MECHANISMS, EVIDENCE, AND EMERGING CLINICAL CONSENSUS

– Written by Omar Alsayrafi, Qatar

INTRODUCTION

Bone stress injuries (BSIs) represent a spectrum of skeletal overload conditions commonly encountered in athletes exposed to repetitive impact activities such as running, jumping and cutting¹. These injuries range from early stress reactions—characterised by bone marrow oedema on MRI—to overt stress fractures featuring cortical disruption—and they impose substantial time-loss and morbidity in athletic populations². A recent epidemiological review in endurance athletes emphasised BSIs as a critical injury burden in female trail-runners and off-road competitors³. The aetiology of BSIs is multifactorial: mechanical load exceeding the bone’s adaptive remodelling capacity, metabolic insufficiencies, hormonal factors, and inadequate recovery all play key roles^4,5. Despite advances in diagnosis, prevention and conservative management (including activity modification, nutritional interventions and load-management strategies) the resolution of BSIs remains protracted in many cases and recurrence rates remain significant⁶.

In parallel, extracorporeal shock-wave therapy (ESWT) has emerged over the past two decades as a non-invasive therapeutic modality originally developed for urolithiasis and increasingly adopted in musculoskeletal medicine. ESWT uses acoustic pressure waves to induce mechanotransductive effects in tissues, stimulating angiogenesis, osteogenesis, and tissue regeneration. In athletes, ESWT has been utilised for tendon, bone, and overuse conditions with favourable safety profiles and minimal training interruption. Recent consensus work has established expert-recommended procedural parameters and contraindications for ESWT in sports injury settings⁴.

The intersection of these two fields—BSIs in athletes and ESWT as a regenerative tool—offers promise. A recent observational study on athletes treated with focused ESWT (fESWT) for BSIs reported significantly shortened return-to-run times when initiated within three months of diagnosis⁷. Such emerging evidence supports the rationale for exploring ESWT specifically for BSIs in athletic contexts. Moreover, an international Delphi consensus on BSIs emphasised the need for multidisciplinary collaboration, timely biological adjuncts, and structured load-management to optimise outcomes¹.

Given the high burden of BSIs among competitive athletes and the evolving mechanobiologic understanding of ESWT, the purpose of this review is to synthesise current concepts of BSIs, to describe the physical and biological principles of ESWT, and to explore how focused ESWT may be integrated into the management of BSIs in athletes—highlighting the most recent evidence, practical considerations and future directions.

RADIAL AND FOCUSED EXTRACORPOREAL SHOCK-WAVE THERAPY

Extracorporeal shock-wave therapy (ESWT) can be broadly classified into radial (rESWT) and fESWT forms, each differing in their generation mechanism, energy profile, and tissue penetration characteristics⁸. Radial devices use pneumatic projectiles to produce lower-pressure acoustic waves that disperse energy superficially—typically affecting tissues within 2–3 cm of the skin surface⁹. These are most effective for soft-tissue pathologies such as tendinopathies, plantar fasciitis, and myofascial pain syndromes¹⁰. In contrast, focused ESWT employs electrohydraulic, electromagnetic, or piezoelectric technologies that converge acoustic energy at a defined focal depth (up to 6 cm), achieving substantially higher energy flux densities (EFD ≈ 0.10–0.30 mJ/mm²)¹¹. This capacity for precise targeting enables treatment of deeper structures, including bone, entheses, and calcifications, and underpins the use of fESWT in the management of bone stress injuries (BSIs) in athletes¹².

Recent comparative biomechanical and clinical analyses (2022–2025) demonstrate that while both rESWT and fESWT reduce pain and modulate nociceptor activity, only fESWT consistently stimulates angiogenesis, osteogenesis, and mechanotransductive gene activation^4,13. The International Society for Medical Shockwave Treatment (ISMST) now recommends fESWT over radial for osseous indications or when deeper tissue repair is desired¹⁴ (Table 1).

TYPES OF FOCUSED ESWT

Focused shockwaves can be generated by three primary technologies—electrohydraulic, electromagnetic, and piezoelectric—each defined by its energy-generation method and focal characteristics¹⁵.

1. Electrohydraulic fESWT: The original technology, using underwater spark discharge to generate high-amplitude pressure waves that converge through an ellipsoidal reflector. It offers the deepest tissue penetration and is preferred for high-energy applications such as delayed unions or bone stress injuries.
2. Electromagnetic fESWT: Employs a rapidly oscillating electromagnetic field that drives a membrane or coil, creating reproducible acoustic pulses with uniform energy density and longer device life. It is widely used in sports medicine practice for its balance between power and comfort.
3. Piezoelectric fESWT: Uses hundreds of piezoceramic crystals arranged on a concave surface that expand simultaneously when electrically charged, generating a highly precise and focal wave. The narrow focal volume enhances selectivity and patient comfort but limits maximum penetration depth.

Although the biological effects among these systems are comparable when treatment parameters are standardised, electrohydraulic devices provide the broadest focal zone and deepest reach, electromagnetic systems ensure consistent reproducibility, and piezoelectric devices excel in superficial precision. It is worth mentioning that according to ISMST guidelines, fESWT should only be used by certified physicians.

MECHANISMS OF ACTION OF EXTRACORPOREAL SHOCK-WAVE THERAPY

General Biological Mechanisms of ESWT

The therapeutic basis of extracorporeal shock-wave therapy (ESWT) lies in mechanotransduction, the process by which mechanical energy is transformed into biochemical and molecular signalling that initiates tissue regeneration. When a shockwave passes through soft or mineralized tissue, it induces rapid pressure gradients, shear forces, and micro-cavitation. These biophysical effects deform cellular membranes, activate stretch-sensitive ion channels, and trigger cascades of intracellular events that modify gene expression and promote repair¹¹.

At the cellular and molecular level, ESWT modulates several critical biological processes:

1. Angiogenesis: ESWT up-regulates vascular endothelial growth factor (VEGF) and endothelial nitric oxide synthase (eNOS), increasing microvascular perfusion and oxygen delivery to ischemic or injured tissue¹⁶.
2. Stem-cell activation: Shockwaves mobilize mesenchymal stem cells (MSCs) from bone marrow and peripheral circulation, enhancing local regenerative capacity¹¹.
3. Osteogenesis and fibroblast stimulation: Elevated expression of bone morphogenetic proteins (BMP-2, BMP-7), transforming growth factor-b (TGF-b), and RUNX2 promotes new bone and collagen matrix synthesis¹¹.
4. Pain modulation: Down-regulation of pain mediators such as substance P and calcitonin gene-related peptide (CGRP) decreases peripheral nerve sensitivity.
5. Anti-inflammatory effects: Reduced expression of interleukin-1b (IL-1b), tumor necrosis factor-a (TNF-a), and cyclo-oxygenase-2 (COX-2) mitigates chronic inflammatory signalling while enhancing macrophage-mediated clearance of damaged tissue¹⁷.

Collectively, these pathways lead to enhanced local blood flow, accelerated tissue metabolism, and improved structural remodelling. Animal and clinical studies show that ESWT can increase capillary density by 40–60 % and collagen deposition by 35 % within four weeks after treatment. These effects explain its proven efficacy in chronic tendinopathies, fasciopathies, and soft-tissue overuse injuries commonly seen in athletic populations¹⁸.

Specific Mechanisms of fESWT in Bone Stress Injuries (BSIs)

In bone tissue, fESWT induces unique mechanobiologic responses that target the underlying pathophysiology of bone stress injuries. The acoustic energy penetrates the cortical surface and generates micro-strain and shear stress analogous to physiological loading, thereby restoring the normal remodelling cycle disrupted by repetitive stress.

Key bone-specific effects include:

1. Osteocyte stimulation and mechanosensing: fESWT activates osteocytes—the primary mechanosensors of bone—prompting nitric oxide and prostaglandin E₂ release, which enhance osteoblast activity and suppress excessive osteoclastic resorption¹⁹.
2. Osteoblast proliferation and differentiation: Increased activity of alkaline phosphatase and up-regulation of osteogenic genes (RUNX2, COL1A1, osteocalcin) foster mineralized matrix formation²⁰.
3. Neovascularization at the cortical–periosteal interface: Up-regulation of VEGF and angiopoietin-2 improves nutrient and oxygen supply to micro-damaged bone, accelerating callus formation⁶.
4. Remodelling and bone-marrow oedema resolution: fESWT enhances local perfusion and venous outflow, aiding clearance of interstitial fluid and reducing oedema visualized on MRI⁹.
5. Biochemical modulation of repair signalling: fESWT transiently elevates bone morphogenetic proteins and transforming growth factor-b within 3–10 days of treatment, driving early osteoid formation and cortical bridging²¹.

Clinical and experimental evidence support these findings. In a 2023 study using dynamic contrast MRI, treated BSIs demonstrated a 30 % increase in perfusion and faster marrow-edema resolution compared with controls. Histological samples from shockwave-treated cortical bone show organized lamellar deposition and reduced necrotic zones. These biologic effects translate into meaningful clinical outcomes—faster pain resolution, earlier weight-bearing, and shorter return-to-sport intervals compared with conventional therapy¹.

By simultaneously enhancing angiogenic supply and osteogenic turnover, fESWT re-establishes the equilibrium between bone resorption and formation that is disturbed by repetitive mechanical stress, addressing the root cause of BSIs rather than merely alleviating symptoms⁶.

MEDICAL APPLICATIONS OF EXTRACORPOREAL SHOCK-WAVE THERAPY (ESWT)

Since its introduction into orthopaedics in the 1990s, extracorporeal shock-wave therapy (ESWT) has evolved into a versatile, evidence-based tool for the management of diverse musculoskeletal and soft-tissue disorders. Originally applied for urolithiasis, ESWT is now routinely used to treat tendinopathies (Achilles, patellar, lateral epicondyle), enthesopathies (plantar fasciitis, proximal hamstring tendinopathy), calcific shoulder tendinopathy, myofascial trigger points, and non-union or delayed-union fractures. Recent trials also demonstrate benefit in avascular necrosis of the femoral head, bone marrow oedema syndromes, and osteoarthritis-related pain, with improvements in function and radiologic appearance. Beyond musculoskeletal medicine, ESWT has found applications in dermatology (chronic ulcers, wound healing), urology (erectile dysfunction, Peyronie’s disease), and neurology (spasticity management after stroke or cerebral palsy). The biological versatility of ESWT—combining angiogenic, anti-inflammatory, and mechanotransductive effects—makes it uniquely suited for regenerative rehabilitation. In sports medicine, it is valued for its safety, short treatment sessions, and the ability to maintain athletes’ training continuity with minimal downtime¹⁴.

TREATMENT PROTOCOLS AND CLINICAL GUIDELINES FOR ESWT IN BONE STRESS INJURIES (BSIS)

Clinical protocols for extracorporeal shock-wave therapy (ESWT) in the treatment of bone stress injuries (BSIs) have become increasingly standardized following recent consensus statements from the International Society for Medical Shockwave Treatment (ISMST) and the European Shockwave Therapy Association (ESTES). Current guidelines recommend the use of fESWT for osseous indications due to its superior energy penetration and mechanotransductive activation of osteogenic pathways. Typical treatment parameters include EFDs between 0.18–0.30 mJ/mm², 2,000–4,000 impulses per session, delivered at 1–4 Hz over three to four sessions spaced 7–14 days apart. Early intervention—initiating fESWT within 12 weeks of diagnosis—is associated with significantly faster pain reduction and improved radiologic healing compared with delayed treatment.

For high-risk BSIs (navicular, femoral neck, anterior tibial cortex), imaging guidance using ultrasound or fluoroscopy is advised to ensure precision and avoid neurovascular structures. Each session should be complemented by load modification, nutritional optimization (vitamin D and calcium sufficiency), and a graded return-to-sport program to minimize re-injury risk. Post-treatment care generally includes 24–48 hours of reduced weight-bearing, ice application for comfort, and gradual reloading under physiotherapy supervision. Adherence to these parameters has consistently produced functional recovery rates of 80–90 % and return-to-sport within 8–10 weeks, highlighting fESWT’s effectiveness as a non-invasive adjunct in sports-medicine rehabilitation^1,14 (Table 2).

SUMMARY

The use of fESWT has become a clinically validated adjunct in the management of bone stress injuries (BSIs) among athletes, supported by consistent evidence of accelerated healing, pain reduction, and faster return to play²². Based on international consensus guidelines^4,14, fESWT should be considered as a first-line biological therapy for BSIs that fail to improve after two to four weeks of optimized conservative care, or when imaging identifies high-risk anatomical sites such as the navicular, anterior tibial cortex, or femoral neck.

Advantages: fESWT provides non-invasive stimulation of angiogenesis and osteogenesis, enabling tissue regeneration without anaesthesia, surgery, or prolonged immobilization²². Athletes typically resume light training within one week and achieve functional recovery within 8–10 weeks—approximately 40 % faster than with rest alone. Furthermore, its reproducibility, minimal side effects, and compatibility with ongoing rehabilitation make it ideal for elite sport environments.

Side effects and contraindications: Reported adverse reactions are mild and transient—local erythema, swelling, and transient discomfort resolving within 24–48 hours. Serious complications are exceedingly rare when treatment is performed by trained clinicians following standard parameters. Absolute contraindications include active infection, malignancy at the treatment site, unhealed growth plates, pregnancy, and coagulation disorders. Relative contraindications encompass acute inflammation, metallic implants in the energy path, and severe neuropathy¹⁶.

Future possibilities: Current research is expanding toward precision shockwave delivery, incorporating AI-based imaging to individualize energy dosing and focal depth. Integration with regenerative adjuvants—such as platelet-rich plasma, stem-cell therapy, and exosome-based biologics—is being studied to potentiate angiogenic and osteogenic pathways. Large-scale multicentre trials are needed to establish standardized protocols by sport, injury grade, and anatomical site, and to determine long-term outcomes on reinjury prevention.

In summary, fESWT represents a safe, effective, and biologically grounded intervention for bone stress injuries in athletes. Its incorporation into multidisciplinary rehabilitation protocols—alongside nutritional optimization and load management—offers a powerful, evidence-based approach to restore bone integrity and athletic performance while minimizing downtime and recurrence¹.

Omar Al-Seyrafi MD

Sports Medicine Physician

Aspetar Orthopaedic and Sports Medicine Hospital

​Doha, Qatar

Contact: omar.alsayrafi@aspetar.com

References

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