CA2135235A1 - Cam lock orthopaedic fixation screw - Google Patents

Abstract

ABSTRACT

A cam-locking orthopaedic fixation device for anchoring a bone graft in a bore formed in a bone mass. The device has a head, a nose remote from the head, and a body, extending between the head and the nose, with a series of threaded crests only partially circumferentially surrounding the body. At least one side of the body is smooth and free of thread crests.

Description

~`` 2~3523~i ~OC~ OR~P~TC

sAc~G~o~D OF 2~E ~VX~o~
1. ~
The present i~ventio~ relates to orthopedîc fixation screws and methods and m~re paxticulaxl~ to such sc~ews and methods i~ which a b~ne graft is a~chored in a bore for~ed in a bone mass. ~:

2.
~he anterior cruciate ligament (ACr~ 25mm-40m~
in length and is ~xequen~ly injured in co~tact an~
other a~tivities. Such injuries ca~ cause instability i~,the knee to the exte~t that ACL reconstruction maY ::
be re~uired.
The xeplacement o~ ~he ACL with the ce~t~al third o~ the pa~ellar ~endon using a bo~e-tendon-bone grat is a known method for r~s~oring knee stability. In this ~xocedurs, the cent~al third of the pa~ellar tendo~ a~d ~ortions of bone at either end thereo~ are taken as a graft. ~ tunnel is bored in the distal femu~ and proxi~al tibia, i.e., where they join at the knee. The bone-tendon~bone gra~t is disposed with one bone se~ment in o~e o~ the tunnels and the other bone segment in the other tunnel. Wi~h the grat so dis~osed, each o~ the bone segments are anchored by sc~ewing an inter~erence screw into the t~mnel between a ~unnel wall and the bone segme~t thereby anchori~g ~he segment in the tun~el.
Su~h ~roce~ure is illustrated and described in UAS~ Patent No. 4,9~7,421 ~o Goble et al. ~o~ p~ocess 2135~3~

of e~dosteal fixation o~ a ligament . ~he Goble et al .
m~thod.suffers from several disadvantages. ~irst, ~he interference screw is cannulated, i,e., it has an æial bore for ridin~ a guide wire into the boxe. The wire S must be i~serted into the bore adiacent the bone gxa~t be~ore the screw can be installed. The yuide wire prevents dive~gence o~ the screw as i~ is screwed into the space between the graft and the tun~el wall. A
s~ecial driver, also ha~ing an æial boxe ~or recei~ing the guide w~re, must be provided to install the screw.
Threading the wire through the bore is an additional surgic~l s~e~, in itself undesirable, which has the potential for creating metal deb~is. In addition, the suide wires can bend or kink. The screw of ~he Goble et al. ap~lication provides an ex~remely steep taper a~ the leadin~ end thereof which ra~idly com~resses ~he gra~t as the screw is ins~alled.

5UN~ARY OF THE INVENTIOW
The p~esen~ i~ention comprises a cam-loc~ing ortho~edic ~ixation screw or ancho~i~g a bone gra~t in a bore ~orm~d i~ a ~o~e mass. The screw includes a ~ad, a nose remote ~xom ~he head, and a body havin~
cont.inuously ta~ered threads ta~ering ~om the head o~
the screw to the nose o~ the screw wherein one side o~
the screw, along ~he longitudinal axis is ~lat and unthread~d.
In ~ccoxdan~o with the p~esent invention, a method c_ .

2~352~

for securins a bone graft in an eno5teal tu~nel is presented. The meth~d includes drilli~g an endosteal :
bore of a size sufficient to ~orm a ~pace b~twee~ the bone gr~ft and a wall of the bore w~en the graft is S inserted in the bore, insertIng the ~raft in the one .
end of the bore, i~serting the bo~e s~rew i~to the space without rotating the screw and wi.~hout cutting . . ;
the bone, the bo~e screw havin~ a~ asymmetrical cross section, a~d therea~ter rotati~g the screw until it9 ; .
threads engage the.bo~e graft and the ~ore wall thereby : ~ ~
lockin~ the screw in place and ~ixing the graft in the : . ;
bore.
rhe p~sent invention ob~iates the need for using a cannulatcd inter~erence scr~w a~d ~urther ~ro~ides i~proved ~radual com~ressio~ of the gxa~t as the ~ixation sc~ew is installed.
The foregoing and other objects, features and advantage~ of the invention will become more readil~ ;
ap~Lent from the ~ollowing detailed descxiption o~ a preferred embodiment which ~roceeds with refere~ce to the drawings.

BRIEF DE;SCRIP rIoN OP q~E DR~WINGS
~S Fi~. 1 is a~ enlarged view o~ a cam-lock oxthopedic ixation screw and a portion oE a dri~er there~or con~ructed in accoxdance with the presen~
inven~ion.

2~35,~35 Fig. 2 is a ~iew along line 2 2 in Fig. 1.
Fig. 3 is a~ enlarged view, partly in cross-section, o~ an alternative ~mbodiment of the cam-loc~
or~hopedic ~i~ation screw oE Fig. 1.
Fig~ 4 is a view, ~artly Ln cro~s-section, of the screw o~ Fig. 3 prior to placement into the bo~e.
Fi~. 5 is a view, similar to Fig. ~, aEter th~
screw has been inserted into the bon~.
Fig. 6 is a view similar to ~ig. 4, a~ter the screw has been rota~ed and ~ully installed respo~sive to a~roximatel~ 90O of screw rotation.

DETAII-ED DESCRIPTION OF ~rHE PREPERRED EMBODI~r Turning irst ~o Pig. 1, i~dicated gen~rally at 10 is an orthopedic ~ixation device for anchoring a bone gra~t i~ a boxe formed i~ a bone mass. Deviee 10 includes a driYer 12 and screw 1~. The screw includes a nose 16, ~ threaded body 18 and a head 20. The nose is remote ~rom the head and threaded body 18 has continuously tapexed threads 22 which ~aper rom a~proximately midway betwe~n head 20 and nose 16. One side 24 o~ the screw is asymme~xical and preEe~ably ~la~ and ~nthreaded. The ~xese~t embodiment o screw lg has a uniEorm ~itch o~ te~ threads per inch alo~
2~ the threaded ~o~t~on the~eo~ and has a no~e 16 that has a ~la~, leading Eace 26.
The head 20 o~ screw 1~ includ~s an axial he~agonal socket 32~ The socket walls are ~a~allel to 2~5235 ~he axis of screw 14 and are sized to recei~e a conventional hexagoDal driver. The height o the ~hread crest becomes progressively less betwee~ about thxead crest 34 and th~ head 20 o~ the screw. A
S substa~tially 30 chamfer 36 is formed at the juncture bet~een ~ear sur~ace 30 and the root o~ threaded body por~ion 18. ~he ~rogressive reduction of thread c~est height thus ~orms a spiral betwee~ crest 34 and chamfer 36 as viewed in Fig. 2. Preexably, screw 14 is either constructed of a biocompa~ible ~aterial, or has a . ~ :
su~face coating of biocoI~patible materia~, which is sultable for lo~gte~m emplacement in association wit~
cancellous bone and so~t tissues.
Driver 1~ includes a sha~t 38 ha~in~ a driving end 40 ormed on one end and a handle (~o~ shown), similar to ~e handle o~ a screw driver, ~ormed o~ the o~her end thereo~. Drivin~ end 40 co~prises a hexagonal d~iver havin~ walls which taper inwardly between th~
juncture 42 of driving end 4~ with sha~t 38 and the outer end 44 of dri~ing end 40. As can be seen i~ Fig.
1, the distanc~ between juncture 42 and end g4 is slightly less than the de~th o~ socket 32. ~he relative sizes o~ dri~ing ~nd 40 and socket 32 ~xe such that ~he hexagonal walls o~ dxivin~ end 40 e~ag~ the interior walls of socket 32 as the screw socket is ~itted o~er driving end ~0~ Such engagement oca,ur~
jU5~ be~ore rear sur~ace 30 .reaahes juncture ~2~ Given that the interior walls of socke~ 32 ~re substa~tially '-'`'~'i' ,.

2~2~5 ~arallel to the longitudinal axis o~ driver 12 whi~e the walls of driving end gO taper as described abo~, the screw can be fitted onto the end of ~river 12 by pushi~ the screw until drivi~g end ~0 and socket 3 S ar~ tightly engaged.
Fig. 3 illustrates an alternative e~bodiment o~
the ~resent invention. Indicated generally at 14A is a cam lock orthopedic fixatio~ screw similar to the device illustrated in Fig. 1. The maLn d~fference is that screw 14A compris~s an elongate nose 16A. Nose 16A
includes a hemispherical leading face 21. The nose 16 is ~re~exably at least twice the length o~ the diameter of th~ nose. A ~a~ered portion 17 extends ~or approximately three complete threads ~rom nose 16~ to th~eaded body 18.
Turning now to Fig. 4, a bone mass 46 has a bore ~8 ~ormed therein. In ~he case of ACL reconstructive surge~y, the bore is formed in either the distal ~e~ur or proximal tibia, or both when screw 14A is used to anchor both ends o a bone-tendon-bone gra~. Bore 4R
is also refexred to herein as an endosteal tunnel. One end of the bone~tendon-bone gra~t ~s shown received in th~ bore g8. Gra~t 5~ includes a tendon 52 and a bone portion 54 connected to the tendo~. The othQr end o the te~don 52 tnot shown) similaxly includes a bone poxt~on connected there~o.
I~ use, an ortho~edic su~geon bores hole g8 in bone mass 46 whic~, or puxposes o~ the ~rese~t 6 .~ `
"'' ~ "' 2~ 3~23~

explanation, is assumed to be the distal femu~ This is accompli~hed using a conventionRl orthopedic drill and may be done endoscopically as may be the remainder o~
the following-described procedure. After bore 48 is drilled as shown in Fig. 4, one end o~ the graft ~0 is positioned i~ the bore as illustrated. Screw 14A is ~itted o~to drivex 12 as described abov.e so that socket 32 is firmly engaged with drivi~g ~nd 40. The surgeon grasps dri~er 12 ~y its handle ~not shown) and positions screw 14A as illustra~ed in Fig. 5; i.e., screw 14A is ~ecei~ed in the space between gra~ 50 and the interior wall of bore ~8. Screw 14A is re~e~red to herein as being received without in~ererence into t~e space between the gra~t and the ~all of the boxe w~e~e asymmetrical sicle 24 is ~ositio~ed flush against the gr~t 50. This describes the relative sizes of the sc~ew and the gap between graft 50 and bore 48 and the fact that when screw 14A is positioned as show~ in Fig.
5, no threads are engaged with either gra~t 50 or bore 48.
Next, the surgeon rotates screw 14A until the threads o~ the screw engage the gra~ 50 and bore 48, thereby lockin~ the sarew in place and ~ixing the graft in the bore, as show~l in Fig. 6. Pre~erabl~, the surgeon rotates the screw a~roximately 90 to lock th~
screw i~to ~lace. Once ~he scxew is positio~ed as shown i~ Fig. 6, the surgeon may withdxaw driving end 40 ~rom ;'~Y
socket 32. It should be no~ed that i~ i~ becomes 7 ; ~:
, ' .,: :.":
,: ~

2135~5 necessary to remove the screw duri~g a later su~gical procedure, soc~et 32 cooperates with a tandard hex driver. ~f a driver like driver 12 is not a~ailable when the sc~ew is to be removed, it may be removed with a standard hex driver.
Other screws, like screw 14 or lgA, can be used in corres~onding bores in the proximal t~bia (not shown) to anchor the other end o~ gra~t SO in a similar manner to tha~ describ2d above for anchoring the graft ~o the distal femur.
Havin~ illustrated and descxibed the principles o~
my invention in a preferred embodiment the~eo, it should be readily a~parent to those skilled in the art that the ~nvention can be modi~ied in arrangement and detail wi~hout departing f~om such principles. I claim all modifications coming withi~ the spirit and scope o~
the accompanying claims.

Claims (5)

1. A cam-locking orthopaedio fixation device for anchoring a bone graft in a bore formed in a bone mass, the device comprising:
a head;
a nose remote from the head; and a threaded body continuously tapered threads tapering from the head of the device to the nose of the device wherein one side of the screw along the longitudinal axis is flat and unthreaded.

2. A device of claim 1 further comprising an elongate nose.

3. A device of claim 1 further comprising a surface constructed of a biocompatible material suitable for long term emplacement in association with cancellous bone and soft tissues.

4. A biocompatible cam-locking orthopaedic fixation device for anchoring a bone graft in a bore formed in a bone mass, the device comprising:
a head comprising means for coupling a driving tool to the head, the head adapted for insertion into a space between a wall of a bore in bone and a bone graft in endosteal ligament reconstruction surgery;
a nose remote from the head;
a longitudinal body extending between the head and the nose of the device; and thread crests extending only partially circumferentially around the body, each thread crest extending to a height above the body, the height of thread crests being uniform from the head of the device to about midway along the body and diminishing from about midway to the nose of the device.

5. A device according to any one of the preceding claims wherein the thread crests have a pitch of ten threads per inch.