Distal Injury

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Distally the quadriceps tendons merge together before inserting on the patella. MR appearance of the quadriceps tendon is that of a layered structure usually trilaminar (56%), although occasionally one (6%), two (30%), or four (8%) layers are seen. The superficial layer represents the rectus femoris, the deep layer the vastus intermedius, and the middle layer consists of variable contributions of the vastus lateralis and medialis [37] (Fig. 12).

Distal injury to the quadriceps is an unusual injury most commonly occurring in individuals over 40 [38]. Injury may occur as result of direct trauma but usually related to forced eccentric contraction in a mildly flexed position often in effort to regain balance during falls [39]. Spontaneous ruptures and

Distal Quadriceps Contusion

Fig. 10. (A) Focal edema around the central tendon of the rectus femoris on axial fluid sensitive image. The central location of injury suggests longer rehabilitation time. (B) Coronal IR images in a different patient with a long segment (>13 cm) injury of the central tendon. (C) Focal peripheral injury of the rectus femoris involving a large cross-sectional area of the muscle. (D) Chronic central tendon lesion of rectus femoris that has healed. Note fibrous proliferative scar tissue and lack of adjacent edema (arrow).

bilateral ruptures have been described in those with systemic metabolic disease and anabolic steroid use [40-42]. Because of the large forces required to disrupt the tendon proper, most injury involves the myotendinous junction or underlying weakened tendon [39].

Fig. 11. Edema surrounding rectus femoris tendon 2 cm from its proximal insertion compatible with partial tear (arrow).

Imaging plays an important role as disruptions of extensor mechanism may be surprisingly misdiagnosed ranging from 39% to 67% of cases [43]. Radiographs may show extensive soft tissue swelling and loss of quadriceps tendon shadow, displaced calcifications, or patella baja [44]. MR imaging is the preferred modality of evaluation because of excellent anatomic depiction particularly in the setting of soft tissue swelling and hematoma, which allows accurate treatment planning [45-49]. Partial tears can be differentiated between complete tears as no intact fibers are seen with complete tears. Ultrasound may also be effective but again operator experience is needed [50].

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