This invention relates to a hypodermic needle. There are several medical situations where it is desired to deliver substances by injection to a relatively large volume of tissue. If a substance is delivered by a single point injection, the problems that may arise are (a) the substance cannot spread throughout the volume in sufficient time, (b) too much dilution may occur during the spreading, (c) the distribution of the substance within the volume may be very inhomogeneous, and (d) unwanted spreading to regions away from the target volume may occur. One solution to this problem is to give smaller injections at several sites within the target volume. This approach has at least three disadvantages: (a) multiple needle stab wounds are created, (b) accuracy of placement is limited, and (c) the time for the procedure is increased.
A particular example of these difficulties arises in the treatment of liver cancers. Cancers within the liver can be killed with large doses of alcohol. One surgical approach is to expose the liver using open or laparoscopic surgery and inject the tumour at many sites using the same needle. One severe problem of this approach is that considerable bleeding results from the many stab wounds and, more seriously, this bleeding can carry tumour cells into the peritoneal cavity.
Thus, there is a need for a device capable of delivering substances to a relatively large volume of tissue without incurring the above-noted disadvantages of the prior art.
According to the invention there is provided a hypodermic needle comprising a front, hollow needle having movably secured therein one or more further, hollow needles, each said further needle and part of the hypodermic needle being movable relative to one another between a stressed position of the or each further needle, in which each said further needle is substantially parallel to the first needle, and an unstressed position of the or each further needle, in which the free end of each said further needle lies beyond the axial and/or radial terminus of the first needle. Preferably, in the unstressed position the or each said further needle protrudes beyond both the axial and radial termini of the first needle.
An advantage of this arrangement lies in the ability of the or each further needle to spread outwardly from the first hollow needle, thereby permitting injection into a large volume of tissue from a single puncture wound (in the case of plural, further needles); and/or allowing injection to one or more sites remote from the terminus of the first needle.
The creation of a single wound minimises bleeding; reduces the above-noted risk of transfer of cancer cells; and speeds the operation.
Preferably each said further needle is moveable relative to the remainder of the hypodermic needle and lies within the first needle when occupying its stressed position and protrudes from the first needle when occupying its unstressed position. This is the preferred means for advancing the or each further needle to its unstressed position, although alternative arrangements are possible. For example, instead of advancing the or each further needle from within the first needle, an encircling band may be moveable on a bundle of stressed, further needles to release them to their unstressed condition.
Preferably each said further needle is generally straight when occupying its stressed position and curved when occupying its unstressed position, thereby permitting its free end to project beyond the axial and radial terminus of the first needle when the further needle occupies its unstressed position.
The advantageously allows the further needles to be stored within the first needle eg during the puncturing operation and when the apparatus is being filled or transported.
In particularly preferred embodiments, each said further needle includes a circular arc when occupying its unstressed position. The or each said further needle may also include an arc in the range of curvature of 60xc2x0-110xc2x0, when occupying its unstressed position. The arc may in alternative embodiments lie outside this range of curvature, or may be of infinitely large radius, ie. one or more of the further needles may optionally include a straight portion. The foregoing features advantageously assist the or each further needle to advance through, eg. tissue without causing collateral damage thereto.
Preferably each said further needle is formed of or from a superelastic shape memory alloy (SMA), in particular a heat treated alloy comprising approximately 56% Ni and 44% Ti by weight. Preferably the cold drawn alloy is heat treated at approximately 500xc2x0 C. for about 10 minutes whilst secured on a former, thereby conferring the preferred shape on the further needles when occupying the unstressed position. These features permit the ready transition from a substantially straight to a substantially curved configuration on advancement of the further needles from within the first, hollow needle. The superelastic shape memory alloy is particularly suitable for embodiments of a said further needle the ratio of whose unstressed radius of curvature to its diameter lies in the range of 100:1 to 10:1.
An SMA is preferred to spring stainless steel because it has a recoverable strain some tens times greater than steel. Thus for a given curve the SMA tube can have up to ten times the diameter of a steel tube; conversely, for a give tube diameter, SMA can have a curve radius down to a tenth of that for steel. Nonetheless, it may be suitable to use steel or other non-superelastic materials for the further needles, eg. in embodiments in which the needle radius of curvature lies outside the range specified above.
Preferably the lengths of two or more of the further needles differ from one another. This, advantageously, assists in the distribution of the substance to the tissues.
Preferably the free end of the or each said longer, further needle is spaced axially and radially from the free ends of the other said further needles when the further needles occupy their extended positions.
Conveniently, the or each said further needle communicates with the interior of a hollow, elongate tube movably lying within the first said needle, the end of the hollow tube remote from the said terminus of the first needle engaging or including a movable actuator member for advancing and retracting the or each said further needle relative to the first needle. This provides a convenient and simple means of moving the or each further needle between its stressed and unstressed positions.
Preferably the interior of the hollow tube communicates with an adaptor for receiving the nozzle of a hypodermic syringe. The hypodermic needle of the invention may also optionally include a detent for securing the hollow tube in a position corresponding to retraction of the or each further needle. This feature improves the safety of the device, since it permits releasable locking of the further needle(s) in a stressed (inoperative) position.
The invention is also considered to reside in the use of a superelastic shape memory alloy in the manufacture of a hypodermic needle.