Apparatus is provided for treating a native joint of a subject. The apparatus comprises a flexible cuff shaped and sized to be worn, at least in part, around the native joint of the subject. A magnet is coupled to the flexible cuff such that when the flexible cuff is worn by the subject, the magnet is positioned within 8 cm, e.g., within 6 cm, from a joint cavity of the native joint. The apparatus additionally comprises a ferrofluid for placing in the joint cavity. The ferrofluid is typically maintained in place within the joint cavity by the magnet which is coupled to the cuff. Other applications are also described.
