Distal femoral fixation: a biomechanical comparison of trigen retrograde intramedullary (i.m.) nail, dynamic condylar screw (DCS), and locking compression plate (LCP) condylar plate.
BACKGROUND
The purpose of this study was to establish if there are biomechanical differences between implants in stiffness of construct, microdisplacement, and fatigue failure in a supracondylar femoral fracture model.


METHODS
A retrograde intramedullary (i.m.) nail, dynamic condylar screw (DCS), and locked condylar plate (LCP) were tested using 33-cm long synthetic femurs. A standardized supracondylar medial segmental defect was created in the distal femur bone models. A gap away from the distal joint axis and parallel to the knee axis was created for axial testing of the specimens (Arbeitsgemeinschaft fur Osteosynthesefragen [AO] type 33-A) and a T-fracture (33-C) was created for the fatigue testing of the specimens. Peak displacements were measured, and analysis was done to determine construct stiffness and gap micromotion in axial loading. Cyclic loading was performed for fatigue testing.


RESULTS
It was observed that there were statistically significant differences in micromotion across the fracture gap and overall stiffness of various implant constructs. The stiffness of the i.m. nail, DCS, and LCP were 1,106, 750, and 625 N/mm, respectively. The average total micromotion across the fracture gap for the i.m. nail, DCS, and LCP were 1.96, 10.55, and 17.74 mm, respectively. In fatigue testing, the i.m. nail distal screws failed at 9,000 cycles, the DCS did not fail (80,000 cycles completed), and the LCP failed at 19,000 and 23,500 cycles.


CONCLUSIONS
When considering micromotion and construct stiffness, the i.m. nail had statistically significant higher stiffness and significantly lower micromotion across the fracture gap with axial compression. Hence, the i.m. nail tested had the greatest stability for type 33-A fractures. However, the nail demonstrated the least amount of resistance to fatigue failure with type 33-C fractures, whereas the DCS did not fail with testing in any pattern.
Heiney
Jake P
JP
Department of Orthopaedic Surgery, Promedica Health System, Toledo, Ohio, USA. jake.heinymd@promedica.org
Barnett
Michael D
MD
Vrabec
Gregory A
GA
Schoenfeld
Andrew J
AJ
Baji
Avinash
A
Njus
Glen O
GO
D000704:Analysis of Variance; D001696:Biomechanical Phenomena; D001858:Bone Nails; D001860:Bone Plates; D001863:Bone Screws; D005264:Femoral Fractures / Q000503:physiopathology / Q000601:surgery*; D005594:Fracture Fixation, Intramedullary / Q000295:instrumentation* / Q000379:methods*; D008422:Materials Testing; D011474:Prosthesis Design; D011475:Prosthesis Failure; D012044:Regression Analysis; D013193:Stainless Steel; D013314:Stress, Mechanical; D014025:Titanium
D013193:Stainless Steel; D014025:Titanium