the lumbar disc prosthesis referred to herein basically comprises two pieces that can be adjoined to one another , both pieces adopting a kidney - shaped peripheral formation , the two pieces offering a bumpy external surface , with drilling of the horizontal and transversal material to form small , sharp pyramidal elevations covering the entire external configuration of both parts of the prosthesis . the upper piece of the lumbar disc , on the plane on which it makes contact with the lower piece , contains an ample oval - shaped , totally rounded cavity which can house the likewise oval - shaped protruding part of the lower piece to conform an oval - shaped central core with a central belt , thereby limiting all of the movements to the normal physiological limits of the invertebral disc . in particular , it is the only disc that limits rotation to levels within the normal range , also limiting lateralisation , flexion and extension under conditions that are appropriate for the function which the prosthesis is intended to perform , incorporating a blocking system that prevents either piece of the prostheses from moving forward to cause a dislocation . another feature of this lumbar disc prosthesis is that is comes with assembly bolts that make it possible to block the disc with a rear mooring , the same one that is used to perform a lumbar arthrodesis . to join the pieces together , special bolts are used consisting of a smooth cylindrical body with a sharp end , while the head , which is the last part to be assembled and which is fixed to the upper outside part , is threaded on the outside so that when the bolts are housed in an oblique position , they will go through both pieces ( the lower one through the oval - shaped domed protrusion ) and the upper part which will house the sharp end , threaded finally by their respective heads at the entrance of the screw itself into the sides of the upper part , conforming the fully assembled lumbar disc prosthesis . for a better understanding of the general features described above , enclosed herewith are figures which graphically and schematically represent a preferred practical embodiment of the lumbar disc prosthesis of the invention . it should be noted , given the eminently informative nature condition of the drawings in question , that the figures shown therein should be examined with discernment and without limitation , which figures represent the following : fig1 shows a frontal view of the outside face of the upper part which adopts a kidney shape , the entire surface presenting a bumpiness formed of transversal and longitudinal slots that produce a plurality of small , sharp pyramidal protrusions . fig2 shows a frontal view of the inside face of the upper piece , with an oval - shaped central cavity and threaded orifices on one edge to house the blocking bolts . fig3 shows the same frontal view of the inside as fig2 , in which the blocking bolts are assembled , positioned in an oblique arrangement , threaded by their heads to the upper part of the prosthesis . fig4 shows a profile cross - section of the upper part , where the oval - shaped central cavity and the threaded orifices for the introduction of the blocking bolts are seen . fig5 shows a frontal view of the inside of the kidney - shaped lower piece presenting an oval - shaped central protrusion with a central bolt , with the arrangement of orifices which run obliquely through the oval - shaped protrusion for the blocking bolts carrying the outside face with a serrated edge along the entire periphery . fig6 shows a longitudinal profile of the lower piece according to fig5 , where the oval - shaped protrusion and the orifices for the blocking bolts can be seen . fig7 shows a longitudinal side view of the fitting system for the two pieces comprising the lumbar disc prosthesis , the outer surfaces of which two pieces are slightly jagged . fig8 shows an elevation view of one of the bolts . fig9 shows a longitudinal projection view of one of the blocking bolts , with threading on the outside of the head . always referring to the attached drawings , it should be noted that in the different figures designed therein , numerical elevations have been incorporated related to the descriptions of the characteristics and operations described below , thereby facilitating their immediate location . hence , ( 1 ) and ( 2 ) are the complementary upper and lower parts of the disc prosthesis , respectively , the outer surfaces of which parts ( 1 ) and ( 2 ) are serrated ( 3 ) caused by a plurality of longitudinal and transversal slots constituting small elevated pyramids with their sharp edges . the inside plane of the upper piece ( 1 ) has an oval - shaped cavity ( 4 ) constituting a union with the lower piece ( 2 ), with threaded orifices ( 5 ) on the periphery and one of the longitudinal sides followed by a smaller diameter cylindrical prolongation which extends to the oval - shaped central cavity , the aforementioned orifices being position from the edge in an oblique arrangement so that the orifices themselves on the inside wall opposite the oval - shaped cavity ( 4 ), are prolonged in the position ( 6 ), permitting the assembly and fastening of the lower piece ( 2 ). to enable the assembly of the prosthesis , the internal and central plane of the lower part ( 2 ) contains an oval - shaped central protrusion ( 7 ) perfectly adaptable to the cavity ( 4 ) also oval - shaped , of the upper piece ( 1 ), this piece ( 2 ) having in its central protrusion two orifices ( 8 ) arrangement obliquely and in conjunction with the threaded ( 5 ) and blind ( 6 ) orifices to permit the assembly of the blocking bolts ( 9 ) with the sharp point ( 10 ) and the threaded head ( 11 ), thereby fitting both pieces ( 1 ) and ( 2 ) together to form the lumbar prosthesis , the assembly also containing bolt covers ( 12 ) to cover the threaded sector ( 5 ) of the upper piece ( 1 ) of the prosthesis . having amply described each and every one of the parts constituting the lumbar disc prosthesis of the invention , all that remains is to note that the different parts can be made from a variety of materials in a variety of shapes and sizes , and the possibility of introducing construction variation , provided that they do not alter the essential aspects of the invention which is the objective of this utility model application .
the invention refers to a new type of disc prosthesis for application to the lumbar area especially designed to permit movement within the normal physiological limits of the invertebral disc , permitting lateralisation , flexion and extension under conditions which are as close as possible to the physiological ones .