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From Sports Medicine Research: In the Lab & In the Field

Written by: Mark Rice

Reviewed by: Stephen Thomas

Risk factors of recurrent hamstring injuries: a systematic review

de Visser H, Reijman M, Heijboer M, Bos P. Br J Sports Med. 2011 Oct 19. [Epub ahead of print] (Link to abstract)

We have all been there, in the heat of competition, or deep into a practice, one of our athletes goes down with a hamstring strain. We immediately begin managing inflammation and pain, but how often do we sit back and ask ourselves “is there something that predisposed this athlete to injury?” In this article De Visser et al. attempted to answer that question. While there is no shortage of articles available detailing hamstring injuries, injury classification, and treatment; there is currently very little data available on hamstring re-injury risk factors. By performing a systematic review of available literature, the authors were able to identify 131 prospective articles on hamstring re-injury risk factors post acute injury. Of the studies identified, only 5 studies possessed the adequate inclusion criteria: 1) subjects diagnosed with a Grade 1-3 acute hamstring strain on physical exam or Grade 0-3 when identified through MRI or sonography in conjunction with physical exam (using the Peetrons study criteria) 2) Prospective study with 2 week minimum follow-up after return to sport 3) Full-text available. The data from these studies show that the hamstring re-injury incidence rate is anywhere from 13.9-63.3% during the same season and up to 2 years after the initial injury. Due to the low number of studies identified (n = 5), the authors were able to discover limited evidence for 3 potential re-injury risk factors. First, 2 articles identified that athletes which initially sustained a Grade 1 hamstring strain were more likely to re-injure the affected hamstring (24.1-35%) than other individuals who sustained a Grade 0 (0-9.3%) or Grade 2 (6.3%) initial injury. Another identified risk-factor for hamstring re-injury was an ipsilateral ACL reconstruction. When compared to athletes that haven’t undergone ACL reconstruction, the re-injury incidence rate is 66.6% vs 17.1%, irrespective of graft type. One final item identified as a risk factor for re-injury was a larger tear area upon initial injury as identified by MRI, 47.03 vs 12.42 cm³. Finally, one other item that was identified for a lower risk of re-injury was the rehabilitation program format. Programs focusing on ‘agility and stabilization’ were more successful at limiting re-injury than ‘stretching and strengthening’ programs, 7.7% vs 70% respectively.

This article is of interest for a several reasons. Not only does it identify items that seem to be fairly elementary risk factors for hamstring re-injury, but the inclusion of ACL reconstruction presents an intriguing pathway for further discussion. Is there some level of neuromuscular compromise as far as the hamstrings are concerned post-ACL reconstruction and is this an area to begin focusing on even further in order to not only protect the reconstructed knee, but also to limit any re-injury to the hamstrings? While this study has very limited data to draw upon, it does shine some light on areas that we need to take into consideration at the onset of an initial hamstring strain as well as post-ACL reconstruction. This study also illustrates that perhaps the hamstring responds better to agility like exercises as opposed to strengthening. That isn’t to say that strengthening should be forsaken, but as the athlete recovers and gets closer to returning to play, perhaps the balance between strength exercises and agility exercises may need to shift more towards the latter. Another item that might need to be taken into consideration is some form of diagnostic imaging to be able to truly determine the severity of a hamstring injury. While an MRI might be cost prohibitive, the use of ultrasound might be an attractive option to help us visualize the injury, for structuring our or rehabilitation protocols as well as giving us an idea what the likelihood of re-injury realistically might be for the individual. What are your thoughts on this study? Do any of the risk-factors surprise you? What sort of efforts do you make after your athlete sustains their first hamstring injury to prevent subsequent injury?

From Sports Medicine Research: In the Lab & In the Field

Written by: Lisa Chinn

Reviewed by: Jeffrey Driban

Preventive effect of eccentric training on acute hamstring injuries in men’s soccer: A cluster-randomized controlled trial

Petersen J, Thorborg K, Bachmann Nielsen M, Budtz-Jorgensen E, Holmich P (2011). Am J Sports Med, 39 (11), 2296-2303. (Link to abstract)

Hamstring muscle strains are very common in sports, especially soccer. The majority of injuries seem to occur when the hamstrings are contracting eccentrically, indicating a need for research on the efficacy of eccentric exercises on the prevention of hamstring injuries. This study used a cluster-randomized controlled trial to evaluate whether a 10-week training program using the Nordic hamstring exercise could lower the incidence of new and recurrent hamstring injuries. 54 male Dutch soccer teams were randomly assigned to either the 10-week intervention group (23 teams, 461 players) or a control (27 teams, 482 players) condition. The intervention was the Nordic hamstring exercise, a partner exercise in which one participant is supporting the ankles/lower legs of a second partner who is kneeling. The kneeling partner attempts a forward-falling motion (keeping hips/body rigid and in-line with legs) using his hamstring muscles to resist the fall. During team training sessions, coaches were asked to perform the exercise up to 3 times a week for a minimum of 10 weeks during a mid-season, non-competitive break (27 sessions). Hamstring injury (new and recurrent) and severity (days missed) were recorded for a year following the intervention. The control group reported 52 hamstring injuries (32 new and 20 recurrent) whereas the intervention group had a total of 15 injuries (12 new and 3 recurrent). Comparing the two groups, the Nordic hamstring intervention group significantly reduced total hamstring injury rates, as well as new and recurrent injuries. A numbers needed to treat analysis found that to prevent one hamstring injury (new or recurrent) 13 players need to perform the intervention. The intervention did not influence injury severity.

This study was the first to report the reduction of hamstring injury using the Nordic hamstring exercise in a cluster-randomized controlled trial study design. This simple, partner implemented eccentric exercise was found to reduce total hamstring injury rate by more than 60% and recurrent rate by approximately 85%. Overall, this study evaluated how integrating a quick eccentric exercise can help athletes who have sustained a hamstring injury reduce the risk of recurrent injury. As sports medicine professionals, we know the importance of including strengthening exercises into our rehabilitation programs for injured athletes. However, often times we feel we need the newest high-tech, expensive equipment and gadgets to accomplish our goals. This study clearly shows that, in the case of hamstring rehabilitation, this may not be true. Although this study did not evaluate the affect of the Nordic hamstring exercise in rehabilitation protocols specifically, it does show potential for the incorporation of this simple exercise into rehab. The Nordic hamstring exercise only requires a partner for support and can be performed almost anywhere (clinic, field, turf, etc). Not only can this exercise be done to prevent recurrent injury, sports medicine personnel can encourage coaches to implement this into their regular training programs because of the ease of implementation and short amount of time needed to complete the exercise. One of the weaknesses of this study is that it only included male soccer players. What are your thoughts on other sports performing this exercise, will it be as affective? Also, what about in females? As sports medicine professionals, is this an exercise you have incorporated into your hamstring rehabilitations? If no, would you consider it? If yes, do you feel it is as successful as this study’s results?