[Shaft lengthening in hip replacement: experimental studies on bending stiffness]

Cortical atrophy of the proximal femur can be seen after wearing a total hip prosthesis for several years because loads are borne distally at the prosthesis tip. To achieve stable prosthesis implantation on the one hand and proximal bone regeneration on the other hand in hip revision arthroplasty, lengthening of the shaft component distributes loading forces to the femoral shaft first. It concentrates them to the proximal femur later through a higher elasticity.

In a three-point bending study the bending stiffness of an elastic slotted hip prosthesis shaft lengthening (HSL) was compared with that of the Synthes universal femoral nail (MN) and the unslotted HSL.

The slotting of the elastic HSL has a significant influence on its bending stiffness; it lies 1,287 N/mm (76%) over that of the MN, but 1,855 N/mm (38%) under that of the unslotted HSL. Altogether the slotted HSL is rather more comparable to the MN than to the unslotted HSL regarding its bending conduct.

The results confirm the elasticity of the slotted HSL in the style of conventional intramedullary nailing and encourage-above all in the context of previous clinical studies-its further use.