According to the CPT Assistant you would code 73520 and add a 52 modifier. This is what the CPT Assistant says:
Radiology
Question
Can code 73520 still be used to report a bilateral hip x-ray performed with two views on each side even if an anteroposterior view of the pelvis is not also performed or is it more appropriate to report code 73510 twice?
AMA Comment
According to the American College of Radiology, an anteroposterior (AP) view of the pelvis, as well as additional views of both hips, is the appropriate method of examination when a bilateral hip study is ordered. In addition to the AP view of the pelvis, at least one more view of each hip, typically a coned-down frog leg lateral view, is obtained amounting to three views: one AP view of the pelvis which includes both hips; one frog-leg lateral of the right hip; and one frog-leg lateral of the left hip.
However, if a bilateral study is performed without an AP view of the pelvis, then code 73520, Radiologic examination, hips, bilateral, minimum of two views of each hip, including anteroposterior view of pelvis, may be reported with modifier -52, Reduced services, appended to indicate that the study was not performed in its entirety. CPT code 73510, Radiologic examination, hip, unilateral; complete, minimum of two views, is not intended to describe a bilateral hip study, but a complete radiological examination with a minimum of two views performed on a single hip.
If right and left hip studies are separately ordered and performed, and there are separate interpretations and written reports signed by the interpreting physician, then it would be appropriate to report the code 73510 two times. In this case, modifier -59, Distinct procedural service, should be appended to the second code to indicate that it is a distinct procedure.
Since modifiers are carrier specific, it is recommended that the provider check with their local carrier and other third-party payers for their guidelines on the use of modifiers.