| 摘要 |
A trocar assembly includes a low-profile retractable shield (14) deployed immediately adjacent to a cutting element (10) with a cross-sectional area which is small relative to the total cross-section of the assembly. In preferred examples, the total cross-sectional area protected by the shield element is less than about 0.4, and most preferably less than about 0.2, of the total cross-sectional area of the assembly. As a result, the shield extends itself as soon as the cutting element clears the tissue wall, prior to penetration of the remainder of the end portion of the assembly. Optionally, such a shield may be used in combination with a conventional, large-area shield to provide two-stage protection. Implementations of this principle, together with various locking mechanisms and additional features, are described in the context of various trocar configurations.
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