Syntax

Syntactic actants

Actant 1: whose shoulder it is
(a) Genitive
(b) Possessive
Он положил руку на плечо сына. He put his hand on his son's shoulder.
Его плечи были чёрные от загара. His shoulders were brown from the sun.
NB When the word плечо functions as a subject and does not have a descriptive modifier, the construction плечо у + Genitive is often preferred to (a) and (b), above:
Плечи у него были чёрные от загара. His shoulders were brown from the sun.

Restrictive modifiers

(a) adjectival modifier
левое/правое плечо the left/right shoulder
Левое плечо у него было поцарапано. His left shoulder was scratched.