Closed reduction of forearm refractures with flexible intramedullary nails in situ.
BACKGROUND
Refractures of the forearm after flexible intramedullary nailing are rare. An alternative to nail replacement is closed reduction with the nails in situ. We successfully performed this maneuver on a thirteen-year-old boy. However, no data on the stability of previously bent nails are available. The purpose of the present study was to assess the mechanical stability of titanium and stainless steel flexible intramedullary nails after one cycle of reversed bending.


METHODS
In an in vitro study, ten titanium and eighteen stainless steel 3.0-mm flexible intramedullary nails were subjected to an increasing lateral bending force until the point of first plastic deformation. As an analogy to the clinical case, they were then bent to an angle of 21 degrees and were manually reduced back to their original straight position and the experiment was repeated. The forces needed to achieve first plastic deformation and modified spring constants (force/deflection) were calculated and were compared between the native and previously bent nails.


RESULTS
The average force required for permanent deformation of the previously bent nails was reduced by 37% for both titanium and stainless steel nails (from 21 to 13.2 N for titanium nails [p < 0.01] and from 25 to 15.7 N for stainless steel nails [p < 0.001]). The average modified spring constant decreased by 15.1% (from 0.814 to 0.691 N/ degrees ) for titanium nails (p < 0.001) and by 12.2% (from 0.991 to 0.870 N/ degrees ) for stainless steel nails (p < 0.001). Overall, steel nails were stiffer and stronger than titanium nails were. There was no macroscopic evidence of metal fracture or fatigue after one cycle of reversed bending to 21 degrees.


CONCLUSIONS
Closed reduction of a forearm refracture with flexible intramedullary nails in situ is a safe, noninvasive, and effective alternative to nail replacement. However, mechanical stability of the nails is significantly reduced after the procedure. Therefore, the patient should be instructed to avoid any excessive forces to the forearm until fracture union has been documented radiographically, and casting for a limited time may be appropriate.
Muensterer
Oliver J
OJ
Department of Pediatric Surgery, University of Munich, Dr. von Hauner Children's Hospital, Germany. oliver.muensterer@helios.med.unimuenchen.de
Regauer
Markus P
MP
D000293:Adolescent; D001858:Bone Nails; D002370:Casts, Surgical; D005543:Forearm Injuries / Q000628:therapy*; D005594:Fracture Fixation, Intramedullary / Q000295:instrumentation*; D050723:Fractures, Bone / Q000628:therapy*; D006801:Humans; D008297:Male; D008349:Manipulation, Orthopedic / Q000379:methods*; D019563:Mechanics; D012008:Recurrence; D016896:Treatment Outcome