  The trace of $n$-framed surgery on a knot in $S^3$ is a 4-manifold homotopy
equivalent to the 2-sphere. We characterise when a generator of the second
homotopy group of such a manifold can be realised by a locally flat embedded
2-sphere whose complement has abelian fundamental group. Our characterisation
is in terms of classical and computable 3-dimensional knot invariants. For each
$n$, this provides conditions that imply a knot is topologically $n$-shake
slice, directly analogous to the result of Freedman and Quinn that a knot with
trivial Alexander polynomial is topologically slice.
