Measuring instrument for use in orthopaedic surgery

Abstract

A measuring instrument ( 2 ) for use during an orthopaedic surgical procedure to measure first and second distances from a reference point on a bone to first and second measurement points respectively. The measuring instrument has a first scale ( 24 ) for displaying the first distance and a second scale ( 28 ) for displaying the second distance. It includes a mask ( 26 ) which can be positioned against the second scale after the first distance has been measured in a position that is selected relative to the second scale dependent on the measured first distance, to restrict the length of the second scale that is visible to the user.

1 . A measuring instrument for use during an orthopaedic surgical procedure to measure first and second distances from a reference point on a bone to first and second measurement points respectively, the measuring instrument having a first scale for displaying the first distance and a second scale for displaying the second distance, the instrument including a mask which can be positioned against the second scale after the first distance has been measured in a position that is selected relative to the second scale dependent on the measured first distance, to restrict the length of the second scale that is visible to the user. 
     
     
         2 . The measuring instrument of  claim 1 , which includes a reference structure which can be located relative to reference point, and at least one measurement structure which can be moved relative to the reference structure to a position which correlates to one of the first and second measurement positions. 
     
     
         3 . The measuring instrument of  claim 2 , in which the measurement structure includes a plate member having a first face which is directed towards the reference structure and a second face which is directed away from the reference structure. 
     
     
         4 . The measuring instrument of  claim 2 , which includes (a) a first scale provided by a first scale portion on the reference structure and a second scale portion on the measurement structure, the first scale indicating the position of the measurement structure relative to the reference structure and so indicating the first distance, and (b) a second scale which is provided by a third scale portion on the measurement structure and the first scale portion, the second scale indicating the position of the measurement structure relative to the reference structure and so indicating the second distance. 
     
     
         5 . The measuring instrument of  claim 4 , in which the mask restricts the length of at least one of the first and third scale portions that is visible to the user. 
     
     
         6 . The measuring instrument of  claim 2 , which includes (a) a first measurement structure for measuring the first distance between the reference point and the first measurement point, the first measurement structure and the reference structure being capable of movement relative to one another, and (b) a second measurement structure for measuring the second distance between the reference point and a second measurement point, the second measurement structure and the reference structure being capable of movement relative to one another. 
     
     
         7 . The measuring instrument of  claim 6 , which includes a plate member which has a first face which is directed towards the reference structure and a second face which is directed away from the reference structure, the first face forming part of one of the first and second measurement structures and the second face forming part of the other of the first and second measurement structures. 
     
     
         8 . The measuring instrument of  claim 6 , in which the first measurement structure and the second measurement structure have components in common. 
     
     
         9 . The measuring instrument of  claim 2 , in which the reference structure includes a formation which can be positioned against the reference point to enable the reference structure to be located relative to the reference point. 
     
     
         10 . The measuring instrument of  claim 9 , which is for use in a knee replacement procedure to measure the size of a patient's femur, in which the formation comprises a stylus for contacting the anterior cortex of the femur to locate the reference structure relative to the anterior cortex. 
     
     
         11 . The measuring instrument of  claim 2 , in which the measurement structure includes a component for fixing the measurement structure against movement relative to the bone in at least one degree of freedom. 
     
     
         12 . The measuring instrument of  claim 11 , which includes an intramedullary rod, and in which the fixing component can be connected to the intramedullary rod. 
     
     
         13 . The measuring instrument of  claim 11 , in which the measurement structure includes (a) a formation for locating the measurement structure relative to the first measurement point or the second measurement point, and (b) a driver for moving the formation relative to the connector component. 
     
     
         14 . The measuring instrument of  claim 11 , in which the reference structure can be positioned on the measurement structure relative to the reference point while the measurement structure is connected against movement relative to the bone. 
     
     
         15 . The measuring instrument of  claim 1 , in which the mask can be fastened against the second scale in a plurality of different positions, each position corresponding to a different size of the first measured distance. 
     
     
         16 . The measuring instrument of  claim 1 , in which the mask is fastened against the second scale so that it can slide relative to the second scale to allow it to be placed in a selected position corresponding to the size of the first measured distance. 
     
     
         17 . A measuring instrument for use during an orthopaedic surgical procedure to measure first and second distances from a reference point on a bone to first and second measurement points respectively, which comprises:
 a. a reference structure which can be located relative to the reference point on the bone,   b. a first measurement structure for measuring the first distance between the reference point and the first measurement point, the first measurement structure and the reference structure being capable of movement relative to one another, and the instrument including a first scale provided by a first scale portion on the reference structure and a second scale portion on the first measurement structure, the first scale indicating the position of the first measurement structure relative to the reference structure and so indicating the first distance,   c. a second measurement structure for measuring the second distance between the reference point and a second measurement point, the second measurement structure and the reference structure being capable of movement relative to one another, the instrument including a second scale which is provided by a third scale portion on the second measurement structure and the first scale portion, the second scale indicating the position of the second measurement structure relative to the reference structure and so indicating the second distance,   d. a mask which can be located against the first scale portion in a position that is selected according to the size of the first measurement, the mask restricting the length of at least one of the first and third scale portions that is visible.   
     
     
         18 . The measuring instrument of  claim 17 , in which the first measurement structure and the second measurement structure have components in common. 
     
     
         19 . The measuring instrument of  claim 18 , which includes a plate member which has a first face which is directed towards the reference structure and a second face which is directed away from the reference structure, the first face forming part of one of the first and second measurement structures and the second face forming part of the other of the first and second measurement structures. 
     
     
         20 . The measuring instrument of  claim 18 , which includes a driver which can be operated to move the plate member between the first and second measurement points. 
     
     
         21 . The measuring instrument of  claim 20 , in which the driver includes a connector by which can be fixed in at least one degree of freedom against movement relative to the bone, and an adjuster controlling the distance between the connector and the plate member. 
     
     
         22 . The measuring instrument of  claim 17 , in which the second scale portion and the third scale portion are provided on a common component. 
     
     
         23 . The measuring instrument of  claim 17 , the instrument including a driver assembly associated with at least one of the first and second measurement structures, the driver assembly including a connector by which the driver assembly can be fixed in at least one degree of freedom against movement relative to the femur, and an adjuster for adjusting the position of the measurement structure relative to the connector. 
     
     
         24 . The measuring instrument of  claim 23  which is intended for measurement of the distal femur in a knee replacement procedure, which includes an intramedullary rod which can be fitted in the femoral intramedullary canal, in which the connector can be connected to the intramedullary rod. 
     
     
         25 . A kit for use in a surgical procedure to implant a knee joint prosthesis, which comprises:
 (a) a measuring instrument as claimed in  claim 1 , in which the mask includes at least one posterior cut reference surface, and   (b) a femoral component trial which includes an anteriorly facing bone contacting surface on a posterior condyle, in which the said bone contacting surface defines a posterior cut plane,   in which the posterior cut reference surface when the mask is positioned on the second scale of the instrument appropriately having regard to the measured first distance, lies in the posterior cut plane which is defined by the femoral component trial when the femoral component trial is positioned on the resected femur.   
     
     
         26 . A kit for use in a surgical procedure to implant a knee joint prosthesis, which comprises:
 (a) a measuring instrument as claimed in  claim 17 , in which the mask includes at least one posterior cut reference surface, and   (b) a femoral component trial which includes an anteriorly facing bone contacting surface on a posterior condyle, in which the said bone contacting surface defines a posterior cut plane,   in which the posterior cut reference surface when the mask is positioned on the second scale of the instrument appropriately having regard to the measured first distance, lies in the posterior cut plane which is defined by the femoral component trial when the femoral component trial is positioned on the resected femur.