Surgery – Instruments – Orthopedic instrumentation
Reexamination Certificate
1998-12-09
2001-07-24
Hirsch, Paul J. (Department: 3732)
Surgery
Instruments
Orthopedic instrumentation
C606S053000
Reexamination Certificate
active
06264660
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a surgical instrument for the mechanical removal of bone cement according to the preamble of claim
1
, and a process for the production of shock waves adapted for the removal of bone cement according to the preamble of claim
16
.
Surgical instruments of the above type are required in orthopedic operations, for instance when after the removal of a hip joint prosthesis the remaining bone cement, e.g. made from PMMA, has to be removed, and for providing an accurate lodgment of the newly inserted hip joint prosthesis. For removing the cement, use is made e.g. of chisel tools which are driven into the cement with the aid of a hammer to thus split off the cement from the bone in the bone-marrow cavity.
The removal of bone cement is largely required in orthopedic surgery in order to exchange or consolidate date endoprostheses which have become loose or infected. Also other applications are possible.
Particularly in hip endoprosthetics, prostheses are exchanged with increasing frequency. In prostheses fixed by cement, the removal of the bone cement is bothersome and time-consuming. As of yet, the removal of the cement is performed by chisels of various shapes; however, such chisels pose problems as to their safe use, e.g. in the depth of the marrow cavity where visual inspection is difficult. Besides the large time requirements, damage may be caused to the bones, rendering the new implantation of a prosthesis impossible or resulting in an excessive loss of bone substance.
Further, pneumatic hammers are known (EP 0 144 005, W095/22934) wherein a piston element is pneumatically reciprocated in a cylinder, wherein, at the distal end of the cylinder, the piston element exerts an impact onto a chisel tool axially supported in the housing. In such a system, the chisel tool is accelerated to speeds slightly above 3 m/s, and the stroke of the chisel tool is about 8 mm. The large stroke entails the danger that the chisel tool accidentally penetrates into the bone substance.
Thus, the above surgical instrument is merely suited to imitate the heretofore manually performed blow of a hammer. However, it has been found that the efficiency of such a pneumatically operated chisel does not meet the requirements in the removal of bone cement and involves the risk of damage to the bone.
Further known surgical instruments are operable to melt and remove thermoplastic bone cement by means of ultrasonic vibrations (U.S. Pat. No. 5,221,282). Using such an instrument, the bone cement will become ductile from about 100° C. and then can be removed. In the process, temperatures up to 200° C. are generated at the tip of the tool and may cause damage to the bone. The smoke generated during the removal of bone cement produces released monomers having a toxic effect.
SUMMARY OF THE INVENTION
Thus, it is an object of the invention to provide a surgical instrument for the removal of bone cement of the above mentioned type, and a process for the production of shock waves which is suited to remove bone cement with considerably increased effectiveness.
In the invention, it is advantageously provided that the piston element comprises a projectile which can be accelerated to a high final speed and induces a shock wave into the chisel tool comprising a shock wave transmission probe and having a probe tip transmitting the shock wave to the bone cement.
With the above ballistic gain, an undesired generation of heat is not to be expected, and the removal of cement is easily controllable. The time required for removing the cement, particularly when exchanging a prosthesis, is noticeably reduced. Cement can be removed without any substantial damage to the bone.
Thus, the transmission of the shock waves is not performed by a stroke of the whole chisel tool but substantially by the change of length of the shock wave transmission probe at the probe tip as induced by the shock wave. This makes it possible to generate high accelerations and speeds at the probe tip, allowing for the transmission of impact energy many times higher than in conventional pneumatically operated chisels because, in the laws of impact energy transmission, the speeds are reflected as raised to the second power.
The final speed of the projectile striking onto the shock wave transmission probe is about 5 to 20 m/s, preferably about 10 to 15 m/s. With such an impact velocity of the projectile, also an associated maximum speed of up to 20 m/s can be observed at the probe tip.
The velocity amplitude of the probe tip is below 1.5 mm and preferably less than 1 mm. The change of length is partially caused by the elastic deformation of the shock wave transmission probe and normally is between 0.5 and 1 mm on the whole.
The shock wave energy generated by the projectile is in the range between about 0.3 J and 2 J, preferably between about 0.5 J and 1.0 J.
The shock waves are generated by an impact frequency of the projectile of about 6 to 20 Hz, preferably about 8 to 10 Hz. The diameter of the shock wave transmission probe is in the range between about 1 and 6 mm, preferably between 2 and 4 mm.
The shock wave transmission probe is guided axially in the housing, and a damping spring element, acting in the axial direction, is arranged between the shock wave transmission probe and the housing. In this manner, the shock wave transmission probe is decoupled from the housing in the axial direction.
Further, it can be provided that the projectile transmits the impact pulse onto an intermediate element arranged in flush abutment on the shock wave transmission probe.
The shock wave transmission probe can be hollow, and the intermediate element can comprise a shell being closed towards its proximal end and having at least one radial outlet opening. Such an intermediate element in connection with a hollow shock wave transmission probe is suited for connection of a suction means for sectional removal of the detached bone cement.
The acceleration path of the projectile is preferably about 100 to 200 mm. Thus, the acceleration path is a multiple of the diameter of the projectile.
The shock wave transmission probe can be flexible so that the shock wave cannot be transmitted in a rectilinear fashion.
Further, a magnetic holder for the projectile can be arranged on the proximal end of the cylinder. The magnetic holder will hold the projectile in the proximal final position until the projectile is again accelerated towards the shock wave transmission probe.
Preferably, pneumatic drive means are provided to accelerate the projectile.
The shock wave transmission probe can be guided in a working channel of an endoscope. The optically monitored local use of the probe tip on the cement also in the depth region of the marrow cavity which otherwise cannot be visually observed, will increase the effectiveness of the cement removal as well as reduce the danger of undesired damage to bones and soft parts. This obviates the need for additional operative measures, e.g. the forming of bone windows.
Further, the endoscope can be provided with a lens cleansing means on the distal end. For cleansing, the optical lens of the endoscope is rinsed at the distal end of the. endoscope, preferably with Co
2
.
REFERENCES:
patent: 2376187 (1945-05-01), Reiter
patent: 2421354 (1947-05-01), Reiter
patent: 2437014 (1948-03-01), Arnesen et al.
patent: 2655921 (1953-10-01), Haboush
patent: 2725878 (1955-12-01), Reiter
patent: 3640280 (1972-02-01), Slanker et al.
patent: 4919113 (1990-04-01), Sakamoto et al.
patent: 5518502 (1996-05-01), Kaplan et al.
patent: 5902413 (1999-05-01), Puszko et al.
patent: 5931833 (1999-08-01), Silverstein
patent: 5980528 (1999-11-01), Salys
Klopfenstein Denis
Menne Andreas
Merkle Wolfgang
Schmidt Joachim
Simon Bernard
Diller, Ramik & Wight.
Ferton Holding
Hirsch Paul J.
Priddy Michael B.
LandOfFree
Surgical instrument for mechanical removal of bone cement,... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Surgical instrument for mechanical removal of bone cement,..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Surgical instrument for mechanical removal of bone cement,... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2451659