This invention relates to the field of trephine cutting tools of the type used for obtaining samples from humans, animals, and other living or deceased specimens.
In the treatment and study of disease and the therapeutic processes and in biomedical studies such as space medicine bone study, it is desirable to collect small specimens of bone from a vertebrate test subject for microscopic and other laboratory study. A guiding and supporting arrangement for conveniently and safely collecting such samples is, for example, shown in the copending patent application, having one common inventor herewith, Ser. No. 06/751,393, filed Jul. 3, 1985 and issued 31 Mar. 1987 as U.S. Pat. No. 4,653,509, and deals principally with accurately positioned sample collection from small animal test subjects.
The use of a hollow annular cross-sectioned drill bit having small sawteeth disposed at the working end thereof, i.e., a trephine cutter, for the collection of tissue samples from living test subjects has been known for some time. A frequent problem with the known sample collecting arrangements occurs, however, during the post-sample collection steps wherein the sample is removed from the trephine cutter bit. Heretofore it has been common practice to employ hydraulic pressure or a push rod or some similar forcing apparatus for disengaging the collected sample from the trephine cutter bit. In the course of this disengagement, sufficient pressure is often applied to the collected sample to cause compression damage or sample density alteration as a by-product of the disengagement sequence. For most present-day study purposes, such disturbances of the collected sample are a disabling, sample-destroying consequence. An awareness of such destructive effects occurring during sample collection is, for example, indicated in the article "Closed Vertebral Biopsy" by L. S. Fyfe, A. P. J. Henry, and R. C. Julkolland, published in the Journal of Bone and Joint Surgery, Vol 65-B, No. 2, Mar. 1983, wherein the collection of tissue specimens of two millimeters diameter or more is suggested for best accuracy. In the case of bone samples, the tendency of sampled tissue to clog or obstruct the sample collecting apparatus has in particular been a problem with the existing trephine arrangements. The periosteum tissue surrounding bone members in a vertebrate specimen has particular affinity for surgical instruments and thereby materially complicates the sample retrieval process using most existing trephine equipment.
The patent art discloses inventive attention to the field of trephine sample collection. This attention is evidenced in the patents of W. Ackerman, U.S. Pat. No. 2,919,692; I. Hallac, U.S. Pat. No. 3,605,721; K. Jamshidi, U.S. Pat. No. 3,628,524; P. W. Hoffsess, U.S. Pat. No. 3,893,445; and L. S. Matthews, U.S. Pat. No. 4,306,570, all of which concern trephine or biopsy sample apparatus providing some arrangement for disengaging the collected sample--arrangements such as a push rod extruder or multiple collecting device diameters. It may be noted, however, that none of these patents is concerned with a trephine sample collecting arrangement wherein the cutter bit can be disassembled to provide convenient access to the sample and also assure the absence of compression disturbances to the sample. The prior art has therefore been unable to provide a fully satisfactory apparatus for collecting high-quality trephine samples conveniently and practically.