I. Pinching of the tissues behind the knee.
II. The tendency of the stump, when it is short, to tilt forward in the bucket ([Fig. 108]).
Pinching of the flesh behind the knee in flexion takes place between the edge of the leg piece and that of the thigh corset.
If the top of the bucket is horizontal, it must inevitably occur, even if the edge of the thigh corset is well cut away ([Fig. 106]).
It can be avoided by cutting away these two edges into concavities opposite each other.
Figs. 105 and 106.—Limb in which the upper edge of the leg bucket is almost horizontal; in the sitting position (Fig. 106) the flesh at the back of the thigh is pinched even if the lower end of the thigh corset is well cut away.
In the French limbs made of leather it is usual to make the leg piece very high in front, i.e. as high as the middle of the patella. This is quite useless. The posterior border is cut down to a depth of two fingers' breadth below the axis of the joint. Pinching is thus avoided, but the posterior support is insufficient, the stump tilts forward as described above and the bucket gapes in front ([Fig. 108]). If the top of the bucket is horizontal—as in certain American limbs—there is, as we have already said, pinching of the popliteal tissues and compression of the popliteal vessels and nerves (Fig. 106). A concavity is therefore necessary, but one reaching to one finger's breadth below the axis of the joint is sufficient. In front the edge of the bucket reaches up to the joint line, this is quite sufficient to enclose the bony prominences ([Fig. 109]).
The posterior concavity of the leg piece is combined with a concavity in the thigh piece varied in accordance with the thickness of the popliteal soft parts.
