Spinal nociceptive transmission by mechanical stimulation of bone marrow.
“in addition to the periosteum, many unmyelinated calcitonin gene-related peptide-labeled fibers innervate bone marrow.”
“nociceptors in bone marrow are likely to be excited by increased pressure in bone marrow, possibly resulting in activation of pain pathways including the spinal dorsal horn (SDH)”
“mechanical stimulation to bone marrow, which induces an increase in intraosseous pressure, elicits nociceptors located in bone marrow.”
“both electrical stimulation and increase in pressure within bone marrow generate a blood pressure increase that may be indicative of nociceptive activation.”
“An increase in intraosseous pressure has been shown to activate fine-diameter afferent nerve fibers arising from bone marrow, as do irritant and inflammatory agents such as H+and K+ ions and histamine and bradykinin.”
Recreational runners with patellofemoral pain exhibit elevated patella water content.
“Increased bone water content resulting from repetitive patellofemoral joint overloading has been suggested to be a possible mechanism underlying patellofemoral pain (PFP). To date, it remains unknown whether persons with PFP exhibit elevated bone water content. The purpose of this study was to determine whether recreational runners with PFP exhibit elevated patella water content when compared to pain-free controls. Ten female recreational runners with a diagnosis of PFP (22 to 39years of age) and 10 gender, age, weight, height, and activity matched controls underwent chemical-shift-encoded water-fat magnetic resonance imaging (MRI) to quantify patella water content (i.e., water-signal fraction). Differences in bone water content of the total patella, lateral aspect of the patella, and medial aspect of the patella were compared between groups using independent t tests. Compared with the control group, the PFP group demonstrated significantly greater total patella bone water content (15.4±3.5% vs. 10.3±2.1%; P=0.001), lateral patella water content (17.2±4.2% vs. 11.5±2.5%; P=0.002), and medial patella water content (13.2±2.7% vs. 8.4±2.3%; P<0.001). The higher patella water content observed in female runners with PFP is suggestive of venous engorgement and elevated extracellular fluid. In turn, this may lead to an increase in intraosseous pressure and pain.”
It would be interesting if running caused greater patella(kneecap) size and this increase in patella size was intraosseous pressure related. But I couldn’t find evidence of running increasing patella size. The change in water content is low so it’s possible that that increase in hydrostatic pressure was not significant enough. All it would take is one example of running increasing patella size though.