referring to fig1 and 2 , the preferred brace mechanism designated by the reference numeral 10 is shown . the brace mechanism comprises a four - bar linkage system with its links specifically arranged to approximate the polycentric joint movement of the human knee . the brace mechanism 10 has two primary links , an upper extension link 12 which is constructed to extend up the patient &# 39 ; s leg for anchoring and a lower extension link 14 which is directed down the patient &# 39 ; s leg for anchoring . the precise length of the extensions is not critical and terminal pads 16 may be eliminated depending on the anchoring means employed . in most cases , the extension links will be anchored by incorporation into a leg cast , which after curing is cut at the knee joint to allow pivot at the knee . the upper and lower extension links are crooked at their connective ends 18 , 20 to improve alignment of the motion centers of the brace mechanism with the corresponding motions of the knee while maintaining the natural placement and narrow width to the elongated extension links . the crooked ends are spaced from one another and interconnected by crossed connecting links 22 and 24 . the crossed connecting links each have two spaced pivotal axes , 26 &# 39 ; and 28 &# 39 ;, and 30 &# 39 ; and 32 &# 39 ;, with interconnecting pivot pins 26 , 28 , 30 and 32 , one connected to the upper extension link 12 and one connected to the lower extension link 14 . each extension link has two axes of connection , one for each connecting link . while the distance between pivotal axes on the two crossed connecting links are substantially equal , the distance &# 34 ; x &# 34 ; between the pivotal axes 26 &# 39 ; and 28 &# 39 ; on the upper extension link 12 is less than the distance &# 34 ; y &# 34 ; between the pivotal axes 30 &# 39 ; and 32 &# 39 ; on the lower extension link 14 . this symmetrical arrangement of the pivot axes effects the peculiar motion desired . while the distance &# 34 ; x &# 34 ; is approximately 3 / 8 inch and the distance &# 34 ; y &# 34 ; is approximately 5 / 8 inch , the specific distance of each is variable allowing adaptations of the mechanisms to small or large bone structure or slight variations in motion , so long as the dimension between the axes on the upper extension link is less than the dimension between the axes on the lower extension link . when the extension links are aligned , the pivots are offset in approximately a .[. 30 °.]. . iadd . 45 ° . iaddend . line from the vertical to optimize the angular displacement of the extension links on bending of the knee . in the preferred embodiment , the connecting link 22 is plate - like in configuration to accommodate a variable stop to limit articulation of the brace mechanism . included in the link is a guide slot 34 with slide stops 36 with a flat key face 37 which allows the stop to slide along the slot to restrict articulation at points desired by the attending physican , for example , when only a slight pivot to the knee can be permitted for a serious injury . the relatively large radius of the arc of the slot is designed to reduce stresses on the stops during use . the degree of articulation permitted by the stops can be adjusted with the aid of an arrow marking 33 stamped on the elbow of the lower extension link 14 in conjunction with scale markings 35 stamped on the plate like connecting link 22 . the scale markings indicate the degree of articulation from a vertical alignment of the upper extension link and the lower extension link . also located on link 22 are locating marking 39 comprising stamped arrows with a locating hole 38 . the hole is used to position and align the extension links of a pair of the brace mechanisms alongside each side of the leg on the tka ( trochanter , knee , ankle ) axis with the hole positioned on the bone prominance of the femur which is located and premarked by the physician . the proximate placement of the outer brace mechanism of the pair on a patient is shown in fig5 . referring to fig3 an alternate embodiment 40 of the brace mechanism is shown . the parts are substantially identical to the mechanism 10 of fig1 and fig2 with the two connecting links 42 and 44 identical in configuration . in this embodiment , no provision is made for a stop mechanism and the alignment means 46 comprises the intersecting point 46 of the back edges of the two connecting cross links when the extension links are aligned . operationally , the movement is the same . referring to fig4 a second alternate embodiment 48 of the brace mechanism is shown . the construction is similar to the embodiment 40 with the addition of a stop pin 50 to limit articulation to a vertical aligned position and a slide lock 52 to lock the brace mechanism in the aligned position . the stop pin 50 is threaded to the toe of the upper extension link 12 and projects therefrom to contact the edge of the modified connecting link 54 . the connecting link 54 is modified to include a tab extension 56 which aligns with the upper extension link 12 , when the two extension links are aligned . the slide lock 52 comprises a rectangular collar member which slides on the upper extension link 12 and can be lowered to encompass the tab extension 56 . this embodiment is used when articulation of the leg at the knee is to be prevented and permitted only during brief periods of supervised exercise or manipulation . referring to fig5 the brace mechanism 10 is schematically shown on one side of a user &# 39 ; s leg 50 . it is to be understood that the brace mechanism is used in pairs on either side of the leg for operational support . while a simple tape wrap 60 is shown retaining the mechanism against the leg , in most cases the mechanism would be largely covered by a leg .[. cost .]. . iadd . cast . iaddend . or orthopedic bracing , exposing only the linkage portion of the mechanism to permit the desired articulation . in fig6 the comparative instant centers of rotation of the human knee a - a &# 39 ;, the invented asymmetrical four - bar link mechanism b - b &# 39 ;, a prior art symmetrical four - bar link mechanism c - c &# 39 ;, and a typical gear - type mechanism d - d &# 39 ; are shown . progressing from a common .[. center . ].. iadd . centrodes . iaddend ., each of the dual .[. center .]. . iadd . centrodes . iaddend . diverge as the systems move from alignment ( where the leg is straight ) to an angled position ( where the leg is bent ). the non - mirror - like motion of the polycentric human knee and subject brace mechanism with their one curved and one straight trajectories are shown to differ substantially from the mirror - like motions of the prior art systems . the conformity of motion of the brace mechanism to the actual motion of the knee is important not only for uniformity in the degree of support , but when the extension links are anchored within a cast , to prevent the links from pushing or pulling on the cast in position fashion , which will cause inherent stress on the site of injury . while in the foregoing embodiments of the invention have been set forth in considerable detail for the purposes of making a complete disclosure of the invention , it should be apparent to those of skill in the art that numerous changes may be made in such details without departing from the spirit and principles of the invention .
an anatomic fracture brace mechanism for knee braces to provide lateral restraint and delimited supportive motion of the knee joint permitting weight bearing ambulation of the patient during healing of leg fractures or other traumas , a fracture brace being constructed with a brace mechanism utilizing an asymmetrical four - bar , cross - linkage to follow , as closely as mechanically practical , the polycentric motion of the human knee .