FIXATION SYSTEM FOR HOFFA FRACTURES

Description

Introduction

[0001] The femur articulates distally with the tibia at the knee. On the femoral side of the knee, the distal end of the femur defines a pair of rounded protuberances, known as condyles, arranged medially and laterally relative to one another. Each condyle is supported by a corresponding side of a tibial plateau created by the proximal end of the tibia.

[0002] Trauma to the femur near the knee can fracture the bone in a generally frontal plane, near or within one of the condyles, to produce a Hoffa fracture. This type of fracture generates a condylar fragment that should be stabilized to encourage osteosynthesis for restoring the integrity of the femur and function of the knee. The standard procedure for fixing a Hoffa fracture is installation of a pair of anterior-posterior (AP) bone screws, from an anterior side of the femur, across the Hoffa fracture, and into the posteriorly-located condylar fragment, to secure the condylar fragment to an anterior portion of the distal femur. However, other options for fixing a Hoffa fracture are needed, especially when the distal femur has sustained multiple fractures.

[0003] US 2009 / 275987 A1 describes a bone plate extender and extension system. This system includes a first bone plate extender and may additionally include a bone fixation element and / or an additional bone plate. The bone plate extender may be affixed to a bone portion at one end, for instance, a fractured bone portion, via a bone fixation element, and associated with a second bone plate at an opposite end, so as to facilitate alignment and stabilization of the bone and thereby correct and treat a bone fracture. The bone plate extender may include an extended body, which includes a bone plate engagement portion, a bone fixation portion, and an intercalating portion there between.

[0004] US 2005 / 234458 A1 describes systems, including methods, apparatus, and kits, for expanded stabilization of bones.

[0005] US 2013 / 060251 A1 relates to a bone plate for stabilizing a fractured greater tuberosity, wherein the bone plate comprises one or more apertures for fixing the one plate to bone; one or more hook-arm receivers; one or more attachable hook-arms comprising one or more prongs and a device for attachment to the bone plate. Methods for stabilizing a fractured greater tuberosity using the described bone plates and kits comprising the same are also described.Summary

[0006] The presently claimed invention is defined in claim 1 while preferred embodiments are set forth in the dependent claims.

[0007] Associated surgical methods are also described herein to aid understanding the presently claimed invention. These methods do not form part of the presently claimed invention.

[0008] According to the presently claimed invention, a system for fixing a distal femur having a Hoffa fracture creating a condylar fragment comprises: a main plate having an elongated body portion and a head portion, wherein the elongated body portion is configured to be secured to a shaft region of the distal femur, wherein the head portion is wider than the body portion and configured to be secured to an end region of the distal femur, and wherein the main plate has a proximal end, a distal end, and a pair of longitudinal edges opposite one another on the main plate and each extending from the proximal end to the distal end of the main plate; a coupling member; an outrigger plate that is shorter, narrower, and thinner than the main plate, the outrigger plate having a mounting region and an arm, the mounting region being configured to be mounted on the head portion with the coupling member at a rotational position selected from two or more permitted rotational positions of the mounting region, such that the outrigger plate extends past one of the longitudinal edges of the main plate, wherein the arm defines a plurality of apertures and is configured to be secured to the condylar fragment with fasteners received in the plurality of apertures such that the outrigger plate spans and stabilizes the Hoffa fracture, wherein the head portion defines a first aperture and an upper surface of the head portion of the main plate defines a series of first surface features surrounding less than the full circumference of the first aperture of head portion and wherein the mounting region defines an aperture and a lower surface of the outrigger plate defines a series of second surface features surrounding less than the full circumference of the aperture and wherein the main plate and the outrigger plate collectively form an interface using the first and second surface features that permits the outrigger plate to be mounted at only a finite series of predefined rotational positions with respect to the main plate.Brief Description of the Drawings

[0009] The embodiments which form part of the presently claimed invention are illustrated in the figures 1-10, 16 and 17.

[0010] The examples shown in the other figures do not form part of the presently claimed invention but represent background art that is useful for understanding the presently claimed invention. Figure 1 is a fragmentary, lateral view of a femur and a tibia of a left leg, taken around the knee, with the femur having multiple fractures including a Hoffa fracture, with a plate assembly of an exemplary fixation system installed on the femur and spanning the Hoffa fracture, and with a Hoffa-fracture-spanning, independent, anterior-to-posterior (AP) fastener of the fixation system exploded from one of two alternative installed positions, in accordance with an embodiment of the presently claimed invention. Figure 2 is an exploded, isometric view of the plate assembly of Figure 1, taken in the absence of the femur and the tibia. Figure 3 is a fragmentary side view of the plate assembly of Figure 1, taken generally along line 3-3 of Figure 2 with plates of the plate assembly secured to one another. Figure 4 is a distal end view of the plate assembly of Figure 1, taken generally along line 4-4 of Figure 2 with plates of the assembly secured to one another. Figure 5 is a fragmentary, plan view of a head portion of a main plate of the plate assembly of Figure 1, taken around an aperture of the head portion and a series of radial teeth associated with the aperture. Figure 6 is a bottom view of an outrigger plate of the plate assembly of Figure 1. Figure 7 is a side view of the outrigger plate of Figure 6. Figure 8 is a top view of the outrigger plate of Figure 6. Figure 9 is a side view of a coupling member of the plate assembly of Figure 1. Figure 10 is a top end view of the coupling member of Figure 9. Figure 11 is an exploded isometric view of another exemplary plate assembly for the fixation system of Figure 1. Figure 12 is a bottom view of an outrigger plate of the plate assembly of Figure 11. Figure 13 is a side view of a coupling member of the plate assembly of Figure 11. Figure 14 is an oblique top view of the coupling member of Figure 13. Figure 15 is a bottom view of the coupling member of Figure 13. Figure 16 is a side view of a longer, more bent embodiment of an outrigger plate for the plate assemblies of Figures 1 and 11. Figure 17 is another view of the outrigger plate of Figure 16. Figures 18-21 are respective lateral, posterolateral, anterior, and posterior views of the distal region of a femur, with exemplary Hoffa fracture patterns and AP fastener trajectories marked, in accordance with examples of the present disclosure. Figure 22 is a fragmentary view of one of a series of different fixation configurations that were tested for stabilization of a model femur having a Hoffa-like cut, in accordance with examples of the present disclosure Detailed Description

[0011] The present disclosure provides a system and method (not claimed) for fixing a distal femur having a Hoffa fracture. The system comprises a main plate, an outrigger plate, and a coupling member that mounts the outrigger plate to the main plate. In an exemplary method (not claimed), an elongated body portion of the main plate may be secured to a shaft region of the distal femur, and a wider head portion of the main plate may be secured to an end region of the distal femur. The outrigger plate may be mounted on the head portion of the main plate, and an arm of the outrigger plate may be fastened to a condylar fragment of the femur with one or more fasteners, such that the outrigger plate spans and stabilizes the Hoffa fracture.

[0012] The fixation systems and methods disclosed herein may offer various advantages for femoral fixation, including any combination of the following. The pair of AP screws used in a standard procedure for Hoffa fixation can interfere with plate fixation of other femoral fragments, because the AP screws can block fastener trajectories determined by apertures of the plate. The systems and methods of the present disclosure can reduce the number of AP screws needed for Hoffa fixation, or eliminate the AP screws altogether, thereby permitting more plate apertures to receive fasteners and thus more effective bone fixation with the plate. Also, the systems and methods may offer a surgeon the option of expanding the footprint and fixation capability of a main (primary) bone plate on the distal femur by mounting an outrigger (secondary) plate over the main plate, if needed. The outrigger plate may be oriented selectably with respect to the main plate, according to the fracture configuration of the femur. Before or after attachment to the femur, an arm of the outrigger plate may be conformed to the local contour of the femur, and particularly a condylar fragment thereof. The size and geometry of the outrigger plate may facilitate deformation of the arm to adjust the arm's shape intra-operatively.

[0013] Further aspects of the present disclosure are described in the following sections: (I) fixation system for Hoffa fractures, (II) methods of fixing Hoffa fractures, (III) composition of system components, and (IV) examples.I. Fixation System for Hoffa Fractures

[0014] This section describes an exemplary bone fixation system 50 to fix at least a Hoffa fracture 52 of a femur 54; see Figures 1-17.

[0015] Figure 1 shows fixation system 50 installed above a knee joint 56. The knee joint is created where lateral and medial condyles 58, 60 of the distal end of femur 54 articulate with a tibial plateau 62 formed by a proximal end of a tibia 64. In Figure 1, anatomical axes are oriented as follows. A proximal-distal anatomical axis extends generally vertically, with proximal being above distal. An anterior-posterior anatomical axis runs generally horizontally, with anterior being leftward of posterior. A medial-lateral anatomical axis runs perpendicular to the plane of the drawing, with lateral being closer than medial.

[0016] Femur 54 may have sustained one or more fractures that are stabilized by fixation system 50, and which separate the femur into two or more pieces of bone. For example, the femur may be divided by Hoffa fracture 52 and, optionally, at least one other fracture 66a, 66b, which may (or may not) be located more proximally (i.e., farther from hip joint 56) than the Hoffa fracture. The at least one other fracture may include a fracture that is more anterior than Hoffa fracture 52, which may be a shaft (diaphyseal) fracture 66a, and / or a non-shaft (metaphyseal / epiphyseal) fracture 66b located distal to the femoral shaft and thus closer to Hoffa fracture 52.

[0017] A Hoffa fracture is any condyle-associated fracture (i.e., intracondylar and / or supracondylar) of the distal femur that is arranged at least generally in a frontal (coronal) plane, namely, within about 45 degrees of parallel to the frontal plane. The fracture creates a condylar fragment 68 including at least part of lateral condyle 58 and / or medial condyle 60, and, optionally, at least part of a respective lateral epicondyle and / or a medial epicondyle located proximally adjacent the condyle. Condylar fragment 68 may be formed from an at least predominantly posterior region of distal femur 54. The condylar fragment may represent, by volume, only a minority of an end portion 70 of the distal femur, where the end portion is the entire fraction of the femur located distal to the femoral shaft.

[0018] The fixation system includes a plate assembly 72 and at least one AP (anterior-to-posterior) fastener 74 (also called an independent fastener) that separately and respectively span Hoffa fracture 52 outside and inside femur 54. The plate assembly has a main plate 76 (also called a primary plate), an outrigger plate 78 (also called an ancillary or secondary plate), and a coupling member 80 that firmly attaches plates 76, 78 to one another, optionally independent of bone and / or at a selectable orientation. Each of main plate 76 and outrigger plate 78 may be secured to femur 54 with respective sets of fasteners 82a, 82b, which may be threaded fasteners, such as bone screws. The outrigger plate optionally may be secured to condylar fragment 68 with fasteners that are smaller (narrower / shorter) than the fasteners for the main plate. In the depicted embodiment, each of fasteners 82b extending through apertures of outrigger plate 78 are smaller in diameter and shorter than each of fasteners 82a extending through apertures of main plate 76. Each fastener of the fixation system (e.g., fasteners 74, 82a, and 82b) independently may, for example, be a screw, peg, pin, staple, cable, wire, rivet, or the like.

[0019] AP fastener 74 is shown in Figure 1 exploded from two alternative installed configurations, indicated by a branched arrow at 84 extending approximately along an anterior-posterior anatomical axis defined by the femur. The AP fastener may be oriented relatively more perpendicular to Hoffa fracture 52, and at least a majority of fasteners 82b may be oriented relatively more parallel to the fracture. The AP fastener(s) may provide primary fixation of the Hoffa fracture, and plate assembly 72 may provide supplemental fixation thereof. Each AP fastener may, for example, be a bone screw having an external thread 86 to engage bone, and a head 88 at which the bone screw engages a driver for advancing the screw into bone. The head may be disposed at an anterior side 90 of the femur, and the bone screw may extend posteriorly in the bone from the anterior side. The external thread may be configured to engage femur 54 on both sides of Hoffa fracture 52, or the bone screw may be a lag screw with a thread that engages only condylar fragment 68, among others. AP fastener 74 may stabilize bone independently of plate assembly 72. For example, the AP fastener may provide no attachment of plate assembly 72 to bone, and may not enter any aperture of the plate assembly when installed.

[0020] Outrigger plate 78 may be firmly attached to main plate 76 by coupling member 80 at a fixed orientation, which may be selected from a plurality of different permitted orientations. One alternative orientation for the outrigger plate is shown in phantom outline in Figure 1. The outrigger plate may be adjusted to any of the permitted orientations by rotating the outrigger plate relative to the main plate in a plane about an orthogonal axis extending through and defined by a pair of coaxially aligned apertures of the plates, before coupling member 80 is tightened to fix the orientation. The outrigger plate is configured to be adjustable discretely in the plane by one or more predefined angular increments, or is adjustable and then fixed over a continuous range of orientations in the plane. If adjustable discretely, the orientations may be uniformly offset from one another. A suitable predefined angular increment of adjustment for the plate assembly may, for example, be less than 30, 20, or 15 degrees, among others, and / or greater than 2, 3, or 4 degrees, among others.

[0021] Figures 2-4 show plate assembly 72 in exploded and assembled configurations. Main plate 76 forms a platform onto which outrigger plate 78, if needed, may be mounted by coupling member 80. The main plate is larger and sturdier than the outrigger plate, to provide primary fixation of the femur (for one or more fractures other than the Hoffa fracture). For example, each of the length and / or the average width of the main plate, independently may be at least about 1.5, 2, 3, 4, or 5 times the length and / or average width of the outrigger plate. Also or alternatively, the average thickness of the main plate may be at least about 20%, 40%, 60%, 80%, or 100% greater than the average thickness of the outrigger plate. Accordingly, the outrigger plate is much more amenable than the main plate to deformation intra-operatively, for adjusting the shape of the outrigger plate, but may be configured to bear a much smaller load than the main plate.

[0022] Main plate 76 may have any suitable structure. According to the presently claimed invention, the main plate has a distal head portion 92 extending from a proximal body portion 94, and optionally formed integrally with one another (see Figure 2). Head portion 92 is wider, on average, than body portion 94. The head portion may be contoured to fit onto a surface region of end portion 70 of the femur (also see Figure 1), and thus may have an inner, bone facing surface that is complementary to the surface region. Body portion 94 is elongated and, in some cases, substantially linear. The body portion is substantially longer than the head portion of the main plate, such as at least 2, 3, 4, or 5 times as long. The inner, bone facing surface of the body portion may be concave transversely to provide a better fit of the body portion onto the femoral shaft. Each of head portion 92 and body portion 94 defines a plurality of apertures 96, any of which may be internally threaded, to provide locking attachment to corresponding, externally-threaded fasteners that extend into the femur. Each of apertures 96 may be circular, or may be elongated orthogonal to a through-axis of the aperture.

[0023] Main plate 76 defines a centerline 98 that extends between opposite ends of the plate (i.e., between a proximal end 100 formed by body portion 94 and a distal end 102 formed by head portion 92). The centerline is generally centered between opposite longitudinal edges of the plate, namely, an anterior edge 104 and a posterior edge 106. Centerline 98 may be curved, as in the depicted embodiment, or linear.

[0024] Head portion 92 (and / or body portion 94) also defines an attachment site 108 at which outrigger plate 78 is configured to overlap with, and be attached to, main plate 76 (see Figures 2 and 5). The attachment site includes at least one of apertures 96, labeled as 96a, which may be the same diameter as other apertures 96 of the main plate, offering a surgeon the option of inserting identical threaded fasteners into bone from the attachment site and other apertures of the main plate, if the surgeon chooses not to use the outrigger plate. Each of apertures 96, including aperture 96a, may have an internal thread that is complementary to an external thread of the same threaded fastener.

[0025] Aperture 96a may have any suitable position within head portion 92 of main plate 76. The aperture may be offset from centerline 98. For example, the through-axis and / or all of aperture 96a may be spaced posteriorly from centerline 98, and / or aperture 96a may be located closer to posterior edge 106 than anterior edge 104. In some embodiments, the main plate may be conceptually divided in a pair of lateral portions each bounded in part by the centerline and a different one of the longitudinal edges of the main plate, and the outrigger plate may overlap only one of the lateral portions when mounted to the main plate. Head portion 92 of the main plate may have at least one other aperture 96 that is spaced distally or proximally from aperture 96a, and / or at least one other aperture 96 that is spaced anteriorly from aperture 96a. Accordingly, the position of aperture 96a may be described as proximal (or distal) and / or posterior within the head portion of the main plate. Attachment site 108 and / or aperture 96a may be defined at least in part by protrusion of the head portion that protrudes laterally with respect to centerline 98.

[0026] The thickness of head portion 92 may decrease at attachment site 108, to reduce the combined thickness of main plate 76 and outrigger plate 78 where they overlap. For example, head portion 92 may define a recess 110 (e.g., a planar recess) in the outer surface of attachment site 108 that is configured to receive part of the outrigger plate (see Figure 5).

[0027] Outrigger plate 78 may have any suitable structure (see Figures 2-4 and 6-8). According to the presently claimed invention, the outrigger plate may has mounting region or head 112 configured to overlap main plate 76 at attachment site 108, with the mounting region disposed over an outer surface of the main plate that faces away from the femur. The mounting region may form a loop 114 through which coupling member 80 extends. The outrigger plate also has a non-overlapping arm or tail 116, which projects transversely away from the main plate at posterior edge 106 thereof. Arm 116 may have a smaller average width than mounting region 112. The arm may be elongated (linearly or non-linearly), and defines a plurality of apertures 118, which may (or may not) be internally threaded, to provide locking attachment to corresponding, externally-threaded fasteners 82b that extend into the femur (also see Figure 1). Apertures 118 of arm 116 of the outrigger plate may (or may not) be smaller in diameter than apertures 96 of the main plate and / or of an aperture 119 of loop 114, such as less than about 80%, 70%, or 60% of the diameter of apertures 96 and / or aperture 119.

[0028] The outrigger plate may have a junction region 120 between mounting region 112 and arm 116 that creates an offset in elevation between these parts of the outrigger plate (see Figures 4 and 7). More particularly, the junction region may bend inward and then slightly outward at positions respectively adjacent and spaced from mounting region 112. With this configuration, once the outrigger plate is mounted on the main plate, the inner (bone-facing) surface of arm 116 may be approximately flush with the inner surface of head portion 92, such that both surfaces can contact the femur.

[0029] Outrigger plate 78 may be curved longitudinally, in the plane of the plate, to avoid a site of muscle attachment on the femur. For example, the outrigger plate may have a curved centerline 121 when projected orthogonally onto a plane parallel to mounting region 112 (see Figures 6 and 8).

[0030] The main plate also defines a lower interface region of an interface at which main plate 76 and outrigger plate 78 grip one another (see Figures 2 and 5-7). The lower interface region is configured to mesh with a complementary, upper interface region defined by mounting region 112, at only a finite series of orientations of plate 78. The interface restricts rotation of the main plate and outrigger plate relative to one another about a central through-axis of the attachment site, after the regions of the interface are tightened against one another with coupling member 80. According to the presently claimed invention, the lower interface region has a plurality of radially-arranged protrusions 122 (see Figure 5) that mesh with corresponding radial indentations 124 defined by the inner surface of mounting region 112 (see Figures 6 and 7). The angular offset of the protrusions (and / or the angular offset of the indentations) from one another determines the increment of angular adjustment permitted by the interface. For example, in the depicted embodiment, the protrusions and indentations provide a 12-degree increment of adjustment at the interface, although any suitable increment of adjustment may be provided. The protrusions and indentations may be formed along any suitable portion of the circumference of respective apertures 96a and 119. According to the presently claimed invention, the protrusions are formed along less than one-half of the circumference of aperture 96a, to simplify manufacturing and reduce the change of breakage of the main plate at attachment site 108. In non-claimed examples, the complementary surface features of the interface may be omitted, such that the interface relies primarily on friction to resist rotational slippage of the main plate and the outrigger plate relative to one another. In these examples, one or both of the surfaces of the interface that face and contact one another may be roughened (e.g., grit blasted) to create a texture that resists slippage.

[0031] Outrigger plate may be firmly mounted to the main plate over a range of orientations. The range may be at least about 25, 30, 35, 40, 45, or 50 degrees, among others. The outrigger plate may overlap none of the other screw-receiving apertures 96 of the head portion, besides aperture 96a, over the range of orientations, thus avoiding obstruction that would prevent placement of screws into these apertures.

[0032] Figures 9 and 10 show coupling member 80 in more detail. The coupling member, which may be described as a set screw, may have an elongated shaft 126 and an enlarged head 128 located at the trailing end of shaft 126. The shaft may have an external thread 130 to engage bone. The coupling member also may have another external thread 132 formed distally on head 128 for threaded engagement with a complementary internal thread of aperture 96a (also see Figure 2). Head 128 may be nonthreaded proximally where the head will be encircled by loop 114 (also see Figure 8). The head further may have a flange 134 at a trailing end thereof. When the coupling member is tightened against the outrigger plate, mounting region 112 of the outrigger plate may be clamped between flange 134 of coupling member 80 and attachment site 108 of main plate 76, to fix the orientation of the outrigger plate. A driver-engagement structure 136 may be defined internally and / or externally by head 128, to allow a driver to rotationally advance the coupling member into operative engagement with plates 76, 78.

[0033] Figures 11-15 show another plate assembly 72' for bone fixation system 50, not according to the presently claimed invention. Plate assembly 72' is similar in structure and function to its unprimed relative (see Figure 2), but differs as follows. First, main plate 76 has an attachment site 108 with protrusions 122 fully encircling the through-axis of aperture 96a. Second, outrigger plate 78 defines indentations 124 that fully encircle aperture 119 of loop 114 (see Figure 12). The presence of more protrusions and indentations than in plate assembly 72 provides more extensive meshing and better purchase at the interface between the plates, while making both plates slightly less sturdy. Third, coupling member 80 of plate assembly 72 is replaced by two separate components, namely, a coupling member 138 and an optional bone screw 140. In some examples, bone screw 140 may be identical to fastener 82b.

[0034] Coupling member 138 is effectively a truncated version of coupling member 80 that is missing shaft 126 (compare with Figure 9), such that coupling member 138 does not extend substantially into bone. The truncated coupling member has external thread 132 for engagement with aperture 96a of the main plate, a nonthreaded region that is encircled by loop 114 of the outrigger plate, and flange 134 (see Figure 13).However, a seating protrusion 142 may be formed on the underside of the flange (and may be included in coupling member 80). The protrusion may be sized to be received in loop 114 of the outrigger plate. The protrusion may function to center aperture 119 of the loop on the central axis of the coupling member as the coupling member is tightened, and, optionally, to engage an edge of aperture 119, to prevent transverse motion of the outrigger plate.

[0035] Coupling member 138 may define any suitable structure for operative engagement with a driver, to allow the coupling member to be turned with the driver. For example, the coupling member may define a transverse slot 144 and a circumferentially distributed arrangement of cutouts 146, which may be complementary to a suitable driver(s) (see Figures 14 and 15). Each cutout 146 may be formed in an internal thread 148 defined by the coupling member. The internal thread may be utilized to lock bone screw 140 to the coupling member after the coupling member has been tightened and the driver removed (also see Figure 11), or coupling member 138 may be assembled with bone screw 140 first, and then the assembly installed as a unit. Bone screw 140 can extend into bone, to secure the main plate and / or the outrigger plate to a region of bone located directly under attachment site 108 of main plate 76.

[0036] Figures 16 and 17 show a longer version of outrigger plate 78 for plate assembly 72 or 72'.II. Methods of Fixing Hoffa Fractures

[0037] This section describes exemplary methods of fixing a femur having at least a Hoffa fracture, with the systems of the present disclosure. The method steps of this section and / or disclosed elsewhere herein, may be performed in any suitable order and combination, using any combination of the devices (and / or device features) of the present disclosure.

[0038] A fractured bone may be selected for fixation. The bone may be a femur 54 that has been fractured to create a Hoffa fracture 52 and, optionally, at least one other fracture in a distal region of the femur. The Hoffa fracture may create any suitable number of condylar bone fragments 68, such as 1, 2, 3, 4, 5, or more. In other examples, the bone may be a humerus having a distal fracture, optionally including a humeral condyle.

[0039] At least one AP fastener 74 may be placed into femur 54. Placement of one or more fasteners 74 may be performed before, after, or both before and after installation of plates 76 and 78. Each fastener 74 may be placed into a pre-drilled hole in the femur, or may be self-drilling to form its own hole. The path followed by each fastener 74 into the femur may be defined by a pre-installed K-wire. For example, the hole for fastener 74 may be drilled around the K-wire, with the K-wire guiding axial travel of a drill. Before drilling and fastener 74 insertion, the path of the K-wire may be visualized with fluoroscopy, to check whether the path will result in proper fastener placement. The fastener may be inserted in an anterior to posterior direction, such that the fastener extends across the Hoffa fracture.

[0040] Main plate 76 may be secured to femur 54 with a plurality of plate fasteners 82a, such as bone screws. Full insertion of plate fasteners 82a into one or more apertures of the main plate may be obstructed by one or more AP fasteners. Accordingly, one or more apertures of head portion 92 may be left unoccupied. In some examples, the main plate may be positioned on the femur and secured, with outrigger plate 78 pre-mounted on the main plate.

[0041] Outrigger plate 78 may be firmly attached to main plate 76 with a coupling member at a selected orientation. The outrigger plate also may be secured to condylar fragment 68 with one or more plate fasteners 82b. At least one fastener 82b may be placed into bone from the coupling member, and may be locked to the coupling member by threaded engagement.III. Composition of System Components

[0042] The plates, coupling member, and fasteners of the present disclosure may have any suitable composition. Each may be formed of any suitable biocompatible material(s) and / or bioresorbable (bioabsorbable) material(s). Illustrative biocompatible materials that may be suitable include (1) metal (for example, titanium or titanium alloy, cobalt-chrome alloy, stainless steel, etc.); (2) polymer / plastic (for example, ultra-high molecular weight polyethylene (UHMWPE), polymethylmethacrylate (PMMA), polytetrafluoroethylene (PTFE), polyetheretherketone (PEEK), and / or PMMA / polyhydroxyethylmethacrylate (PHEMA)); (3) bioresorbable material or polymer / plastic (for example, polymers of α-hydroxy carboxylic acids (e.g., polylactic acid (such as PLLA, PDLLA, and / or PDLA), polyglycolic acid, lactide / glycolide copolymers, etc.), polydioxanones, polycaprolactones, polytrimethylene carbonate, polyethylene oxide, poly-β-hydroxybutyrate, poly-β-hydroxypropionate, poly-δ-valerolactone, poly(hydroxyalkanoate)s of the PHB-PHV class, other bioresorbable polyesters, and / or natural polymers (such as collagen or other polypeptides, polysaccharides (e.g., starch, cellulose, and / or chitosan), any copolymers thereof, etc.)); (4) bone material or bone-like material (e.g., bone chips, calcium phosphate crystals (e.g., hydroxyapatite, carbonated apatite, etc.)); or (5) any combination thereof.

[0043] The main plate and the outrigger plate may be formed of the same or different materials. For example, each may be formed of metal, of the same or different composition.IV. Examples

[0044] The following examples describe further fixation systems and methods of the present disclosure. These examples are intended for illustration only, and should not limit the entire scope of the present disclosure.Example 1. Exemplary Hoffa Fractures and AP Fastener Trajectories

[0045] This example describes further aspects of Hoffa fractures and suitable AP fastener trajectories therefor. Figures 18-21 show respective lateral, posterolateral, anterior, and posterior views of the distal region of a femur, with exemplary Hoffa fracture patterns 52a-c and AP fastener trajectories 150a-c marked. Respective femoral entry sites 152a-c for trajectories 150a-c are shown in Figure 20.Example 2. Testing Fixation Configurations with a Model Femur

[0046] This example describes exemplary test results obtained with a test system 160; see Figure 22.

[0047] System 160 includes a model femur 162 having a Hoffa-like cut 164 that creates a condylar fragment 68. Fixation devices were attached to model femur 162 in various configurations, and then an increasing axial load was applied to the condylar fragment while monitoring the condylar fragment for displacement. This analysis permitted determination of the stiffness and maximum load for each fixation configuration. Figure 22 illustrates a fixation configuration generated with a working model of plate assembly 72 (see Figure 1), a single AP fastener 74, and a rim plate 166 spanning Hoffa-like cut 164. The rim plate may be curved, as depicted, or linear, in plan view.

[0048] Fixation configurations that were tested are listed in the following table: Table 1. Tested fixation configurations Designation Fixation Configuration ATwo AP fasteners 74BTwo AP fasteners 74 + main plate 76COne AP fastener 74 + main plate 76DOne AP fastener 74 + plate assembly 72EOne AP fastener 74 + plate assembly 72 + rim plate 166FPlate assembly 72 + rim plate 166

[0049] The relative strength and stiffness of the configurations were found to be C < A / B < D < E / F, where A is similar to B, and E to F. Accordingly, the use of plate assembly 72 may allow only one AP bone screw to be installed, and the use of plate assembly 72 plus rim plate 166 may allow a surgeon to omit installation of AP bone screws 74 altogether.

Claims

1. A system (50) for fixing a distal femur having a Hoffa fracture (52) creating a condylar fragment, the system (50) comprising: a main plate (76) having an elongated body portion (94) and a head portion (92), wherein the elongated body portion (94) is configured to be secured to a shaft region of the distal femur, wherein the head portion (92) is wider than the body portion (94) and configured to be secured to an end region of the distal femur, and wherein the main plate (76) has a proximal end (100), a distal end (102), and a pair of longitudinal edges opposite one another on the main plate and each extending from the proximal end (100) to the distal end (102) of the main plate; a coupling member (80); an outrigger plate (78) that is shorter, narrower, and thinner than the main plate (76), the outrigger plate (78) having a mounting region (112) and an arm (116), the mounting region (112) being configured to be mounted on the head portion (92) with the coupling member (80) at a rotational position selected from two or more permitted rotational positions of the mounting region (112), such that the outrigger plate (78) extends past one of the longitudinal edges of the main plate (76), wherein the arm (116) defines a plurality of apertures (118) and is configured to be secured to the condylar fragment with fasteners received in the plurality of apertures (118) such that the outrigger plate (78) spans and stabilizes the Hoffa fracture (52); wherein the head portion (92) defines a first aperture (96a) and an upper surface of the head portion (92) of the main plate (76) defines a series of first surface features (122) surrounding less than the full circumference of the first aperture (96a) of head portion (92) and wherein the mounting region (112) defines an aperture (119) and a lower surface of the outrigger plate (78) defines a series of second surface features (124) surrounding less than the full circumference of the aperture (119) and wherein the main plate (76) and the outrigger plate (78) collectively form an interface using the first and second surface features that permits the outrigger plate (78) to be mounted at only a finite series of predefined rotational positions with respect to the main plate (76).

2. The system of claim 1, wherein the coupling member (80) has an external thread (132) that is complementary to an internal thread formed in each of a plurality of apertures (96) defined by the head portion (92) of the main plate (76).

3. The system of any one of claims 1 to 2, wherein the head portion (92) of the main plate (76) defines a plurality of apertures (96) configured to receive bone screws, and wherein the aperture (119) of the outrigger plate (78) is configured to be mounted coaxial to the first aperture (96a) of the head portion (92), and wherein the first aperture (96a) is configured to be spaced proximally or distally on the distal femur from at least one aperture of the plurality of apertures (96) of the head portion (92) and is configured to be spaced posteriorly on the distal femur from at least one aperture of the plurality of apertures (96) of the head portion.

4. The system of claim 3, wherein the plurality of apertures (96) of the head portion (92) have the same diameter as one another.

5. The system of any one of claims 1 to 4, wherein the main plate (76) defines a longitudinal center line (98) that conceptually divides the main plate (76) into a pair of lateral portions each bounded in part by the center line (98) and a different one of the longitudinal edges, and wherein the outrigger plate (78) is configured to overlap only one of the lateral portions when mounted to the main plate (76).

6. The system of any one of claims 1 to 5, wherein the mounting region (112) is wider than the arm (116) and configured to be clamped between the head portion (91) of the main plate (76) and a flange (134) of the coupling member (80), to mount the outrigger plate (78) firmly to the head portion (91) of the main plate (76).

7. The system of any one of claims 1 to 6, wherein the aperture (119) of the mounting region (112) is configured to be aligned coaxially with an aperture (96) of the head portion (91) and to be engaged by the coupling member (80), and wherein the aperture (119) of the mounting region (112) is larger than each aperture of the plurality of apertures (118) of the arm (116).

8. The system of any one of claims 1 to 7, further comprising a further fixation device configured to span the Hoffa fracture (52) independently of the main plate (76) and the outrigger plate (78), without entering any aperture of either plate.

9. The system of claim 8, wherein the further fixation device includes a threaded fastener (88) configured to extend into the distal femur from an anterior side thereof and across the Hoffa fracture (52).

10. The system of any one of claims 1 to 9, wherein the outrigger plate (78) has a curved centerline in an orthogonal projection of the outrigger plate (76) onto a plane parallel to the mounting region (112).