Willem Röell (1700 –1775) was Frederik Ruysch’s successor as praelector of the Amsterdam Surgeons' Guild.The painting shows him demonstrating to three wardens how the knee joint works. The guild assistant left looks on. Exceptional features of the depiction are the frontal podium arrangement and the full-length reproduction of the persons depicted. The realism with which Troost paints the corpse is also conspicuous. Originally the painting is likely to have been intended somewhat larger, as a preliminary drawing shows. The surgeons commissioned this painting from Troost not long after the fire that seriously damaged Rembrandt’s Anatomy lesson of Dr Deijman. Troost's painting may have been partly intended as a replacement for the Rembrandt in the guildhall.