Jones fracture fixation: a biomechanical comparison of partially threaded screws versus tapered variable pitch screws.
BACKGROUND
Stabilization of fifth metatarsal Jones fractures with intramedullary screw fixation is the most common method for surgical fixation when operative treatment is indicated. Conventional partially threaded screws of various diameters are routinely used for Jones fracture fixation. Recently, the use of tapered variable pitch screws has become popular, but information regarding their performance in Jones fracture fixation is limited. No previous studies have compared conventional and tapered variable pitch screws in Jones fracture fixation under physiologic cyclic loading conditions.


OBJECTIVE
To determine whether biomechanical differences exist between appropriately sized conventional partially threaded screws and tapered variable pitch screws under physiologic cyclic loading conditions with regard to Jones fracture fixation.


METHODS
Controlled laboratory study.


METHODS
Simulated Jones fractures were created in 23 matched pairs of fresh-frozen fifth metatarsals. One bone from each pair was stabilized with a conventional partially threaded screw and the contralateral bone with a tapered variable pitch screw. Initial compression, as well as fracture site compression, angulation, and bending stiffness, was compared between groups throughout 1000 physiologic cyclic loads.


RESULTS
Conventional partially threaded screws obtained significantly greater initial compression compared with tapered variable pitch screws. Significantly greater compression was maintained throughout cyclic loading with conventional screw fixation compared with tapered variable pitch screws. Fracture site angulation was significantly greater using tapered variable pitch screws from the tenth load cycle through completion of cyclic loading. Despite a trend toward increased fracture site bending stiffness when using conventional screws, no difference in fixation stiffness was demonstrable between the 2 screw types.


CONCLUSIONS
In this cadaveric Jones fracture fixation model, conventional partially threaded screws provided improved fracture site compression and decreased fracture site angulation but offered no advantage in improving fracture site stiffness compared with tapered variable pitch screws. These results provide empirical evidence to guide implant selection decision making for operative fixation of Jones fractures.


CONCLUSIONS
While the use of tapered variable pitch screws is a potential alternative for fixation of fifth metatarsal Jones fractures, conventional partially threaded screws may provide better biomechanical stability, the effect of which on fracture healing is unknown.
Department of Orthopaedic Surgery, Duke University Medical Center, Durham, North Carolina, USA. justin_orr77@msn.com
Justin D
JD
Orr
Richard R
RR
Glisson
James A
JA
Nunley
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001696:Biomechanical Phenomena; D001863:Bone Screws; D002102:Cadaver; D005260:Female; D005593:Fracture Fixation, Internal / Q000295:instrumentation* / Q000379:methods; D050723:Fractures, Bone / Q000601:surgery; D006801:Humans; D008297:Male; D008682:Metatarsal Bones / Q000293:injuries* / Q000601:surgery*; D008875:Middle Aged