Patent Description:
While the specification concludes with claims which particularly point out and distinctly claim the invention, it is believed the present invention will be better understood from the following description of certain examples taken in conjunction with the accompanying drawings, in which like reference numerals identify the same elements.

<FIG> shows an exemplary HFD in the form of a skull clamp (<NUM>) that uses <NUM>-point fixation. Skull clamp (<NUM>) comprises a pair of arms (<NUM>, <NUM>) with each arm (<NUM>, <NUM>) having a lateral portion (<NUM>, <NUM>) and an upright portion (<NUM>, <NUM>). Arms (<NUM>, <NUM>) are adjustable laterally relative to each other so skull clamp (<NUM>) accommodates various patient head sizes. Skull clamp (<NUM>) includes a rocker arm assembly (<NUM>) that holds two pins (<NUM>) on one side of skull clamp (<NUM>). In the illustrated version, rocker arm assembly (<NUM>) is connected with skull clamp (<NUM>) at an end of upright portion (<NUM>). Opposite rocker arm assembly (<NUM>) at an end of upright portion (<NUM>) is a single pin holder (<NUM>) holding a single pin (<NUM>).

<FIG> shows an arm (<NUM>) of rocker arm assembly (<NUM>) in cross section. Arm (<NUM>) comprises a curved shaped in the illustrated version, and a pair of bores (<NUM>) within arm (<NUM>). In this manner, bores (<NUM>) are configured to retain pins (<NUM>) at each respective end of the arm (<NUM>). Arm (<NUM>) further angles inward such that longitudinal axes (A1, A2) defined by bores (<NUM>) of arm (<NUM>) extend in a converging manner as shown.

<FIG> shows a stabilization arrangement with a head of a patient that is elliptically shaped using skull clamp (<NUM>). In the illustrated version, the contact angles defined by the pins and their interface with the patient's head are shown by diagonally extending lines (L1, L2) that form a triangular shape. The term "contact angle" as used herein should be understood to also include the penetration angle when the stabilization involves the pin or contact feature penetrating the bone as opposed to only contacting the bone without penetration. Thus, the term "contact angle" is understood to be inclusive of both the angle of contact and the angle of penetration depending on the configuration of the stabilization. In this example, arm (<NUM>) of a rocker arm assembly (<NUM>) is configured with a curved shape designed to work with an elliptically shaped head of a patient to provide for a desired contact angle. In some examples where the patient's skull is elliptically shaped, or in other words where the head shape resembles an ellipsoid, the position of all three pins form an isosceles triangle. This provides load distributing among all three pins and the pins are configured with contact angles of ninety or about ninety degrees. In other words, the pins contact and may be driven into the cranial bone at ninety or about ninety degrees or perpendicular or substantially perpendicular to the cranial bone.

<FIG> shows a stabilization arrangement where skull pin (<NUM>) defines a longitudinal axis (A3), and skull pin (<NUM>) is positioned in contact with an elliptically shaped portion of the head of a patient. A tangent line (T1) is shown at the point of contact where skull pin (<NUM>) contacts the head. The contact angle (θ1), defined as the angle between longitudinal axis (A3) of skull pin (<NUM>) and tangent line (T1), is shown as ninety or about ninety degrees. In this perpendicular or substantially perpendicular arrangement, skull pin (<NUM>) makes a rigid and stable connection with the head.

In certain neurosurgical procedures, the patient's skull is pinned in a planar region of the cranial bone rather than an elliptical region as discussed above. The planar region of the cranial bone can be planar, generally planar, or substantially planar over some distance of the bone structure. For the avoidance of doubt, the term "planar region" as used herein should be understood to encompass not only a planar region, but also a generally planar region, substantially planar region, a quasi-planar region, and/or other variations of these terms as will be understood by those of ordinary skill in the art in view of the teachings herein. By way of example only, and not limitation, pinning in a planar region of the cranial bone can be the case in procedures in which the patient is positioned face down (prone position). For instance, in order to perform a surgery in the occipital region, in the posterior fossa, or at the cervical spine, in at least some instances the pins are placed in a planar region of temporal bone and parietal bone.

If using the rocker arm assembly and pins described above, when pinning into a planar region of cranial bone, the contact angle of the pins will differ compared to using that same rocker arm assembly and pins when pinning into an elliptical region of cranial bone. Thus, trying to achieve an about ninety-degree contact angle for the pins would not be attainable when pinning in these different bone geometries using identical rocker arm assemblies and pins. For instance, if pinning using a rocker arm assembly and pins configured for use with an elliptically shaped head to provide for ninety degree contact angle of the pins, such as rocker arm assembly (<NUM>) having pins (<NUM>) as shown in <FIG>, using the same rocker arm assembly and pins with a planar region of cranial bone can impede achieving a contact angle of ninety degrees or thereabouts. The result here can be a loss in stability and rigidity of the stabilization.

By way of example, <FIG> shows portions of rocker arm assembly (<NUM>) of <FIG> used with a planar portion of cranial bone (<NUM>) of the head of the patient. In this example, when pinning into a planar region of cranial bone as shown in <FIG>, the angle of contact is greater than ninety degrees. More specifically, the contact angles (α1, α2) are defined as the angle between longitudinal axes (A4, A5) of respective skull pins (<NUM>) and tangent line (T2).

By way of further example, <FIG> shows portions of rocker arm assembly (<NUM>) of <FIG> without pins (<NUM>), and again being used with a planar portion of cranial bone (<NUM>) of the head of the patient. In this example, when pinning into a planar region of cranial bone as shown in <FIG>, the angle of contact is greater than ninety degrees. More specifically, the contact angles (α3, α4) are defined as the angle between longitudinal axes (A6, A7) of respective bores (<NUM>) and tangent line (T2).

As described above with respect to <FIG> and <FIG>, contact angle can be defined based on the orientation of bores (<NUM>) or the orientation of pins (<NUM>). In some instances where pins (<NUM>) are straight and bores (<NUM>) define concentric receptacles for receiving pins (<NUM>), the longitudinal axes defined by bores (<NUM>) and pins (<NUM>) will be the same. In this instance, the contact angles will be the same whether defined by the orientation of bores (<NUM>) or the orientation of pins (<NUM>). However, in some other examples, bores (<NUM>) may be omitted where pins (<NUM>) may be formed with or as part of arm (<NUM>). In such an example, the contact angle will be defined based on the orientation of the pins (<NUM>). Still in some other examples, bores (<NUM>) and pins (<NUM>) can be shaped or configured such that they do not have the same or a common longitudinal axis, and thus would define different contact angles as defined herein. By way of example only, and not limitation, this could be the case where pins (<NUM>) are angled or curved instead of straight. In view of the teachings herein, other configurations for rocker arm assembly (<NUM>), with pins (<NUM>) and bores (<NUM>), where pins (<NUM>) and bores (<NUM>) have different longitudinal axes, and thus different contact angles as defined herein, will be apparent to those of ordinary skill. In application, where the contact angle defined by the bores and the contact angle defines by the pins differs, the contact angle as defined by the contact features or pins is a key factor when considering the stability of a patient stabilization as it is those contact features or pins that contact the patient's head.

<FIG> shows an exemplary HFD in the form of a skull clamp (<NUM>) that uses <NUM>-point fixation. Skull clamp (<NUM>) comprises pair of arms (<NUM>, <NUM>) with each arm (<NUM>, <NUM>) having lateral portion (<NUM>, <NUM>) and upright portion (<NUM>, <NUM>). Arms (<NUM>, <NUM>) are adjustable laterally relative to each other so skull clamp (<NUM>) accommodates various patient head sizes. Skull clamp (<NUM>) includes a rocker arm assembly (<NUM>) that holds two pins (<NUM>) on one side of skull clamp (<NUM>). In the illustrated version, rocker arm assembly (<NUM>) is connected with skull clamp (<NUM>) at end of upright portion (<NUM>). Opposite rocker arm assembly (<NUM>) at end of upright portion (<NUM>) is a single pin holder (<NUM>) holding a single pin (<NUM>).

Turning now to <FIG> and <FIG>, <FIG> shows portions of exemplary <NUM>-pin rocker arm assembly (<NUM>) that is configured for use with skull clamp (<NUM>) like shown in <FIG>, but which also may be configured for use in place of rocker arm assembly (<NUM>) of skull clamp (<NUM>) as shown in <FIG>, as well as other types of HFDs. In the illustrated version of <FIG>, <NUM>-pin rocker arm assembly (<NUM>) is used with a planar portion of cranial bone (<NUM>) of the head of the patient. In this example, the angle of contact is ninety degrees or about ninety degrees. This is the case for both pins (<NUM>) configured to be used with the <NUM>-pin rocker arm assembly (<NUM>). More specifically, the contact angles (α5, α6) on each side of arm (<NUM>) are defined as the angle between longitudinal axes (A8, A9) of respective pins (<NUM>) and tangent line (T2).

With this configuration, using <NUM>-pin rocker arm assembly (<NUM>), provides for achieving a ninety-degree contact angle, or thereabouts, for each of the pins retained by rocker arm assembly (<NUM>) when stabilizing when pinning into a planar region of the skull of the patient's head. In other words, pins (<NUM>) are perpendicularly pinned into the planar region of cranial bone in this arrangement shown in <FIG>. Stated another way, rocker arm assembly (<NUM>) enables the surgeon or user to realize a perpendicular bone contact or penetration of pins (<NUM>) in rocker arm assembly (<NUM>) even though a planar region of cranial bone is pinned or used as a stabilizing location.

By way of further example, <FIG> shows portions of rocker arm assembly (<NUM>) of <FIG> without pins (<NUM>). In this example, rocker arm assembly (<NUM>), with arm (<NUM>) and bores (<NUM>), is configured for use in pinning into a planar region of cranial bone. Thus, when pinning into a planar region of cranial bone as shown in <FIG>, the angle of contact is ninety degrees or about ninety degrees. More specifically, the contact angles (α7, α8) on each side of arm (<NUM>) are defined as the angle between longitudinal axes (A10, A11) of respective bores (<NUM>) and tangent line (T2).

As described above with respect to <FIG> and <FIG>, contact angle can be defined based on the orientation of bores (<NUM>) or the orientation of pins (<NUM>). In some instances where pins (<NUM>) are straight and bores (<NUM>) define concentric receptacles for receiving pins (<NUM>), the longitudinal axes defined by bores (<NUM>) and pins (<NUM>) will be the same. In this instance, the contact angles will be the same whether defined by the orientation of bores (<NUM>) or the orientation of pins (<NUM>). However, in some other examples, bores (<NUM>) may be omitted where pins (<NUM>) may be formed with, or as part of, arm (<NUM>). In such an example, the contact angle will be defined based on the orientation of the pins (<NUM>). Still in some other examples, bores (<NUM>) and pins (<NUM>) can be shaped or configured such that they do not have the same or a common longitudinal axis, and thus would have different contact angles as defined herein. By way of example only, and not limitation, this could be the case where pins (<NUM>) are angled or curved instead of straight. In view of the teachings herein, other configurations for rocker arm assembly (<NUM>) with pins (<NUM>) and bores (<NUM>), where pins (<NUM>) and bores (<NUM>) have different longitudinal axes, and thus different contact angles as defined herein, will be apparent to those of ordinary skill in the art. In application, where the contact angle defined by the bores and the contact angle defines by the pins differs, the contact angle as defined by the contact features or pins is a key factor when considering the stability of a patient stabilization as it is those contact features or pins that contact the patient's head.

In one version of exemplary <NUM>-pin rocker arm assembly (<NUM>), arm (<NUM>) may be approximately <NUM> x <NUM> x <NUM> - <NUM>, with two perpendicular pin receptors or bores (<NUM>) at the ends of arm (<NUM>) at a distance of about <NUM> - <NUM> between each other. In another version of exemplary <NUM>-pin rocker arm assembly (<NUM>), arm (<NUM>) is smaller, such that arm (<NUM>) is approximately <NUM> x <NUM> x <NUM> - <NUM>, with two perpendicular pin receptors or bores (<NUM>) at the ends of the arm at a distance of about <NUM> - <NUM> between each other. With this smaller configuration, <NUM>-pin rocker arm assembly (<NUM>) may be configured for use with pediatric patent's or patent's having smaller head size.

In comparing rocker arm assembly (<NUM>) with rocker arm assembly (<NUM>), in each case respective pins (<NUM>, <NUM>) define a longitudinal axis or centerline as shown in <FIG>. In some examples, the centerlines of each of the pair of pins intersect forming an angle, such as β1 in <FIG> for rocker arm assembly (<NUM>). This angle defines an angle of the arc, and may also be referred to herein as the radius or degree of curvature of the arm. With rocker arm assembly (<NUM>) as illustrated, angle β1 is forty degrees.

With rocker arm assembly (<NUM>) as illustrated in <FIG>, the centerlines or longitudinal axes of pins (<NUM>) are parallel and thus do not intersect to define an angle. In other examples where the centerlines or longitudinal axes of pins (<NUM>) are close to parallel, but not exactly parallel, they intersect to define an angle as mentioned above. In such cases where these axes are close but not exactly parallel, the angle defined is less than forty degrees. Thus, with rocker arm assembly (<NUM>), the angle represented by β2 may be something that is equal to or greater than about zero degrees (as defined by β2 in <FIG>) and less than forty degrees. It should be noted that herein a zero-degree angle for β2 is being defined as the case when the axes defined by pins (<NUM>) are parallel.

In this manner, a rocker arm assembly configured for pinning with a planar region of cranial bone can have a degree of curvature of the arm, defined by the angle formed by the longitudinal axes or centerlines of each of the pair of pins, that is greater than or equal to about zero degrees and less than forty degrees. For instance, when β2 is equal to zero degrees, arm (<NUM>) of rocker arm assembly (<NUM>) has a straight, non-curved shape. When β2 is greater than zero but less than about forty degrees, arm (<NUM>) of rocker arm assembly (<NUM>) can have a slight curvature. Thus, it should be understood that in some versions arm (<NUM>) is straight, while in some other versions arm (<NUM>) may have a curvature, but to a lesser degree than the curvature of rocker arm assemblies that are designed for pinning elliptically shaped cranial bone. Still in some other examples this range for the angle may be between about zero degrees and about thirty degrees, or between about zero degrees and about <NUM> degrees, or between about zero degrees and about <NUM> degrees. In view of the teachings herein, other such ranges will be apparent to those of ordinary skill in in the art.

In another comparison of rocker arm assembly (<NUM>) with rocker arm assembly (<NUM>), in each case respective bores (<NUM>, <NUM>) define a longitudinal axis or centerline as shown in <FIG>. In some examples, the centerlines of each of the pair of bores (<NUM>, <NUM>) intersect forming an angle, such as β3 in <FIG> for rocker arm assembly (<NUM>). This angle defines an angle of the arc, and may also be referred to herein as the radius or degree of curvature of the arm (<NUM>). With rocker arm assembly (<NUM>), angle β3 is forty degrees.

With rocker arm assembly (<NUM>) as illustrated in <FIG>, the centerlines or longitudinal axes of bores (<NUM>) are parallel and thus do not intersect to define an angle. In other examples where the centerlines or longitudinal axes of bores (<NUM>) are close to parallel, but not exactly parallel, they intersect to define an angle as mentioned above. In such cases where these axes are close but not exactly parallel, the angle defined is less than forty degrees. Thus, with rocker arm assembly (<NUM>), the angle represented by β4 may be something that is equal to or greater than about zero degrees (as defined by β4 in <FIG>) and less than forty degrees. It should be noted that herein a zero-degree angle for β4 is being defined as the case when the axes defined by bores (<NUM>) are parallel.

In this manner, a rocker arm assembly configured for pinning with a planar region of cranial bone can have a degree of curvature of the arm, defined by the angle formed by the longitudinal axes or centerlines of each of the pair of bores, that is greater than or equal to about zero degrees and less than forty degrees. For instance, when β4 is equal to zero degrees, arm (<NUM>) of rocker arm assembly (<NUM>) has a straight, non-curved shape. When β4 is greater than zero but less than forty degrees, arm (<NUM>) of rocker arm assembly (<NUM>) can have a slight curvature. Thus, it should be understood that in some versions arm (<NUM>) is straight, while in some other versions arm (<NUM>) may have a curvature, but to a lesser degree than the curvature of rocker arm assemblies designed for pinning elliptically shaped cranial bone. Still in some other examples this range for the angle may be between about zero degrees and about thirty degrees, or between about zero degrees and about <NUM> degrees, or between about zero degrees and about <NUM> degrees. In view of the teachings herein, other such ranges will be apparent to those of ordinary skill in in the art.

As mentioned above, rocker arm assemblies, like rocker arm assembly (<NUM>) are configured for use with elliptically shaped cranial bone. Such rocker arm assemblies comprise an angle-defined by the longitudinal axes or centerlines of either the pair of bores within the arm of the rocker arm, or the pair of pins within the arm of the rocker arm-of forty degrees or more. When such rocker arm assemblies are used to pin into planar regions of cranial bone, the result can be contact angles that deviate significantly from a perpendicular penetration angle such that a stable and/or rigid stabilization may be compromised. However, as shown and described above with respect to rocker arm assembly (<NUM>), using a stabilization configuration where the angle-defined by the longitudinal axes or centerlines of either the pair of bores within the arm of the rocker arm, or the pair of pins within the arm of the rocker arm-is less than forty degrees provides for the ability to achieve a stable and/or rigid stabilization of a patient in procedures that involve pinning the head in planar regions of cranial bone as the contact angle can be maintained at or close to ninety degrees.

Claim 1:
A head fixation device to stabilize a head of a patient, the device comprising:
(a) a rocker arm assembly (<NUM>, <NUM>) comprising an arm (<NUM>, <NUM>), wherein the rocker arm assembly defines a rotational axis about which the arm is rotatable;
(b) two contact features (<NUM>, <NUM>) retained by the rocker arm assembly or two bores configured to each selectively retain a contact feature (<NUM>, <NUM>) for contacting the head of the patient, wherein the contact features are configured to contact the head of the patient, wherein each of the contact features or each of the bores defines a longitudinal axis that extends through a distal end of the contact feature configured to contact the head of the patient or through the bore, and
(c) a pin holder (<NUM>) opposite the rocker arm assembly, wherein the pin holder includes a third contact feature or bore configured to contact the head of the patient,
characterized in that the contact features or bores form an isosceles triangle and an angle defined by the two longitudinal axes of the contact features or bores retained by the rocker arm assembly is less than about <NUM> degrees.