BRIDGING OF DIAPHYSEAL BONE DEFECTS WITH A MODULAR INTERMEDULARY SPACER SYSTEM

Abstract

Introduction: Improved treatment of primary tumors leads to an increased life expectancy and thus to an increasing number of patients with bone metastases. Techniques like auto- or allogenic bone grafts, vascularised bone transfer and distraction osteogenesis often require multistage surgical procedures and inhibit full early limb function. Diaphyseal replacement using nails, plates and bone cement do not guarantee long term bone stability. Due to this experiences a new diaphyseal replacement device for humerus, femur and tibia has been developed.

Materials and Methods: The diaphyseal replacement implant OSTEOBRIDGE^™ consists of two semi-circular cylindrical shells. The spacer is clamped around two nails via eight screws. Different sizes of spacers and nails can be used to bridge the bone loss correctly.

The outer diameter of the spacer ranges from 20–25–30 mm and the length from 40 to 70 mm. Two or three spacers can be combined via a special connector. Nails in the length 60 to 200 mm and the Ø 7 to 18 mm with the possibility of static or dynamic interlocking complete the modular system entirely made from Ti-6Al-4V.

Biomechanical Testing: Static compression tests to determine the maximum longitudinal forces of the clamp connection spacer/nail were performed, 4-point bending tests with the complete system to investigate the fatigue resistance were undertaken and torsional test to evaluate the rotational stability.

Prospectiv clinical evaluation: In between 2004 and 2006 35 patients were treated with the OSTEO-BRIDGE^™ system.

The indication: Tumor: Humerus 8, Femur 16, Tibia 2, Postinfectious: Tibia 4, Posttramatic Femur 4, Tibia 2.

Results:

• Biomechanical testing: the clamp connection spacer/ nail can neutralize axial loads which can not be expected in human beings. The clamp connection spacer/nail Ø 10 mm resisted an average axial load of 8,5 kN. This can be compared to a force of 850 kN (equivalent to 10 multiples of 85 kg body weight). The bending test with a nail Ø 10 mm shows that the spacer can resist long term loads from an occurring stress of 400 N/mm² in the nail.

• Clinical evaluation: All spacers are still in place and all are full functioning, except 2; one spacer in the femur had to be replaced by a second spacer due to bone cement incorporated during first operation.

One spacer was removed during amputation for recurrency of osteosarcoma. No infection, no loosing were reported.

Discussion: The OSTEOBRIDGE^™ spacer system allows to replace lost daiphyseal bone over long distances with proved biomechanical stability. An advantage seems to be the early bony bridging over the spacer within the first 9 months. There might be another advantage in using the spacer as a container for antitumor, bactericidal or bone growth stimulating drugs.