Intramedullary screw fixation of Jones fractures

Background. Jones fractures of the fifth metatarsal can be stabilized using intramedullary screw fixation techniques. A range of screw diameters from 4.5 mm to 6.5 mm can be used, but the optimal screw for this procedure has yet to be defined. In clinical practice, we have observed that failure is m ore likely when smaller diameter screws are used. Methods: Experimental Jon es fractures were created in 23 pairs of human cadaver fifth metatarsals, w hich were fixed using either 5.0 mm or 6.5 mm screws. Fracture stiffness an d pull-out strengths were measured for either screw type and their relation ships with bone mineral density and medullary canal diameter were determine d. Results: There was no significant difference in the bending stiffness of fr actures stabilized with 5.0 mm and 6.5 mm screws; however, different mechan isms of failure were noted for either screw type. Poor thread purchase with in the medullary canal was noted with the 5.0 mm screws, while excellent pu rchase was noted with 6.5 mm screws. Pull-out strength testing revealed sig nificantly higher pullout strengths for the larger 6.5 mm screws. There was no significant difference in bone mineral density or medullary canal diame ter between right and left metatarsals. Conclusions: Fifth metatarsals can often accommodate a 6.5 mm screw for the stabilization of Jones fractures. Larger diameter screws did not result in greater fracture stiffness in our model, but did result in significantly g reater pull-out strengths. Clinical Relevance: Larger diameter screws may be more appropriate for intr amedullary screw fixation of Jones fractures.