Purpose: To analyze the causes of repeat knee arthroscopy in the same knee.

Materials and methods: We reviewed 923 patients that had undergone knee arthroscopy during 2005 and assessed those that had already undergone previous arthroscopy of the same knee that year or in previous years and analyzed the causes.

Results: Of the 923 patients that required knee arthroscopy 169 (18.3%) had undergone previous surgery. Four (2.3%) had undergone 3 previous arthroscopies, 27 (15.9%) two and 138 (81.6%) one. In 59.8% of cases, the symptoms that led to repeat arthroscopy were non-traumatic continuous pain. The other cases required repeat arthroscopy due to new trauma, or meniscal or anterior cruciate ligament (ACL) tears. The patients with affected menisci (104) underwent partial meniscectomy, 31% had a posterior cruciate ligament (PCL) tear and 58% had menisci remains with or without osteochondral lesions.

Repeat arthroscopies of ACL tears treated by ligamentoplasties (41) were due to plasty tears in 46% of cases and adhesions in 27%. In patients that underwent 3 arthroscopies, the main diagnosis was plasty tear in 45% of the total sum of 2^nd and 3^rd arthroscopies. Mean time between first and second arthroscopy was 28 months and between second and third arthroscopy 12 months.

The relative risk of undergoing a new arthroscopy during the same year as meniscectomy was 1.12% and as ACL ligamentoplasty 0.95%.

Conclusions: Not all repeat arthroscopies are caused by previous complications. The main clinical reasons for a repeat arthroscopy can be traumatic or non-traumatic, with a greater frequency of the latter. We found that the risk of repeat arthroscopy was greater during the first year in meniscal tears than in ACL tears.