# US 10,441,438 B1 · Preoperative femoral implant sizing

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- Number: US 10,441,438 B1
- Document ID: US10441438B1
- Status: Granted
- Kind: B1
- Application number: 15/686,787
- Filed: 2017-08-25
- Granted: 2019-10-15
- Earliest claimed: 2016-08-26
- Assignees: Smith & Nephew, Inc.
- Applicants: Smith & Nephew, Inc.
- Inventors: Mohammed Rahman; Yangqiu Hu; Kyle Lonidier
- Web page: https://patentgrep.com/patent/US10441438B1

## CPC

- A61B 34/10: Computer-aided planning, simulation or modelling of surgical operations
- A61F 2/4657: {Measuring instruments used for implanting artificial joints (for surgical instruments A61B90/06)}
- A61B 34/00: Computer-aided surgery; Manipulators or robots specially adapted for use in surgery
- G06T 7/0012: {Biomedical image inspection}
- G06T 7/62: of area, perimeter, diameter or volume
- G06T 7/70: Determining position or orientation of objects or cameras (camera calibration G06T7/80)
- A61B 2034/105: {Modelling of the patient, e.g. for ligaments or bones}
- A61B 2034/108: {Computer aided selection or customisation of medical implants or cutting guides}
- A61F 2/3859: {Femoral components}
- A61F 2002/4658: {for measuring dimensions, e.g. length}
- A61F 2002/4668: {for measuring angles}
- G06T 2207/30008: Bone
- A61B: DIAGNOSIS; SURGERY; IDENTIFICATION (usefulness limited to only animals A61D)
- A61F: FILTERS IMPLANTABLE INTO BLOOD VESSELS; PROSTHESES; DEVICES PROVIDING PATENCY TO, OR PREVENTING COLLAPSING OF, TUBULAR STRUCTURES OF THE BODY, e.g. STENTS; ORTHOPAEDIC, NURSING OR CONTRACEPTIVE DEVICES; FOMENTATION; TREATMENT OR PROTECTION OF EYES OR EARS; BANDAGES, DRESSINGS OR ABSORBENT PADS; FIRST-AID KITS (dental prosthetics A61C)
- G06T: IMAGE DATA PROCESSING OR GENERATION, IN GENERAL

## Abstract

A method according to one embodiment includes locating distal lateral and medial condyles and posterior lateral and medial condyles a femoral bone model, and determining a posterior resection plane based on locations of the distal lateral and medial condyles, one or more dimensions of a prospective femoral implant, and one or more surgical preferences. The method may further include determining a first distance between the posterior medial condyle and the posterior resection plane and a second distance between the posterior lateral condyle and the posterior resection plane, determining a difference between a target value and an average of the first distance and the second distance, wherein the target value is associated with a thickness of the prospective femoral implant, and selecting a desired femoral implant size based on the difference between the target value and the average determined for each of a plurality of possible femoral implant sizes.

## Claims

### Claim 1

A method of femoral implant sizing in advance of a surgical procedure on a patient's knee, the method comprising:
preoperatively acquiring an image of a distal femur of the patient;
generating, by a computing system, a femoral bone model from the image;
locating, by the computing system, a distal medial condyle, a distal lateral condyle, a posterior medial condyle, and a posterior lateral condyle of the femoral bone model;
determining, by the computing system, a posterior resection plane based on a location of the distal medial condyle, a location of the distal lateral condyle, one or more dimensions of a prospective femoral implant of a selected size, and one or more surgical preferences;
determining, by the computing system, a first distance between the posterior medial condyle and the posterior resection plane and a second distance between the posterior lateral condyle and the posterior resection plane;
determining, by the computing system, a difference between a target value and an average of the first distance and the second distance, wherein the target value is associated with a thickness of the prospective femoral implant; and
selecting, by the computing system, in advance of the surgical procedure on the patient's knee, a desired femoral implant size of a plurality of possible femoral implant sizes based on the determined difference between the target value and the average of the first distance and the second distance determined for each of the plurality of possible femoral implant sizes.

### Claim 2 (depends on 1)

The method of claim 1, wherein determining the posterior resection plane comprises:
determining a primary plane that includes the distal medial condyle and the distal lateral condyle;
determining an offset of a cortex plane relative to the primary plane based on the selected size and the one or more surgical preferences;
identifying a boundary curve indicative of an intersection of the cortex plane and the femoral bone model;
locating an apex point of the boundary curve, wherein the apex point is an anterior-most point of the boundary curve;
determining an apex plane that includes the apex point and is perpendicular to an anterior-posterior direction; and
determining a posterior resection plane based on the apex plane and the one or more dimensions of the prospective femoral implant of the selected size.

### Claim 3 (depends on 2)

The method of claim 2, wherein determining the primary plane comprises determining a plane that includes a first distal-most point of the distal medial condyle and a second distal-most point of the distal lateral condyle.

### Claim 4 (depends on 2)

The method of claim 2, wherein the apex point is an anterior-most point of the boundary curve.

### Claim 5 (depends on 1)

The method of claim 1, wherein selecting the desired femoral implant size comprises selecting a femoral implant size of the plurality of possible femoral implant sizes associated with a smallest determined difference between the target value and the average of the first distance and the second distance.

### Claim 6 (depends on 1)

The method of claim 1, wherein determining the difference between the target value and the average of the first distance and the second distance comprises determining the difference, d, according to d=|½(DISTLAT+DISTMED)−(impThk+1.5 mm)|,
wherein DISTMED is the first distance;
wherein DISTLAT is the second distance; and
wherein impThk is the thickness of the prospective femoral implant.

### Claim 7 (depends on 1)

The method of claim 1, wherein selecting the desired femoral implant size comprises selecting a desired femoral implant size based on the determined difference between the target value and the average of the first distance and the second distance determined for each of the plurality of possible femoral implant sizes and each of a plurality of permitted flexion angles.

### Claim 8 (depends on 1)

The method of claim 1, wherein selecting the desired femoral implant size comprises selecting a most optimal femoral implant size of the plurality of possible femoral implant sizes.

### Claim 9 (depends on 1)

The method of claim 1, further comprising:
receiving, by the computing system, model data indicative of the femoral bone model;
determining, by the computing system, the plurality of possible femoral implant sizes of the prospective femoral implant and a plurality of permitted flexion angles of the prospective femoral implant; and
selecting, by the computing system, a size of the plurality of possible femoral implant sizes and a flexion angle of the plurality of permitted flexion angles,
wherein determining the posterior resection plane comprises determining a posterior resection plane based on one or more dimensions of the prospective femoral implant of the selected size of the plurality of possible femoral implant sizes; and
wherein selecting the desired femoral implant size comprises selecting a desired femoral implant size based on the determined difference between the target value and the average of the first distance and the second distance determined for each of the plurality of possible femoral implant sizes and each of the plurality of permitted flexion angles.

### Claim 10 (depends on 1)

The method of claim 1, wherein the one or more surgical preferences comprise at least one of an anterior resection preference, a distal resection preference, or a maximum permitted flexion angle.

### Claim 11 (depends on 1)

The method of claim 1, wherein determining the first distance between the posterior medial condyle and the posterior resection plane comprises determining a first distance between a posterior-most point of the posterior medial condyle and the posterior resection plane; and
wherein determining the second distance between the posterior lateral condyle and the posterior resection plane comprises determining a second distance between a posterior-most point of the posterior lateral condyle and the posterior resection plane.

### Claim 12 (depends on 1)

The method of claim 1, further comprising performing a surgical procedure on the patient using the prospective femoral implant of the desired femoral implant size.

### Claim 13 (depends on 1)

The method of claim 1, further comprising resecting the distal femur of the patient in preparation for attachment of the prospective femoral implant of the desired femoral implant size to the resected distal femur of the patient.

### Claim 14

A computing system for femoral implant sizing in advance of a surgical procedure on a patient's knee, the computing system comprising:
at least one processor; and
at least one memory comprising a plurality of instructions stored thereon that, in response to execution by the at least one processor, causes the computing system to:
preoperatively acquire at least one image of a distal femur of the patient;
generate a femoral bone model from the at least one image;
locate a distal medial condyle, a distal lateral condyle, a posterior medial condyle, and a posterior lateral condyle of the femoral bone model;
determine a posterior resection plane based on a location of the distal medial condyle, a location of the distal lateral condyle, one or more dimensions of a prospective femoral implant of a selected size, and one or more surgical preferences;
determine a first distance between the posterior medial condyle and the posterior resection plane and a second distance between the posterior lateral condyle and the posterior resection plane;
determine a difference between a target value and an average of the first distance and the second distance, wherein the target value is associated with a thickness of the prospective femoral implant; and
select a desired femoral implant size of a plurality of possible femoral implant sizes, in advance of the surgical procedure on the patient's knee, based on the determined difference between the target value and the average of the first distance and the second distance determined for each of the plurality of possible femoral implant sizes.

### Claim 15 (depends on 14)

The computing system of claim 14, wherein to determine the posterior resection plane comprises to:
determine a primary plane that includes the distal medial condyle and the distal lateral condyle;
determine an offset of a cortex plane relative to the primary plane based on the selected size and the one or more surgical preferences;
identify a boundary curve indicative of an intersection of the cortex plane and the femoral bone model;
locate an apex point of the boundary curve, wherein the apex point is an anterior-most point of the boundary curve;
determine an apex plane that includes the apex point and is perpendicular to an anterior-posterior direction; and
determine a posterior resection plane based on the apex plane and the one or more dimensions of the prospective femoral implant of the selected size.

### Claim 16 (depends on 14)

The computing system of claim 14, wherein to select the desired femoral implant size comprises to select a femoral implant size of the plurality of possible femoral implant sizes associated with a smallest determined difference between the target value and the average of the first distance and the second distance.

### Claim 17 (depends on 14)

The computing system of claim 14, wherein to determine the difference between the target value and the average of the first distance and the second distance comprises to determine the difference, d, according to d=|½(DISTLAT+DISTMED)−(impThk+1.5 mm)|,
wherein DISTMED is the first distance;
wherein DISTIAT is the second distance; and
wherein impThk is the thickness of the prospective femoral implant.

### Claim 18

One or more non-transitory machine-readable storage media for femoral implant sizing in advance of a surgical procedure on a patient's knee comprising a plurality of instructions stored thereon that, in response to execution by a computing device, causes the computing device to:
preoperatively acquire at least one image of a distal femur of the patient;
generate a femoral bone model from the at least one image;
locate a distal medial condyle, a distal lateral condyle, a posterior medial condyle, and a posterior lateral condyle of the femoral bone model;
determine a primary plane that includes the distal medial condyle and the distal lateral condyle;
determine an offset of a cortex plane relative to the primary plane based on the selected size and one or more surgical preferences;
identify a boundary curve indicative of an intersection of the cortex plane and the femoral bone model;
locate an apex point of the boundary curve, wherein the apex point is an anterior point of the boundary curve;
determine an apex plane that includes the apex point and is perpendicular to an anterior-posterior direction;
determine a posterior resection plane based on the apex plane and one or more dimensions of the prospective femoral implant of the selected size;
determine a first distance between the posterior medial condyle and the posterior resection plane and a second distance between the posterior lateral condyle and the posterior resection plane;
determine a difference between a target value and an average of the first distance and the second distance, wherein the target value is associated with a thickness of the prospective femoral implant; and
select a desired femoral implant size of the plurality of possible femoral implant sizes in advance of the surgical procedure on the patient's knee, based on the determined difference between the target value and the average of the first distance and the second distance determined for each of the plurality of possible femoral implant sizes and each of the plurality of permitted flexion angles.

### Claim 19 (depends on 18)

The one or more machine-readable storage media of claim 18, wherein to select the desired femoral implant size comprises to select a femoral implant size of the plurality of possible femoral implant sizes associated with a smallest determined difference between the target value and the average of the first distance and the second distance.

### Claim 20 (depends on 18)

The one or more machine-readable storage media of claim 18, wherein to determine the difference between the target value and the average of the first distance and the second distance comprises to determine the difference, d, according to d=|½(DISTLAT+DISTMED)−(impThk+1.5 mm)|,
wherein DISTMED is the first distance;
wherein DISTLAT is the second distance; and
wherein impThk is the thickness of the prospective femoral implant.