For most adults, the optimal position for bone marrow aspiration is the lateral decubitus position (lying on one side with knees drawn up) or the prone position, with the needle entering at the posterior superior iliac spine. This site is safe, easy to palpate, far from major vessels and organs, and allows a trephine biopsy through the same skin puncture. The sternum and anterior iliac crest are alternatives when the posterior approach is not possible.
This guide covers site selection, patient positioning, landmarking, technique adjustments for difficult patients, and how positioning links to sample quality and safety. For background on why and when the test is done, see our article on bone marrow aspiration indications and recent advances.
Why Positioning Matters
Bone marrow examination is central to diagnosing many hematological disorders, from unexplained cytopenias to acute leukemias and myeloma. A good position does three things: it exposes a reliable bony landmark, keeps the patient still and comfortable, and lets the operator apply controlled pressure perpendicular to the bone.
Poor positioning is a common reason for a dry tap caused by technique rather than disease, a hemodiluted sample, or an inadequate core. In my practice, taking an extra minute to position and palpate properly saves far more time than a repeat procedure.
Choosing the Aspiration Site
| Site | Patient position | Advantages | Limitations |
|---|---|---|---|
| Posterior superior iliac spine | Lateral decubitus or prone | Safest; aspirate and trephine from one site; ample marrow | Harder to palpate in obesity; patient cannot see the procedure, which some find reassuring and others do not |
| Anterior iliac crest | Supine | Useful when the patient cannot lie on side or front | Thicker cortex; smaller marrow cavity; more uncomfortable |
| Sternum (manubrium or upper body) | Supine | Superficial, easy landmark; rich marrow in adults | Aspiration only, no trephine; risk of penetrating the posterior table; not used in children |
| Anteromedial proximal tibia | Supine, leg supported | Accessible in infants | Only in very young children, when tibial marrow is still active |
The posterior iliac crest is the default for adults and older children. The sternum should be reserved for experienced operators and used with a needle guard.
Lateral Decubitus Versus Prone
Lateral decubitus position
The patient lies on one side, back close to the edge of the couch, with hips and knees flexed toward the chest in a fetal curl. The upper leg can be flexed slightly more than the lower one. This rotates the pelvis forward and brings the posterior superior iliac spine into relief.
- Comfortable for most patients, including those who are breathless or frail
- Easier to keep an airway view if sedation is used
- Watch that the pelvis stays vertical; rolling forward or back alters the needle angle
Prone position
The patient lies face down, often with a pillow under the pelvis to flatten the lumbar curve. The two posterior superior iliac spines are easier to compare side by side, which helps in patients with obesity.
- Stable platform for firm, perpendicular pressure
- Less suitable for patients with respiratory compromise, late pregnancy, abdominal distension, or those receiving sedation
Either is acceptable; choose the one that gives you the clearest landmark and the most settled patient.
Landmarking and Technique Adjustments
Finding the posterior superior iliac spine
Trace the iliac crest backward until it ends in a bony prominence, often marked by a skin dimple above the buttock. The entry point is usually just over this prominence. Mark it before cleaning the skin, then infiltrate local anesthetic down to and including the periosteum, the sensitive membrane covering the bone.
Obesity
In patients with high body mass, the prone position with a pelvic support often helps. A longer needle may be needed, and imaging guidance can be considered when landmarks cannot be felt.
Osteoporotic or very dense bone
Soft bone offers little resistance, so advance slowly to avoid overshooting. Very hard bone, seen in some sclerotic conditions, requires steady rotational pressure rather than force.
Sternal approach
With the patient supine, the needle enters the midline of the manubrium or upper sternal body, with the guard set so that it cannot pass beyond the posterior cortex. Never perform a sternal trephine biopsy, and avoid the sternum in children because the bone is thin.
Sampling Quality and Interpretation
The first small volume drawn gives the best specimen for morphology; larger draws dilute the sample with peripheral blood. Further aspirates for flow cytometry, cytogenetics, and molecular studies can be taken after slight repositioning of the needle. These tests assess marrow cells by lineage, maturity, and genetic abnormality.
A true dry tap, where no marrow is obtained despite good technique, often points to fibrosis or a densely packed marrow, and makes the trephine core essential. For patient-oriented context on what the results can show, our guide to blood disorders is a useful resource to share.
Safety and Post-Procedure Care
Bone marrow aspiration is a low-risk procedure. Recognized complications include:
- Bleeding or hematoma, more likely with severe thrombocytopenia, coagulopathy, or anticoagulants
- Infection at the puncture site
- Pain during aspiration, typically a brief, deep pulling sensation
- Rarely, needle breakage or, at the sternum, penetration into the chest
After the procedure, apply firm pressure, then have the patient lie on the puncture site (supine for posterior iliac samples) for a short period. Check the site before discharge and advise simple analgesia, keeping the dressing dry, and reporting fever, spreading redness, or persistent bleeding.
Key Takeaways
- The posterior superior iliac spine, approached in the lateral decubitus or prone position, is the optimal and safest site for most adults.
- Lateral decubitus suits frail, breathless, or sedated patients; prone suits patients with obesity when landmarks are hard to feel.
- The sternum is for aspiration only, in adults, with a guarded needle.
- The proximal tibia is reserved for infants.
- Careful landmarking and small first draws improve sample quality and reduce repeat procedures.
Aspiration technique is one small part of good hematology practice, but it has an outsized effect on diagnostic yield and patient experience.
Frequently Asked Questions
Is lateral or prone better for bone marrow aspiration?
Neither is universally better. Lateral decubitus is more comfortable for many patients and safer with sedation, while prone gives a stable platform and clearer landmarks in larger patients. Choose based on the individual patient and your own experience.
Why is the posterior iliac crest preferred over the sternum?
It has a large marrow cavity, lies away from vital structures, and allows both aspiration and trephine biopsy. The sternum is thin, carries a small risk of serious injury, and cannot be used for a core biopsy.
Can bone marrow aspiration be done if the patient cannot lie flat or on their side?
Yes. The anterior iliac crest can be approached with the patient supine, and in adults the sternum is another option. Some operators also perform posterior iliac sampling with the patient sitting and leaning forward.
What causes a dry tap?
A dry tap may reflect technique, such as incorrect needle placement, or disease, such as marrow fibrosis or a tightly packed leukemic marrow. When it occurs, a trephine biopsy is needed to assess the marrow.
