Session VI - Basic Science / Injury Prevention / Spine

Sat., 10/10/09 Basic Sci./Injury Prevent./Spine, Paper #64, 10:10 am OTA-2009

The Use of Endothelial Progenitor Cells to Promote Bone Healing: A Defect Model in the Rat Femur

Kivanc Atesok, MD (n); Ru Li, PhD (n); Emil H. Schemitsch MD, FRCS(C) (n);
Musculoskeletal Research Lab, Division of Orthopaedics, Department of Surgery,
St. Michael’s Hospital, University of Toronto, Toronto, Ontario, Canada

Purpose: Vascular ingrowth is an essential mechanism in fracture healing. Endothelial progenitor cells (EPCs) have been proven to contribute to formation of new vessels. The objective of this study was to evaluate the effects of local EPC therapy on the stimulation of angiogenesis at a fracture site and the promotion of bone healing by increasing osteogenesis and callus formation.

Methods: Fisher-344 rats were used as the animal model for this study. Rat bone-marrow EPCs were isolated and cultured for 7 to 10 days in endothelial cell growth medium. A segmental bone defect (4 mm) was created in the rat femur diaphysis and stabilized with a mini-plate. A gel foam piece impregnated with a solution of EPCs (1 x 106) was placed into the fracture gap. Control animals received only saline–gel foam with no cells. In total, 56 rats were studied: 28 in EPC and 28 in control groups. Seven animals were sacrificed from each group at 1, 2, 3, and 10 weeks postoperatively. Plain radiographs of the operated femur were taken before sacrifice to verify callus formation. Radiographic assessment for the animals sacrificed at 1, 2, and 3 weeks were performed by scoring the radiographs on a scale from 0 to 5 according to the percentage and the intensity of the bone filling at the osteotomy site. For the animals sacrificed at 10 weeks, presence of union was the main radiographic assessment parameter. Operated femurs were harvested and the specimens from the osteotomy site were collected. Histological assessment of the hematoxylin-eosin–stained slides was performed for new vessel formation and the amount of bone tissue. Additionally, micro-CT scans were performed for the operated femurs from the animals sacrificed at 10 weeks postoperatively (n = 14).

Results: Radiographically, at 10 weeks all 7 animals in the EPC group had union with considerable bridging callus formation; in the control group however, none of the animals had union. At 3 weeks, the mean score for the EPC group was 4.5, with 5 out of 7 animals having bridging callus, whereas for the control group, the mean score was 2.2 with no bridging callus formation (P <0.05). At 2 weeks, EPC-treated animals had a mean score of 2.4, and the control group had a score of 1. Bone formation was insignificant at 1 week in either group; however, the scores tended to be higher in the EPC group animals than the controls (0.6 to 0.3, respectively). Histological evaluation at all time intervals revealed that the specimens from EPC-treated animals had abundant spicules of trabecular bone containing predominantly bone cells, osteoid, and new vessels. Conversely, control animals had scarce trabecular bone with markedly less bone cells and vessels. Micro-CT assessment showed significantly higher mean values for the parameters of bone volume (36.58 to 10.57, P <0.001), bone volume density (0.26 to 0.17, P <0.001), bone surface (353.75 to 152.08, P <0.001), trabecular number (1.28 to 0.91, P = 0.063), and trabecular thickness (0.21 to 0.15, P <0.001) for the EPC group compared to controls, respectively.

Conclusion: Local EPC therapy stimulates angiogenesis and increases osteogenesis and callus formation after fracture. Our report encourages further investigation of the local use of EPCs as a potential therapy to promote bone regeneration at a fracture site.

Disclosure: (n=Respondent answered 'No' to all items indicating no conflicts; 1=Board member/owner/officer/committee appointments; 2=Medical/Orthopaedic Publications; 3=Royalties; 4=Speakers bureau/paid presentations; 5A=Paid consultant or employee; 5B=Unpaid consultant; 6=Research or institutional support from a publisher; 7=Research or institutional support from a company or supplier; 8=Stock or Stock Options; 9=Other financial/material support from a publisher; 10=Other financial/material support from a company or supplier).

• The FDA has not cleared this drug and/or medical device for the use described in this presentation   (i.e., the drug or medical device is being discussed for an “off label” use).  ◆FDA information not available at time of printing. Δ OTA Grant