Abstract:
An orthotic caliper having at least two lockable steels for attachment to the respective limb members of the human body and having a locking pivotal connection between the steels, characterized by a releasable locking member which can be loaded in compression by the steels and which acts directly on at least one of the steels, and preferably on both of them, to lock them in a desired position when so loaded.

Description:
FIELD OF THE INVENTION 
     This invention relates to orthotic calipers comprising at least two pivotally-connected &#34;steels&#34; for attachment to the respective limb members of the human body. It is especially concerned with calipers provided with locking knee joints. 
     DESCRIPTION OF THE PRIOR ART 
     In GB-A-2,260,083 we have described an orthotic caliper of the construction outlined above having a pivotal connection between the two steels which is adapted to be held in a specific locked position by a releasable catch. In a particular construction illustrated in that Specification the pivotal connection takes the form of locking links which do not go overcentre, while the releasable catch takes the form of a hook having an angled engagement to take up play in the linkage formed by the locking links. 
     SUMMARY OF THE INVENTION 
     The present invention constitutes a development of that described and illustrated in GB-A-2,260,083. In essence, the new orthotic caliper which we have devised comprises a locking member which is loaded in compression by the steels and which acts directly on at least one steel, and preferably both steels, of the caliper. This locking member takes the place of the locking links provided in the earlier form of caliper mentioned above. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In order that the invention might be thoroughly understood, a specific example of an orthotic caliper in accordance with it will now be described with reference to the accompanying drawings in which: 
     FIG. 1 is a part-sectional side view of the main portion of the caliper; 
     FIG. 2 is a view similar to FIG. 1 but with the two steels of the caliper at an obtuse angle with respect to each other; and 
     FIG. 3 is a view similar to FIGS. 1 and 2 but with the two steels at an acute angle with respect to each other. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The orthotic caliper shown in the drawings comprises an upper steel 10 and a lower steel 12 which are provided with straps (not shown) or other fastening means whereby the steels can be attached to respective limb members of the human body. Normally the caliper would be used for attachment to the limb members of a leg, the upper steel 10 being attached to the thigh of the leg and the lower steel 12 being attached to the shin of the leg. 
     The two steels 10 and 12 are pivotally connected together by a single link 14, the link 14 having a pivotal connection at 16 with the upper steel 10 and a pivotal connection 18 with the lower steel 12. This permits the two steels 10 and 12 to pivot about their respective pivotal axes 16 and 18 into a variety of angular positions two of which are shown by way of example only in FIGS. 2 and 3. 
     As will be seen, there is a gap between the lower end surface 20 of the upper steel 10 and the upper end surface 22 of the lower steel 12. Arranged for movement along a line X--X is a wedge 24 having flat surfaces 26 and 28 adapted to abut corresponding surfaces 30 and 32 on the end surfaces 20 and 22 of the steels 10 and 12. The wedge 24 has a rod 34 extending along the line X--X, the rod 34 being provided at the end remote from the wedge with a plunger or piston 36 which is movable within a cylindrical chamber 38. This cylindrical chamber is formed in a portion of the link 14. 
     The construction is such that, in operation of the caliper, the wedge 24 acts as a locking member which is loaded in compression by the steels. Further, this new design of caliper makes use of friction forces to pull the locking wedge 24 into engagement with the surfaces 30 and 32 on the steels 10 and 12 once a compression spring 40 within the cylindrical chamber 38 has brought the wedge into a position of initial engagement with those surfaces. In addition to this, the frictional forces hold the wedge in position whilst under load. 
     A novel feature of the caliper is that the flexion locking surfaces 30 and 32 are machined directly onto or into the upper and lower steels 10 and 12, so that these two surfaces form, in effect, a slot into which the locking wedge 24 fits tightly. As will be appreciated, the manner in which the locking wedge is mounted allows it to &#34;float&#34; to some extent so that it centralizes between the locking surfaces 30 and 32. 
     The locking surfaces 30 and 32 on the two steels are preferably flat, which means that they can be easily ground to high accuracy before final assembly of the caliper, thereby avoiding the need for final adjustment by filing the locking surfaces. 
     A further important feature of the caliper is that the pivotal connection between the two steels comprises two spaced-apart pivot points 16 and 18 which thus provide the joint with dual pivots. This allows it to follow the true centre of rotation of the patient&#39;s knee. 
     It is to be noted that, in the extended position of the steels shown in FIG. 1, the plunger or piston 36 projects outwardly from its cylindrical chamber 38 so as to serve as a push-button. This makes for easy operation of the caliper to release it from the locked position shown in FIG. 1. It is, however, to be understood that similar leavers or other additional means can be combined with the plunger or piston 36 to suit individual patients having special requirements. 
     The compressive loading of the wedge 24 between the two steels results in a very considerable increase in strength as compared to other calipers on the market. As far as we are aware existing calipers all suffer from some shear loading in their locking components, and this is often a source of failure. In addition to all this, the simplicity of the components used in the caliper described above makes the manufacture and assembly of the caliper less expensive that existing products. 
     Yet another advantage of the invention is that the caliper can be shaped to suit the patient&#39;s knee much more closely than with other calipers used hitherto. 
     Existing calipers sometimes use pivoting locking members provided with curved locking surfaces. This generally is the disadvantage that the number of associated components required--with their inter-dependent tolerance problems--frequently requires manual adjustment of the locking surfaces. In addition to this, the curved locking surfaces cannot essentially be formed &#34;true&#34;.