Tibial plateau fracture repairs augmented with calcium phosphate cement have higher in situ fatigue strength than those with autograft.
OBJECTIVE
This study compared the biomechanical fatigue strength of calcium phosphate augmented repairs versus autogenous bone graft (ABG) repairs in lateral tibia plateau fractures.


METHODS
Eight matched pairs of tibias (six male, two female; age, 75 ± 14 years) were harvested from fresh-frozen cadavers. Reproducible split-depression fractures were simulated and repaired by an orthopaedic traumatologist using a lateral tibial plateau plate. One tibia from each donor was randomly assigned to either calcium phosphate (Callos; Acumed, Hillsboro, OR) or ABG as augmentation. The femoral component of a hemitotal knee arthroplasty was attached to the actuator of a servohydraulic press and centered above the repair site. Cyclic, physiological compression loads were applied at 4Hz starting with a maximum load of 15% body weight and increasing by 15% body weight every 70,000 cycles. Loading conditions were determined from calculations of weight distribution, joint contact area, and gait characterization from existing literature. Repair site depression and stiffness were measured at regular intervals. Specimens were then loaded to failure at 1 mm/min.


RESULTS
Calcium phosphate augmented repairs subsided less and were more stiff during the fatigue loading than were ABG repairs at the 70,000, 140,000, and 210,000 cycle intervals (P < 0.03) All repairs survived to 210,000 cycles. The average ultimate load of the calcium phosphate repairs was 2241 ± 455 N (N = 6) and 1717 ± 508 N (N = 8) for ABG repairs (P = 0.02).


CONCLUSIONS
Calcium phosphate repairs have significantly higher fatigue strength and ultimate load than ABG repairs and may increase the immediate weightbearing capabilities of the repaired knee.
Biomechanical Testing Facility, San Francisco General Hospital, SFGH/UCSF Orthopaedic Trauma Institute, University of California at San Francisco, San Francisco, CA, USA.
Erik
E
McDonald
Thomas
T
Chu
Michael
M
Tufaga
Meir
M
Marmor
Ravinder
R
Singh
Duran
D
Yetkinler
Amir
A
Matityahu
Jenni M
JM
Buckley
R Trigg
RT
McClellan
D000368:Aged; D001843:Bone Cements / Q000627:therapeutic use*; D002130:Calcium Phosphates / Q000627:therapeutic use*; D019245:Compressive Strength; D005260:Female; D006801:Humans; D008297:Male; D008422:Materials Testing; D013977:Tibia / Q000187:drug effects / Q000503:physiopathology* / Q000601:surgery*; D013978:Tibial Fractures / Q000503:physiopathology* / Q000628:therapy*
D001843:Bone Cements; D002130:Calcium Phosphates; C020243:calcium phosphate