Letter to the editor

In the November issue of the Journal, van Os et al. [1] report equal engraftment efficacy in mice by intrafemoral and intravenous (retro-orbital) administration of syngeneic bone marrow. The authors justify their investigations on the grounds that ‘‘It is thought that when cells are injected directly into the place where they need to be (in the bone marrow), they shortcut the homing process and are able to provide better and faster engraftment.’’ This thinking may have prevailed among the authors, but was relegated to the stack of disproven hypotheses nearly half a century ago [2]. Equivalence of the intravenous and intraosseal injection routes is also repeatedly referred to and discussed in several handbooks [3–5]. It is also common medical knowledge that fluids injected into an osseous cavity are rapidly passed into the circulation. The marrow cavity is enclosed by rigid structures penetrated by blood vessels only. If fluid is forced into the cavity, an equal volume must leave the cavity through these vessels into the venous system. The feasibility of intraosseous blood transfusions, first described in laboratory animals in 1922 [6], was used extensively by military medics during World War II and remains a recommended technique for treating life-threatening hypovolemia when immediate vascular access is not available [7]. Dirk W. van Bekkum Rotterdam, The Netherlands