The Effectiveness of Acetic Acid Iontophoresis for Calcific Tendinitis of the Shoulder

What Is Iontophoresis?

Iontophoresis (meaning ion transfer) refers to the use of mild electric current for trans-dermal drug delivery (i.e. through the skin)¹. The discovery of iontophoresis dates back to 1747. At the time, it was known that the skin had a selective permeability to lipophilic (lipid soluble) chemicals, and that the skin acted as a barrier to hydrophilic (water soluble) chemicals. This affected the local administration of corticosteroids and non-steroidal anti-inflammatory drugs (NSAIDs) with regards to the treatment of various musculoskeletal conditions, as these are hydrophilic. Consequently, it was then suggested that hydrophilic drugs might be introduced into the subcutaneous tissue through human skin via the application of a direct current. This brought about what is known today as iontophoresis, a form of trans-dermal drug delivery².

Iontophoresis occurs via two predominant mechanisms: electro-migration and electro-osmosis. Electromigration is defined as the, "the repulsion of positively charged cations by an anode (positive electrode) and negative charged anions (negatively charged ions) by a cathode (negative electrode)"¹. Electro-osmosis is defined as the, "convective movement of water by electric current"¹. An iontophoretic device essentially acts as a circuit, with a power source that can be connected to the skin through two compartments (anodal and cathodal compartment). As previously mentioned, iontophoresis is partially based on electrorepulsion. Therefore, a positively charged compound is typically placed in the anodal compartment while a negatively charged compound remains in the cathodal compartment.¹

What Is Calcific Tendinitis of the Shoulder?

Shoulder pain is common in the general population, with a point prevalence between approximately 7-26%³, and significantly impacts the performances of daily tasks such as dressing, eating, working, personal hygiene, etc. The most common cause of shoulder pain in primary care is rotator cuff disorders⁴. The rotator cuff is crucial for the dynamic stability of the shoulder joint and is composed of four muscles: the infraspinatus, supraspinatus, subscapularis and teres minor. The prevalence of rotator cuff disorders increases with age and increases in those participating in occupational activities or sports requiring repetitive overhead use of the arms.

Calcific tendinitis is an uncommon rotator cuff disorder, typically in patients who present with a rapid onset of severe should pain and who have calcium deposits visible in the tendons of the rotator cuff muscles on imaging tests⁵. It is more commonly seen in middle-aged working females and more commonly affects the supraspinatus tendon. Furthermore, it is associated with smoking and occupational activities that require awkward positions and heavy lifting⁶. The exact pathophysiological mechanisms underlying calcific tendinitis remain unclear. However, it has been suggested that fibrosis, tendon necrosis and degeneration promote the deposition of calcium on previously healthy tendons⁶. Although the prevalence of patients with shoulder pain who concordantly have calcium deposits in the rotator cuff tendons is approximately 6.8%, the prevalence of calcium deposition in the rotator cuff tendons of asymptomatic individuals has been found to range from 2-20%⁷. The latter emphasizes the importance of clinical reasoning when using the results of imaging tests for diagnosis and development of treatment plans.

Non-Surgical Treatment for Calcific Tendinitis of the Shoulder

Patients with calcific tendinitis of the shoulder could undergo spontaneous pain relief and calcification resorption. However, there is considerable variability and the latter may take years. Therefore, conservative treatments such as physiotherapy are ideal to optimize the rehabilitation process. Electrotherapy modalities such as iontophoresis (with acetic acid) have also been used as part of the conservative treatment for calcific tendinitis of the shoulder⁵. As previously mentioned, electromigration is one of the principal mechanisms underlying iontophoresis. Acetic acid is an organic anion (negatively charged ion). Therefore, when applied under the cathode (negative electrode), it will be repelled toward the anode (positive electrode) with the use of the electric current. The calcium depositions found in the shoulder typically consist of hydroxyapatite crystals, which are soluble in acidic pH. Consequently, this would suggest a reduction of the calcium deposit through the use of acetic acid iontophoresis⁸.


Due to its non-invasive nature, iontophoresis is a frequently used modality for calcific tendinitis of the shoulder⁷. However, does the scientific literature support its use?

One study by Perron et al. published in 1997 assessed the effects of acetic acid iontophoresis and ultrasound on calcifying tendinitis of the shoulder⁹. The sample consisted of twenty-two adults (7 men, 15 women) with a calcifying tendinitis of the shoulder, separated into control and experimental groups. The control group received no treatment. The experimental group received nine treatments including acetic acid iontophoresis (5% acetic acid solution via the negative electrode, 5mA galvanic current, 20 minutes) followed by continuous ultrasound (0.8 w/cm², l MHz, 5 minutes). A significant reduction in the area and density of calcium deposition was found over time in both the experimental and controls groups, but not significant different was found between groups. Therefore, the authors concluded that calcium deposition reduction was a result of natural resorption rather than treatment.

Another study published in 2001 also assessed the combined effect of acetic acid iontophoresis and ultrasound for calcific tendinitis of the shoulder¹⁰. Their sample included 34 patients (23 women, 11 men). Pain intensity was assessed via a visual analogic scale (VAS), and calcification size was assessed via radiograph (x-ray) both prior to initiating treatment, and then after 20 and 40 treatment sessions. Treatment sessions consisted of  consisted of acetic acid iontophoresis at 5% (5 days/week), followed by pulsating ultrasound for 5 minutes (5 cm effective radiation area). After 20 sessions, 35.9% of the shoulders treated had no more pain and the calcification had disappeared. in 64.1% of the patients, pain had decreased. After 40 sessions, the calcification had disappeared in 46% of the subjects, was reduced in 19% of the subjects, and pain was reduced to 85% of its original intensity. The results of this particular study provide great promise for the combined effectiveness of acetic acid iontophoresis and ultrasound for calcific tendinitis of the shoulder. HOWEVER, two significant limitations severely affected the validity of this study: small sample size and no control group! A more recent prospective, quasi-experimental before-after intervention study published in 2016 also demonstrated a significant decrease in pain (VAS) and calcification size in forty-four participants with calcific tendinits of the shoulder⁶. However, once again, there was no control group. Therefore, it is impossible to assess whether the improvements were due to the treatment prescribed or due to natural resorption of the calcification.

Moreover, a double-blind randomized controlled trial published in 2003 also assessed the effects of acetic acid iontophoresis on calcific tendinitis of the shoulder. Their sample consisted of thirty-six subjects (nine eventually dropped out, leaving twenty-seven subjects), randomized into 1 of 2 groups: 10 sessions of physiotherapy during 6 weeks plus acetic acid iontophoresis (n=18), and physiotherapy with sham acetic iontophoresis for the control group (n=18). Their results demonstrated improvements in both groups with regards to  the Shoulder Pain and Disability Index (SPADI) score, the mean number of calcifications per subject, and range of motion of the shoulder for abduction, internal rotation and external rotation. Therefore, the authors concluded that the addition of acetic acid iontophoresis to physiotherapy did not result in better clinical and radiological effects than physiotherapy alone.

Lastly, a Cochrane systematic review was conducted to examine the effectiveness of electrotherapy modalities for rotator cuff disease⁵. The study concluded that based on the available evidence, no clinically important benefits were observed with the application of acetic acid iontophoresis, as the quality of evidence available is either low or very low.

Clinical Application

To conclude, there is conflicting evidence for the use of acetic acid iontophoresis in the treatment of calcific tendinis of the shoulder. At the time being, its effectiveness is not supported by research, as some studies demonstrated no added benefit of acetic acid iontophoresis, whereas those that did were very poorly designed, affecting the quality of evidence. There is a definite need for more high quality evidence (randomized controlled trials) in this field.

Written by: 
Anthony Teoli MScPT, Registered Physiotherapist


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DISCLAIMER: This blog is not meant for diagnostic or treatment purposes. It should not substitute for professional diagnosis and treatment. This blog was not created to provide physiotherapy consultations, nor was it created to obtain new clients. The content of this blog is a resource for information only. This blog was created to serve as an information resource for both the general population and health professionals. 


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