Yes. In the eyes of OWCP, a back strain is not considered a serious medical condition that justifies extensive medical treatment or disability compensation payments.
Your accepted condition is what controls treatment, surgery, and compensation. For example, a herniated disc in your back at L4-5 with referred (nerve) symptoms such as numbness and tingling radiating down the legs is an accepted condition more likely to result in aggressive treatment or surgery provided by OWCP. Such treatment must be based on medical evidence and be medically necessary and causally related to your accepted condition(s).
NOTE: The above are general statements. Every case is different. Seek legal help based on the unique facts of your case.