BACKGROUND: Magnetic resonance imaging (MRI) allows for detailed evaluation of hamstring injuries; however, there is no classification that allows prediction of return to play. PURPOSE: To correlate time for return to play in professional football players with MRI findings after acute hamstring strains and to create an MRI scoring scale predictive of return to sports. STUDY DESIGN: Descriptive epidemiologic study. METHODS: Thirty-eight professional football players (43 cases) sustained acute hamstring strains with MRI evaluation. Records were retrospectively reviewed, and MRIs were evaluated by 2 musculoskeletal radiologists, graded with a traditional radiologic grade, and scored with a new MRI score. Results were correlated with games missed. RESULTS: Players missed 2.6 ± 3.1 games. Based on MRI, the hamstring injury involved the biceps femoris long head in 34 cases and the proximal and distal hamstrings in 25 and 22 cases, respectively. When \u3c 50% of the muscle was involved, the average number of games missed was 1.8; if \u3e 75%, then 3.2. Ten players had retraction, missing 5.5 games. By MRI, grade I injuries yielded an average of 1.1 missed games; grade II, 1.7; and grade III, 6.4. Players who missed 0 or 1 game had an MRI score of 8.2; 2 or 3 games, 11.1; and 4 or more games, 13.9. CONCLUSIONS: Rapid return to play (\u3c 1 week) occurred with isolated long head of biceps femoris injures with \u3c 50% of involvement and minimal perimuscular edema, correlating to grade I radiologic strain (MRI score \u3c 10). Prolonged recovery (missing \u3e 2 or 3 games) occurs with multiple muscle injury, injuries distal to musculotendinous junction, short head of biceps injury, \u3e 75% involvement, retraction, circumferential edema, and grade III radiologic strain (MRI score \u3e 15). CLINICAL RELEVANCE: MRI grade and this new MRI score are useful in determining severity of injury and games missed-and, ideally, predicting time missed from sports
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