Figure 4. With the stylet in place, align the needle along the long axis of the humerus and perpendicular to the cortical
surface of the greater tubercle. To penetrate the cortex, apply forward pressure while rotating the needle clockwise and counterclockwise.
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Proximal humerus. For sampling the proximal humerus, place the animal in lateral recumbency. With your nondominant hand, grasp the elbow to
stabilize the limb and flex the shoulder, aligning the humerus parallel to the body wall. The site of aspiration is the flattened
area between the greater tubercle and the humeral head.1-4,7,9 Align the needle along the long axis of the bone, and apply penetrating force (forward pressure) perpendicular to the cortical
surface (Figure 4).
Femur. For the femur, place the animal in lateral recumbency. Stabilize the femur by grasping the stifle with your nondominant hand.
Slight internal rotation of the stifle will enhance exposure of the proximal femur. Position the needle medial to the greater
trochanter within the fossa, and direct it toward the stifle aligned with the femoral shaft.1-4,7,9 As with the humerus, apply penetrating force perpendicular to the cortical surface (Figure 5 [figure no longer available]).
Iliac crest. For the iliac crest, place the animal in sternal recumbency with the hindlimbs under the animal so the crest protrudes. This
site may be difficult to approach in an obese animal. Identify the widest portion of the dorsal aspect of the wing of the
ilium, placing a finger on either side. Position the aspiration needle perpendicular to the crest, and direct it ventrally
(Figure 6 [figure no longer available]).1-4,7,9
Failure to maintain a perpendicular relationship to the cortex causes the needle to travel along (or within) the cortex instead
of through it. Use steady forward pressure combined with a twisting rotation of the needle to penetrate the cortex and advance
the needle into the marrow space 1 to 2 cm depending on the animal's size. Decreased resistance when the needle enters the
marrow cavity may or may not be appreciated. If the needle is correctly seated, it will have absolutely no give or wiggle
room and will move in unison with the humerus or femur upon flexion of the shoulder or hip, respectively.7
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