Understanding bone safety zones during bone marrow aspiration from the iliac crest: the sector rule

Should the trocar suddenly lose contact with bone during bone marrow aspiration, it may result in visceral injury. The anatomy of the ilium and the structures adjacent to the iliac bone were studied to determine the danger of breach by a trocar introduced into the iliac crest.

The authors followed two series of patients, one series to do measurements of distance and angles of the structures at risk to the iliac bone and the other to evaluate the risk of a trocar being directed outside the iliac wing during bone marrow aspiration. The authors also examined 24 pelvices by computed tomography (CT) scans of mature adults (48 iliac crests). Lines dividing the iliac wing into six equal sectors were used to form sectors (e.g. sector 1 anterior, sector 6 posterior). Vascular or neurological structures were considered at risk if they were accessible to the tip of a 10-cm trocar introduced into the iliac crest with a possible deviation of 20° from the plane of the iliac wing on the three-dimensional reconstruction. The authors tracked bone marrow aspiration of six different surgeons and calculated among 120 patients (480 entry points) the number of times the needle lost contact with bone in each sector of aspiration.

The sector system reliably predicted safe and unsafe areas for trocar placement. Among the 480 entry points in the 120 patients, 94 breaches were observed and higher risks were observed in the thinner sectors. The risk was also higher in obese patients and the risk decreased with more experienced surgeons. The trocar could reach the external iliac artery on pelvic CT scans in the four most anterior sectors with a higher frequency in women. Posterior sectors were at risk for sciatic nerve and gluteal vessel damage when the trocar was pushed deeper than 6 cm into the posterior iliac crest. In cadavers, the dissection demonstrated nine vascular or neurological lesions.

Using the sector system, trocars can be directed away from neural and vascular structures and toward zones that are likely to contain larger bone marrow stock.