Lower Limb Prosthesis Receiving Cavity (2) —— The Secret of Rectangular Thigh Prosthesis Receiving Cavity

The traditional thigh prosthesis adopts the plug-in receiving cavity with open end, which can not ensure the load-bearing of the ischium, and is easy to cause skin damage. At present, the full contact receiving cavity has been widely used, which not only makes the force more reasonable, but also easy to achieve the suction suspension. A gas valve can be installed at the bottom of the full contact receiving cavity. When the receiving cavity is loaded, the residual limb will be squeezed downward to exhaust the air at the bottom; when the residual limb is lifted, the negative pressure will appear at the bottom, so that the prosthesis will be sucked on the residual limb, so that the prosthesis does not need another suspension device, and it is easy to wear, but when the circumference of the residual limb is reduced, it will fall off due to air leakage.

The characteristics of quadrangle receiving cavity are large internal and external diameter and small front and rear diameter. Because of the small anterior and posterior diameter, the shape of the mouth is transverse, and the ischial tubercle is located on the sitting bracket of the upper edge of the posterior wall of the receiving cavity. There are four depressions in the quadrilateral receptive cavity, which will not cause excessive compression of the starting point of adductor longus, rectus femoris, gluteus maximus and cochineal muscles and limit the contraction of muscles. This kind of receiving cavity is widely used in the field of thigh prosthesis at present, because it is in full contact with the stump, not only realizes the load-bearing of the ischium, but also has good suspension ability.

According to the structure of quadrilateral receptive cavity and the condition of amputated limb muscles, it is generally possible to make good alignment, but there are a few amputated patients with tenderness points and blood circulation problems after wearing for a long time. Most of the reasons are related to the biomechanical characteristics of quadrilateral receptive cavity. If the two bearing points of the feet and the center of gravity of the human body are connected into a triangle when standing in static state, the two sides are actually the directions of the two force components of the ground against the human body, that is to say, in fact, the ground reaction force is not parallel to the gravity line.

In other words, the prosthetic pair line is not the actual force line of action. According to the gait analysis, the center of gravity of the body gradually transits from the swinging leg to the supporting leg during walking. In order to avoid falling during walking, it is necessary to provide a force to balance the additional moment caused by the change of the center of gravity caused by one foot off the ground. Therefore, in the process of walking, the gluteus externus muscles of standing legs contract to maintain pelvic balance and prevent the body's center of gravity from sinking downward. In the process of walking, the soft tissue and ischial tubercle of the stump transfer the driving force between the human body and the ground reaction force with the help of the prosthesis, and most of the supporting force directly acts on the ischial tubercle fulcrum. Because the action line of the contraction force of gluteus abductor does not pass through the fulcrum of ischial tubercle, it will generate a thrust in the ischial tubercle when it contracts, and at the same time, the thigh residual limb bone in the receiving cavity will also enhance this thrust. Therefore, it is believed that this thrust caused by the contraction of gluteal abductor muscle during walking is the main cause of the pain at the ischial node. Generally, tenderness occurs at the upper edge of the inner wall of the receiving cavity and causes the upper and outer sides of the receiving cavity to rise. In view of this situation, the front and back walls of the upper edge of the receiving cavity can be extended about 30 ° outwards, and the residual limbs can be squeezed towards the outer wall of the receiving cavity when bearing the load. The receiving cavity will generate an inward pushing reaction force, so that the edge of the receiving cavity will bear a certain pressure.

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