Biomechanical evaluation of Hackethal's intramedullary bundle pin fixation of humeral neck fractures.

Humeral neck fractures can be stabilized using a bundle of intramedullary pins as described by Hackethal. In order to decrease the risk of pin migration, packing of the medullary cavity with as many pins as possible is sometimes recommended, but others believe that stability can be decreased by destruction of cancellous bone in the humeral head by a large bundle of pins. A surgical neck fracture was created with a saw in 30 frozen cadaveric humeri. Bone quality was evaluated by radiography and densitometry. Fractures were stabilized using Hackethal's technique of retrograde intramedullary pinning with varying numbers of 2.5-mm diameter pins; increasing torsion or bending moments of force were then applied to the bones studied. Stability was found to improve with an increasing number of pins and with higher humeral head density. Based upon these findings, the use of a large number of pins is recommended to reduce the risk of pin migration. Up to eight pins, the risk of destruction of cancellous bone in the humeral head appears very low.