nez: The expression. is found in three places (one being a free quotation of another): Job 4:4, "Thou hast made firm the feeble (kara`, "bending," "bowing") knees," and Heb 12:12, "Wherefore lift up the hands that hang down, and the palsied (the King James Version "feeble") knees." The Greek word used here (paralelumena, "paralyzed," "motionless") implies the loss of junction, interrupted articulation, the cutting off of vital strength; compare Greek cholos, "lame," and see Delitzsch in his Commentary on Heb, in the place cited
Such an affection of the knees may be due to different causes. It is, e.g., a very frequent symptom of the disease known in the Orient as beriberi, when the muscles of the lower leg shrink to such a degree as to render voluntary locomotion impossible. It always disables its victim, and is therefore often expressive of general debility, e.g. in Ps 109:24, where such weakness is described as the outcome of protracted fasting in Eze 7:17 and 21:7, "All knees shall be weak as water," the expression indicates a complete relaxation of the muscles. Fear effected the same condition in Belshazzar’s case, when he saw the writing on the wall (Da 5:6), "The joints of his loins were loosed, and his knees smote one against another" (compare Na 2:10).
The "sore boil .... in the knees, and in the legs," a disease announced in De 28:35 as a punishment upon Israel for disobedience, cannot now be fully determined. Driver (in his commentary on the passage) thinks of elephantiasis, which is possible but not probable on account of the additional statement, "whereof thou canst not be healed, from the sole of thy foot unto the crown of thy head" which would be unexplained, as elephantiasis rarely presents a form in which the whole body is sympathetically affected. I rather think of some form of bubonic plague, which causes very high fever all over the body. In De 28:27 in the enumeration of plagues mention is made of the "boil of Egypt," and some commentators have explained this as "bubonic plague." There is, however, no doubt that the "boil or botch of Egypt" is identical with the disease known to modern medicine as bouton du Nil, Biskra button, Bagdad or Aleppo sore.