In 1921 the Swiss surgeon BIRCHER published the first report on ar throscopy of the knee joint. The initial trials with the method revealed problems, mainly technical in origin, which caused it to be abandoned and forgotten until recently. Modern technical improvements, for which Japanese orthopaedic surgeons, above all WATANABE, were mainly responsible, have now led to a revival of interest in this method of investigation. The quality and versatility of the instruments currently available and the experience of the endoscopists who use them are such that arthroscopy of the knee joint is becoming an indispensable diagnostic aid. Arthroscopy is superior to arthrotomy in every respect; it is not only simpler but can be carried out on an ambulatory basis under local anaesthesia. In addition, it provides more information than arthrotomy, and the arthroscopic findings can be simply documented photographically. The complication rate is extremely low; cumulated statistics recently obtained from six clinics revealed no case of infection following nearly 4,000 arthroscopies. The main indication for arthros copy is the "painful, diagnostically obscure knee joint" in the widest sense. The procedure is also useful for further investigation of knee joint lesions which have already been diagnosed, as it allows their type and extent to be diagnosed more precisely, and the indication for surgery in a given case can be assessed more clearly. Unnecessary surgery can often be a voided in this manner. Arthroscopic biopsy is simple, and a variety of operations (e. g.weiterlesen