Workman's Compensation has offered a settlement, should I take it?

A few years ago I injured my knee and had surgery. Later the doctor thought I might have torn a something but could not get any more medical treatment due to lack of insurance and money. I continued to do my exercises at home. In time I felt good and got a job. After working for some time at my place of employment I injured that knee again. I've been on workman's comp for 6 months now. I've been to the doctor and they say I need surgery. The problem is they say my injury happened prior to my employment but workman's comp was going to pay for surgery anyways. I got a letter in the mail with a settlement offer of $24,000.00 from the insurance company. Why did they send me this offer? My parents insurance will cover my surgery and I will have to make a co-pay. Should I take the settlement?