Interfragmentary movement in diaphyseal tibia fractures fixed with locked intramedullary nails.
OBJECTIVE
Biomechanical study on cadaveric bones using physiological loading conditions to quantify interfragmentary movements in a tibial shaft fracture model fixed by intramedullary nailing.


METHODS
Six fresh frozen human cadaveric tibiae were sequentially tested in axial, torsional, 4-point bending, and shear loading configurations. Tests were performed in intact specimens and osteotomized specimens equipped with interlocked intramedullary nails. The amount of clearance of the nail within the intramedullary canal was measured on computed tomography scans. Linear and angular deformations of the fragments were continuously measured in all directions to obtain the exact interfragmentary movements.


RESULTS
The amount of movement at the site of the fracture was substantial. Especially shear and torsion resulted in gap movements of up to 10 mm. Movements in the transverse plane were significantly larger than axial movements for all loading conditions. For torsion and bending, a significant portion of the movement of the fracture gap resulted from the flexibility of the intramedullary nail; for compression and shear, the majority of the movement was related to the clearance of the nail within the bone.


CONCLUSIONS
Clearance of the implant within the medullary canal, the flexibility of the implant itself, and the compliance of the implant (nail and locking screws) within the bone determine the extent of movement. The implant flexibility and the clearance are strongly dependent on the thickness of the intramedullary nail.
Augat
Peter
P
Biomechanics Research Laboratory, Paracelsus Medical University, Salzburg, Austria. biomechanik@bgu
Penzkofer
Rainer
R
Nolte
Alexander
A
Maier
Michael
M
Panzer
Stefanie
S
v Oldenburg
Geert
G
Pueschl
Klaus
K
Simon
Ulrich
U
Bühren
Volker
V
D000328:Adult; D001696:Biomechanical Phenomena; D001858:Bone Nails; D002102:Cadaver; D019245:Compressive Strength; D005594:Fracture Fixation, Intramedullary / Q000295:instrumentation* / Q000379:methods; D017102:Fracture Healing / Q000502:physiology*; D006801:Humans; D008297:Male; D008422:Materials Testing; D008875:Middle Aged; D009068:Movement / Q000502:physiology*; D010027:Osteotomy; D033081:Shear Strength; D013978:Tibial Fractures / Q000503:physiopathology / Q000601:surgery*; D054159:Torsion, Mechanical