In vitro pullout strength of screws inserted in adult equine third metacarpal bone after overdrilling a 4.5-mm threaded insertion hole.
OBJECTIVE
To determine and compare the in vitro pullout strength of 5.5-mm cortical versus 6.5-mm cancellous bone screws inserted in the diaphysis and metaphysis of adult equine third metacarpal (MCIII) bones, in threaded 4.5-mm cortical bone screw insertion holes that were then overdrilled with a 4.5-mm drill bit to provide information relevant to the selection of a replacement screw if a 4.5-mm cortical screw is stripped.


METHODS
In vitro pullout tests of 5.5-mm cortical and 6.5-mm cancellous screws in equine MCIII bones.


METHODS
Two independent cadaver studies each consisting of 14 adult equine MCIII bones.


METHODS
Two 4.5-mm cortical screws were placed either in the middiaphysis (study 1) or distal metaphysis (study 2) of MCIII bones. The holes were then overdrilled with a 4.5-mm drill bit and had either a 5.5-mm cortical or a 6.5-mm cancellous screw inserted; screw pullout tests were performed at a rate of 0.04 mm/second until screw or bone failure occurred.


RESULTS
In diaphyseal bone, the screws failed in all tests. Tensile breaking strength for 5.5-mm cortical screws (997.5 +/- 49.3 kg) and 6.5-mm cancellous screws (931.6 +/- 19.5 kg) was not significantly different. In metaphyseal bone, the bone failed in all tests. The holding power for 6.5-mm cancellous screws (39.1 +/- 4.9 kg/mm) was significantly greater than 5.5-mm cortical screws (23.5 +/- 3.5 kg/mm) in the metaphysis. There was no difference in the tensile breaking strength of screws in the diaphysis between proximal and distal screw holes; however, the holding power was significantly greater in the distal, compared with the proximal, metaphyseal holes.


CONCLUSIONS
Although tensile breaking strength was not different between 5.5-mm cortical and 6.5-mm cancellous screws in middiaphyseal cortical bone, holding power of 6.5-mm cancellous screws was greater than 5.5-mm cortical screws in metaphyseal bone of adult horses.


CONCLUSIONS
If a 4.5-mm cortical bone screw strips in MCIII diaphyseal bone of adult horses, either a 5.5-mm cortical or 6.5-mm cancellous screw, however, would have equivalent pullout strengths. A 6.5-mm cancellous screw, however, would provide greater holding power than a 5.5-mm cortical screw in metaphyseal bone.
Sedrish
S A
SA
Department of Veterinary Clinical Sciences, School of Veterinary Medicine, Louisiana State University, Baton Rouge, USA.
Moore
R M
RM
Kelly
K
K
Martin
G S
GS
Burba
D J
DJ
D000818:Animals; D001696:Biomechanical Phenomena; D001863:Bone Screws / Q000592:standards / Q000662:veterinary*; D002102:Cadaver; D018483:Diaphyses / Q000502:physiology / Q000601:surgery; D006736:Horses / Q000601:surgery*; D008663:Metacarpus / Q000502:physiology / Q000601:surgery*; D011897:Random Allocation; D013718:Tensile Strength