Why shock wave therapy can’t be imitated in patient care

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Extracorporeal shockwave therapy (ESWT) is a versatile, noninvasive treatment that can induce healing mechanisms for poorly vascularized and chronically injured musculoskeletal tissues, and can provide extended analgesic relief for joints and other tissues with degenerative diseases. Although ESWT applications in other aspects of medicine (eg, lithotripsy) and in human and equine sports medicine have preceded its widespread use in dogs, this therapeutic modality has a rapidly increasing body of evidence to support its application in canine rehabilitation.

Physics

ESWT consists of the conversion of low-frequency, single high-velocity acoustic waves into mechanical energy that is transmitted through tissues according to their acoustic impedance, and is released at tissue interfaces. This creates a rapid pressure wave, followed immediately by a vacuum in pressure and resultant collapse of cavitation bubbles that leads to free radical production, release of anti-inflammatory cytokines, and angiogenic and growth factors at the site of interaction. These changes at the cellular level contribute to enhanced healing mechanisms and improved analgesia at the sites of injury where the tissues interface.¹

Shockwave energy pulses can either be focused or unfocused. The 2 types of focused shockwave generators include electrohydraulic and electromagnetic units. Piezoelectric shockwave therapy creates unfocused pressure waves rather than true shockwaves, which are lower in energy as they create more dispersed, radial waves that also have shallower penetration. Energy released is measured in terms of mJ/mm², and can vary from less than
1 mJ/mm² to more than 6 mJ/mm² in clinical applications. Evidence of efficacy exists for positive outcomes with all 3 types of systems, but the vast majority of available studies have evaluated the use of the electrohydraulic shockwave system.

Tendon and ligament healing

ESWT has demonstrated efficacy in decreasing pain and improving healing of tendons and ligaments in multiple species, including dogs. Specific evidence supports its use in canine patellar ligament desmitis and biceps and supraspinatus tendinopathy.^2,3 Patellar ligament desmitis is a common postoperative complication of tibial plateau leveling osteotomies (TPLOs) in dogs, but the clinical significance of its radiographic changes appears to be variable. That being said, a number of dogs do appear to be clinically affected, and ESWT has demonstrated decreased thickness of the distal patella at 6 and 8 weeks after surgery compared with controls.² TPLOs are a common surgical intervention for military working dogs, and the author has observed a number of cases with radiographic distal patellar ligament thickening and pain on palpation that improved, along with subjective lameness, after 1 to 2 rounds of ESWT.

Results from a study evaluating records of dogs with shoulder tendinopathies (unilateral supraspinatus tendinopathy, unilateral or bilateral biceps tendinopathy) that underwent ESWT with or without therapeutic exercise showed that 85% of dogs had good or excellent outcomes at a range of follow-up times, 11 to 220 weeks after treatment.³ The response appeared to be improved with more severe lesions, but selection bias may be a complicating factor in this retrospective investigation. Another retrospective evaluation of dogs treated with ESWT for shoulder tendinopathies, instability or, in 1 case, osteochondroma, showed improved outcomes despite their having failed prior interventions.⁴ Three of 9 dogs had resolved lameness and 6 of 9 had improved lameness at 3 to 4 weeks post treatment. Longer-term follow-up by telephone suggested either improved lameness or normal gait in 64% of these cases.

Tendons and ligaments can be among some of the most difficult tissues to induce healing, and many historical treatments have included surgical release and/or injection with corticosteroids. Although those interventions may be necessary in the occasional refractory case, ESWT appears to provide a viable, efficacious option for some tendinopathies that have failed to respond to prior conservative management techniques. Mechanisms for tendon and ligament healing through ESWT may include local induction of blood vessel growth via angiogenic factors, release of anti-inflammatory cytokines, and growth factors not easily available to these tissues. Additionally, ESWT appears to stimulate collagen synthesis, mesenchymal stem cell release, and tenocyte proliferation. Finally, ESWT possesses energy that may break down calcification in mineralized tendinopathies.^3,4

Bone healing

Biologic therapies are also found effective in the management of tendon and ligament injuries, alone or in combination with ESWT protocols; however, one of the most unique characteristics of ESWT is its ability to initiate or accelerate bone healing. Shockwaves create microcracks in trabecular bone, leading to the formation of a fracture hematoma and recruitment of osteoinductive growth factors, release of mesenchymal stem cells from the marrow, increase in bone morphogenetic protein and nitric oxide, and induction of mitogen-activated protein kinases, which contribute to bone regeneration. Bone subjected to ESWT has greater ash and calcium content, increased mineral density, and greater peak stress and elastic modulus, referring to its ability to handle loads. In humans with nonunion fractures, ESWT had a similar success rate to surgical intervention (76% vs 79%).⁵

Dogs with radial nonunion fractures had complete bony union at 12 weeks after an ESWT protocol, whereas 80% of controls remained at nonunion at the end of the treatment period.⁶ ESWT can also improve bone healing rates after TPLOs in dogs, which have significant implications in the sporting and working dog arenas where increased clinical sequalae of faster healing decreases the impact of secondary effects such as disuse atrophy and compensatory tissue and gait imbalances. Kieves and others⁷ found that the median healing scores of TPLOs were significantly higher at 8 weeks after surgery in dogs treated with focused electrohydraulic ESWT when compared with a sham treatment, with no complications observed as a result of the intervention. Findings from another study⁸ demonstrated that dogs treated with ESWT after TPLO had increased vertical ground reaction forces and 2-cm greater thigh circumference than controls at 8 weeks after surgery. Similar decreases in healing time have been achieved in humans, dogs, and rabbits with tibial fractures,^9-11 which have some risk for delayed and nonunion due to limited blood supply from surrounding tissue and stress shielding from fixation methods.

Osteoarthritis

ESWT has been evaluated for the management of osteoarthritis (OA) in several joints in canine patients. One group found that dogs with stifle OA treated with electrohydraulic ESWT had trends of improved peak vertical force and stifle range of motion, whereas dogs with OA that did not receive the treatment had a significant decrease in peak vertical force during the study period. Both treated and control dogs demonstrated improvements in a number of functional assessment scores, suggesting a significant placebo effect for that particular outcome measure.¹² Dogs treated with radial ESWT for hip OA had improved peak vertical force and symmetry indices with respect to lameness at 3 months after treatment; however, limb asymmetry increased again by 6 months after treatment.¹³

Neurodegenerative diseases and spinal pain

Chronic, degenerative conditions causing thoracolumbar and lumbosacral pain (intervertebral disc disease, degenerative lumbosacral stenosis, compressive radiculopathy) can be among the most frustrating to treat for rehabilitation practitioners. ESWT has been shown to be effective in improving pain and function in humans and horses with thoracolumbar pain. Shockwave therapy has improved pain and functional outcomes more than physical rehabilitation alone in people with thoracolumbar pain,^14,15 and was found to be superior to steroid injections for people with facet joint pain in another study.¹⁶ In a study of horses with thoracolumbar pain, ESWT increased mechanical nociceptive threshold in 10 of 12 horses at a number of follow-up time points.¹⁷ ESWT’s role in analgesia is not completely understood, but it appears to have a bimodal treatment effect: acute antinociceptive activity (3-4 days) followed by a chronic phase of analgesia accompanied by tissue healing over 3 to 4 weeks. When ESWT is applied over peripheral nociceptors, it causes transient degradation of nerve polarization through the degeneration of nerve endings. Shockwaves may also play a role in myofascial pain relief by breaking up actin and myosin cross-links in trigger points.¹⁴

Multimodal therapy

Canine rehabilitation practitioners have many tools at their disposal, and the use of ESWT in conjunction with therapeutic exercise, drugs, or other modalities is of interest in the multimodal management of patients with many conditions that benefit from rehabilitation. In the study evaluating dogs with biceps and supraspinatus tendinopathies in response to ESWT, the treatment was efficacious regardless of whether therapeutic exercise was also included. Although therapeutic exercise conferred no additional benefit as far as the outcomes assessed in this study, one could argue that additional advantages exist for incorporating ESWT and therapeutic exercise safely within a comprehensive treatment plan. Other benefits of therapeutic exercise, including improvements in muscle mass, proprioception, and joint range of motion, were not evaluated in this study. It is plausible that ESWT allowed for more pain-free execution of exercises and an increased response toward goals that were not specifically examined in this study.

Although concurrent use of ESWT and biologic therapies is not well described in dogs, results of studies in other species have garnered interest in the combination. Horses treated with ESWT or other anti-inflammatory modalities or drugs prior to administration of mesenchymal stem cell treatment for tendinopathies, desmopathies, or articular lesions had significantly improved responses to the treatment.¹⁸ Humans treated for knee OA with ESWT combined with intra-articular platelet-rich plasma had improved response scores over those who received either treatment alone.¹⁹ Data from an in vitro study with human chondrocytes suggested that ESWT induced the surface expression of the hyaluronan cell receptor CD44, allowing increased exposure to Hyaluronic Acid (HA) and potentially facilitating degenerative cartilage repair.²⁰

Advantages and disadvantages

ESWT can be implemented at a relatively low frequency, decreasing the number of visits to the clinic compared with other modalities for geriatric and/or arthritic patients that may have mobility concerns. Typical protocols may include 2 to 3 initial treatments at 2 to 3 weeks apart, followed by occasional rescue treatments as needed up to every 3 to 6 months. The therapy can be implemented in conjunction with therapeutic exercise, aquatic therapy, pharmacologic therapy, and other modalities as part of a comprehensive, multimodal rehabilitation plan. ESWT lacks the risk of some potential adverse effects, such as bacterial inoculation with local injections. One of the historical disadvantages of focused, high-energy ESWT has been the painful execution of the procedure, requiring sedation for the vast majority of treatments, which can be a challenge in compromised patients. However, recent advances have been made, such as the PulseVet X-Trode that distributes energy over a larger area, decreasing peak pulse and allowing most patients to tolerate treatment without sedation. The practitioner should be aware that some patients may be sensitive to the acoustic pulses, which are still quite loud despite the energy dispersion, and should adjust patient care accordingly. Additional potential adverse effects may be transient soreness, petechiae, and/or ecchymoses at the treatment site, usually only for up to 48 to 72 hours after the session.¹

ESWT is a unique and highly adaptable treatment modality with a growing list of applications in human and veterinary physical therapy and rehabilitation. Its noninvasive execution, wide range of capabilities for a growing number of musculoskeletal conditions, potentially synergistic role in a multimodal treatment plan, and prolonged analgesic effect make it an essential tool for the canine rehabilitation practitioner.

References

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3. Leeman JJ, Shaw KK, Mison MB, Perry JA, Carr A, Shultz R. Extracorporeal shockwave therapy and therapeutic exercise for supraspinatus and biceps tendinopathies in 29 dogs. Vet Rec. 2016;179(15):385. doi:10.1136/vr.103487
4. Becker W, Kowaleski MP, McCarthy RJ, Blake CA. Extracorporeal shockwave therapy for shoulder lameness in dogs. J Am Anim Hosp Assoc. 2015;51(1):15-19. doi:10.5326/JAAHA-MS-6175
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6. Johannes EJ, Kaulesar Sukul DM, Matura E. High-energy shock waves for the treatment of nonunions: an experiment in dogs. J Surg Res. 1994;57(2):246-252. doi:10.1006/jsre.1994.1139
7. Kieves NR, MacKay CS, Adducci K, et al. High energy focused shock wave therapy accelerates bone healing: a blinded, prospective, randomized canine clinical trial. Vet Comp Orthop Traumatol. 2015;28(6):425-432. doi:10.3415/VCOT-15-05-0084
8. Barnes K, Lanz O, Werre S, Clapp K, Gilley R. Comparison of autogenous and cancellous bone grafting and extracorporeal shock wave therapy on osteotomy healing in the tibial tuberosity advancement procedure in dogs: radiographic densinometric evaluation. Vet Comp Orthop Traumatol. 2015;28(3):207-214. doi:10.3415/VCOT-14-10-0156
9. Haffner N, Antonic V, Smolen D, et al. Extracorporeal shockwave therapy (ESWT) ameliorates healing of tibial fracture non-union unresponsive to conventional therapy. doi:10.1016/j.injury.2016.04.010 Injury. 2016;47(7):1506-1513.
10. Wang CJ, Huang HY, Chen HH, Pai CH, Yang KD. Effect of shock wave therapy on acute fractures of the tibia: a study in a dog model. Clin Orthop Relat Res.2001;387:112-118. doi:10.1097/00003086-200106000-00015
11. Hsu RW, Tai CL, Chen CY, Hsu WH, Hsueh S. Enhancing mechanical strength during early fracture healing via shockwave treatment: an animal study. Clin Biomech (Bristol, Avon). 2003;18(6):S33-S39. doi:10.1016/s0268-0033(03)00082-2
12. Dahlberg J, Fitch G, Evans RB, McClure SR, Conzemius M. The evaluation of extracorporeal shockwave therapy in naturally occurring osteoarthritis of the stifle joint in dogs. Vet Comp Orthop Traumatol. 2005;18(3):147-152.
13. Mueller M, Bockstahler B, Skalicky M, Mlacnik E, Lorinson D. Effects of radial shockwave therapy on the limb function of dogs with hip osteoarthritis. Vet Rec. 2007;160(22):762-765. doi:10.1136/vr.160.22.762
14. Notarnicola A, Maccagnano G, Gallone MF, et al. Extracorporeal shockwave therapy versus exercise program in patients with low back pain: short-term results of a randomised controlled trial. J Biol Regul Homeost Agents. 2018;32(2):385-389.
15. Lee S, Lee D, Park J. Effects of extracorporeal shockwave therapy on patients with chronic low back pain and their dynamic balance ability. J Phys Ther Sci. 2014;26(1):7-10. doi:10.1589/jpts.26.7
16. Nedelka T, Nedelka J, Schlenker J, Hankins C, Mazanec R. Mechano-transduction effect of shockwaves in the treatment of lumbar facet joint pain: comparative effectiveness evaluation of shockwave therapy, steroid injections and radiofrequency medial branch neurotomy. Neuro Endocrinol Lett. 2014;35(5):393-397.
17. Trager LR, Funk RA, Clapp KS, et al. Extracorporeal shockwave therapy raises mechanical nociceptive threshold in horses with thoracolumbar pain. Equine Vet J. 2020;52(2):250-257. doi:10.1111/evj.13159
18. Bernardino PN, Smith WA, Galuppo LD, Mur PE, Cassano JM. Therapeutics prior to mesenchymal stromal cell therapy improves outcome in equine orthopedic injuries. Am J Vet Res. 2022;83(10):ajvr.22.04.0072. doi:10.2460/ajvr.22.04.0072
19. Su W, Lin Y, Wang G, et al. Prospective clinical study on extracorporeal shock wave therapy combined with platelet-rich plasma injection for knee osteoarthritis. Abstract in English. Zhongguo Xiu Fu Chong Jian Wai Ke Za Zhi. 2019;33(12):1527-1531. doi:10.7507/1002-1892.201905007
20. Vetrano M, Ranieri D, Nanni M, et al. Hyaluronic acid (HA), platelet-rich plasm and extracorporeal shock wave therapy (ESWT) promote human chondrocyte regeneration in vitro and ESWT-mediated increase of CD44 expression enhances their susceptibility to HA treatment. PLoS One. 2019;14(6):e0218740. doi:10.1371/journal.pone.0218740