A biomechanical investigation of the effects of static fixation and dynamization after interlocking femoral nailing: a finite element study.
BACKGROUND
Interlocking nail systems have been widely used to treat long bone fractures. The use of an interlocking nail system with a static fixation technique or a dynamic fixation technique was evaluated according to the outcomes of clinical applications. The biomechanical characteristics of dynamic fixation techniques are unclear, and the surgical rule, involving the removal of the locking screws farthest from the fracture site, is based mainly on surgeons' experiences. There has been no study that investigated the biomechanical characteristics of dynamic fixation techniques and the validity of this surgical rule.


METHODS
Three-dimensional nonlinear finite element models were developed. The conventional static fixation technique and two types of dynamic fixation techniques (removal of the proximal screw or removal of the distal screws) for the repair of two types of fractures (a proximal femoral fracture or a distal femoral fracture) are discussed.


RESULTS
The results show that the dynamic fixation techniques could significantly reduce the stress exerted by the interlocking nail system and produce a greater contact pressure at the fracture site as compared with that of the static fixation technique. The interlocking nail system with removal of the distal screws resulted in greater contact area than that with removal of the proximal screw for the proximal femoral fracture. Similarly, the interlocking nail system with removal of the proximal screw had larger contact area than that with removal of the distal screws for the distal femoral fracture.


CONCLUSIONS
The results of this study could help surgeons to understand the biomechanical characteristics of dynamic fixation techniques and provide evidence to support the use of a specific dynamic fixation technique.
Department of Orthopedic Surgery, Shin Kong Wu Ho-Su Memorial Hospital, College of Medicine, Fu Jen Catholic University, Taipei, Taiwan, Republic of China.
Kao-Shang
KS
Shih
Ching-Chi
CC
Hsu
Tzu-Pin
TP
Hsu
D001696:Biomechanical Phenomena; D001858:Bone Nails; D005264:Femoral Fractures / Q000503:physiopathology* / Q000601:surgery*; D020342:Finite Element Analysis; D005594:Fracture Fixation, Intramedullary / Q000295:instrumentation / Q000379:methods*; D006801:Humans; D013314:Stress, Mechanical