1.      Introduction 

Soft tissue lesions of shoulder including rotator cuff tendinopathy are common causes of shoulder pain and disability[1].Rotator cuff tendinopathy, associated with supraspinatus partial thickness tendon tearsconstitutes more than 50 % of patients with shoulder pains[2].Tendinopathy is a general term describing painful conditions of tendonssecondary to overuse[3].Tendonitis refers to existence of an inflammatory process in tendons. However, several studies have shown that actually thereis little or no inflammatory process in overuse injuries of tendons[4-6].Tendons are relatively avascular, and their regenerations are limited[7].As many treatments of rotator cuff tendinopathyare unyielding and rehabilitation time can be long-lasting,new treatment options targeting the inflammatory process such as Platelet-Rich Plasma (PRP) can be considered for managing of this pathology[8].

PRP injection can deliver the needed cellular and humeralmediators for healing cascade.Plateletgranules as a rich source ofgrowth factors can provide supra-physiological levels of these factors at injury site[9].It has been shown that use of autologousplatelets can help to revascularize the tendon injury site and accelerate its healingand ameliorate painand functional limitations in rotator cuff pathologies[10-13].Although, the effect of PRP injections on rotator cufftears has been investigated and compared with cortisone injection in 2 recent studies from Europe [14]and Egypt[10],we did not have access to the results of these studies at the time ofwritingofour research proposal .Also, to our knowledge, the effect of PRP injections on chronic rotator cufftendinopathy as compared to standard injection therapy with corticosteroidhas not been investigated in patients withmore than 40 years old yet.Therefore, the aim of  this study was comparative evaluation of PRP and corticosteroid injections in chronic rotator cuff tendinopathy in sample of Iranian patients with more than 40 years old. 

2.      Materials and Methods 

In a randomized clinical trial ,35 patients (20 women and 15 men, meanage 47±4 years) who had referred to the University Hospital loghmanin Tehran between 2015 to 2017 were registered in our study. Patients were included if they were ≥40 years, had persistent shoulder pain for at least 3 months, had 3 positive shoulder physical examination tests (among 4 tests including Neer, Hawkin, Speed and Job tests) and confirmed rotator cuff tendinopathy by Magnetic Resonance Imaging (MRI).Patients were excluded if they were diabetic, pregnant, anemic(hemoglobin less than 11mg/dl), thrombocytopenic(platelet count less than 150000 per micro liter).Also patients who had complete rupture ofrotator cuff tendons in MRI, reported radicular pain, had other inflammatory conditions such as Rheumatoid arthritis,Fibromyalgia and Polymyalgia rheumatica, suffered from other shoulder pathologies such as frozen shoulder, had previous shoulder dislocation or joint laxity or used other physical therapy modalitiesorlocal corticosteroid injection in previous 3 months or NSAID drugs in last week before injection(PRP or corticosteroid)were ruled out.A writtenconsent form was completed and signed by all the includedpatients .The research was approved by the Ethics Commit­tee of ShahidBeheshti University of Medical Sciences, and conducted in accordance with the principles of the Declara­tion of Helsinki. Patients were followedin 1,3 and 6 months for assessment of their pain [by Visual Analogue Scale(VAS)],active shoulder range of motion(by goniometer),functional abilities[by WORC(Western Ontario Rotator Cuff) and DASH(the Disabilities of the Arm, Shoulder and Hand)questionnaires] and force of muscles(by manual testing).Both questionnaires have been translated to Persian and validated in Iranian Patients with shoulder pain[15,16]. 

All injections were performed by the first author into subacromialspace via posterolateral direction.Using aseptic technique, the needle is inserted just inferior to the posterolateral edge of the acromion and directed toward the opposite nipple[17].For all patients,after injection,the arm sling was used for 24 hours and then shoulder range of motion exercises started as tolerated.Other physical therapy modalities were not used after injection. The patients were allowed to use 500 mg Acetaminophen tablet every 6 hours for their pain control. NSAIDs were not allowed for 6 months after injection.In the PRP group, using Standardkit (Arjangian), 8.5 ml of blood was taken from the antecubital vein and subsequently 1.5 mL of acid citrate dextrose solution was added to the sample as an anticoagulant.The blood sample was then centrifuged for 15 minutes at 1400 rpm resulting in three layers: the lower layer made up of red blood cells, the intermediate layer is composed of white blood cells and buffy coat, and the upper layer is composed of plasma. The buffy coat layer and the plasma layer were later collected and centrifuged for another 7 minutes at 2800 rpm in order to concentrate platelets.Finally,2 to 3 ml of PRP was collected.Local anaesthetic agent was not injected with PRP. The patients were injected just once by 25 gauges,1.5 inches needle.In the corticosteroid group, patients received a corticosteroid injection [80 mg triamcinolone acetonide, suspension(Depo-Medrol) plus 2cc lidocaine 2%] by means of a 5-ml syringe and 25 gauges,1.5 inches needle.Independent-sample two-tailed t tests were used to analyse mean differences of outcome measures between PRP and corticosteroid groups. The significance level was set at 0.05.Statistical analysis was done using SPSS 16 software and related tests. 

3.      Results 

Allpatients in both groups had statistically significant better functional, shoulder range of motion and strength scores and pain relief in VAS after injection in 1,3 and 6 months compared to baseline.(Paired T test with p value less than 0.01).There were not statistically significant differences in improvements of mean functional, shoulder range of motion and strength scores and pain relief in VAS in 1,3 and 6 months between PRP and corticosteroid group (P value more than 0.05). 

4.      Discussion 

According to data of present study, although there were statistically significant better functional, shoulder range of motion and strength scores and pain relief after injection of PRP or corticosteroid, there were not statistically significant differences in improvement between two groups in mentioned outcome measures in 1,3 and 6 months.In several studies, it has been shown that PRP injection can improve pain, function and MRI outcomes in patients with rotator cuff tendinopathy[18-20].It has been shown that platelet concentrates contain factors such as transforming growth factors, and fibroblast growth factors which can promote tendon cell proliferation, collagen synthesisand vascularisationin vitro and in vivo[21-23].Also,PRP and other growth factor containing biologicals have been used in addition to rotator cuff tear surgery with some positive effects[24,25].Complications of PRP injections in musculoskeletal conditions are rare and include local infection and pain at the site of injection[26]. 

On the contrary, Kesikburun et al[27], have not found any difference between injecting PRP or saline for treatment of rotator cuff tendinopathy or partial tendon ruptures at a 1-year follow-up[27].Also, some authors have not found any beneficial effect using PRP during shoulder surgery[28,29].Although local corticosteroid injection has been a proven therapeutic tool for short term pain relief in shoulder tendinopathies,the potential adverse effects of corticosteroid injections especially for the old patients, should alsobe taken into account[30].Localcorticosteroid injectioncan weaken the injected tendon and may make it more prone to rupture by changing the collagen fascicles[31].In two recent studies,the effect of PRP injections on rotator cuff tears has been investigated and compared with cortisone injection in 6weeks, 12 weeks and 6 months after injection. Authors of these studies have concluded that compared with cortisone injections, PRP injections show earlier benefit although a statistically significant difference after 6 months could not be found.It seems that the above differences between results of mentioned studies with current study are due to methodological variations in these studies including number of patents, patient selection, randomization, PRP preparation, platelet concentrationsin injected liquids, and number of injection. For example, if we used 3 sequential injection of PRP instead of 1 injection as used in Von Wehren et al study[14],it might be possible that our outcome measures became different. Or lack of significant differences in results between our groups may be due to small number of our participants. 

Our study had some limitations. First the small number of patients which was due to narrow inclusion criteria and lack of cooperation of patients in follow ups.Second,we could not do ultrasound guided injections and platelet count measurements of PRP samples due to lack of facilities. Third we could not follow patients for more than 6 months. Further studies with a larger number of patients,more extended follow upsand more controlled conditions are needed. 

5.      Conclusion 

Although we could not find any significant differences between PRP versus corticosteroid injection in terms of pain relief, shoulder range of motion, strength and function improvements, it may be reasonable to use PRP injection in patients with more than 40 years old instead of corticosteroid injection in chronic rotator cuff tendinopathy because of lack of known severe adverse effects of PRP in these group of patients and potential risk of complications of corticosteroid injection especially for the elderly.

Table 1:The basic data of participants in two groups are presented.

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