Mechanical strength of fracture callus in osteopenic bone at different phases of healing.
OBJECTIVE
To quantify and compare peak bending force and stiffness of fractured femurs during healing of ovariectomized (OVX) and sham-operated (SHAM) rats.


METHODS
Temporal biomechanical animal study.


METHODS
Rat femurs were fractured and surgically fixed by a qualified surgeon. The inherent instability of the fixation system employed produced delayed union of the fracture. All biomechanical assessments were performed with servohydraulic test machines (Instron Inc., Canton, MA, U.S.A.; and MTS Corp., Eden Prairie, MN, U.S.A.).


METHODS
OVX was performed sixteen weeks before femur fracture, and the effect of OVX on healing fractures was determined.


RESULTS
Peak bending force and stiffness of the healing femurs at four, six, and eight weeks after fracture.


RESULTS
Peak bending loads of the healing fractured femurs in the OVX and SHAM animals were not significantly different. Peak bending loads for the OVX animals at four and six weeks were significantly lower than the peak load at eight weeks (p < 0.05), whereas no difference was found in the peak load with respect to time for the SHAM animals. Both SHAM and OVX animals had greater bending stiffness of the healing fractured femur after eight weeks of healing than at four weeks (p < 0.05).


CONCLUSIONS
OVX is known to reduce cancellous bone mass and strength, but the effect of OVX on healing of fractures in cortical bone is controversial. This study, using a delayed-union model, found no significant differences between OVX and SHAM animals in the breaking strength of healing fractures.
Wheeler
D L
DL
Department of Orthopaedics, University of Florida, Gainesville 32610, USA.
Eschbach
E J
EJ
Montfort
M J
MJ
Maheshwari
P
P
McLoughlin
S W
SW
D000818:Animals; D001696:Biomechanical Phenomena; D001851:Bone Diseases, Metabolic / Q000503:physiopathology*; D002146:Bony Callus / Q000503:physiopathology*; D005260:Female; D017102:Fracture Healing; D051381:Rats; D017207:Rats, Sprague-Dawley; D013997:Time Factors