The Berkeley Endoskeletal Below Knee Modular System
In the prosthetic industry a trans-tibial prosthetic leg is often referred to as a “BK” or below the knee prosthesis.
The Berkeley Endoskeletal Below Knee Modular System ..
At first glance, a manual locking knee seems a logical choice. However, experience has shown that this is rarely required and should be reserved as a prescription of last resort. Only additional medical disabilities such as blindness will require this mechanism. Unlocking the knee joint in order to sit requires the use of one hand in the unilateral case; expecting a bilateral amputee to cope with dual locking knees and dual locking hips is unrealistic. Furthermore, in the event of a fall backwards, fully locked joints may prevent the amputee from bending his trunk to protect his head from impact.
One of the inherent limitations of the Canadian design is that the prosthesis must be significantly short (1 cm+) to avoid forcing the amputee to vault for toe clearance. Fig 21B-3. and Fig 21B-4. illustrate why this is so. At toe-off, the heel rises up during knee flexion and pulls the hip joint firmly against its posterior (extension) stop. The thigh segment remains vertical until the knee has reversed its direction of motion and contacted the knee stop. Only then does the thigh segment rotate anteriorly and cause the hip joint to flex. In essence, the prosthesis is at its full length during midswing. Since the patient has no voluntary control over any of the passive mechanical joints, the prosthetist is forced to shorten the limb for ground clearance.
Dynamic testing of below-knee prosthesis: assembly …
Another hip joint option is the Otto Bock four-bar knee disarticulation joint mounted in reverse as proposed by Peter Tuil of The Netherlands (Fig 21B-6.). Benefits claimed are parallel to those expected from a polycentric knee unit: increased ground clearance during swing phase due to the inherent "shortening" of the linkage in flexion and enhanced stability at heel strike amputees comment favorably on the smooth deceleration and good appearance while sitting that this joint offers.
In an effort to overcome this limitation, the hip flexion bias system was developed for the young, active amputee who wished to walk rapidly. At toe-off, kinetic energy from the coil spring is released, and the prosthetic thigh is thrust forward. Not only does this provide the amputee with a more normal-appearing gait, it also improves ground clearance. As a result, the prosthesis can be lengthened to a nearly level configuration in most cases (Fig 21B-5.). However, two potential problems have been noted with this approach. One is the development of annoying squeaks in the spring mechanisms after a few months of use, which sometimes tend to recur inexorably. A more significant concern is that as the spring compresses between heel strike and midstance, it creates a strong knee flexion moment. Unless this is resisted by a stance control knee with a friction brake or a polycentric knee with inherent stability, the patient may fall. Since the friction-brake mechanisms lose their effectiveness as the surface wears, the polycentric knee is the preferred component with this hip mechanism.
Dynamic testing of below-knee prosthesis: assembly and components H
Many authors have noted that the rejection rates for lower-limb prostheses are the highest at these proximal levels. The energy requirements to use such prostheses has been reported to be as much as 200% of normal ambulation. At the same time, the lack of muscle power at the hip, knee, and ankle/foot results in a fixed, slow cadence. As a practical matter, only those who develop sufficient balance to ambulate with a single cane (or without any external aids at all) are likely to wear such a prosthesis long-term. Those who remain dependent on dual canes or crutches for balance eventually realize that mobility with crutches and the remaining leg, without a prosthesis, is much faster and requires no more energy expenditure than using a prosthesis does.
The friction-brake stance control (safety) knee is probably the second most frequently utilized component. Because there is very little increase in cost or weight and reliability has been good, many clinicians feel that the enhanced knee stability justifies this approach, particularly for the novice amputee. Missteps causing up to 15 degrees of knee flexion will not result in knee buckle, which makes gait training less difficult for the patient and therapist. The major drawback to this knee is that the limb must be non-weight bearing for knee flexion to occur. Although this generally presents no problem during swing phase, some patients have difficulty in mastering the weight shift necessary for sitting. It should be noted that use of such knee mechanisms bilaterally must be avoided. Since it is impossible for the amputee to simultaneously unload both artificial limbs, sitting with two stance control knees becomes nearly impossible.
08/04/2011 · BELOW KNEE (TRANS-TIBIAL) PROSTHESIS
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It is well accepted that any fluid-control mechanism (hydraulic or pneumatic) results in a smoother gait. Motion studies conducted at Northwestern University have confirmed that a more normal gait for the hip dis-articulation/transpelvic amputee is also produced. Gait analysis has demonstrated that utilization of a hydraulic knee in a hip disarticulation prosthesis results in a significantly more normal range of motion at the hip joint during the walking cycle than is possible with conventional knees. In addition, a more rapid cadence was also possible.
Below Knee Prosthesis - Offering total contact ..
One of the most important orthopaedic surgical advances of this century, knee replacement was first performed in 1968. Improvements in surgical materials and techniques since then have greatly increased its effectiveness. Total knee replacement means resurfacing the bones of your knee joint with a prosthesis.
are used to replace parts missing below the knee
In general, a softer forefoot requires special care during dynamic alignment to ensure that knee buckle does not occur inadvertently. However, when used in concert with a polycentric knee, the reverse occurs: the prosthesis actually becomes more stable during late stance phase. The polycentric knee mechanism strongly resists a bending moment, which leads to its powerful stability at heel strike. It flexes during swing phase only if the forefoot remains firmly planted on the floor as the body "rides" the prosthesis over it. This creates a shearing force that disrupts the linkage and permits easy flexion of the knee. Because the softer flexible keel delays this shearing moment, the polycentric knee is actually more stable in late stance than with a more rigid foot.
Patent US5728170 - Below-knee prosthesis - Google …
For many years, the use of fluid-controlled knee mechanisms for high-level amputees was considered unwarranted since these individuals obviously walked at only one (slow) cadence. The development of hip flexion bias mechanisms and more propulsive foot designs have challenged this assumption. Furthermore, a more sophisticated understanding of the details of prosthetic locomotion has revealed an additional advantage of fluid control for the hip-level amputee.
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