Differential ($p,2p$) cross sections to various final states have been measured for eight different nuclei in the Ni region at an incident energy of 17 MeV, for the case of protons emerging at an angle of \ifmmode\pm\else\textpm\fi{}90\ifmmode^\circ\else\textdegree\fi{}. The coincident proton energy spectrum shows that the ($p,2p$) reaction consists of a ($p,{p}^{\ensuremath{'}}$) reaction followed by the boiloff of a proton. An attempt has been made to explain the observed cross sections by assuming that the ($p,{p}^{\ensuremath{'}}$) reaction is a compound process and that the subsequent proton boiloff is given by statistical theory. In this model, the relative probability for populating various final states depends on the spin cutoff parameter of the decaying compound nucleus, as well as the total radiation width. It is found that it is also necessary to take into account that the proton widths obey a Porter-Thomas distribution in order to reproduce the observed proton-$\ensuremath{\gamma}$ competition near threshold. The measured total radiation width, using typical values of the spin cutoff parameter, is approximately a factor of 5 below the average values obtained from neutron-capture work and a factor of 2 below the value obtained from an extrapolation of the giant dipole resonance. A direct study of the spin cutoff parameter was possible only for ${\mathrm{Fe}}^{54}$. For the other even-even nuclei, the excited states are weak or obscured by contaminants, while for the odd-even targets, the ($p,{p}^{\ensuremath{'}}$) spectrum indicates that a significant portion of the ($p,{p}^{\ensuremath{'}}$) reaction is due to a direct process. The ${\mathrm{Fe}}^{54}$ cross sections are best fit by increasing the value of the spin cutoff parameter to a value above that obtained by assuming a rigid-body value for the moment of inertia.