Single action locking pedicle screwdriver

An instrument for attaching a driver shaft to a screw assembly using a thrusting motion. The instrument has a main shaft, a locking tube, and a driver shaft. The locking tube is slidably mounted within the main shaft and the driver shaft is slidably mounted within the locking tube. The locking tube is configured to urge a jaw assembly of the instrument into a tensioned engagement with a body member of the screw assembly. A locking mechanism is also included and is configured to lock the driver shaft in a fixed position relative to the locking tube. The locking mechanism may be configured to lock the driver shaft with respect to the locking tube after a distal end of the main shaft engages the screw assembly using the single action.

FIELD OF THE INVENTION

The present invention is related to a medical instrument and in particular to a medical instrument for attaching a driver shaft to a screw assembly using a single action.

BACKGROUND OF THE INVENTION

Instruments for screwing or driving screws into bone material are known. The screws are typically presented to the surgeon in a tray, wherein the heads of the screw are exposed. To maintain a sterile environment, the heads of the screw are configured to engage the instrument. Accordingly, the surgeon stabs the head of the screw with an end of the instrument to engage the screw head in a temporary setting, and then must secure the head to the instrument. Current instruments require two hands to perform such an act. One hand is used to engage the head in a temporary setting. However a second hand is needed to secure the head of the screw to the instrument. Specifically, one hand supports the driver while the other hand rotates a sleeve in a labor intensive action to threadedly engage the screw head to the end of the instrument. Accordingly it remains desirable to have an instrument which requires the use of a single hand to engage the head of a screw. It further remains desirable to have an instrument which engages the head of the screw in a single motion.

SUMMARY OF THE INVENTION

An instrument for attaching a driver shaft to a screw assembly using a single action, e.g. a one-push motion is provided. The instrument has a main shaft, a locking tube, and a driver shaft. The locking tube is slidably mounted within the main shaft and the driver shaft is slidably mounted within the locking tube. The locking tube is configured to urge an end portion of the instrument into a tensioned engagement with an inner surface of the head of the screw. A locking mechanism is also included and is configured to lock the locking tube and/or the driver shaft in a fixed position relative to the main shaft when the main shaft is translated distally. The locking mechanism is further configured to be actuated upon a distal advancement of the main shaft. The locking mechanism may be configured to lock the driver shaft with respect to the locking tube and the main shaft after a distal end of the main shaft engages the screw assembly using the single action.

The instrument may also include a housing having a cover and a release knob. The housing is configured to be gripped by a user, and store the locking mechanism. The main shaft has a proximal end that is coupled to the housing and a distal end with a screw jaw assembly for selectively attaching to the screw assembly. The locking tube within the main shaft has a proximal end that is coupled to the housing and a distal end that is proximate the screw jaw assembly for lockingly engaging jaws of the screw jaw assembly with the screw assembly. The driver shaft within the locking tube also has a proximal end that extends through the housing and a distal end that extends through the screw assembly jaw for engaging and driving a screw of the screw assembly.

The screw jaw assembly has a pair of oppositely disposed jaws and each of the jaws has a contoured edge that is dimensioned to engage a portion of a body member of the screw assembly. In addition, the contoured edge of each jaw can be complementary in shape with an edge of a jaw slot or landing that is part of the body member.

The distal end of the locking tube slides between and applies a force to the pair of oppositely disposed jaws in an outwardly direction during the single action. In addition, the force pushes the contoured edge of each of the pair of jaws against the jaw slot edge on the body member and thereby lockingly engages the screw jaw assembly and the main shaft to the screw assembly.

The locking tube can include the locking mechanism mentioned above in the form of a driver shaft lock that is operable to lockingly engage the driver shaft in a fixed position relative to the locking tube by translating the distal movement of the main shaft. Specifically, the driver shaft is locked with respect to the locking tube and/or the main shaft when the main shaft is advanced distally to a predetermined location on the driver shaft. Accordingly, the head of the screw is fixed to the end of the instrument, and the driver shaft is fixed with respect to the main shaft and the locking tube in a single action.

In an illustrative example, the driver shaft lock can be a pair of locking plates that bind against the driver shaft when the distal movement of the main shaft pivots a pair of opposing edges of the locking plates into a binding engagement of the driver shaft. In another illustrative example of a drive shaft lock, the driver shaft lock can be a spring loaded detent, a pin and groove catch, and the like. In is appreciated that the distal end of the driver shaft is engaged with a head of the screw when the driver shaft lock lockingly engages the driver shaft.

The instrument can also include a screw jaw assembly tensioner that is operable to pull on the screw jaw assembly in a direction towards the housing and away from the distal end of the driver shaft. The pull or force on the screw jaw assembly in the direction towards the housing ensures that the driver shaft is in tight engagement with the head of the screw and thereby removes any slack between the instrument and the screw assembly. In this manner a desirable tactile feel is provided to a surgeon that is holding the instrument and screwing a screw into a surgical site.

DETAILED DESCRIPTION OF THE INVENTION

An instrument10that simplifies secure attachment of a screw assembly using a single-action locking mechanism500actuated by a distal advancement of the instrument10is provided. As such, attachment, locking and alignment of a screw assembly400to the instrument10is accomplished by simply thrusting the end of the instrument10into the head404of the screw assembly400and wherein the thrust not only locks the instrument to the screw assembly, but may also generate a preload condition within the screw assembly400.

Turning now toFIG. 1, an embodiment of the instrument10is shown at reference numeral10. The instrument10has a main shaft250having a locking tube210, a housing300, and a driver shaft100. The driver shaft100has a distal end104opposite a proximal end102. In addition, a handle known to those skilled in the art (not shown) can be attached to the proximal end102in order to assist a surgeon rotating the driver shaft100. The main shaft250is a generally tubular structure having open ends. The main shaft250includes a screw jaw assembly260. Housing300is connected to the locking tube210by means of cam screws222.

Preferably, the driver shaft100is formed of a solid, durable and rigid material accepted for medical use. The locking tube210is also of a tubular dimension, having an outer diameter less than an inner diameter of the main shaft250and more than a diameter of the driver shaft100. The driver shaft100and the locking tube210are slidably mounted within the main shaft250, a portion of the driver shaft100is slidably mounted within the locking tube210.

The instrument10further includes a locking mechanism500configured to activate and lock the locking tube210to the driver shaft100with respect to the main shaft250when the locking tube is translated between the jaw assembly260by sliding the housing300distal towards the jaw assembly260. When the driver shaft100is locked, the locking tube210is operable to pull on the screw jaw assembly260in a direction towards the housing300and away from the distal end of the driver shaft104. Preferably, the pull or force on the screw jaw assembly260in the direction towards the housing300ensures that the driver shaft100is in tight engagement with the head of a screw404(seeFIG. 4) and thereby removes any slack between the instrument10and the screw assembly400to allow the transmission of tactile feedback of a screw being screwed into a patient.

FIG. 2illustrates the instrument10with the driver shaft100slidably mounted within the main shaft250and the distal end104extending past or through the jaw assembly260. Also shown inFIG. 2is a screw assembly400that contains a screw402and a body member410, all of which to be discussed in greater detail below. The force applied by the instrument10aligns the screw402and body member410with the driver shaft100.

FIGS. 3 and 4provide an exploded view of the instrument10, particularly the housing300and locking mechanism500. As shown inFIG. 3, a proximal end of the main shaft250has a locking plate spring clip252and an inner housing254with a cam raceway256, a cam locking ramp258and a housing cover screw slot257. In addition to the proximal end of the main shaft250, a locking tube210which is dimensioned to be slidably mounted within the proximal end is shown. The locking tube210includes a distal end213and a locking tube housing214. The locking tube housing214has a housing cover screw aperture216which affords for a housing cover screw218to be threadably engaged. In the alternative to the locking plate spring clip252being part of the main shaft250, the locking tube housing214can include the locking plate spring clip252.

The locking tube housing214may further include a locking plate pivot slot215, a cam torsion spring217and a pair of apertures219. Locking plates220with a post221can be included, as well as a pair of cam screws222. It is appreciated that the post221can be located off-center with respect to a width of the locking plates220. In addition, the off-center location of the post221affords for tilting of the plates220when the post221contacts the locking plate spring clip252as discussed below. A locking plate spring223keeps the locking plates from tilting and allows free passage of the driver shaft100. The locking plate spring223is dimensioned to fit within the housing214and engage with a spring end cap224are also shown. Dimensioned to cover or fit outside of the main shaft inner housing254is a housing cover270. The housing cover270has a pair of housing cover screw apertures272as well as a pair of coupling ball indentations274.

A release knob280is also shown, the release knob280having a driver shaft aperture282, a pair of cam screw slots284, ball bearings286, and ball bearing seat surfaces288. It is appreciated that the release knob280can have a ribbed flange289that affords for turning of the release knob by a surgeon or assistant's hand. As shown byFIGS. 1-4, the driver shaft100and the locking tube210fit within the main shaft250. In addition, assembly of the main shaft inner housing254, locking tube housing214, housing cover270, release knob280and the various components associated therewith and described above, makeup or constitute the housing300and affords for the single action motion described above and discussed in greater detail below.

With regards to engagement of the screw jaw assembly260of the instrument10with the screw assembly400,FIG. 4provides an enlarged view of the distal end of the instrument10just before and proximate to being attached to the screw assembly400. As shown in the figure, the jaw assembly260has a pair of oppositely disposed jaws261with a slit263therebetween. In addition, the jaws261are flexible in that they can be moved towards each other and away from each other due to the design/slit263. Each of the jaws261has a jaw tip266and an outer edge262with an outwardly extending projection264.

The screw assembly400has a threaded screw402with a tip403and a female screw head404. It is appreciated that the female screw head or screw socket404is complementary with the distal end104of the driver shaft100as is known to those skilled in the art. In addition, the screw assembly400has a body member410that is movably mounted to the screw402via the screw head404. In some instances, the screw head404has a spherical shape and the body member410has spherical shaped socket that is complimentary in size to the spherical shaped screw head404. The body member410can have internal threads412that are used to threadingly engage a setscrew for retaining a fixation rod within a channel413of the body member410as is known to those skilled in the art. The body member410also has a slot or landing414that has an outer edge415with an indentation416. It is appreciated that the outer edge415is complementary with the outer edge262of the jaw261and thus the projection264of the jaw261fits within and is complementary with the indentation416of the landing414.

Turning now toFIG. 5, a schematic illustration of the instrument10being inserted into the body member410of the screw assembly400is shown. As shown in the figure, the distal end104of the driver shaft100has been engaged with the screw head404and as the main shaft250of the instrument10is pushed in a downward direction towards the screw assembly400, the main shaft250and thus the jaw assembly260approaches the body member410.

Further motion of the main shaft250in a direction towards the screw assembly400is shown inFIG. 6in which the jaw assembly260is entering within the landings414of the body member410. Finally,FIG. 7illustrates the jaw assembly260fully inserted within the body member410such that the projections264of the jaw261are engaged with the indentations416of the landing414. In addition, it is appreciated that the space or distance between opposing indentations416of the body member410are such that the pair of oppositely disposed jaws261are placed in a slight compressive state. Stated differently, the jaws261are lockably engaged with the body member410by a slight outer force of the jaws against the body member410and the landings414.

Turning now toFIGS. 8-11, details of the housing300and its interworkings and mechanism during attachment of the jaw assembly260to the screw assembly400are shown and discussed. In particular,FIG. 8provides a perspective view of the driver shaft100, main shaft250, and locking tube210without the presence of the housing cover270. As shown in this figure, the driver shaft100is slidably mounted within the locking tube210and the locking tube210is slidably mounted within the main shaft250. In addition, the housing214of the locking tube210is located or slidably mounted within the inner housing254of the main shaft250. The locking tube housing214has the pair of cam screws222attached thereto via apertures219, as well as the housing cover screw218and locking plates220with post221.

It is appreciated fromFIG. 8that the locking tube housing214can slide within the inner housing254of the main shaft250. In addition, the housing cover270with housing cover screw apertures272allow for the transmission of axial force on the housing cover270to be transmitted to the locking tube210via the housing cover screw218.

The cam raceway256and cam locking ramp258of the inner housing254provide an initial resistance against torsional load from the cam torsion spring217and prevent unnecessary axial motion of the locking tube210until the jaw assembly260is engaged with the screw assembly400. Stated differently, the slope or angular path of the cam raceway256provides a resistance to the downward movement of the locking tube housing214, and thus the locking tube210, relative to the main shaft250. However, once the jaw assembly260has been lockably engaged with the screw assembly400as shown inFIG. 7, increased axial force during the single action results in the cam screws222and thus the housing214to advance towards the screw assembly400. As shown inFIG. 9, both the cam screw222and housing cover screw218move in a downward direction a distance ‘D’ which results in the distal end213of the locking tube210to move towards the screw assembly400and in between the pair of oppositely disposed jaws261of the jaw assembly260a distance ‘D’. The movement down the raceway causes the cam torsion spring217to rotate and cause a torsional tensioning of the spring. This torsional load is stored by the spring and released at the bottom of the raceway when the cam screws enter the cam locking ramp258as described in more detail below.

Just before the cam screws222reach the bottom of the raceway256the post221of the locking plates220contacts the locking plate spring clip252and affords for the locking plates220to tilt and bind against the driver shaft100. In this bind or locked position, the driver shaft is held in a fixed position relative to the locking tube210. Thus all further axial motion as the cam screws222round the bottom corner of the raceway256and moves down the bottom angled slot258causes the driver shaft100to preload the screw head404against the body member410and thus the screw to be rigidly locked to the driver. Once the cam screws222reach a bottom portion of the cam raceway256as shown inFIG. 10, downward movement of the housing cover270stops. Stated differently, contact between the locking plate post221and the locking plate spring clip252tilts the locking plates220and thus causes the center aperture225to catch or bind against the driver shaft100as illustrated inFIG. 11.

It is also at this location that the locking tube210and its distal end213are in a locked position. In particular, the locking tube210produces an outward force on the jaws261such that the projections264of each of the jaws261are engaged with the indentations416of the landing414that is part of the body member410. It should be appreciated that at this position of the instrument10with respect to the screw assembly400, the distal end104is within and engaged with the female screw head404, however this is not required.

Turning now toFIG. 12, an illustrative example of a preload mechanism500is provided. The preload mechanism500is configured to simultaneously urge the distal end104of the driver shaft100towards the screw head404and pull the body member410away from the distal end104. For example, one embodiment of the preload mechanism is a jaw assembly tensioner600that pulls the pair of opposing jaws261attached to the body member410away from the distal end104of the driver shaft100. In particular, the cam screws222located within the locking ramp258as illustrated in the figure provide for the locking tube210and driver shaft100to be locked together. Also, movement of the cam screws222down the cam locking ramp258causes the main shaft250and jaw assembly260to be pulled back against the distal end104of the driver shaft100and thereby cause the preload condition where the screw head404is driven against the body member410. Thus, the jaw assembly tensioner600is configured to generate a preload condition within the screw head404by generating an opposing force between the jaw assembly260and the driver shaft100.

In operation, with the locking tube210and driver shaft100locked together per the locking plates220, movement of the cam screw222may be provided down and/or along the cam locking ramp258. In particular, movement of the cam screw222along the cam locking tamp258affords for the main shaft250and jaw assembly260to be pulled back against the distal end104of the driver shaft100. The movement of the cam screw222along the cam locking ramp258is provided by the cam torsion spring217, and more so by turning or rotating of the release knob280such that the cam screw222is forced down the ramp258. This pulling or tension of the main shaft250against the distal end104that is engaged with the female screw head404provides a preload condition where the screw head404is driven against or placed in compression with a ball socket of the body member410. Furthermore, torsional load stored in the torsion spring217biases the cam screw222to advance down or along the cam locking ramp258such that a tightening or tensioning force that creates the preload condition is provided.FIG. 13shows a schematic illustration of the preload condition with respect to the screw head404, distal end104of the driver shaft100, and the jaw assembly260.

In this manner, the instrument10lockingly engages the screw assembly400and affords for the screw402to be driven or screwed into a bone portion of a patient. In addition, once the screw has been properly placed within the bone portion of the patient, the instrument10is released from the screw assembly400by turning of the release knob280such that the cam screw222travels up along the cam locking ramp258and further up the cam raceway256. Upon this action, the locking plates untilt and release the driver shaft100. Furthermore, the locking tube210moves in a direction away from the screw assembly400such that the outer force on the pair of oppositely disposed jaws261is no longer provided by the distal end213. This then allows for the surgeon to pull upon the instrument10and the jaw assembly260to be removed from the body member410. Naturally, the distal end104of the driver shaft100is also pulled away from the screw head404.

The present invention improves upon the prior art by affording for a male tip104of the driver shaft100to engage a female socket404of the screw402while simultaneous sliding of the housing300down the driver shaft100ensures that the screw jaw assembly260engages the screw assembly400in a simple, secure and aligned manner. Stated differently, after the driver tip104is in place with respect to a female socket404of a screw assembly400, the inventive instrument allows jaws261to engage and be attached to landings414that are machined proximate a slotted opening in the body member410.

As the housing300of the instrument is moved down towards the screw assembly400, the mating or complementary projection/indentation features264and416cause the jaws261to snap into place and positively engage the landings414on the screw body member410. With the jaws261in place and securely attached to the body member410, a continued sliding of the housing300moves an inner sleeve, e.g. the distal end213of the locking tube210, between the pair of oppositely disposed jaws261and locks the jaws261into the screw assembly400. The distal end213of the locking tube210interferes between the jaws261and the driver shaft100to prevent the jaws261from flexing radially inward. Furthermore, after the jaws261are locked to the screw assembly400, the post221of the locking plates220affords tilting of the locking plates220, such that the locking plates220bind against the driver shaft100and the shaft is locked into a fixed position relative to the housing300. This combination of housing300movement towards the screw assembly400, sliding of the locking tube distal end213between the jaws261, and tilting of the locking plates220to bind the driver shaft100provides the locking mechanism500for the instrument10.

In addition to the above, a timed cam action allows the cam screw222that is part of the locking tube housing214to slide down the cam locking ramp258and create the same preloaded condition and feel of the driver shaft100against the screw assembly400that exists when the sleeve is tightened in a standard screwdriver as discussed above. It is appreciated that the cam screw222, cam locking ramp258, etc., can also be part of the instrument locking mechanism500, however this is not required. Stated differently, the instrument10can have a two-stage or two-part locking mechanism500in which the first-stage locks the jaws261to the screw assembly400via the locking tube210and locks the driver shaft100via the locking plates220. Also, the second stage removes any slack between the driver shaft distal end104and the screw head404via the cam screw222and cam locking ramp258. In the alternative, the instrument10can be considered to have a one-stage locking mechanism500that locks the jaws261and the driver shaft100, and a separate tensioning mechanism. However, it is appreciated the locking mechanism500and jaw assembly tensioner600provided herein are illustrative and the locking mechanism and jaw assembly tensioner600for use in the instrument10provided herein are actuated with the single action/stabbing motion. In this manner, a driver, e.g. a pedicle screwdriver, can be easily coupled to a screw assembly using a simple single action/one-push motion of the driver. The action or motion may thus be performed in a single direction commonly used to thrust a screwdriver into frictional/compressive engagement of the driver tip within the screw head. Currently, such single direction action is used to temporarily hold the screw assembly400to the driver tip until the surgeon performs additional acts to further retain the instrument to the screw assembly.

The instrument also provides a rigid connection with the screw as a result of the one-push motion and thus affords for a tactile feedback to a surgeon as the screw is advanced into a bone of a patient. The applied tension aligns the screw and body member axially with the instrument. It is appreciated that the feedback is generated by friction between the bone and a surface of the screw which can generate subtle vibrations that can only be transmitted through a rigid preloaded connection between the driver and the screw. As noted above, such a rigid preload is accomplished in prior art instruments by threading a sleeve of the instrument into the screw body. However, the preload of the inventive instrument is accomplished by locking the housing300to the driver shaft just as a cam screw/pin enters a ramp with a slope that is approximately equal to a pitch of the threaded sleeve. Furthermore, a torsion spring that is rotated to generate a torsion load drives the cam screw/pin down the ramp to produce a tightening force that preloads the screw and the screw body assembly.

It is appreciated that changes and modifications to the embodiments disclosed herein will be apparent to one skilled in the art and yet fall within the scope of the present invention. Therefore, such changes, modifications, and the like are part of the invention and the specification and the following claims, both of which provide the scope of the invention, should be interpreted broadly.