Biomechanical comparison of different pin configurations during percutaneous pinning for the treatment of proximal humeral fractures

We investigate the influence on fracture stability of different pin configurations during percutaneous pinning for the treatment of proximal humeral fractures. We performed a matched-paired study of 18 pairs of adult fresh-frozen humeri (36 humeri), which were divided into 4 groups. A 2-part surgical neck fracture model was used in all humeri, and 4 terminal threaded pins (2.5 mm in diameter) were used for fixation. Parallel-type pinning (box type) was carried out in 2 groups, and convergent-type pinning (fan-shaped type) was used in the other 2 groups. For each specimen, both anti-shear ultimate load and anti-torsion ultimate load were measured. There was no statistical difference between the parallel pin construct and convergent construct with regard to anti-shear resistance (P = .73). However, the parallel pin construct had a significant advantage over the convergent construct regarding anti-torsion resistance. The parallel pin construct has better torsional stability when 1 cm is used for the pin-to-pin distance. We suggest that parallel pin fixation should be applied whenever possible.