Surgery – Instruments – Orthopedic instrumentation
Patent
1995-07-24
1997-05-20
Buiz, Michael
Surgery
Instruments
Orthopedic instrumentation
606 60, 606 72, 606 73, A61B 1756
Patent
active
056308175
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a device for the fastening onto a rod of a member such as a screw, hook or the like in particular for a rachidian orthopaedy instrumentation.
One already knows various fit orthopaedic instrumentations or equipment such as those known under the name of HARRINGTON and which permit to straighten out and to stay the rachis or spinal column of a patient for example suffering from a scoliosis.
In these known orthopaedic instrumentations, members in particular provided to be anchored onto the vertebrae of the rachis to be propped, as for example like screws or hooks are connected to each other by a rod to which they are fastened. In general the fit orthopaedic contrivance comprises two rods the shape of which is defined in accordance with the position in which the rachis to be stayed should be held and which are implanted on either side, respectively, of the back face of this rachis.
Each member is held against motion on the corresponding rod with the assistance of a suitable fastening device. For example the document FR-A-2,458,271 (KEENE) describes an orthopaedic instrumentation in which each anchoring member is held immovable on a threaded rod through the medium of a fastening device comprising a U-shaped body made fast to the said member and between the legs of which the rod may be mounted radially. An intermediate sleeve may be mounted on the one hand onto the rod and on the other hand in sliding relationship between the legs of the body whereas clamping means are provided to exert a pressure upon the body through the medium of the sleeve.
One has also proposed in the prior art devices for the fastening of a member onto a rod comprising surface asperities such as knurls or chequerings. In these devices the clamping means are constituted by a set screw mounted onto the sleeve and adapted to exert a radial force upon the rod in order to make the latter fast to the sleeve by crushing the asperities to increase the adherence between the latter and the rod.
With these known devices however, the mounting of the sleeves onto the corresponding rod constitutes a complicated handling prior to putting the equipment in place thereby making wearisome and undesirably increasing the duration of the surgical operation necessary for the implanting of this appliance.
Moreover if the rod comprises machinings such as threadings or notches as this is the case with the KEENE or HARRINGTON instrumentations, the forces applied upon the members are generating concentrations of stresses at the level of the machinings of the rod which may cause its break.
Furthermore if the rod comprises surface asperities, the latter have a tendency to become battered at the level of its zones of contact with the sleeve or the screw so that the tightening hence the immobilization of the member onto the rod are frequently being altered after the implanting of the contrivance. In one case or in the other one, these defects may be detrimental to the behaviour of the anchoring members and be the cause of a modification of the geometry of the instrumentation. This geometry modification causes a loss of correction or of reduction and a mobilization of the anchoring members under the effect of the stresses imposed upon the patient.
The secondary effect of this mobilization may be the cause of a corrosion through friction called "fretting corrosion".
Therefore the present invention has as its object to propose a fastening device which copes in particular with the inconveniences of the prior art stated above.
To reach this goal the fastening device according to the invention is characterized in that the sleeve exhibits substantially the shape of a split ring which may be slipped over the advantageously smooth rod, the said clamping means being disposed onto the ring plumb with the slot thereof and in that the rod under the effect of the tightening exerted by the clamping means spreads apart the free ends of the wings of the slit ring in order that the free ends of the wings be radially pressed on the one hand upon the legs of
REFERENCES:
patent: 5067955 (1991-11-01), Cotrel
patent: 5176680 (1993-01-01), Vignaud et al.
patent: 5368594 (1994-11-01), Martin et al.
patent: 5380326 (1995-01-01), Lin
patent: 5474555 (1995-12-01), Puno et al.
patent: 5476462 (1995-12-01), Allard et al.
Rokegem Pascal
Steib Jean-Paul F.
Buiz Michael
Eurosurgical
Leonardo Mark S.
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