Knitting was the term used to describe the rejoining of two ends of a fractured bone or other severed body parts. Whether or not it constituted major surgery depended on which parts required knitting.
In 2370, "Anna" began to tell Jean-Luc Picard that a restrictor device she'd placed on him would hold his three broken ribs in place, and he finished what he thought she was going to say, that it would allow them to knit. (TNG: "Liaisons")
In 2375, Quark required two bones at the back of his skull to be knit together after his brother Rom swung a baseball bat without looking. Later, Miles O'Brien was out of action after he tore his rotator cuff; although Doctor Julian Bashir had repaired it, O'Brien's ligaments required time to knit together with his clavicular joint. (DS9: "Take Me Out to the Holosuite")