A system for registration of a bone structure, comprising: a registration probe (108; 200) having a two-dimensional array of a plurality of ultrasonic transducers (110; 204; 302; 402) coupled to a rounded tip (202; 300; 400) of the probe (108; 200), wherein the ultrasonic transducers (110; 204; 302; 402) are configured to provide ultrasonic data; and a processing circuit configured to: receive ultrasonic data from the plurality of ultrasonic transducers (110; 204; 302; 402); determine which of the ultrasonic transducers (110; 204; 302; 402) are in contact with anatomy (304; 406) of a patient; register the anatomy (304; 406) of the patient to a model of bone using registration points; the system being characterised in that the processing circuit is further configured to: select a subset of the ultrasonic transducers (110; 204; 302; 402) based on the determination of which of the ultrasonic transducers (110; 204, 302, 402) are in contact with anatomy (304; 406) of the patient, the ultrasonic transducers of the subset being the ultrasonic transducers that are in contact with anatomy of the patient; generate the registration points based on the ultrasonic data of the selected subset of ultrasonic transducers (110; 204; 302; 402). a registration probe (108; 200) having a two-dimensional array of a plurality of ultrasonic transducers (110; 204; 302; 402) coupled to a rounded tip (202; 300; 400) of the probe (108; 200), wherein the ultrasonic transducers (110; 204; 302; 402) are configured to provide ultrasonic data; and a processing circuit configured to: receive ultrasonic data from the plurality of ultrasonic transducers (110; 204; 302; 402); determine which of the ultrasonic transducers (110; 204; 302; 402) are in contact with anatomy (304; 406) of a patient; register the anatomy (304; 406) of the patient to a model of bone using registration points; the system being characterised in that the processing circuit is further configured to: select a subset of the ultrasonic transducers (110; 204; 302; 402) based on the determination of which of the ultrasonic transducers (110; 204, 302, 402) are in contact with anatomy (304; 406) of the patient, the ultrasonic transducers of the subset being the ultrasonic transducers that are in contact with anatomy of the patient; generate the registration points based on the ultrasonic data of the selected subset of ultrasonic transducers (110; 204; 302; 402). receive ultrasonic data from the plurality of ultrasonic transducers (110; 204; 302; 402); determine which of the ultrasonic transducers (110; 204; 302; 402) are in contact with anatomy (304; 406) of a patient; register the anatomy (304; 406) of the patient to a model of bone using registration points; the system being characterised in that the processing circuit is further configured to: select a subset of the ultrasonic transducers (110; 204; 302; 402) based on the determination of which of the ultrasonic transducers (110; 204, 302, 402) are in contact with anatomy (304; 406) of the patient, the ultrasonic transducers of the subset being the ultrasonic transducers that are in contact with anatomy of the patient; generate the registration points based on the ultrasonic data of the selected subset of ultrasonic transducers (110; 204; 302; 402). select a subset of the ultrasonic transducers (110; 204; 302; 402) based on the determination of which of the ultrasonic transducers (110; 204, 302, 402) are in contact with anatomy (304; 406) of the patient, the ultrasonic transducers of the subset being the ultrasonic transducers that are in contact with anatomy of the patient; generate the registration points based on the ultrasonic data of the selected subset of ultrasonic transducers (110; 204; 302; 402).