A recent survey about the undiagnosed neck injuries associated with PCS. This article seems to strongly suggest that, in many cases of PCS, symptoms are entirely due to the neck injury rather than to the brain injury itself. For instance, the following sentence is quoted from the survey:

In addition, a prospective Norwegian study of 348 participants identified through a questionnaire that headaches persisting for more than 3 months after trauma and diagnosed as PCS are often related to a musculoskeletal pathology. In other words, the head or brain injury does not cause the persistent symptoms [23]. These results show the importance of potential cervical impairment in patients with mTBI [4, 14, 16, 17].


https://www.hindawi.com/journals/jsm/2016/1590161/