RESUMO
OBJECTIVE: To determine whether cancellous bone at metaphysis plays a significant role in generation of holding power of the cancellous screw. DESIGN: Maximal holding power of the cancellous screw at distal metaphysis of the femur with and without cancellous bone inside was determined by applying a load to push out the screw. BACKGROUND: Generation of screw holding power from the cancellous bone can arise by a mechanism of compression of cancellous bone between screw threads when a screw is inserted by non-tapping technique. Metaphysis has intermediate amount of cancellous and cortical bone when compared with diaphysis and intercondyle of a long bone. METHODS: Eight pairs of fresh cadaveric femurs were used. One femur of a pair was removed of cancellous bone at the distal metaphysis; cancellous bone of the other was preserved. A full thread cancellous screw was inserted into the distal femoral metaphysis. An axial load was applied at the screw tip to push out the screw by using a universal testing machine. RESULT: Mean push-out force of the screw at distal femoral metaphysis without cancellous bone inside was 1824.76 N and stiffness was 746.76 N/mm. Mean push-out force of the screw at distal femoral metaphysis with preservation of cancellous bone was 2015.86 N and stiffiness was 853. 09 N/mm. The statistical analysis of both groups showed no significant differences. CONCLUSIONS: This study confirmed that cancellous bone at metaphysis plays no significant role in generation of holding power of the cancellous screw. RELEVANCE: Because metaphyseal cancellous bone plays no role in generation of screw holding power, only a well-inserted cancellous screw into bone cortices can achieve good screw holding power at metaphysis of a long bone.
