On November 6, 2019, the Federal Trade Commission unanimously found that the consummated merger of two sellers of prosthetic knees violated United States antitrust law, ordering the purchaser to divest completely the acquired assets to an FTC-approved buyer. The case is notable because the transaction was not reportable under the Hart-Scott-Rodino (“HSR”) Act, but the FTC nevertheless reviewed the deal subsequent to closing and found it to be anticompetitive. The Commission’s decision serves as another reminder that the antitrust agencies have the authority to review transactions that are not subject to filing under the HSR Act and that the buyer can be subject to post-closing remedies including complete divestiture.