Determining the offset of the head part of an orthopaedic joint prosthesis stem component
AssigneeDepuy International Limited
InventorsJames Brooks, Andrew Burton
Life of this patent
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Abstract
A method of determining the offset of the head part of an orthopaedic joint prosthesis stem component, relative to the neck of the stem part on which the head part can be fitted, involves obtaining a first and second images of the patient's joint on a non-coincident first and second planes. Template parts are fitted to the first and second images of the bone, which have markings on them which can be placed relative to the head part and the stem part respectively of the patient's bone, and scales for measuring first and second displacements which are the distances between the axis of the head part and the axis of the neck of the patient's bone measured in the first and second planes.
Claims17
A method of determining the polar offset of a head of an orthopaedic joint prosthesis relative to a neck of a stem to which the head can be connected for an implantation procedure involving a patient's joint, the orthopaedic joint prosthesis comprising a connector for connecting the head to a stem, wherein the head has an eccentric recess sized to receive the connector, and the connector has an eccentric connection feature for connection to the stem, comprising the steps of:
- obtaining a first image of the patient's joint in a first plane;
- obtaining a second image of the patient's joint in a second plane, wherein the planes are non-coincident and wherein an angle between the first plane and the second plane is known;
- positioning a template having a scale and markings thereon to the first image of the bone relative to the head and the stem;
- measuring a first displacement offset defined as the distance between the axis of the head and the axis of the neck of the patient's bone measured in the first plane;
- positioning a template having a scale and markings thereon to the second image of the bone relative to the head and the stem;
- measuring a second displacement offset defined as the distance between the axis of the head and the axis of the neck of the patient's bone measured in the second plane, wherein one of the first displacement offset and the second displacement offset is greater than zero;
- and
- determining, by using the first displacement offset and the second displacement offset and reference data, the polar offset of the axis of the head relative to the axis of the neck of the stem in terms of polar coordinates r and θ, wherein r is a distance between the axis of the head and the axis of the neck of the stem, and θ is a measure of an angular location of the axis of the head around the axis of the neck of the stem.
Dependencies are inferred from the claim text.