Assessment of a synthetic anterior cervical ligament in a spinal fusion model in sheep.
BACKGROUND
The anterior cervical ligament is routinely excised during cervical interbody fusion. Loss of this ligament may predispose to instability at the fusion site. Anterior plating restores stability but leads to a risk of stress shielding. An alternative approach would be to use a less rigid fixation system that would provide anterior support while allowing micromotion that could enhance bone healing within the fusion site.


OBJECTIVE
To determine whether augmentation of an interbody fusion with a synthetic ligament enhances fusion.


METHODS
Prospective randomized study in a large animal model of cervical fusion.


METHODS
The primary outcome was evidence of interbody fusion, as determined by radiography, computed tomography (CT), histology and biomechanical testing.


METHODS
Twelve skeletally mature sheep underwent single level (C2-3) anterior discectomy and interbody fusion using fresh frozen allograft. In six animals, the fusion was augmented with a braided polyethylene device rigidly fixed to C2 and C3 with screws. Sheep were euthanized 12 weeks postoperatively. Specimens were radiographed and then examined by CT. Six fusion sites (three control, three augmented) were used for nondestructive biomechanical testing to assess the stability of the fusion site. The remaining specimens were processed for undecalcified histology.


RESULTS
As determined by radiography, the augmented group had 83% solid union as compared with 67% in the control group (p<.05). There was no difference regarding bone graft dislodgment between the two groups. The extension stiffness of the augmented group was significantly higher (p<.05) than that of controls, but there was no significant difference between the two groups in flexion stiffness. There was no significant difference in bone formation in the two groups as determined by CT and histology, although there was a trend for increased endochondral ossification in the augmented repairs. There was no evidence of significant adverse tissue reactions to the ligament.


CONCLUSIONS
Use of a synthetic ligament was associated with a moderate increase in fusion rate and a statistically significant increase in fusion site stiffness in extension. The use of an augmentation device, such as this synthetic ligament, may be beneficial in cervical fusion, especially when multilevel surgery is being contemplated.
Department of Orthopedic Surgery, State University of New York Upstate Medical University, 750 East Adams Street, Syracuse, NY 13210, USA. allenm@mail.upstate.edu
Matthew J
MJ
Allen
Yong
Y
Hai
Nathaniel R
NR
Ordway
Choon-Keun
CK
Park
Bo
B
Bai
Hansen A
HA
Yuan
D000818:Animals; D001696:Biomechanical Phenomena; D016025:Bone Transplantation; D002574:Cervical Vertebrae / Q000000981:diagnostic imaging / Q000473:pathology; D020007:Implants, Experimental; D016268:Internal Fixators; D007593:Joint Instability / Q000000981:diagnostic imaging; D008022:Ligaments / Q000601:surgery; D008297:Male; D008422:Materials Testing; D023421:Models, Animal; D010012:Osteogenesis; D020959:Polyethylene; D012756:Sheep; D013123:Spinal Fusion / Q000379:methods; D014057:Tomography, X-Ray Computed
D020959:Polyethylene