1 tc The MT has the passive form, and so a subject has to be added: “[a man] is chastened.” The LXX has the active form, indicating “[God] chastens,” but the object “a man” has to be added. It is understandable why the LXX thought this was active, within this sequence of verbs; and that is why it is the inferior reading.
2 tc The Kethib “the strife of his bones is continual,” whereas the Qere has “the multitude of his bones are firm.” The former is the better reading in this passage. It indicates that the pain is caused by the ongoing strife.