In the present study, PRP and AWB both lead to significant improvement in pain, function and pain pressure threshold in patients with chronic tennis elbow. However, this improvement was similar in both treatment groups which meant the effect of PRP therapy in tennis elbow management was shown to be almost same as AWB. Mayo score improvement reached minimal clinically important difference reported for Mayo score change following therapy in inflammatory joint disease in both treatment groups . Also, success rate defined as 25% decrease in pain scores compared to baseline was achieved in both groups.
The efficacy of PRP injection for short term and long term pain relief in lateral epicondylitis was evaluated in previous studies [9, 11, 12].
There are many studies in favour of PRP in chronic tendinopathies. In 2006, Mirsha and his colleagues evaluated treatment of chronic severe elbow tendinosis with PRP. Eight weeks after the treatment, patients who had received PRP noted significant improvement in pain scores compared to control group . The effectiveness of PRP compared with corticosteroid injections in patients with chronic lateral epicondylitis was also determined in a study by Peerbooms. He found that regarding pain reduction and functional improvement, corticosteroid was better initially and then declined, whereas the PRP group progressively improved, however this study also lacked a control group .
In 2013 Ahmad Z et al. carried out a systematic review of the current evidence on the effects of PRP in lateral epicondylitis on clinical outcomes. In this review, five randomized controlled trials were included. The largest randomized controlled trial found that PRP had significant benefit compared with corticosteroids with regard to pain and disabilities of the arm, shoulder and hand scores at 1 and 2 year time points. The review highlights the limited but evolving evidence for the use of PRP in lateral epicondylitis; however, further research is suggested by that study to understand the concentration and preparation that facilitates the best clinical outcome . In another systematic review by Taylor DW seven studies were evaluated. This review demonstrated favourable outcomes in tendinopathies in terms of improved pain and functional scores. The authors concluded that PRP use in tendon and ligament injuries has several potential advantages, including faster recovery and possibly, a reduction in recurrence, with no adverse reactions described .
Contrary to the results of our study and the studies mentioned above, there are some studies showing no significant improvement in pain scores after PRP injection. Such a study was conducted by Shiple BJ conducted to compare the effectiveness of a single injection of platelet-rich plasma (PRP), glucocorticoid (GC), or saline in reducing pain in lateral epicondylitis. The pain intensity scale of the Patient-Rated Tennis Elbow Evaluation (PRTEE) questionnaire was the main outcome measure (least to most pain = 0-50 points) .
Krogh and his colleagues in 2013 randomized 60 subjects into three groups: PRP, corticosteroid or saline injection. All participants had had tennis elbow for at least 3 months. They found at three months no significant difference in terms of pain or functional improvement between the groups. The lack of sufficient number of platelets in PRP derivatives in above mentioned studies or different methods of PRP preparation might be one reason for not getting positive effects from PRP injection .
On the other hand, the efficacy of autologous whole blood injection in treatment of chronic tennis elbow has been evaluated in a number of studies. In our study autologous whole blood injection lead to significant pain and functional improvement in chronic tennis elbow.
In a trial in 2010, Kazemi found that at 8 weeks post-injection that AWB appeared to be more efficacious in all outcomes (including pain and function) than steroid injection [P <0.001]. However, there was a high risk of bias in that study because of inadequate randomization method .
In 2012, Dojode et al. compared autologous blood injection to steroid injection in 60 patients with chronic tennis elbow. They found that the steroid group demonstrated better pain relief at 1 and 4 weeks follow-up. However, at 12 weeks and 6 months, there was significantly better pain reduction in the whole blood group than in the steroid group. Also, there was a greater recurrence rate in the steroid group compared to the AWB group (37% vs. 0%) .
However, recent reviews of clinical trials revealed limited evidence supporting the effectiveness of autologous blood injections for chronic tendinopathies. According to these reviews, even though refractory chronic tendinopathy might be responsive to AWBs and despite the proven efficacy of PRP on tissue regeneration in experimental studies, but the data available to date are limited by quality and size of study, as well as length of follow up and are currently insufficient to recommend this modality for routine clinical use [27–30].
In the present study, there was no significant difference in pain reduction and functional improvement between PRP and AWB injection in chronic tennis elbow in 12 month follow up. The effect of autologous whole blood in comparison with PRP has been investigated in some other studies; in a systematic review in 2009 by Rabago, four injection therapies for lateral epicondylosis: prolotherapy, polidocanol, whole blood and platelet-rich plasma, whole blood injections were assessed, They reported significant improvement in functional scores and in maximal grip strength compared with baseline in the intervention groups. They concluded that according to existing data for autologous whole blood and PRP injection, these therapies could be effective in treating tennis elbow, but as the authors concluded the results of this systematic review were limited by lack of large definitive clinical trials .
Creaney conducted a study of 150 people comparing whole blood to PRP for the treatment of lateral epicondylitis. The participants had all previously failed to respond to a more ‘conservative’ treatment like stretching and eccentric exercise. Using the criteria of an improvement of 25 points on the patient-related tennis elbow evaluation score (PRTEE), improvement was noticed in both groups and there was no significant difference in the success rate between either . The results of our study were in agreement with the results of this study.
In a systematic review in 2012, conducted to determine the efficacy of autologous blood concentrates in decreasing pain and improving healing and function in patients with orthopaedic bone and soft-tissue injuries, the authors evaluated twenty three randomized trials and ten prospective cohort studies and concluded that there is uncertainty about the evidence to support the increasing clinical use of platelet-rich plasma and autologous blood concentrates as a treatment modality for orthopaedic bone and soft-tissue injuries including tennis elbow .
In a systematic review and network meta-analysis of randomized controlled trials by Krogh in 2013, the comparative effectiveness and safety of injection therapies in patients with lateral epicondylitis were assessed. Both autologous blood and platelet-rich plasma were also statistically superior to placebo in clinical trials .
Generally, there is moderate evidence from two fair quality (1+) RCTs that platelet-rich plasma is no more efficacious than autologous blood injections for the treatment of lateral epicondylitis [32, 34].
The main factors which may cause controversy in the studies mentioned above regarding the efficacy of PRP or whole blood might arise from lack of standardization of study protocols, platelet-separation and injection techniques whether ultrasound guided or blind, and outcome measures.
Both PRP and whole blood therapies have been claimed to promote healing through the action of various growth factors on the affected tendon . The mechanism of action is proposed to be a healing response in the damaged tendons triggered by the growth factors in the blood. These growth factors trigger stem-cell recruitment, increase local vascularity and produce an instructional biological microenvironment for local and migrating cell activities .
It is believed that platelet-rich plasma can augment or stimulate healing by turning on the same biological healing process that normally occur in the human body after musculoskeletal injury. However, not only platelet-rich plasma, but also platelet-poor plasma, stimulates cell proliferation and total collagen production [37, 38]. Increased production of endogenous growth factors have been found in human tendons treated with PRP [3, 12, 21]. The above mechanism helps explain why PRP alone or whole blood application can have a lasting effect on the healing process [23–25].