Two-Part Surgical Neck Fractures of the Proximal Part of the Humerus A Biomechanical Evaluation of Two Fixation Techniques.

SL Edwards,NA Wilson, L Zhang, S Flores, BR Merk JBJS(Am). 2006; 88:2258-2264.

Proximal humeral fracture is the second most common type of upper limb fracture with an incidence of 10% of patients over the age of 65 years. 15-20% of these fractures have substantial displacement (>1cm), angulation (>45 degree) rotation or involvement of tuberosity. Successful internal fixation of these fractures is difficult because of osteoporotic bone. Several techniques have been described to fix these fractures. The purpose of this study was to compare the biomechanical stability of a proximal humeral intramedullary nail and a locking plate used in the treatment of communited two part fracture of the surgical neck in human cadaver models.

24 cadaveric humeri were matched in bone mineral density and anthropometric measurements. They were fractured by excising 10mm wedge of bone simulating a comminuted fracture of the surgical neck. These specimens were fixed with either a titanium proximal humeral nail (PHN) or a 3.5mm locking compression plate (LCP-PH). These were separated into four groups with six humeri in each: PHN bending, LCP-PH bending, PHN torsion, or LCP-PH torsion. Bending group were cyclically loaded to a varus bending moment of 0 to 7.5 Nm and torsion group were cyclically loaded with an axial torque of +/-2 Nm.

The LCP-PH implant had a significantly stiffer bone-implant construct compared to the PHN implant. In bending, LCP-PH group had a significantly less mean displacement compared to PHN group. In torsion, LCP-PH group had a significantly less mean angular rotation compared to the PHN group.

LCP-PH has superior biomechanical characteristics compared with the PHN group in both varus bending and torsion in cadaveric specimens. The drawback of this study is that in vivo forces are complex to stimulate. Other clinical concerns such as operative time, soft tissue stripping and blood loss can lend to the choice of a PHN over the LCP-PH in spite of it being biomechanically inferior in osteoporotic bone.

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