NON-INVASIVE QUANTITATIVE KNEE JOINT IN VIVO INSTABILITY ANALYZER

Abstract: The knee joint analyzer has means (34) for fixing the thigh and femoral condyles and means (36) for fixing the foot and malleoli of the patient. Said fixing means (36) are connected to an axial load and torque loading mechanism (37) for applying incremental loads and torques to the knee joint via load and torque transducers (2, 3, 4) which can be continuously measured, amplified and registered on a plotter (21) allowing the assessment of translational stability in the sagittal and coronal planes and rotational stability in the coronal and transverse planes of the knee joint of the patient.

Description: Non-invasive quantitative knee joint in vivo instability analys This invention relates to a non-invasive quantitative knee join in vivo instability analyzer with means for fixing the thig and femoral condyles, and means for fixing the foot an malleoli . Background of the Invention Of all joints in the human body the knee joint is the mos vulnerable to traumatic injury. These injuries arise from a wid range of causes, including vehicular accidents, but particularl from a wide spectrum of sporting and athletic activities. I order to reduce the number of such injuries and ensur successful joint reconstruction, accurate methods are require for diagnosing both chronic and early ligamentous instabilitie which, if not treated, may render the knee significantly mor susceptible to injury. Knee instability is defined as an abnormal rotational and/or translational movement of the tibial plateaux in relation to the femoral conyles, occurring about one or more axes or in " -one or more planes of motion and resulting in a functional deficit. Knee stability is provided by the complex interaction of a multitude of factors, including ligaments and other soft-tissue restraints, condylar geometry, active muscular control, and tibio-femoral contact forces generated during weight-bearing activities. Instability is caused when one or more of the structures which normally contribute to knee stability are injured. The magnitude of the instability induced by such a disruption is, however, difficult to quantify. There are four types of instability which involve no rotation of the tibia with respect to the femur: (a) Valgus instability (b) Varus instability (c) Posterior instability (d) Anterior instability. There are also four types of simple rotatory instability: (a) Anteromedial rotatory instability (b) Anterolateral rotatory instability c) Posterolateral rotatory instability (d) Fosteromedial rotatory instability The rotatory instabilities of type b/c, a/b, and a/b/c may be combined. At present, the clinical assessment of knee joint instability is carried out subjectively by setting the hip and knee at roughly the required angles, applying unknown forces to the lower 'limbs, and observing the resulting displacements. The success of such methods depends to a large extent on the judgement and experience of the examining physician who attempts in the examination to isolate only the passive restraints provided by the ligaments. This limited and subjective evaluation of th joint explains the frequent disparity between the results of stability examination and the observed in-vivo joint function. Clearly, reliable non-invasive quantitative objective technique for the assessment of knee joint instability are needed if ove or under treatment is to be avoided. Further, if the progress o patients is to be monitored over a period of time, reliabl comparisons of knee stabilities cn different occasions, o between different individuals, are required. The need to objectively assess knee stability has bee recognised by many workers, and a number of different device have been devised and tested with varying degrees of success. Most of these devices were designed to exclusively assess one, two, cr in an extremely few instances [e.g. Markolf e al. , Orthopaedic Fesearch Society, No. 110 (1975); Mo. T17 (1976) an J._one & Int. Surg. , 58A, No.5 (July, 1976); δOA, 554-574 (July, 19 n B)] three types cf instability; th anterior-poste ior drawer sign, valgus-varus rotation, an tibial tc.Ξic.n. This necessarily limited the amount of information w ic could be : -?'_e -? -.< i1÷. le to the orthopaedic surgeon caring for the patient. In a few cases, the levels of force applied during the tests were specified and real-time responses could be obtained, nevertheless, the precise manner in which loads were applied was not defined. thus reducing the validity of the measurements - ■ ttair.ei. Furthermore, in all the techniques described there has been no mention of any objective means employed to ensure that the stability measured arose from the passive restraints and was not due to protection of the knee joint by its musculature. Muscle forces, neuromuscular coordination, and the other factors all determine whether there is a functional stability or otherwise. From Siu et al. [Biomechanics Symposium, ASME; New York, 193-196(1981)3 a. computerised knee analyser is known to assess mediolateral stability in the human knee joint in vivo. The knee is thereby subjected to a maximum bending moment of 20 NM through a moto ised loading mechanism. From Shoemaker et al . [J.Bone & Jnt.Surg. , 64-A, 208-216 (Feb., 1982)] an instrumented clinical knee testing apparatus is known capable of assessing tibial axial rotational instability. Torque and resulting angular displacement are recorded with the aid of electrically operated transducers. The equipment used allows different angles of knee and hip flexion. The known knee joint analysers have failed to satisfactorily produce a reliable system for the non-invasive quantitative assessment of human knee instability in vivo. They can be criticised on four main points: (1) Recordings of muscular activity are not possible (2) Failure to define the mechanical parameters of the tests carried out with the analyser ( ctors such as the rate of loading may significantly affect the results obtained) (3) Failure of comprehensive assessment of the knee joint (4) Impossibility to measure dynamic stability resulting fro muscular contraction and weight-bearing. Summary of the Invention Accordingly, the present invention aims to provide a devic which ■-".r. be used reliably to quantify knee instabilities b performing four non-invasive stability tests: (1) β::te icr-postei i r drawer sign; (2) valgus-varus rotation; (3) tibial torsion; and (4) medial-lateral drawer sign. Another object ■; f the invention is to provide a device capabl of assessing the effects of muscular contraction an weight-bearing cn the knee joint stability. Still another object of the invention is to provide a device capable of ΞO<=?Cifying the maximum loads and rate of loading. Yet another object of the invention is to provide a device capable of producing a real-time graphical response of the knee joi t . Yet another object of the invention is to provide a device capable of assessing the stabilizing effect on the joint of the tibiofemoral contact force, thus giving an indication -of the integrity of the joint congruency. Yet another object of the invention is to provide a device capable of measuring the torques generated by muscle contraction. Other objects will, in part, be obvious and will, in part, appear hereinafter. The invention accordingly comprises the several steps and the relation of one or more steps with respect to each of the others, and the apparatus embodying the features of construction, combinations of elements and arrangement of parts which are adapted to effect such steps, all as exemplified in the following detailed description, and the scope of the inven i n will be indicated in the claims. Briefly, r.y apparatus is aimed at allowing the safe and accurate r.easurerr- nt of knee stability in various test planes, incorporating the following functions: ( "- } comfortable seating of the patient (2) provision fcr securely c imping the thigh and femoral condyl s (3) provision for securely clamping the foot and malleoli (4) adjustability for different leg lengths 5) adjustability for varying degrees of knee and hip flexion (5) loading the tibia axially with continuous measurement of applied load (7) loading the tibia anteriorly or posteriorly with continuous measurement of load applied and resulting anterior or posterior displ cement (8) loading the tibia medially or laterally with continuous measurement of load applied and resulting medial or lateral displacement (S) applying valgus or varus no ep.ts to the knee with continuous measurements of applied moment and resulting valgus or varus rotation (10) applying external or internal axial torques to the tibi with continuous measurement of torques applied and external o internal tibial rotation (11) measurement of activity of muscles around the knee joint (12) monitoring continuously EMG signals from musculature. Brief Description of the Drawings For a fuller ur ers nding of the nature and objects of th invention, reference should be made to the following detaile escription, taken in connection with the accompanying drawings in which: FIG . 1 i s a perspect i τ, e view of the test knee analyzer ; FIG . 2 is an exploded vi-ew o f the central pivot and lockin .n.echa ism ; FIG. 1 is perspective view showing the transducer system of th knee analyzer according to the invention; and FIG. 4 is schematic representation of the measurement an recording system of the knee analyzer according to th invention. Description of the Preferred Embodiments Referring now t. FIG. 1 of the drawings, the apparatus according to the invention consists essentially of a dental chair 31 -- J - " .71e iy the addition of a rigid frame 32 to which fixtures can be securely attached. The chair 31, being heavy, provides a stable testing base, while its adjustability allows subjects of various sizes to be accomodated with knees flexed throughout the range of 0° to 90° flexion. Additionally, subjects can be placed supine, to relax the hamstrings, by adjusting the movable chairback 33. The chair 31 comprises a thigh clamp 34 for fixing the thigh 35 and the femoral condyles and a plate 36 to which is strapped the T- ' ϊ t's ot . The entire clamping system consists of two distinct parts: one for the thigh and femoral condyles, and the other for the foot and malleoli. The thigh 35 is supported posteriorly by a curved thigh plate 41 which has been stiffened sufficiently for it to appear rigid under the loads to which it is subjected. To fix the thigh to "- e thigh plate 41, two velcro straps 42 are used. The design adopted consists of a lateral and medial rectangular aluminium block 43 with circular recess to which a sand-filled leather pouch 44 is glued. A screw 45 is fixed to the centre of the block 43, enabling it to be adjusted. Said screw 45 passes through a hole in an adjustable clamp fixed to the metal framework 32 surrounding the knee. The pouches 44 can be advanced tc clamp the condyles and locked in position using the two lock nuts 66. Two straps are fixed to the pouches 44; one strap (not visible in the figure) to support the popliteal region, froπ- O lot-. -and the other strap 47 to provide a third point of fixation of a tourniquet 43 to the thi_h clamp 34. Between the tc;m:qu=t 48 and the patella is placed a sand-filled fabr c pouch 49 which conforms to the shape of th patellar region and provides a pain-free firm fixation. Th pneumatic three-bladder tourniquet 48 forms a half-cuff aroun the thigh, and when inflated presses the thigh firmly agains the thigh-plate 41, and the patella against the popliteal strap. The foot rests against a plate 36, of which the length can b adjusted, with the heel supported on an adjustable pad made o aluminium, covered with plastazote. The foot is strapped to sai plate 35 by a velcro strap 61 which passes around the metatarsal region. To said foot plate 36 are fixed two metal strips 62 which provide fixation for the pads 63 which are used to clamp the malleoli. Said pads 63 are similar to the pouches 44 used to claπp the femoral condyles. The malleoli are further fixed via a velcro strap surrounding said metal strips 62. The apparatus according to the invention has two separate loading systems. Firstly , the axial loading system used to simulate load bearing on the limb and secondly, the loading system used to displace the tibia relative to the femur in the actual stability test. The axial load and torque loading mechanism 37 comprises the foot plate 36 which is mounted on a shaft 12 which runs parallel to the axis of the limb and is butted onto the end of a screw 13 which terminates distally in a small handwheel 14. When said handwheel 14 is rotated it advances the screw 13, thus pushing the foot-plate mounting shaft 12 proximally, and hence applies an axial load to the limb. Said foot-plate shaft 12 is supported in a number of bearings 15 and is interrupted by an axial load transducer 16 and a torque transducer 17. It also carries a pulley 18 by means of which axial torques can be applied to the imb. The footplate 36 is connected to said loading mechanism 37 via load, torque and angular displacement transducers (2,3,4 and 6). The position of the loading mechanism. 37 can be adjusted to suit the patient's leg l -.; : by sliding it along a guide bar 38 which in turn is attached to a cross-arm 39 at a central-pivot '" a- ovt which it -_ rotate '.the central pivot and locking uiecha ism is represented in FIG. _ in more detail). This cross-arm 33, i-Lic Is rigidly attached to the chair 3 provides adjustment ir. the r ic l plane to cater for various angles of knee flexion. For the measurement of linear displacement in the knee, adjustable a1-3*3 fitted with linear displacement trans¬ ducers are provided which are attached to the cross arm 39. For the application of loads to the knee in various planes, adjustable arrr.s fitted with pullies are provided. The system of pullies and weights is operated manually. The test loading system consists of a dead loading system. Cords 24 attached to fittings applied to the lower limb are passed over pullies 18 mounted on adjustable arms and bearing weights 23 added to hangers tied to their other ends. Interposed in the cords 24 are transducers for measuring the applied loads (Figs. 3 and ) . 86/00767 11 Linear displacement is measured by linear motion conductiv plastic potentiometers 1AP and 1ML. These produce an electrica signal directly proportional to the linear mechanical movemen • of the shaft ; conductive plastic resistance elements provid virtually infinite resolution and long life expectancy. Th potentiometric transducer provides a full scale output equal t the applied volta ε so that there is no need for an amplifier o other circuitry. The transducers should preferably have nominal . ' .echar.ical stroke of 50 mm, an electrical stroke of 50 0,3 - T and dr. i dependent linearity of ± 0,3 . Angular displacement is measured by rotary motion conductiv plastic centir.uc _ ■ _ potentiometers 1VV and 1TT which provide a -rl otz'ical s: r.-:.l directly proportional to the rotary mechanical .?._ve~er.t cf the shaft . he transducer has p re erabl .5ch_.:.ical travel _f 350^, an electrical travel of 350 ± 5*, an an independent linearit-- of ± 3%. Forces applied to the knee are measured by load transducers 2, 2 and 4 with foil strain gauges bonded onto a Z beam type body. The axial load transducer 4 has a capacity range of preferably 0- 2,5 KM, whilst the displacing load transducers 2 and 3 have a capacity range of 0-0, K . All load transducers 2, 3 and 4 have an infinite resolution, and a terminal non-linearity of< 0,05 %. Axial torque is measured by a standard torque transducer 6 which comprises a solid stainless steel shaft, onto which strain gauges *.re bonded. The torque transducer 6 has a capacity range of 0- 500 Nm, and a non-linearity of ± 0,25 %. The displacement transducers 1 give large voltage outputs in the range of 0 - 5 V and can therefore be directly connected to the recording instrument 21 without the need for amplification. The load transducers 2, 3 and 4 require an excitation voltage of 10 V and have a normal sensitivity of 3 mv/V. Therefore their outputs have to be amplified using a commercially available transducer pre-amplifier 23. The torque transducer 6 requires an excitation voltage of 2,4 V DC and should have a sensitivity of 3 mv/V. The output is amplified by a matching amplifier 22. The knee response curve is obtained by connecting the outputs from the test load and displacement transducers to the x and y chanr.els of a X-Y plotter (Figure 4) . The load signal car- also be fed for synchronization purposes, to a four-channel chart recorder to which the axial load and .K outputs are also connected.

Claims: 67 1 3 Claims 1. Non-invasive quantitative knee joint in vivo instabilit analyzer with means (34) for fixing the thigh and femora condyles, and means (35) for fixing the foot and nallaoli, cha a e i ed in that said means (36) are connected to an axia load and torque loading mechanism (37) fcr applying incrementa lαάfis n-v Sjrq es to the knee joint via load and torqu f-raπsd cer. (?,?,4) and that means (21) are provided for th c nt ir._c .Ξ m as em t of the applied loads a d torques allowing the Assessment of t anslat i rnal stability in the sagittal un coronal planes and rotational stability in the coronal and transverse planes of the knee j ir.t. 2. Knee joint analyo-.r according to claim 1, wherein the loads are applied via a system of pullies (18), cords (24) and weights 3. nee joint analyzer according to claim " or 2, wherein the loads are of quasi-static nature. 4. Knee joint analyzer according to one of the claims 1 to 3, wherein the fixing means (34) and the loading mechanism (37) are mounted on a patient's chair (31). 5. Knee joint analyzer according to one of the claims 1 to 4, wherein the position of the loading mechanism (37) is adjustable to suit the patient's leg length by sliding it along the guide bar (38-) which in turn is attached to the cross-arm (39) at the central-pivot (10) about which it can rotate. 6. Knee joint analyzer according to one of the claims 1 to 5 , wherein transducers (2,3,) are interposed in the cords (24) for measuring the applied loads, in particular, the forces and moments applied to the knee. 7. Knee joint analyzer according to claim 1 or 6 , wherein means (6) are provided to allow measurement of the torques generated by muscle contraction around the knee joint. 8. Knee joint analyzer according to one of the claims 1 to 7, wherein means (4) are provided for loading the tibia axially to allow cont nuous measurement of the applied load. 9. Knee joint analyzer according to one of the claims 1 to 8, wherein means are provided for loading the tibia anteriorly or posteriorly to allow continuous measurements of the load applied and the resulting anterior or posterior displacements. 10. Knee joint analyzer according to one of the claims 1 to 9 , wherein means are provided for loading the tibia medially or laterally to allow continuous measurements of the load applied and the resulting medial or lateral displacement. ι * 11. Knee joint analyzer according to one of the claims 1 to 10, wherein means are provided for applying valgus or varus moments to the knee to allow continuous measurements of the applied moment and the resulting valgus or varus rotation. 12. Knee joint analyzer according to one of the claims 1 to 11, wherein means are provided for applying external or internal axial torques to the tibia to allow continuous measurements of torques applied and external or internal tibial rotation. * 3. Knee joint analyzer according to one of the claims 1 to 12, wherein means are provided for monitoring continuously EMG signals from the knee musculature.

Inventors: AL-TURAIKI MOHAMMED H S, AL-TURAIKI, MOHAMMED, H., S.
Applicants: AL TURAIKI MOHAMMED H S, LUSUARDI WERTHER G, AL-TURAIKI, MOHAMMED, H., S., LUSUARDI, WERTHER, G.
Application year: 1986
Main classification: A61B5
IPC codes: A61B5