Fixation of humeral surgical neck fracture using contoured pins versus straight pins: a mechanical study

The conventional procedure for displaced fracture of the surgical neck of the humerus uses straight pins inserted from the lateral aspect towards the head of the humerus. The objective of this study was to compare the mechanical properties of fixation by contoured (curved) pins to those fixed with regular straight pins. A transverse osteotomy was made in 30 fresh-frozen sheep humeri in the proximal metaphyseal bone region, and pins were inserted using either three parallel straight pins or three contoured pins in different planes. The assemblies were subjected to bending or rotational stresses at the fracture site. Loads versus deformations were acquired during loading and rigidity was calculated. Results showed that in bending, fixation with straight pins was 31% more rigid compared to contoured pins (p < 0.001), and in torsion, fixation using contoured pins was 21% more rigid compared to straight pins (p < 0.001). A combination of the two fixation types should be considered.