Bone Marrow Aspirate (BMA) and Bone Marrow Aspirate Concentrate (BMAC)

Although the terms Bone Marrow Aspirate (BMA) and Bone Marrow Aspirate Concentrate (BMAC) are sometimes used interchangeably, they describe two different biological preparations. Understanding the differences may help patients have informed discussions about the treatment options that may be appropriate for their individual circumstances.

What is Bone Marrow Aspirate (BMA)?

Bone Marrow Aspirate (BMA) is obtained by withdrawing a small volume of liquid bone marrow, most commonly from the posterior iliac crest (the back of the pelvis), using a specialised needle under sterile conditions.

Bone marrow is a naturally occurring biological tissue containing a diverse mixture of cells and signalling molecules involved in the body’s normal tissue maintenance and repair processes. These include:

• Mesenchymal stromal cells (MSCs)
• Haematopoietic stem and progenitor cells
• Platelets
• White blood cells
• Red blood cells
• Growth factors
• Cytokines
• Chemokines
• Other naturally occurring biological signalling molecules

BMA represents bone marrow in its natural, unprocessed form.

What is Bone Marrow Aspirate Concentrate (BMAC)?

Bone Marrow Aspirate Concentrate (BMAC) is produced by processing bone marrow aspirate using a specialised centrifugation system.

This process concentrates selected cellular and biological components while reducing the proportion of red blood cells and plasma. The resulting preparation generally contains higher concentrations of many of the cells and signalling molecules naturally present in bone marrow.

Depending on the harvesting and processing technique, BMAC may contain increased concentrations of:

• Mesenchymal stromal cells (MSCs)
• Haematopoietic stem and progenitor cells
• Platelets
• Mononuclear cells
• White blood cells
• Growth factors
• Cytokines
• Other biological signalling molecules

The exact composition varies between individuals and is influenced by factors such as patient age, aspiration technique, processing method and centrifugation protocol.

Why Concentrate Bone Marrow?

The rationale for concentrating bone marrow is to increase the concentration of naturally occurring biological components that are thought to contribute to normal tissue repair.

Current scientific understanding suggests these biological effects occur primarily through complex cellular communication and regulation of the local tissue environment rather than by directly replacing damaged tissue.

Although laboratory and preclinical research has demonstrated a range of biological effects, the relationship between higher cellular concentrations and improved clinical outcomes continues to be investigated.

Is BMAC Better Than BMA?

At present, there is no clear evidence that BMAC is superior to unprocessed BMA for every musculoskeletal condition.

While concentrating bone marrow increases the concentration of many biological components, this does not necessarily translate into improved clinical outcomes for every patient or every condition.

The choice between BMA and BMAC depends on several factors, including:

• The tissue being treated.
• The underlying pathology.
• The severity of the condition.
• Current scientific evidence.
• Patient-specific factors.
• Procedural considerations.
• Shared decision-making between practitioner and patient.

Why Are These Procedures Called Orthobiologics?

Neither BMA nor BMAC should be described as a “stem cell treatment.”

Although both preparations contain mesenchymal stromal cells, these cells represent only a very small proportion of the total cellular population within bone marrow.

Current research suggests that any potential clinical effects are more likely to result from the combined activity of many different biological components—including platelets, immune cells, cytokines, growth factors and other signalling molecules—rather than from a single cell type.

For this reason, these procedures are more accurately described as orthobiologic treatments, reflecting their use of the patient’s own biological tissues to support the body’s normal tissue repair processes.

Clinical Applications Reported in the Literature

BMA and BMAC have been investigated across a wide range of musculoskeletal conditions. The strength of evidence varies considerably between indications, and treatment recommendations should always be individualised.

Published research has investigated these preparations in selected patients with conditions including:

• Bone marrow oedema.
• Early avascular necrosis.
• Delayed fracture healing and non-union.
• Osteoarthritis.
• Focal cartilage defects.
• Osteochondral lesions.
• Degenerative disc disease.
• Chronic tendon disorders.
• Selected ligament injuries.
• Meniscal pathology.
• Subchondral bone disorders.

For some conditions involving bone or subchondral pathology, BMAC has shown encouraging results in early clinical studies. For other conditions, such as tendon and ligament disorders, platelet-rich plasma (PRP) has been more extensively investigated. However, the available evidence continues to evolve, and no single orthobiologic preparation has been shown to be superior for all musculoskeletal conditions.

Choosing the Appropriate Orthobiologic

Orthobiologic procedures should be selected according to the biological characteristics of the tissue being treated rather than applying a single approach to every condition.

Different preparations offer different biological properties:

• PRP provides a concentrated source of platelets and growth factors and has been widely investigated for tendon disorders, ligament injuries and mild to moderate osteoarthritis.
• Platelet-poor plasma (PPP) has been investigated for selected applications where its biological properties may be appropriate.
• BMA provides the native composition of bone marrow with minimal processing.
• BMAC provides a concentrated preparation of selected cellular and biological components naturally found within bone marrow.

The most appropriate treatment, if any, depends on the individual’s diagnosis, imaging findings, overall health, treatment goals and the current evidence available.

Current Evidence

Research investigating BMA and BMAC continues to expand. While laboratory studies and early clinical research have demonstrated promising biological and clinical findings for selected musculoskeletal conditions, the quality of evidence varies considerably between indications.

High-quality randomised controlled trials remain limited for many applications. Ongoing research continues to define the most appropriate patient selection, preparation methods and clinical indications.

Key Points

• BMA is unprocessed bone marrow obtained from the patient’s own pelvis.
• BMAC is bone marrow aspirate that has been processed to concentrate selected cellular and biological components.
• Both are autologous procedures using the patient’s own tissue.
• Neither procedure should be described as a stem cell treatment.
• Current evidence suggests that any potential biological effects are likely to result from the combined activity of multiple cells and signalling molecules rather than a single cell type.
• Treatment recommendations should always be individualised following a comprehensive clinical assessment and informed consent.

Disclaimer

The information provided on this page is intended for general educational purposes only. It should not be interpreted as medical advice or as a recommendation that any particular procedure is appropriate for an individual patient. Decisions regarding orthobiologic procedures should be made following a comprehensive clinical assessment, consideration of current evidence, discussion of potential benefits and limitations, and shared decision-making between practitioner and patient.

Tendinopathy	PRP	Strongest evidence for tendon healing
Ligament injury	PRP → BMAC if chronic	Escalate for refractory cases
Muscle injury	PRP	Better evidence base
Peripheral nerve	PRP / PPP	Anti-inflammatory and neurotrophic effects
Osteoarthritis	PRP → BMAC	Greater biological stimulus for advanced disease
Bone marrow oedema	BMAC	Osteogenic and reparative cell concentration
AVN	BMAC	Supports bone regeneration
Non-union	BMAC	Higher osteogenic potential
Disc degeneration	BMAC	Concentrated progenitor cells and cytokines
Cartilage defects	BMAC	Chondrogenic support
Meniscal pathology	PRP or BMAC	Depends on tear complexity and chronicity
Intraosseous procedures	BMAC	Greater concentration of reparative cells