Introduction

Calcific tendonitis, also known as rotator cuff calcific tendinopathy, refers to a common, painful condition of the shoulder joint. This condition involves the deposition of calcium hydroxyapatite salts within the rotator cuff muscles, which stabilise the shoulder joint. Calcific tendonitis can significantly limit shoulder movement and quality of life. Conservative treatments like physical therapy and anti-inflammatory drugs work well in many situations; however, more specialised therapies could be needed for persistent symptoms. Extracorporeal shock wave therapy (ESWT) has emerged as a promising non-invasive treatment for calcific tendonitis of the shoulder. It offers an effective alternative to surgery by using high-energy sound waves to break down calcium deposits. This article will give you all you need to know about extracorporeal shock wave treatment.¹

Understanding  calcific tendonitis

Estimates of the prevalence of calcific tendonitis vary significantly, with studies reporting anything from 2.7-22%. The condition is more common in people assigned female at birth and affects both shoulders in 10-20% of cases. The peak age of incidence is between the ages of 30-50.¹

Calcific tendonitis causes pain and may also cause restriction of movement in the shoulder joint due to the deposition of calcium hydroxyapatite salts within the rotator cuff muscles. The rotator cuff muscles are a group of four muscles (supraspinatus, infraspinatus, teres minor and subscapularis) which connect the shoulder blade to the head of the humerus (the long bone of the upper arm) and help give the shoulder joint stability.¹ 

Frequently, the symptoms eventually resolve without intervention; however, this can take several years. Diagnosis is usually made using plain x-rays of the shoulder, on which the calcium deposits can be visualised.² Ultrasound scanning is an alternative method of diagnosis, which may yield further information, including the migration of calcium deposits into the soft tissues of the shoulder joint.³ Magnetic resonance imaging (MRI) may also be used in select cases. In addition to identifying calcium deposits, MRI is useful in identifying complications of calcific tendonitis, such as tears of the rotator cuff muscles.

Initially, so-called conservative treatment is recommended for most cases of calcific tendonitis. This involves rest, physiotherapy and the use of anti-inflammatory painkillers, such as ibuprofen or naproxen. Injections of corticosteroid drugs into the shoulder joint are also used. Conservative treatment is considered to have been unsuccessful if the symptoms persist longer than six months.² Further options for treatment include non-surgical options - extracorporeal shock wave therapy and ultrasound guided barbotage (in which, using ultrasound guidance, a needle is repeatedly placed into the shoulder joint to break up calcium deposits), and surgical options.^4,5 

Extracorporeal shockwave therapy presents a treatment option which may avoid the need for surgery with an excellent safety profile and only minimal side effects.⁴

Disease Process in Calcific Tendonitis

The nature and cause of calcific tendonitis are not fully understood; however, there appears to be a change in the normal tendon cells (tenocytes) into cells similar to those found in cartilage (chondrocytes). A change in one cell type to another cell type is known as metaplasia, and it is this process that appears to precipitate calcific tendonitis. This occurs in the beginning phase of the disease, the so-called pre-calcific stage. At this point, there are no symptoms.⁶

The next phase of the illness is the calcific phase, during which calcium deposits form around the tendons of the rotator cuff muscles. This is further divided into three separate parts: the formative, silent and resorptive phases. In the formative phase, when calcium crystals are deposited, mild pain usually occurs. This is followed by a resting phase not characterised by microscopic changes but by an increase in pain. Finally, the resorptive phase, in which new blood vessels infiltrate the area and an inflammatory process begins with the body’s white blood cells attacking the calcium deposits and removing them and setting off a chain of inflammation leading to swelling around the tendons. Clinically, this results in the development of more severe, acute pain.⁶

The final phase of calcific tendonitis is the repair stage (or post-calcific stage), during which the calcium deposits are replaced by wound healing tissue (granulation tissue) and damaged tendon tissue is repaired.⁶

Mechanism of extracorporeal shock wave therapy (ESWT)

Initially used to break up kidney stones so they can be passed in the urine (lithotripsy), extracorporeal shockwave therapy has been adapted for a number of medical uses and has been studied in the treatment of calcific tendonitis since the 1990s. Shockwaves are acoustic waves which transmit mechanical energy directly to the tissues of the body.

There are two types of shockwaves with medical applications: focused and radial waves. Focused waves deliver a pulse of energy directly to the target site, whereas radial waves spread out and dissipate the further they get from the skin. Most studies of ESWT in calcific tendonitis use focused waves. The amount of energy delivered in each shockwave is measured as the amount of energy delivered to a specific area, usually measured in mJ/mm². Shockwaves can be characterised as low, medium and high intensity by this measurement. Both low-and high-intensity waves have been studied in calcific tendonitis. The shockwaves are produced by a generator (either electro-magnetic, electro-hydraulic or piezo-electric in nature) and transmitted to the target area via a handheld wand.⁷

ESWT is thought to work via several mechanisms in the treatment of calcific tendonitis. Firstly, mechanical force from the shockwaves helps to break up the calcium deposits on the tendons. High-energy shock waves are more effective than low-energy waves for this purpose, as evidenced by clinical studies comparing the two. Secondly, ESWT is thought to work on a molecular level to aid the process by which white blood cells (macrophages) remove calcium during the resorptive phase. ESWT has been shown to aid the production of growth factors such as vascular epithelial growth factor (VEGF), which promotes the production of new blood vessels in healing tissue and induces tissue growth factors (such as Insulin-like growth factor -1) that aid tissue repair. Finally, ESWT has an effect on pain perception and can desensitise nerve cells and affect the action of a chemical called Substance P, which modifies pain perception, with the overall result of reducing pain.⁸

Indications for ESWT in Calcific Tendonitis

ESWT is a treatment option for patients who have not responded to conservative treatment. As mentioned earlier, conservative treatment involves rest, specific strengthening and stretching exercises directed by a physiotherapist and the use of non-steroidal antiinflammatory drugs e.g. ibuprofen. Lack of improvement within six months represents a failure of conservative treatment.²

The two main options for non-surgical treatment of calcific tendonitis are ESWT and ultrasound-guided needle barbotage, also known as ultrasound-guided percutaneous aspiration of calcific tendonitis (U-PICT). In the latter procedure, under local anaesthetic, and using ultrasound guidance to locate calcium deposits, a needle is repeatedly introduced to disrupt the calcium deposits. Saline solution is injected via the needle to “wash” the area and aspirated, usually via a second needle. In this way, calcium deposits are broken up and removed. Some studies comparing ESWT and ultrasound guided needle barbotage have reported better outcomes in the needle barbotage group, although improvements were found in both groups. Recent studies have also suggested that combining both ESWT and needle barbotage is a more effective strategy in calcific tendonitis.⁹

Surgery for calcific tendonitis may be either arthroscopic (keyhole surgery) or open surgery. Studies comparing arthroscopic surgery and ESWT have shown better outcomes in the surgical group in terms of symptom resolution (although improvements in both groups), but there have been variable results in other studies.⁹ Nevertheless, ESWT compares favourably in terms of its excellent safety profile, cost, time off work required for treatment and relatively minor adverse effects.

Procedure

One of the difficulties in studying the effectiveness of ESWT for calcific tendonitis is that there is no general consensus on a protocol for the optimum number, intensity or duration of treatments required. One suggested protocol describes two treatments of ESWT (1500-2500 impulses per session) given 12-16 days apart. The shockwaves are delivered via a handheld wand held either directly in contact with the skin or with a thin sheet of polyethylene foil between the wand and the skin. Typically, the procedure is uncomfortable but tolerable. Common complications include localised reddening or bruising of the skin and localised swelling.¹⁰ A NICE (National Institute for Health and Care Excellence) review of ESWT for calcific tendonitis commented that two case reports had described osteonecrosis (death of part of the bone) of the head of the humerus in patients who had undergone the treatment; however, it was unclear whether this had any direct relationship to the procedure.  

Evidence for effectiveness of ESWT for calcific tendonitis

Whilst there are many individual studies which have suggested some effectiveness of ESWT in calcific tendonitis, there is a huge problem in evaluating these studies owing to the variation in the intensity and number of treatments used and, as stated above, the lack of a universally agreed optimum treatment protocol for ESWT. 

A 2020 Cochrane systematic review ( a type of study taking into account the results of multiple different studies using rigorous academic standards) assessed a total of 32 clinical trials of ESWT in rotator cuff disease with and without calcification. It concluded that there was insufficient evidence for the effectiveness of ESWT. Furthermore, in view of the fact that the procedure does have side effects, despite these being relatively minor, it could not recommend ESWT for calcific tendonitis. The study authors conceded that, because of the variation in the doses of ESWT used, it was possible that ESWT was not effective because patients had received too low a dose in these trials and recommended better quality research with a consensus on optimum dose/frequency in the future. In the UK, NICE does not recommend ESWT for the routine treatment of calcific tendonitis and only recommends its use in clinical research settings.¹¹ 

A 2023 meta-analysis (a type of study taking into account the results of multiple different studies) which compared surgical interventions for calcific tendonitis and both non-surgical methods (ESWT and ultrasound guided needle barbotage) concluded that the outcomes were better for surgery compared to non-surgical methods, but it did find improvements with both non-surgical methods.⁹

A 2024 meta-analysis comparing ultrasound guided needle barbotage and ESWT concluded that the needle barbotage group had better outcomes than the ESWT group.¹²

Studies comparing high-intensity and low-intensity shockwave therapy have shown increased effectiveness in the high-intensity group.¹³

So, overall, despite some studies showing the effectiveness of ESWT in calcific tendonitis, the overall consensus from expert bodies informing healthcare policy at present appears to be that better quality research is needed and that current evidence does not support the effectiveness of ESWT in calcific tendonitis.

Summary

Calcific tendonitis is a painful condition of the shoulder joint caused by the deposition of calcium in the muscles that stabilise the shoulder. Many cases will resolve with simple measures, including rest, physiotherapy and anti-inflammatory drugs. In persistent cases, there are both surgical and non-surgical options for treatment. Extracorporeal shock wave therapy (ESWT) presents a non-surgical treatment option with relatively few complications, which works by mechanically breaking up calcium deposits and accelerating the healing process. However, research data on the effectiveness of ESWT is difficult to interpret because of the wide variations in how the treatment is administered. A 2020 Cochrane review of ESWT for calcific tendonitis did not support its effectiveness, and NICE (National Institute for Health and Care Excellence) currently only recommends the treatment in clinical research settings. Nevertheless, there is still ongoing research into the use of ESWT in calcific tendonitis.