Transient soft-tissue edema associated with implantation of increasing doses of rhBMP-2 on an absorbable collagen sponge in an ectopic rat model.
BACKGROUND
Recombinant human bone morphogenetic protein-2 (rhBMP-2) is an osteoinductive protein. However, soft-tissue edema adjacent to the site of rhBMP-2 implantation has been reported. This animal study was designed to examine soft-tissue edema associated with increasing rhBMP-2 doses with implantation on an absorbable collagen sponge (ACS) and with injection directly into muscle.


METHODS
Thirty-six Lewis rats received intramuscular implantation of rhBMP-2 on an ACS (Part I) or intramuscular injection of rhBMP-2 solution (Part II). Part-I sites received rhBMP-2/ACS at doses of 0 μg, 30 μg (normal), 129 μg (mid), or 450 μg (high). Part-II sites received rhBMP-2/ACS or rhBMP-2 intramuscular injection at doses of 10 μg (normal) or 150 μg (mid). A previous rat model showed 10 μg to be 100% effective at inducing osseous spinal fusion. In our study, T2-weighted magnetic resonance imaging (MRI) was performed at two and seven days to assess edema volume, and statistical comparisons were carried out with analysis of variance (ANOVA). Cellular response, vascularity, and ossification were examined histologically.


RESULTS
Quantitative MRI demonstrated similar peri-implant edema volumes in the control (buffer on an ACS) and normal-dose rhBMP-2 groups. Higher doses resulted in increased edema volume. Edema decreased significantly from two to seven days. Similar capillary densities were observed in all rhBMP-2 groups at two days, and there was dose-dependent increased ossification at seven days. Compared with the rhBMP-2 injection, implantation of the rhBMP-2/ACS resulted in increased edema. This edematous response was transient in all groups. Minimal or no ossification occurred after the rhBMP-2 injections.


CONCLUSIONS
Transient peri-implant soft-tissue edema occurred in a dose-dependent manner following implantation of rhBMP-2/ACS in this rat model. The normal dose of rhBMP-2/ACS produced edema similar to that in the controls. Finally, rhBMP-2 solutions injected directly into muscle resulted in minimal soft-tissue edema.
Spine Center, Division of Orthopaedic Surgery, Department of Surgery, Cedars-Sinai Medical Center, Los Angeles, CA 90048, USA. baehw@yahoo.com
Hyun W
HW
Bae
K Brandon
KB
Strenge
Nomaan
N
Ashraf
Jeffrey M
JM
Badura
Steven M
SM
Peckham
William F
WF
McKay
D020341:Absorbable Implants / Q000009:adverse effects*; D000818:Animals; D055396:Bone Morphogenetic Protein 2 / Q000008:administration & dosage / Q000009:adverse effects*; D003094:Collagen / Q000008:administration & dosage / Q000009:adverse effects*; D004305:Dose-Response Relationship, Drug; D004487:Edema / Q000209:etiology*; D007273:Injections, Intramuscular / Q000009:adverse effects; D009135:Muscular Diseases / Q000209:etiology*; D051381:Rats; D011917:Rats, Inbred Lew
D055396:Bone Morphogenetic Protein 2; D003094:Collagen