Autologous Bone Marrow Aspirate Does Not Accelerate Healing After Osteochondral Allograft
Key findings
- Of 58 patients who underwent cartilage repair with osteochondral allograft (OCA) transplantation, six-month postoperative MRI showed excellent osseous integration at the graft–host junction
- Augmenting OCAs with autogenous bone marrow aspirate did not result in superior imaging outcomes, compared with no augmentation
- A potential explanation is that the Osteochondral Allograft MRI Scoring System is not sensitive enough to detect small but potentially clinically relevant differences in graft integration
After cartilage repair with osteochondral allograft (OCA) transplantation, bone healing occurs through the relatively slow process of creeping substitution. Patients are at risk of graft failure while osseous integration is incomplete, so graft augmentation with autogenous bone marrow has become a strategy of interest as a way to accelerate healing.
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Bone marrow aspirate concentrate (BMAC) contains a high concentration of mesenchymal stem cells, but it's controversial whether concentration or centrifugation significantly increases the number of stem cells compared with unmanipulated autologous bone marrow aspirate (BMA).
Furthermore, using BMA without subsequent concentration is substantially less expensive, carries less infection risk and avoids potential regulatory issues about homologous use. In addition, BMA, unlike BMAC, contains various bone marrow components that have the capacity to create a microenvironment that promotes tissue regeneration.
Research fellow Jakob Ackermann, MD, of the Sports Medicine Center at Massachusetts General Hospital, Andreas H. Gomoll, MD, of the Hospital for Special Surgery, and colleagues retrospectively examined prospective data on patients who underwent OCA with or without BMA. In Arthroscopy, they report having detected excellent osseous integration at the graft–host junction six months postoperatively but no difference between the two treatment groups in imaging outcomes.
Study Design
The study involved 58 patients who underwent fresh OCA transplantation for focal cartilage defects of the knee, performed by a single surgeon between July 2013 and July 2017. In October 2015, that surgeon began augmenting OCA plugs with BMA obtained from the ipsilateral distal femur. All other intraoperative and postoperative aspects of the treatment remained unchanged.
The patients underwent magnetic resonance imaging (MRI) at an average of 5.6 months postoperatively (range, 4–8 months).
Patients treated with or without BMA were matched 1:1 by lesion location, OCA size, age, body mass index and prior surgery on the index knee. The inclusion of 29 patients in each group was considered sufficient to assess the integration of OCAs using the Osteochondral Allograft MRI Scoring System (OCAMRISS).
MRI Results
- 83% of OCAs had a normal graft cartilage signal
- 85% had >76% cartilage fill
- 86% showed osseous integration at the graft–host junction
- 76% did not show any cystic changes in the subchondral bone; However, 97% showed abnormal subchondral bone marrow edema
BMA Augmentation vs. No Augmentation
- There were no significant differences between the treatment groups in any OCAMRISS subscale, including osseous integration and subchondral cyst formation
- There was no association between osseous integration at the graft–host interface and patient age, body mass index or graft size
Possible Explanations
It may be that the concentration of MSCs provided by BMA, especially from the distal femur, is inadequate to enhance bony healing compared with the healing of non-augmented grafts.
Another possibility is that the OCAMRISS, which reports overall MRI appearance after OCA transplantation, is not sensitive enough to detect small but potentially clinically relevant differences in graft integration. Nine of 13 subscales, including osseous integration and subchondral bone marrow edema, score only the absence/presence of the MRI feature, partly discounting the varying degree of severity.
For example, a positive yet only mildly increased graft signal intensity on postoperative MRI may be considered normal, whereas severe edema may raise concerns about treatment failure, yet both are judged abnormal on the OCAMRISS. This is a particular concern considering that 97% of grafts in this study showed abnormal subchondral bone marrow edema.
The OCAMRISS may need to be improved before it can be relied on for evaluating graft integration on postoperative MRI.
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