In many heart surgery procedures, the sternum of the patient has to be severed in the longitudinal direction and then the halves of the sternum including the ribs extending therefrom have to be spread apart in order to allow the operating surgeon to work on the heart. For the purpose of spreading said operation opening, retractors (also referred to as blockers or spreaders) are used.
It may happen that the operating surgeon works for several hours in said operation area which is kept open by a retractor. In order to avoid the retractor itself being interfering or obstructive, it should lie on the patient as flat as possible. As experience teaches, the operating surgeon frequently puts down his heels of hand on the retractor frame for protecting the wrists. Especially any small angular contours or any shapes protruding in uncomfortable manner bar the way to do so.
Moreover, the retractor must not have any contours which would cause surgical threads and suture material being caught or hooked in. This is why all geometries should be designed so as to be smooth and planar.
The frame of the retractor, usually consisting of one or more racks which form a longitudinally adjustable crossbar, two valve arms which are formed on the longitudinal ends of the crossbar or fixed thereon, and a drive box which is mounted on the crossbar, do not present a noteworthy dimensioning problem. Such a retractor is relatively flat with all known embodiments.
The only component which is always considered annoying by all operating surgeons with all the retractors being available on the market, is the drive crank by means of which the longitudinal displacement of the crossbar for spreading the sternum is manually performed. It has to be large enough so that it can be grasped well and fits ergonomically in the hand to some extent. With this, it projects some centimeters beyond the flat drive box and is the only component which protrudes from the flat silhouette of the retractor.
As a very small, space-saving crank indeed would be less interfering, but is not practicable for handling, a detachable crank is the best technical solution so far. EP 1 471 831 B1 discloses a drive of a blocker of the present type, in which the crank can be taken off from the drive associated to the retractor. This is a drive in which a square shaft projects from a drive box which is mounted on the retractor. A crank comprising a correspondingly mating female square is fitted in form-locking fashion on said square shaft. As the case may be, the two elements also comprise a latching element, e.g. a ball pressure piece and a mating feature as latching position for securing the assembled state.
However, the detachable crank according to EP1 471 831 B1 has the disadvantage that it indeed reduces the interfering contour of the drive when removed, but does not completely eliminate it. A square shaft or a bolt of any other shape will always exist and may be perceived by the operating surgeon as inexpedient. In particular, the crank in the assembled state is usually not reliably adapted on the square shaft of such a drive. The form-locking plug connection is only effected in one plane. Removing the crank from the drive (from the square shaft), i.e. the inversion of the plug-in process, is not counteracted at all or only to a very low degree possibly by means of a ball pressure piece or similar latching element, in this case in force-locking manner. In any case, said latching element does not have an autonomous actuation means, i.e. it is automatically operated upon pulling off the crank from the crank stud and hence represents only a weak resistance. This is why the crank, determined by the system, can be pulled off just as easy as it is attached. In use, however, the operating surgeon will exert onto the crank not only radial forces, but also unintentional compressive and tensional forces in the longitudinal direction of the square shaft axis. This is why the crank may come loose from the assembled state in case of an insufficient securing and impede the work with the retractor.
Basically, there is the possibility to secure the crank on the square shaft by means of a shaft nut, for instance. It would also be possible to provide splints or similar securing elements preventing any unintentional removal of the crank from the square shaft (crank stud). This form of axial securing, however, always requires a second hand and/or a second assembly/disassembly step, reducing the functionality of the retractor.