Apparatus for maintaining bone portions in a desired spatial relationship

Abstract: The apparatus for retaining bone portions (V), such as vertebrae of a spinal column, in a desired spatial relationship includes a longitudinal plate (10) extendable along the bone portions. The plate (10) has a first major side surface (48) for facing the bone portions (V) and a second major side surface (50) for facing away from the bone portions (V). The first and second major side surfaces (48, 50) of the plate (10) are spaced apart from each other a first distance at one location (52) along a longitudinal axis of the plate (10) and spaced apart a second distance which is less than the first distance at a second location (54) along the longitudinal axis of the plate.

Description: The present invention relates to an apparatus which is used to retain bone portions, such as vertebrae of a spinal column, in a desired spatial relationship. A known apparatus for retaining vertebrae of a spinal column in a desired spatial relationship includes a longitudinal plate extendable along the spinal column. The plate includes a plurality of elongate slots extending along a longitudinal axis of the plate. A fastener has a first end portion that engages a vertebrae of the spinal column and a second end portion which extends through one of the slots in the plate. A nut threadably engages the second end portion of the fastener and clamps the plate to the fastener. The known longitudinal plates have a uniform stiffness along their length to prevent stress from being applied to healthy and deformed vertebrae to which the plate is connected. However, low stress deformation of bone is important in bone remodeling since the bone remodels to support applied loads. When the known plates are connected to bone, the surrounding bone of healthy vertebrae is shielded from applied stresses and the bone of the healthy vertebrae resorts. Furthermore, the known stiff plates cause increased loads to be applied to a spine disk between the uppermost vertebra that the plate is connected to and an adjacent vertebra to which the plate is not connected. These increased loads cause degeneration of the disk. The document WO 91 11967 discloses an apparatus for retaining vertebrae in a desired spatial relationship as defined in the preamble of claim 1 and comprises a longitudinal plate extendable along the spinal column. The longitudinal plate has a first side surface for facing the vertebrae and a second side surface opposite to the first side surface. A fastener has a first end portion engageable with a vertebrae and a second end portion engageable with the longitudinal plate. The connecting means are engageable with the second end portion of the fastener for connecting the longitudinal plate to the fastener. The connecting means includes surface means for defining a recess for receiving a portion of the longitudinal plate. The longitudinal plate has even thickness along its longitudinal extension. Thus, such a plate can cause bone resorption and disk degeneration. The document US 4,955,886 discloses a reconstruction or fracture plate for bridging a discontinuity in a patient's long bone, such as a femur and has a central portion for placement over the bone discontinuity, a first end portion having a dual-tapered width and thickness profile having a first plurality of screw holes and a second end portion defining a second plurality of screw holes. The first and second plurality of screw holes each have asymmetrically arrayed centerlines relative to plate longitudinal and transversal axes and the screw holes may have asymetrically arrayed centerlines relative to each other. Both the first and second end portions may have dual-tapered profiles. However, this document neither discloses nor suggests that this longitudinal plate is to be bent, nor does it disclose or suggest that the rigidity, i.e. the resistance against bending, is to decrease from one end to the other end. In accordance with the present invention, an apparatus for retaining vertebrae in a desired spatial relationship comprises a longitudinal plate whose longitudinal axis extends parallel to the general axis of the spinal column. The plate includes a first side surface for facing the vertebrae, a second side surface opposite to the first side surface, a first, lower end and a second, upper end. A fastener has a first end portion suitable to be connected to a vertebrae and a second end portion. Connecting means are provided for connecting the plate to the fastener. The plate tapers from the above mentioned first end to the above mentioned second end (54). Accordingly, the plate has a relatively flexible portion that can be connected to the uppermost vertebra that the plate is to be connected to. The relatively flexible portion helps prevent bone resorption and disk degeneration. The foregoing and other features of the present invention will become apparent to one skilled in the art upon consideration of the following description of the preferred embodiments of the invention with reference to the accompanying drawings, wherein: Fig. 1 is a posterior view of a human spinal column in which an apparatus constructed in accordance with the present invention has been implanted; Fig. 2 is a left lateral view, taken generally along the line 2-2 of Fig. 1; Fig. 3 is a sectional view, taken generally along the line 3-3 of Fig. 1, illustrating the manner in which fasteners are used to connect longitudinal plates with a vertebra; Fig. 4 is an enlarged sectional view of a connector member of Fig. 1; Fig. 5 is an enlarged side view of a longitudinal plate of Fig. 1; and Fig. 6 is a sectional view of the longitudinal plate, taken generally along the line 6-6 of Fig. 5. A pair of surgically implantable longitudinal plates 10 (Fig. 1) for maintaining bone portions, such as vertebrae of a spinal column, are connected with several vertebrae V of a spinal column 12 by fasteners 20. Each plate 10 can be curved to conform to a desired curvature of the spinal column 12, as illustrated in Fig. 2. Although the plates are shown maintaining three vertebrae in a desired spatial relationship, they may be used to maintain any number of vertebrae in a desired spatial relationship. Also, the plates may be used to maintain bone portions, such as portions of a broken bone, in a desired spatial relationship. The plates 10 are connected to respective vertebrae V by fasteners 20 (Fig. 3) made of suitable biocompatible material, such as titanium or stainless steel. Each of the fasteners 20 has a threaded inner end portion 22 having a coarse helical thread convolution 24 which engages the vertebra V. An outer end portion 26 of the fastener 20 is provided with a relatively fine thread which engages an internal thread convolution on a nut 28 preferably made of a suitable biocompatible material, such as titanium or stainless steel. Wrenching flats (not shown) are provided on the outermost end of the outer end portion 26 of the fastener 20. Torque is applied to these wrenching flats to turn the relatively coarse helical thread convolution 24 into the vertebra V. Once the fastener 20 has been connected to the vertebra and the plate 10, the outer end portion of the fastener may be cut away to minimize the overall length of the fastener. An intermediate portion 32 of the fastener has a flat outer side surface 33 which abuttingly engages a spacer washer 34. When the clamp nut 28 is tightened, the plate 10 is securely clamped against a flat outer side surface 36 of the washer 34, which is connected with the fastener 20. The washer 34 spaces the plate 10 away from the vertebra V and may have any desired thickness or not be used at all. If the washer 34 is not used, the plate is clamped against the surface 33 of the intermediate portion 32 of the fastener 20. Although it is contemplated that the fastener 20 could have many different constructions, it is preferred to construct the fastener 20 in accordance with U.S. Patent No. 4,854,311 which is assigned to the assignee of the present invention. Each of the plates 10 has a length which is at least sufficient to enable the plate to span at least two of the vertebrae V. In the embodiment of the invention illustrated in Fig. 1, the plates 10 span three vertebrae V. Of course, the length of the plates 10 in any particular installation will depend upon the condition to be corrected and the number of vertebrae V to be held in a desired spatial relationship relative to each other by the bone plates. Each of the plates 10 is identical and includes first and second longitudinally extending side portions 40 and 42 (Fig. 1). The side portions 40 and 42 extend parallel to each other and to a longitudinal axis 43 of the plate 10. The first and second side portions 40 and 42 define a slot 44 in the plate 10 that extends along the axis 43. The plate 10 (Figs. 2 and 5) has a lower surface 48 for facing the vertebrae V and an upper surface 50 for facing away from the vertebrae V. As can be seen in Fig. 5 and, even clearer in Fig. 2, the surfaces 48 and 50 are spaced apart a first distance adjacent a first end 52 (Figs. 2 and 5) of the plate 10 and spaced apart a second distance, less than the first distance, adjacent a second end 54 of the plate. Thus, the plate 10 tapers from the first end 52, i.e. the lower end as seen in Fig. 2, to the second end 54, i.e. the upper end as seen in Fig. 2. Accordingly, the plate 10 is more flexible adjacent the upper end 54 than adjacent the lower end 52 to prevent stress shielding of the vertebrae connected with the end 54 and degeneration of a spine disk (not shown) located between the uppermost vertebra connected with the end 54 and the adjacent vertebra not connected to the plate. The side portion 40 (Fig. 6) of the plate 10 has an inner surface 60 defining the slot 44 and an outer surface 62 located laterally from the inner surface of the side portion 40. The inner surface 60 of the first side portion 40 extends at an angle A relative to a line 64 extending substantially perpendicular to the lower surface 48. The outer surface 62 of the side portion 40 extends at an angle B relative to the line 64. Preferably, angles A and B are equal and are approximately 2.4°. Therefore, the inner and outer surfaces 60 and 62 extend at an angle of approximately 4.8° relative to each other. The side portion 42 of the plate 10 has an inner surface 70 defining the slot 44 and an outer surface 72 located laterally from the inner surface 70 of the side portion 42. The inner surface 70 of the second side portion 42 extends at an angle C relative to a line 74 extending substantially perpendicular to the lower side surface 48. The outer surface 72 of the second side portion 42 extends at an angle D relative to the line 74. Preferably, angles C and D are equal and are approximately 2.4°. Therefore, the inner and outer surfaces 70 and 72 extend at an angle of approximately 4.8° relative to each other. Also, the outer surfaces 62 and 72 extend at an angle relative to each other. A connecting member 80 (Fig. 1) connects the fastener 20 to the plate 10 in any desired position along the slot 44. The connector member 80 (Fig. 3) has first and second recesses 82 and 84 for receiving the first and second side portions 40 and 42 of the plate 10. The first and second recesses 82 and 84 have an interference fit with the first and second side portions 40 and 42 of the plate 10. First and second side surfaces 88 and 90 (Fig. 4) and a bottom surface 92 extending between the first and second side surfaces define the recess 82. The first side surface 88 extends at an angle W relative to a line 94 extending substantially perpendicular to the bottom surface 92 of the recess 82. The second side surface 90 extends at an angle X relative to the line 94. Preferably, the angles W and X are equal and are approximately 2.5°. Therefore, the side surfaces 88 and 90 extend at an angle of approximately 5° relative to each other. First and second side surface 98 and 100 and a bottom surface 102 extending between the first and second side surfaces 98 and 100 define the recess 84. The first side surface 98 of the recess 84 extends at an angle Y relative to a line 104 extending substantially perpendicular to the bottom surface 102 of the recess 84. The second side surface 100 of the recess 84 extends at an angle Z relative to the line 104. Preferably, the angles Y and Z are equal and are approximately 2.5°. Therefore, the first and second side surfaces 98 and 100 of the recess 84 extend at an angle of approximately 5° relative to each other. The connecting member 80 includes an opening 110 through which the second end portion 26 of the fastener extends. The opening 110 is located between the recesses 82 and 84. The connector member 80 includes a frustoconical recess 112 for receiving a frustoconical portion of the nut 28. The first side portion 40 (Fig. 6) of the plate 10 has a width measured from the inner side surface 60 to the outer side surface 62 and along the upper surface 50. The bottom surface 92 (Fig. 4) of the recess 82 has a width measured from the first side surface 88 to the second side surface 90. Preferably, the width of the first side portion 40 measured along the upper surface 50 is greater than the width of the bottom surface 92 of the recess 82 to cause an interference fit. The second side portion 42 (Fig. 6) of the plate 10 has a width measured from the inner side surface 70 to the outer side surface 72 and along the upper surface 50. The bottom surface 102 (Fig. 4) of the recess 84 has a width measured from the first side surface 98 to the second side surface 100. Preferably, the width of the second side portion 42 measured along the upper surface 50 is greater than the width of the bottom surface 102 of the recess 84 to cause an interference fit. When the plates 10 are to be mounted on a spinal column 12, a plurality of fasteners 20 are connected to the vertebrae. After the plates 10 have been bent to the desired configuration, the plates 10 are placed on the fasteners 20. If washers 34 are to be used, the washers are placed on the fasteners 20 before placing the plates 10 on the fasteners. The plate 10 is preferably placed with the more flexible end 54 toward the head of the patient and connected with healthy vertebrae. The plates 10 can be positioned along the fasteners 20 with the fasteners in any desired position along the slot 44. Once the plates 10 have been positioned relative to the fasteners 20, connecting members 80 are placed on the fasteners with the recesses 82 and 84 receiving side portions 40 and 42 of the plates 10. Nuts 28 are threaded onto fasteners 20 to cause the interference fit between the recesses 82 and 84 and the side portions 40 and 42 and fix the positions of the plates relative to the fasteners. The nuts 28 cause the connecting members 80 to clamp the lower side surfaces 48 of the plates 10 against surfaces 36 of the washers 34 if the washers are used, or against surfaces 33 of the fasteners 20 if the washers are not used.

Claims: An apparatus for retaining vertebrae (V) in a desired spatial relationship, comprising a longitudinal plate (10) whose longitudinal axis extends in the mounted state parallel to the general axis of the spinal column (12), said plate (10) including a first side surface (48) for facing the vertebrae (V), a second side surface (50) opposite to said first side surface (48), a first, lower end (52) and a second, upper end (54), a fastener (20) having a first end portion (22) suitable to be connected to a vertebrae (V) and a second end portion (26), and connecting means (80) for connecting said plate (10) to said fastener (20), characterized in that said plate (10) tapers from said first end (52) to said second end (54). An apparatus as set forth in claim 1, characterized in that said plate (10) includes first and second side portions (40, 42) extending parallel to each other and the longitudinal axis, said first and second side portions (40, 42) defining an elongate slot (44) extending along the longitudinal axis of said plate (10) and intersecting said first and second side surfaces (48, 50), said second end portion (26) of said fastener (20) being extendable through said slot (44), said connecting means (80) including surface means (88, 90, 92; 98, 100, 102) for defining first and second recesses (82, 84) for receiving said f irst and second side portions (40, 42) of said plate (10), said surface means (88, 90, 92; 98, 100, 102) defining said first and second recesses (82, 84) having an interference fit with said first and second side portions (40, 42). An apparatus as set forth in claim 2, characterized in that said surface means (88, 90, 92; 98, 100, 102) defining said recess (82; 84) includes first and second side surfaces (88, 90; 98, 100) and a bottom surface (92; 102) extending between said first and second side surfaces, said first side surface (88; 98) extending at an angle relative to said second side surface (90; 100). An apparatus as set forth in claim 3, characterized in that said first and second side surfaces (88, 90; 98, 100) extend at an angle to a line (94; 104) extending substantially perpendicular to said bottom surface (92; 102). An apparatus as set forth in claim 2, characterized in that said plate (10) includes first and second longitudinally extending laterally outer surfaces (62, 72) extending between said first and second side surfaces (48, 50) , said first and second laterally outer surfaces (62, 72) extending at an angle relative to each other. An apparatus as set forth in claim 5, characterized in that said surface means (88, 90, 92; 98, 100, 102) defining said recess (82; 84) includes first and second side surfaces (88, 90; 98, 100) and a bottom surface (92; 102) extending between said first and second side surfaces, said first side surface (88; 98) extending at an angle relative to each other. An apparatus as set forth in claim 2, characterized in that said surface means (88, 90, 92) defining said first recess (82) includes first and second side surfaces (88, 90) and a bottom surface (92) extending between said first and second side surfaces (88, 90), said first side surface (88) of said first recess (82) extending at an angle relative to said second side surface (90) of said first recess (82), said surface means (98, 100, 102) defining said second recess (84) including first and second side surfaces (98, 100) and a bottom surface (102) extending between said first and second side surfaces (98, 100), said first side surface (98) of said second recess (84) extending at an angle relative to said second side surface (100) of said second recess (84). An apparatus as set forth in claim 2, characterized in that said connecting means includes a connecting member (80) including said surface means (88, 90, 92; 98, 100, 102) defining said recess (82; 84), said connecting member (80) clamping one of said first and second side surfaces (48, 50) of said plate (10) against a substantially flat surface (33) connected with said fastener (20). An apparatus as set forth in claim 8, characterized in that said connecting member (80) includes surface means for defining an opening (110) through which said second end portion (26) of said fastener (20) is extendable.

Inventors: DINELLO ALEXANDRE M, ENGELHARDT JOHN, DINELLO, ALEXANDRE M., ENGELHARDT, JOHN
Applicants: DEPUY ACROMED INC, DEPUY ACROMED, INC.
Application year: 1996
Main classification: A61B17
IPC codes: A61B17