IX Contents 1 Physical Characteristics of Shock Waves 1 Physics 1 AcousticPropertiesofMedia 2 Cavitation 3 ShockWaveGeneration 4 2 Dose-Dependent Effects of Extra- corporeal Shock Waves on Rabbit Achilles Tendon 7 Introduction 7 MaterialsandMethods 8 Results 10 Sonography 10 Histopathology 11 Discussion 14 3 Dose-Dependent Effects of Extra- corporeal Shock Waves on Rabbit Sciatic Nerve 17 Introduction 17 MaterialsandMethods 17 Results 18 Discussion 21 4 Dose-Dependent Effects of Extra- corporeal Shock Waves in a Fibular- Defect Model in Rabbits 23 Introduction 23 MaterialsandMethods 24 Results 27 Discussion 29 5ExtracorporealShockWave Application in the Treatment of Chronic Plantar Fasciitis 33 Introduction 33 MaterialsandMethods 33 Inclusion Criteria 33 Exclusion Criteria 33 Randomization 33 Group I 33 Group II 33 MethodofTreatment 35 MethodofEvaluation 36 Primary Outcome Measure 36 Secondary Outcome Measures 36 Statistics 36 Results 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 6Months 36 Additional Treatment during the 5 Years 36 Discussion 36 Conclusion 36 6ExtracorporealShockWave Application in the Treatment of Chronic Tennis Elbow 39 Introduction 39 MaterialsandMethods 40 Inclusion Criteria 40 Exclusion Criteria 41 Group I 41 Group II 41 MethodofTreatment 41 MethodofEvaluation 43 Statistics 43 ContentsX Results 44 Additional Treatment 44 Complications 44 Discussion 45 Conclusion 45 7ExtracorporealShockWave Application in the Treatment of Chronic Calcifying Tendinitis of the Shoulder 49 Introduction 49 MaterialsandMethods 49 Inclusion Criteria 50 Exclusion Criteria 50 Group I 51 Group II 51 MethodofTreatment 53 MethodofEvaluation 53 Radiological Evaluation 54 Statistics 54 Results 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 8ExtracorporealShockWave Application in the Treatment of Nonunions 61 Introduction 61 MaterialsandMethods 61 Inclusion Criteria 61 Exclusion Criteria 63 MethodofTreatment 63 MethodofEvaluation 64 Results 64 Discussion 67 References 71 Index 79 Fig. 1.1 Atypicalshockwave is characterized by a positive pressure step (P + )havingan extremely short rise time (t r ), followedbyanexponential decay to ambient pressure. It typically lasts several hundred nanoseconds. 1 Physical Characteristics of Shock Waves 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 shockwaveis defined as an acousticwave,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) withrisetimesoflessthan10nanoseconds,a short lifecycle (10ms), and a frequency spec- trum ranging from the audible to the far end of the ultrasonic scale (16Hz–20MHz). 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 timecurvedescribesthetransientshockwave 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 waveshavetobecollected.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 ordertobeappliedwheretreatmentis 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 + 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,andz-directionsisphysicallydefinedbythe –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- ersanareaofabout50mmintheaxisofthe 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/ c ( p 2 (t,A)dt)dA Unit: millijoule (mJ) A: area in which the shock wave is existent : 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 directionofpropagation.Itisameasureofthe energy per square area that is being released by the sonic pulse at a specific point: Energy Flux Density (ED) = dE/dA = 1/ c ( p 2 (t)dt) Unit: millijoule/millimeter 2 (mJ/mm 2 ) 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 = c, the product of density and speed of sound c (unit: newtonsecond/meter 3 ;Ns/m 3 ). Water (1.48 × 10 6 Ns/m 3 ), fat tissue (1.33 × 10 6 Ns/m 3 ), andmuscletissue(1.6710 6 Ns/m 3 )haveasim- ilar impedance. The impedance of air is much lower (429Ns/m 3 ); the impedance of bone is much higher (6.6 × 10 6 Ns/m 3 ). If the imped- ance of two media is different, a part of the shock wave energy is reflected. The specific reflected sound amplitude p r is calculated as follows: p r =p 0 (Z 2 –Z 1 )/(Z 2 +Z 1 ) where Z 1 and Z 2 are the impedances of medium 1 and of medium 2, respectively. The reflected energy is calculated from the square of the amplitude. Iftheimpedanceofthesecondmediumis 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 Waves2 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 portionoftheshockwaveisreflectedintothe 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 totheexternalpressureoftheliquid. 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 100–800m/s, sufficient, for example, to perforate aluminum membranes or plastics. The needle-shaped hemorrhages (petechiae) on the skin after shock wave ther- Cavitation 3 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 shockwaveenergyinthetargettissue.The size and shape of the ellipsoid control the focalsizeandtheamountofenergywithin the target (Fig. 1.7). 1 Physical Characteristics of Shock Waves4 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 Page intentionally left blank 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 10 years, 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/mm 2 coincided with essential points of Melzack’s (1994) concept of hyper- stimulation analgesia. High-energy shock waveswithanenergyfluxdensityofmore than 0.2 mJ/mm 2 , 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 pericapsular 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). 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/mm 2 (low energy) Group II: 1000 shock wave impulses of an energy flux density of 0.28mJ/mm 2 (medium energy) Group III: 1000 shock wave impulses of an energy flux density of 0.60mJ/mm 2 (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/mm 2 . 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- mensAG,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 50 mm, 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)weretreated 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 7.5MHz 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 Tendon8 . Extra- corporeal Shock Waves in a Fibular- Defect Model in Rabbits 23 Introduction 23 MaterialsandMethods 24 Results 27 Discussion 29 5ExtracorporealShockWave Application in the Treatment of Chronic. 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 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