M25.16Non-Billable (Header)Fistula, kneeChild CodesM25.161Fistula, right kneeM25.162Fistula, left kneeM25.169Fistula, unspecified kneeCode Hierarchy└M25Other joint disorder, not elsewhere classified└M25.1Fistula of joint└M25.16Fistula, knee└M25.16Fistula, knee