Low-Power Laser Treatment in Patients with Frozen Shoulder: Preliminary Results

ABSTRACT

Objective: In this study I sought to test the efficacy of low-power laser therapy (LLLT) in patients with frozen shoulder. Background Data: The use of low-level laser energy has been recommended for the management of a variety of musculoskeletal disorders. Materials and Methods: Sixty-three patients with frozen shoulder were randomly assigned into one of two groups. In the active laser group (n  31), patients were treated with a 810-nm Ga-Al-As laser with a continuous output of 60 mW applied to eight points on the shoulder for 30 sec each, for a total dose of 1.8 J per point and 14.4 J per session. In the placebo group (n  32), patients received placebo laser treatment. During 8 wk of treatment, the patients in each group received 12 sessions of laser or placebo, two sessions per week (for weeks 1–4), and one session per week (for weeks 5–8). Results: Relative to the placebo group, the active laser group had: (1) a significant decrease in overall, night, and activity pain scores at the end of 4 wk and 8 wk of treatment, and at the end of 8 wk additional follow-up (16 wk post-randomization); (2) a significant decrease in shoulder pain and disability index (SPADI) scores and Croft shoulder disability questionnaire scores at those same intervals; (3) a significant decrease in disability of arm, shoulder, and hand questionnaire (DASH) scores at the end of 8 wk of treatment, and at 6 wk post-treatment; and (4) a significant decrease in health-assessment questionnaire (HAQ) scores at the end of 4 wk and 8 wk of treatment. There was some improvement in range of motion, but this did not reach statistical significance. Conclusions: The results suggested that laser treatment was more effective in reducing pain and disability scores than placebo at the end of the treatment period, as well as at follow-up.

INTRODUCTION

patients are sometimes referred to physical medicine and rehabilitation centers with a diagnosis of frozen shoulder.

There is discord in the literature over the exact definition of frozen shoulder, because many terms are used to describe this syndrome. These terms include adhesive capsulitis, periarthritis, bicipital tendinitis, subdeltoid bursitis, and stiff or painful shoulder, among others.^1,2 Cyriax and others define frozen shoulder as the glenohumeral stiffness that results from restriction of the anterosuperior joint capsule and the coracohumeral ligament.^3,4 It is estimated that frozen shoulder affects 2%–5% of the general population.² Pain is usually the first symptom, and it makes the patient reluctant to move the affected arm. This lack of movement leads to involuntary stiffness. Surprisingly, the non-dominant shoulder is affected more frequently than the dominant one.⁴

There is some disagreement about whether the underlying pathological process is an inflammatory condition, a fibrosing condition, or even an algoneurodystrophic process.² Evidence points to synovial inflammation with subsequent reactive capsular fibrosis. A dense matrix of type I and type III collagen is laid down by fibroblasts and myofibroblasts in the joint capsule; subsequently, this tissue contracts.^3,4 Many protocols have been advocated for the treatment of frozen shoulder, though only limited data from randomized controlled trials are available.⁵ Two recent reviews concluded that there was not enough data to either support or refute the efficacy of any of the commonly used interventions for this condition,^5,6 including nonsteroidal anti-inflammatory drugs, corticosteroid injections, and physiotherapy regimens such as manipulation/mobilization, transcutaneous electrical nerve stimulation, massage, diathermy, ice, and ultrasound, and thus more well-designed clinical trials are needed.^5–8

Low-level laser therapy (LLLT) has been used as a noninvasive, non-thermal modality to treat a variety of muscul loskeletal conditions.^9–17 To our knowledge, there has been no report on the effects of LLLT in the treatment of frozen shoulder.

The aims of this study were to determine whether a course of LLLT for 8 wk in patients with frozen shoulder is superior to treatment with placebo for improving pain, disability, and range of motion at the end of 4 wk and 8 wk of treatment. Another goal was to determine if any benefits remained after 8 more weeks (16 wk after beginning treatment).

MATERIALS AND METHODS

This was a prospective, randomized, placebo-controlled, double-blind trial, performed at the Peania Physical Therapy Center. The Apostolos Pavlos Hospital Ethics Committee gave approval for the study.

The subjects selected for inclusion were women and men attending Peania Physical Therapy Center, either self-referred or referred by their doctor or physiotherapist. The diagnosis of frozen shoulder was made on the basis of a history of limited motion of the glenohumeral joint, with pain at the extremes of the available range of motion. The inclusion criteria were: painful and limited passive glenohumeral mobility; more restricted lateral rotation (8°) relative to abduction and medial rotation; and no clear signs (e.g., painful arc, positive resistance testing, or loss of power) that the shoulder pain was caused by another condition.³

The exclusion criteria were: insulin-dependent diabetes mellitus; bilateral symptoms; systemic inflammatory joint disease (such as rheumatoid arthritis or polymyalgia rheumatica); treatment with corticosteroid injections or physiotherapy during the preceding 6 mo; serious infection; uncontrolled hypertension; peptic ulceration for which oral steroids are contraindicated; surgery, dislocation, or fracture(s) of the shoulder; calcification about the shoulder joint; pregnancy; or a complete rotator cuff tear.¹

Eligible patients were given a detailed description of the intended treatment procedure and were informed about the pos-

sibility of receiving placebo therapy, and their right to withdraw from the study at any time. After receiving this information in writing, the patients gave their informed consent. Seventy-four subjects who met the inclusion criteria were admitted to the study.

Randomization

An assistant at the center randomized subjects into one of two groups by asking them to select one of 74 identical opaque sealed envelopes. The envelopes contained a study number and a group number: 1 (placebo) or 2 (laser). The group number corresponded to the settings on a switch on the laser unit. Each group consisted of 37 patients. Neither the assistant of the center, the treating physiotherapists, nor the patients had any knowledge of which group was receiving the active laser treatment.

Eleven patients (six from the experimental group and five from the control group) left the study to seek another treatment method because they still had symptoms after six treatments. The study was completed with 63 patients. The active laser group was made up of 19 men and 12 women, and the placebo laser group was made up of 21 men and 11 women.

Treatment protocols

The treatment was applied around the shoulder joint. The therapy system used in this trial was the class 3B Laser M 1000, manufactured by Level-Laser Co. (Moglano Veneto-Milano, Italy). The device was a Ga-Al-As laser, wavelength 810 nm, continuous mode, 60 mW of power, spot size 0.5 cm², duty cycle 50%, energy density 3.6 J/cm², and the duration of treatment per point was 30 sec. The dose per point was 1.8 J and the total dose per session was 14.4 J.^17,18

The placebo laser apparatus appeared to be identical to the active laser device. The laser’s output was checked by an independent party before the start and at the end of the study, and also at regular intervals during the study.

The most painful points on the capsule of the glenohumeral joint (eight points), as indicated by the patient and checked with an algesiometer, were chosen as the target location. The target area was delineated with a waterproof marker during the first visit (Fig. 1). Before laser treatment was applied, the target area was cleaned with alcohol (95%) to minimize any backscatter or reflection from oily skin. The probe was placed directly onto

the skin perpendicularly in the center of the circumscribed area, thereby preventing energy loss due to divergence.

During 8 wk of treatment, the patients in the two groups received 12 sessions of laser or placebo treatment. For the first 4 wk the subjects received two sessions per week, and for the next 4 wk they received one treatment session per week. For protection from the laser’s beam all subjects wore protective glasses. Both groups were treated under the same conditions, and the patients were treated individually to avoid influencing one another. No complications were reported. All patients were instructed to execute pendulum and pain-free active exercises at home.⁶

Evaluations

A physical therapist at the center, who was unaware of the treatment type being received by each patient, performed the clinical assessments at baseline and at weeks 4, 8, and 16.

Overall pain, night pain, and activity-related pain were assessed using a visual analog scale (VAS). The VAS consisted of a continuous horizontal line, 100 mm in length, with end points marked “no pain” at one end, and “worst pain” at the other. The patient was asked to use the VAS to rate the severity of the pain experienced. The distance between the extreme left of the scale (“no pain”) and the subject’s mark was measured to the nearest millimeter. High levels of reliability and validity of this VAS have been reported.¹⁹

Shoulder disability was measured by the shoulder pain and disability index (SPADI), which consists of 13 items divided into two subcategories: (1) disability (eight items) and (2) pain (five items). The items are arranged on a 10-point Likert scale, where 0 represents no pain and 10 represents the worst imaginable pain. The SPADI score is calculated by summing and then averaging the scores of the two subcategories, with a possible total score of 100. The reliability of the SPADI when used in primary care populations is high.^20–22

The Croft shoulder disability questionnaire, which includes 22 items, was used to evaluate shoulder disability. The patients answered each item “yes” or “no,” and the number of positive responses is summed to give a score, with 22 being the highest score possible; higher scores indicate more severe disability.²³

Functional activities and symptoms of the patients were evaluated using the disability of arm, shoulder, and hand (DASH)

questionnaire, for which subjects gave their answers to each of 30 items.²⁴ The DASH score is expressed as a percentage.

Shoulder disability was assessed by the health-assessment questionnaire (HAQ), which is a well-validated, 19-item, arthritis-specific functional assessment measure. Patients were asked to rate two or three items each in eight areas of daily life.²⁴ Each item on the HAQ is scored on a scale from 0 (no disability) to 3 (greatest disability).

An inclinometer was used in a standardized protocol to measure active total shoulder flexion and abduction (i.e., scapular and glenohumeral movement combined), and external glenonohumeral rotation in neutral abduction.²⁵

Statistical analysis

After assessing the normal distribution of the data, the Student’s unpaired t-test was used to compare descriptive characteristics of the active laser and placebo laser groups pretreatment. Repeated measures ANOVA was used to identify any significant differences in pain (as assessed by the VAS, SPADI, Croft shoulder disability questionnaire, DASH, and HAQ), and range of motion in flexion, abduction, and external rotation within groups, between groups, and between the treatment and the follow-up periods. Multiple comparisons by the Bonferroni post hoc method and Student’s t-test for independent samples were used to highlight any significant differences. Continuous variables were summarized as mean and standard deviations. p Values 0.05 were considered statistically significant, and all results are expressed as mean  standard deviation. All analyses were performed using SPSS 12.0 for Windows (SPSS, Inc., Chicago, IL, USA).

RESULTS

There were no significant differences between the active laser and placebo groups in the mean baseline values of their demographic characteristics (age 55.51  5.84 vs. 56.83

6.82 y, gender (M:F) 19:12 vs. 21:11, and duration of symptoms 26.5  12.8 vs. 27.1  13.6 wk).

Effects of laser on pain

There was a significantly greater decrease of overall pain in the active laser group than in the placebo laser group at 4 wk 

(p  0.005) and 8 wk (p  0.05) of treatment, and at 16 wk post-randomization (p  0.05) (Table 1 and Figs. 2 and 3). A pattern similar to that for overall pain was observed for night pain and active pain (Figs. 4 and 5). The results showed that, relative to the placebo laser group, the active laser group had a significant decrease in night pain at 4 wk (p  0.05) and at

8 wk (p  0.001) of treatment, and at 16 wk post-randomization (p  0.001). Similarly, the differences in activity pain between the active laser and placebo laser groups were statistically significant at the end of 4 wk (p  0.005) and at the end of 8 wk (p  0.01) of treatment, and remained so at 16 wk postrandomization (p  0.05).

Effects of laser on disability

The results showed that, relative to the placebo laser group, the active laser group had a significant decrease in the SPADI score at 4 wk (p  0.05) and at 8 wk (p  0.01) of treatment, and at 16 wk post-randomization (p  0.01) (Fig. 6). According to the Croft scores, there was a statistical decrease at 4 wk (p  0.05) and at 8 wk (p  0.05) of treatment, and at 16 wk post-randomization (p  0.005) (Fig. 7). Pain was decreased in the active laser group according to the DASH score at 8 wk (p  0.05) of treatment, and at 16 wk post-randomization (p

0.005) (Fig. 8). Finally, relative to the placebo group, the laser group had a significant decrease in HAQ score at 4 wk (p0.001) and at 8 wk (p  0.005) of treatment (Fig. 9).

Effects of laser on the range of motion

Although there was an increase in the range of motion according to the measurement parameters, there was no statistically significant difference between the active laser and placebo laser groups (Figs. 10, 11, and 12).

DISCUSSION

The clinical presentation of frozen shoulder occurs in three phases. First is the painful freezing phase, which lasts 10–36 wks. In this initial phase, the symptoms are pain and stiffness around the shoulder capsule with no history of injury. A nagging constant pain is worse at night, with little response to non-steroidal anti-inflammatory drugs. Second is the adhesive phase, which occurs at 4–12 mo. The severity of pain subsides gradually, but stiffness remains. Pain is apparent only at the extremes of movement, and there is gross reduction of glenohumeral movements, with near total loss of external rotation. Third is the resolution phase, which lasts 12–42 mo, and follows the adhesive phase with spontaneous improvement in the range of movement.¹ Although spontaneous resolution of frozen shoulder may be greatest by 30 mo after onset without any form of treatment, in many patients symptoms do not improve without appropriate therapy. The purpose of the present study was twofold: first, to investigate the efficacy of low-level laser irradiation in patients

with frozen shoulder during 8 wk of treatment; and second, to determine whether benefit is maintained at 16 wk post-randomization. Improvement was observed in pain perception and disability that lasted up to 7 wk, but there was no improvement in the range of motion.

According to an extensive review of the literature, the results reported here are the first on the effects of laser treatment in patients suffering from frozen shoulder. Other researchers have conducted studies to determine the effects of laser therapy on different syndromes of the shoulder girdle. England et al.²⁶ studied the effects of a repetitively pulsed 904-nm laser in 30 patients who suffered from supraspinatus or bicipital tendinitis of the shoulder. After six treatments, the subjects that received laser treatment had improved the active flexion-extension and abduction of the shoulder, as well as the pain intensity.

Saunders²⁷ investigated the efficacy of low-power laser irradiation in patients with supraspinatus tendinitis. She measured pain intensity, range of motion, and strength of shoulder muscles. She reported a significant difference in range of motion, shoulder strength, and pain in patients that received active laser treatment in comparison with a placebo group.

Vecchio et al.²⁸ investigated the efficacy of laser irradiation (Ga-Al-As, 830 nm, 30 mW CW) in 30 patients with rotator cuff tendinitis. Ten points around the shoulder were irradiated with 4.2 J per point. After 16 sessions, there was an increase in the range of motion and muscle strength, and a decrease of pain intensity.

Tendinitis is an inflammation that depends on intrinsic and extrinsic factors. In many situations, these factors can be improved and the cycle of inflammation can be decreased with laser therapy.^17,29 Conversely, in frozen shoulder there are a number of changes in the joint tissues, for instance, adhesions, pannus, and decreased lubricity. Therefore this is a different syndrome, and cannot be compared with shoulder rotator cuff tendinitis or tendinitis, since these syndromes have a different diagnosis.³⁰ Furthermore, the immobilization causes significant changes in the synovial joints.⁴ The effects of stress deprivation affect the intra-articular ligaments and the extra-articular and periarticular connective tissues, causing a deficiency in the orientation of collagen fibers. The joint stiffness includes restricted extensibility of collagen by fixed contact in strategic sites. This random collagen formation restricts the normal fiber sliding motion.^4,29,30 Shoulder flexibility, which depends on the

stretching ability of the collagen that is located in the ligaments of the glenohumeral joint and the synovia, is significantly restricted in frozen shoulder. This causes restriction of movement in the glenohumeral joint and has detrimental effects on scapulothoracic rhythm.^25,31 Moreover, in the fascia there are free nerve endings that produce pain and cause great difficulty for a patient’s daily activities.

The subjects of our study that received low-level laser treatment were improved with respect to pain and disability, but there was no significant difference in comparison with the placebo laser subjects in range of motion, supporting the view that the laser treatment has analgesic effects. The exact biological mechanisms by which laser photostimulation can improve healing of the injured tissues, both acute and chronic, is not yet understood. However, it is believed that laser irradiation can reduce inflammation and pain by changing prostaglandin E₂ concentrations or by removing algesiogenic substances with an increase in the microcirculation,^32,33 facilitates collagen production and tendon healing,³⁴ and reduces muscle pain by reducing oxidative stress³⁵ or by blocking axonal transport.³⁶

The analgesia provided by laser treatment allows other therapeutic procedures, such as exercise, to be performed more comfortably. Decreasing this pain increases the confidence of the patient and facilitates shoulder relaxation, which are essential for recovery.

Although the patients were at the diminishing portion of the inflammatory phase, we found that LLLT affects only the surrounding shoulder muscles and not the capsule. It is believed that this effect could be related to the depth of the shoulder capsule, since a measurement on MRI shows that it lies up to 2 cm from the skin.²⁵  We found a non-significant improvement in range of motion of the shoulder joint, despite decrement in all disability scores.

We have empirically observed that the restoration of mobility is delayed following treatment for frozen shoulder. Many patients are performing activities of daily living without full range of motion, and many do not regain range of motion.

Validity, reliability, and credibility of the study

Unfortunately, studies of low-level laser application have been prone to several methodological shortcomings. These include: (1) a diversity of subjects with respect to the parameters being measured; (2) too few subjects; (3) lack of blindness; (4) no monitoring of the laser parameters of energy density or intensity; (5) no follow-up period; and (6) no focus on a possible dose-response relationship between the laser treatment and changes in the profile of the target parameters.^9–16

We took several steps to avoid these experimental weaknesses. We recruited patients from a rural region. We believe that our sample is representative, as a homogenous population lives in East Attica. Of the 74 patients initially enrolled, 63 completed the experimental protocol; this is high compared to the average number of participants in other published studies.^5,6 We quantified and standardized the intensity and duration of every session, and ensured that the subjects adhered strictly to the protocol. Last, we included an 8-wk follow-up period that is generally acceptable by patients, since it is unethical to leave the untreated patients (the placebo laser group) without treatment for more than 8 wk. This length of time can usually be tolerated by patients without undue distress.^1–3

CONCLUSION

We have demonstrated that an 8-wk course of low-level laser treatment for frozen shoulder is highly effective with respect to pain and disability, but does not result in increased range of motion. It appears that LLLT does not affect the underlying capsular pathology, adhesion, and collagen biology. Further research should be directed toward determining ways of increasing range of motion, perhaps by using a combination of laser treatment and exercise.

ACKNOWLEDGEMENTS

I would like to thank all of the participants for their enthusiastic contribution and patience shown during this project. I am also to thankful to Dr. P. Baltopoulos, orthopedist; Apostolos Pavlos Hospital for referring the patients in Peania Physical Therapy Center; Dr. P. Athanasopoulou, Open University, for reviewing and correcting the manuscript; physical therapists M. Stergioula and A. Panopoulos for their assistance; and Mr. Baroutas D., the manager of the Peania Physical Therapy Center, for their help during the study.

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