The shoulder joint moves on its own, but it also moves in coordination with the movement of the arm.
Literal
Shoulder-joint [topic-は], independently move [besides-ほか], arm [genitive-の] movement [to-にも] in-linkage move.
An anatomy/biomechanics sentence. ~ほか ('besides X,' 'in addition to X') is a noun meaning 'other,' used here as a 'in addition to X' connector: '[X] のほか...' — slightly more formal than ~だけでなく. 連動する ('to move in coordination,' 'to be linked/synchronized') is a Sino-Japanese verb used for mechanical, electrical, or biomechanical linkages. The particle に on 腕の動きに marks the thing being coordinated with — 連動する takes its partner with に. Together the sentence conveys a nice image of two modes: independent motion and linked motion.