Abstract:
Apparatus to guide blades or saws of femoral cuts for knee prosthesis, consisting of four blocks, two blocks which move only vertically and two blocks which move only horizontally. Cams are provided which are accompanied by followers and have helix tracks whose pitch permits the apparatus to adapt to different prostheses.

Description:
BACKGROUND OF THE INVENTION 
     The present invention concerns an ancillary apparatus for knee prosthesis. 
     It is known that knee breaks and/or diseases particularly arthritic diseases are becoming today more frequent, above all, in the increasing sport activities field as in the non-sport practicing population because of age or life lengthening and/or simply greater mobility. 
     The instruments for knee interventions have seen an enormous expansion and innumerable are the proposals and structures suggested in the literature or applied in hospital practice also, and mainly in the attempt to suggest and finally provide an apparatus of universal character, i.e., able to be applied to the knee in different forms and sizes which knowingly vary from one person to the other. 
     Among the numerous patents and patent publications, may be mentioned U.S. Pat. Nos. 4,892,093, 5,474,559, 5,749,876, European Patent Publications No. 0538,152, No. 0538,153, No. 0555,003, and French Patents No. 2,664,157, No. 2,679,766, No. 2,629,339, No. 2,681,779. 
     French Patent No. 2,679,766 discloses a femoral cut device for the correct positioning of prosthesis implants in the femoral and sagittal planes, which however needs several guides of cutting blades of different sizes for prosthesis to adapt to the different articulation sizes: some risks in the correct guide positioning are possible. 
     The resection apparatus according to French Patent No. 2,664,157 includes a guide for the cutting blades in two blocks, one movable with the bevelling cuts support and one adjustable in height for the anterior cut. 
     In the PCT-Publication WO96/01588 (corresponding to U.S. Pat. No. 5,749,876 and EP No. 0721314) the apparatus for the knee condyles resection and for the positioning of a prosthesis comprises: a support with an inferior basis; a guide of the blades of the anterior and posterior cuts, either chamfer or not; an intramedullary femoral rod, and tracer or contact means, said guide having three blocks two of which are mobile and adjustable in height; further one of the blocks comprises means to guide one of the anterior, posterior chamfer (or not) cuts, and the other two blocks comprise guide means for the remaining cuts. 
     There is no doubt that the proposed solutions and devices, above all those according to said U.S. Pat. No. 5,749,876, have merit, however, they are never free of structural complexities which, moreover, involve operative complications; further they have production and running costs which strongly handicap a generalized diffusion. 
     The first object of the present invention is to provide an instrumentation particularly simple, compact, reliable and universal both in structural and operative terms. 
     Another object of the invention is to provide adjustment and control means which are decidedly advantageous compared with the corresponding ones of the prior art. 
     SUMMARY OF THE INVENTION 
     The present invention concerns an ancillary apparatus for knee prosthesis, in particular for guiding the femoral cut blades or saws which permit the insertion of the prosthesis components mostly adapted to the conformation of each patient, said apparatus comprising several blade-guide blocks vertically approached, in this case a first inferior (lower or bottom) block ( 4 ) for posterior cut guide, a superior or head block for the anterior cut, two median (intermediate) blocks ( 2  and  3 ) for posterior ( 2 ), anterior ( 3 ) chamfer cuts, and means ( 5 ,  6 ) of support, seal and motion of said blocks. 
     According to a first feature of the invention the apparatus is characterized in that said anterior and superior (i.e., terminal) blocks are only vertically movable, have at least two vertical holes for the passage of motion means, at least one horizontal hole for the insertion of means complementary to said means and front slits which are inclined to a horizontal line, are remote in respect to the inferior and superior edges of said end blocks; the intermediate blocks move only horizontally, are provided with holes corresponding to the holes and inclined slits on the edges of said intermediate blocks. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The various features and advantages of the invention will better appear from the following description of the (not-limitative) embodiments shown in the accompanying drawings in which: 
     FIG. 1 is a perspective and partially exploded view of the four blocks in the instrumentation according to the invention; 
     FIG. 2 is a partially exploded perspective view of two motion cams; 
     FIG. 3 is a partially perspective and enlarged view of only the right portion  40  of block  4 ; 
     FIGS. 4A and 4B are the vertical cross-sections with a plane having the line A′, A″ as traced on said right portion  4 D of block  4 , FIG. 4A showing the uncompressed spring and FIG. 4B showing the compressed spring; 
     FIG. 5 is an exploded and perspective view of the cam follower; 
     FIG. 6 is the front view of the four compacted blocks, with cams  5  and  6  inserted in all vertical holes and with the cam IA followers inserted in the two horizontal holes  10 - 10 ′, and with the insert of the anatomic angle AAI fixation set in the two recesses  19 - 19 ′ of the two median blocks; 
     FIG. 7 is a top view of the flat face  7 D of block  2 ; 
     FIGS. 8 to  8 D are top views of five embodiments of the anatomic angle AAI adjusting insert having an H form; 
     FIG. 9 is a front view of AAI; 
     FIG. 10 is a perspective view of the insert AAI joint in the two recesses  19 - 19 ′ worked in the two intermediate blocks  2  and  3 ; and 
     FIG. 11 is a schematic cross-section of the apparatus according to the invention, on a knee together with the five made cuts. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 shows the four saw-guide blocks from  1  to  4  in exploded position, i.e. detached from each other. The end blocks namely the upper (superior)  1  and lower (inferior)  4  block, as well as the median blocks  2  and  3  show vertical hole couples  8 - 9 ,  8 ′- 9 ′,  28 - 29 ,  38 - 39 , respectively, for the passage of the motion means  5  and  6  (FIG.  2 ). 
     The terminal blocks  1  and  4  are horizontal blocks  10 - 10 ′ for the insertion of the means IA complementary to said means  5  and  6 . In an advantageous and preferred embodiment of the invention, the motion means  5  and  6  are cams and the complementary means are cam followers. 
     The superior block  1  and the inferior block  4  show slanting slits  12 ,  12 ′, respectively, for the anterior cut AC ( 12 ) and posterior cut PC ( 12 ′) (see FIG.  11 ), as well as horizontal holes  10 ,  10 ′ for the insertion of the cam follower device IA. 
     The head (superior) block  1  has additionally the slit  18  for the distal cut DC ( 18 ) in FIG.  11 . The slits  12  and  12 ′ are sufficiently remote in respect to the edges  15  and  16 , respectively, whereas the slits  13  and  13 ′ are preferably near the edges  17  and  17 ′. The median blocks  2  and  3  have facing recesses  19  and  19 ′. 
     According to a feature of the invention, the terminal blocks  1  and  4  are moved only vertically and median blocks  2  and  3  are moved only in a horizontal plane. 
     The motion means are of the cam type  5  and  6  and, typically, show on a nucleus or central axis CA two portions with a minor diameter  51 - 51 ′,  52 - 52 ′ in which are provided the helix tracks H-H′, H″—H″, as well as two portions with major diameter  53 — 53 ′,  53 ″- 53 ″ in which are present the grooves Gs-G 1 , G&#39;s-G′ 1 , respectively. 
     At the superior edge of CA, CA′ are engaged the handles M, M′. 
     In the perspective view of FIG. 3 is represented on an enlarged scale only the right portion  4 D of block  4 , in order to better show the horizontal hole  10 ′ with its continuation  10 C which will act as the cavity for the spring SP of the cam follower that is shown in exploded form in FIG.  5  and consists of a central hub or boss MOZ from which protrude two shafts PR and PM having a diameter lower than that of MOZ. On the pin PR is keyed roller RO which facilitates the rotation of the whole piece MOZ+PR+PM for horizontal displacement. 
     FIGS. 4A and 4B show block  4  with hole  10 ′ in which penetrates the central shaft CA (see FIGS. 4A-4B and  5 ) extending up to the anterior face of roller RO mounted on pin PR of hub MOZ whose second pin PM acts on spring SP. Obviously the pieces MOZ+RO+PM+SO which form the follower IA of cam  5 - 6  have been previously inserted in cavity  10 C which is on the continuation of shaft CA. 
     Once spring SP and means MOZ with roll RO have been inserted in the cavity  10 C, the end CA″ of shaft CA is pushed against the face  90  of roll RO through which MOZ compresses spring SP whereby we go from the configuration with relaxed spring SP (u) of FIG. 4B to the configuration with compressed spring SP(c) of FIG.  4 A. Once said spring SP(c) is compressed, cam  5  is inserted in hole  8 ′ till the end  51 ″ of the inferior portion with minor diameter  51 ′ is engaged with a part of roller RO face  90 ; with said engagement of roller RO ( 90 ) with the inferior portion  51 ″, it is possible to re-extract the central shaft CA (pulling knob M′″) because the inferior base  51 ″ of the lower part  51 ′ of cam  5  insisting on face  90  of roller RO keeps the spring compressed as in FIG.  4 A. 
     Shaft CA can now be unthreaded and in the free portion so obtained the cam  5  is vertically pushed down till roller RO engages track H′. With this insertion of RO into H′ the surgeon turns the handle M whereby roller RO re-ascends said track H′ and translates along vertical axis Y—Y of cam  5  thereby vertically displacing block  4 . 
     The same procedure takes place for the cam  5  superior portion  51 , i.e., after that the cam has been taken in position of FIG. 4A, also the superior part  51  of  5  engages its follower IA housed in the cavity  10   c  of the superior block  1 . Blocks from  1  to  4  can be seen compacted in FIG. 6, blocks  1  and  4  containing the superior followers IAs and IAs′ being inserted in the hole  10 ′ and  10 ′″ of block  4 . 
     In FIG. 6, reference AAI indicates the anatomical degree insert with the relevant hole  65  inserted in the recess  19  of block  2  and recess  19 ′ of block  3 . Overall, in FIG. 6 as well as in FIGS. 2 and 3, the slits  13  and  13 ′ associated to the median block  2  and  3  are indicated as formed of two pieces. They can be formed of only one piece (monopiece) as  12  and  12 ′ which, at the limit, can also consist of several pieces (multipieces). 
     In general, the rotation of handles M, M′ of cams  5  and  6  amounts to a half revolution, i.e. 180°. Preferably it proceeds at determinated steps of the pawls and springs associated to M and M′ (not shown because they are conventional). 
     FIG. 7 is a top view of the top SS 2  of block  2  and shows the dashed holes  11  and  11 ′ in which are inserted the pins P 11  and P 11 ′ which go in engagement in the superior grooves Gs and G&#39;s of the superior portions  53  and  53 ′ of  5  and  6  (FIG.  2 ). 
     Similarly pins or plungers P 21  and P 21 ′ (FIG. 10) will be inserted in holes  21 - 21 ″ of blocks  3  and will engage inferior grooves G 1  and G′ 1 . These engagements of the four pins or plungers P 11 -P 11 ′ and P 21 -P′ 21  with the four grooves G&#39;s-G 1 —G&#39;s-G 1  (FIG. 2) will inhibit vertical movement of the “ensemble” of the four assembled blocks  1 - 4 . 
     The insert of anatomical angle AAI (FIG. 7) has a hole  86  whose median axis or central line  97  coincident with the anatomical axis AX has an inclination over the geometrical or mechanical axis MA, which can generally vary between 4° and 10° preferably between 5° and 9°. Therefore according to the patient anatomical axis AX the surgeon will select the insert AAI with the inclination adequate to the involved patient anatomical axis. 
     The top views of FIGS. 8,  8 A,  8 B and  8 C (similar to FIG. 7) show the five inserts from AAI ( 1 ) to AAI ( 5 ) with the inclinations from 5° to 9° capable to cover the case majority. FIG. 9 is a front view of a typical insert AAI, the insert from AAI ( 1 ) to AAI ( 5 ) being seen from the top. 
     FIG. 10 shows the partial perspective of a median block, in this case block  3  with the insert AAI entered in the recess  19 ′; to this end insert AAI has a H-shape with four protruberances  96 - 97  (forward, anterior) and  98 - 98 ′ (rearward, posterior) which ledge or partially extend over the lateral faces  96 - 97  (anterior) and  98 - 99  (posterior) of block  3 . 
     FIG. 11 is a side view (for example, according to arrow F of FIG. 6) of the assembly of blocks  1 ,  2 ,  3 , and  4 , each block being represented together with the inclined axis of its own slit  12 ,  12 ′ (generally, inclination of about 3° or 5°) and  13 ,  13 ′ (45° inclinations). 
     In the assembly center, namely through the control portion of block  2 , goes (passes) rod R placed on the anatomical axis AX. APK indicates the anatomical profiles of femur Fe and the cuts made by the blades or saws guided by blocks  1 - 4  are indicated by references AC ( 12 ), anterior cut PC ( 12 ′), posterior cut, SAC ( 13 ′) anterior chamfered cut, SPC  13  posterior chamfered cut, and DC ( 18 ) distal cut. 
     The assembling sequence of the apparatus according to the invention is: insertion of anatomical axis AX in block  3 ; insertion of cams  5  and  6  within said block  3 ; insertion of pins P 12  and P′ 12  in the holes  21  and  21 ′ of block  3 ; engagement of the major diameter portions  53 ′ and  53 ″ in the holes  28 - 29  of block  2 ; engagement of pins P 11  and P′  11  into holes  11  and  11 ′ to assure the assembly seal; insertion into the holes  10 ′ and  10 ″ of block  4  of cam followers, namely of spring SP and hub MOZ together with roll RO; compression of said spring, withdrawing of shaft CA and insertion of the threaded portions  51 ′- 51 ″ and  52 - 52 ″ up to the click or release engagement with the relevant rollers; and repetition of the engagement of the helixes H and H″ with the respective rollers. 
     The hospital attendants will have no difficulty in carrying out this assembly whereas the surgeon must substantially limit himself to maneuver the handles M and M′ which, because of the helix profiles in the portions  51  and  51 ′ of the cams, and of the eccentricity of the major diameter portions  53 ,  53 ′ respectively (i.e. in respect of  51  and  51  ′) provide the vertical movements of blocks  2  and  3  in relation to blocks  1  and  4 . 
     For illustrative clarity, the invention has been described with particular reference to the embodiments represented in the accompanying drawings. It is obvious that all the changes, alternatives, substitutions and the like to said embodiments which are in the reach of one skilled in the art, and are to be considered as falling within the scope and spirit of the following claims.