‘Top down' mechanisms of central sensitization refer to pain amplification that exists independent of peripheral inflammation and other nociceptive input. This concept is supported by the frequent disagreement between the degree of damage or inflammation in the joint and the severity of symptoms reported by the patient.
Conversely, a 'bottom-up' mechanism would indicate peripheral sources of nociceptive input such as joint inflammation and damage sensitize the CNS to pain.
According to this review, chronic injury and/or inflammation, such as that due to OA, drives central nervous system sensitization. If a patient with chronic pain has surgery to address a peripheral issue, such as a fibromyalgia patient receiving a total knee replacement, would pain symptoms improve?
In this study, only 48 of 150 patients improved. The patients who stayed the same or worsened, had higher levels of fatigue, depression, and surgical site pain at baseline. This study highlights the importance of assessing 'top down' drivers of pain in cases emphasizing a 'bottom up' approach.
Don't treat an MRI. Treat the patient.