News Column

Patent Application Titled "Surgical Instrument for the Positioning of an Alignment Element" Published Online

June 12, 2014



By a News Reporter-Staff News Editor at Politics & Government Week -- According to news reporting originating from Washington, D.C., by VerticalNews journalists, a patent application by the inventors Hananouchi, Takehito (Amagasaki, JP); Vangeneugden, Dieter (Overpelt, BE), filed on July 12, 2012, was made available online on May 29, 2014.

The assignee for this patent application is Materialise N.v.

Reporters obtained the following quote from the background information supplied by the inventors: "In most joint arthroplasty, replacement and/or reconstruction surgery procedures, and in particular in hip and shoulder joint surgery, a joint is replaced by a prosthetic implant. The main goal of such interventions is to relieve (arthritic) pain and/or to restore severe physical joint damage. When prosthesis fails, a revision surgery is carried out. However, this procedure is technically more difficult and time-consuming than the primary intervention and the outcome is often less satisfactory, both because there is less bone stock to work with and because the removal of adherent cement or prosthetic components may result in fracture or perforation of the bone. Furthermore, with each successive joint revision, the risk of infection and symptomatic loosening of the prosthesis may increase substantially. Accordingly, one of the most important aspects of joint surgery procedures is the correct, accurate and stable placement of the primary implant.

"Correct implant placement is important in shoulder surgery, and particularly important in hip surgery. The majority of acetabular implants used in hip surgery are currently placed using the press-fit technique. In this technique, the patient's acetabulum is first reamed with a sequence of hemispherical reamers with increasing diameters, such that a hemispherical cavity is created at the location where the implant should be placed. The final (largest) reamer typically has a diameter smaller than that of the implant. In a further step, the implant is attached to an impactor and placed upon the pelvis of the patient, such that the implant supports on the rim of the reamed cavity and the orientation of the implant is anatomically suitable. Finally, the impactor is hit with a hammer until the implant sits inside the reamed cavity. Thereafter, the implant is released from the impactor.

"The general consensus in the field is that the orientation of the implant determines the success of the surgery and the lifespan of the implant (Hayakawa et al., Archives of orthopedic and trauma surgery Vol. 129 (2009):1151-1156). However, the current procedure shows several shortcomings for obtaining a good orientation. Indeed, the only anatomical visual reference during final placement is the orientation of the transverse ligament (Pearse et al., Hip international Vol. 18 (2008):7-10), to which the top plane of the implant should be oriented in parallel. Accordingly, rotation around the axis of the transverse ligament remains a variable parameter. In addition, the transverse ligament is generally obscured from the surgeon's view, further hampering the orientation process. Furthermore, the impactor and hammer are both rather bulky, making it difficult to keep the impactor in a stable orientation.

"Few practical solutions have been proposed for these problems. US patent application 2009/0163922 (Meridew, Metzger) describes a patient-specific guide to be positioned and optionally attached to the acetabular rim, designed to interface with the impactor so as to enforce the correct orientation. However, it is very doubtful whether such a device could be able to withstand the momentum applied to it during impaction.

"US patent application 2010/0082035 and International patent application WO 2011/060536 disclose patient-specific surgical instruments for facilitating implantation of an acetabular cup prosthesis in a bone of a patient. The guides may be used for positioning a guide pin bone guide pin to the patient's acetabulum. However, such guides only provide a limited accuracy.

"Accordingly, there is a need for alternative and improved surgical devices, and in particular surgical guiding instruments, which provide the ability to correctly and accurately insert, place and orient an implant into a patient's joint."

In addition to obtaining background information on this patent application, VerticalNews editors also obtained the inventors' summary information for this patent application: "The present invention relates to surgical instruments for use in arthroplasty. The instruments are intended for facilitating surgery on ball-and-socket joints in the human or animal body. In surgery on the human body, the instruments are therefore useful for hip and shoulder joint surgery, particularly for the positioning of an acetabular cup implant or glenoid implant. The surgical instruments allow for positioning of an alignment element, where the desired position and orientation of the alignment element is typically based on pre-operational planning. The alignment element can be an indicator pin, wire, screw or drill, which acts as a navigator for the surgeon to address an optimal pre-operationally planned implant alignment direction, in the reaming and/or the impacting phase of the surgical procedure.

"The surgical instruments according to the present inventions are surgical fixtures. In a first aspect, the present invention provides surgical fixtures for positioning an alignment element. The fixtures according to the present invention comprise one or more patient-specific contact elements which together fit onto areas on a socket of a ball-and-socket joint, onto areas around said socket and/or onto the rim of said socket in at least three contact points. Where the socket is a glenoid cavity, the areas around the socket may include the glenoidal rim and the periglenoidal region (e.g. infraglenoidal tuberculum, supraglenoidal tuberculum and collum scapulae, etc.) and might include the acromion and processus coracoideus (coracoid process). Where the socket is an acetabulum, the areas around the socket may include the periacetabular region (e.g. the limbus acetabuli, sulcus supra-acetabularis, superior ramus, etc.).

"In particular embodiments, the contact points have an arrangement wherein the angle between the line connecting one contact point and the center of the circle or ellipse best fitting the socket rim and the line connecting the adjacent contact point and said center is never greater than 180.degree.. The surgical fixtures further comprise a positioning element which is rigidly attached to the fixture. This positioning element is provided with one or more holes which allow the insertion of the alignment element. Additionally, in particular embodiments, the positioning element is detachable from the rest of the fixture.

"In particular embodiments, one (of the) contact element(s) is positioned on the fixture such that, when positioned on the bone, it interacts with an anatomical feature present on the rim of the socket or on the bone in or around the socket. In further embodiments, this anatomical feature is the posterior notch of the transverse ligament, or the coracoid process.

"In particular embodiments, the invention provides patient-specific surgical fixtures for positioning an alignment element on the acetabular socket of a pelvic bone, comprising a one-piece structure with one or more patient-specific contact elements which fit onto one or more discrete areas on the socket. More particularly these one or more contact elements fit around and/or onto the acetabular rim, whereby at least one of said one or more contact elements interact with the posterior notch of the transverse ligament of the rim of said acetabulum so as to ensure a tight fit of said fixture on the acetabular rim. The fixture further comprises a positioning element which can be or is rigidly attached to said one-piece structure comprising contact elements, which positioning element is provided with one or more holes which allows the insertion of said alignment element.

"In certain embodiments of the fixtures described herein, the surgical fixtures comprise at least two contact elements, or at least three contact elements. Together, the contact elements fit onto areas on the socket, around the socket and/or on the socket rim in at least three contact points, whereby the contact points have an arrangement wherein the angle between a line drawn between one contact point and the center of the circle or ellipse best fitting the socket rim and a line drawn between the adjacent contact point and said center is never greater than 180.degree.. In further embodiments, the surgical fixture comprises at least two contact elements, wherein the positioning element corresponds to one of the contact elements.

"In certain embodiments of the fixtures described herein, the one or more holes in the positioning element allow the insertion of said alignment element outside of said socket.

"In certain embodiments of the fixtures described herein, the positioning element is detachable from the rest of said fixture.

"In certain embodiments of the fixtures described herein, the one or more contact elements which fit onto areas on the rim of said socket in at least three contact points are irreversibly fixed to each other.

"As indicated hereabove, the positioning element may be detachable from the rest of the fixture. In particular embodiments, the connection between the positioning element and the rest of the fixture is adapted or weakened, such that the positioning element can be detached from the rest of the fixture by breaking said connection with surgical cutting elements. In other embodiments, the connection between the positioning element and the rest of the fixture is ensured by an element selected from a dovetail coupling, interlocking features, a pinned system and a snap-fit mechanism.

"In particular embodiments, the surgical fixtures according to the present invention further comprise a connecting structure, wherein the positioning element and/or one or more of the one or more contact elements extend from the connecting structure.

"As indicated hereabove, the positioning element comprises one or more holes. In certain embodiments, the position and/or direction of at least one hole is in accordance with pre-operational planning. In certain embodiments, at least one hole is part of a drill guide. In certain embodiments, the positioning element comprises a first and a second hole with a different diameter, wherein the first hole allows the insertion of the alignment element and wherein the second hole allows the insertion of a fixation element. In further embodiments, the positioning element comprises two or more holes which allow the insertion of a fixation element. In particular embodiments, the alignment element is selected from the group comprising a pin, a wire, a screw and a drill.

"In particular embodiments, the surgical fixtures according to the present invention are manufactured via additive manufacturing.

"In a further aspect, the present invention provides methods for the manufacture of the patient-specific surgical fixtures according to the present invention. The methods comprise the steps of: i. obtaining volume information of the socket of a ball-and-socket joint from a patient; ii. obtaining the installation direction of a socket implant for the patient; iii. identifying and selecting parts of the bone surrounding the implant zone which are suitable for inserting an alignment element; iv. identifying and selecting parts of the bone in or surrounding the implant zone which are suitable for use as a base for the contact surface or surfaces of the surgical fixture; v. designing and producing a surgical fixture based on the information obtained in steps i, ii, iii, iv and v.

"In a further aspect, the present invention provides methods for guiding a socket implant in a socket of a ball-and-socket joint, comprising the steps of: 1) positioning a surgical fixture according to the present invention onto the socket; 2) using one of the holes provided by the fixture to insert a wire, pin, drill or screw into the bone surrounding the socket; 3) removing the surgical fixture from the socket; 4) using the wire, pin, drill or screw to guide the implant in the correct direction onto the socket according to the pre-operational planning.

"In particular embodiments, step 1) involves a rotational movement of the fixture to obtain the desired orientation onto the socket and step 3) comprises detaching the positioning element from the rest of the fixture, and optionally from the bone, so as to allow thereafter, a reversal of the rotational movement of step 1) to remove the rest of the fixture from the bone.

"The patient may be an animal or human patient. Therefore the socket may be any socket of a ball-and-socket joint in an animal or human body. In human patients, the socket of a ball-and-socket joint may be an acetabulum or a glenoid cavity. In particular embodiments, the socket is an acetabulum. In other embodiments, the socket is a glenoid cavity.

"The surgical fixtures according to the present invention allow for a fast and accurate positioning of an indicator pin, wire, screw or drill, and allow for an efficient removal of the fixture from the anatomy after use.

BRIEF DESCRIPTION OF THE DRAWINGS

"The following figures of specific embodiments of the invention are merely exemplary in nature and are not intended to limit the present teachings, their application or uses. Throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features.

"FIG. 1A, A', A'': Schematic representation of the relative position of patient-specific contact points (4) and their orientation relative to the acetabular rim (7) or glenoid cavity rim (16) and the acetabulum (13) or glenoid cavity (15) according to a particular embodiment of the present invention. B, B', B'', C, C', C'': Schematic representation of the arrangement and shape of patient-specific contact surfaces (14) and their orientation relative to the acetabular rim (7) or glenoid cavity rim (16) and the acetabulum (13) or glenoid cavity (15) according to a particular embodiment of the present invention.

"FIG. 2 A, B: Drawing of an acetabulum (13) surrounded by the acetabular rim (7) and the posterior notch of the transverse ligament (8).

"FIG. 3 Surgical fixture (1) according to a particular embodiment of the present invention, positioned onto an acetabulum (A), and not positioned on a bone (B, C). The fixture comprises a central connecting structure (12), a positioning element (3) and four contact elements (2, 2'), each comprising a contact surface (4). The fixture also comprises an extension (10) for manipulation of the fixture. The positioning element (3) also functions as a drill guide (9), comprises holes (5, 6) and is connected to the rest of the fixture via a weakened connection (11).

"FIG. 4 A: Surgical fixture (1) according to a particular embodiment of the present invention, comprising a positioning element (3) and a contact element (2) comprising a contact surface (4). The fixture further comprises two extensions (10). The positioning element (3) is also a drill guide (9), comprises holes (5, 6). B: the same surgical fixture (1) positioned on an acetabulum of a pelvic bone (17).

"FIG. 5 A: surgical fixture (1) according to a particular embodiment of the present invention, positioned on an acetabulum (7) of a pelvic bone. B, C: surgical fixture (1) according to a particular embodiment of the present invention, not positioned on a bone

"In the figures, the following numbering is used: 1--surgical fixture; 2, 2'--contact element; 3--positioning element; 4, 4'--contact point; 5--hole for insertion of alignment element; 6--hole for fixation element; 7--acetabular rim; 8--posterior notch of the transverse ligament; 9--drill guide; 10--extension; 11--adapted connection; 12--connecting structure; 13--acetabulum; 14--contact surface; 15--glenoid cavity; 16--glenoid cavity rim; 17--pelvic bone"

For more information, see this patent application: Hananouchi, Takehito; Vangeneugden, Dieter. Surgical Instrument for the Positioning of an Alignment Element. Filed July 12, 2012 and posted May 29, 2014. Patent URL: http://appft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=%2Fnetahtml%2FPTO%2Fsearch-adv.html&r=1346&p=27&f=G&l=50&d=PG01&S1=20140522.PD.&OS=PD/20140522&RS=PD/20140522

Keywords for this news article include: Materialise N.v.

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