There are one or two studies linking a cooked, palaeolithic diet with lower levels of inflammation, inflammation being one of the main causes of osteoarthritis.There are also a number of  studies done on the link between  AGEs/Advanced Glycation End Products and age-related diseases such as osteoarthritis:-
"Among the consequences of chronic AGE consumption can be osteoarthritis [34,35] and atherosclerotic calcification [36], which underlie the chronic complications of diabetes [29, 37]."  taken from:-

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4323205/
also:-
http://link.springer.com/article/10.1007%2Fs11926-003-0081-x

http://www.ncbi.nlm.nih.gov/pubmed/15077303
AGEs/Advanced Glycation End products are one of the 5 main types of heat-created toxins formed by cooking, so a cooked-palaeolithic diet, while causing less inflammation than diets containg wheat or dairy in them,  would not be as effective against osteoarthritis as a raw, palaeolithic diet.
Of course, even wild animals on natural diets can get arthritis etc.,  as AGEs also accumulate with age , not just via a cooked diet, so arthritis cannot be fully cured by diet, but the symptoms can at least be lessened by adopting certain  dietary approaches.

Geoff