The ischiocondylar (hamstring) portion of adductor magnus is the posterolateral component arising from the ischial tuberosity alongside the true hamstrings, inserting on the adductor tubercle rather than the linea aspera. It is often called the fourth hamstring because it shares origin, innervation (tibial division of sciatic), and action (hip extension) with the biceps femoris, semitendinosus, and semimembranosus, distinguishing it from the fan-shaped adductor (obturator-innervated) portion.
| Origin | Ischial tuberosity (lower medial surface), alongside the common hamstring origin |
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| Insertion | Adductor tubercle on the medial femoral condyle (distinct from the adductor portion which inserts on the linea aspera) |
| Nerve Supply | Tibial division of the sciatic nerve (L4) — distinct from the adductor portion which is innervated by the obturator nerve |
| Blood Supply | Perforating branches of the profunda femoris artery |
| Actions | Extension of the hip (primary action of this portion, working with the true hamstrings); medial rotation of the thigh; contributes to deceleration of the swing limb during gait |
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The hamstring portion of adductor magnus is an important consideration in proximal hamstring repair surgery and in hamstring EMG studies, where it contributes to posterior thigh activation patterns. In adductor magnus strain, the ischiocondylar portion may be selectively injured, producing posterior medial thigh pain rather than the classic posterocentral hamstring strain pain pattern. The adductor hiatus (the gap in the adductor magnus where the femoral vessels pass to the popliteal fossa) lies between the two portions of the muscle.
High-load hip extension activities can selectively strain the hamstring portion of adductor magnus at the ischial tuberosity, producing posteromedial thigh pain overlapping with the hamstring injury pattern; MRI distinguishes the hamstring adductor magnus involvement from true hamstring tears by its more medial location at the ischial origin.
