LEG BRACE ASSEMBLY BACKGROUND The present invention relates to medical appliances and more particularly relates to a leg brace for use in supporting limbs which have been injured or which require rehabilitation. More particularly the invention relates to a leg brace assembly which is adjustable to accommodate a variety of leg positions so as to orient a leg in a disposition best conducive to treatment. The invention further provides a leg support assembly allowing multiple degrees of freedom for placing a leg at selective elevations and attitudes. PRIOR ART There are in existence a wide variety of leg braces and assemblies which are intended for leg support. Leg injuries are common in a variety of sports and often require support either immediately following the injury or post operatively. In the event of a sporting injury, the leg may require cradled support to relieve pain or to prevent further injury. Currently there exist various splints and the like to hold the leg securely until the patient can receive orthopaedic treatment. Although the prior art teaches the use of leg braces there is a long felt want in the filed to provide a leg support which provides an alternative to the prior art braces, allows a leg to be disposed at any angle and at any elevation to reduce pain and improve circulation. By way of example of the prior art, United States patent 6,953,442 discloses a knee brace having first and second arms constituting a pair of left and right arms fixed to the bilateral thigh sides along the user's femur The brace has third and 1 fourth arms constituting a pair of left and right arms fixed to the shank bilateral sides along the user's tibia. The lower ends of the first and second arms and the corresponding upper ends of the third and fourth arms are pivotally connected together to provide two pairs of upper and lower arms, so that the third and fourth arms are allowed to pivotally move with a pivotal part as the center correspondingly to the knee motion. Gears and guide grooves which respectively have racks meshing with the gears, extend in parallel to a femur or tibia axial center and provided opposite to the ends of the arms constituting the pairs of left and right arms. The aforesaid brace is the type used for rehabilitation of serious leg injuries such as after surgery . It is a complicated device designed for a specific purpose and is not suitable for field use. United States patent 5,060,640 discloses a knee brace for supporting an injured interior cruciate ligament by using straps that produce a forced couple on the knee joint to keep the tibia properly behind the femur while allowing for adjustment of the amount of anti-drawering to fit the individual needs of the patient. The knee brace may utilize a quadricentric hinge that closely approximates the natural movement of the knee joint and allows for adjustment of the knee brace to account for the natural curvature of the individual patient's leg bones. In another example of the prior art, United States Patent No 5,419,754 discloses a knee brace comprising upper and lower leg-engaging/embracing parts (thigh and calf pieces) connectable around upper and lower parts of the leg above and below the knee joint with the upper and lower leg embracing parts having upper and lower brace members respectively interconnected by at least one joint, 2 wherein the at least one joint means each comprises at least one link member pivotally connected at pivot points to rotate about a pivotal axis on each of the brace members with the at least one link member being provided for holding brace members together, and wherein the end region of a first said brace member has a slot defined between two end arm portions and within the slot space for forming a defining portion thereof. A first gear is provided and such is engaged by a second gear on the end of the second brace member which second gear is displaceable in the slot to engage the first gear and wherein the first and second gears each lie on arcs each concentric with the pivot point of the brace member on which the respective gear is provided, and with the arc of the normally upper brace member being on a smaller radius than the other so that the upper brace member rotates at a faster angular velocity than the lower brace member to proximate the movement of a knee joint. Again this is a complicated arrangement for a specific purpose and is not suitable for convenient filed use for simply supporting a leg. United States Patent 5,330,418 discloses a multi axis controlled motion knee brace with a four bar joint and method for producing same The knee brace has a pair of femoral and tibial links and a four bar joint mechanism by which a lateral side one of the femoral links is pivotally connected to a lateral side one of the tibial links and a four bar joint mechanism by which a medial side one of the femoral links is pivotally connected to a medial side one of the tibial links. The locations of 3 the pivot points for the pivot plates on the links are set in accordance with parameters which are designed to produce a multi axis motion of a reference point which will constrain the tibia to slide rearwardly relative to the femur in an initial range of flexion of the knee from a straight leg position and then to rotate relative thereto along an arcuate path. The known leg braces have been limited in their applications because they are restricted in their degrees of freedom and are each built for a specific limited purpose. Nor are they suitable for field use. One of the problems with the known leg braces is that they are difficult to set and maintain an optimum leg position and orientation. There is a long felt want in the industry to provide an alternative to the known braces and leg support assembles and particularly those which are used in the field. INVENTION The present seeks to ameliorate the aforesaid disadvantages of the prior art by providing a medical appliance and more particularly a leg brace for use in supporting limbs which have been injured or which require rehabilitation. More particularly the invention provides a leg brace assembly which is adjustable to accommodate a variety of leg positions so as to orient a leg in a disposition best conducive to treatment. The invention further provides a leg support assembly allowing multiple degrees of freedom for placing a leg at selective elevations and attitudes. 4 It is one object of the invention to provide an improved lag brace which is simple to operate in the field and which has multiple degrees of freedom. It is a further object of the invention to provide an improved leg brace which provides a simple alternative to the known braces and which may be disposed in multiple orientations. In one broad form the present invention comprises: a leg support assembly comprising; a cradle having a generally concave recess for supporting a leg of a user, a ground engaging tripod support stand supporting said cradle; means allowing the cradle to move relative to the stand to enable adjustment of the leg attitude while supported on the cradle; wherein the cradle is pivotally attached to said support stand the cradle further comprises means for securing the users leg to the cradle allowing adjustment of the leg by adjustment of the attitude of the cradle; the assembly further comprising support means which allows the cradle to tilt and or rotate about a substantially vertical and horizontal axes. In its broadest form the present invention comprises: a leg support assembly comprising; a cradle having a generally concave recess for supporting a leg of a user, a ground engaging support stand supporting said cradle; means allowing the cradle to move relative to the stand to enable adjustment of the leg attitude while supported on the cradle. In another broad form the present invention comprises: a leg support assembly comprising a ground engaging tripod stand; 5 a cradle a for supporting a leg of a user and which is supported by said stand; cradle elements which are telescopically adjustable to allow adjustment of the length of the cradle; means allowing the cradle to move relative to the stand; means for securing the leg to the cradle. According to a preferred embodiment, the cradle is capable of pivotal movement about horizontal and / or vertical axes so as to allow adjustment of the attitude of the cradle and leg position. In another broad form the present invention comprises: a leg support assembly comprising; a cradle having a curved wall defining a generally concave recess terminating in opposite free ends and which receives and supports a leg of a user, the cradle further comprising a plurality of openings at or near the free ends of the sidewalls which receive adjustable straps which span transversely between slots on opposing side walls to retain a user's leg between a base of the recess and the straps thereby enabling restraint of the leg. In another broad form the present invention comprises: a cradle for use with a leg support assembly comprising: a ground engaging support stand for supporting said cradle; means on the support stand allowing the cradle when fitted to the stand to move relative to the stand to enable adjustment of the leg attitude while supported on the cradle, the cradle having a generally concave recess for supporting a leg of a user. Preferably the support means is a tripod stand which allows the cradle to assume a variety of elevations and angles. Preferably the means allowing the cradle to move relative to the stand comprises at least one pivot. According to a preferred embodiment, the cradle is capable of pivotal 6 movement about horizontal and / or vertical axes so as to allow adjustment of the attitude of the cradle and leg position. BRIEF DESCRIPTION OF DRAWINGS The present invention will now be described in more detail according to preferred but non limiting embodiments and with reference to the accompanying illustrations wherein: Figure 1 shows a side elevation of a leg support assembly according to a preferred embodiment; Figure 2 shows the assembly of figure 1 supporting a leg of a user. Figure 3 shows a perspective view of a cradle from the cradle assembly of figures 1 and 2 according to a preferred embodiment. Figure 4 shows a perspective view of a second cradle from the cradle assembly of figures 1 and 2 according to a preferred embodiment. Figure 5 shows a plan view of the cradle element of figure 4 Figure 6 shows an end view of the cradle element of figure 3 Figure 7 shows an end view of the cradle element of figure 4 according to one embodiment. Figure 8-11 show alternative cradle elements each having difference end profiles. DETAILED DESCRIPTION The invention will be described according to various embodiments Referring to figure 1 there is shown a side elevation view of a leg support assembly 1 according to a preferred embodiment. Leg support assembly 1 comprises, a support 7 stand 2 which supports a pivoting cradle 3. Cradle 3 is preferably constructed from co operating telescopic cradle elements 4 and 5 which are adapted to telescopically slide axially to increase or decrease cradle length. Cradle 3 pivots about connector 2a. Figure 2 shows the assembly of figure 1 supporting a leg of a user. Typically, a leg 6 of a user will be simply supported in cradle 3. Cradle elements 4 and 5 will be slidably adjusted to accommodate various leg lengths. Cradle 3 further comprises straps 7, 8 and 9 which allow fastening of leg 6 to cradle 3. Cradle 3 according to one embodiment, is supported by stand 10 which is preferably a tripod allowing adjustment of the attitude of cradle 3 through various degrees of freedom which include height adjustment, rotation about a vertical axis, rotation about a horizontal axis to adjust angle of repose. This is enabled by the mechanics of connector 2a and enables a user to place the leg of a user at a desired angle depending upon the dictates of the particular medical requirements for response of the limb. Figure 3 shows a perspective view of a cradle element 4 from the support assembly 1 of figures 1 and 2 according to a preferred embodiment. Cradle element 4 comprises a wall 11 defining a recess 12 which receives part of leg 6 as shown in figure 2. According to one embodiment, wall 11 includes slots 13, 14, 15 and 15 which receive and retain retaining straps . Wall 11 has a generally concave shape and is contoured to conform generally cradle element 5 so as to allow telescopic adjustment between elements 4 and 5. . Figure 4 shows a perspective view of a cradle element 5 from the support assembly 1 of figures 1 and 2 according to a preferred embodiment. Cradle element 5 8 comprises a wall 16 defining a recess 17 which receives part of leg 6 as shown in figure 2. According to one embodiment, wall 16 includes slots 18, 19, 20 and 21 which receive and retain retaining straps . Wall 16 has a generally concave shape and is contoured to conform generally cradle element 4 so as to allow telescopic adjustment between elements 4 and 5. Figure 6 shows an end view of the cradle element of figure 3. Figure 7 shows an end view of the cradle element of figure 4 according to one embodiment. Figures 8-11 show alternative cradle elements 30, 31 , 32 and 33 each having difference end profiles. Cradles 30 - 32 are each adapted with respective pivots 34, 35 and 36 which engage a support member such as that shows in figures 1 and 2. . Pivoting in the horizontal and vertical directions is available along with height adjustment. According to a preferred embodiment, the cradle elements comprise a concave recess with walls of selected circumferential lengths. This contains a patients leg laterally and also provides added stiffness to the wall. The arc defined by the circumferential length may be increased according to the level of containment required. As can be seen from figures 5 - 11 there are a variety of non limiting cradle shapes which can accommodate a variety of leg shapes including those in plaster requiring a wider crescent . It will be appreciated by persons skilled in the art that the invention described herein is also adaptable to alternative applications. It will be recognised by persons skilled 9 in the art that numerous variations and modifications may be made to the invention as broadly describe herein without departing from the spirit and scope of the invention 10