Let $m,k$ be positive integers with $k\le m$. Does anyone know some hypergeometric identities that imply 
$$\sum_{j=0}^k\frac{(-1/2)_{k-j}(m+1)_j(-m)_j}{(1/2)_j(k-j)!j!}
=\frac{(-m-\frac{1}{2})_k(m+\frac{1}{2})_k}{(\frac{1}{2})_kk!}$$ 
where $a_k=a(a+1)\cdots (a+k-1)$ is the Pochhammer's symbol.