A. Field of the Invention
This invention relates to sealing sleeves for sealing residual limbs in suction retention prosthetic sockets.
B. Related Art
Residual limb are inserted like pistons in cup-shaped prosthetic sockets. It is therefore known to utilize ambient air pressure and partial vacuum to retain a prosthetic socket on a residual limb. The residual limb for this effect must be kept hermetically sealed against the inner prosthetic socket wall or against a liner donned over the residual limb.
When sealing is adequate, a force applied to remove the prosthetic socket from the residual limb will generate a partial vacuum acting against it. On the other hand, the force of retention collapses immediately when air enters any gap between the residual limb and the prosthetic socket.
European patent document EP 0 632 765 discloses a prosthetic socket fitted with a seal which maintains sealing between a residual limb and a prosthetic socket.
For such purpose, the prosthetic socket is fitted with a peripheral groove located at a distance from its distal end and which receives a sealing ring. The sealing ring consists of an annular core coated with a layer of elastomer. A sealing lip is formed on the ring and extends toward the inside volume of the prosthetic socket.
The purpose of the sealing lip—which hugs the skin of the residual limb—is to compensate for the fluctuations in diameter of the residual limb. Because the prosthetic socket is made of a rigid material, its inside width is constant. On the other hand, the residual limb volume changes over the long and short-terms. The long-term fluctuations are caused by changes in tissue volume, whereas the short-term fluctuations, for example, depend on the blood pressure and circulation in the residual limb. It is known that at higher temperatures the extremities tend to swell while at lower temperatures their diameters decrease. This phenomenon may be observed, for instance, even in a healthy individual under his/her watch wristband.
The lip seal is folded toward the closed prosthetic socket end when the patient inserts the residual limb into the prosthetic socket. The lip seal will then rest against the residual limb solely on account of being prestressed.
The moment a force is applied to remove the prosthetic socket from the residual limb, a slight partial vacuum is set up between the residual limb and the prosthetic socket volume within the distal end and the lip seal. The magnitude of the said partial pressure is approximately proportional to the enlargement of the annular gap between the residual limb and the prosthetic socket.
In the known design, the pressure gradient at the lip seal is in a direction that causes lifting of the lip seal from the residual limb, thereby permitting air to enter the annular gap and, because of the ensuing loss of suction, retention is lost.
The magnitude of the partial vacuum needed to detach the sealing lip depends on the radial prestressing force pressing the sealing lip against the residual limb. It has been observed that a comparatively large prestressing force is required, which in turn may entail interference with blood circulation in the region between the sealing lip and the distal end of the residual limb.