# Patent

## Title
Methods for patient-specific shoulder arthroplasty

## Abstract

A method of determining an optimal position of a glenoid implant. The method includes identifying a center point of a patient's glenoid fossa based on an image of the patient's glenoid fossa; determining the optimal position of the glenoid implant based on the location of the center point relative to a medial point of the patient's scapula; and selecting orientation of an alignment pin based on the determined optimal glenoid implant position such that the glenoid fossa will be prepared to receive the glenoid implant at the optimal position when the glenoid fossa is prepared with a cutting device or guide coupled to the alignment pin.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of U.S. Provisional Application No. 61/552,079, filed on Oct. 27, 2011, the entire disclosure of which is incorporated herein by reference.
This application is related to the following concurrently filed U.S. patent applications, each of which is incorporated herein by reference: U.S. application Ser. No. 13/653,868 “Patient-Specific Glenoid Guides”; U.S. application Ser. No. 13/653,878 “Patient-Specific Glenoid Guide”; and U.S. application Ser. No.13/653,886 “Patient-Specific Glenoid Guide and Implants”.


FIELD
The present disclosure relates to methods for patient-specific shoulder arthroplasty.
BACKGROUND
This section provides background information related to the present disclosure, which is not necessarily prior art.
The shoulder joint is the third most replaced joint in the body. During surgery, a Steinman pin is often used as an instrument guide. The Steinman pin is placed in the scapula, and is precisely positioned to guide the reamer to prepare the joint for an implant that will recreate natural version/inclination in the joint, or any other desired version/inclination. The pin is typically positioned based on a visual assessment of the joint and the surgeon's experience. While orienting the pin in this manner is sufficient, a method and apparatus to facilitate placement of the pin and recreation of natural version and inclination, or any optimal version and inclination, would be desirable.
SUMMARY
This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features.
The present teachings provide for a method of determining an optimal position of a glenoid implant. The method includes identifying a center point of a patient's glenoid fossa based on an image of the patient's glenoid fossa; determining the optimal position of the glenoid implant based on the location of the center point relative to a medial point of the patient's scapula; and selecting orientation of an alignment pin based on the determined optimal glenoid implant position such that the glenoid fossa will be prepared to receive the glenoid implant at the optimal position when the glenoid fossa is prepared with a cutting device or guide coupled to the alignment pin.
The present teachings also provide for a method of determining an optimal position of a glenoid implant. The method includes identifying a center point of the patient's glenoid fossa based an image of the patient's glenoid fossa; determining the optimal position of the glenoid implant based on a linear line extending between the center point and an area proximate to a most medial surface of the patient's scapula; and selecting orientation of an alignment pin based on the determined optimal glenoid implant position such that the glenoid fossa will be prepared to receive the glenoid implant at the optimal position when the glenoid fossa is prepared with a cutting device or guide coupled to the alignment pin.
The present teachings further provide for a device for optimally positioning a glenoid implant during repair of a patient's shoulder joint. The device includes a patient specific surface designed to be received within the patient's glenoid fossa. An alignment pin guide extends from a first opening defined by the patient specific surface. The alignment pin guide is positioned and angled to guide insertion of the alignment pin into the glenoid fossa such that the alignment pin passes through a center of the glenoid fossa towards a medial point of the patient's scapula, thereby orientating the alignment pin such that the glenoid fossa will be prepared to receive the glenoid implant at an optimal position when the glenoid fossa is prepared with a cutting device or guide coupled to the alignment pin. The device can be removed from cooperation from the patient's glenoid fossa without removing the alignment pin.
Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.



DRAWINGS
The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure.
FIG. 1 is a lateral view of a scapula and a damaged glenoid fossa in need of repair, a center of the glenoid fossa is identified and used to identify optimal version and inclination in accordance with the present teachings;
FIG. 2A illustrates methods for achieving optimal glenoid version and inclination according to the present teachings;
FIG. 2B illustrates a processor, display, and input device for performing methods according to the present teachings;
FIG. 3 illustrates providing optimal glenoid version and inclination based on the location of the center of the glenoid fossa relative to a most medial surface of the patient's scapula;
FIG. 4 illustrates providing optimal glenoid version and inclination based on the location of the center of the glenoid fossa relative to a most medial portion of the patient's medial glenoid fossa;
FIG. 5 illustrates use of a native glenoid face to provide optimal glenoid version and inclination; and
FIG. 6 is a perspective view of a patient specific alignment guide according to the present teachings coupled with a glenoid fossa.



Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings.
DETAILED DESCRIPTION
Example embodiments will now be described more fully with reference to the accompanying drawings.
With initial reference to FIG. 1, a human scapula is illustrated at reference numeral 10. The scapula 10 includes a glenoid fossa 12. As illustrated, the glenoid fossa 12 is damaged, such as due to wear, and is in need of repair. To prepare the glenoid fossa 12 to receive an implant at predetermined, optimum version and inclination, which may include natural version and inclination, the present teachings identify and use anatomic landmarks and algorithms to design a patient specific alignment pin positioning guide, which is illustrated at reference number 50 of FIG. 6 and will be described further herein.
With additional reference to FIG. 2A, methods for orienting an alignment pin, such as a Steinman pin for aligning a reamer, in order to provide optimal glenoid version and inclination, are illustrated at reference numeral 110. With initial reference to block 112, the center of the glenoid fossa 12 is first identified. The center of the glenoid fossa 12 can be identified in any suitable manner.
For example, a three-dimensional (3D) model of the patient's scapula 10 can be created based on CT images of the patient. The CT images can be provided in the form of DICOM images, which typically include about 200 CT image “slices” of the patient's scapula 10. Any suitable software can be used to process the DICOM images to isolate the scapula 10 from surrounding bone or non-bony regions, such as “ORS Visual” segmentation software from Object Research Systems. The 3D model of the scapula 10 is then made from the images using any suitable software that can create a 3D model, such as “ORS Visual.” The 3D model is then imported into any suitable CAD software, such as Siemens NX or Solidworks, for example. To identify the center C, any suitable software (such as Siemens NX or Solidworks) or manual measurements based on the 3D model can be used, as well as a combination of both.
For example, using the CAD software the center C or an approximation thereof can be identified with a best fit circle referenced off three equally spaced points at the rim of the glenoid fossa 12. The location of the center C can then be refined based on the location of each of the following parts of the glenoid fossa 12: the anterior rim 14, the posterior rim 16, the superior rim 18, and the inferior rim 20. These parts of the glenoid fossa 12 can be automatically identified using suitable software, or can be identified manually using the CAD software by selecting points on the glenoid fossa 12, such as with a mouse (reference no. 154 of FIG. 2B, which is further described herein). Once the center C of the glenoid fossa 12 is identified, the center C can be used to identify orientation of a Steinman pin that will facilitate preparation of the glenoid fossa 12 to receive an implant at a predetermined, optimal version and inclination, as described herein.
With reference to blocks 114-120 of FIG. 2A, the center C can be used to virtually orient the alignment pin using suitable software, such as the Siemens NX CAD software, in a variety of different ways. FIG. 2B illustrates a processor 150, which can run the CAD software and DICOM image processing software. A user can interact with and operate the software using display 152 and a suitable input device, such as mouse 154. With initial reference to block 114, a transverse plane (or line) that passes through both the center C of the glenoid fossa 12 and the most medial surface (MS) of the scapula 10 can be identified to represent the position of the alignment pin to provide version control, as illustrated in FIG. 3. The most medial surface (MS) can be identified using suitable software, such as the CAD software, or manually identified on the display 152 using the mouse 154. The plane can be identified manually and drawn on the CAD model using the mouse 154, or can be identified using suitable software.
Inclination control can be identified using the natural inclination of the glenoid, which can be defined by marking two points, either manually using the mouse 154 or automatically using the software. The first point can be on the superior rim 18 of the glenoid fossa 12, and the second point can be on the inferior rim 20 of the glenoid fossa 12. The alignment pin can be arranged such that it is perpendicular to a line connecting the inferior and superior points of the glenoid fossa 12, and extends along the line of FIG. 3, which extends through both the center C of the glenoid fossa 12 and the most medial surface (MS) of the scapula 10. The pin can also be oriented about 8° inferior to the C-MS line, which is based on an average position of the general population, or at any other suitable angle. Inclination can also be determined by matching a best fit sphere to the glenoid surface and connecting the center of the best fit sphere to the center C of the glenoid fossa 12, which can be performed manually using the CAD software or automatically with the CAD software and the mouse 154 or other suitable software run by the processor 150.
With reference to block 116, version control can also be defined by connecting the center C of the glenoid fossa 12 to the most medial point of the glenoid fossa 22, which is identified in FIG. 4 at MGV, with a line representing the position of the alignment pin either automatically or manually using the CAD software and the mouse 154. Other than referencing the most medial point of the glenoid fossa, the alignment pin is virtually aligned in the same manner described above in the discussion of block 114.
With reference to block 118 and FIG. 5, the native, undamaged face of the glenoid fossa 12 (to the extent present) can be used to reconstruct anatomic version. If enough of the natural glenoid surface 30 is present, the surface can be mapped using the CAD software or other suitable software to create an axis normal to the surface that passes through the center point C of the glenoid fossa 12. A best fit sphere can be used to create the orientation of the native glenoid surface. This created plane axis can then be used as the pin axis to orient the alignment pins.
With further reference to block 120, the inner cortex of the scapula 10 can be referenced to orient the alignment pin. After the center C of the glenoid fossa 12 is identified, a plane can be drawn using the CAD software and the mouse 154 from the center C to an area midway between anterior and posterior cortices of the scapula 10. This will ensure that the alignment pin is placed directly in the center of the inner scapula cortex.
Once the alignment pin is virtually positioned on the display 152 as described at blocks 114-120, the surgeon or other suitably trained person can adjust the virtual position of the alignment pin on the display 152 as necessary at block 122 to customize version and inclination. For example, the alignment pin may be adjusted such that it does not extend directly through the most medial surface (MS) of the scapula 10, but is rather angled to meet patient-specific needs.
Once the desired orientation of the alignment pin has been virtually set on the display 152 using suitable software, a patient specific alignment guide (FIG. 6 at 50) is formed, and then seated within the patient's glenoid fossa 12 at block 122 of FIG. 2A. The alignment guide 50 includes a patient specific surface 52 that corresponds to, and is a negative of, the patient's glenoid fossa 12. Extending from the patient specific surface 52 are one or more alignment pin guides 54, such as a first alignment pin guide 54A and a second alignment pin guide 54B. Each of the guides 54A and 54B are sized and shaped to receive a first alignment pin 56A and a second alignment pin 56B respectively. At block 124, the first alignment pin 56A is inserted through the first alignment pin guide 54A to within the scapula 10 during a regular “non-reverse” procedure, and the second alignment pin 56B is inserted through the second alignment pin guide 54B to within the scapula 10 during a reverse procedure. The alignment pins 56A and 56B will be positioned according to the orientation assigned virtually using the software in order to provide natural version and inclination, or any other predetermined optimal version and inclination.
With additional reference to block 128, after the first alignment pin 56A or the second alignment pin 56B is set in the scapula 10, the alignment guide 50 is removed from the glenoid fossa 12. A suitable reamer is then coupled to the set alignment pin 56A or 56B, which will properly position the reamer to prepare the glenoid fossa 12 to receive an implant at block 130 positioned to provide the predetermined optimal version and inclination. At block 132, the implant is attached to the glenoid fossa 12.
The present teachings can also be adapted to a reverse shoulder procedure. With a reverse procedure, the alignment guide 50 may be provided with additional apertures surrounding the alignment pin guides 54A and 54B to receive fasteners for a reverse shoulder glenoid base plate. The base plate can be oriented to provide optimal version and inclination determined as set forth above. The inclination can be at an inferior tilt of about 10° in addition to the 8° inferior tilt identified above.
The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.

## Claims

1. A method of determining a desired implantation position of a glenoid implant comprising:
identifying a center point of a glenoid fossa on a virtual model of a patient's scapula using software run by a processor, the software identifying the center point using a best fit circle referenced off of three equally spaced points at the glenoid fossa, the three equally spaced points located at three of the following: an anterior rim, a posterior rim, a superior rim, and an inferior rim, wherein at least the center point is visually displayed on the virtual model and the virtual model is created from an anatomical image of a patient's scapula;
determining the desired implantation position of the glenoid implant as a line that passes through both the center point and a medial point of the virtual model of the patient's scapula identified using the software; and
selecting an orientation of a virtual alignment pin using the software and visually displaying the orientation of the virtual alignment pin on the virtual model at an angle from the determined desired implantation position;
inserting a surgical alignment pin into the patient's scapula, the surgical alignment pin positioned according to an orientation assigned virtually using the software and corresponding to the orientation assigned to the virtual alignment pin.

2. The method of claim 1, further comprising determining a version of the glenoid implant based on the location of the center point relative to a most medial point of the scapula.

3. The method of claim 2, wherein the version of the glenoid implant is determined based on a linear line extending from the center point toward the most medial point of the scapula identified using the software, the linear line visually displayed on the virtual model.

4. The method of claim 3, wherein the linear line is oriented about 8° inferior to the most medial point of the patient's scapula.

5. The method of claim 3, further comprising designing a virtual guide customized to the glenoid fossa, the guide including a receptacle configured to orient the virtual alignment pin relative to the linear line.

6. The method of claim 5, further comprising fabricating an alignment guide based upon the designed guide customized to the patient's glenoid fossa, and connecting a reamer to a physical alignment pin and reaming a patient's glenoid fossa, the physical alignment pin positioned according to an orientation assigned virtually using the software and corresponding to the orientation assigned to the virtual alignment pin, the alignment guide configured to guide the reamer to prepare the glenoid to receive the implant at a physical position corresponding to the desired position.

7. The method of claim 1, wherein the desired position of the glenoid implant is determined based on the location of the center point relative to a most medial portion of a glenoid vault.

8. The method of claim 1, wherein the desired position of the glenoid implant is determined based on the location of the center point relative to an axis normal to a surface that passes through the center point.

9. The method of claim 1, wherein the desired position of the glenoid implant is determined based on the location of the center point relative to an inner cortex of the scapula.

10. The method of claim 1, further comprising determining the desired position assuming the glenoid implant is a reverse glenoid implant, and orienting the virtual alignment pin at an inferior tilt about 18° inferior to a most medial point of the scapula.

11. The method of claim 1, wherein the three equally spaced points at the glenoid fossa and a most medial point of the scapula are identified either automatically used the software or manually using the software and user input.

12. A method of determining a desired implantation position of a glenoid implant comprising:
providing software run with a processor to create a virtual three-dimensional model of a scapula created from an anatomical image of patient's scapula;
identifying a center point of a glenoid fossa on the virtual three-dimensional model using the software, the software identifying the center point using a best fit circle referenced off of three equally spaced points at the glenoid fossa, the three equally spaced points located at three of the following: an anterior rim, a posterior rim, a superior rim, and an inferior rim, wherein at least the center point is visually displayed on the virtual three-dimensional model;
determining the desired implantation position of the glenoid implant as a linear line extending between the center point and a most medical surface of the virtual model of the patent's scapula identified using the software, wherein the linear line is visually displayed on the virtual three-dimensional model; and
selecting orientation of a virtual alignment pin using the software and visually displaying the orientation of the virtual alignment pin on the virtual three-dimensional model at an angle from the desired implantation position;
inserting a surgical alignment pin into the paient's scapula, the surgical alignment pin positioned according to an orientation assigned virtually using the software and corresponding to the orientation assigned to the virtual alignment pin.

13. The method of claim 12, wherein the linear line is oriented about 8° inferior to the most medial point of the patient'scapula.

14. The method of claim 12, further comprising determining an inclination of the glenoid fossa by orienting the virtual alignment pin perpendicular to a second line that extends between the inferior rim of the glenoid fossa and the superior rim of the glenoid fossa, wherein the second line is visually displayed on the three-dimensional model.

15. A method of determining a desired implantation position of a glenoid implant comprising:
identifying a center point of a glenoid fossa on a virtual three-dimensional model using software run by a processor, the software identifying the center point using a best fit circle referenced off of three equally spaced points at the glenoid fossa, the three equally spaced points located at three of the following: an anterior rim, a posterior rim, a superior rim, and an inferior rim, wherein at least the center point is visually displayed on the virtual three-dimensional model and the virtual three-dimensional model is created from an anatomical image of a patient's scapula;
determining the desired implantation position of the glenoid implant as a linear line extending between the center point and a most medial surface of the virtual model of the patient's scapula identified using the software, wherein the linear line is visually displayed on the virtual three-dimensional model;
selecting an orientation of a virtual alignment pin using the software and visually displaying the orientation of the virtual alignment pin on the virtual three-dimensional model at an angle from the determined desired implantation position;
inserting a surgical alignment pin into the patient's scapula, the surgical alignment pin positioned according to an orientation assigned virtually using the software and corresponding to the orientation assigned to the virtual alignment pin.

16. The method of claim 15, further comprising fabricating a custom guide having a patient-specific surface that is formed as a negative of the patient's glenoid fossa into the patient's glenoid fossa.

17. The method of claim 16, further comprising preparing the patient's glenoid fossa to receive the glenoid implant by connecting a reamer to the surgical alignment pin and reaming the glenoid fossa, the surgical alignment pin guides the reamer such that the glenoid implant will provide predetermined glenoid version when connected to the patient's glenoid fossa.

18. The method of claim 16, further comprising removing the custom guide from the patient's glenoid fossa without removing the surgical alignment pin.

19. The method of claim 15, wherein the linear line is oriented about 8° inferior to the most medial point of the patient's scapula.