Exam 5: Prosthetics TransFem ReadGuide/Chart; Knees, etc.

Question 1

What are 7 types of prosthetic knees that we discussed?

Answer 1

1. Manual Locking
2. Outside hinges
3. Single-axis (conventional)
4. Multi-axis (polycentric, or 4-bar)
5. Hydraulic
6. Pneumatic
7. Microprocessor

Question 2

Single Axis knee

• What is it?
• Alignment Stability
• Amputee Stability
• Indications (1)
• Advantages (2)
• Disadvantages (2)
• Swing Control
  
  • Type
  • Advantages (2)
  • Disadvantages (3)
• Breaking (stance control)

Answer 2

What is it?

• single axis knee simulates a simple hinge and allows the prosthetic shin to swing freely in flexion and extension. Stance-phase knee stability is achieved by a combination of positioning of the knee unit with respect to the weight line (alignment) and muscular control (hip extensors).

Lightweight, durable, and low maintenance, but because of its unrestricted movement, it has no inherent mechanical stability.

Not appropriate for individuals with short residual limbs who lack the mechanical advantage of a long femoral lever for muscular control.

Rate of advancement of the shin during swing phase (determined by friction setting of the knee) can be individualized, cadence responsi elnise is minimal.

Alignment Stability

• low

Amputee Stability

• high

Indications

• Long limb with good voluntary control (rarely used)

Advantages (2)

1. Durable
2. Inexpensive

Disadvantages (2)

1. poor stability
2. Does not simulate multi-axis nature of human knee

Swing Control

• Type
  
  • Free swinging but has some swing control through
    
    • Extension aide (aids extension) with mechanical friction (primarily resists extension)
• Advantages (2)
  
  1. durable
  2. inexpensive
• Disadvantages (3)
  
  1. Consant speed of movement (not able to adjust to varying cadence)
  2. may loosen
  3. Debris may interfere

Breaking (stance control)

• Stance control knee in <15 degress flexin (aka weight activated or safety knee)
• book says stability is acheived by a combination of positioning of the knee unit with respect to the weight line (alignment) and muscular control 9activity of hip etensors)

Question 3

Manual locking knee

• What is it?
• Alignment Stability
• Amputee Stability
• Indications
• Advantages
• Disadvantages
• Swing Control (type, advantages, disadvantages)
• Breaking (stance control)

Answer 3

What is it?

• Basically a single axis knee with the addition of a locking pin mechanism.
  
  • The pin automatically locks with a distinctive click when the knee is fully exteneded.
• The prosthetic wearer can manually unlock the knee by manipulating a pully or lever system attached to the outside of the socket. (to sitt for example)
• Stays in locked postion and doesn’t bend during swing
• Giving up normal swing phase, in order to be sure it won’t buckle

Alignment Stability

• most

Amputee Stability

• none needed

Indications

1. Last resort
2. Usually for post-op instability (book says maybe early training in TF amputee)
3. rarely used

Advantages

• Most stable

Disadvantages

• gait deviations (knee cannot flex)
• needs to be short to facilitate swing

Swing Control (type, advantages, disadvantages)

• N/A (knee locked straight)

Breaking (stance control)

• N/A (locked)

Question 4

Outside hinges knee

• What is it?
• Alignment Stability
• Amputee Stability
• Indications (1)
• Advantages (1)
• Disadvantages (2)
• Swing Control (type, advantages, disadvantages)
• Breaking (stance control)

Answer 4

What is it?

• Until the 1970s it was the only available knee alternative for knee disarticulation. It has external hinges similar to those used on a knee-ankle-foot orthosis. Offered no swing phase control. One manufacturer provides a yoke attachment permitting use of a fluid-controlled cylinder with these hinges, but durability is still a concern. Although external hinges result in the least possible protrusion of the thigh segment when sitting, a somewhat wider mediolateral dimension is the inevitable result. This causes cosmesis problems. Eventually a multi-axis hydraulic knee joint for a knee disarticulation was developed that is generally superior to the external hinge knee (http://www.oandplibrary.org/alp/chap19-02.asp)

Alignment Stability

• Least

Amputee Stability

• high

Indications (1)

• knee disarticulation only

Advantages (1)

• none listed (but it is one of two options I found for a knee articulation)

Disadvantages (2)

• poor cosmesis
• knee axis asymmetry

Swing Control (type, advantages, disadvantages)

• N/A (free swinging knee)

Breaking (stance control)

• I think it is N/A because it is a free swinging joint like a single-axis knee
  
  • however, the chart shows < 15 degrees flexion (I think this is a typo)

Question 5

Three types of polycentric knees

Answer 5

1. Pneumatic
2. Hydraulic
3. Micro-processor Controlled (aka C-leg)

** Polycentric is also called “multi-axis” or “4 bar”

Question 6

Multi-axis knee

• What is it?
• Alignment Stability
• Amputee Stability
• Indications (3)
• Advantages (3)
• Disadvantages (3)

Answer 6

What is it?

• In contrast to the single axis knee, which has a fixed center of rotation, the polycentric knee has a moving center of rotation. Like the human knee, the polycentric knee rotates around more than one axis through a four or more bar linkage system. A proximal and posterior location of the instantaneous center of rotation promotes knee stability during the stance phase of gait. As the knee unit flexes during swing phase, the polycentric axis of motion leads to relative “shortening” of the distal prosthesis (shin and foot components), enhancing toe clearance.
• Three types of multi-axis knees
  
  1. Pneumatic
  2. Hydraulic
  3. Microprocessor

Alignment Stability

• high

Amputee Stability

• low

Indications (3)

• Knee disarticulation
• short TF RL
• long TF RL

Advantages (3)

• Excelent Stability
• Knee center symmetry
• Good swing clearance

Disadvantages (3)

• Not heavy duty
• increased weight
• requries charging (microprocessor)

Question 7

Hydraulic knee

• What is it?
• Alignment Stability
• Amputee Stability
• Indications (4)
• Genral Advantages (3)
• General Disadvantages (2)
• Swing Control
  
  • advantages (1)
  • disadvantages (3)
• Breaking (stance control)

Answer 7

What is it?

• A type of multi-axis knee that is cadence responsive
• The forward progression of the prosthetic shin changes as gait speed changes. This is because the flow of hydraulic fluid through narrow channels within the prosthetic knee unit provides a frictional resistance, which increases with the speed of compression. (this friction is different from the friction that resists an extension aide. It actually provides friction against knee flexion, so that the more friction the faster the knee extends when unloaded)
  
  • This variable resistance permits a swing phase that more closely simulates normal gait. As gait speed increases, the shin of the prosthesis also extends more rapidly.
• like pneumatic, but oil inside instead of gas

Alignment Stability

• high

Amputee Stability

• low

Indications (4)

1. knee disarticulation
2. short RL
3. long RL
4. Usually hydraulic is the type of knee people use if they are not using a microprocessor

Genral Advantages (3)

1. excellent stability
2. Knee center symmetry
3. good swing clearance

General Disadvantages (2)

1. not havey duty
2. increased weight

Swing Control

• advantages (1)
  
  • increased [hydraulic] resistance with increased cadence (cadence responsive - see above)
• disadvantages (3)
  
  1. high cost
  2. weight (heavier than a pneumatic)
  3. extremes of temperature cause problems more than in pneumatic

Breaking (stance control)

• stance control knee in <15 degrees flexion (aka weight-activiated or safety knee)

Question 8

Pneumatic knee

• What is it?
• Alignment Stability
• Amputee Stability
• Indications (3)
• Genral Advantages (3)
• General Disadvantages (2)
• Swing Control
  
  • advantages (2)
  • disadvantages (2)
• Breaking (stance control)

Answer 8

What is it?

• A type of multi-axis knee that is cadence responsive
  
  • Similar to hydraulic knee but uses air pressure instead of liquid oil.
    
    • Air compresses when you load it or flex it and then it will give that back
    • Sort of like the energy storing foot
  • The forward progression of the prosthetic shin changes as gait speed changes. This is because of gas in the chambers, which compresses. The resistance of the gas increases with the speed of compression. The more resistance the faster the knee extends when unloaded. (or something like that)
  • This variable resistance permits a swing phase that more closely simulates normal gait. As gait speed increases, the shin of the prosthesis also extends more rapidly.

Alignment Stability

• high

Amputee Stability

• low

Indications (3)

1. knee disarticulation
2. short RL
3. long RL

Genral Advantages (3)

1. excellent stability
2. Knee center symmetry
3. good swing clearance

General Disadvantages (2)

1. not havey duty
2. increased weight

Swing Control

• advantages (2)
  
  • increased [pneumatic] resistance with increased cadence (cadence responsive - see above)
  • unaffected by temperature changes
• disadvantages (2)
  
  • High speeds may overpower the available resistance
  • book says they have less precise cadence control and require just as much mantenance as a hydraulic fluid.

Breaking (stance control)

• stance control knee in <15 degrees flexion (aka weight activated or safety knee)

Question 9

Microprocessor controlled knee

• What is it?
• Alignment Stability
• Amputee Stability
• Indications (4)
• General Advantages (3)
• General Disadvantages (2)
• Swing Control
  
  • advantages (3)
  • disadvantages (3)
• Breaking (stance control)

Answer 9

What is it?

• Dr. Mincer also calls it a C-leg
• A type of multi-axis knee that is cadence responsive
• C-leg (most important for us to remember) and Rheo are examples of two brands
  
  • C-leg can anticipate movement
• Microprocessor knees are typically equipped withh sensors that monitor the knee position during swing and pressure sensors detecting and evaluating ground related forces during stance. Sensor tech is capable of measuring angles, moments, and pressures at the rate of 50 times per second. Customized adjustments are commonly made to microprocessor knees using a laptop or handheld computer. Unique software algorithms determine the phase of gate, then immediately adjust the knee functions to compensate during both the stance and swing phases of gait. Most knee mechanisims provide a stumble recovery feature that limits unintentional bending of the knee that sometimes occurs when walking on uneven terrain. The microprocessor enables the pt to move in a natural way, which makes it easier to navigate stairs, slopes, and uneven terrain.
• Usually sensors include sampling at ankle/foot

Alignment Stability

• high

Amputee Stability

• low

Indications (4)

1. knee disarticulation
2. short RL
3. long RL
4. K2-4 for low-mod impact activities

Genral Advantages (3)

1. excellent stability
2. Knee center symmetry
3. good swing clearance

General Disadvantages (3)

1. not havey duty
2. increased weight
3. requires charging

Swing Control

• advantages (3)
  
  1. adjusts resistance (to flexion) instantly based on flex/ext angle and foot contact
  2. allows controlled decent
  3. more knee flexion ROM
• disadvantages (3)
  
  1. high cost
  2. high weight
  3. sensitive to moisture, etc.

Breaking (stance control)

• Active; <35 degrees

Question 10

What is the main concern for prosthetic knees?

Answer 10

MAIN CONCERN is that they DON’T BUCKLE

Be sure that any knee is going to prevent buckling while walking

Question 11

What are the two main funcitons of prosthetic knees?

Answer 11

1. Remain stable as body weight rolls forward over the prosthetic food during stance phase
   
   1. prevent buckling (most important!!)
2. Smoothly flex and extend through the swing phase of gait.

**The major categories of commonly used prosthetic knee units vary with respect to how, and to what degree, they accomplish these two tasks.

Question 12

What determines the speed or rate of shin advancement during swing?

Answer 12

mechanical properities (friction or resistance) of the prosthetic knee unint

Question 13

T/F: various knee units are available in endoskeletal and exoskeletal versions

Answer 13

True

Question 14

T/F: It is reccomended that teh amputee throw the foot out in preparation for initial contact

Answer 14

False

Most knees have extension assist so

• Amputee does not and should not throw foot out in preparation initial contact
• amputee must learn to trust this

Question 15

What is extension assist?

Answer 15

think of it as a rubber band across the front of the knee (all you have to do is unload it and it extends)

Question 16

How does foot selection differ for the TF amputee?

Answer 16

They can use any of the prosthetic feet and ankle options available, but there are some important considerations:

1. The foot’s impact on stability of the prosthetic knee in stance- quick foot flat (hard heel cushions and soft posterior bumpers) is preferable as it enhances stance phase stability, especially in short residual limbs or with weak hip extensors
2. Dynamic response feet and flexible keels may prove advantageous to active individuals, and allow faster walking speeds
3. Distal weight- higher the distal weight, the greater the energy consumption for the transfemoral amputee

pg 757 in 2nd edition

Question 17

What are three important considerations for foot selection for a TF amputee?

Answer 17

1. The foot’s impact on stability of the prosthetic knee in stance- quick foot flat (hard heel cushions and soft posterior bumpers) is preferable as it enhances stance phase stability, especially in short residual limbs or with weak hip extensors
2. Dynamic response feet and flexible keels may prove advantageous to active individuals, and allow faster walking speeds
3. Distal weight- higher the distal weight, the greater the energy consumption for the transfemoral amputee

pg 757 in 2nd edition

Question 18

What are the three variables influencing knee stability during stance?

Answer 18

1. Musclular stability: ability to voluntarily control the knee using muscular power
2. Alignment stability: alignment of knee unit with respect to weight line
3. Mechanical stability: inherent mechanical stability of knee unit (like the directions of movement it allows and how it allows it - for example single axis vs multi-axis - or amount of friction or extension assist it has built into it, etc {for example manual locking vs free swinging)

Question 19

What is the biggest priority for TF prosthetic design and how do muscular function, alignment, and mechanical knee stability interact to achieve this?

Answer 19

The most important goal in transfem prosthetics is to obtain optimal knee stability throughout stance phase of gait

3 variables influencing knee stability during stance

1. ability to voluntarily control the knee using muscular power (muscular stability)
2. alignment of knee unit with respect to weight line (alignment stability)
3. inherent mechanical stability of knee unit (mechanical stability)

Question 20

what is transfemoral socket flexion?

Answer 20

when the proximal end of the socket is more posterior and the distal end of the socket is more anterior

(the position you would expect the socket to be in if the person wearing was in hip flexion)

Question 21

How does initial TF socket flexion assist knee stability?

What additional compensation does this position prevent?

Answer 21

• Enhance muscular control by placing socket in slight flexion. Slight elongation of the hip extensors enhance their contractile ability just enough to develop an effective force (against posterior wall of socket) to keep the prosthetic knee extended.
• Also reduces the individual’s tendency to substitute for the weakness of hip extensor muscles with excessive pelvic lordosis.

Question 22

What instructions should be given regarding use of RL compression when not wearing a prosthesis?

Answer 22

• The importance of the consistent use of a shinker or elastic wrap whenever the prostheis is not being worn (including overnight while sleeping) cannot be overemphasized (several places in the 3rd edition, including pg 671 and pg 676)
  
  • An increase in limb circumference after only 15-30 minutes without wearing a shrinker or compressive elastic wrap is common.
  • If edema prevents donning the prosthesis and achieving suction, you can try applying a compression garment or elastic wrap for 15-20 minutes before donning the prosthesis again.
• Rapid reduction of limb size occurs over the first few weeks to months after delivery of the prosthesis, therefore compression should be used whenever the prosthesis is not in use. (pg 765 last paragraph in 2nd edition)

Question 23

What number of sock ply signals the need for a new socket?

Answer 23

(pg 765 in 2nd edition, last paragraph)

1. TT prostheses: 10 or more
2. TF prosthesis: 10-15 in transfemoral

Question 24

Describe TF Checkout

(and think about how it ocmpares to TT alignment)

(Reading guide question was: “contrast TF prosthetic checkout to TT checkout.”)

I did not include TT checkout here, but it is in the reading guide)

Answer 24

Remember to check skin: signs of excessive pressure/shear/friction

Remeber to ask pt how the prosthesis feels in each position

Ensure socket is donned properly

• check for proper ply of socks, gapping
• If socket is too loose, the person will feel
  
  • medial socket pressure at pubic ramus (groin)
  • excessive distal end pressure
• If socket is too tight socket will be difficult to don and may not slide all the way in
• Check for total socket fit by placing a small amouunt of lcay or powder or a thin film of lipstick inside the socket before donning. When prosthesis is removed, relatively even traces of the substance should be found on the socks/skin of residual limb.
• Make sure the prosthesis is not rotated

Check sitting/kneeling (sitting more important, points are for sitting)

• feet flat on floor with hip flexed to ~90 degrees
• Check that upper posterior thigh is not impoined between the socket and seat
• check that pt has at least 90 degrees hip flexion (without anterior wall impinging
  
  • don’t pinch between socket and belt if belt suspension is worn
• As the person stands up, Check fo gaps in the posterior-lateral corner of the sicket brim and proximal residual limb
  
  • this could cause loss of suction
  • A solution could be to instruct pt to use an isometric contraction of the thigh whenever going through the motions of sitting down or standing up to prevent the muscles from going slack within the socket.

Check brim contours (will be a bit different for the quad socket vs ICS)

• quad socket
  
  • should have channel for adductor longus
  • lateral wall completely encases the greater trochanter and fits snugly around the gluteal muscles as the socket wraphs toward the posterior wall.
• ICS
  
  • ischial tuberosity and pubic ramus are contained in a fosso well within the socket
  • Brim caputres more of the adductor muscle complex
  • snug fit against the lateral gluteal muscles

Standing Alignment

• focus on level pelvis
  
  • could palpate ASIS
  • Could use LASAR Posture (a peice of equipment that can assist the practitioner in examining static alignment)
  • Could use hip leveling guide device (a type of bubble level)
  • Do not assess in supine because this will give you false information (prosthesis fit changes with weightbearing forces)
  • Initial TF prosthesis may be up to 1/4 inch shorter than intact side to enhance toe clearance.
    
    • more than 1/4 inch causes back pain, gait deviation, and higher eergy cost.
• Check even weight bearing, shoe contact
  
  • no gapping/wearing of shoes (check with a piece of paper)- can affect alignment
• Check suspension, look for gapping or pistioning as you would with TT socket (make a mark at top of socket during WB then unload socket and check how far it moved)

Dynamic Alignment

• gait deviations, etc.

Question 25

Describe Steps in Pre-Gait Activities

Answer 25

In parallel bars with feet 2-4” apart;

Do each step progressing through the following support: initially BUE (bilateral UE) support, then remove contralateral hand, then remove both hands

• Static standing balance BUE support
  
  • Concentrate on what it feels like inside the socket
  • let pt practice contracting glute max
• Dynamic Standing Balance
  
  1. Side to side (shifts)
  2. Forward-Backwards
     
     • prosthetic foot forwards first, start small.
  3. Diagonal both directions (pressure moves heel to toe)
     
     • prosthetic foot forward first, start small
  4. Stool stepping with sound limb

Question 26

Describe Steps in Gait Activity progression (8 main steps)

Answer 26

In parallel bars with feeet 2-4” apart

1. Sound limb stepping PWB (arm support on //), emphasizing pelvic rotaiton and letting knee flex in terminal stance
2. Prosthetic limb stepping PWB, emphasizing pelvic rotation and letting knee flex in terminal stance
3. Prosthetic limb stepping FWB, emphasizing pelvic rotation and letting knee flex in terminal stance and remvoing contralateral hand then both hands
4. Sound limb stepping FWB forward and back, emphasizing pelvic rotation and remving contralateral hand, then both hands
5. Vary stride length
6. Sidstepping toward contralaterals ide against resistance at pelvis, then toward ipsilateral side
7. Risisted gait (at pelvis) to facilitate pelvic rotation, and removing contralateral hands the both hands
8. Outside //, facillitate arm swing and trunk rotation
9. Unassisted ambulation with varying cadence and stride length

Question 27

In general, for gait training and pre-gait activities, which hand do you remove from support first?

Answer 27

hand contralateral to prosthetic limb

Question 28

In general, for prosthetic gait and pre-gait activities, which foot do you train in a forward position first?

Answer 28

prosthetic foot