Clinical and morphological changes following 2 rehabilitation programs for acute hamstring strain injuries: a randomized clinical trial

Abstract

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-.

FIGURE 1

The percent cross-sectional area of injured muscle was estimated by considering all muscles that exhibited T2 hyperintensity.

FIGURE 2

Flow diagram outlining enrollment and testing procedures.

FIGURE 3

Coronal and axial T2-weighted MRI scans taken after injury (A and B) and after completion of rehabilitation (C and D). The tendon of the injured limb can initially appear wavy (A; arrow). Scar tissue begins to form during the course of rehabilitation and is clearly visible on MRI scans obtained after completion of rehabilitation (C and D; arrows). Edema and hemorrhage (T2 hyperintensity) can extend into the fascial plane (A and B). Over the course of time, fascial drainage can lengthen the craniocaudal extent of injury and result in MRI measurements longer than the actual muscle/tendon damage. T2 hyperintensity was often more concentrated during the initial MRI examination (A and B), compared to a more diffuse signal present in the follow-up MRI examination (C and D). Abbreviation: MRI, magnetic resonance imaging.

FIGURE 4

Coronal and axial T2-weighted magnetic resonance images of subject 3, taken after initial injury (A and B) and 7 days after reinjury (C and D). The location of reinjury was similar to the initial injury. Early signs of scar tissue formation can be seen on the second set of images (C and D; arrows).