Biomechanical comparison of tension band- and interfragmentary screw fixation with a new implant in transverse patella fractures.
OBJECTIVE
The aim of the present study was to compare the primary fixation stability and initial fixation stiffness of two established fixation techniques, the tension band wiring technique and interfragmentary screw fixation, with a mini-screw fragment fixation system in a model of transverse patella fracture. It was hypothesised that the biomechanical loading performance of the fragment fixation system would not significantly differ from the loading characteristics of the two established methods currently investigated.


METHODS
Ninety-six calf patellae were used in this biomechanical model. A standardized transverse patella fracture was induced and three different fixation methods, including the modified tension band wiring technique, interfragmentary screw fixation, and the mini-screw fragment fixation system, were used for fragment fixation. Specimens were mounted to a loading rig which was secured within a material testing machine. In each fixation group, eight specimens were loaded to failure at a simulated knee angle of either 0 degrees or 45 degrees . Another eight specimens were submitted to a polycyclic loading protocol consisting of 30 cycles between 20N and 300N at a simulated knee angle of 0 degrees or 45 degrees . The residual displacement between the first and the last cycle was recorded. Differences in the biomechanical performance between the three fixation groups were evaluated.


RESULTS
No significant differences between the three fixation groups were observed in the parameters maximum load to failure and linear fixation stiffness with monocyclic loading. Specimens being loaded at 45 degrees showed significantly lower maximum failure loads and linear stiffness when compared with 0 degrees . During polycyclic loading, no significant differences in the residual displacement were observed between the groups at 0 degrees loading angle, while at 45 degrees , residual displacement was significantly higher with tension band fixation when compared with interfragmentary screw fixation or the fragment fixation system.


CONCLUSIONS
The biomechanical performance of the fragment fixation system was comparable to interfragmentary screw fixation and superior to the tension band wiring technique. Given the advantages of a system which provides interfragmentary compression and which simplifies fracture fixation after open or closed reduction, we believe the fragment fixation system to be an adequate alternative in the osteosynthesis of transverse patella fractures.
Dargel
J
J
St.-Vinzenz Hospital, Department of Trauma, Orthopaedics, Hand- and Reconstructive Surgery, Teaching Hospital, University of Cologne, Merheimer Strasse 221-223, D-50733 Cologne, Germany. dargel@dshs-koeln.de
Gick
S
S
Mader
K
K
Koebke
J
J
Pennig
D
D
D000368:Aged; D000818:Animals; D001696:Biomechanical Phenomena; D015519:Bone Density / Q000502:physiology; D001863:Bone Screws; D001864:Bone Wires; D002417:Cattle; D005260:Female; D005593:Fracture Fixation, Internal / Q000295:instrumentation* / Q000379:methods; D050723:Fractures, Bone / Q000601:surgery*; D006801:Humans; D008422:Materials Testing / Q000379:methods; D023421:Models, Animal; D010329:Patella / Q000293:injuries* / Q000601:surgery; D013314:Stress, Mechanical; D013718:Tensile Strength