University of New South WalesSydney, New South Wales, AustraliaDepartments of Family Medicineand Orthopedic SurgeryUniversity of WisconsinMadison, Wisconsin, U.S.A.
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For the sport medicine clinician, muscle strains can be one of the most frustrating injuries to treat. Despite apparently thorough management plans, objective testing, and clinical evaluation before return to play, these injuries often recur, with the impression that the clinician has failed by allowing the athlete to return to sport too early. The inexperienced or lay person will offer a simple solution: that these recurrences could have been prevented by allowing athletes a little extra time for healing before return to play. Analysis of recurrence data from the Australian Football League (AFL) injury surveillance system (Table 1) 1,2 shows that the situation may not be all that simple. While a fair proportion of muscle strains recurred during the first week after return, there was a persistent significantly increased risk of recurrence for many weeks after return to play. This pattern contrasts with a muscle contusion injury, for which after a single week of increased risk for recurrence, there is a quick return-to-baseline level of risk (Table 1). The cumulative risk of recurrence for a hamstring strain for the remainder of the season was 30.6%. By comparison, in the AFL over the same period, the cumulative recurrence risk for thigh contusion was 12%, for concussion was 5%, for knee medial collateral ligament strain was 11%, and for ankle sprain was 15%. 2 Although the pessimist will cite that an unacceptable 12.6% of hamstring strains recur during the first week after return to play, the optimist, who is often the coach, will be reassured that 87.4% of players successfully complete their next game. The realist will understand that even the majority who make it through that first game are still at high risk in the ensuing weeks. Therefore, although most athletes do not suffer recurrences of a muscle strain injury, those who are successful must negotiate a lengthy period of increased susceptibility. These results for AFL football have not been reproduced for other sports to the best of our knowledge, but clinical experience suggests similar trends.This lengthy period of increased susceptibility for recurrent injury is not surprising when the pathophysiology of muscle stretch injury and repair is examined in laboratory studies. 3,4 Despite our clinical impressions that an average muscle strain will resolve with an appropriate rehabilitation program in 2–3 weeks, recent evidence shows that there is still ongoing muscle regeneration in the presence of mature scar tissue formation. 3 The early postinjury period is marked by upregulation of Type III collagen mRNA expression with relatively little myosin mRNA expression. 3 This observation extends to the protein level where Type III collagen is present prior to any histological evidence of myofiber regeneration. Clinicians and therapists face an ongoing dilemma of requiring some new collagen formation for the muscle–tendon unit to carry load and generate torque about a joint while at the same time seeking minimal scar formation in order to minimize stiffness. Basic science studies are needed to delineate factors that regulate and control new collagen synthesis.Imaging studies of athletes diagnosed with muscle strain injury have shown that the injury can be much more extensive than initially appreciated by clinical examination. 5–7 These findings, together with unpublished data from one of the authors (T.M.B.) that repeat magnetic resonance imaging of athletes who have been cleared for return to sport often show persistent high signal changes and muscle edema on T2 images, should prompt us to consider the clinical strategies used to determine recovery from injury.