Knee Joint for Artificial Limbs

The present invention relates to a knee joint for a so-called primary artificial leg.

The invention provides a knee joint for an artificial leg which is of mechanically simple construction but is nevertheless durable and effective and which comprises a knee member having a part spherical convex lower surface pivoted about an axis to a knee housing having a part spherical concave lower surface conforming to that of the knee member, the knee member having a spring-loaded locking plunger posterior to the pivot axis and having a generally vertical line of action which in flexed positions of the joint travels over and is supported in a retracted position by the part spherical surface of the knee housing or by a guideway formed therein or thereon and in the unflexed position thereof latches into a seating to prevent flexion of the joint.

The knee joint permits the use of an endoskeletal shin casting which is of modular construction and the knee member which is of wood and is connected to a stump socket can readily be adapted to the requirements of a particular patient. Thus it combines the traditional artificial limb technology in wood above the knee with the more modern modular endoskeletal technology for the part of the limb below the knee and enables limbs that are simple in construction and light in weight to be made.

In an advantageous construction a rib upstanding from the curved top surface of the knee housing defines a guideway leading to the socket that is defined in a spigot upstanding from said curved surface, the anterior face of the spigot cooperating in the unflexed position of the joint with an extension stop in the concave lower surface of the knee member to define the unflexed position of the joint. The socket in the spigot intrudes into or closely approaches the envelope of curvature of the knee member, the knee member is relieved behind the extension stop to avoid interference with the spigot as the joint unflexes, and the plunger is arranged so that its position of maximum extension does not substantially protrude beyond the envelope of curvature of the knee member. With this arrangement the joint cannot become accidentally locked in the fully flexed state by entrapment of the locking plunger with the top anterior surface of the knee housing, and the extension stop is concealed between the knee member and the knee housing throughout substantially the whole angular range of travel of the knee. A top posterior portion of the spigot preferably defines a flexion stop face that abuts part of the knee member to define a fully flexed state of the joint.

Preferably there is provided a demountable fastening in the shin member by which it may be clamped onto a shin tube. Such a joint comprises a socket defined by a main bore in which the shin tube is received, an auxiliary bore directed perpendicular to the axis of the main bore and intersecting it over a small arc, first and second collets which fit in the auxiliary bore and have bearing faces shaped to conform to the curvature of the shin tube, and clamping bolt means for urging the first and second collets together so that they press on the shin tube and retain it in the socket. The demountable joint combines manufacturing simplicity with ease of assembly and good fatigue life and has the particular advantage that the shin tube need not be weakened by drilling or slitting.

An embodiment of the invention will now be illustrated in the accompanying drawings in which:

FIG. 1 shows in vertical section the region adjoining the knee of an artificial leg;

FIG. 2 is a view in vertical section of a demountable fastening for fixing the shin tube into the socket of the shin member in the artificial leg of FIG. 1; and

FIG. 3 is a view of the joint in horizontal section on the line A--A of FIG. 2.

In FIG. 1 a thigh stump socket (not shown) is fixed to a knee member in the form of a shaped block 10 of wood, polyurethane foam or other conveniently worked material. The height of block 10 may be adjusted e.g. by cutting with a saw to meet the needs of an individual patient for whom the limb is intended. A relatively large vertical bore 13 from the top face of block 10 leads to a smaller bore 14 that opens through the lower face of the knee block which is part spherical at a position posterior of the position of knee bolt and bearings 12. An extension buffer 33 mounted on a plate 33a is let into the curved lower face of the knee member 10 below bolt 12 as viewed, partially in phanton in FIG. 1. The portion of the block 10 posterior of the extension buffer 33 is formed with a channel 11 or is otherwise relieved, and a plunger 18 in housing 16 is mounted in the bore 14 so that it has a vertical line of action and its tip in its position of maximum downward extension projects beyond the relieved portion of the block surface but not significantly beyond the envelope of curvature of the lower face of the block. By this means, as will become apparent below, the tip of the plunger cannot latch onto the top anterior edge of the knee socket and thereby accidentally lock the knee in a fully flexed or hyperflexed state. Plunger 18 is urged downwardly by coil spring 17 in housing 16, has bearing portions towards its upper and lower ends that slideably guide it in the housing for vertical movement and is directly connected at its upper end to Bowden cable 25 which may be pulled upwardly to release the joint. Plunger 18 has a conical tip provided with an anti-friction pip 22 of Teflon or like material.

The knee housing 30 may be a casting in light alloy or an injection moulding in glass filled nylon and is pivoted to the knee member by bolt 12. Its upper face presents a part spherical concave surface conforming generally to the curvature of the lower face of the knee member. It is supported on a pylon tube 32 to which it is connected by a demountable compression joint described below. The upper face of the housing 30 is formed with an upstanding rib 29 whose curved top face forms a smooth track or cam surface leading to a spigot 31 also upstanding from the top face of the housing 30 at a posterior location. The track defined by rib 29 leads to a frustoconical seating or socket 34 into which the tip of plunger 18 locates when the knee and shin portions of the leg are in the unflexed position shown. By this means the plunger and seating automatically take up wear so that the knee has no play in its unflexed locked state that would be damaging to patient confidence. The knee is locked both against flexion and against over-extension by the plunger 18. Pulling on cable 25 directly raises and disengages plunger 18 from socket 34 after which anti-friction pip 22 travels over the top face of rib 29 as the knee flexes, the said rib either supporting the plunger in its retracted position or allowing it to extend as the knee flexes and camming it towards its retracted position as the knee is unflexed. The extension buffer 33 and backing plate 33a are formed with notches, as shown in phantom in FIG. 1, to accommodate the rib 29 as the knee is unflexed. The unflexed position of the knee is further defined by abutment of the anterior face of spigot 31 with the extension buffer 33. The arrangement has the advantage that the extension buffer 33 is removed from its normal position in the anterior face of the knee member 11 where clothing is prone to catch between itself and the top anterior edge of knee housing 30 but instead the extension buffer 33 is concealed by housing 30 throughout substantially the whole of its range of travel. At the fully flexed position of the knee, flexion stop 35 on the top posterior surface of spigot 31 contacts portion 36 on the knee member 10 to prevent hyperflexion of the knee. As the knee is returned from the flexed to the straight position the plunger 18 travels back over the top face of rib 29 and automatically latches back into the seating or socket 34.

In FIG. 2, the upper end of a shin pylon tube 32 is a push fit in a socket 40 defined by a vertical bore in the lower face of knee housing 30. A reinforcing insert 41 is a push fit in the top of tube 32. It is formed towards its lower end with a horizontally directed reinforcing annulus 42 which is capable of withstanding high compressive loads and at its top with an outwardly directed locating flange 43 which acts as an abutment for the top end of the tube 10. As more clearly seen in FIG. 3 the socket 40 is formed with a horizontal bore that intersects the vertical bore in which tube 32 fits over a small arcuate portion thereof. A pair of collets 44, 45 fit into the horizontal bore, one of them 45 having a plain through-hole and the other 44 having a threaded through hole. Each collet has a shaped bearing surface 46 conforming to the curvature of the outer surface of the tube 32 which can only be inserted fully home in the socket 40 when the bearing surfaces 46 are appropriately positioned. It will be noted that in the assembled joint the horizontal bore registers with the reinforcing annulus 42 of the insert 41. A clamping bolt 47 is inserted through collet 45 into collet 44 in which it is threadedly located.