Comparison of multistage versus one-stage destabilization of a type II external fixator used to stabilize an oblique tibial osteotomy in dogs.
OBJECTIVE
To compare the biomechanical effects of multistage versus one-stage destabilization of a type II external skeletal fixator (ESF) used to stabilize an oblique unstable tibial osteotomy in dogs.


METHODS
In vitro, in vivo, and ex vivo experimental study.


METHODS
Twelve healthy adult dogs.


METHODS
The biomechanical characteristics of the type II ESF used in this study were determined. This fixator was applied to both tibiae of two groups of 6 dogs to stabilize a 2-mm-wide oblique osteotomy. One fixator on each dog remained unchanged throughout the 11-week study (control group). The fixator on the opposite limb was destabilized late and acutely in one group of dogs (single-stage) and early and progressively in the other (multistage). Clinical examination, radiographic examination, and force-plate analysis were used to evaluate the results. All dogs were euthanatized at 11 weeks. All tibiae were scanned to determine the cross-sectional area of the callus in the center of the osteotomy and subjected to biomechanical tests to determine mean pull-out strength of pins and callus strength and stiffness.


RESULTS
Stiffness of the type II ESF used in this study was 578 N/mm in axial compression, 0.767 Nm/deg in torsion, 261 N/mm in medio-lateral bending, and 25 N/mm in cranio-caudal bending. Peak vertical forces of the hindlimbs were significantly lower at 2.5 and 5 weeks than before surgery. Peak vertical forces of the hindlimbs did not change before and after destabilization. No significant differences could be detected between the two destabilization sequences or between all control tibiae and pooled destabilized tibiae with regards to radiographic evaluation of the healing osteotomy, cross-sectional periosteal callus area, mean pull-out strength of transfixation pins, callus strength, and callus stiffness.


CONCLUSIONS
Bone healing of unstable osteotomies stabilized with a type II ESF is not significantly enhanced by staged destabilization of the fixation as performed in this study.
Auger
Jerome
J
Department of Clinical Sciences, Faculté de Médecine Vétérinaire, University of Montreal, Saint-Hyacinthe, Quebec, Canada J2S 7C6.
Dupuis
Jacques
J
Boudreault
Francis
F
Pare
Philippe
P
Beauregard
Guy
G
Breton
Luc
L
D000818:Animals; D001696:Biomechanical Phenomena; D001858:Bone Nails / Q000662:veterinary; D004285:Dogs / Q000293:injuries / Q000601:surgery*; D016267:External Fixators / Q000592:standards / Q000662:veterinary*; D005592:Fracture Fixation / Q000379:methods / Q000592:standards / Q000662:veterinary*; D010027:Osteotomy / Q000662:veterinary*; D011859:Radiography; D013978:Tibial Fractures / Q000000981:diagnostic imaging / Q000601:surgery / Q000662:veterinary*