Determining a range of motion of an artificial knee joint

Abstract

A data processing method for determining a range of motion of an artificial knee joint which connects a femur and a tibia via a medial ligament and a lateral ligament, wherein at least the femur comprises an implant which forms a medial condyle and a lateral condyle, the method comprising the steps of: acquiring the maximum lengths of the lateral ligament and the medial ligament for a particular flexion angle of the knee joint; calculating a first virtual position between the femur and the tibia in which the lateral condyle of the femoral implant touches the tibia and the medial ligament is stretched to its maximum length; calculating a maximum valgus angle of the range of motion from the first virtual position; calculating a second virtual position between the femur and the tibia in which the medial condyle of the femoral implant touches the tibia and the lateral ligament is stretched to its maximum length; and calculating a maximum varus angle of the range of motion from the second virtual position.

1 - 18 . (canceled) 
     
     
         19 . A method for predicting post-operative range of motion, the method implemented by one or more medical navigation computing devices and comprising:
 determining for each of a plurality of flexion angles of a knee joint of a patient:
 a first relative position of a tibia and a femur of the patient, and a lateral ligament length of the knee joint based on the first relative position, when the knee joint is under varus stress; and 
 a second relative position of the tibia and the femur, and a medial ligament length of the knee joint based on the second relative position, when the knee joint is under valgus stress; 
   generating, for each of the flexion angles, a maximum varus angle and a maximum valgus angle for one or more of a femoral implant or a tibial implant based on the lateral and medial ligament lengths;   determining a range of motion envelope for the one or more of the femoral implant or the tibial implant from the maximum varus and valgus angles; and   outputting the range of motion envelope to facilitate implant selection for a subsequent arthroplasty to be performed on the patient.   
     
     
         20 . The method of  claim 19 , further comprising modifying the range of motion envelope based on a received parameter for the one or more of the femoral implant or the tibial implant, wherein the received parameter corresponds to a size or a position of the one or more of the femoral implant or the tibial implant. 
     
     
         21 . The method of  claim 19 , further comprising generating one or more transformation matrices representing one or more of the first or second relative positions between the tibia and the femur. 
     
     
         22 . The method of  claim 19 , further comprising defining a tibial cutting plane, wherein the medial and lateral ligament lengths are determined in relation to the tibial cutting plane. 
     
     
         23 . The method of  claim 22 , wherein the tibial cutting plane is a virtual tibial plane defined within a generated surface model of the tibia. 
     
     
         24 . The method of  claim 22 , wherein the tibial cutting plane is defined based on a cut to an upper end of the tibia and the lateral and medial ligament lengths are measured perpendicular to the tibial cutting plane. 
     
     
         25 . A non-transitory computer readable medium having stored thereon instructions for predicting post-operative range of motion comprising executable code that, when executed by one or more processors, causes the one or more processors to:
 obtain a first maximum length of a lateral ligament and a second maximum length of a medial ligament for a flexion angle of an artificial knee joint, wherein the artificial knee joint connects a femur and a tibia via the lateral and medial ligaments and at least the femur comprises an implant which comprises a medial condyle and a lateral condyle;   determine a first maximum valgus angle from a first virtual position between the femur and the tibia in which the lateral condyle is disposed proximate the tibia and the medial ligament is stretched to the second maximum length;   determine a first maximum varus angle from a second virtual position between the femur and the tibia in which the medial condyle is disposed proximate the tibia and the lateral ligament is stretched to the first maximum length; and   output a range of motion of the artificial knee joint generated based on the first maximum valgus and varus angles to facilitate implant selection for a subsequent arthroplasty.   
     
     
         26 . The non-transitory computer readable medium of  claim 25 , wherein the executable code, when executed by the one or more processors, further causes the one or more processors to:
 obtain the first and second maximum lengths for each of a plurality of flexion angles of the artificial knee joint;   determine a second maximum valgus angle from each of a plurality of third virtual positions between the femur and the tibia in which the lateral condyle is disposed proximate the tibia and the medial ligament is stretched to one of the second maximum lengths;   determine a second maximum varus angle from each of a plurality of fourth virtual positions between the femur and the tibia in which the medial condyle is disposed proximate the tibia and the lateral ligament is stretched to one of the first maximum lengths; and   generate and output a range of motion envelope for the artificial knee joint based on the second maximum valgus and varus angles.   
     
     
         27 . The non-transitory computer readable medium of  claim 25 , wherein the executable code, when executed by the one or more processors, further causes the one or more processors to determine when the lateral or medial condyle is disposed proximate the tibia based on whether the lateral or medial condyle is in contact with the tibia. 
     
     
         28 . The non-transitory computer readable medium of  claim 25 , wherein the executable code, when executed by the one or more processors, further causes the one or more processors to determine the first or second maximum length based on a distance between a point on the femur at which the lateral or medial ligament, respectively, connects and a plane defined with respect to the tibia. 
     
     
         29 . The non-transitory computer readable medium of  claim 25 , wherein the executable code, when executed by the one or more processors, further causes the one or more processors to, in order to determine the first or second virtual position:
 determine a contact position in which the lateral or medial condyle contacts the tibia; and   rotate the femur about a point between the lateral or medial condyle and the tibia until an opposing one of the lateral or medial ligaments is stretched to the first or second maximum length, respectively.   
     
     
         30 . The non-transitory computer readable medium of  claim 29 , wherein the executable code, when executed by the one or more processors, further causes the one or more processors to rotate the femur when an axis of rotation is parallel to a plane defined with respect to the tibia. 
     
     
         31 . The non-transitory computer readable medium of  claim 25 , wherein the executable code, when executed by the one or more processors, further causes the one or more processors to determine the first maximum valgus and varus angles using a surface model of the femur in which the lateral or medial condyle is modelled as one or more ellipses. 
     
     
         32 . The non-transitory computer readable medium of  claim 25 , wherein the executable code, when executed by the one or more processors, further causes the one or more processors to generate the first or second maximum length from one or more transformation matrices that represent one or more relative positions between the femur and the tibia. 
     
     
         33 . A medical navigation computing device, comprising:
 a display device;   a non-transitory computer-readable data storage medium comprising program instructions stored thereon; and   one or more processors coupled to the non-transitory computer-readable data storage medium and configured to execute the stored program instructions to:
 determine, for each of a plurality of flexion angles, a first maximum length of a lateral ligament of a patient and a second maximum length of a medial ligament of the patient in relation to a plane defined with respect to the tibia and based upon a transformation matrix that represents a relative position between a femur and a tibia of the patient; 
 generate a maximum varus angle and a maximum valgus angle for a femoral implant or a tibial implant based on the first and second maximum lengths; and 
 generate, and output to the display device, a range of motion envelope comprising the maximum varus and valgus angles at one or more of the flexion angles for the femoral or tibial implant to facilitate implant selection for a subsequent arthroplasty. 
   
     
     
         34 . The medical navigation device of  claim 33 , wherein the one or more processors are further configured to execute the stored program instructions to determine the maximum valgus and varus angles using a surface model of the femur in which a representation of a lateral or medial condyle is based on a shape of the femoral implant. 
     
     
         35 . The medical navigation device of  claim 33 , wherein the one or more processors are further configured to execute the stored program instructions to generate a tibial plane based on a determined location of one or more markers attached to each of the femur and tibia, wherein the first and second maximum lengths are determined in relation to the tibial plane. 
     
     
         36 . The medical navigation device of  claim 35 , wherein the one or more processors are further configured to execute the stored program instructions to determine the first and second maximum lengths perpendicular to the tibial plane. 
     
     
         37 . The medical navigation device of  claim 33 , wherein the one or more processors are further configured to execute the stored program instructions to output to the display device an indication of a range of motion over the flexion angles along an axis in order to display the range of motion envelope. 
     
     
         38 . The medical navigation device of  claim 33 , wherein the range of motion envelope is further based on a position of the femoral implant relative to the femur or another position of the tibial implant relative to the tibia.