Presentation on theme: "TF SOCKET BIOMECHANICS"— Presentation transcript:
1 TF SOCKET BIOMECHANICS In this presentation, we will study the quadrilateral socket principles.General considerationTop view of the above knee socket known as a "plug fit socket".The section is round it is essentially and has an inner configurationapproximating the cylindrical shape of above knee stump.The amputee's stump is inserted into the socketas a plug into a cylinder.If the tissues of the stump were equally firmand pressure tolerant, a uniform distributionof stump socket pressures would be desirable.
2 RELIEF FOR THE ADDUCTOR TENDON The quadrilateral socket contours can achieve a better pressure distribution.RELIEF FORTHE RECTUS FEMORISBULGE FORTHE SCARPA TRIANGLERELIEF FOR THE ADDUCTOR TENDONRELIEF FORTHE GLUTEUS MAXIMUSISCHIUM
3 w SOCKET CHARACTERISITICS The vertical components of the forces appliesto the stump by the socket( F1,F2,F3.F4,F5.F6,F6)wmust be equal to:the body weight W supported by the prosthesisOn the picture , the forces appliedto the stump by the walls of the socket arerepresented by F1,F2,F3,F4,F5 and F6.
4 But only the vertical components A1,A2,A3,A4,A5,A5,A6 of these forces will be effective in opposing the downward force W exerted by the stumpw
5 Comments:A knee disarticulation and some supra condylar amputations, can toleratehigh weight bearing forces on the distal end of the stump.wF1,F2,F3,F4,F5,F6The forces F1 + F2 + F3 + F4 + F5 + F6 are applied by an essentiallyhorizontal surface.The sum of F1 + F2 + F3 + F4 + F5 + F6 is equal and opposite to the weight W.
6 CHARACTERISTICS OF THE WALLS OF A QUADRILATERAL SOCKET A) POSTERIOR WALLThe ischial seat and gluteus shelf arehorizontal surfaces : they are supportingthe major portion of the body weightThe posterior wall can act:to stabilize the trunk "1"( action of the hip extensors).to control the knee flexion "2"to stabilize the prosthetic knee "3".Comments:as the major part of the weight can be borne by the posterior brim, the support which must be supplied by the remaining wallsof the socket is correspondingly reduced.
7 B) ANTERIOR WALLThe anterior wall of the socket be relatively high in order to maintainthe ischial tuberosity in its proper place on the ischial seat.The anterior wall is applying a counter force to resist to the anterior pelvisrotation and sliding forward, as the weight line is anterior to the ischial seat) .The anterior wall also provides more area over which to distribute the forcesapplied to the stump.Anterior wall height : 5 to 6 cm higher than the posterior wall.Comments :The height of the anterior wall should not restricted the hip flexion ( 90 °).- the sitting position has to be comfortable
9 The inward bulge in the area of Scarpa's triangle helps to provide a more effective stabilizing counterforceBulge for Scarpa triangleRelief for RectusFemoris tendonRelief for AdductorLongus tendonComments:Because of the relative softness of the tissues of the Sarpa's triangle area,the inward bulge provides for the initial compression of the tissues.
10 C) LATERAL WALLNormal gaitDuring the swing phase, the pelvis tends to drop slightlyon the unsupported side. This tendency is opposedprimarily by the action of the gluteus medius.This can be explained as follows:One moment M1 tends to make the pelvis dropto the unsupported side.W = patient weightM1 = W x DwDw = distance between the weight lineand the centre of the hip jointA counter moment of force M2 which resists to M1Fg= the force developed by the gluteus MediusDf= distance between the hip joint to the line of action of Fg.M2 = Fg x DfTo keep the pelvis stabilized during the gait: M1 = M2
11 F1 W x Dw = F1 x Df W Dw Df S For an amputee: The lateral wall of the sockets plays an importantrole of stabilizing the pelvis during sound limbswing phase.W : Patient Body weightWDw: perpendicular distance from the supportpoint " S" ( ischial tuberosity) to the line ofaction of the weight.DwF1: counter force applied by the wall.F1SDf: perpendicular distance fromthe support point to the line of action of F1.DfThe magnitude of the counter forces necessary tostabilize the pelvis is indicated by the formula:W x Dw = F1 x Df
12 The line of action of the weight passes medial "Dw" the support point "S" (ischial tuberosity) which is located on the ischial seat.The pelvis tends to drop to the unsupported side due to patient weight W causing a corresponding lateral movement of the stump.The gluteus medius is stabilizing the hip jointand maintaining femur in relative fixed positionThe lateral wall is exerting a resistingcounter force F1 on the lateral aspect of the stump.The counterforce is distributed overthe area of lateral aspect of the stump "F1".The femur in a relatively fixed position with respectto the pelvis.acting at a perpendicular distanceDf from the support point "S".
13 ConclusionFor long stump, stabilizing counter force is smaller than for short stump( df is longer).For short stump. a greater counterforce are distributed over smaller area tostabilize the pelvis.To reduce the moment created par patient weight , patient can make alateral trunk bending, (it will reduce dw).When the pelvis tends to drop, tissues of the lateral aspect of the stumpare compressed until they generate the necessary counter force.Relief has to be made on the lateral wall at the lateral distal end extremityof femur level to avoid extra pressure on the stump during stance phase.- To stabilize the hip , the gluteus medius should exert enough force.- Lateral wall has to be adducted in order to place the Gluteus Mediusin a right position to stabilize the pelvis.
14 D) MEDIAL WALLTHE MEDIAL WALL SHOULD:PROVIDE EVEN PRESSURE ONTHE ADDUCTOR MUSCLESCONTAIN MEDIAL TISSUES ANDPREVENT ANY ADUCTOR ROLLNOT MAKE ANY PRESSURE INTOTHE PERINEUMMEDIAL WALL IS:PARALLELE TO THE LIGNE OFPROGRESSIONHEIGTH IS SLIGHTLY LOWER THAN ISCHIAL SEAT( IT CAN BE AT THE SAME HEIGHT.