Needle assembly with removable depth stop

A needle assembly (10) includes a needle (14) attached to mounting structure (12), and is used to insert the needle into the body of a patient. A depth stop unit (50) of the needle assembly provides a stop surface (58) to limit the distance the needle can be inserted into the body. The depth stop unit may include a depth stop (52) that is adjustable to selectively change the depth to which the needle can be inserted. The entire depth stop unit can be removed from the needle assembly to permit the full length of the needle to penetrate into the body.

CROSS REFERENCE TO RELATED APPLICATION

This application includes subject matter in common with co-assigned U.S. patent application Ser. No. 11/146,173, entitled Bayonet Release of Safety Shield for Needle Tip, filed Jun. 6, 2005, and published as U.S. 2006-0276772. The subject matter of this application is incorporated herein in its entirety by reference for all purposes.

BACKGROUND OF THE INVENTION

This invention relates generally to needles used in medicine and more particularly to a needle assembly having a depth stop to limit penetration of the needle into the subject, which depth stop can be selectively removed from the needle.

In some medical applications needles are used to make relatively deep penetrations into the body in order to perform their tasks. For instance where it is necessary to obtain a biopsy sample, the needle may have to penetrate deep inside tissue to the location from which the sample is to be taken. However, there are also situations where the needle has to penetrate a substantial distance through tissue in order to inject a drug or withdraw fluid. One specific example is that of accessing the intramedullary canal of bone. This may be done to collect a specimen of bone marrow or fluid from the intramedullary canal. It is also possible that a drug or other fluid may be infused into the canal through the needle.

To penetrate the hard cortical bone surrounding the intramedullary canal, the needle must be hard and strong, and substantial force has to be applied to the needle. The needle is typically mounted on a handle that can be grasped by a medical technician to supply the necessary force to penetrate the cortical bone to reach the intramedullary canal. It is important that the medical technician exercise care so that the needle is not driven elsewhere in the body other than the target bone. Depending upon the location of the bone selected for penetration, the bone may be near to organs or blood vessels that could be damaged by a misdirected needle. For example, if the needle penetrates too deeply, it could damage an untargeted area of the body. Thus, the use of a bone needle assembly of this type requires the simultaneous exercise of substantial force and precision.

One way to reduce the chance that the needle will damage the body is to provide a depth stop that limits the depth of penetration of the needle into the body. Typically the depth stop is disposed around the needle below the handle and can engage the exterior of the body to stop the inward thrust of the needle. The depth stop reduces the length of the needle that is available for penetrating into the body. The appropriate depth of penetration can vary widely from one patient to the next. For example, an obese patient may require penetration of several inches of skin and soft tissue to reach the bone, while a thin patient requires very little penetration to reach the bone. Moreover, the location of the target bone may call for a different depth of penetration. To meet this need, depth stop units have been provided that permit the depth stop to be adjusted to expose a greater or lesser length of the needle for penetration into the body. While these adjustable depth stop units provide greater flexibility they do not fully meet the need for variability in needle length. Moreover, some procedures have less reason to use the depth stop than others. Medical technicians differ on their preference for use of needle assemblies incorporating depth stops.

In instances where a depth stop is present in the needle assembly, a substantial length of the needle will never be available for use to penetrate into the body because it will remain covered by the depth stop. This is true even if the depth stop is adjusted to expose the maximum possible length of the needle for penetration. Accordingly, it is necessary to keep on hand multiple needle assemblies having different lengths and/or needle assemblies that do not have depth stops.

SUMMARY OF THE INVENTION

In one aspect of the present invention, a convertible needle assembly generally comprises a mounting structure and a needle having a longitudinal axis and a sharp end, the needle being mounted on the mounting structure and projecting outwardly from the mounting structure so that the sharp end is generally remote from the mounting structure. A depth stop adapted to limit the depth of penetration of the needle is releasably connected by a rotary connector to the needle assembly. The released depth stop is removable from the needle for increasing the possible depth of penetration of the needle.

In another aspect of the present invention, a bone needle assembly generally comprises a handle and a needle having a longitudinal axis and a sharp end. The needle is mounted on the handle at a location away from the sharp end of the needle and projects outwardly from the handle. A depth stop unit comprises a positioning stem and a depth stop mounted on the position stem and movable along a length of the stem to different selected positions along the stem and along the longitudinal axis of the needle. The depth stop has a stop surface adapted to limit the depth of penetration of the needle. A rotary connector of the depth stop unit is adapted to releasably connect the stem to the needle assembly. The rotary connector is capable of releasing connection of the stem so that the stem and depth stop may be removed from the needle for increasing the possible depth of penetration of the needle.

In still another aspect of the present invention, a method of adjusting a permissible depth of penetration of a needle of a needle assembly generally comprises releasing a rotary connection of a depth stop unit to the needle assembly. The depth stop unit includes a depth stop positioned along a longitudinal axis of the needle and limiting the depth of penetration of the needle to a first depth. The depth stop unit is slid off of the needle to expose an additional length of the needle for penetration of the needle to a second depth greater than the first depth.

DETAILED DESCRIPTION

Referring now to the drawings and in particular toFIGS. 1-3, a bone needle assembly constructed according to the principles of the present invention is indicated generally at10. The bone needle assembly includes a handle12(broadly, “mounting structure”), and a needle14, all reference numbers indicating their subjects generally. The needle14includes a stylet18and a cannula20that can receive the stylet. The handle12includes a first or proximal handle member (indicated generally at22) mounting the stylet18, and a second or distal handle member (indicated generally at24) mounting the cannula20. “Proximal” and “distal” refer to the relative location of the handle members to a medical technician when the needle assembly is in use. The proximal handle member22is in contact with the palm of the technician's hand in use, and the distal handle member24is on the opposite side of the proximal handle member from the palm. It will be understood that a needle could include only a single component part, or more than two parts within the scope of the present invention. Similarly, a handle could be a single part or more than two parts. Moreover, the present invention has application to needle assemblies other than bone needle assemblies, and other than to needle assemblies having a depth stop. It is envisioned that the present invention also has use outside the field of needles.

The cannula20has an axial passage extending the length of the cannula and opening at both ends of the cannula. A distal tip28of the cannula20is beveled and sharpened. A proximal end portion of the cannula20is received in the distal handle member24. The stylet18is solid and includes a sharp distal tip32, and a proximal end portion received in the proximal handle member22. The stylet18can be inserted through the axial passage opening in the proximal end portion of the cannula20and received entirely through the axial passage of the cannula so that its sharp distal tip32projects axially outward from the distal tip28of the cannula. The stylet18provides the tool for penetrating the cortical bone, and can be removed from the cannula20once the intramedullary canal is accessed by the needle14.

The handle12formed by the proximal and distal handle members22,24has an ergonomic shape that can be comfortably received in a medical technician's hand, and allows the technician to easily control the needle assembly10as he or she applies the substantial forces needed to penetrate the bone. More specifically, the top or proximal surface38of the proximal handle member22is rounded in conformance with the shape of the palm of the hand. The bottom or distal surface40of the distal handle member24is also rounded but is undulating in shape thereby forming finger wells40A for receiving the technician's fingers. The proximal and distal handle members22,24can be securely connected together when the stylet18is received in the cannula20, so that the handle12acts essentially as a single piece when used to drive the needle14through a patient's skin and into the bone. The proximal and distal handle members22,24can be disconnected and moved apart for removing the stylet18from the cannula20.

To assemble the proximal handle member22and stylet18with the distal handle member24and cannula20, the sharp distal tip32of the stylet is inserted into the central open portion of the distal handle member so that it enters the axial passage of the cannula. The proximal and distal handle members are turned from their aligned position to a position in which the proximal handle member22is perpendicular to the distal handle member24(not shown). When the handle members22,24are fully brought together, they are turned toward alignment with each other. This results in the handle members22,24being interconnected in the position illustrated inFIGS. 1 and 2. Thereafter, it will require nearly a 90 degree turn of the proximal handle member22relative to the distal handle member24to disconnect these components. Accordingly, accidental separation of the handle members22,24in use is resisted. Wavy ribs46on the distal handle member24are provided for gripping the distal handle member to disconnect and separate the distal handle member from the proximal handle member22. The wave shape of the ribs46suggests to the medical technician (because the ribs extend both around a longitudinal axis LA of the needle and along the needle axis) that first twisting and then axial movement is needed to achieve separation of the proximal handle member22and stylet18from the distal handle member24and cannula20.

The proximal end portion of the stylet18extends into the open center of the proximal handle member22, and is secured is a suitable manner to the proximal handle member. For instance, the handle member22may be molded around the stylet18or the stylet may be attached to the proximal handle member by an adhesive. The proximal handle member22can be formed of polymeric or other material. Although shown as opaque in the drawings, the handle member22could be partially or totally transparent. A proximal end portion of the cannula20extends into a tubular, projecting portion66of the distal handle member24located at its center. The cannula20is mounted on the distal handle member24in a suitable manner. For instance, the distal handle member24may be molded around the cannula20or the cannula may be adhered to the distal handle member. The distal handle member24can be formed of polymeric or other suitable material. Although shown as opaque, the handle member24could be partially or totally transparent.

The needle assembly10further comprises a depth stop unit (broadly, “an operative member), generally indicated at50. The depth stop unit includes a depth stop52that has a generally conical portion54with a cylindrical nose56projecting therefrom, calling to mind roughly the shape of a space capsule. The conical portion54has an annular bottom stop surface58that is engageable with the body of the patient to limit the penetration depth of the needle14into the body. A hub59generally in the center of the bottom of the depth stop52is sized and shaped to receive and hold a tube (not shown) by a releasable interference fit. The tube covers the sharp ends28,32of the cannula20and stylet32, and is removed by pulling off of the hub59prior to usage of the needle assembly10.

The depth stop unit50further includes an elongate, tubular threaded member, indicated generally at60, on which the depth stop52is threadably mounted. The threaded member60has an axially extending passage61(FIG. 3) that extends completely through the length of the threaded member. The passage61receives the needle14through the threaded member60. Referring toFIG. 5, the threaded member60includes a positioning stem62having threads64. A connector (indicated generally at66) of the threaded member60comprises two arms68projecting upward from the positioning stem and having radially inwardly projecting fingers70at their free ends. The arms68are located on diametrically opposite sides of the threaded member60. The connector66can releasably attach the threaded member60and depth stop52to the distal handle member24, as will be described more fully hereinafter. Although the positioning stem62and connector66are shown as one piece, a connector could be formed separate from the positioning stem. Moreover, the positioning stem62could be eliminated and the connector66could directly attach the depth stop52to the distal handle member24without departing from the scope of the present invention.

As shown inFIG. 4, the depth stop52has an axially extending passage74extending through the entire length of the depth stop and including a larger diameter portion74A and a smaller diameter portion74B at its bottom end (as oriented inFIG. 4). The larger diameter portion74A receives the positioning stem62of the threaded member60into the depth stop. The smaller diameter portion74B allows the needle14to pass out of the depth stop52. The larger diameter portion74A has threads76that mate with the threads64of the positioning stem62. Rotation of the depth stop52about a longitudinal axis of the threaded member60(which generally coincides with the longitudinal axis LA of the needle14) in the direction indicated by arrow A1inFIG. 1causes the depth stop to move relative to the positioning stem62toward a distal end of the threaded member. Rotation of the depth stop52on the positioning stem62in the opposite direction indicated by arrow A3inFIG. 1causes the depth stop to move toward the proximal end of the threaded member60. Movement toward the distal end of the threaded member60has the effect of shortening the length of the needle14located between sharpened distal tips28,32of the cannula20and stylet18and the stop surface58of the depth stop52. The possible depth of penetration of the needle14into the body is therefore reduced. Moving the depth stop52toward the proximal end of the threaded member60increases the length of the needle14located between the sharpened tips28,32and the stop surface58of the depth stop52. The possible depth of penetration of the needle14into the body is therefore increased. Thus by rotating the depth stop52on the positioning stem62, a particular limited depth of penetration of the needle14into the body of the patient can be selected. Among other things, this can prevent the needle14overshooting its target bone and inadvertently damaging another area inside the body.

The adjustment of the depth stop52along the length of the threaded member60allows considerable variance in the effective length of the needle14and selected depth of penetration. However, in some instances it will be necessary or desirable to employ substantially the full length of the needle14projecting outward from the tubular portion66of the distal handle member24to reach the target bone. The depth stop unit50can be removed from the needle assembly10by disconnecting the threaded member60from the distal handle member24.

The threaded member60is attached to the distal handle member24by the fingers70of the arms68being received in circumferentially extending slots80formed in a projecting tubular portion (generally indicated at82) of the distal handle member (see,FIGS. 7 and 9). The tubular portion82includes a hole83that receives the cannula20(removed inFIGS. 7 and 9) and allows for passage of the stylet18into the cannula. A threaded member or depth stop could be attached at other locations on a needle assembly without departing from the scope of the present invention. The slots80each are open on one circumferential end of the slot and include an end wall84on the other end of the slot. The end wall84locates the fingers70and positions the threaded member60relative to the handle12. The fingers70and slots80are shaped for retaining the fingers in the slots thereby to prevent inadvertent disconnection of the threaded member from the distal handle member24. More specifically, each of the fingers70has a triangular recess70A located generally in the center of the finger. Each slot80has a corresponding triangular projection80A in the center of the slot.

When the triangular projections70A are received in the triangular recesses80A, the threaded member60is held against rotation relative to the tubular portion82of the distal handle member24(FIGS. 1 and 9). Thus, the threaded member60is prevented from inadvertent disconnection from the distal handle member24. By applying sufficient force, the interlocked connection of the triangular recesses70A and triangular projections80A can be overcome to release the threaded member60from the distal handle member24. To connect the threaded member60to the distal handle member24, the threaded member is rotated in a direction opposite arrow A3from itsFIG. 2position back to itsFIG. 1position. A tapered leading edge portion70B of each finger70first enters its respective slot80and eventually engages the triangular projection80A. The tapered shape of the leading edge portion70B allows each arm68to be resiliently deflected by a small amount in a radially outward direction with respect to the longitudinal axis LA of the needle14. As the threaded member60continues to be rotated, each triangular recess70A is eventually brought into registration with the corresponding triangular projection80A. The resilience of the material of the arms74forces the recesses70A down onto the triangular projections80A so that the projections are partially received in the recesses to retain the connection. The technician will experience a tactile or audible snap as a result of this registering event that confirms the threaded member60is secured in place. By applying sufficient torque in the direction of arrow A3, the fingers76can rotate to move the triangular recesses70A off of the triangular projections80A through deflection of the arms78. It will be understood that the shape of a projection and recess may be other than triangular. Moreover, the projection could be on a finger and a recess could be in a slot of a handle. Still further, the retention feature could be omitted within the scope of the invention.

To release the threaded member60, and hence the depth stop unit50from connection with the distal handle member24, the connector66(and hence the entire threaded member60) is rotated about 90 degrees in the direction indicated by arrow A3from its connected position shown inFIG. 1to a release position shown inFIG. 2. Rotation of the connector66moves the fingers70out of the slots80so that the depth stop unit50is no longer connected to the distal handle member24. The connection may be described as “bayonet”. However, it will be understood that other types of connections, including non-rotary connections may be used within the scope of the present invention. Generally speaking, a quick release connection is desirable (but not mandatory in the present invention). For rotary connections, it is desirable to release connection with less than a 360 degree turn of the connector and more desirable to require a turn of less than 180 degrees to release connection. The bayonet connection illustrated in the drawings requires only about a 90 degree turn to achieve both connection and disconnection. Connection can be made by turning the connector66of the threaded member60from the position inFIG. 2back to the position ofFIG. 1.

Once the threaded member60is disconnected from the distal handle member24by this motion, the depth stop unit50can freely slide down the needle14and off of its distal end so that the depth stop unit is entirely removed from the needle assembly10, as is illustrated inFIG. 3. The entire length of the needle14projecting outwardly from the tubular portion82is now available for penetrating into the body of the patient to the target bone. If desired, the depth stop unit50can be reattached to the needle14because the disconnection is non-destructive.

Generally circumferentially extending ribs88are located on the depth stop52at the intersection of the conical portion54and the cylindrical portion56. It will be understood that ribs (not shown) could be placed at other locations, such as on the arms68of the threaded member60. The ribs88are spaced apart axially of each other along the longitudinal axis of the threaded member60. The wave shape of the ribs88suggests by its circumferential extent that removal of the depth stop unit50requires rotary motion about the axis of the threaded member60and needle14. The axial extent of the ribs88suggests a second movement along the axis is needed. These provide indications to the medical technician of how to release the depth stop unit50and then slide it off of the needle assembly.

When introducing elements of the present invention or the preferred embodiment(s) thereof, the articles “a”, “an”, “the” and “said” are intended to mean that there are one or more of the elements. The terms “comprising”, “including” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. Moreover, the use of “up”, “down”, “top” and “bottom” and variations of these terms is made for convenience, but does not require any particular orientation of the components.