Frozen Shoulder: A Sticky Problem - Part 2

In the first of this two-part article, Andrew Hamilton discussed the etiology of ‘frozen shoulder’ and the efficacy of conservative treatment options. In part two, Andrew examines the evidence for the benefits or otherwise of newer, more technological therapies for this condition, including pulsed radiofrequency therapy and guided ultrasound.



As we saw in part one of this article, frozen shoulder, more technically known as adhesive capsulitis (AC), is comparatively rare in athletes. However, when it does occur, the very long timescales required for resolution can make it particularly disruptive. To summarise from the previous article, the evidence supporting the benefits of conventional treatments such as traditional physiotherapy and manual therapy under anesthesia is far from conclusive. The literature better supports other approaches, such as steroid/anti-inflammatory injection and specific stretching modalities; however, the evidence is somewhat limited and far from overwhelming, even with these treatments.

A Technological Approach

A rapid return to full shoulder functionality is a priority for all athletes. This is especially true at higher levels of sport, where the loss of fitness and ability to practice skills can profoundly impact an athlete’s future. Therefore, clinicians may wish to explore less conventional treatment approaches to speed up recovery when a diagnosis of AC is made in an athlete.

In recent years, the use of extracorporeal shock wave therapy has become an increasingly popular alternative mode of treatment for AC. This treatment mode is noninvasive,  rapidly administered, and not dependent upon patient compliance outside of the clinic. The critical question is how outcomes compare the use of modalities with conventional treatment.

Extracorporeal Shock Wave Therapy

Extracorporeal shock wave therapy (ESWT - also called extracorporeal shock wave lithotripsy) is a non-invasive treatment that uses the mechanical force of a powerful acoustic shock wave within injured tissues to reduce pain and speed healing of the affected area. The shockwave application may be radial (affecting a more diffuse volume of tissue nearer the surface) or focussed (affecting a smaller volume of deeper tissue) – see figure 1.

The exact mechanism by which ESWT exerts its actions within the tissue is poorly understood. The hypotheses for its effects include⁽¹⁾:

• ESWT disrupts fibrous tissue, allowing for the subsequent promotion of revascularization and healing.
• The direct and indirect impact of the shock waves cause damage to the cell membranes and reduce the ability of nociceptors to generate sufficient potential to transmit pain signals.
• The high-energy shock waves break up fibrous/calcified deposits, thereby loosening structures, promoting calcium resorption, decreasing pain, and improving function.

In reality, the therapeutic action of ESWT likely arises from a combination of these actions.

Figure 1: Radial vs. focused ESWT

In radial ESWT (above), the shockwave has a low amplitude but a prolonged duration. The pressure wave generated dissipates as tissue depth increases. Focussed ESWT (below) uses much higher-amplitude pressure waves of much shorter duration. The pressure wave becomes more concentrated as tissue depth increases.

How Effective is ESWT?

Much of the early research around ESWT focussed on using ESWT for treating calcific shoulder tendinitis (a related pathology to AC). For example, a 2011 systematic review study pooled data from nine previous studies that examined the effectiveness of extracorporeal shockwave therapy (ESWT) in reducing pain and improving shoulder function⁽²⁾. All studies had follow-up periods of at least six months, and the researchers concluded that

"there was consistent evidence of midterm effectiveness of ESWT in reducing pain and improving shoulder function."

and that

"ESWT is a potential alternative to surgery with good mid-term effectiveness and minimal side effects."

However, the longer-term effectiveness of ESWT was less clear (due to the lack of a follow-up period beyond one year in the studies), and little insight was provided into the appropriate doses of ESWT required to produce an optimum response.

One of the earliest AC-specific studies into the use of ESWT was carried out by Taiwanese researchers, who compared ESWT with oral steroids⁽³⁾. Forty patients were enrolled in the 12-week study and randomly divided into steroid or ESWT treatment groups. Both groups showed significant improvement in the Oxford Shoulder Score evaluation throughout the study period; however, compared to the steroid group, the ESWT group experienced significantly better improvements in the range of movement from week four and significantly better ‘activities of daily life’ score from week six.

In the same year, another (and more robust) study on using ESWT for AC was also published⁽⁴⁾. This study compared six months of focussed ESWT with sham ESWT (i.e., no intervention) on patients with diagnosed AC in a hospital setting. The patients in the intervention group received shock wave therapy once a week for four weeks. Patients received ESWT from anterior and posterior directions (averaging 1200 shocks between 0.1-0.3 mJ/mm2) up to the maximum pain tolerance threshold in the shoulder. The control group received sham shockwave therapy once a week for four weeks while the device was turned off and placed on the patient’s shoulder for the same length of time.

The results showed that ESWT produced significantly superior results to the sham treatment. Mean pain and disability scores (see figure 2) were reduced compared to sham, while flexion, extension, and abduction, internal, and external (but not internal) rotation improved. Measures showed that the most recovery occurred within two months of commencing ESWT; after this time, the healing process slowed down.

Figure 2: Disability scores following four weeks of sham (control) ESWT⁽⁴⁾

ESWT vs. Physiotherapy

ESWT might be superior to no treatment, but how does it compare to conventional physiotherapy-based treatment? A 2015 study divided 30 frozen shoulder patients into two groups: an ESWT group of 15 patients and a conservative physical therapy group of 15 patients⁽⁵⁾. Two times per week for six weeks, the extracorporeal shock wave therapy group underwent extracorporeal shock wave therapy, while the conservative physical therapy group underwent general physical therapy. Analysis of the outcomes showed that both groups experienced significant improvements in pain and shoulder function scores; however, the ESWT group showed significantly better scores than the conservative physical therapy group.

In one of the most recent AC-specific studies on ESWT, researchers studied the effects of ESWT on pain and range of motion in 30 patients with frozen shoulders⁽⁶⁾. This study randomly assigned 15 patients to a conventional physical therapy group and 15 to an ESWT group. Both groups underwent treatment three times a week for four weeks. The ESWT group underwent treatment using a focussed head, with wave amplitude adjusted to the patient’s pain threshold. The control group, meanwhile, received a range of conservative physical therapies, including hot packs (20 minutes), ultrasound (5 minutes), and interference current therapy (100bps, 15 minutes). Like the study above, while both groups experienced improvements at the end of the four weeks, the ESWT group had a lower pain level and a higher range of motion than the control group.

Ultrasound-guided Pulsed Radiofrequency Therapy

An even more recent technology for treating conditions such as AC is ‘ultrasound-guided pulsed radiofrequency’ (or UGPRF for short). UGPRF administers short pulses of radiofrequency waves (around 500,000Hz) to tissues via a needle electrode. Technicians use ultrasound imaging to guide the placement of the electrode. The advantage of UGPRF over standard radiofrequency procedures is that the tissue temperatures remain below 42C, leaving cells undamaged. Thus, this procedure is safe for use near the dorsal root ganglion or peripheral nerves, such as the suprascapular nerve (SSN). Like ESWT, the precise mode of action of UGPRF is uncertain. Some evidence suggests that UGPRF toggles ionic channels in the nerve membrane on and off.

Unlike ESWT, where there is a significant body of data in the literature, UGPRF is relatively new. The lack of quality studies makes it difficult to draw firm conclusions about its efficacy in treating AC. In particular, until a few years ago, there were no adequately controlled studies concerning PRF lesioning to the SSN in patients with AC using ultrasound-guided techniques. One of the first controlled studies compared the effect of physical therapy alone with physical therapy and PRF lesioning of the SSN using ultrasound⁽⁷⁾. The results showed that the intervention group had a notably shorter onset of significant pain relief (6.1 vs. 28.1 days) and a much more substantial reduction of VAS scores at week 1 (40% vs.4.7%) than the control group. Moreover, a comparison of the two groups indicated more significant improvement in the intervention group at all times in VAS and shoulder pain, passive range of movement, and disability index scores – an effect that persisted for at least 12 weeks.

A 2019 study assessed the effectiveness and safety of 12 weeks of UGPRF in patients diagnosed with frozen shoulder⁽⁸⁾. This high-quality study consisted of excellent methodology, including a large subject pool in a randomized, double-blind, sham-control trial. The researchers randomly allocated 136 patients to either a treatment group (68) or a sham group (68). The patients in the treatment group received UGPRF. In contrast, the subjects in the sham group underwent a sham UGPRF, with the same procedures (i.e., insertion of needles guided with ultrasound) and durations but with no pulsed radio frequencies applied.

At the end of six weeks, and again at 12 weeks, patients in the UGPRF treatment group experienced significantly better pain relief (as measured by VAS), more significant improvement of shoulder disorder scores (assessed by SPADI score), and an enhancement of quality of life (as measured by the SF-36 scale) when compared to those in the sham group. However, the researchers added a couple of caveats. The first was that the study did not include follow-up assessment after the treatment period; secondly, given there is so little other data on UGPRF in patients with AC, more studies are needed before we can be confident of the precise benefits and most efficient method of administration.

Summary

Although rare, AC in athletes is potentially debilitating, in large part due to the persistence of the condition. One option clinicians should consider is using more technological approaches such as ESWT and UGPRF. Over the past decade, several studies using ESWT to treat AC and related conditions have produced positive results - in many cases superior to conventional physiotherapy treatment. While this is a relatively recent technology, the evidence in favor of ESWT is, on balance, quite persuasive. The use of UGPRF for AC treatment is still in its infancy, but initial results appear promising. While more research is needed, studies suggest it is worth considering when other approaches have proved unsuccessful.

References

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