Difference in mean pre-operative KOOS-scores and mean KOOS-scores at final follow-up. In all categories of the KOOS-questionnaire there is a difference in scores of about 20%. All articles reporting KOOS-scores see an improvement in all categories at final follow-up. As shown sport activities and quality of life are scored as being acceptable at final follow-up, which is important as they tend to state that their quality of life is below average before index surgery.