Screw Length Associated With Fracture Gapping of Fifth Metatarsal Base Fracture With Intramedullary Screw Fixation: A Cadaveric Study.

Intramedullary screw fixation is a well-established surgical treatment for fifth metatarsal Jones fractures, due to its minimally invasive nature, and potential early return to activity. Due to the curvature of the fifth metatarsal, optimal length of the screw is needed to prevent gapping at the fracture site. The placement of a straight screw induces straightening of a naturally curved bone. The purpose of this study was to aid surgeons in determining an appropriate screw length for intramedullary fixation of a fifth metatarsal Jones fracture in order to prevent fracture gapping. A transverse osteotomy of the fifth metatarsal was made in 10 cadaver specimens at the level of a traditional Jones fracture. Inserted screws were sequentially increased in length until plantar gapping at the fracture site was noted. The angle (degree) of plantar gapping was measured with each increase in screw length and diameter. The mean length of the cadaveric fifth metatarsals was 73.76 mm (range 67.42-81.73). The mean screw length that caused gapping at the fracture site was 49.89 mm (range 44-55), representing 67.05% (range 61.26-75.35) of the fifth metatarsal length. The correlation coefficient revealed that gapping of the fracture site is most likely to occur when the screw length is 66% the length of the metatarsal length (r = 0.66; 95% confidence interval: 0.06-0.91; p = .04). The angle of the initial gapping was 2.85° (range 2°-4°). With an incremental increase in screw length, the angle was 3.85° (range 3°-6°), and with an incremental increase in screw diameter, the angle was 3.70° (range 2°-5°). Our study demonstrated that screw lengths exceeding 66% of the metatarsal length lead to plantar fracture gapping. Additionally, gapping was accentuated with larger diameter screws due to angle variance.