# Patent

## Title
Methods and apparatus for determining pin placement during hip surgery

## Abstract

New apparatuses and methods for their design and use are disclosed that can be used to assist a surgeon in placing a guide pin during hip surgery. Specifically, a hip surgery method is disclosed in which an image of a patient's femur can be obtained and used to design and prepare a mold that contains an aperture for guiding a drill at the desired location and angle. During surgery the mold can be quickly and accurately positioned on the exposed femur head. Then, a drill bit can be inserted through the aperture and an opening for a pin can be drilled into the femur head. The mold can have a unique contoured surface adapted to fit to the femur head in a single unique position such that the opening is made in a unique desired position. The apparatuses and methods facilitate faster, more accurate surgery and are less invasive.

## Background
PRIORITY CLAIM
This application claims priority to U.S. Provisional Application Ser. No. 60/990,872, filed Nov. 28, 2007 and entitled “METHODS AND APPARATUS FOR DETERMINING PIN PLACEMENT DURING HIP SURGERY” and U.S. Provisional Application Ser. No. 60/949,135, filed Jul. 11, 2007 and entitled “METHOD AND APPARATUS FOR DETERMINING PIN PLACEMENT DURING HIP SURGERY”, the entire contents of which are hereby incorporated by reference.


TECHNICAL FIELD
The present application relates generally to an apparatus and methods for hip surgery.
BACKGROUND
In the resurfacing of a femur head in a patient's hip, installation of a new surface on the femur head with resurfacing device can require that a guide for a drill be installed on a suitable axis of the head/neck of the patient's femur. The axis of the drill guide is determined prior to surgery by a surgeon through analysis of an X-ray or other image of the femur. Prior to implanting the new surface device, the femoral head is typically machined to a suitable shape having a central axis. The axis is determined by the drill guide. The success of the surgery, in important part, is determined by the placement of the drill guide. It has long been a problem in the art to accurately locate the drill guide, so that the resurfacing device itself can subsequently be accurately fitted.
SUMMARY
New apparatuses and methods for their design and use are disclosed that can be used to assist a surgeon in more rapidly and accurately placing a guide pin during hip surgery. Specifically, a hip surgery method is disclosed in which an image of a patient's femur can be obtained and used to design and prepare a mold that contains an aperture for guiding a drill at the desired location and angle. During surgery the mold can be quickly and accurately positioned on the exposed femur head. Then a drill bit can be inserted through the aperture and an opening for a pin can be drilled into the femur head. The mold can have a unique contoured surface adapted to fit to the femur head in a single unique position. The apparatuses and methods facilitate faster, more accurate surgery and are less invasive.
Additional features and advantages are described herein, and will be apparent from, the following Detailed Description and the figures.



BRIEF DESCRIPTION OF THE FIGURES
FIG. 1 is a perspective view of a femoral head positioned for insertion in to an example block-shaped alignment mold.
FIG. 2 is another perspective view of the femoral head positioned for insertion in to the example block-shaped alignment mold.
FIG. 3 is a cross-sectional view of the femoral head positioned for insertion in to the example block-shaped alignment mold.
FIG. 4 is a perspective view of the femoral head positioned for insertion in to an example cone-shaped alignment mold.
FIG. 5 is a flow chart of an example method for determining pin placement during hip surgery.



DETAILED DESCRIPTION
A mold for a femur head is disclosed that is defined, in part, by a contoured surface adapted to contact the surface of a femur head. The mold further defines an aperture that can be used as a guide for a drill bit that can be used to drill an opening in the femur head for holding a pin, such as a guide pin, during a femur resurfacing procedure.
The mold can be made of any abrasion resistant hard material, of which many are known, that can be used to guide a drill bit during hip surgery. As can be appreciated, suitable materials will be able to withstand sterilization procedures such that they can be used in surgery and will not be toxic to the surgeon or patient. Suitable materials include metals and plastics, particularly thermosetting plastics.
Turning to FIG. 1 and FIG. 2, a patient's femur 100 can be measured before a surgery using a scanner such as an X-ray machine, a magnetic resonance imaging (MRI) device, and/or a computed tomography (CT) scanner and the like. A surgeon then can use the image(s) to determine the desired location and angle for insertion of a pin into the femur head. Data from the scanner and the surgeon's selections can then be used to create a mold 102 that fits the femur head 104. For example, MRI data may be transmitted to a company with software that evaluates critical angles and geometry associated with the femur and uses a computer aided design/computer aided manufacturing (CAD/CAM) system to produce the mold 102. In a preferred method, the mold 102 is designed so that it has a unique contoured surface 106 that is adapted to mate with a unique portion of the surface of the femur head 104. Such a design facilitates positioning of the mold 102 on the femur head 104 such that an aperture 112 can guide a drill bit into an optimal location for placement of the pin during surgery. In such a position, the aperture 112 defines an axis in the femur head 104, which may substantially correspond with an axis in the femur head 104 that is in line with a femur neck 114. The mold 102 can then be shipped to the hospital and prepared for surgery.
In some surgical procedures it can be desirable to also place a cut into the femur head 104 such as in a procedure known as an osteotomy. To facilitate making a suitable cut, a slot or guide 116 can be included in the mold 102. The slot 116 can be included in the mold 102 such that it defines an angle, a position and/or a depth for such a cut into the femur head 104 when the mold 102 is positioned on the femur head 104.
In certain embodiments the mold 102 can be designed such that it contains one or more pin placement apertures 110 for anchor pins 108. The mold 102 can then be placed on the femur 100, and the anchor pins 108 can be inserted through the pin placement apertures 110 into the femur head 104 to securely affix the mold 102 to the femur head 104 while the mold 102 is used during surgery.
FIG. 3 illustrates a mold 102 in contact with a femur head 104 and further illustrates a uniquely contoured contact surface 106 of the mold 102 in contact with a unique contour of the femur head 104. As can be seen in the embodiment of FIG. 3, when affixed to femur head 104, the aperture 112 of the mold 102 can be substantially aligned with an axis of the femur head 104 in line with the femur neck 114. FIG. 3 further illustrates the pins 108 extending through the pin placement apertures 110 and into the femur head 104 to securely hold the mold 102 to the femur head 104.
The mold 102 may have any suitable shape so long as the aperture 112 can be accurately positioned over the femur head 104. As illustrated in FIG. 4, for example, the mold 102 may have a conical shape and still maintain an aperture 112 for a drill guide and for the anchor pins 108 and a guide slot 116 for an osteotomy. As can be appreciated by one of skill in the art, other shapes are also possible.
A hip surgery method is also disclosed in which an image of a patient's femur is obtained using methods such as X-rays, magnetic resonance imagery or other such techniques. The image is then used to design and prepare a mold that contains a suitably sized aperture for guiding a drill at the desired location and angle. This can most conveniently be accomplished using CAD/CAM equipment. A flow chart of an example method for determining pin placement during hip surgery is illustrated in FIG. 5.
In surgery, the embodiments are used after first exposing a patient's hip and femur head 104. The mold 102 is positioned onto the femur head 104. FIG. 3 illustrates an embodiment in which the mold 102 can only fit on to the femur head 104 in a single unique position due to the unique contoured surface 106 of the inside of the mold 102 that matches a unique contoured surface of the femur head 104. The small anchor pins 108 may be inserted through the pin placement apertures 110 in the side of the mold 102 to secure the mold 102 in place. Once the mold 102 is secured, a larger pin, drill, and/or guide wire may be inserted though the main aperture 112 of the mold 102 and into the head 104 and/or neck 114 of the patient's femur 100. Once the main pin (or other device) is in place, the mold 102 can preferably removed.
In embodiments in which the mold 102 fits the femoral head 104 in one position, the exact pin location (i.e., the entry point of the pin into the femoral head 104 and the axis of the pin relative to the femoral neck 114) is determined by the main aperture 112 of the mold 102. In addition, the size of the pin can be confirmed by the size of the main aperture 112 of the mold 102. As a result, the present technique is faster, more accurate, and less invasive than previous techniques.
The pin can be used as a guide for a cutting instrument that can be used for resurfacing the femur head 104. The central aperture of a resurfacing tool can be positioned on the pin and the tool used to remove a portion of the surface of the femoral head 104 to form a new surface on the perimeter of the femoral head 104. The femur head 104 can be reshaped into any shape that can receive a surface replacement device that creates a new femur head surface. Suitable shapes include conical shapes, tapered or conical shapes for example.
Once the femur head 104 has been reshaped, the resurfacing tool can be removed. The pin can also be removed. A replacement device bearing a new femur head surface can then be positioned on the femur head 104. The replacement device can have a portion adopted to match the reshaped surface of the femoral head 104. Further, the replacement device can have a protruding pin adapted to fit within the opening in the central axis of the femur head 104.
During the procedure the surgeon may also use the slot 116, when present, to cut the femoral head 104 (e.g., osteotomy of the femoral head 104) to prepare the femoral head 104 to receive a femoral head component. When the mold 102 only fits on to the femoral head 104 in one position, the exact location and angle of the cut can be precisely determined by the slot 116 of the mold 102. The slot 116 can be used by positioning a cutting device into the slot 116 and making a cut into the femur using the slot 116 as a guide.
It should be understood that various changes and modifications to the presently preferred embodiments described herein will be apparent to those skilled in the art. Such changes and modifications can be made without departing from the spirit and scope of the present subject matter and without diminishing its intended advantages. It is therefore intended that such changes and modifications be covered by the appended claims.

## Claims

1. An apparatus for facilitating a resurfacing of a femur head which is configured to articulate with a hip, the apparatus comprising:
a mold formed based on data indicative of a shape of the femur head, the mold including a contoured contact surface for contacting opposite sides of the femur head in a single predetermined position, the mold defining a first aperture, a second aperture, and a slot, the slot being configured to guide a cutting device;
a guide pin for insertion in the first aperture, the guide pin being configured to guide a bone resurfacing tool; and
a first anchor pin for insertion in the second aperture, the first anchor pin being configured to affix the mold to the femur head.

2. An apparatus for facilitating a resurfacing of a femur head which is configured to articulate with a hip, the apparatus comprising:
a mold formed based on data indicative of a shape of the femur head, the mold including a contoured contact surface for contacting opposite sides of the femur head in a single predetermined position, the mold defining a first aperture, a second aperture, and a slot, the slot being configured to guide a cutting device;
a guide pin for insertion in the first aperture, the guide pin being configured to guide a bone resurfacing tool; and
a first anchor pin for insertion in the second aperture, the first anchor pin being configured to affix the mold to the femur head,
wherein the single predetermined position is such that the first aperture is substantially aligned with an axis in the femur head that is in alignment with a femur neck.