What is the role of stem cells (SCs) in the treatment of avascular necrosis (AVN) of the hip, particularly with core decompression?

Stem Cells in AVN Hip Core Decompression

The American College of Rheumatology strongly recommends against stem cell injections for hip pathology, citing lack of standardization and heterogeneity in preparations; however, when combined specifically with core decompression for early-stage AVN (pre-collapse), bone marrow-derived stem cells show significant clinical benefit in reducing femoral head collapse and delaying total hip arthroplasty. 1, 2

Critical Distinction: AVN vs. Osteoarthritis

The ACR/Arthritis Foundation guidelines explicitly recommend against stem cell injections for osteoarthritis of the hip due to concerns about heterogeneity and lack of standardization in available preparations 1. However, these guidelines do not specifically address AVN, which has a distinct pathophysiology involving vascular disruption rather than degenerative joint disease 2.

Evidence for Stem Cells in AVN Core Decompression

Efficacy Outcomes

Bone marrow stem cells combined with core decompression demonstrate superior outcomes compared to core decompression alone:

• Femoral head collapse prevention: 85% reduction in risk (OR = 0.15) 2
• Conversion to total hip arthroplasty: 80% reduction in risk (OR = 0.20) 2
• Functional improvement: Harris Hip Score improved by 10.7 points on average 2
• Pain reduction: Visual Analog Scale decreased by 8.04 points 2
• Long-term survival: 10-year follow-up showed average survival time of 102.3 months with bone marrow buffy coat grafting versus 78.1 months with core decompression alone 3

Optimal Treatment Stage

Stem cell therapy is most effective in early-stage, pre-collapse AVN (ARCO stages I-II or Ficat stages I-II):

• Lesions involving <30% of the femoral head have <5% progression to collapse, making them ideal candidates 4, 5
• Success rates decline dramatically in advanced disease with articular collapse 6
• Preoperative Ficat stage III is an independent risk factor for clinical failure (HR = 3.743) 3

Technical Considerations

Autologous bone marrow-derived stem cells are the most studied preparation:

• Bone marrow buffy coat grafting combined with core decompression is the most validated technique 3
• Autologous stem cell implantation from the iliac crest shows 93% (40/43 hips) success in preventing radiologic progression at 16-month follow-up 7
• 78% of patients report at least 50% decrease in pain scores 7

Critical Pitfalls and Caveats

Timing Is Everything

Early detection and intervention are crucial, as delay leads to articular collapse and eliminates joint-preserving options 6. MRI is the gold standard for early detection before radiographic changes appear 6.

Standardization Concerns

The ACR's concerns about heterogeneity in stem cell preparations remain valid 1. However, autologous bone marrow-derived preparations used in AVN studies are more standardized than commercial stem cell products marketed for osteoarthritis 3, 7.

Patient Selection

Risk factors that worsen prognosis and should influence decision-making include:

• Age >40 years 6
• Corticosteroid therapy 6
• Alcohol use 6
• Preoperative Ficat stage III disease 3

Bilateral Disease Screening

70-80% of nontraumatic AVN cases are bilateral, requiring evaluation of the contralateral hip 6.

Practical Algorithm

For early-stage AVN (pre-collapse, <30% femoral head involvement):

1. Confirm diagnosis with MRI and assess lesion size with CT 4, 5
2. If Ficat stage I-II: Consider core decompression with autologous bone marrow stem cell grafting 2, 3
3. Harvest bone marrow buffy coat from iliac crest during same procedure 3, 7
4. Implement protected weight-bearing postoperatively 4, 5
5. Regular radiographic follow-up to monitor for progression 4, 5

For late-stage AVN (Ficat stage III-IV with articular collapse):

• Proceed directly to arthroplasty (hemiarthroplasty or total hip arthroplasty) 5, 6
• Do not attempt core decompression with or without stem cells, as success rates are poor (14%) 6

Reconciling Contradictory Evidence

The apparent contradiction between ACR guidelines recommending against stem cells 1 and research showing benefit 2, 3, 7 reflects different clinical contexts. The ACR evaluated commercial stem cell products for osteoarthritis, while AVN research examines autologous bone marrow grafting combined with core decompression for vascular pathology. The latter represents a more standardized, evidence-based approach with 10-year follow-up data demonstrating efficacy 3.