Miner was using a 30 ton ram and a 16 lb hammer to replace pins on a D10 undercarriage. While swinging the hammer to loosen the pins, ee felt some pain in back. EE reported this to employer, but didn't want medical care. Unbeknownst to the operator, employee sought chiropractic care. On 2/20/18 employee asked the operator to provide medical care and filed a claim.