THE IMPACT OF VASOACTIVE SUBSTANCES ON INTRAOSSEOUS PRESSURE AND BLOOD-FLOW ALTERATIONS IN THE FEMORAL-HEAD - A STUDY BASED ON MAGNETIC-RESONANCE-IMAGING

In beagle dogs, the alterations of intraosseous pressure and blood sup ply in the femoral head that result from the administration of vasoact ive substances were examined, and the changes were documented by magne tic resonance imaging (MRI). Vasoactive substances were infused into t he medial and lateral circumflex femoral arteries of 12 beagle dogs. A ll infusions were done under standardised conditions with simultaneous measurements of venous blood flow and intraosseous pressure distribut ion in the proximal femur. The drugs were infused in three cycles of 3 0 min each separated by 30 min recovery periods, followed by MRI exami nation at the end of each experiment. At an intraosseous pressure of 1 4.3 (+/- 4.2) mmHg in the femoral head epiphysis (I), 11.6 (+/- 2.7) m mHg in the greater trochanter (II) and 9.3 (+/- 3.2) mmHg in the femor al shaft (III), a baseline flow of 96.2 (+/- 18.8, n = 12) ml/min was measured in the femoral vein. After infusing bradykinin at a:concentra tion of 10(-6) moles, which is commonly known to lead to cerebral and subcutaneous oedema formation by vessel dilatation, the intraosseous p ressure increased to (I): 49.1 (+/- 6.2) mm Hg, (TI): 42.5 (+/- 5.8) m mHg and (III): 38.3 (+/- 7.1) mmHg in the three measured femoral areas (n = 3). After the bradykinin injection, femoral vein flow increased to a peak value of 238.4 (+/- 43.4) ml/min and then dropped to 62.3 (/- 14.2) ml/min after discontinuation of the bradykinin infusion. In a second and third series of tests, hyperosmolar (20% NaCl) and hypoosm olar (distilled water) solutions were applied, also resulting in incre ased but lower mean intraosseous pressure values (17.3 +/- 4.1 and 25. 7 +/- 5.1 ml/min, respectively) in all regions. When administering bra dykinin, MRI scans taken immediately after completion of the experimen t showed substantial oedema in the femoral muscular system, but withou t any changes of osseous signals in T-1- or short time inversion recov ery (STIR)-weighted images, nor did any changes occur when solutions o f 20% NaCl or distilled H2O were injected. The results of our experime nts demonstrate that acute increases of intraosseous pressure do not c ause MRI signal alterations. We therefore conclude that in addition to the described pressure increase, other intraosseous alterations must occur to lead to the detectable signal changes found among patients wi th diagnosed femoral head necrosis. Finally, the short time period bet ween the rise in intraosseous pressure and performing a conventional M RI may be one reason for missing the development of an intraosseous oe dema. On the other hand, conventional MRI might have additional disadv antages for detecting intraosseous fluid compared with a dynamic imagi ng modality.