I noticed this was reported on sumo forum. Perhaps it could explain Kotooshu’s lackluster performance in the last few days of the basho. However I didn’t see any evidence of him favoring one leg over another. Perhaps the pain killers had some adverse effects on his performance. Time will tell.
quoted from here
Kotooshu was driven to the hospital right after his bout with Kaio on Day 15 of 2010 Natsu basho. He will undergo a surgery on May 24. This prevents him from flying to Bulgaria, where he was expected as a special guest to the European Sumo Championship, to be held on May 26 – 27, 2010.
According to Topsport.bg and Gong.bg here is the chronolgy of his injury:
During the night of 20-21 May, Kotooshu felt acute pain in his right knee, which had been injured a while ago. Because of the pain he could hardly sleep through the night. On the next day (Day 13 of the Natsu Basho) was his bout against Harumafuji. Getting a painkilling shots, he managed to win the bout. After a series of tests he was diagnosed with partial tear of his meniscus.
On the next day (Day 14 of the Natsu Basho), again with painkilling shots, he fought against Hakuho. The bout was the longest of the day and declared “the most beautiful bout of the basho”. It ended with Hakuho throwing Kotooshu off the dohyo. During his landing his knee was twisted severely.
In spite of the excruciating pain, Kotooshu decided to finish the Basho and on Day 15 he met Kaio. After losing the bout, on his way down off the dohyo, his knee blocked out completely and he couldn’t move. Kotooshu was taken to the hospital imediately. The MRI showed complete tear of his meniscus. He spent the night at the hospital and an arthroscopic surgery was scheduled for May 24.
According to the doctors a full recovery is expected in 3-4 weeks.