Bone Marrow Aspiration/core
||The sites that are most accessible for bone marrow
aspiration in the dog are the proximal humerus (a), proximal femur (b) and the wing of the ilium (c), approached either from the dorsal crest or lateral face. The easiest
sites from which to obtain bone marrow in the cat are the proximal femur and proximal
The most common needle types used for aspiration of
bone marrow are the Illinois sternal-iliac and the Rosenthal needles (pictured). Needles
are available in 16 and 18 gauges, 1 or 1-15/16 inch long. Aspiration-style needles have
an inner stylet that is used to penetrate the cortex of the bone, then removed to aspirate
marrow. Before introducing the needle into the bone, check to make sure the stylet totally
occludes the lumen of the needle. If the lumen is not filled by the stylet, pieces of cortical bone may enter the lumen of the needle as it is driven into
the bone. These pieces of cortical bone will plug the needle, preventing aspiration of
you have relatively short fingers, the Rosenthal needle is held with the back of the
needle pressed at the junction between fingers and palm. This gives you maximum driving
force and stability. The stylet does not lock in place and must be held in the needle with
digital pressure as the needle is advanced into the bone to prevent the lumen of the
needle from becoming obstructed with cortical bone
with longer fingers, the needle can be held between the index and middle finger, and the
thumb can be used to hold the stylet in place.
Bone marrow aspiration
is performed in the dog with lidocaine local anesthesia and in cats, under short duration
general anesthesia. The skin surface is clipped of hair and aseptically prepared as for
surgery. Sterile gloves are usually worn. If local anesthesia is being used, the agent is
placed in the skin, muscle and on the periostium of the bone.
A small skin incision is made
with a scalpel blade. The bone marrow needle is used to bluntly cut through the muscle.
Once the needle is in contact with the surface of the bone it is rotated into the bone
with a clockwise/counter-clockwise motion. It takes a considerable amount of force to
drive the needle through the cortex of the bone.
||To obtain marrow from the lateral aspect
of the wing of the ilium the animal is restrained in lateral recumbency.
Palpate the dorsal crest of the
wing of the ilium and move down approximately 1 cm (* marks the site of bone penetration on photo below). The marrow cavity is
shallow in this location (see below). The needle cannot be seated very deeply or it will
pass through the marrow cavity and into or through the cortical bone on the opposite side
of the wing. This technique is not recommended for use in small dogs (~25 lb or less) or
cats due to the tendency to penetrate both cortices. Obese or very large dogs may have too
much paralumbar fat &/or muscle for the needle to pass through before reaching the
surface of the bone.
Bone marrow can be aspirated from the
dorsal crest of the wing of the ilium. The animal is restrained in sternal recumbancy or
standing. Hold the crest of the ilium between your fingers. The dorsal surface of the
crest is rounded, and the needle tends to slide off the bone into soft tissues if you
don't maintain control of it. The needle is directed parallel to the long axis of the wing
of the ilium. The needle can be firmly seated in this location.
||Bone marrow can be obtained from the
proximal humerus of most animals, including those of small body size or obese condition.
The bone marrow needle can be seated firmly in this location as the marrow cavity is
thick. Run your finger down the spine of the scapula. The first prominance you feel is the
acromion (a). The next prominance is the greater tubercle of the humerus (b). The needle
is inserted at the distal end of this bony prominance (c). Maintain control of the needle
as you are seating it into the bone. There is a tendency for the needle to slide down the
surface of the bone instead of penetrating the cortex, causing damage to adjacent soft
||The needle should be inserted at an angle
~450 from a line parallel to the long axis of the humerus. Needle insertion too
proximal may result in entry into the scapulohumeral joint. Needle insertion at an angle
perpendicular to the humerus may result in entry into the bicipital bursa that
communicates with the scapulohumeral joint on the medial side of the limb.
||To obtain bone marrow from the proximal
humerus, the animal is restrained in lateral recumbency. The elbow (a) is rotated inward
such that the shoulder joint is turned outward. This positions the greater tubercle (b) in
a location that is easier for you to get the bone marrow needle seated in the bone.
||The proximal femoral shaft usually
contains red marrow and is relatively accessible for aspiration in the cat. The needle may
not be of sufficient length to reach this site in large dogs. The needle is seated in the
trochanteric fossa between the lesser and greater trochanters.
||Hold the stifle in one hand with your
thumb laying along the long axis of the femur and the thumb nail over the greater
trochanter. Make a small skin incision with a scalpel blade and insert the needle under
your thumb until the tip of the needle contacts the periostium of the intertrochanteric
fossa. Keep the needle parallel to your thumb. If you do not remain parallel to your thumb
(and hence the femur) the needle may exit the cranial or caudel cortex of the bone.
Remember that the sciatic nerve is caudel to the femur and can be injured if the needle
slips caudel to the femur.
||A 12 or 20 ml syringe is used to aspirate
bone marrow. It may be necessary to pull back on the syringe plunger to 10-15 ml to create
enough negative pressure to break marrow particles loose from the endosteal surface.
Aspirate only a small amount of marrow. Aspiration of large volumes results in dilution of
the marrow sample with peripheral blood. When marrow just enters the barrel of the syringe
(arrow), stop aspirating. Larger volumes of marrow can be drawn into an EDTA solution and
the marrow particles (spicules) picked out with a needle or pipette.
A small drop
of marrow is placed on each of several slides. Marrow clots very rapidly.
It is important to make the
smears immediately after obtaining the marrow sample.
If the marrow sample was
heavily contaminated with peripheral blood during sampling it still may be possible to
"salvage" such a sample. Smearing a drop of marrow that has heavy blood
contamination results in a cytology sample of low cellularity with regard to marrow
elements. The sample may be salvaged using the following technique.
Procurement of a core of marrow
A Jamshidi needle is used
to obtain a core of marrow for histologic evaluation. The stylette (a) is locked into the
hollow part (b) of the needle with a threaded cap, not shown in the photo. (c) is a thin
wire used to dislodge the core of marrow from the needle.
A core of marrow can be obtained from
the proximal humerus, proximal femur or dorsal crest of the wing of the ilium. The
landmarks for starting the needle are the same as described for aspiration of marrow from
the proximal humerus. Once the needle penetrates the cortex of the bone, the stylette is
removed. The needle is advanced 1 to 2 cm. At that point, the entire needle is
"stirred" in the marrow to break loose the core of marrow. Do this by rotating
the blue cap of the needle in a circle which will also rotate the tip of the needle in a
circle in the marrow, breaking loose a core in the lumen of the needle. The needle is
removed from the marrow using a clockwise or counterclockwise (not back and forth) motion.
Rotating the needle out in one direction allows a second opportunity to break loose the
core. If the core is still attached and you withdraw the needle, rotaing back and forth,
you may pull the needle off the core and leave the core in the marrow cavity.
||The stylette is inserted into
the tapered tip of the needle and the core is pushed out of the needle.