Three different interlocking intramedullary nails for unstable reverse oblique inter-trochanteric fractures: a bio-mechanical comparative study
Keywords:Unstable intertrochanteric fractures, Reverse oblique fractures, Intramedullary nail, Sawbone model, Peak strain
Background: Biomechanical testing, intramedullary devices have proven advantageous over the extramedullary devices in the management of unstable intertrochanteric fractures. Reverse oblique type of intertrochanteric fractures are highly unstable and intramedullary nails are currently the method of internal fixation. The currently available nails seems to provide rotational, axial and angular stability, but biomechanical analysis of the strain pattern in the bone and implant in this fractures are lacking. The aim of this experimental study was to analyse the strain in three different long femoral nail-bone units under physiological loading when implanted in Saw bone model after creating a reverse oblique intertrochanteric fracture.
Methods: A total of 12 sawbones were divided in to 4 equal groups. Group 1 was intact saw bones and were used as controls. Group 2, Group 3 and Group 4 were implanted with Depuy, Stryker and Synthes nails respectively after creating a reverse oblique intertrochanteric fracture. All the four groups were axially loaded with 100 N increments until physiological loads. The strain patterns were measured at the posteromedial cortex and the peak strains were extracted at partial weight bearing i.e. 500 N and full weight bearing physiological loads i.e. 1000 N.
Results: There was no significant difference in peak strains among the groups at partial loads. However at 1000 N loads the peak strain in the DePuy nail-bone unit was significantly high compared to the other two nail-bone units and the controls.
Conclusions: These results question the safety of immediate full weight bearing following surgery when treating the reverse oblique unstable fractures with DePuy intramedullary nails. A period of partial weight bearing following fixation of reverse oblique fractures would be wise when using DePuy nails.
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