These lyrics are available lots of places, and you'll find that they're identical to these except for the word "hnjáliðum" (in my 'version), which is often written as "hniáliðum". I don't know if i and j are interchangable, but I do know that "kiknar í hnjáliðum" translates to "the joints of the knee gives way" whereas the same word with an i doesn't exist according to my dictionary.