Effect of teriparatide [rhPTH(1,34)] and calcitonin on intertransverse process fusion in a rabbit model.
METHODS
Randomized, double-blinded, placebo controlled animal study.


OBJECTIVE
To evaluate the effect of teriparatide and calcitonin after an intertransverse process spinal fusion in a rabbit model.


BACKGROUND
It is widely recognized that some osteoporosis medications, including bisphosphonates, can interfere with bone healing. Although prescribed frequently in the treatment of osteoporosis, the effect of teriparatide and calcitonin on spinal fusion has not been fully elucidated. We hypothesized that teriparatide, being the only anabolic medication for osteoporosis treatment, would have a beneficial effect on spine fusion.


METHODS
Fifty-one New Zealand white rabbits underwent a posterolateral L5-L6 intertransverse process arthrodesis using autogenous iliac crest bone graft. The rabbits were randomly divided into 3 groups. All animals received daily subcutaneous injections of group I (n = 17) 1 mL of saline placebo; group II (n = 17) 10 microg/kg/day of teriparatide; group III (n = 17) 14 IU/animal of calcitonin during the 8-week postoperative period. Postmortem analyses included manual palpation, radiographic, biomechanical, and histologic assessment. Three random 10x fields were examined/graded within the cephalad, middle, and caudal regions of each section (810 fields). Fusion quality was graded using the Emery histologic scale (0-7 based on fibrous/bone content of the fusion mass).


RESULTS
Histologic fusion rates for teriparatide averaged 86.7% and was significantly greater than the autograft control group (50%) (P = 0.033). Radiographically, there was a strong trend towards teriparatide being superior to the calcitonin group (85.7% vs. 56.3%, respectively; P = 0.07). The average Emery grading score was 5.99 +/- 1.46 SD for the autologous group and 6.26 +/- 0.93 SD for the teriparatide group (P = 0.031). Although not significant, the teriparatide group showed less motion in flexion/extension, lateral bending, and axial rotation.


CONCLUSIONS
Our results suggest that teriparatide enhances spinal fusion while calcitonin has a neutral effect. The teriparatide group had the best histologic fusion rate and Emery scores, while the calcitonin group was similar to the saline controls. Although not significant, the teriparatide group had a strong trend towards superior radiographic fusion over the calcitonin group.
Lehman
Ronald A
RA
Department of Orthopaedics and Rehabilitation, Walter Reed Army Medical Center, Washington, DC, USA. ronald.lehman@amedd.army.mil
Dmitriev
Anton E
AE
Cardoso
Mario J
MJ
Helgeson
Melvin D
MD
Christensen
Christine L
CL
Raymond
JoLynne W
JW
Eckel
Tobin T
TT
Riew
K Daniel
KD
D000818:Animals; D001696:Biomechanical Phenomena / Q000187:drug effects; D050071:Bone Density Conservation Agents / Q000494:pharmacology; D016723:Bone Remodeling / Q000187:drug effects*; D016025:Bone Transplantation; D002116:Calcitonin / Q000494:pharmacology*; D016009:Chi-Square Distribution; D008159:Lumbar Vertebrae / Q000187:drug effects* / Q000601:surgery*; D011817:Rabbits; D011897:Random Allocation; D016059:Range of Motion, Articular / Q000187:drug effects; D013123:Spinal Fusion; D013194:Staining and Labeling; D019379:Teriparatide / Q000494:pharmacology*; D014945:Wound Healing / Q000187:drug effects
D050071:Bone Density Conservation Agents; D019379:Teriparatide; D002116:Calcitonin