Hamstrings span 2 joints, i.e., hip and knee and extend hips flex knees
3+1 muscles, viz., biceps femoris, semimembranosus, semitendinosus + adductor magnus
Musculotendinous junction is not distinct area, but a wide zone of transition of 10-12cm
Biceps:
Long head: medial facet of ischial tuberosity (conjoint tendon with semitendinosus). Conjoined tendon is posteromedial and semimembranosus is anterolateral
Short head: lateral linea aspera, lateral supracondylar line, intermuscular septum (it does not span 2 joints)
Short head of biceps is deep to long head
Insertion: fibular head, lateral tibial condyle, fascia of leg (large insertion prone to tear)
Long head is supplied by the tibial portion of sciatic and short head by peroneal portion and this dual nerve supply is one of the causes for increased injuries
Short head of biceps femoris may be absent, or fail to share same insertion as long head
Semitendinosus:
The proximal fibers arise from inferomedial impression on the upper aspect of ischial tuberosity as conjoint tendon with long head of the biceps.
Bulbous inferior to ischial tuberosity. Semimembranosus tendon lies anterolaterally (Semimembranosus can be confused for semitendinosus, because the proximal tendon of semitendinosus is not always distinct)
Distally forms a long tendon (site of rupture)
Insert onto tibia with gracilis muscle at Gerdy tubercle
Supplied by 2 branches from tibial nerve, the lower branch in common with nerve to semimembranosus
Semimembranosus:
Origin: superolateral aspect of ischial tuberosity, beneath proximal half of semitendinosus
Lies anteromedial to other hamstrings
Proximally the tendon is elongated with connections to adductor magnus and origin of long head of biceps
It has a sharp medial border and appears like a cord
Distally is composed of muscle with short unipennate and multipennate fibers (c.f. semitendinosus, which is thin and bandlike)
Multiple insertions: medial tibial condyle (anterior, direct and inferior arms), posterior oblique ligament (capsular arm), posterior joint capsule, arcuate or oblique popliteal ligament. the 3 arms are deep to MCL. A U or J shaped bursa is seen between MCL and these arms
in 50% population, it insert onto posterior horn of lateral meniscus
Supplied by a branch from tibial division of sciatic nerve
May be quite large, or may be double muscle which arises from sacrotuberous ligament; may be absent
References:
Koulouris G et al. Hamstring Muscle Complex: An Imaging Review. RadioGraphics 2005;25:571-586
