Cervical plate system

A system for securing a bone to a plate having an upper surface and a lower surface and apertures extending from the upper surface to the lower surface, the apertures having inside concave edge walls spaced apart a given inner diameter and having an upper surface opening and a lower surface opening, each having a diameter smaller than the inner diameter, comprising:

• a screw including a head portion and a threaded shank with a distal tip and a central longitudinal axis, the head portion having a central opening exposed at the proximal end of the screw and an annular wall around the central opening, the annular wall having an inner and an outer surface, the outer surface having a relaxed outer diameter substantially equal to the inner diameter of the aperture and having a plurality of slots that separate the annular wall into a plurality of petals, wherein the inner surface of the annular wall includes a plurality of shallow recesses and a corresponding plurality of deep recesses, wherein at least one of the petals has an inner surface of the annular wall having at least two of the shallow recesses, the screw further including an internal surface of defined shape originating in the central opening for engagement by a matingly-configured screw driving tool for driving the screw into the bone;
• and
• a locking disc rotatably disposed within the central opening and having a periphery of defining a plurality of extending protrusions, the locking disc rotatable between a first rotational position and second rotational position, the locking disc having a central aperture that surrounds the internal bore of the screw to permit access to the internal bore, and at least a pair of proximally opening notches configured for engagement to effectuate rotation of the disc;
• and
• a tool with a handle, a shaft extending from the handle and having a distal end configured to mate with the internal bore of the screw to permit selective rotation of the screw, and a sleeve member axially slideable along and rotatable about the shaft and having a distal end with structure that mates with the pair of proximally opening notches in the locking disc to permit selective rotation of the disc;
• wherein the shallow recesses, the deep recesses, and the protrusions are configured so that when the locking disc is in the first rotational position, the protrusions are disposed in the deep recesses with a clearance permitting the petals to flex inwardly to insert the screw head into the aperture past the upper surface opening, and when the locking disc is rotated to the second rotational position two of the protrusions are disposed in and engage with a corresponding two of the shallow recesses formed on the inner surface of at least one of the petals, to establish a corresponding two engagements with the petal substantially at its free relaxed state, to prevent the petal from flexing inwardly, whereby the head is selectively captured within the concave edge walls of the plate aperture.

A method of securing to a bone a plate having an upper surface and a lower surface and apertures extending from the upper surface to the lower surface, the apertures having inside concave edge walls spaced apart a given inner diameter and having an upper surface opening and a lower surface opening, each having a diameter smaller than the inner diameter, comprising:

• positioning a selected aperture of the plate adjacent a desired location on the bone;
• aligning a bone screw through the selected aperture and into contact with the bone at a desired angular orientation, the screw including
• a threaded shank with a distal tip,
• a head portion having a central opening exposed at the proximal end of the screw and an annular wall around the central opening, the annular wall having an inner and an outer surface, the outer surface having a relaxed outer diameter substantially equal to the inner diameter of the aperture and having a plurality of slots that separate the annular wall into a plurality of petals, wherein the inner surface of the annular wall includes a plurality of spaced shallow recesses and a plurality of deep recesses, wherein at least one of the petals has at least two of the shallow recesses,
• an internal bore of defined shape originating in the central opening for engagement by a driving tool, and
• a locking disc rotatably disposed within the central opening and having a periphery of defining a plurality of extending protrusions, the locking disc rotatable between a first rotational position and a second rotational position, the locking disc having a central aperture that surrounds the internal bore of the screw to permit access to the internal bore, and at least a pair of proximally opening notches configured for engagement to effectuate rotation of the disc, wherein the shallow recesses, the deep recesses, and the protrusions are configured so that when the locking disc is in the first rotational position at least one of the petals is flexible inwardly to permit inserting the screw head into the aperture past the upper surface opening, and when the locking disc is rotated to the second rotational position the two of the protrusions are disposed in and engage with a corresponding two of the shallow recesses formed on the inner surface of at least one of the petals, with the petal substantially at its free relaxed state, to establish a corresponding two engagements to prevent the petal from flexing inwardly;
• engaging the internal bore of the screw with a driving tool having a handle and a shaft with a distal end configured to mate with the internal bore, driving the distal tip of the screw against the bone and selectively rotating the screw until it penetrates the bone to a desired depth, the driving tool further including
• a sleeve member axially slideable along and rotatable about the shaft, the sleeve member including a flange for effectuating movement of the sleeve relative to the shaft, and a distal end with structure that mates with the pair of proximally opening notches in the locking disc;
• and
• manipulating the flange first to slide the sleeve into mating engagement with the pair of proximally opening notches in the locking disc and second to rotate the locking disc from the first rotational position to the second rotational position, whereupon the head is captured by the concave wall edges of the plate aperture.

A bone plate system, comprising:

• a plate having an upper surface and a lower surface and an aperture extending from the upper surface to the lower surface, the aperture having inside concave edge walls spaced apart a given inner diameter and having an upper surface opening and a lower surface opening, each having a diameter smaller than the inner diameter;
• a screw including a head portion at a proximal end and a threaded shank with a distal tip, the head portion having a mating structure exposed through a central opening at the proximal end, for engaging a matingly-configured screw driving tool for driving the screw, and having an annular wall around the central opening, the annular wall having an inner and an outer surface, the inner surface including a plurality of shallow recesses and a plurality of deep recesses, the annular wall having a plurality of slots that separate the annular wall into a plurality of petals such that each petal has a portion of the inner surface having at least two of the shallow recesses, the outer surface having a relaxed outer diameter substantially equal to the inner diameter of the aperture and;
• and
• a locking disc rotatable within the central opening and having a periphery defining a plurality of protrusions, each protrusion having a high point configured for selective engagement within one of the shallow and one of the deep recesses,
• wherein the shallow recesses, the deep recesses, and the protrusions are configured so that when the locking disc is in a first rotational position, the protrusions engage with the deep recesses in the inner surface of the annular wall with a clearance to enable inward flex of the petals of the screw head sufficient for insertion through the upper surface aperture opening into the aperture, and when the locking disc is in a second rotational position, the respective high point of least two of the protrusions engage with a corresponding at least two of the shallow recesses formed on the inner surface of each of the petals, to establish a corresponding two engagements preventing the petals from flexing inwardly, thereby preventing the screw head from being compressed sufficiently to pass through the upper aperture opening, thereby providing for capturing the head within the concave edge walls of the plate aperture.