WO2013126744A2 - Side-loading low-profile uniplanar screw and methods of implementation - Google Patents

Abstract

A screw apparatus and a method of implementing a screw apparatus are disclosed. The screw apparatus includes a screw head including a top portion, a base portion, and at least one sidewall portion. The at least one sidewall portion connects the top portion and the base portion. The top portion and the base portion are positioned opposite one another along a longitudinal axis. The top portion, the base portion, and the at least one side wall portion define a recess positioned between the top portion and the base portion. The screw apparatus also includes a screw shaft extending from the base portion of the screw head along the longitudinal axis. The screw shaft is rigidly connected to the screw head. The screw shaft includes a plurality of threads. The screw apparatus includes a mobile-bearing positioned in the recess in the screw head. The mobile-bearing is rotatably coupled to the screw head and includes a rod seat.

Description

SIDE-LOADING LOW-PROFILE UNIPLANAR SCREW AND METHODS

OF IMPLEMENTATION

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims priority to U.S. Provisional Application No.

61/602,380, filed February 23, 2012, entitled "SIDE-LOADING LOW-PROFILE UNIPLANAR SCREW," which application is incorporated herein by reference in its entirety.

TECHNICAL FIELD

[0002] The present embodiments relate generally to a screw apparatus and methods of implementing the same. The present embodiments relate generally to orthopedic devices. More specifically, various inventive embodiments disclosed herein relate to side-loading low-profile uniplanar screws for orthopedic devices that are typically placed within or adjacent to vertebrae (e.g., pedicles). It should be noted, however, that various screw apparatus embodiments disclosed herein may also be used in other orthopedic applications. For example, the screws apparatuses may be used for repositioning fractured bones relative to one another, or used in an external fixator for trauma patients.

BACKGROUND

[0003] During spinal fusion surgery, bone screws may be fixed to adjacent vertebrae and may be interconnected by rods that span the screws to stabilize the spine during the healing process. At other times, the rods may span between the vertebral screws to hooks or clamps that are fixed to another vertebra or rib. The screw heads often include a slot that is intended to receive a rod or connector. The rod may be at least partially secured within the slot by a cap or set screw. The rods interconnecting the bone screws may span one or more vertebral levels (e.g., one to three vertebral levels for a spinal fusion of a degenerative condition, eight to twelve vertebral levels for scoliosis, etc.). Bone screws may be classified as monoaxial, polyaxial, or uniplanar based on their adjustability.

[0004] Monoaxial bone screws are the most simplistic and are not particularly versatile in connection with accommodating screw placement and alignment. The screw head of a monoaxial screw allows adjustment to the rod only in the direction perpendicular to the longitudinal axis of the screw. When the rod is secured in the slot of the monoaxial bone screw, the longitudinal axis of the rod is substantially perpendicular (i.e., at a 90° angle to) to the longitudinal axis of the monoaxial bone screw.

[0005] Polyaxial screws are commonly used to overcome the variations in screw placement and alignment. The relationship between the screw axis and the rod axis in a polyaxial screw may be variable but may still be locked in place (e.g., the screw head of a polyaxial screw may be configured to swivel approximately 20° off the screw axis when unlocked). This adjustability allows rods to be connected to multiple screws that may be placed medial or lateral to one another and permits lordotic and kyphotic spinal alignments. Conventional polyaxial screws are typically larger and bulkier than monoaxial screws (e.g., because of the structures that provide for the screw head of a polyaxial screw to swivel).

[0006] Uniplanar screws have screw heads that may deviate from the screw axis, such screws being configured for movement in one plane of the rod; they typically do not adjust to medial or lateral rod positions (like polyaxial screws). This type of screw is more commonly used in scoliosis surgery where there may be a degree of cranial or caudal angulation (such as the sagittal plane of the spine), but where there is little medial lateral screw placement deviation and the surgeon additionally needs rigid control of the screw to manipulate it in the coronal and axial plane of the spine. Similar to polyaxial screws, uniplanar screws generally are large and bulky because of the configuration of their single plane swivel mechanism.

[0007] Because many scoliosis patients are children or smaller-sized adults and because many scoliosis fusions are performed in the kyphotic thoracic spine with less soft tissue coverage, the larger, bulkier polyaxial and uniplanar screws may cause pain and irritation to the patient. In some cases, the pain and irritation may rise to the level where a second surgery to remove the screws and rods is necessary.

[0008] Some orthopedic screws for attachment to the vertebrae, have a slot in the side of the screw head. These screws are generally referred to as side-opening screws such that a connector, such as a rod, enters through the side instead of the top of the screw head. Side-opening screws are commonly used in spinal fixation systems that are laterally based (i.e. systems where rib fixation is needed). Side-opening screws typically have a lower profile than the other screws. [0009] Disadvantages result with conventional side-opening screws. Side-opening screws may have less adjustability than other screws, such as top-opening screws, but typically have a lower profile than the other screws. Side-opening screws tend to be more bulky than other screws and, therefore, may cause pain and irritation to patients. Some conventional side-opening low-profile bone screws are highly constrained because they behave like monoaxial bone screws; they only allow the rod to slide in the direction perpendicular to the longitudinal axis of the screw. Other conventional side -opening screws have a swivel opposite to the shaft of the screw head. The swivel allows the rod to rotate within the screw head similar to a conventional uniplanar screw. Disadvantages result because the swivel rotates toward an apex of converging surfaces of the rod and screw head, thereby reducing the allowable angular force or mechanical moment applicable to a rod in a desired direction of rod rotation. Converging surfaces are areas where there is no gap between the rod and the screw head.

SUMMARY

[0010] The inventor has appreciated that inventive embodiments disclosed herein provide a screw apparatus and methods of implementing the same.

[0011] Accordingly, various exemplary embodiments disclosed herein provide a screw apparatus including a screw head including a top portion, a base portion, and at least one sidewall portion. The at least one sidewall portion connects the top portion and the base portion. The top portion and the base portion are positioned opposite one another along a longitudinal axis. The top portion, the base portion, and the at least one side wall portion define a recess positioned between the top portion and the base portion. The screw apparatus also includes a screw shaft extending from the base portion of the screw head along the longitudinal axis. The screw shaft is rigidly connected to the screw head. The screw shaft includes a plurality of threads. The screw apparatus includes a mobile-bearing positioned in the recess in the screw head. The mobile -bearing is rotatably coupled to the screw head and includes a rod seat.

[0012] In various embodiments, the recess is configured in the screw head for side-loading of the rod into the recess, whereby the rod is movable into the recess through lateral motion of the rod in a direction orthogonal to a surface of the sidewall.

[0013] The screw apparatus includes a rod-securing element coupled to the screw head in accordance with various embodiments. [0014] The shaft and the screw head may be integrally connected as a unitary structure.

[0015] The mobile -bearing includes a convex surface engaging a concave surface of the base portion of the screw head within the recess, in accordance with various embodiments.

[0016] The mobile-bearing may include a convex surface engaging a surface of the base portion having a flat portion within the recess.

[0017] In various embodiments, the mobile -bearing is rotatably coupled for uniplanar rotation.

[0018] The mobile-bearing may be trans latably coupled to the screw head, in accordance with various embodiments.

[0019] The mobile-bearing may be rotatably coupled to the screw head via a pin extending from the mobile-bearing into an opening in the sidewall portion of the screw head.

Alternatively, the mobile-bearing may be rotatably coupled to the screw head via a pin extending from the sidewall into an opening in the mobile-bearing.

[0020] In various embodiments, the opening includes a frustoconical shape.

[0021] In various embodiments, the mobile-bearing is translatably coupled to the screw head via a pin extending from the mobile-bearing into an elongated opening in the base portion of the screw head.

[0022] The mobile-bearing is rotatably coupled to the screw head via a pin extending from the base portion into an elongated opening in the mobile-bearing, in accordance with various embodiments.

[0023] The mobile-bearing may be rotatably coupled for rotation in the range of 0 to 20 degrees.

[0024] The rod seat of the mobile-bearing may include a concave surface configured to receive a rod having a curved peripheral wall.

[0025] In various embodiments, the rod-securing element is removably coupled to the top portion of the screw head via a threaded aperture in the top portion of the screw head.

[0026] The rod-securing element may include a fulcrum configured for engaging a rod positionable in the rod seat.

[0027] The rod-securing element may include a keyed recess for engagement with a tool shaped to fit the keyed recess for removably coupling the rod-securing element to the screw head. [0028] In various embodiments, the screw apparatus includes a rod positioned in the rod seat, the rod extending through the recess such that the rod traverses the longitudinal axis.

[0029] The side wall may extend less than 180 degrees around the longitudinal axis.

[0030] In various embodiments, the screw head includes a tool engagement feature in the screw head, wherein the tool engagement feature shaped for mating engagement with a tool configured to apply torque to the screw head. The tool engagement feature may include a plurality of flats disposed on opposing surfaces of the screw head.

[0031] In some embodiments, the mobile-bearing is asymmetrical and may include a J- shaped geometry. In some embodiments the mobile-bearing is symmetrical and may include a U-shaped geometry.

[0032] Various exemplary embodiments provide a method of implementing a screw apparatus. The method includes rotatably coupling a mobile-bearing to a screw head. The mobile -bearing includes a rod seat, the screw head includes a top portion, a base portion, and at least one sidewall portion. The at least one sidewall portion connects the top portion and the base portion. The top portion and the base portion are positioned opposite one another along a longitudinal axis. The top portion, the base portion, and the at least one side wall portion define a recess positioned between the top portion and the base portion. The screw head includes a screw shaft extending from the base portion of the screw head along the longitudinal axis. The screw shaft is rigidly connected to the screw head. The screw shaft includes a plurality of threads. The mobile-bearing is positioned in the recess. The method also includes positioning a rod in the rod seat of the mobile -bearing such that the rod extends through the recess such that the rod traverses the longitudinal axis. The method further includes coupling a rod-securing element to the screw head such that the rod-securing element engages the rod positioned in the rod seat.

[0033] In various embodiments, the method includes rotatably adjusting the position of the mobile-bearing before coupling the rod-securing element to the screw head.

[0034] In various embodiments, coupling the rod-securing element to the screw head includes engaging the rod positioned in the rod seat such that the mobile-bearing is immobile.

[0035] Positioning the rod in the rod seat may include side-loading the rod into the recess, whereby the rod is positioned into the recess through lateral motion of the rod in a direction orthogonal to a surface of the sidewall. [0036] It should be appreciated that all combinations of the foregoing concepts and additional concepts discussed in greater detail below (provided such concepts are not mutually inconsistent) are contemplated as being part of the inventive subject matter disclosed herein. In particular, all combinations of claimed subject matter appearing at the end of this disclosure are contemplated as being part of the inventive subject matter disclosed herein.

BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The skilled artisan will understand that the drawings primarily are for illustrative purposes and are not intended to limit the scope of the inventive subject matter described herein. The drawings are not necessarily to scale; in some instances, various aspects of the inventive subject matter disclosed herein may be shown exaggerated or enlarged in the drawings to facilitate an understanding of different features. In the drawings, like reference characters generally refer to like features (e.g., functionally similar and/or structurally similar elements).

[0038] Figure 1 is an exploded view of a side-loading low-profile, uniplanar bone screw in accordance with an exemplary inventive embodiment.

[0039] Figure 2A is a side elevated view of a portion of the screw of Figure 1 without a rod.

[0040] Figure 2B is a side view of the screw of Figure 2A.

[0041] Figure 2C is a front view of the screw of Figure 2 A.

[0042] Figure 2D is a top view of the screw of Figure 2A.

[0043] Figure 3 A is a cross-sectional view of the screw of Figure 2C taken along line 3A-3A.

[0044] Figure 3B is a cross-sectional view of the screw of Figure 2D taken along line 3B-3B.

[0045] Figure 4A is a side elevated view of a portion of the screw of Figure 1 with the rod at a 0° angle to a lateral axis of the screw.

[0046] Figure 4B is a side view of the screw of Figure 4A.

[0047] Figure 4C is a front view of the screw of Figure 4 A.

[0048] Figure 4D is a top view of the screw of Figure 4A.

[0049] Figure 5 A is a cross-sectional view of the screw of Figure 4D taken along line 5A- 5A. [0050] Figure 5B is cross-sectional view of the screw of Figure 4D taken along line 5B-5B.

[0051] Figure 6A is a side elevated view of the screw of Figure 1 with the rod at a 10° angle to the lateral axis of the screw.

[0052] Figure 6B is a side view of the screw of Figure 6A.

[0053] Figure 6C is a front view of the screw of Figure 6A.

[0054] Figure 6D is a top view of the screw of Figure 6A.

[0055] Figure 7A is a cross-sectional view of the screw of Figure 6D taken along line 7A- 7A.

[0056] Figure 7B is cross-sectional view of the screw of Figure 6D taken along line 7B-7B.

[0057] Figure 8 is an exploded view of a side-loading low-profile, uniplanar bone screw.

[0058] Figure 9A is a side elevated view of a portion of the screw of Figure 8 with the rod at a 0° angle to a lateral axis of the screw.

[0059] Figure 9B is a side view of the screw of Figure 9A.

[0060] Figure 9C is a front view of the screw of Figure 9 A.

[0061] Figure 9D is a top view of the screw of Figure 9A.

[0062] Figure 10A is a cross-sectional view of the screw of Figure 9D taken along line 10A- 10A.

[0063] Figure 10B is cross-sectional view of the screw of Figure 9D taken along line 10B- 10B.

[0064] Figure 11A is a side elevated view of the screw of Figure 8 with the rod at a 10° angle to the lateral axis of the screw.

[0065] Figure 1 IB is a side view of the screw of Figure 11 A.

[0066] Figure 11C is a front view of the screw of Figure 11A.

[0067] Figure 1 ID is a top view of the screw of Figure 11A.

[0068] Figure 12A is a cross-sectional view of the screw of Figure 1 ID taken along line 12A-12A. [0069] Figure 12B is cross-sectional view of the screw of Figure 1 ID taken along line 12B- 12B.

[0070] Figure 13A is a cross-sectional view of a screw head in accordance with an exemplary inventive embodiment.

[0071] Figure 13B is a cross-sectional view of a screw head when the mobile-bearing has rotated.

[0072] The features and advantages of the inventive concepts disclosed herein will become more apparent from the detailed description set forth below when taken in conjunction with the drawings.

DETAILED DESCRIPTION

[0073] Following below are more detailed descriptions of various concepts related to, and embodiments of, inventive apparatuses and methods for a screw apparatus. It should be appreciated that various concepts introduced above and discussed in greater detail below may be implemented in any of numerous ways, as the disclosed concepts are not limited to any particular manner of implementation. Examples of specific implementations and applications are provided primarily for illustrative purposes.

[0074] Referring generally to the Figures, various embodiments of a bone screw apparatus are shown. The bone screw apparatus in accordance with various inventive embodiments includes a side-loading low-profile uniplanar bone screw. The side-loading low-profile uniplanar bone screw may be referred to herein as a side-opening low-profile bone screw, a bone screw, screw, or screw apparatus. The bone screw includes a mobile-bearing. The mobile- bearing is configured to be movable relative to the main body of the bone screw and, thereby, permits adjustments of a rod disposed therein within at least a single plane. Stated otherwise, by using the mobile-bearing, the head of the bone screw or screw head in accordance with inventive embodiments disclosed herein need not be movable with respect to the screw shaft in order to provide for uniplanar adjustment of the rod relative to the screw apparatus. Because the head of the bone screw does not need to be movable with respect to the screw shaft, the screw apparatus can be configured to be smaller and less bulky, thereby decreasing the likelihood of pain and irritation to a patient. Accordingly, the mobile-bearing allows for the screw to be less bulky than conventional side-opening monoaxial, polyaxial and uniplanar bone screws, while still providing uniplanar movement of the rod relative to the bone screw (e.g., cranial or caudal angulation of the rod axis relative to the screw axis).

[0075] Referring to Figures 1-7B, a side-loading low-profile uniplanar bone screw or screw apparatus 1, for adjusting a position of a rod 2, includes a main body 4, a mobile-bearing 16 and a rod-securing element 8. The bone screw 1 is a bone screw apparatus that is configured to provide adjustability, including rotation and translation in various embodiments, of the rod 2 in a single plane, as will be discussed in more detail herein.

[0076] The main body 4 includes a screw shaft 22. Shaft 22 extends from base portion 46 of screw head 14. Shaft 22 include a threaded portion having a plurality of threads in accordance with various embodiments (the threaded portion of the shaft is not shown in Figures 2A-7B). The threaded portion of the shaft 22 is located at or proximate to a first end 28 of the bone screw 1 , generally opposite a second end 30 of the bone screw 1. The threaded portion is intended to be at least partially received within a bore (hole, cavity, etc.) formed in a person's bone. The bone may be any suitable bone, such as the spine. The threads of the threaded portion are configured to threadably engage the bore to secure the main body 4 to the spine.

[0077] The main body 4 also includes a screw head 14 that extends from the shaft 22 and is located at or proximate to the second end 30 of the bone screw 1. The main body 4 generally defines a longitudinal screw axis 26-26 of the bone screw 1. The screw head 14 includes at least one sidewall 65 connecting base portion 46 to top portion 45 and may include a plurality of sides, such as first side 61, a second side 62, a third side 63 and a fourth side 64. The first side 61 has a first opening 41 (Figures 1, 2A and 4A). The second side 62 is directly adjacent to the first side 61 and has a second opening 42 (Figures 1, 2 A and 4A). The third side 63 is directly adjacent the second side 62 and parallel to the first side 61. The third side 63 has a third opening 43 (Figures 1, 2 A and 4A). The fourth side 64 is directly adjacent to the first and third sides 61, 63 (Figures 1, 2A and 4A). The fourth side 64, including sidewall portion 65, generally has no opening (Figures 1, 2A and 4A). The opening s 41, 42, and 43 which are bounded by top portion 45, base portion 46, and side wall 65 define a slot or recess 66 positioned between top portion 45 and base portion 46. The second opening 42 is configured to receive the rod 2 such that the rod 2 may enter the screw head 14 through the second opening 42. The first and third openings 41, 43 are large enough to receive the rod 2 once the rod 2 enters the screw head 14 through the second opening 42. While the rod 2 may be introduced into recess 66 of screw head 14, for example via side loading or laterally moving rod 2 in a direction orthogonal to an internal surface 67 of sidewall 65, the rod 2 may also enter the screw head 14 through the first and/or third openings 41, 43, for example via axial motion of rod 2 with respect to a longitudinal axis of rod 2. (i.e. along axis 197 in Figure 1).

[0078] Screw head 14 may include top side or top portion 45 and bottom side or base portion 46 (Figure 1). The top side 45 may include an opening 7 (Figures 2A and 4A) for receiving the rod-securing element 8. The outer circumference 47 of the top side 45 may be annular or a continuously extending circumference 47 (i.e. the outer circumference 47 has no gaps or holes), such that when the rod-securing element 8 is received in the opening 7, the rod-securing element 8 is securely fastened to the screw head 14. Opening 7 may be a threaded opening having internal threads 21 and rod-securing element 8 may have corresponding external threads 20 for secure engagement with threads 21 in opening 7. Such a secure engagement and connection is generally distinct from top-loading screws having a top side with a semi-annular, semi-circular, or discontinuously extending outer circumference (i.e. the outer circumference has gaps or holes, such that the outer circumference may have) such that the rod-securing element is less engaged and/or less secure in comparison to a rod-securing element engaged with an annular or circumferential opening as shown and described herein in connection with various embodiments. The bottom side 46 of the screw head 14 connects the screw head 14 to the shaft 22. Shaft 22 may be integrally connected to base portion 46 of screw head 14 as a unitary structure. The rigid or immobile connection of base portion 46 and screw shaft 22 advantageously permits screw 1 to be provided in a lower profile form than that of a screw capable of handling similar loads in a form where the screw head is mobile or adjustable with respect to the screw shaft.

[0079] The screw head 14 may include a bottom surface 31 (Figures 3B, 5A-5B and Figure 7A). The bottom surface 31 in recess 66 is configured to at least partially receive the mobile- bearing 16 and to allow for movement of the mobile-bearing 16 relative to the main body 4. The bottom surface 31 supports and abuts the mobile-bearing 16 after the bottom surface 31 at least partially receives the mobile-bearing 16. The bottom surface 31 may be substantially curved. For example, the bottom surface 31 may include a substantially concave portion or recess 37 from back to front and side to side (Figures 1, 2A-2B, 3B, 4A-4B, 5B, 6A-6B and 7B). The substantially concave portion 37 is configured to facilitate movement of the mobile-bearing 16 relative to the main body 4. Alternatively, the bottom surface 31 may not be curved. For example, the bottom surface may be substantially flat from back to front and side to side (not shown). The substantially flat bottom leads to a decreased range of rotational motion of the mobile-bearing relative to the rod-securing element when compared to the range of rotational motion for a substantially curved bottom surface. Alternatively, the bottom surface 31 may be substantially curved in one direction and substantially flat in another (not shown). Screw head 14 may also include one or more flats 49 or recesses configured for engagement by a tool for applying torque to screw 1 during engagement of the screw with a bone.

[0080] The mobile-bearing 16 moves away from an apex or contact point 145 (Figure 7A) of the rod 2 and the surface 31 of the screw head 14 and is positioned at a diverging region 146 (Figures 6A, 6C and 7A) of the screw head 14, thereby allowing for a greater angular force or mechanical moment to be applied to the rod 2 in a desired direction of rod rotation than that of conventional side-opening screws. The diverging region 146 of the screw head 14 is located at the bottom surface 31 of the screw head 14 and is an area defined by a gap between the rod and the screw head. The contact point 145 is defined by a location at which the rod contacts the surface 31 of screw head 14 when rod 2 rotates with mobile-bearing 16. Generally, there are two contact points.

[0081] The mobile-bearing 16 comprises a swing or rod seat 16 (Figure 1) that is configured to receive the rod 2. Rod seat 16 may include a concave surface configured to receive a rod, such as rod 2, having a curved peripheral wall. The mobile-bearing 16 includes a front side 81, a back side 82, and first and second sides 83, 84 that connect the front side 81 to the back side 82. The front side 81 may be flush with or slightly below a top surface 48 (Figure 1) of the second side 62 when the mobile-bearing 16 is received in the screw head 14 such that the front side 81 of the mobile-bearing 16 does not interfere with or prevent the screw head 14 from receiving the rod 2. The front side 81 is substantially parallel to the back side 82. The back side 82 extends above the top surface 48 in the illustrated embodiment such that the mobile -bearing 16 has an asymmetrical profile forming a J-shaped geometry or profile. As illustrated herein, some embodiments of the mobile-bearing (e.g. mobile-bearing 116 shown in Figure 8) may include a front side and back side having substantially the same height providing a symmetrical profile, such that the mobile-bearing has a U-shaped geometry or profile. [0082] The back side 82 of the mobile -bearing 16 includes an opening 17. The opening 17 receives a pin 9 that is configured to couple the mobile-bearing 16 to the screw head 14. When the mobile-bearing 16 is coupled to the screw head 14, a bottom surface 52 of the rod 2 abuts surface 99 of the mobile-bearing 16 and the mobile-bearing 16 abuts the bottom surface 31 of the screw head 14 (Figure 5B). The pin 9 is configured to be received in an opening 77 in the fourth side 64 of the screw head 14 (Figures 3B and 5B). The pin 9 helps guide or facilitate movement of the mobile-bearing 16 relative to the main body 4 and may serve as an axis of rotation 56-56 about which the mobile-bearing 16 rotates. When the mobile-bearing 16 is moved relative to the main body 4, the interaction of the pin 9 with the openings 17, 77 causes the mobile-bearing 16 to move in a desired path. This path is in a plane 97-97 (Figure 4C) corresponding to or substantially parallel to the plane in which the rod 2 is adjustable.

[0083] The mobile-bearing 16 is configured to tilt relative to the longitudinal axis 26-26 and a lateral axis 27-27 of the bone screw 1. The lateral axis 27-27 is perpendicular to the longitudinal axis 26-26. The pin 9 allows the mobile-bearing 16 to tilt relative to the

longitudinal and/or lateral axes 26-26, 27-27 as the rod 2 tilts relative to the rod-securing element 8.

[0084] The diameter of the openings 17, 77 may be substantially the same size as or larger than the diameter of the pin 9. When the diameter of the openings 17, 77 is substantially the same size as the diameter of the pin 9, the pin 9 moves very little if at all with respect to the longitudinal and/or lateral axes 26-26, 27-27 of the screw head 14. When the diameter of the openings 17, 77 is larger than the diameter of the pin 9, the mobile -bearing may move a great deal with respect to the longitudinal and/or lateral axes 26-26, 27-27 to facilitate translational and/or rotational motion of the mobile-bearing. The wider the diameter of the openings 17, 77 relative to the diameter of the pin 9, the greater the maximum degree of rotation for the rod 2 about an axis 56-56 (Figure 3A), which is substantially perpendicular or perpendicular to the longitudinal and lateral axes 26-26, 27-27, and the more the rod 2 can translate. Consequently, a greater degree of bearing 16 displacement upon the bottom surface 31 occurs, which results in greater stress and friction between bearing 16 and bottom surface 31 to give secure fixation of mobile-bearing 16 when the rod-securing element 8 is tightened in the opening 7 to engage rod 2. [0085] The mobile-bearing 16 facilitates rotation of the rod 2 about the rod-securing element 8 when the mobile-bearing 16 moves relative to the main body 4. When a lateral axis 197-197 (Figure 1) of the mobile-bearing 16 is aligned with the lateral axis 27-27 of the bone screw 1 and substantially perpendicular to and centered along the longitudinal axis 26-26 of the bone screw 1 (Figures 4A-5B), such that the rod 2 is at a substantially 0° angle 30 to the lateral axis 27-27, the rod 2 does not rotate about the rod-securing element 8 (i.e. the rod 2 is in the neutral position). When the lateral axis 197-197 is not aligned with the lateral axis 27-27 (Figures 6A-7B), such that the rod is at a non-zero angle 30 to the lateral axis 27-27 (i.e. the rod is adjusted within the plane to be at an angle 30 to the neutral position), the rod 2 rotates about the rod-securing element 8. Specifically, the rod 2 rotates about a tip 18 (e.g. fulcrum) of the rod-securing element 8. As shown in Figures 6A-7B the rod 2 is at a substantially 10° angle 30 to the lateral axis 27-27.

[0086] The amount the rod 2 can rotate depends on the position of the center of the mobile- bearing 16 relative to the longitudinal axis 26-26, which extends through the fulcrum 18 of rod- securing element 8. Additional factors influencing rod rotation are the height 96 of the mobile- bearing 16 as measured from the bottom surface 31 of the mobile-bearing 16 to the top surface 99 of the mobile-bearing 16 relative to the size of the side openings 41, 43 (Figures 3B and 5B). The angle of rotation 30 may range from substantially 0° to substantially 20° (degrees) where the maximum angle of rotation 30 ranges from substantially 12° to substantially 20°. Preferably, the maximum angle of rotation 30 is substantially 15° and the minimum angle of rotation is substantially 0°.

[0087] The mobile-bearing 16 may include a substantially convex portion 86 that generally corresponds to the shape of the substantially concave portion 37 of the screw head 14. The substantially convex portion 86 and the substantially concave portion 37 may be substantially elongated from front-to-back and from side to side. This elongation facilitates translational movement of the mobile-bearing 16 relative to the main body 4, allowing the mobile-bearing 16 to function in a sled or cradle-like manner. This configuration also allows relatively large portions of the surface of the mobile-bearing and screw-head to remain in contact after an adjustment of the position of the mobile-bearing 16 relative to the main body 4. This may be particularly beneficial once the rod 2 is secured relative to the screw 1 because the friction between the substantially concave portion 37 and the substantially convex portion 86 can help maintain the rod 2 in a desired position relative to the main body 4. Accordingly, the interaction between the portions 37, 86 facilitates rotational (e.g., pivotal) movement of the mobile-bearing 16 relative to the main body 4. This configuration also allows for a lower profile of the screw 1 than if the bottom surface of the screw head was substantially flat.

[0088] The rod-securing element 8 is configured to secure the rod 2 between the mobile- bearing 16 and the rod-securing element 8 and relative to the screw head 14. The rod-securing element 8 abuts the rod 2 when the rod-securing element 8 secures the rod 2. Preferably, the rod- securing element 8 abuts a top surface 51 (Figure 5 A) of the rod 2 when the rod-securing element 8 secures the rod 2. The rod-securing element 8 may comprise a set screw that engages the rod 2.

[0089] The rod-securing element 8 includes an engagement feature 91, such as keyed recess for receiving a tool such as a hex key (Figures 2D and 4D) that allows the rod-securing element 8 to be secured relative to the screw head 14 before the mobile-bearing 16 moves within the screw head 14. The engagement feature 91 may be an opening in the rod-securing element 8 that is configured to be engaged by a tool to facilitate rotation within, and thereby securing of, the rod- securing element 8 to the screw head 14.

[0090] The rod-securing element 8 includes a fulcrum 18 (Figure 1). The fulcrum 18 abuts the rod 2 when the rod-securing element 8 secures the rod 2. The fulcrum 18 applies a force to the rod 2 that helps maintain the rod 2 in a desired position when the rod-securing element 18 secures the rod 2 because the fulcrum 18 abuts and presses on the rod 2. The fulcrum 18 may comprise a conical-shape. The taper 19 of the fulcrum 18, when the fulcrum 18 comprises a conical shape, is preferably the portion of the fulcrum 18 that abuts the rod 2. The taper 19 may be pointed (Figures 1, 2A, 2C, 3A-3B, 4A, 4C, 5A-5B, 6C and 7A-7B) or curved (not shown). The curved fulcrum helps prevent the fulcrum from damaging the rod, but allows for a smaller maximum degree of rotation of the rod than the pointed fulcrum. The rod 2 rotates about the fulcrum 18. The rod 2 may rotate about the fulcrum 18 when the mobile-bearing 16 translates and/or rotates.

[0091] The fulcrum 18 may be in line with a top surface of the opening 17 (Figures 2B-2C, 3B, 4B-4C, 5A-5B, 6C and 7A-7B) or spaced a distance from a top surface of the opening 17. When the fulcrum 18 is in line with the top surface of the opening 17, the rod 2 moves fairly little to not at all with respect to the fulcrum in a direction parallel to the lateral axis 27-27 of the screw head 14. In contrast, when the fulcrum is spaced a distance from a top surface of the opening 17, the rod 2 moves easily with respect to the fulcrum in a direction parallel to the lateral axis 27-27 of the screw head 14.

[0092] Referring to Figures 8-12B, a side-loading low-profile bone screw 101 is shown that is substantially similar to the bone screw 1 of Figures 1-7B. In contrast to the bone screw 1, however, the bone screw 101 includes a mobile-bearing 116 that comprises a sliding rod support or rod seat and the screw head 114 includes an opening 137 instead of opening 77.

[0093] Like the mobile-bearing 16, the mobile -bearing 116 moves away from an apex 145 (Figure 12 A) of the rod 2 and the surface 31 of the screw head 114 and is positioned at a diverging region 146 (Figures 11 A and 12A) of the screw head 114, thereby allowing for a greater angular force or mechanical moment to be applied to the rod 2 in a desired direction of rod rotation than that of conventional side-opening screws. Also, like the mobile -bearing 16, the diverging region 146 of the screw head 114 is located at the bottom surface 31 of the screw head 114 and is an area defined by a gap between the rod and the screw head. Also like the mobile- bearing 16, the apex 145 is an area defined by where the rod contacts the screw head when the rod rotates. Generally, there are two apexes.

[0094] The mobile-bearing 116 comprises a sliding rod support (Figure 8) that is configured to receive the rod 2. The mobile-bearing 116 includes a front side 181, a back side 182, and first and second sides 183, 184 that connect the front side 181 to the back side 182. The front, back, first and second sides 181, 182, 183, 184 may be flush or slightly below the top surface 48 of the screw head 114 such that the front, back, first and second sides 181, 182, 183, 184 do not interfere or prevent the screw head 114 from receiving the rod 2. The front side 181 may be substantially parallel to the back side 182 and the first side 183 may be substantially parallel to the second side 184. The front side 181 generally is level with and, therefore, does not generally extend above the top surface 48 once the mobile-bearing 116 is received in the screw head 114.

[0095] The front side 181 of the mobile-bearing 116 may include a slot or elongated opening 117 for receiving a pin 127 (Figures 10A and 12A). The slot 117 may be any suitable width or length. Preferably the slot 117 is wider and higher than the outer diameter of the pin 127 so that the pin 127 can slide within the slot 117, thereby allowing the sliding rod support 116 to move in a direction parallel and perpendicular to the lateral axis 27-27 to facilitate translational and/or rotational motion. Alternatively, the width and height of the slot may be substantially the size of the diameter of the pin so that the pin moves very little if at all with respect to the lateral axis of the screw head. The wider the width of the slot relative to the diameter of the pin, the greater the maximum degree of rotation for the rod about axis 26-26 and the more the rod 2 can translate. The width and height of the slot 117 may each be between substantially 3 - 6 mm. When the mobile-bearing 116 is moved relative to the main body 4, the interaction of the pin 127 with the slot 117 causes the mobile-bearing 116 to move in a desired path. This path is in the plane 97-97 corresponding to or substantially parallel to the plane in which the rod 2 is adjustable.

[0096] The mobile-bearing 116 is configured to tilt relative to the longitudinal axis 26-26 and lateral axis 27-27 of the bone screw 101. The pin 127 allows the mobile-bearing 116 to tilt relative to the longitudinal and/or lateral axes 26-26, 27-27 as the rod 2 tilts relative to the rod- securing element 8.

[0097] The mobile-bearing 116 facilitates rotation of the rod 2 about the rod-securing element 8 when the mobile -bearing 116 moves relative to the main body 4. When the lateral axis 197-197 (Figure 9 A) of the mobile-bearing 116 is aligned with the lateral axis 27-27 of the bone screw 101 and substantially perpendicular to and centered along the longitudinal axis 26-26 of the bone screw 101 (Figures 9A-10B), such that the rod 2 is at a substantially 0° angle 30 to the lateral axis 27-27, the rod 2 does not rotate about the rod-securing element 8 (i.e. the neutral position). When the lateral axis 197-197 is not aligned with the lateral axis 27-27 (Figures 11A- 12B), such that the rod is at a non-zero angle 30 to the lateral axis 27-27 (i.e. the rod is adjusted within the plane to be at an angle 30 to the neutral position), the rod 2 rotates about the rod- securing element 8. As shown in Figures 11A-12B the rod 2 is at a substantially 10° angle 30 to the lateral axis 27-27.

[0098] The amount the rod 2 rotates depends on the position of the center of the mobile- bearing 116 relative to the axis 26-26 which extends through the fulcrum 18 of the rod-securing element 8. Additional factors influencing rod rotation are the height 196 (Figures 10B) of the mobile -bearing 116 as measured from the bottom surface 31 of the screw head 14 to the surface 199 of the mobile-bearing 116 relative to the size of the side openings 41, 43 (Figure 10B). The angle of rotation 30 may range from substantially 0° to substantially 20° where the maximum angle of rotation 30 ranges from substantially 12° to substantially 20°. Preferably, the maximum angle of rotation 30 is substantially 15° and the minimum angle of rotation 30 is substantially 0°.

[0099] Like the mobile-bearing 16 of Figures 1-7B, the mobile -bearing 116 may include a substantially convex portion 186 (Figure 8) that generally corresponds to the shape of the substantially concave portion 37 of the screw head 114. The substantially convex portion 186 may be substantially elongated from front-to-back and from side to side. This elongation facilitates translational movement of the mobile-bearing 116 relative to the main body 4, allowing the mobile-bearing 116 to function in a sled or cradle-like manner. This configuration also allows relatively large portions of the surface of the mobile-bearing and screw-head to remain in contact after an adjustment of the position of the mobile-bearing 116 relative to the main body 4. This may be particularly beneficial once the rod 2 is secured relative to the screw 101 because the friction between the substantially concave portion 37 and the substantially convex portion 186 can help maintain the rod 2 in a desired position relative to the main body 4. Accordingly, the interaction between the portions 37, 186 facilitates rotational (e.g., pivotal) movement of the mobile-bearing 116 relative to the main body 4. This configuration also allows for a lower profile of the screw 101 than if the bottom surface of the screw head was

substantially flat.

[00100] The pin 127 is configured to be received in an opening 137 (Figures 10B and 12B) of the screw head 114 so that the pin 127 connects the mobile-bearing 116 to the screw head 114. The opening 137 may extend from the second side 62 of the screw head 114 to the fourth side 64 of the screw head 114 (Figures 10B and 12B).

[00101] While Figures 8-12B, relate to a mobile-bearing 1 16 having a slot 117 and the screw head 114 having an opening 137, the screw head may include the slot and the mobile-bearing may include the opening.

[00102] Referring to Figures 13A-13B, the shape of the opening 217 in the back side of the mobile-bearing 217 may differ from the shape of the opening 17 of Figures 1-7B. Unlike Figures 1-7B where the opening 17 is substantially cylindrical or cylindrical shaped, the opening 217 may be substantially frustoconical or frustoconical shaped such that the mobile -bearing 216 may rotate substantially 2-8° more than the mobile-bearing 16 of Figures 1-7B. The additionally rotation of the mobile-bearing, is especially beneficial when a rod connects to multiple screw heads.

[00103] The frustoconical shape allows the mobile-bearing 216 to rotate about axis 26-26 and plane 226-226, which is perpendicular or substantially perpendicular to the axis 26-26. When the shape of the opening 217 is substantially frustoconical or frustoconical shaped, the mobile- bearing 216 may be about 10% smaller than mobile-bearing 16 or the screw head 214 may be about 10% larger than screw head 14. Alternatively, the opening in the back side of the mobile- bearing may be another shape, such as substantially triangular or triangular shaped.

[00104] As utilized herein, the terms "approximately," "about," "substantially" and similar terms are intended to have a broad meaning in harmony with the common and accepted usage by those of ordinary skill in the art to which the subject matter of this disclosure pertains. It should be understood by those of skill in the art who review this disclosure that these terms are intended to allow a description of certain features described without restricting the scope of these features to the precise numerical ranges provided. Accordingly, these terms should be interpreted as indicating that insubstantial or inconsequential modifications or alterations of the subject matter described and are considered to be within the scope of the disclosure.

[00105] It should be noted that the term "exemplary" as used herein to describe various embodiments is intended to indicate that such embodiments are possible examples,

representations, and/or illustrations of possible embodiments (and such term is not intended to connote that such embodiments are necessarily extraordinary or superlative examples).

[00106] For the purpose of this disclosure, the term "coupled" means the joining of two members directly or indirectly to one another. Such joining may be stationary or moveable in nature. Such joining may be achieved with the two members or the two members and any additional intermediate members being integrally formed as a single unitary body with one another or with the two members or the two members and any additional intermediate members being attached to one another. Such joining may be permanent in nature or may be removable or releasable in nature.

[00107] It should be noted that the orientation of various elements may differ according to other exemplary embodiments, and that such variations are intended to be encompassed by the present disclosure. It is recognized that features of the disclosed embodiments can be incorporated into other disclosed embodiments.

[00108] It is important to note that the constructions and arrangements of the side-loading low-profile uniplanar screw or components thereof as shown in the various exemplary embodiments are illustrative only. Although only a few embodiments have been described in detail in this disclosure, those skilled in the art who review this disclosure will readily appreciate that many modifications are possible (e.g., variations in sizes, dimensions, structures, shapes and proportions of the various elements, values of parameters, mounting arrangements, use of materials, colors, orientations, etc.) without materially departing from the novel teachings and advantages of the subject matter disclosed. For example, elements shown as integrally formed may be constructed of multiple parts or elements, the position of elements may be reversed or otherwise varied, and the nature or number of discrete elements or positions may be altered or varied. The order or sequence of any process or method steps may be varied or re-sequenced according to alternative embodiments. Other substitutions, modifications, changes and omissions may also be made in the design, operating conditions and arrangement of the various exemplary embodiments without departing from the scope of the present disclosure.

[00109] All literature and similar material cited in this application, including, but not limited to, patents, patent applications, articles, books, treatises, and web pages, regardless of the format of such literature and similar materials, are expressly incorporated by reference in their entirety. In the event that one or more of the incorporated literature and similar materials differs from or contradicts this application, including but not limited to defined terms, term usage, describes techniques, or the like, this application controls.

[00110] While various inventive embodiments have been described and illustrated herein, those of ordinary skill in the art will readily envision a variety of other means and/or structures for performing the function and/or obtaining the results and/or one or more of the advantages described herein, and each of such variations and/or modifications is deemed to be within the scope of the inventive embodiments described herein. More generally, those skilled in the art will readily appreciate that all parameters, dimensions, materials, and configurations described herein are meant to be exemplary and that the actual parameters, dimensions, materials, and/or configurations will depend upon the specific application or applications for which the inventive teachings is/are used. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific inventive embodiments described herein. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that, within the scope of the appended claims and equivalents thereto, inventive embodiments may be practiced otherwise than as specifically described and claimed. Inventive embodiments of the present disclosure are directed to each individual feature, system, article, material, kit, and/or method described herein. In addition, any combination of two or more such features, systems, articles, materials, kits, and/or methods, if such features, systems, articles, materials, kits, and/or methods are not mutually inconsistent, is included within the inventive scope of the present disclosure.

[00111] Also, the technology described herein may be embodied as a method, of which at least one example has been provided. The acts performed as part of the method may be ordered in any suitable way. Accordingly, embodiments may be constructed in which acts are performed in an order different than illustrated, which may include performing some acts simultaneously, even though shown as sequential acts in illustrative embodiments.

[00112] All definitions, as defined and used herein, should be understood to control over dictionary definitions, definitions in documents incorporated by reference, and/or ordinary meanings of the defined terms.

[00113] The indefinite articles "a" and "an," as used herein in the specification and in the claims, unless clearly indicated to the contrary, should be understood to mean "at least one."

[00114] The phrase "and/or," as used herein in the specification and in the claims, should be understood to mean "either or both" of the elements so conjoined, i.e., elements that are conjunctively present in some cases and disjunctively present in other cases. Multiple elements listed with "and/or" should be construed in the same fashion, i.e., "one or more" of the elements so conjoined. Other elements may optionally be present other than the elements specifically identified by the "and/or" clause, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, a reference to "A and/or B", when used in conjunction with open-ended language such as "comprising" can refer, in one embodiment, to A only (optionally including elements other than B); in another embodiment, to B only (optionally including elements other than A); in yet another embodiment, to both A and B (optionally including other elements); etc.

[00115] As used herein in the specification and in the claims, "or" should be understood to have the same meaning as "and/or" as defined above. For example, when separating items in a list, "or" or "and/or" shall be interpreted as being inclusive, i.e., the inclusion of at least one, but also including more than one, of a number or list of elements, and, optionally, additional unlisted items. Only terms clearly indicated to the contrary, such as "only one of or "exactly one of," or, when used in the claims, "consisting of," will refer to the inclusion of exactly one element of a number or list of elements. In general, the term "or" as used herein shall only be interpreted as indicating exclusive alternatives (i.e. "one or the other but not both") when preceded by terms of exclusivity, such as "either," "one of," "only one of," or "exactly one of." "Consisting essentially of," when used in the claims, shall have its ordinary meaning as used in the field of patent law.

[00116] As used herein in the specification and in the claims, the phrase "at least one," in reference to a list of one or more elements, should be understood to mean at least one element selected from any one or more of the elements in the list of elements, but not necessarily including at least one of each and every element specifically listed within the list of elements and not excluding any combinations of elements in the list of elements. This definition also allows that elements may optionally be present other than the elements specifically identified within the list of elements to which the phrase "at least one" refers, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, "at least one of A and B" (or, equivalently, "at least one of A or B," or, equivalently "at least one of A and/or B") can refer, in one embodiment, to at least one, optionally including more than one, A, with no B present (and optionally including elements other than B); in another embodiment, to at least one, optionally including more than one, B, with no A present (and optionally including elements other than A); in yet another embodiment, to at least one, optionally including more than one, A, and at least one, optionally including more than one, B (and optionally including other elements); etc.

[00117] In the claims, as well as in the specification above, all transitional phrases such as "comprising," "including," "carrying," "having," "containing," "involving," "holding,"

"composed of," and the like are to be understood to be open-ended, i.e., to mean including but not limited to. Only the transitional phrases "consisting of and "consisting essentially of shall be closed or semi-closed transitional phrases, respectively, as set forth in the United States Patent Office Manual of Patent Examining Procedures, Section 2111.03.

[00118] The claims should not be read as limited to the described order or elements unless stated to that effect. It should be understood that various changes in form and detail may be made by one of ordinary skill in the art without departing from the spirit and scope of the appended claims. All embodiments that come within the spirit and scope of the following claims and equivalents thereto are claimed.

Claims

1. A screw apparatus comprising:

a screw head including a top portion, a base portion, and at least one sidewall portion, the at least one sidewall portion connecting the top portion and the base portion, the top portion and the base portion positioned opposite one another along a longitudinal axis, the top portion, the base portion, and the at least one side wall portion defining a recess positioned between the top portion and the base portion;

a screw shaft extending from the base portion of the screw head along the longitudinal axis, the screw shaft rigidly connected to the screw head, the screw shaft including a plurality of threads; and

a mobile -bearing positioned in the recess, the mobile-bearing rotatably coupled to the screw head, the mobile -bearing including a rod seat.

2. The apparatus of claim 1 , wherein the recess is configured in the screw head for side- loading of the rod into the recess, whereby the rod is movable into the recess through lateral motion of the rod in a direction orthogonal to a surface of the sidewall.

3. The apparatus of claim 1, further comprising a rod-securing element coupled to the screw head.

4. The apparatus of claim 3, wherein the rod-securing element is removably coupled to the top portion of the screw head via a threaded aperture in the top portion of the screw head.

5. The apparatus of claim 3, wherein the rod-securing element includes a fulcrum configured for engaging a rod positionable in the rod seat.

6. The apparatus of claim 3, wherein the rod-securing element includes a keyed recess for engagement with a tool shaped to fit the keyed recess for removably coupling the rod-securing element to the screw head.

7. The apparatus of claim 1 , wherein, wherein the shaft and the screw head are integrally connected as a unitary structure.

8. The apparatus of claim 1 , wherein the mobile-bearing includes a convex surface engaging a concave surface of the base portion of the screw head within the recess.

9. The apparatus of claim 1 , wherein the mobile-bearing includes a convex surface engaging a surface of the base portion having a flat portion within the recess.

10. The apparatus of claim 1, wherein the mobile-bearing is rotatably coupled for uniplanar rotation.

11. The apparatus of claim 1, wherein the mobile -bearing is translatably coupled to the screw head.

12. The apparatus of claim 1, wherein the mobile-bearing is rotatably coupled to the screw head via a pin extending from the mobile-bearing into an opening in the sidewall portion of the screw head.

13. The apparatus of claim 1, wherein the mobile-bearing is rotatably coupled to the screw head via a pin extending from the sidewall into an opening in the mobile-bearing.

14. The apparatus of claim 13, wherein the opening includes a frustoconical shape.

15. The apparatus of claim 1, wherein the mobile -bearing is translatably coupled to the screw head via a pin extending from the mobile-bearing into an elongated opening in the base portion of the screw head.

16. The apparatus of claim 1, wherein the mobile-bearing is rotatably coupled to the screw head via a pin extending from the base portion into an elongated opening in the mobile-bearing.

17. The apparatus of claim 1, wherein the mobile -bearing is rotatably coupled for rotation in the range of 0 to 20 degrees.

18. The apparatus of claim 1, wherein the rod seat includes a concave surface configured to receive a rod having a curved peripheral wall.

19. The apparatus of claim 1, further comprising a rod positioned in the rod seat, the rod extending through the recess such that the rod traverses the longitudinal axis.

20. The apparatus of claim 1, wherein the side wall extends less than 180 degrees around the longitudinal axis.

21. The apparatus of claim 1, wherein the screw head includes a tool engagement feature in the screw head, the tool engagement feature shaped for mating engagement with a tool configured to apply torque to the screw head.

22. The apparatus of claim 21, wherein the tool engagement feature includes a plurality of flats disposed on opposing surfaces of the screw head.

23. The apparatus of claim 21, wherein the mobile-bearing is asymmetrical.

24. The apparatus of claim 23, wherein the mobile-bearing has a J-shaped geometry.

25. The apparatus of claim 21, wherein the mobile-bearing is symmetrical.

26. The apparatus of claim 25, wherein the mobile-bearing has a U-shaped geometry.

27. A method of implementing a screw apparatus, the method comprising:

rotatably coupling a mobile-bearing to a screw head, the mobile-bearing including a rod seat, the screw head including a top portion, a base portion, and at least one sidewall portion, the at least one sidewall portion connecting the top portion and the base portion, the top portion and the base portion positioned opposite one another along a longitudinal axis, the top portion, the base portion, and the at least one side wall portion defining a recess positioned between the top portion and the base portion, the screw head having a screw shaft extending from the base portion of the screw head along the longitudinal axis, the screw shaft rigidly connected to the screw head, the screw shaft including a plurality of threads, the mobile-bearing positioned in the recess; and

positioning a rod in the rod seat of the mobile-bearing such that the rod extends through the recess such that the rod traverses the longitudinal axis.;

coupling a rod-securing element to the screw head such that the rod-securing element engages the rod positioned in the rod seat.

28. The method of claim 27, further comprising rotatably adjusting the position of the mobile- bearing before coupling the rod-securing element to the screw head.

29. The method of claim 27, wherein coupling the rod-securing element to the screw head comprises engaging the rod positioned in the rod seat such that the mobile-bearing is immobile.

30. The method of claim 27, wherein positioning a rod in the rod seat comprising side-loading the rod into the recess, whereby the rod is positioned into the recess through lateral motion of the rod in a direction orthogonal to a surface of the sidewall.

31. The method of claim 27, wherein, wherein the shaft and the screw head are integrally connected as a unitary structure.

32. The method of claim 27, wherein the mobile-bearing includes a convex surface and the base portion includes a concave surface within the recess and wherein rotatably coupling the mobile-bearing to the screw head includes engaging the convex surface of the mobile-bearing with the concave surface of the base portion of the screw head.

33. The method of claim 27, wherein the mobile-bearing is rotatably coupled for uniplanar rotation.

34. The method of claim 27, further comprising translatably coupling the mobile-bearing to the screw head.

35. The method of claim 27, wherein the mobile -bearing is rotatably coupled to the screw head via a pin extending from the mobile-bearing into an opening in the sidewall portion of the screw head.

36. The method of claim 27, wherein the mobile -bearing is rotatably coupled to the screw head via a pin extending from the sidewall into an opening in the mobile-bearing.

37. The method of claim 36, wherein the opening includes a frustoconical shape.

38. The method of claim 27, further comprising translatably coupling the mobile-bearing to the screw head via a pin extending from the mobile-bearing into an elongated opening in the base portion of the screw head.

39. The method of claim 27, wherein rotatably coupling the mobile-bearing to the screw head further comprises coupling via a pin extending from the base portion into an elongated opening in the mobile-bearing.

40. The method of claim 27, wherein the mobile -bearing is rotatably coupled for rotation in the range of 0 to 20 degrees.

41. The method of claim 27, wherein the rod seat includes a concave surface configured to receive a rod having a curved peripheral wall.

42. The method of claim 27, wherein the rod-securing element is coupled to the top portion of the screw head via a threaded aperture in the top portion of the screw head.

43. The method of claim 27, wherein the rod-securing element includes a fulcrum configured for engaging the rod positioned in the rod seat.

44. The method of claim 27, wherein coupling the rod-securing element to the screw head comprises engaging a keyed recess of the rod-securing element with a tool shaped to fit the keyed recess.

45. The method of claim 27, wherein the side wall extends less than 180 degrees around the longitudinal axis.

46. The method of claim 27, further comprising engaging a tool engagement feature of the screw head with a tool shaped for mating engagement with the tool engagement feature and applying torque to the screw head.

47. The method of claim 27, wherein the tool engagement feature includes a plurality of flats disposed on opposing surfaces of the screw head.

48. The method of claim 27, wherein the mobile-bearing is asymmetrical.

49. The method of claim 48, wherein the mobile-bearing has a J-shaped geometry.

50. The method of claim 27, wherein the mobile-bearing is symmetrical.

51. The method of claim 50, wherein the mobile-bearing has a U-shaped geometry.