Introduction
The hamstring is the most commonly injured muscle of competitive athletes. However, there is a lack of evidence for the effectiveness of any possible therapeutic intervention. The Dutch Hamstring Injection Therapy study researches the platelet-rich plasma (PRP) injection’s effectiveness to treat muscle injury with positive outcomes and faster return to play. The study attempts to discover the benefits of PRP with a 1-year follow-up since the primary research yielded no positive results with a 2-month re-injury rate. It uses an appropriate design with wider age criteria than the previous study. The current research possesses major strengths, facilitating the study’s accuracy, and weaknesses that raise more questions for future research.
Key Elements of the Study
The Dutch Hamstring Injection Therapy study is an additional rationale study of an earlier publication in the New England Journal of Medicine with secondary outcomes scores and a 1-year follow-up. This is a randomized trial of platelet-rich plasma injections in acute hamstring muscle injury. The original study was conducted due to the World Anti-Doping Agency’s permission to use intermuscular injections of PRP to treat muscle injuries in 2011 (Reurink et al., 2014). The study examined the effectiveness of the injections regarding the outcome measure and the 2-month re-injury rate (Reurink et al., 2014). The newer research presents the unreported secondary outcomes measure and the 1-year re-injury data.
The design of secondary outcomes scores and 1-year follow-up study differs from the original yet still includes randomization and blinding. The current study set different age criteria of 18 to 50 years old (Reurink et al., 2015). The age frame was extended for the generalisability of the results to the athletic population seen in the sports medicine clinical practice. The research does not include patients with no lesions on MRI and complete muscle raptures or tendon avulsions (Reurink et al., 2015). The former shows no macroscopic sign of tissue damage; the latter are severe injuries that usually require invasive intervention. In the study, the first injection was performed within five days of the injury and the second 5-7 days later (Reurink et al., 2015). However, there is no data on the optimal timing and number of injections or their importance for the healing process; it remains subject to debate in the medical field. As such, the design within the study can be considered appropriate since it introduces a wider variety of patients, as well as minimizes the rate of bias and subjective judgment.
Study’s Results’ Interpretation
The study’s results were similar to the primary outcome measure and time to return to play. The 80 participants of the study were randomly divided into two groups: 41 patients received allocated PRP injections and a control group of 39 who received placebo injections. Clinical examination was performed at baseline, one week and 26 weeks later. It included hamstring flexibility testing and isometric knee flexion force (Reurink et al., 2015). MRI was performed within five days of injury and within seven days after the patient’s return to play. The difference in re-injury rate was analyzed with a Cox proportional hazards model (Reurink et al., 2015). The Hamstring Outcome Score was tested with a linear regression model (Reurink et al., 2015). There were no differences observed between the study groups: around 30% of both sustained a re-injury during the 1-year follow-up period (Reurink et al., 2015). Additionally, no distinction between PRP and placebo injections was found in regards to alterations of subjective, clinical, and MRI measures (Reurink et al., 2015). As such, these results suggest that intermuscular PRP injections bear no benefits to patients with acute hamstring injuries.
Strengths and Weaknesses of the Study
The study can be considered more accurate compared to other studies conducted on the review of PRP injections’ effectiveness due to several major strengths. The main strength of the research is the minimization of bias, leading to the most precise results. It was accomplished by introducing a double-blind placebo control group (Reurink et al., 2015). Additionally, the identical measurements of all the patients were performed by one physician (Reurink et al., 2015). The patients also went through a predefined criteria-based rehabilitation program to minimize the influence of subjective judgment. Another strength of the study is related to generalizability; it includes a large number of competitive amateur athletes rather than professionals. Professional athletes are more likely to progress faster through rehabilitation due to seeking and receiving medical care for less severe injuries (Reurink et al., 2015). As such, the study is more accurate than any previously published works that did not include randomization, blinding, or amateur athletes in the review.
However, The Dutch Hamstring Injection Therapy study has several weaknesses that might have possibly affected the study’s results and application. Firstly, the study did not include the assessment of the adherence of the patients to the rehabilitation program, as well as the supervising physiotherapists in following the recommended protocol (Reurink et al., 2015). Secondly, the timing and the dosage of the PRP injections of the study could have rendered the injections ineffective. Additionally, the population in the study was primarily represented by male competitive athletes (Reurink et al., 2015). All of these limitations can suggest that the results of the study could have been different if it included or consisted of female athletes; the timing and dosage were altered. The adherence to the rehabilitation program might have contributed to the overall outcomes measures.
Take-Home Message
The study has proven that the timing and dosage of PRP injections performed in the study are not beneficial to the male competitive athletes with acute hamstring injuries. The 1-year follow-up re-injury rate confirms the results of the primary study, leaving no doubt in the ineffectiveness of the injections. However, considering the limitations of the study, there are more questions to be answered about acute hamstring injuries and PRP injections. Since the study does not provide any data on the matter, the timing, number, and dosage, as well as their importance or the lack thereof, can be a subject of further research. There is also a possibility that the injections would yield alternative results for female competitive athletes with acute hamstring injuries.
Conclusion
The Dutch Hamstring Injection Therapy study is relevant research that proves the ineffectiveness of PRP injections in acute hamstring injury of competitive male athletes. Due to its randomization and blinding, the study’s results can be considered accurate. However, the timing, number, and dosage of the PRP injections performed in the study could have been insufficient, therefore rendering them ineffective. The research leaves many unanswered questions regarding the importance of timing, number, and dosage of the injections and whether the results would be different with female athletes. The study can serve as an encouragement to other researchers in the medical field to find the answers to these questions.
References
Reurink, G., Goudswaard, G. J., Moen, M. H., Weir, A., Verhaar, J. A., Bierma-Zeinstra, S. M., Maas, M. & Tol, J. L. (2014). Platelet-rich plasma injections in acute muscle injury. The New England Journal of Medicine, 370(26), 2546-2547.
Reurink, G., Goudswaard, G. J., Moen, M. H., Weir, A., Verhaar, J. A., Bierma-Zeinstra, S. M., Maas, M. & Tol, J. L. (2015). Rationale, secondary outcome scores and 1-year follow-up of a randomised trial of platelet-rich plasma injections in acute hamstring muscle injury: The Dutch Hamstring Injection Therapy study. British Journal of Sports Medicine, 49(18), 1206-1212.