Determining the offset of the head part of an orthopaedic joint prosthesis stem component

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.

1 - 18 . (canceled) 
     
     
         19 . A template kit for use in 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 for an implantation procedure involving a patient's joint, comprising:
 a first template part having markings thereon that represent the axis of the head of the patient's bone,   
       a second template part having markings thereon that represent the axis of the neck of the patient's bone, 
       a scale that is provided on at least one of the first and second template parts for use when measuring the distance between the axis of the head part and the axis of the neck of the patient's bone,
 a source of reference data that can provide, based on two such measured distances, the r,θ coordinates of the axis of the head part relative to the axis of the neck of the stem part, where r is the absolute distance between the axis of the head part and the axis of the neck of the stem part, and θ is a measure of the angular location of the axis of the head part around the axis of the neck of the stem part. 
 
     
     
         20 . The kit of  claim 19 , wherein at least one of the first template part and the second template part includes a representation of the cup component of the joint prosthesis with which the head part of the stem component articulates. 
     
     
         21 . The kit of  claim 19 , wherein the reference data are provided in a printed chart. 
     
     
         22 . A method of assembling a joint prosthesis component, which comprises:
 obtaining a first image of the patient's joint on a first plane,   fitting a template part to the first image of the bone, wherein the template part has markings thereon that can be placed relative to the head part and the stem part respectively of the patient's bone, and a scale thereon for use when measuring the first displacement defined as the distance between the axis of the head part and the axis of the neck of the patient's bone measured in the first plane,   providing a head part of a joint prosthesis and a connector for connecting the head part to a stem part, wherein the head part has an eccentric recess therein for receiving the connector, and the connector has an eccentric connection feature for connection to the stem part, and   locating the connector in the recess in the head part, and aligning it to provide a desired offset with reference to the displacement measurement obtained in step (a).   
     
     
         23 . The method of  claim 22 , wherein the head part and the connector are parts of a trial prosthesis instrument. 
     
     
         24 . The method of  claim 22 , wherein the head part and the connector are parts of a prosthesis component implant.