walking 36

Radiographic Evaluations 36

Complications 36

Additional Treatment between 3 and 6 Months 36

Additional Treatment during the 5 Years 36

Discussion 36

Concl usion 36

6 Extracorporeal Shock Wave Application in the Treatment of Chronic Tennis Elbow 39

Introduction 39

Group I 41

Group II 41

Statistics 43

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X

Resul ts 44

Additional Treatment 44

Complications 44

Discussion 45

Concl usion 45

7 Extracorporeal Shock Wave Application in the Treatment of Chronic Calcifying Tendinitis of the Shoulder 49

Introduction 49

Group I 51

Group II 51

Radiological Evaluation 54

Statistics 54

Resul ts 54

Rate of Follow-up 54

Clinical Outcome in the University of California Los Angeles Score 54

Radiological Outcome 55

Radiomorphological Features and Clinical Outcome 56

Hospital Stay 57

Absence from Work 57

Complications 57

Subjective Rating 57

8 Extracorporeal Shock Wave Application in the Treatment of Nonunions 61

Introduction 61

Resul ts 64

Discussion 67

References 71

Index 79

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Fig 1.1 A typical shock wave

is characterized by a positive

pressure step (P + ) having an

extremely short rise time (t r ),

followed by an exponential

decay to ambient pressure It

typically lasts several hundred

nanoseconds.

Physics

Shock waves are the result of the phenomenon

that creates intense changes in pressure, as

evidenced in lightning or supersonic aircraft

These huge changes in pressure produce

strong waves of compressive and tensile forces

that can travel through any elastic medium

such as air, water, or certain solid substances

A shock wave is defined as an acoustic wave, at

the front of which pressure rises from the

ambi-ent value to its maximum within a few

nanosec-onds (Krause 1997, Ogden et al 2001, Ueberle

1997, Wess et al 1997) Typical characteristics

are high peak-pressure amplitudes (500 bar)

with rise times of less than 1 0 nanoseconds, a

short lifecycle (10 ms), and a frequency

spec-trum ranging from the audible to the far end of

the ultrasonic scale (16 Hz–20 MHz)

As shown in Figure 1.1, the pressure rapidly

rises from ambient values to the peak value,

the so-called peak positive pressure (P+), then drops exponentially to zero and negative val-ues within microseconds This pressure versus time curve describes the transient shock wave

at one specific point-like location of the pres-sure field

The pressure disturbance is transient and propagates in three-dimensional space To obtain spatial information on the total shock wave field, numerous samples of the shock waves have to be collected Three-dimensional plots of the P+-values may then give an impression of the pressure field distribution The pulse energy needs to be focused in order to be applied where treatment is needed According to the spatial distribution

of the pressure, the focus of the shock wave is defined as the location of the maximum peak positive acoustic pressure P+ In relation to P+

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Fig 1.2 Three-dimensional pressure distribution

within the x,y,and z plane.

as the reference, the –6 dB focal extent in the x,

y, and z-directions is physically defined by the

–6 dB contour around the focus location In

other words, the focal dimensions are

deter-mined by half of the peak positive pressure

(P+/2) contour (Fig 1.2) This typical

“cigar-shaped” focal extent of the device usually

cov-ers an area of about 50 mm in the axis of the

shock wave axis, with a diameter of 4.0 mm

per-pendicular to the shock wave axis (focal width)

Concentrating the focus of the shock wave field

therefore is of paramount importance for successful therapy (Hagelauer et al 2001) Many physical effects depend on the energy involved Thus, shock wave energy is deemed

to be an important parameter for clinical application, too The energy of the shock wave field is calculated by taking the time integral

over the pressure/time function (Fig 1.1) at

each particular location of the pressure field, for example, in the focal area:

Energy (E) = 1/U c @ ( @ p2(t,A)dt)dA Unit: millijoule (mJ)

A: area in which the shock wave is existent

U : density of the propagation medium c: propagation velocity

p: pressure t: time The concentrated shock wave energy per area

is another important parameter Physicists use the term “energy flux density” to illustrate the fact that the shock wave energy flows through

an area with perpendicular orientation to the direction of propagation It is a measure of the energy per square area that is being released

by the sonic pulse at a specific point:

Energy Flux Density (ED) = dE/dA = 1/U c @ ( @ p2(t)dt)

Unit: millijoule/millimeter2

(mJ/mm2

)

Acoustic Properties of Media

Media are distinguished by their different

mechanical properties, such as elasticity and

compressibility These parameters affect sonic

waves by determining the propagation speed

c, as well as the acoustic impedance Z = U c,

the product of density U and speed of sound c

(unit: newtonsecond/meter3; Ns/m3) Water

(1.48 × 106

Ns/m3

), fat tissue (1.33 × 106

Ns/m3

), and muscle tissue (1 67 1 06Ns/m3) have a

sim-ilar impedance The impedance of air is much

lower (429 Ns/m3); the impedance of bone is

much higher (6.6 × 106Ns/m3) If the

imped-ance of two media is different, a part of the

shock wave energy is reflected The specific reflected sound amplitude pris calculated as follows: pr= p0(Z2– Z1)/(Z2+ Z1)

where Z1 and Z2 are the impedances of medium 1and of medium 2, respectively The reflected energy is calculated from the square

of the amplitude

If the impedance of the second medium is lower than the first, the polarity of the reflected pressure is reversed, i.e., positive pressure becomes negative pressure or underpressure This is especially the case at interfaces between tissue and air, for example, at the

1 Physical Characteristics of Shock Waves

2

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Fig 1.3 If concretions are

impacted in the surrounding

tissue,the so-called Hopkins

effect leads to destruction

beginning at the rear side of

the concretion because the

tensile strength is exceeded

due to the underpressure.

interface of lung tissue Because nearly all the

energy is reflected at this interface, the

deli-cate alveolar tissue is unable to resist the

mechanical forces of the shock wave and will

disrupt

The effect of pressure reversal also occurs at

another interface: When the shock wave

transmitted into a calcific deposit or into bone

hits the posterior border of this medium, a

portion of the shock wave is reflected into the

deposit or into the bone as negative pressure, because the muscle tissue at the back of the deposit or the bone has a lower impedance than the deposit or the bone This reflected wave is then superimposed with the later overpressure portion of the incident wave so that particularly strong tensile forces act on the rear of the deposit or the bone (Hopkins

effect) (Fig 1.3).

Cavitation

Cavitation is defined as the occurrence of

gas-filled hollow bodies in a liquid medium Stable

cavitation bubbles are in equilibrium when

the vapor pressure inside the bubble is equal

to the external pressure of the liquid

When a shock wave hits a cavitation bubble,

the increased external pressure causes the

bubble to shrink, whereby the latter absorbs

part of the sonic energy If the excitant

ener-gies and consequent forces are strong enough,

the bubble collapses, thereby releasing part of

the energy stored in the bubble to the liquid

medium as a secondary shock wave The

radius of a cavitation bubble is about

500 micrometer in water The bubble

col-lapses about 2–3 microseconds after being hit

by the shock wave The resulting collapse pressure of the secondary wave is about one-tenth of the initial shock wave pressure and exists for about 30 nanoseconds Thus, the sonic energy released by the collapsing bub-ble is less by a factor of 1000 than that of the excitant shock wave

Due to the one-sided impact of the excitant shock wave the bubble collapses asymmetri-cally, sending out a jet of water This jet can reach speeds of 100–800 m/s, sufficient, for example, to perforate aluminum membranes

or plastics The needle-shaped hemorrhages (petechiae) on the skin after shock wave

ther-Cavitation 3

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Fig 1.4 Gas-filled bubbles

are first compressed by the positive peak pressure of the shock wave,then expand dramatically due to the underpressure compo-nent of the shock wave.

apy (SWT) are attributed to this cavitation

effect

The underpressure part of the initial shock

wave leads to a contrary effect: microbubbles

grow during underpressure They may reach a

stable size which can be three orders of

mag-nitude larger than the nucleus and can exist for several hundred microseconds If these bubbles are hit by a following shock wave, once again a collapse with cavitation effects is

produced (Fig 1.4).

Shock Wave Generation

Extracorporeal shock waves used in medicine

today are emitted as a result of

electromag-netic, piezoelectric, or electrohydraulic

gener-ation All studies presented in this book were

done using a source of electromagnetic shock

waves

Electromagnetic systems utilize an

electro-magnetic coil and an opposing metal

mem-brane A high current impulse is released

through the coil to generate a strong magnetic

field, which induces a high current in the

opposing membrane, accelerating the metal

membrane away from the coil to the

100,000-fold of gravity, thus producing an acoustic

impulse in surrounding water The impulse is

focused by an acoustic lens to direct the shock

wave energy to the target tissue The lens

con-trols the focus size and the amount of energy

produced within the target (Fig 1.5).

Piezoelectric systems are characterized by

mounting piezoelectric crystals to a spherical

surface When a high voltage is applied to the crystals they immediately contract and expand, thus generating a pressure pulse in surrounding water The pulse is focused by means of the geometrical shape of the sphere

(Fig 1.6).

Electrohydraulic systems incorporate an electrode, submerged in a water-filled hous-ing comprised of an ellipsoid and a patient interface The electrohydraulic generator initi-ates the shock wave by an electrical spark pro-duced between the tips of the electrode Vaporization of the water molecules between the tips of the electrode produce an explosion, thus creating a spherical shock wave The wave is then reflected from the inside wall of

a metal ellipsoid to create a focal point of shock wave energy in the target tissue The size and shape of the ellipsoid control the focal size and the amount of energy within

the target (Fig 1.7).

1 Physical Characteristics of Shock Waves

4

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Fig 1.5 Electromagnetic

shock wave generator.

Fig 1.6 Piezoelectric shock wave generator Fig 1.7 Electrohydraulic shock wave generator.

Shock Wave Generation 5

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2 Dose-Dependent Effects of Extracorporeal Shock Waves

on Rabbit Achilles Tendon

Introduction

Several areas of biomedical research on shock

waves have evolved over the last decade

fol-lowing the introduction of extracorporeal

shock wave lithotripsy into clinical medicine

by Chaussy et al (1980) One major issue

which has been evaluated is related to tissue

effects following shock waves In animal

experiments, it was found that shock waves

create tissue damage in different organs in the

form of vascular damage, primarily involving

the vessel wall Capillaries and veins are

espe-cially involved with focal destruction and

con-secutive haemorrhage Adjacent parenchymal

tissue in the focal area is not spared and

for-mation of venous thrombi is possible

(Bruem-mer et al 1990, Delius 1994, 1997)

Over the past 10years, there have been

sev-eral reports on the beneficial effects of

extra-corporeal shock waves in the treatment of

pseudarthrosis (Rompe et al 2001c,

Schleber-ger and Senge 1992, Valchanou and Michailov

1991, Vogel et al 1997), of calcifying tendinitis

(Loew 1999, Rompe et al 1995, 2001b), and of

tendopathies of the elbow (Rompe et al

1996a, 2001a, vom Dorp 2001) In his review

article, Haupt (1997) mentions the usefulness

of shock waves even in the removal of cement

in replacement prodecures of cemented

endoprostheses, and in the treatment of

avas-cular necrosis of the hip

Beneficial effects of low-energy extracorpo-real shock waves with an energy flux density

up to 0.2 mJ/mm2 coincided with essential points of Melzack’s (1994) concept of hyper-stimulation analgesia High-energy shock waves with an energy flux density of more than 0.2 mJ/mm2, on the other hand, have been shown to induce disintegration of intra-tendinous calcific deposits or enhance growth

of new bone

Concerning the administration of shock waves to tendons, no clinical reports on alter-ation or damage have been published While damaging effects of extracorporeal shock waves on other soft tissues have been exten-sively described—for example, alveolar inju-ries in the lung (Delius et al 1987), subcapsu-lar and pericapsusubcapsu-lar hematomas in the kidney (Köhrmann et al 1994, Schaub et al 1993, Wolff et al 1997), and hepatic necrosis or hematomas (Prat et al 1991, Rawat et al 1991)—the histopathological correlate of shock waves on the tendon and peritendinous tissues has not been investigated thus far The aim of the following study was to evaluate experimentally whether and to what extent extracorporeal shock waves may be harmful

to tendon and adjacent tissue (Rompe et al 1998a)

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Materials and Methods

After approval had been given by the

univer-sity’s Commission for the Prevention of

Cru-elty to Animals, 84 Achilles tendons of 42 New

Zealand rabbits were randomly assigned to

four treatment protocols:

> Group I: 1000 shock wave impulses of an

energy flux density of 0.08 mJ/mm2 (low

energy)

> Group II: 1000 shock wave impulses of an

energy flux density of 0.28 mJ/mm2

(medium energy)

> Group III: 1000 shock wave impulses of an

energy flux density of 0.60 mJ/mm2 (high

energy)

> Group IV: Sham shock wave therapy

(con-trol group)

For randomization, sealed envelopes were

used which were opened immediately before

starting the shock wave application (SWA)

Shock wave energy may be distributed over

large and small areas Physicists use the term

“energy flux density” to illustrate the fact that

the shock wave energy “flows” through an

area with perpendicular orientation to the

direction of propagation Its unit is mJ/mm2

The commonly used unit of kilovolt does not

give any information on the energy in the

focus, and thus this parameter is no longer

recommended for the description of the

med-ical shock wave field (Wess et al 1997)

Extracorporeal shock waves were applied

by an experimental device (OSTEOSTAR,

Sie-mens AG, Erlangen, Germany), characterized

by the integration of an electromagnetic

shock wave generator in a mobile fluoroscopy

unit The shock waves are generated by

pass-ing a strong electric current through a flat coil

This induces a magnetic field, which itself

induces another magnetic field in a metal

membrane overlying the flat coil Just as

simi-lar poles repel each other, so do the generated

magnetic fields of the membrane and the coil

This leads to a sudden movement of the

mem-brane, inducing a shock wave in the

surround-ing liquid By means of an acoustic lens, the

focus of the shock wave source is identical with the center of the C-arm The focal area of the shock waves is defined as the area in which 50% of the maximum energy is reached It has a length of 50mm, in the direc-tion of the shock wave axis, and a radius of 3.5 mm, in the direction perpendicular to the shock wave axis

Prior to extracorporeal shock wave therapy (ESWT) , preparation of each rabbit consisted

of an intramuscular injection of ketamine and atropine sulfate, followed by intravenous anesthesia (ketamine and xylazine) The hind limb was then carefully shaved and the ankle was fixed in neutral position Under ultra-sound control, the tendon was externally marked with a metal clip at 1 cm proximal to the calcaneal insertion Once the marked ten-don was fluoroscopically situated in the cen-ter of the C-arm, the shock wave unit was docked to the lower leg by means of a water-filled cylinder Standard ultrasound gel was used as a contact medium between the cylin-der and the skin One thousand shock wave impulses were administered, with the proce-dure requiring a mean of 32 minutes (20–42 minutes)

The large variation exclusively correlated with the learning curve for the intravenous anesthesia After recovery, the regularly

observed skin erosions (Fig 2.1) were treated

with a disinfectant Sham treatment included

an identical procedure, but the device was not docked to the animal

High resolution ultrasound of the rabbit Achilles tendons was performed from dorsal after sedation with Promazin A Siemens SL

400 with a 7.5 MHz linear array probe was used Strictly longitudinal sections were taken

by an experienced examiner and printed on a thermoprinter (Video Copy Processor P66E, Mitsubishi Electric Corp., Tokyo, Japan) before and from 1–28 days after SWA

The evaluation of the sonograms was per-formed without knowledge of the treatment procedure

2 Dose-Dependent Effects of Extracorporeal Shock Waves on Rabbit Achilles Tendon

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