In early 2000,  I partly tore my right ACL and damaged the medial meniscus while messing up an attempt to do aikiotoshi. I trained carefully in a custom brace for nearly a year (in retrospect, without adequate physical therapy). In January 2001, at a seminar, a visitor used unneeded force on an opening, driving me to that knee and leaving the joint so unstable that I would fall while walking. In June 2001 I underwent surgery and then extensive rehab, returning to training finally in the spring of 2002. During the long hiatus, my "training" was doing research (reviewing the field, interviewing athletic trainers and doctors, and conducting a survey).

Aikido and Knee Injury Survey Summary At A Glance
continue to full survey write-up

Number of Dojo: 101     Members: 3250
Men: 75%     Women: 25%

Acute knee injuries in the past five years: 99
No injuries: 50 dojo    At least one injury: 51 dojo

Acute knee injuries, per dojo basis Total: 4.45%
Men: 4.52%     Women: 4.44%

Acute knee injuries, per total respondents Total: 3%
Men: 3%     Women: 3%

Additional Knee Information

Knees, Aikido and Minimizing Risks
Janet's  article published in the Iaido Journal, November 2003 click to read

Other Knee Information
http://www.physsportsmed.com/

Stretching and WarmUp Info
http://www.momentummedia.com/articles/tc/tc0902/warm-up.htm
http://www.momentummedia.com/articles/tc/tc0702/stretch.htm
http://momentummedia.com/articles/tc/tc1002/myorelease.htm
http://www.stretchyourclients.com/
http://www.cmcrossroads.com/bradapp/docs/rec/stretching/