The largest study of the imaging appearance of quadriceps muscle strains followed 40 professional Australian Rules football players for 3 years and compared the rehabilitation interval (time to return to full-time training) after having completed a predefined rehabilitation regimen . Fifteen cases involved the rectus femoris, six vastus intermedius, one vastus lateralis, and three had normal MRI exam.
This study found central injuries around the central tendon had a statistically significantly longer time to rehabilitation as compared with peripheral injuries or epimyseal injuries that did not involve the central tendon (26.8 versus 9.2 days). The vastus tears had an average rehabilitation interval of 4.4 days. The MR-negative group had rehabilitation interval of 5.7 days. Injuries involving the middle ofthe thigh rather than proximal aspect had longer rehabilitation interval as well (16.2 versus 10.8 days) (Fig. 10). No distal injuries occurred in this study.
Thus, the most significant injuries were rectus femoris central tendon injures greater than 13 cm in length or greater than 15% cross-sectional area resulting in rehabilitation intervals of 32.7 to 35.3 days. These injuries were termed acute bullseye lesions because of MR appearance. Peripheral injures less than 15% of cross-sectional area had the smallest rehabilitation interval of zero days in three cases. One hypothesis for longer rehabilitation times for healing central tendon injuries is that scar tissue from the healing process predisposes to discordant contraction of deep and superficial fibers resulting in chronic irritation and prolonged healing.
This central tendon injury pattern of the rectus femoris has also been described with ultrasound with good MR correlation but the experienced authors of this study suggested that low-grade injuries may be difficult to detect and may be overlooked .
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