What to Expect from a BMAC Procedure for Knee Osteoarthritis — From Consultation to Recovery

If you have been recommended a BMAC (bone marrow aspirate concentrate) procedure for knee osteoarthritis and want to understand exactly what to expect — before, during, and after — this guide walks you through every stage from the initial consultation to your recovery timeline. Knowing what lies ahead removes uncertainty, helps you prepare, and ensures you get the most from the procedure.

At our Miami clinic, we use the Regenexx protocol — the most rigorously developed BMAC protocol available, guided by more published clinical outcome data than any other regenerative medicine organization. Here is precisely what that process looks like.

Step 1: The Consultation — Determining If You Are a Candidate

Not every patient with knee osteoarthritis is an ideal candidate for BMAC. The consultation is where we make that determination honestly.

During your initial visit, Dr. Bonner will review your imaging (MRI and X-ray), take a detailed history, and perform a physical examination of the knee. He evaluates the severity of cartilage loss, the presence of bone marrow lesions, joint space narrowing, alignment, and the involvement of surrounding soft tissue structures such as the meniscus.

BMAC is generally most appropriate for patients with Kellgren-Lawrence grade II–IV knee osteoarthritis who have not had adequate relief from conservative care, and for whom surgery is either not indicated or something they wish to avoid. Bone marrow lesions visible on MRI — areas of subchondral edema that correlate strongly with pain — are a particular indication for the intraosseous delivery approach discussed below.

If you are a candidate, Dr. Bonner will walk you through the procedure in detail, discuss realistic expectations, and answer your questions. If you are not a candidate — or if a different treatment (such as PRP) is more appropriate for your stage of disease — you will be told so directly. Regenexx network providers do not offer procedures to patients who are unlikely to benefit.

Step 2: Pre-Procedure Preparation

In the days leading up to your procedure, preparation is straightforward but important.

You will be asked to stop any anti-inflammatory medications (NSAIDs such as ibuprofen, naproxen, or aspirin) for a period specified by Dr. Bonner — typically 7 days prior. These medications can impair platelet function and potentially reduce the biological activity of the BMAC concentrate. Acetaminophen (Tylenol) is generally acceptable for pain management during this window.

Steroid injections — including cortisone shots — should not be administered in the 4–6 weeks before the procedure, as steroids have been shown to suppress cell viability in the treated tissue. If you have had a recent cortisone injection in the knee, let Dr. Bonner know at your consultation so timing can be adjusted.

On the morning of the procedure, you should eat a normal breakfast and remain well hydrated. Wear comfortable, loose clothing that allows easy access to the knee and the posterior iliac crest (the area of the pelvis where bone marrow is harvested). You will need a driver to take you home afterward — not because the procedure involves general anesthesia, but because at times a combination of sedation and local anesthesia is used that may leave you drowsy for a few hours.

Step 3: Bone Marrow Aspiration — The Harvest

The procedure begins with aspiration of bone marrow from the posterior iliac crest — the back of the pelvis. This is the gold-standard harvest site for regenerative procedures, chosen because it contains the highest concentration of mesenchymal stem cells, growth factors, cytokines, and platelets relative to blood volume.

You will receive local anesthetic at the harvest site, along with light procedural sedation for comfort if needed. The aspiration itself takes approximately 30-45 minutes. Using a specialized aspiration needle under ultrasound or fluoroscopic (live X-ray) guidance, Dr. Bonner carefully draws a measured volume of bone marrow. The technique matters here — the way bone marrow is harvested directly affects the cell yield. Regenexx-trained physicians use a specific aspiration technique that maximizes the recovery of the mesenchymal stem cell fraction.

Most patients report minimal discomfort at the harvest site. Some describe a brief aching or pressure sensation during aspiration, followed by mild soreness at the site over the following 1–2 days — similar to a deep bruise. Serious complications at the harvest site are rare.

Step 4: Laboratory Processing — Concentration and Quality Control

Once harvested, your bone marrow goes directly to an on-site laboratory for processing. This step is what distinguishes a Regenexx BMAC procedure from a standard bedside BMAC procedure performed at most practices.

Standard bedside centrifuge systems — the “point-of-care” kits used at the majority of regenerative medicine clinics — concentrate bone marrow using a fixed, automated protocol. The result is acceptable, but the concentration of the mesenchymal stem cell fraction is limited by what the centrifuge system can achieve in a brief spin cycle.

Regenexx uses proprietary multi-step laboratory processing that goes substantially beyond what bedside systems can achieve. The processing time is longer, the technique is more precise, and the resulting concentrate contains a significantly higher concentration of the cellular and molecular components that drive the regenerative response — including mesenchymal stem cells, platelets, cytokines, and growth factors. Critically, the laboratory also performs quality control testing on your sample before it is cleared for injection.

One additional advantage of the Regenexx processing protocol: the bone marrow aspirate also yields a separate, highly concentrated PRP fraction from your own bone marrow. This bone marrow-derived PRP has a distinct cytokine and growth factor profile compared to peripheral blood PRP, providing complementary signaling to the joint environment and further enhancing the regenerative milieu at the treatment site.

Step 5: Image-Guided Injection — Getting the Cells Where They Need to Go

Placement matters as much as product quality. An excellent biologic injected imprecisely is a wasted procedure.

All BMAC injections at our clinic are performed under image guidance — either ultrasound or fluoroscopy — to ensure accurate delivery into the target tissue. For knee osteoarthritis, the standard approach is intraarticular injection into the joint space, placing the BMAC concentrate directly in contact with the damaged articular cartilage.

However, in patients with MRI-confirmed bone marrow lesions — areas of subchondral bone edema that are strongly associated with pain and cartilage breakdown — Dr. Bonner uses an intraosseous delivery approach. This technique delivers BMAC directly into the subchondral bone under the damaged cartilage, where bone marrow lesions reside and where intraarticular injection cannot reach. Research has demonstrated that intraosseous delivery for bone marrow lesion-associated osteoarthritis produces superior outcomes compared to intraarticular injection alone. [2]

In many cases, both routes are used — intraarticular for the joint surface and intraosseous for the subchondral bone — providing comprehensive coverage of the disease process at multiple anatomical levels.

The injection portion of the procedure takes approximately 20–30 minutes. Most patients tolerate it well with local anesthesia.

Intraarticular vs. Intraosseous BMAC Delivery: Key Differences

Step 6: Immediate Post-Procedure — What Happens After Injection

You will rest in the clinic for 15-30 minutes after the injection for observation. Most patients feel comfortable enough to walk out of the office without assistance, though some experience a mild local inflammatory response in the knee (warmth, swelling, achiness) in the first 24–48 hours. This is a normal and expected part of the regenerative process — the injected material initiates a controlled healing cascade, and the early inflammatory phase is part of that response.

You should not take NSAIDs (ibuprofen, naproxen) for pain management after a BMAC procedure, as these medications suppress the inflammatory signaling pathways that drive the regenerative response. Acetaminophen is preferred if needed. Ice can be used for local comfort.

You will be given written post-procedure instructions before you leave. These cover activity restrictions, pain management, follow-up timing, and signs that should prompt you to call the clinic.

Recovery Timeline: What to Expect Week by Week

One important point on expectations: BMAC does not regenerate cartilage overnight, and some patients show their most meaningful improvement not at 3 months but at 12–24 months as the regenerative and anti-inflammatory effects continue to unfold. The 4-year Pabinger et al. study found that meaningful improvements in IKDC and WOMAC scores persisted and in many cases deepened from year 2 through year 4. [1]

The Role of Physical Therapy

BMAC is not a stand-alone treatment — it is a biological intervention that works best when the joint is mechanically prepared to respond. After the initial recovery period, Dr. Bonner typically recommends a structured physical therapy program to optimize the functional environment of the treated joint. Strengthening the muscles around the knee — particularly the quadriceps and hip stabilizers — reduces mechanical stress on the cartilage surface and allows the regenerative process to occur in a more favorable environment.

The timing and intensity of physical therapy is individualized. Patients who are deconditioned, have significant quad atrophy, or have been limping for a prolonged period may benefit from prehabilitation even before the procedure. Those with straightforward presentations may begin PT at 1 – 2 weeks post-procedure.

Follow-Up and Repeat Procedures

Dr. Bonner typically schedules follow-up appointments at 4 to 6 weeks, 3 months, and 6 months after the procedure to assess your progress. These visits allow objective tracking of your functional improvement and pain scores, and guide decisions about additional intervention.

For some patients — particularly those with advanced joint disease — a second BMAC procedure may be considered after 6–12 months based on response to the first. The decision to repeat the procedure is driven by your clinical trajectory, not by a pre-planned protocol. If you are continuing to improve, additional intervention is generally not needed. If your improvement has plateaued or been partial, a second procedure may extend the benefit.

A 2021 systematic review by Hernigou et al. examining long-term outcomes of BMAC for knee osteoarthritis found that a significant percentage of patients were able to delay or avoid total knee replacement, with sustained pain relief over the follow-up period. [3]

How BMAC Compares to Other Treatments for Knee OA

The Supporting Research

The evidence base for BMAC in knee osteoarthritis has grown substantially over the past decade. Key studies supporting the approach used at our clinic include:

A 2024 systematic review of 8 randomized controlled trials (937 patients) by Han et al. confirmed that BMAC injection provides statistically significant pain relief and functional improvement in knee osteoarthritis compared to hyaluronic acid, with a favorable safety profile and no serious adverse events. [4]

The prospective 4-year follow-up study by Pabinger et al. in severe KL grade III–IV osteoarthritis showed sustained improvement through the full 4 years, with WOMAC scores dropping from 40 to 18 (p < 0.001) and IKDC scores rising from 56 to 73 — with 95% of patients reporting they would choose the procedure again. [1]

For bone marrow lesion-associated OA specifically, a study by Hernigou et al. comparing intraosseous versus intraarticular delivery found that the intraosseous approach produced superior outcomes in patients with MRI-confirmed subchondral bone marrow lesions. [2]

Hernigou et al.’s 2021 long-term data in International Orthopaedics demonstrated that BMAC can delay or avoid knee replacement in a meaningful proportion of patients with advanced osteoarthritis when properly performed. [3]

Frequently Asked Questions

How long does the entire procedure take?

From arrival to discharge, plan for approximately 3–4 hours. The bone marrow harvest takes 30–45 minutes, laboratory processing takes approximately 45–90 minutes, and the injection portion takes another 30–90 minutes. The remainder is preparation, recovery, and observation time.

Is BMAC painful?

The procedure is performed with local anesthesia, so the procedure itself is well-tolerated by most patients. The harvest site (posterior iliac crest) typically causes the most discomfort — described as aching pressure during aspiration — followed by soreness for 1–3 days afterward similar to a deep bruise. Knee discomfort is variable: some patients have minimal soreness after injection, while others experience a temporary inflammatory flare in the first 24–72 hours.

When will I see results?

Most patients begin to notice meaningful improvement in pain and function between 6–12 weeks after the procedure. However, BMAC is not a cortisone shot — the regenerative response unfolds over months. Many patients show continued improvement at 6 months and 12 months. Setting realistic expectations about the timeline is an important part of the consultation process.

Can BMAC be combined with PRP in the same session?

Yes — and at our clinic this is standard practice. The bone marrow processing protocol used in the Regenexx system produces both a BMAC fraction and a separate bone marrow-derived PRP fraction. These are used together, with the BM-derived PRP providing complementary growth factor signaling to the joint. The cytokine profile of bone marrow-derived PRP differs meaningfully from peripheral blood PRP, which is why both are used when available rather than simply adding standard PRP to the treatment.

Is BMAC covered by insurance?

Most BMAC procedures are not covered by standard health insurance, which classifies regenerative orthopedic procedures as elective or experimental. Some self-insured employer health plans and health-sharing programs do cover these procedures. Financing options are available, and many patients view BMAC as a meaningful investment compared to the cost, risk, and recovery time associated with total knee replacement. We will discuss all options at your consultation.

Who is not a good candidate for BMAC?

Patients who are unlikely to benefit from BMAC include those with severe, bone-on-bone arthritis with significant structural deformity (significant varus or valgus malalignment), those with active infection or severe systemic illness, those with bleeding disorders or on anticoagulants that cannot be temporarily held, and those with very poor bone marrow yield (uncommon, but can be assessed on imaging). Dr. Bonner will review your candidacy honestly at consultation — if BMAC is not the right choice for you, he will tell you, and discuss what alternatives may be more appropriate.

How is Dr. Bonner’s BMAC procedure different from what other clinics offer?

Several important differences distinguish the Regenexx approach from standard BMAC procedures:

(1) Proprietary multi-step laboratory processing that achieves a higher concentration of the mesenchymal stem cell fraction than standard bedside kits.

(2) Quality control testing of your sample before injection.

(3) Production of a bone marrow-derived PRP fraction used alongside the BMAC concentrate.

(4) The option for intraosseous delivery under fluoroscopic guidance for patients with bone marrow lesions — a step most providers cannot or do not perform.

(5) Image guidance for all injections, ensuring accurate placement.

You can learn more about these distinctions at our Regenexx network provider page or the BMAC service page.

Next Steps: Is BMAC Right for Your Knee?

If you have been managing knee osteoarthritis with anti-inflammatories, cortisone shots, or physical therapy — and you are not getting adequate relief — or if you have been told you need a knee replacement and want to explore alternatives before committing to surgery, BMAC may be worth evaluating.

The first step is a consultation. Dr. Bonner will review your imaging, assess your candidacy honestly, and give you a clear picture of what BMAC can and cannot do for your specific situation. There is no obligation, and there is no protocol that assumes everyone needs the same procedure.

To schedule a consultation at our Miami clinic, contact us at 786-522-4959 or book online. Learn more about our full range of knee treatments at our knee osteoarthritis treatment page, or explore whether PRP might be a better fit first at our PRP for knee osteoarthritis page. You can also read Dr. Bonner’s detailed article on whether BMAC can help knee osteoarthritis.

References

1. 1. Pabinger C, Lothaller H, Kobinia GS. Intra-articular injection of bone marrow aspirate concentrate (mesenchymal stem cells) in KL grade III and IV knee osteoarthritis: 4 year results of 37 knees. Sci Rep. 2024. DOI: 10.1038/s41598-024-51410-2
   2. Hernigou P, et al. The treatment of bone marrow lesions associated with advanced knee osteoarthritis: comparing intraosseous and intraarticular injections with bone marrow concentrate and platelet products. Int Orthop. 2021. PMID: 33988949
   3. Hernigou P, Delambre J, Quiennec S, Poignard A. Human bone marrow mesenchymal stem cell injection in subchondral lesions of knee osteoarthritis: a prospective randomized study versus contralateral arthroplasty at a mean fifteen year follow-up. Int Orthop. 2021 Feb;45(2):365–373. PMID:32322943
   4. Han JH, Jung M, Chung K, Jung SH, Choi CH, Kim SH. Bone marrow aspirate concentrate injections for the treatment of knee osteoarthritis: a systematic review of randomized controlled trials. Orthop J Sports Med. 2024. PMID: 39640186