Anatomy

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The hamstring complex is composed of three major muscles: biceps femoris and semimembranosus and semitendinosus muscles. The biceps femoris is composed of a long and short head. The long head arises on the medial aspect of the posterior ischial tuberosity with a common tendon insertion with the semitendinosus called the conjoined tendon [25] (Fig. 5A-D). Distally it inserts on the fibular head. Depending on leg positioning and relationship to the ground it can serve as a hip extensor, knee flexor, and external rotator of the hip and knee (Fig. 5E,F).

The short head of the biceps tendon is not biarticular but has a proximal attachment on the lateral aspect of the linea aspera below the gluteal tuberosity and inserts distally on the fibular head [26]. The short head of the biceps can be absent, and unlike the long head that receives innervation via a tibial portion of m wMV9

Fig. 3. Axial fluid sensitive image mid thigh shows increased fluid signal in rectus femoris consistent with contusion. Note enlargement and diffuse edema in this soccer player that sustained a direct blow to the thigh.

Mri Gastrocnemius Contusion

Fig. 4. (A) Prominent acute intramuscular medial gastrocnemius hematoma. Note mixed increased and decreased signal probably related to deoxyhemoglobin. (B) Intermuscular fluid collection presumable a seroma from a resorbed gastrocnemius hematoma. Note dark rim compatible with hemosiderin (arrow).

the sciatic nerve, the short head receives innervation from the common peroneal nerve. This dual innervation has been hypothesized a source of potentially discordant contraction which can lead to injury [27].

The semitendinosus is another biarticular muscle with a common origin of the long head of the biceps femoris via the conjoined tendon (Fig. 5). Distally it has a long tendon, which inserts on the proximal medial tibia posterior to the sartorius. Its function is similar to that of the long head of biceps femoris although because of its medial sided insertion distally it functions as an internal rotator of the hip and knee. It has been classified as a digastric muscle owing to a central raphe where the proximal fibers insert [27].

Semimembranosus is the third major muscle of the hamstring complex with a proximal attachment on the ischial tuberosity anterior the conjoined tendon (Fig. 5). The distal insertion is primarily on the medial posterior aspect of the tibial plateau but has multiple slips extending to surrounding structures such as the medial collateral ligament, and popliteus muscle [26]. Its function is similar to the semitendinosus.

The ischial tuberosity also has insertion sites of the sacrotuberous ligament posteromedially in close proximity to the conjoined tendon insertion. The

Semitendinosus Strain

Fig. 5. (A) Axial T1-weighted images of proximal thighs. Note how T1-weighted images allow good depiction of muscle fat planes. This image is proximal to the ischial tuberosity and shows the sacrotuberous ligament (white arrow) insertion on the tuberosity. (B) Mid tuberosity level shows the anterior semimembranosus insertion (black arrow) and the posterior conjoined tendon of biceps femoris and semitendinosus (white arrow). (C) Inferior aspect of ischial tuberosity shows semimembranosus (black arrow) and conjoined tendon separating (white arrow). Note origin of adductor magnus anteriorly (open arrow). (D) Continued separation of the three tendons. (E) Distally the semitendinosus has a long tendon (arrow) and lies posterior to the semimembranosus. sm, semimembranosus; s, sartorius; g, gracilis; bf, biceps femoris. (F) Tendons of the posterior knee: semimembranosus (arrowhead), semitendinosus (white arrow), gracilis (open arrow), biceps femoris (black arrow). lg, lateral gastrocnemius; mg, medial gastrocnemius.

Fig. 5. (A) Axial T1-weighted images of proximal thighs. Note how T1-weighted images allow good depiction of muscle fat planes. This image is proximal to the ischial tuberosity and shows the sacrotuberous ligament (white arrow) insertion on the tuberosity. (B) Mid tuberosity level shows the anterior semimembranosus insertion (black arrow) and the posterior conjoined tendon of biceps femoris and semitendinosus (white arrow). (C) Inferior aspect of ischial tuberosity shows semimembranosus (black arrow) and conjoined tendon separating (white arrow). Note origin of adductor magnus anteriorly (open arrow). (D) Continued separation of the three tendons. (E) Distally the semitendinosus has a long tendon (arrow) and lies posterior to the semimembranosus. sm, semimembranosus; s, sartorius; g, gracilis; bf, biceps femoris. (F) Tendons of the posterior knee: semimembranosus (arrowhead), semitendinosus (white arrow), gracilis (open arrow), biceps femoris (black arrow). lg, lateral gastrocnemius; mg, medial gastrocnemius.

posterior head of the adductor magnus arises from the anterior inferior aspect of the ischial tuberosity. This portion inserts distally on the adductor tubercle and functions as a hip extensor, as well, but is not typically categorized with the hamstring muscle complex.

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