OBJECTIVETo investigate the influence on fracture stability by different pin construct during percutaneous pinning for the treatment of proximal humerus fractures.

METHODSEighteen pairs (36) adult fresh-frozen humeri were match-paired and divided into 4 groups. Dual-energy bone density scan had been used in order to rule out the influence by different degrees of osteoporosis of the cadaver. Two-part surgical neck fracture model was carried out unanimously in all 36 humeri. Four terminal threaded pins (2.5 mm in diameter) were used in fixation for all specimen. Parallel type pinning (box type) were carried out in 2 groups and convergent type pinning (fan shape) in the other 2 groups. Instron5566 biomechanical tester was applied in determining both anti-shear and anti-torsion ultimate load of each specimen.

RESULTSThere was no statistical difference between parallel pin construct and convergent construct in regard of anti-shear resistance (P = 0.73). But by mean of anti-torsion resistance, the parallel construct had significant advantage over the convergent construct (P = 0.04).

CONCLUSIONAccording to our biomechanical data, parallel pin construct seems to have better torsional stability. We suggest that parallel pin fixation should be applied whenever possible. Convergent pin construct should be considered when parallel construct is not possible or the distance between pins are too small (< 1 cm).