Posterolateral lumbar fusions in athymic rats: characterization of a model.
BACKGROUND
The athymic rat has been used to study the role of osteoinductive products in spinal fusions. This small animal model has been advocated to minimize potential inflammatory responses to allogeneic or xenogenic proteins. Despite past experience, this model has not yet been well characterized.


OBJECTIVE
To further define and validate a posterolateral lumbar fusion model in the athymic rat.


METHODS
Comparison of fusions after animal survival surgery.


METHODS
Forty athymic and 20 normothymic rats.


METHODS
Manual palpation, radiography and histology at 3 and 6 weeks.


METHODS
Single-level intertransverse fusions were performed at the L4-L5 level of 40 athymic rats. Twenty rats were implanted with autograft (athymic/autograft), and 20 had no graft placed (athymic/no graft). An additional 20 autograft fusions were performed on normothymic rats (normothymic/autograft). Half were sacrificed at 3 weeks; half were sacrificed at 6 weeks.


RESULTS
At 3 weeks, 0% of the athymic/no graft rats fused, 20% of the athymic/autograft rats fused and 20% of the normothymic/autograft rats fused by manual palpation. At 6 weeks, 0% of the athymic/no graft rats fused, 30% of the athymic/autograft rats fused and 40% of the normothymic/autograft rats fused by manual palpation. Radiographs were of limited utility in determining fusion, and histology results were roughly concordant with those of manual palpation.


CONCLUSIONS
This work further characterizes the athymic rat posterolateral lumbar fusion model. The absence of a thymus does not appear to affect autograft fusion rates, and no spontaneous fusions were seen when no graft was placed.
Grauer
Jonathan N
JN
Department of Orthopaedics and Rehabilitation, Yale University School of Medicine, PO Box 208071, New Haven, CT 06520-8071, USA. jonathan.grauer@yale.edu
Bomback
David A
DA
Lugo
Roberto
R
Troiano
Nancy W
NW
Patel
Tushar C
TC
Friedlaender
Gary E
GE
D000818:Animals; D016025:Bone Transplantation; D005260:Female; D008159:Lumbar Vertebrae / Q000000981:diagnostic imaging / Q000473:pathology / Q000601:surgery*; D023421:Models, Animal; D010173:Palpation / Q000379:methods; D011859:Radiography; D051381:Rats; D011923:Rats, Nude; D013123:Spinal Fusion