POSITIONING PROBE FOR A DRILL JIG IN KNEE SURGERY

Abstract: An anterior cruciate ligament (ACL) drill jig probe comprises a location portion (10) for securing in an ACL drill jig, a shank (11) extending from the location portion for passing one side of the patella tendon, and a horn (12) extending from a junction (13) with the shank (11) at an obtuse angle (OE) for location against the posterior part of the intercondylar notch as the anatomical reference point for an ACL drill jig with which the probe is to be used. The shank (11) has two lateral bends (16, 17) in opposite directions, both to facilitate passing of the shank round the lateral aspect of the medial femoral condyle and the patella tendon and to allow ready use of the probe with an existing coplanar ACL drill jig. A set of instruments comprises at least two interchangeable probes, one for a left knee and one for a right knee, with opposite handed bends (16, 17), and a coplanar ACL drill jig.

Description: POSITIONING PROBE FOR A DRILL JIG IN KNEE SURGERY This invention relates to knee surgery, more particularly to replacement of the anterior cruciate ligament, hereafter referred to as ACL. A synthetic scaffold-type ACL replacement such as that known by the trade mark ABC of Surgicraft Limited comprising carbon and polyester fibres in a braided zigzag structure has proved successful. Mode of failure analysis using electron- microscopy has shown that most failures (between 9% and 12% over the past 6 years) occur at the internal exit of the tibial drill hole. Two surgically-avoidable mechanisms have been elucidated; crushing of the fibres by impingement between the roof of the intercondylar notch and the edge of the drill hole in extension; and, fatigue damage due to repetitive tension over the sharp edge of the tibial drill hole. Crushing and fatigue damage can be avoided by the use of a substantial radius cutter for the tibial drill hole. Failure by notch impingement can be avoided by ensuring that the tibial drill hole is positioned posterior to the roof of the intercondylar notch when the knee is in full extension, and so the object of the present invention is to provide a drill jig probe which facilitates the correct positioning of the tibial drill hole without direct visualisation (arthrotomy) or indirect visualisation (arthroscopy) . According to the present invention, an ACL drill jig probe comprises a location portion for securing in an ACL drill jig, a shank extending from the location portion for passing one side of the patella tendon, and a horn extending from a junction with the shank at an obtuse angle for location against the posterior part of the intercondylar notch as the anatomical reference point for an ACL drill jig with which the probe is to be used. The shank and the horn are conveniently formed integrally by a length of round rod, e.g. of stainless steel of 4.0mm diameter, but may be of semicircular or other cross- section, with a bend (which may be slightly curved) at the junction between the shank and the horn, and the free end of the horn is preferably rounded-off. The other end of the shank (i.e. remote from the horn) is conveniently secured in a hole in one end of the location portion, which preferably consists of a length of square-section bar, e.g., of stainless steel of 8.0 mm lateral dimensions, with the corners and ends bevelled or rounded-off, and with at least one semicircular notch in one side for secure location in an ACL drill jig with which the probe is to be used. The shank may be straight and coaxial with the location portion, or the shank may have at least one lateral bend (which may be slightly curved) to facilitate passing of the shank round the lateral aspect of the medial femoral condyle and the patella tendon, but the shank preferably has two lateral bends (each of which may be slightly curved) in opposite directions, both to facilitate passing of the shank round the lateral aspect of the medial femoral condyle and the patella tendon and to allow ready use of the probe with an existing coplanar ACL drill jig, so that the tibial drill hole will have an axis oblique in three dimensions to the axis of the horn of the probe and with its exit end axially aligned below a point on the horn above its junction with the shank, which ensures correct positioning of the tibia drill hole with its axis oblique to the sagital, coronal and transverse planes. Because of the bends in the shank the probe becomes "handed" for a left or a right knee, as the case may be, and so the invention preferably also provides a set of instruments comprising at least two interchangeable probes, one for a left knee - and one for a right knee, and a coplanar ACL drill jig. However, because of varying dimensions in knees between patients, the set preferably comprises a plurality of interchangeable probes for a range of left knees and a range of right knees. Embodiments of ACL drill jig probes in accordance with the invention and sets of instruments including such probes will now be described, by way of example only, with reference to the accompanying drawings, in which:- Figure 1 is a side elevation of one such ACL drill jig probe orthogonal to its location portion; Figure 2 is a plan of the probe of Figure 1 orthogonal to the side elevation; Figure 3 is a fragmentary side elevation in the direction of the arrow X in Figure 2; Figure 4 is a perspective view of a set of three ACL drill jig probes in accordance with the invention; Figure 5 is a perspective view of a coplanar ACL drill jig with the probe (b) of Figure 4 applied to a model right knee, along with a drill; Figure 6 is a fragmentary elevation showing how the location portion of the probe is located in the jig; Figure 7 consists of two small scale diagrams showing the disposition of the probes (a) and (b) of Figure 4 in relation to parts of left and right knees respectively; and Figure 8 is an enlarged fragmentary section in a plane coincident with the axis of the tibial drill hole, showing part of the drill which has formed it and part of the probe which has been used for its accurate location. The ACL drill jig probe shown in Figures 1 to 3 of the drawings comprises a location portion 10 for securing in an ACL drill jig 20 (as will be described presently with reference to Figures 5 and 6), a shank 11 extending from the location portion for passing one side of the patella tendon 21 (see also Figure 7), and a horn 12 extending from a junction 13 with the shank at an obtuse angle for location against the posterior part 22 (see Figure 8) of the intercondylar notch 23 as the anatomical reference point for the ACL drill jig with which the probe is to be used. The shank 11 and horn 12 are formed integrally by a length of stainless steel round rod of 4.0 mm diameter with a sharp bend at the junction 13, and the free end 14 of the horn is rounded-off. The other end of the shank 11 is secured as by pinning or cementing in a hole 24 (see Figure 6) in one end of the location portion 10 which consists of a length of stainless steel square-section bar of 8.0 mm lateral dimensions, with the corners and ends bevelled or rounded-off, and with a semicircular notch 15 in one side for secure location in the ACL drill jig with which the probe is to be used. To facilitate passing of the shank 11 round the lateral aspect 25 of the medial femoral condyle and the patella tendon 21 when the probe is used with an existing coplanar ACL drill jig, the shank has two bends 16, 17 in opposite directions, so that the tibial drill hole 26 (see Figure 8) will have an axis oblique in three dimensions to the axis of the horn 12 of the probe and with its exit end (indicated at 18 in Figure 2) axially aligned below a point on the horn 12 above its junction 13 with the shank 11 which ensures the correct positioning of the tibial drill hole without direct visualisation (arthrotomy) or indirect visμalisation (arthroscopy) . Because the bends 16, 17 in the shank 11 cause the probe to be "handed", a set of instruments in accordance with the invention would comprise (in addition to an existing coplanar ACL drill jig) at least one probe as shown and at least one other probe with the bends 16, 17 each of opposite hand; but, to cover variations in anatomical dimensions of different patients knees, a set of instruments would comprise a series of left knee probes and a similar series of right knee probes with appropriate variations in geometry around the following typical values and relationships:- A = 60mm B = 25mm C = 5mm D = 58.7mm H = 30mm a = 45° φ = 120 ,O*= 180 -ck & - 180 - V - = e arcsin (e sin ( ) ) A e = B cos (90 -cL.) f = A sin (&) sin 05) g = D - A + cos 00 As shown in Figure 6, the location portion 10 of a probe having a square section is a close fit in a groove 27 across the body 28 of the coplanar ACL drill jig 20, and is provided with a second semicircular notch 15X of larger diameter than the notch 15 so that engagement of the notches 15, 15X with pegs 29, 29X of corresponding respective diameters projecting into the groove 27 ensure that the probe will be located with the shank 11 and horn 12 projecting in the right direction. The prove is made secure in the jig when a sliding clip 30 is pushed into place over the groove 27. The probes (a) and (b) in Figures 4 and 7 are recommended for general use, while the probe (c) in Figure 4 has a straight shank 11 and is suitable for use in arthroscopic reconstruction with insertion via a central portal.

Claims: - 1 - CLAIMS 1. An ACL drill jig probe comprising a location portion for securing in an ACL drill jig, a shank extending from the location portion for passing one side of the patella tendon, and a horn extending from a junction with the shank at an obtuse angle for location against the posterior part of the intercondylar notch as the anatomical reference point for an ACL drill jig with which the probe is to be used. 2. A probe as in Claim 1, wherein the shank and the horn are formed integrally by a length of round rod with a bend at the junction between the shank and the horn. 3. A probe as in Claim 1 or Claim 2, wherein the bend is slightly curved. 4. A probe as in any one of Claims 1 to 3, wherein the free end of the horn is rounded off. 5. A probe as in any one of Claims 1 to 4, wherein the other end of the shank is secured in a hole in one end of the location portion. 6. A probe as in any one of Claims 1 to 5, wherein the location portion consists of a length of square-section bar, with the corners and ends bevelled or rounded-off, and with a semicircular notch in one side for secure location in an ACL drill jig with which the probe is to be used. 7. A probe as in Claim 6, wherein the location portion is provided with a second semicircular notch of larger diameter than the other notch. 8. A probe as in any one of Claims 1 to 7, wherein the shank is straight and coaxial with the location portion. 9. A probe as in any one of Claims 1 to 7, wherein the shank has at least one lateral bend to facilitate passing of the shank round the lateral aspect of the medial femoral condyle and the patella tendon. 10. A probe as in Claim 9, wherein the shank has two lateral bends in opposite directions, both to facilitate passing of the shank round the lateral aspect of the medial femoral condyle and the patella tendon and to allow ready use of the probe with an existing coplanar ACL drill jig, so that o the tibial drill hole will have an axis oblique in three dimensions to the axis of the horn of the probe and with its exit end axially aligned below a point on the horn above its junction with the shank, which ensures correct positioning of the tibia drill hole. 5 11. A probe as in Claim 9 or Claim 10, wherein the or each lateral bend is slightly curved. 12. A set of instruments comprising at least two interchangeable ACL drill jig probes as defined in any one of Claims 9 to 11, one for a left knee and one for a right knee, 0 and a coplanar ACL drill jig. 13. A set of instruments as in Claim 12 comprising a plurality of interchangeable probes for a range of dimensions of left knees and a range of dimensions of right knees. 5

Inventors: KONG KIN CHONG, MOMBRAY MICHAEL ANTONY SYDEE, PHILLIPS PETER WILLIAM, STROVER ANGUS EVERETT, KONG, KIN, CHONG, MOMBRAY, MICHAEL, ANTONY, SYDEE, PHILLIPS, PETER, WILLIAM, STROVER, ANGUS, EVERETT
Applicants: KONG KIN CHONG, MOMBRAY MICHAEL ANTONY SYDEE, PHILLIPS PETER WILLIAM, STROVER ANGUS EVERETT, SURGICARFT LTD, SURGICRAFT LIMITED
Application year: 1993
Main classification: A61B17
IPC codes: A61B17