An increase of 35%, from 15.2 to 20.5 million, in the number of hospital discharges for persons with a musculoskeletal disease occurred in the periods 1996 to 1998 to 2009 to 2011. This may be due to the aging population. The percentage of persons with a musculoskeletal disease who were hospitalized one or more times in a year was roughly stable, with 11.1% and 11.0% of persons in 1996 to 1998 and 2009 to 2011 hospitalized, respectively. The average number of hospitalizations per person, at 0.2, did not change. (Reference Table 10.2 PDF [1] CSV [2]) 
Links:
[1] https://bmus.latticegroup.com/docs/T10003.2.pdf
[2] https://bmus.latticegroup.com/docs/T10003.2.csv