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The Role of Shockwave Therapy in Lower Extremity Sports Medicine
Regenerative medicine facilitates the repair response of diseased or injured tissue using stem cells or their derivatives. In podiatry, regenerative medicine has a wide variety of potential applications including, but not limited to, wound care, tendonitis, scar tissue, cartilage damage, fusions and nerve damage. Presently, there is increased usage of and acceptance for more noninvasive regenerative techniques, such as extracorporeal pulse activation technology (EPAT or radial ESWT) or extracorporeal shockwave therapy (ESWT).
Shockwave therapy for medical use was originally developed in the 1980s for treatment of renal calculi.1 After progressive development, the technology expanded outside the field of urology, including for autoimmune disease, inflammation, neurologic pathology, cancer, lupus, amyotrophic lateral sclerosis, and other conditions. The use of shockwave therapy has increased in the orthopedic world more recently, particularly in the lower extremity, where there is Food and Drug Administration (FDA) approval for use in plantar fasciitis and Achilles tendonitis.
Shockwaves exhibit a high positive pressure followed by a tensile wave. The positive phase of the shockwave results in direct mechanical force; however, the negative phase generates cavitation and gas bubbles. These bubbles subsequently implode at high speeds, which generates a second set of shockwaves.2 A wave coming between a medium of two tissue types may undergo transmission, dissipation, or reflection. This depends mostly on the density of the tissue or structure. Generally due to poor attenuation when passing through fluids and soft tissues, shockwaves therefore do not cause any harm or tissue damage. To give some perspective the shockwave peak pressure is approximately 1000 times greater than that of an ultrasound wave.3
The actual mechanism or proposed pathophysiologic effect of shockwave therapy are actually not well understood. We do know, however, that direct shockwave with cavitation causes hematoma formation and focal cell death. This will then stimulate new bone or tissue formation.4 Proposed mechanisms of action for ESWT include: promoting neovascularization at the tendon-bone junction, stimulating tenocyte proliferation and osteoprogenitor differentiation, increasing leukocyte infiltration, and amplifying growth factor and protein synthesis to stimulate collagen synthesis and tissue remodeling.4–9 ESWT amplifies this complex process of cell regeneration via cell activation from cytokine receptors.
Shockwave devices have undergone much development and advancement since the first electrohydraulic and subsequent piezoelectric devices, followed by electromagnetic devices with flat or cylindrical coils. All these devices produce focusing pressure pulses. There are considerable differences in the quality of the sound fields, which can determine the type of therapy performed. The radial devices use compressed air or electromagnetic forces to accelerate a “projectile” in the device. The projectile transfers its energy upon impact with an applicator and applies the energy to the tissue.10 There is some controversy with radial-type devices, because although they achieve similar results, radial devices do not produce pressure pulses that resemble the characteristic properties of the classic shockwave. The rise times, tissue depth, and maximal pressure of radial pressure waves are much lower than other ESWT treatment devices.
How ESWT Can Benefit Fracture and Nonunion
Musculoskeletal indications in the lower extremity for ESWT include tendinopathies, osteoarthritis, medial tibial stress syndrome, plantar fasciitis, adhesive capsulitis, and nonunion of long bone fractures. For pain control, one theory is that ESWT modulates the body’s immune response, which then triggers a strong anti-inflammatory cascade. Data from animal models confirm an increase in neoangiogenesis after shockwave therapy.5 The average protocol for usage is one 15-minute treatment per week for 3–5 weeks.
With regard to bone healing, promising early case studies helped gain the acceptance of ESWT for treatment of nonunion bone fractures. This was despite only low-level studies conducted on this topic in the 1990s.11 More recent higher-level studies demonstrate the success of using ESWT to treat fracture nonunions.12,13 Foot fractures can be debilitating in the professional and amateur athlete, possibly taking up to 3 months for normal healing to occur. Basketball players and runners, in particular, often struggle to return to pain-free competition with this type of foot injury.
Furia and colleagues12 conducted a study in 2010 where 23 patients with a fifth metatarsal fracture nonunion in the metaphyseal-diaphyseal region had ESWT at 2000 to 4000 shocks with an energy flux density per pulse of 0.35 mJ/mm2. Twenty other patients with similar fracture nonunions received intramedullary screw fixation. The authors determined that 20 of the 23 nonunions in the shockwave group and 18 of the 20 nonunions in the screw fixation group had healed at 3 months after treatment—with one of those 3 nonunions healing by 6 months. There was one complication in the shockwave group (post-treatment petechiae) and 11 complications in the screw-fixation group, consisting of 9 patients with symptomatic hardware, one refracture, and one patient with cellulitis. Not only does this study demonstrate that ESWT is as effective as surgical intervention for treatment of nonunions, but it also has far fewer complications.
A Closer Look at Shockwave in the Achilles Tendon
Achilles tendinopathy is a common overuse injury and a common cause of posterior heel pain. Thirty to 50% of sports injuries are tendon-related, and Achilles tendinopathy specifically has an 11% prevalence in runners.14,15 Over their lifetime, former distance runners may have a 52% risk of developing Achilles tendinopathy.14,15 While the mainstay of treatment for Achilles tendonitis is tendon loading exercises, some patients have refractory symptoms.
Multiple recent studies support ESWT in Achilles tendinopathy. A 2019 study reviewed data on 66 patients with chronic Achilles tendinopathy who received ESWT.16 According to the disease course, those patients were allocated to a short-term (symptom duration 3–6 months) or long-term (symptom duration 6 months) group. The authors concluded ESWT could effectively relieve pain and improve hindfoot function in patients with chronic Achilles tendinopathy, and in particular could offer functional improvement in patients with short-duration chronic Achilles symptoms.
A Level-1 randomized controlled trial compared the short- and long-term effectiveness of an eccentric loading program followed by stretching exercises combined with ESWT or sham ESWT for treating chronic non-insertional Achilles tendinopathy.17 Dividing 22 men and 28 women evenly into 2 groups, the authors assessed function and pain at baseline, 1 month, and 16 months. They concluded combining calf eccentric loading with stretching exercises resulted in significant improvements in the pain and functional scores in patients with non-insertional Achilles tendinopathy. Adding ESWT led to significantly greater improvements, however.
What You Should Know About ESWT and Plantar Fasciitis/Fasciosis
Plantar fasciitis is one of the most common causes of heel pain and reasons for which patients seek medical care.14 It can have significant impact on activity level and ability to engage in athletic activity. Thickening of the plantar fascia, decreased vascularity, peritendinous inflammation, and loss of normal elasticity can all play a role in persistent plantar fascial pain. Plantar fasciitis usually responds successfully to conservative measures. One will often observe symptom resolution and return to activities in 90% of patients within 10 to 12 months.14 This lengthy recovery is may prove unacceptable in the athletic population. There are excellent studies available that demonstrate good improvement with ESWT treatment for plantar fasciitis. Earlier studies, however, were not as successful in establishing a statistically significant improvement in patient outcomes when treating plantar fasciitis or Achilles tendonitis.
Haake and colleagues reported no statistically significant improvement when treating plantar fasciitis with ESWT.18 The study focused on 272 patients with chronic plantar fasciitis that did not respond to conservative therapy for at least 6 months—135 patients in the ESWT group and 137 in the placebo group. The success rate 12 weeks after intervention was 34% in the ESWT group and 30% in the placebo group. The authors concluded ESWT is ineffective in treating chronic plantar fasciitis.
Studies such as this led insurance companies to not cover shockwave treatments, despite there being good data elsewhere and available randomized double-blind studies. For example, Malay and colleagues published a prospective, double-blind, multicenter trial focusing on a total of 172 patients—115 patients treated with ESWT and 57 in the control group.19 Patients had follow-up for up to 1 year to identify any adverse outcomes possibly related to the shockwave device. On a visual analog scale (VAS) the blind assessor’s objective assessment of heel pain indicated a mean reduction of 2.51 in the shockwave group and 1.57 in the placebo group. On the VAS, the participants’ self-assessment of heel pain showed a mean reduction of 3.39 in the ESWT group and 1.78 in the placebo group. No serious adverse events were observed at any time. The authors concluded that ESWT was both effective and safe for chronic proximal plantar fasciitis.19
In addition, evidence supports that radial ESWT (EPAT) is more effective in treating plantar fasciitis with fewer side effects when compared to corticosteroid injections.17 Corticosteroid injections are considered part of standard of care when treating plantar fasciitis. This can potentially harm athletes playing high-impact sports if performing multiple injections, as it is well known that repeated steroid injections can weaken or cause harm to tissue and bone structures.
In 2016 a study performed by Eslamian and colleagues randomized 40 patients with chronic plantar fasciitis equally to radial ESWT (EPAT) or local methylprednisolone injections.19 Patients had 5 sessions of shockwave or a single steroid injection. Changes in pain level on the VAS in morning and during the day and the Foot Function Index (FFI) throughout the study period were significant in both groups. Patient opinion conveyed good or excellent results in 55% of ESWT and 30% of corticosteroid injection groups. Both interventions facilitated improved pain and functional ability 2 months after treatment. Although intergroup differences were not significant, the Foot Function Index improved more with ESWT and patients were more satisfied with ESWT.
Insights on Shockwave for Muscle Injury
Muscle injuries are common, and are the most prevalent musculoskeletal injury among nearly all sports categories.20,21 These correspond to 46% of football injuries22, 31% of soccer injuries23, and 17.7% in basketball.24 Muscles with proximal and distal insertions involving 2 joints are the most frequently injured. For this reason, most muscle damage occurs in the lower limbs.23,25
A Level IV prospective study of 8 patients demonstrated ESWT combined with physiotherapy was effective for long-term muscle injury, resulting in good performance and the ability to return to sports.25 All patients showed a muscle strength of grade V after eight weeks, while the pain score decreased from 5.75 to 0.5 points on the VAS at the end of the treatment. Patients returned to sports practice after an average 8.14 weeks.25
Sometimes acute versus chronic muscle injury is hard to define; nevertheless, ESWT has demonstrated the ability to treat both conditions well without having to determine separate protocols.
Final Thoughts
Clinicians should keep in mind that contraindications to shockwave treatment include pregnancy, pacemakers or other implanted devices, open wounds, joint replacements, epiphysis, infection, cancerous tissues (patients can be undergoing cancer treatment, need to avoid specific area of cancerous tissue), joint replacements, overlying major nerves or vessels.6
In addition to anecdotal success stories with high impact athletes and the treatment of musculoskeletal injuries, there is ample data to support ESWT. This can be used in both the acute and chronic setting. The main barrier to treatment is access, as this is still mostly a noncovered procedure in the United States. Shockwave therapy is an excellent resource to use in the office setting as an alternative to invasive treatment. It will benefit both the patient and the practice management aspect of your clinic.
Dr. Parthasarathy is in private practice in Silver Spring, Md. She currently serves as Chair of the American Podiatric Medical Association (APMA) Communications Committee and member of the APMA Education Committee. She serves on the Editorial Board of Advisors of Podiatry Today. She is also President Elect of the Maryland Podiatric Medical Association’s Executive Committee. Dr. Parthasarathy was previously a Podiatry Section Chief at the Medstar Montgomery Medical Center in Olney, Md. and is a past recipient of the APMA Rising Star Award (2017).
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