Korean J Pain 2020; 33(4): 344-351
Published online October 1, 2020 https://doi.org/10.3344/kjp.2020.33.4.344
Copyright © The Korean Pain Society.
1Department of Orthopaedic Surgery, National Police Hospital, Seoul, Korea
2Department of Orthopaedic Surgery, Bundang Jesaeng Genenral Hospital, Seongnam, Korea
3Department of Orthopaedic Surgery, Sun’s Hospital, Seoul, Korea
4Department of Orthopaedic Surgery, Incheon Sarang Hospital, Incheon, Korea
5Department of Orthopeadic Surgery, Kyung Hee University College of Medicine, Kyung Hee University Hospital, Seoul, Korea
6Department of Orthopaedic Surgery, Seoul National University College of Medicine, Seoul National University Bundang Hospital, Seongnam, Korea
Correspondence to:Joo Han Oh
Department of Orthopaedic Surgery, Seoul National University College of Medicine, Seoul National University Bundang Hospital, 82 Gumi-ro 173beongil, Bundang-gu, Seongnam 13620, Korea
Handling Editor: Jin Woo Shin
Received: March 23, 2020; Revised: June 9, 2020; Accepted: July 4, 2020
This is an open-access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/), which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background: The effects of far-infrared radiation (FIR) on the treatment of rotator cuff diseases remains unknown. We evaluated the safety and efficacy of FIR after arthroscopic rotator cuff repair with regard to postoperative pain and healing.
Methods: This prospective randomized comparative study included 38 patients who underwent arthroscopic rotator cuff repair due to a medium-sized tear. Patients were randomly divided into the FIR or control group (n = 19 per group). In the FIR group, FIR with an FIR radiator started 1 week postoperatively for 30 minutes per session twice daily. It lasted until abduction brace weaning at 5 weeks postoperatively. We assessed pain using a pain visual analogue scale (pVAS) and measured the range of motion (ROM) of the shoulder at 5 weeks, and 3 and 6 months, postoperatively. The anatomical outcome was evaluated using magnetic resonance imaging at 6 months postoperatively.
Results: At 5 weeks postoperatively, the average pVAS score was lower in the FIR group than in the control group (1.5 ± 0.8 vs. 2.7 ± 1.7; P = 0.019). At 3 months postoperatively, the average forward flexion was higher in the FIR group (151.6° ± 15.3° vs. 132.9° ± 27.8°; P = 0.045), but there was no significant difference at 6 months postoperatively. There was no significant difference in healing failure between the groups (P = 0.999).
Conclusions: FIR after arthroscopic rotator cuff repair could be an effective and safe procedure to reduce postoperative pain, thereby facilitating rehabilitation and better ROM in the early postoperative period.
Keywords: Far-infrared Radiation, Pain Visual Analog Scale, Postoperative Pain, Range of Motion, Rehabilitation, Rotator Cuff Repair, Rotator Cuff Tears, Shoulder Pain
The incidence of rotator cuff tears is increasing rapidly, mainly due to the aging population and advancements in radiological diagnosis. Tears are reported in approximately 30% of those aged ≥ 60 years and nearly 60% of those aged ≥ 80 years [1,2]. Arthroscopic rotator cuff repair has become a common surgical technique for treating rotator cuff tears, and as it is minimally invasive, it may have the additional benefits of reducing postoperative pain and improving early functional recovery . Additionally, there is recent growing interest in various methods for improving functional recovery of patients after arthroscopic shoulder surgery, one of them being the use of far-infrared radiation (FIR) .
FIR is an electromagnetic wave, which is also emitted from the sun, and has wavelengths between 5.6 and 25.0 μm . Depending on its wavelength, infrared radiation can be divided into the following three categories: near-infrared radiation (0.8-1.5 μm), middle-infrared radiation (1.5-5.6 μm), and FIR (5.6-1,000 μm) . FIR has three biological effects, including radiation, resonance, and thermal effects . FIR carries energy that is perceived as heat by thermo-receptors on the surrounding skin and can penetrate up to 4 cm beneath the skin . Moreover, it can resonate with water and organic molecules within the body . According to Wien law, the dominant wavelength of radiation emitted by a body at 35°C is 9.4 μm. This explains why the human body easily absorbs FIR between 4 and 16 μm . The FIR radiator used generates a 2-25 µm wavelength similar to the wavelength of the human body. The human body of an adult consists of 55%-60% water. FIR interacts with water molecules, causing a thermal reaction that raises the temperature of the tissue. The human body responds to this phenomenon by expanding blood vessels. Subsequently, blood circulation increases, more oxygenated blood reaches soft tissue, and at the same time, it stimulates the removal of accumulated toxins .
The FIR effect has been demonstrated by animal studies in rats, which resulted in increased nutrient supply to tissues, accelerated tissue repair, improved waste removal, and elevated pain thresholds [5,10]. Wong et al.  reported that FIR promoted local circulation and improved capillary flow after total knee arthroplasty. Subsequently, FIR may increase tissue oxygenation and improve healing by eliminating chronic inflammation, reducing pain and swelling, relieving muscle spasms, inducing relaxation of musculotendinous structures, and eventually relieving symptoms [5,6]. In orthopedic fields, FIR may be useful for wound healing and analgesia . However, no comparative study has been performed to date that investigates the use of FIR after arthroscopic rotator cuff repair. Moreover, no studies have looked at how FIR may affect postoperative pain-relief, functional recovery, and rotator cuff healing during the tissue healing phase.
In this prospective randomized comparative study, we aimed to evaluate the safety and efficacy of FIR after arthroscopic rotator cuff repair, based on the hypothesis that FIR can improve postoperative pain, functional recovery, and healing effects after surgery.
This prospective randomized study was conducted between June 2017 and January 2019. Its protocol was approved by the Institutional Review Boards of Seoul National University Bundang Hospital (No. E-1704-390-004) of the senior authors’ institution. Written informed consent was obtained from all patients prior to surgery. We included patients aged between 20 and 80 years with a rotator cuff tear of more than 1 cm and less than 3 cm. We excluded patients with (1) shoulder arthritis, (2) a large to massive rotator cuff tear, (3) an isolated subscapularis tear, (4) revision, (5) rheumatoid arthritis or other connective tissue disease, (6) a history of infection, (7) complex regional pain syndrome, (8) a preoperative hepatic or renal impairment, (9) uncontrolled diabetes mellitus or hypertension, (10) allergic skin lesions, (11) human immunodeficiency virus positive, and (12) women of reproductive age who could not undergo FIR. During the study period, we analyzed 38 patients and divided them randomly into the FIR (n = 19) and control (n = 19) groups (Fig. 1).
In the FIR group, FIR with FIR radiator (Aladdin-H®; Taerim Medical Co. Ltd., Seongnam, Korea) was started 1 week after the operation, and lasted until the patient was weaned off abduction brace, which was approximately 5 weeks postoperatively. It was applied on the operated shoulder for 30 minutes per session twice daily. The control group did not receive FIR, and the other rehabilitation interventions were performed in the same manner as those of the FIR group. The FIR radiator was applied at a distance of 30-35 cm from the patient’s skin, and patients themselves marked on a checklist whether FIR was applied to them (Fig. 2).
All procedures were performed under general anesthesia by the senior author (J.H.O), with the patient in the lateral decubitus position, using three arthroscopic portals (anterior, lateral, and posterior). After glenohumeral inspection, subacromial decompression was performed to remove the inflamed bursal tissue. Acromioplasty was conducted with a motorized burr in almost all patients. After footprint preparation was performed to expose the bleeding bony surface with a ring curette, rasp, and shaver, the anteroposterior and retraction tear length was measured with a calibrated probe. Rotator cuff repair was performed using the double row suture bridge technique or modified Mason–Allen technique with several suture anchors .
The postoperative rehabilitation for arthroscopic rotator cuff repair was the same in both groups. After surgery, an ice pack was applied to the operation site for 5 days for all patients. Postoperative pain management was administered to all patients, using the same oral pain medication, such as tramadol, up to 2 weeks postoperatively. To see only the effects of FIR itself, immobilization was maintained using an abduction brace for 5 weeks, for all patients. Shoulder shrugging, active elbow flexion/extension, active forearm supination/pronation, and active hand/wrist motion were encouraged immediately after surgery. Passive range of motion (ROM) was not allowed during the brace-wearing periods. After weaning off the abduction brace, active-assisted and active-ROM exercises were encouraged, and muscle strengthening exercises began 10-12 weeks after surgery. All sporting activities were allowed at 6 months after surgery. Rehabilitation was co-supervised by the Department of Rehabilitation and Orthopedic Surgery.
The primary endpoint was a visual analogue scale for pain (pVAS) at 5 weeks postoperatively, ranging from 0-10 (0, no pain; 10, the worst pain). The pVAS was measured in all patients at each follow-up visit. The secondary endpoints were pVAS and ROM at 3 and 6 months postoperatively, and functional scores at 6 months postoperatively. ROM was measured using a goniometer with the fixed scapular position in 3 planes, including forward flexion (FF), external rotation (ER) at the side, and internal rotation (IR) at the back. FF was measured as the angle between the arm and thorax with the elbow fully extended. ER at the side was measured as the angle between the forearm and thorax with the upper arm in adduction and the elbow in 90° flexion. IR at the back was measured by the vertebral level that the tip of the patient’s thumb could reach while in a sitting position. For convenience of analysis, authors numbered the vertebral levels serially, which are as follows: 1-12 for the 1st-12th thoracic vertebrae, and 13-17 for the 1st-5th lumbar vertebrae .
The functional outcome scores such as the American Shoulder and Elbow Surgeons (ASES) score and Simple Shoulder Test (SST) were also evaluated preoperatively and at 6 months postoperatively [13,14]. The ROM and functional scores were measured by a single researcher (K.S.J) who was blinded to the current study. Additionally, the third endpoint was the tendon-to-bone healing rate of the repaired rotator cuff at 3 months postoperatively, via ultrasound, and at 6 months postoperatively, via magnetic resonance imaging (MRI) . The tendon-to-bone healing rate of the repaired rotator cuff was evaluated as the integrity of the repaired rotator cuff tendon .
All statistical analyses were performed using the Statistical Analysis System statistical software package, ver. 9.4 (SAS Institute, Cary, NC, USA). A
Power analysis was performed to determine the sample size, and the statistical power of the study was calculated by G-Power software ver. 184.108.40.206 (Kiel, Germany). Using the postoperative pVAS average of 3.65 ± 0.21 (FIR group) and 4.05 ± 0.39 (control group) based on the data reported in the literature , we determined that a sample size of 30 patients (15 patients per group) was necessary to achieve a power (1-beta) of 90% at a significant level (alpha) of 5%. Taking the dropout rate of 20% into account, the total sample size should be 19 patients per group. Thus, 38 patients who underwent arthroscopic rotator cuff tear surgery were enrolled in the current study.
Each patient was given a self-checklist to record the exact time and site of the irradiation throughout the treatment period. We confirmed their data, and all patients answered that they complied with the protocol well.
Demographic data, including preoperative pVAS, showed no difference between the FIR and control groups (Table 1). The pVAS at 5 weeks postoperatively, which was the primary outcome, was 1.5 ± 0.8 in the FIR group, which was statistically significantly lower than 2.7 ± 1.7 in the control group (
For the secondary outcomes, pVAS at 3 and 6 months postoperatively were not different between the two groups. The pVAS at 3 months postoperatively was 2.1 ± 0.9 in the FIR group, which was not significantly different from 2.7 ± 1.9 in the control group (
Regarding the third outcome, which was the tendon-to-bone healing rate of the rotator cuff at 3 months postoperatively, via ultrasound, and at 6 months postoperatively, via MRI, there was no significant difference in the healing failure between the two groups. At 3 months postoperatively, no healing failure was found in either group using ultrasound, but there were two healing failure cases (10.5%) in the FIR group and one healing failure case (5.3%) in the control group (
The potential adverse effects of FIR, such as skin burn, rash, infection, wound dehiscence, hypersensitivity reaction, and body temperature elevation, did not occur in our patients. Moreover, there were no other perioperative complications noted in any patient in either group.
This prospective randomized comparative study evaluated the safety and efficacy of FIR after rotator cuff repair, and the current data demonstrated that the pVAS was significantly lower in the FIR group than in the control group at 5 weeks postoperatively. At 3 months postoperatively, the average FF was significantly higher in the FIR group than in the control group; however, other variables including the pVAS were not significantly different. At 6 months postoperatively, there were no differences in the pVAS, ROM, functional scores, or healing failure rate between the two groups, and adverse events from FIR were not observed in the FIR group.
In the medical field, FIR is usually used for patients with lymphedema and vascular disease [8,16]. Its surgical application has been actively investigated for plastic surgery and oral-maxillofacial surgery [17,18]. In plastic surgery, FIR has been proven to induce wound healing by increasing skin microcirculation in rats undergoing flap treatment . In oral-maxillofacial surgery, FIR has been proven to aid wound healing after tooth extraction [18,19]. The application of FIR is still unchartered territory in the orthopedic field. However, we hope that our research will be a cornerstone in proving the efficacy and safety of its clinical use. Further studies into FIR are required not only to evaluate its effectiveness in the clinical setting, such as increasing microcirculation, but also to determine its latent mechanisms.
Pain is an important factor experienced by patients after elective surgery and usually occurs due to the injury of nerve endings and soft tissue damage [6,20]. According to previous studies, 77%-98% of patients experienced postoperative pain, and up to 50% of this same group experienced moderate pain [6,21]. Severe pain adversely affects patients’ biologic, physical, and psychological status .
Additionally, arthroscopic rotator cuff repair causes more severe pain than arthroscopic surgery of other joints owing to bone resection, extensive removal of bursal tissue, insertion of a suture anchor, and soft tissue distension from irrigation fluid . This postoperative pain usually interferes with early rehabilitation, adversely affecting surgical outcomes and extending hospitalization, leading to decreased patient satisfaction . Proper pain control after arthroscopic rotator cuff repair can prevent serious complications by reducing hospitalization, thereby achieving early ROM and muscle strength . In our study, pVAS was significantly lower in the FIR group than the control group 5 weeks postoperatively (
As mentioned previously, proper pain control after arthroscopic rotator cuff repair can lead to early ROM achievements [24,26]. In our study, FF in ROM was significantly higher in the FIR group than in the control group at 3 months postoperatively (
Martin  explained that wound healing involves the following three steps: inflammation, granulated tissue formation, and tissue remodeling. In the first inflammatory phase, transforming growth factor (TGF)-β1 and platelet-derived growth factor are released from macrophages. In the second granulation phase, TGF-β1 activates fibroblasts to produce extracellular matrix proteins, such as collagen and fibronectin. Finally, in the third tissue remodeling phase, TGF-β1 enables fibroblast migration, which is a critical step in wound healing. Toyokawa et al.  reported that FIR can influence skin wound healing by stimulating secretion of TGF-β1 or by activating fibroblasts independent of skin blood flow and skin temperature. They proved that the number of migrating fibroblasts expressing TGF-βl was significantly higher in the FIR group. Secretion of TGF-β1 by platelets and macrophages is thought to be enhanced by FIR; as a result, TGF-β1 stimulates fibroblast migration. Consequently, collagen production was also increased in the FIR group. The production of collagen fibers due to FIR-induced activation of fibroblasts has been considered as a possible mechanism for the promotional effect of FIR on wound healing .
However, in our study, the healing failure rate was not statistically different (
There are several strengths in this study. First, this is the first prospective randomized comparative clinical trial for evaluating the efficacy and safety of FIR after rotator cuff repair. Until now, there have been several studies investigating the clinical application of FIR, mainly for skin or lymphedema [8,29,30]. Therefore, the results of this preliminary analysis seem to be promising and could be applied especially to other orthopedic fields. Second, the current study included homogenous patients in terms of tear size, operation time, difficulties and extent of surgery, and rehabilitation; thus, we can estimate the effects of FIR more objectively. However, our work was subject to several limitations as well. First, this study had a relatively short-term follow-up. Although adverse effects such as hypersensitivity reaction and re-tear of the repaired rotator cuff are known to occur in the early postoperative period, long-term follow-up is needed to evaluate the efficacy and safety of FIR. Second, as we have discussed above, patients with larger tears should be included, and several options of FIR application, such as duration, regularity, and wavelength, should be investigated in a future large-scale and long-term clinical studies to verify the healing effect of FIR. Third, at 3 months after surgery, only FF, except ER and IR, is statistically significant. So, it is a little difficult to conclude that the effect of FIR is on ROMs improvement. Lastly, it is impossible to ensure patient compliance, although we have provided a checklist to record the exact time and site of irradiation throughout the treatment period.
In conclusion, FIR after arthroscopic rotator cuff repair could be an effective and safe procedure to reduce postoperative pain, thereby facilitating postoperative rehabilitation and resulting in better ROM in the early postoperative period. Further studies and clinical trials are needed with respect to the regularity and durations of radiation, effective wavelength range, and rotator cuff healing.
Ji Young Yoon: Writing/manuscript preparation; Joo Hyun Park: Investigation; Kwang Jin Lee: Investigation; Hyong Suk Kim: Investigation; Sung-Min Rhee: Investigation; Joo Han Oh: Supervision.
No potential conflict of interest relevant to this article was reported.
This study was supported by SeongNam Industry Promotion agency (www.snip.or.kr).