Synopsis: Hamstring strain injuries remain a challenge for both athletes and clinicians, given their high incidence rate, slow healing, and persistent symptoms. Moreover, nearly one third of these injuries recur within the first year following a return to sport, with subsequent injuries often being more severe than the original. This high reinjury rate suggests that commonly utilized rehabilitation programs may be inadequate at resolving possible muscular weakness, reduced tissue extensibility, and/or altered movement patterns associated with the injury. Further, the traditional criteria used to determine the readiness of the athlete to return to sport may be insensitive to these persistent deficits, resulting in a premature return. There is mounting evidence that the risk of reinjury can be minimized by utilizing rehabilitation strategies that incorporate neuromuscular control exercises and eccentric strength training, combined with objective measures to assess musculotendon recovery and readiness to return to sport. In this paper, we first describe the diagnostic examination of an acute hamstring strain injury, including discussion of the value of determining injury location in estimating the duration of the convalescent period. Based on the current available evidence, we then propose a clinical guide for the rehabilitation of acute hamstring injuries, including specific criteria for treatment progression and return to sport. Finally, we describe directions for future research, including injury-specific rehabilitation programs, objective measures to assess reinjury risk, and strategies to prevent injury occurrence. Level of Evidence: Diagnosis/therapy/prevention, level 5. J Orthop Sports Phys Ther 2010;40(2):67–81. doi:10.2519/jospt.2010.3047

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Study Design: Prospective randomized comparison of 2 rehabilitation programs. Objectives: The objectives of this study were to compare the effectiveness of 2 rehabilitation programs for acute hamstring strain by evaluating time needed to return to sports and reinjury rate during the first 2 weeks and the first year after return to sport. A third objective was to investigate the relationship between functional testing performance and time to return to sports and reinjury rates after return to sport. Background: Hamstring muscle strains are common in sports and often result in chronic pain, recurrent hamstring strains, and reduced sports performance. Current rehabilitation programs are primarily developed anecdotally and lack support from prospective, randomized research. Methods and Measures: Twenty-four athletes with an acute hamstring strain were randomly assigned to 1 of 2 rehabilitation groups. Eleven athletes were assigned to a protocol consisting of static stretching, isolated progressive hamstring resistance exercise, and icing (STST group). Thirteen athletes were assigned to a program consisting of progressive agility and trunk stabilization exercises and icing (PATS group). The number of days for full return to sports, injury recurrence within the first 2 weeks, injury recurrence within the first year of returning to sports, and lower-extremity functional evaluations were collected for all subjects and compared between groups. Results: The average (±SD) time required to return to sports for athletes in the STST group was 37.4 ± 27.6 days, while the average time for athletes in the PATS group was 22.2 ± 8.3 days. This difference was not statistically significant (P = .2455). In the first 2 weeks after return to sports, reinjury rate was significantly greater (P = .00343, Fisher's exact test) in the STST group, where 6 of 11 athletes (54.5%) suffered a recurrent hamstring strain after completing the stretching and strengthening program, as compared to none of the 13 athletes (0%) in the PATS group. After 1 year of return to sports, reinjury rate was significantly greater (P = .0059, Fisher's exact test) in the STST group. Seven of 10 athletes (70%) who completed the hamstring stretching and strengthening program, as compared to only 1 of the 13 athletes (7.7%) who completed the progressive agility and trunk stabilization program, suffered a recurrent hamstring strain during that 1-year period. Conclusions: A rehabilitation program consisting of progressive agility and trunk stabilization exercises is more effective than a program emphasizing isolated hamstring stretching and strengthening in promoting return to sports and preventing injury recurrence in athletes suffering an acute hamstring strain. Future randomized clinical trials should investigate the potential for progressive agility and trunk stabilization programs in the prevention of hamstring strain injury during sports.

STUDY DESIGN Randomized, double-blind, parallel-group clinical trial. OBJECTIVES To assess differences between a progressive agility and trunk stabilization rehabilitation program and a progressive running and eccentric strengthening rehabilitation program in recovery characteristics following an acute hamstring injury, as measured via physical examination and magnetic resonance imaging (MRI). BACKGROUND Determining the type of rehabilitation program that most effectively promotes muscle and functional recovery is essential to minimize reinjury risk and to optimize athlete performance. METHODS Individuals who sustained a recent hamstring strain injury were randomly assigned to 1 of 2 rehabilitation programs: (1) progressive agility and trunk stabilization or (2) progressive running and eccentric strengthening. MRI and physical examinations were conducted before and after completion of rehabilitation. RESULTS Thirty-one subjects were enrolled, 29 began rehabilitation, and 25 completed rehabilitation. There were few differences in clinical or morphological outcome measures between rehabilitation groups across time, and reinjury rates were low for both rehabilitation groups after return to sport (4 of 29 subjects had reinjuries). Greater craniocaudal length of injury, as measured on MRI before the start of rehabilitation, was positively correlated with longer return-to-sport time. At the time of return to sport, although all subjects showed a near-complete resolution of pain and return of muscle strength, no subject showed complete resolution of injury as assessed on MRI. CONCLUSION The 2 rehabilitation programs employed in this study yielded similar results with respect to hamstring muscle recovery and function at the time of return to sport. Evidence of continuing muscular healing is present after completion of rehabilitation, despite the appearance of normal physical strength and function on clinical examination. LEVEL OF EVIDENCE Therapy, level 1b–. J Orthop Sports Phys Ther 2013;43(5):284-299. Epub 13 March 2013. doi:10.2519/jospt.2013.4452

Hamstring strain re-injury rates can reach 30% within the initial two weeks following return to sport (RTS). Incomplete recovery of strength may be a contributing factor. However, relative strength of the injured and unaffected limbs at RTS is currently unknown. PURPOSE: Characterize hamstring strength and morphology at the time of RTS and six months later. METHODS: Twenty-five athletes that experienced an acute hamstring strain injury participated, following completion of a controlled rehabilitation program. Bilateral isokinetic strength testing and magnetic resonance imaging (MRI) were performed at RTS and 6-months later. Strength (knee flexion peak torque, work, angle of peak torque) and MRI (muscle and tendon volumes) measures were compared between limbs and over time using repeated measures ANOVA. RESULTS: The injured limb showed a peak torque deficit of 9.6% compared to the uninjured limb at RTS (60°/s, p<0.001), but not 6-months following. The knee flexion angle of peak torque decreased over time for both limbs (60°/s, p<0.001). MRI revealed that 20.4% of the muscle cross-sectional area showed signs of edema at RTS with full resolution by the 6-month follow-up. Tendon volume of the injured limb tended to increase over time (p=0.108), while muscle volume decreased 4–5% in both limbs (p<0.001). CONCLUSION: Residual edema and deficits in isokinetic knee flexion strength were present at RTS, but resolved during the subsequent six months. This occurred despite MRI evidence of scar tissue formation (increased tendon volume) and muscle atrophy, suggesting that neuromuscular factors may contribute to the return of strength.