My workers comp case has been denied twice for an injury on the job. Do I need to hire an attorney to prove my injury resulted in doing my job at work

I work in corrections. I was running to an emergency call and twisted my right knee, which resulted days later pain and swelling of the knee. I was seen on the 4th day due to pain but doctor said arthritis. The pain was so unbearable I went back 9 days later because I did not agree that it was arthritis. I did not report it until day 51, thinking the pain was gonna go away. An MRI was done and found fracture to condyule lower femur, torn meniscus lateral and medial. I had surgery for repair and a torn ACL was discovered. Now because I reported it on day 51 instead of between day 1 and 45, comp case is being denied due to possible "early degenerative disease". Need proof that injury was caused from running at work.