Exercise devices – User manipulated force resisting apparatus – component... – Having common force transmitting support frame for user and...
Reexamination Certificate
2001-08-22
2002-08-20
Mulcahy, John (Department: 3739)
Exercise devices
User manipulated force resisting apparatus, component...
Having common force transmitting support frame for user and...
C482S137000, C602S026000
Reexamination Certificate
active
06436018
ABSTRACT:
TECHNICAL FIELD
This invention can be profitably employed in the fields of medicine and sports as it is an indispensable component of knee tutors and of machines used to strengthen or in rehabilitation to restore the muscles of the knee to their former healthy condition.
The knee is the intermediate articulation of the lower limbs. The movement whereby the knee is extended, or rather, the movement of extending the leg from the thigh is performed by means of the quadricep muscle, which is inserted in the foretuberosity of the tibia, a couple of centimeters below the knee. The movement of bending the knee, that is to say the movement of flexing the leg from the thigh is performed by means of the hind muscles of the thigh, as illustrated in FIG.
1
. The flexion-extension movement is always executed at the fore-hind plane.
The articular surfaces that come into contact in the knee are the femoral condyles (the distal, i.e. farther, part of the femur), and the tibia plate (the proximal, i.e. closer, part of the tibia), as illustrated in FIG.
2
. The femoral condyles consist in round surfaces with a bending radius which is rather narrow but which varies; indeed their profile is very similar to a spiral. The tibia plate, or rather the glenoid cavity of the tibia, has a much wider bending radius than the femoral condyles.
The articular mechanics of the knee is therefore complex, and the type of movement that is made is in direct relation to the angle at which the knee is open. Let us consider an extended leg to be the starting point at a 0 angle. In the first 20°-25° of the bend (i.e.: the angle of ordinary walking) the articulation's mechanics entail a sheer rotation between the two articular surfaces: each point of the femoral condyles is in contact with a corresponding point on the tibia plate. If the flexing continues, in the subsequent 110°-115°, approximately, there is a combined sliding and rotating movement of the tibia with reference to the femur. As the leg flexes further the sliding movement gradually progresses end eventually prevails over the over the rotation and a sheer sliding movement occurs: the femoral condyles slide without rotating on the tibia plate. The knee's ligaments limit the articular caps during these sliding movements and ensure the knee's fore-hind stability, enabling the execution of hinge movements whereby the articular surfaces remain in contact.
Thus, in the flexion-extension mechanics of the knee there is no fixed centre of rotation. When the leg is flexed starting from an extended position, in the first 20° there is a centre of rotation located 60 mm from the tibia's articular surface. However, as the bending movement continues, the point of rotation moves on and, at the same time, the radius grows narrower, until it reaches a minimum distance of approximately 12 mm from the tibia (as can be seen in FIG.
2
).
This variation in the radius is transformed into a variation in the distance between a point located in the centre of the femoral condyle which has been identified by tests in the first 20°-25° of the flexion-extension and another point situated on the external malleolus. Indeed, by measuring this distance, experiments reveal that in extending from 135° (position A), to 0° (position B), the variation can increase from 15 to 40 mm (distance R
B
−R
A
), as can be seen in FIG.
3
. The extent of the variation depends on the conformation of the knee in question.
With reference to physiotherapeutic or rehabilitation problems, when it is necessary to support and follow the knee in its movements, one usually resorts to particular mechanical devices which are strapped to the thigh and leg by means of a system of belts (a sling) which guide the articulation in its movements.
These devices are used in knee tutors, in the machines used for passive gymnastics, and in the gym machines for specific muscle training known as leg curl and leg extension machines.
These mechanical devices, which are thus bound to the limb, are hinged to an articulated joint which generally has a fixed centre of rotation and which is unable to provide the combined sliding and rotating movements and change the centre of rotation, thereby producing anomalous tensions. The latter are caused by the different trajectories of the articulated joint's mechanical devices (circle arc) compared to the one theoretically accomplished by the leg (spiral arc). Indeed, as previously described, the leg reduces its radius when it flexes (R
B
−R
A
); this causes the mechanical device to rub against the leg, bringing about a friction which is passed on to the belts of the sling and results in a compressive force.
When the leg is extended, the mechanical device tends to constrict the leg along a circular path, while the leg reduces its rotation radius, and therefore tends to be drawn away from the knee. These compressive and tractive forces, which are proportional to the speed of the movement and to the distance of the knee sling, are then released on the knee caps on the articulation's cartilage (compressive force), and on the knee's ligaments (tractive force) respectively.
The most sophisticated versions of knee tutors currently used in sports feature a complex articulated joint which does indeed try to simulate the compromise between the rotation and sliding movements that typically occur in the knee.
Attempts to solve this problem have been described in the European Patent Application No. 89117781.8 published under No. 0 361 405, in the international Patent Application PCT/US92/01929, published under No. WO 92/15264, and in the International Patent Application PCT/US84/00336 published under No. WO 84/03433.
The knee joint described in the European Patent Application No. 89117781.8 is based on the physiological concept whereby the flexing of the knee consists in the fore movement of the femoral condyles with reference to the tibia condyles, followed by a sheer rotation between the condyles of the above mentioned bones. This joint features three plates, of which the two outer ones feature coaxial holes, while the inner one features two openings where a pair of pins that fit through the above mentioned holes in the outer plates are lodged and guided. One of the openings is small and extends transversally across the longitudinal axis of the tibia and femur, while the other opening is large and is shaped like a circular segment with one end growing wider towards the top.
The first opening, is linear and has the function of reproducing the first fore movement of the femur with reference to the tibia, while the second opening serves the purpose of guiding the subsequent rotation movement.
The upper end of the circular opening is placed on the extension of the longitudinal axis of the arm of the central plate which passes through the centre of the pin lodged in the linear opening, precisely when the pin is halfway through the stroke performed by the pin inside this opening. The centre of the circular segment that constitutes the circular opening consists in the centre of the pin lodged in the linear opening when the pin itself is at the end of the said opening, which is the one farthest from the circular opening.
When the leg flexes, in the first 25° the pin lodged in the circular opening compels the pin in the linear opening to move from its starting position (closer to the circular opening) to its final position (at the end of the linear opening that lies farthest from the circular opening).
As the distance between the centres of the pins is equal to the radius of the circular opening, in this first part of the movement performed by the pin lodged in the linear opening, the pin lodged in the circular opening performs a small vertical movement within and outside the widened part that constitutes the upper part of the circular opening. In this first phase of the flexing movement the two outer plates slide forward with respect to the inner plate (traction or pulling apart phase of the two plates).
Subsequently the two outer plates rotate onto the inner one
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