Question | Answer |
Prosthetic Knees | Used on 90% pts |
Patient Requirements- Physical | Knee disarticulation;
Transfemoral;
Hip disarticulation;
Hemi-pelvectomy;
Bilateral;
Pediatric;
Adult;
Geriatric |
Knee Selection Criteria | Functional- stability, maintenance, durability;
Pt Priorities- function, durability, cosmetics, comfort |
Knee Failure- Alignment | Socket & components not set in appropriate alignment;
Forces improperly interacting with components & causing premature wear;
Pt has changed heel height adding stress to knee |
Knee Failure- Inappropriate Use | Knee used and stressed in conditions that system isn't designed for |
Knee Failure- Proper Adjustment | Knee adjusted incorrectly;
Excessive friction & strong extension assist; stance screw too tight & swing screw too loose; Installed with non-compatible components (foot, pylon connectors) |
Single Axis Advantages & Disadvantages | A: Less moving parts & simple design; Lower fabrication costs
D: Less stable at heel strike; One axis to absorb gait stress |
Polycentric Advantages & Disadvantages | A: Inherent stability at heel strike; Easy to initiate swing phase
D: Tend to be heavier; Increased maintenance |
Manual Lock Advantages & Disadvantages | Fxnal level 1-2
A: xfer prosthesis or limited walking on level surfaces; simple design, non-flexing knee w/ standing/ambulation
D: Pt must unlock knee manually to sit; If pt falls, knee doesn't collapse under them |
Friction Knee Advantages & Disadvantages | Fxnal level 1-2
A: Xfer prosthesis/limited walking on level surface; Simple design, fxnally acts like door hinge
D: Friction setting allows only 1 walking speed; Friction plates wear, require regular maintenance/replacement |
Stance Control Knee Advantages & Disadvantages | Fxnal level 1,2,3
A: Added stability during misstep/uneven surfaces; Breaking mechanism locks knee during stance; Most popular in US; Lightweight
D: Break will wear, knee will fail w/o proper adjustment/maintenance |
Hydraulic Swing Phase Knee Advantages & Disadvantages | Fxnal level 3-4
A: Hydraulic mech provides resistance to flex/ext during swing; Provides variable cadence (change walking speed w/o hesitation)
D: Heavier b/c of hydraulic fluids in cylinder; Require regular maintenance |
Hydraulic Swing & Stance Knee Advantages & Disadvantages | Fxnal level 3-4
A: Hydraulic mech provides resistance to flex/ext during swing & stance; Provides stumble recovery & ability to walk down stairs/ramps
D: Heavier b/c of hydraulic fluids; Require regular maintenance |
Microprocessor Swing Advantages | Fxnal level 3-4;
Resistance to flex/ext during swing; Variable cadence (change speeds w/o hesitation); On board microprocessor analyzes gait, selects appropriate resistance for smooth swing |
Microprocessor Swing Disadvantages | Added expense due to computer technology;
Maintenance is essential |
How does microprocessor swing work? | On board computer analyzes gait 50x/sec;
Calculates knee angle & ankle strain in relation to gait cycle;
System performs continuous hydraulic adjustments to ensure stability, security & efficiency in swing & stance |
How does microprocessor swing work? | Microprocessor hydraulic controlled stance & swing phase fxn;
Dynamic valve control & multiple inputs, stance stability engaged & disengaged PRN;
Less need to concentrate on prosthesis;
Provides max cadence response over wide range of fxnal applicatio |
How does microprocessor swing work? | Stance flexion feature, adjustable;
Hydraulic stance extension, dampening- reduces impact to skeletal structure at heel strike; initiates a natural & smoother transition to mid-stance; mimics natural gait dynamics; beneficial for descending ramps/stairs |
Microprocessor Swing Lithium Ion Battery Recharger | Necessary to power microprocessor;
Solar adapter in testing stages;
Standardized item for UE prosthetics |
Socket Design Criteria | Improve balance;
Improved comfort (standing, walking, sitting);
Improved control;
Improved fxn;
Better stability |
Socket Design Criteria | Natural shaping conforms to mm, tendons, arteries, nerves;
Socket flexibility allows mm mvmt & comfort;
Maximizes socket control, contouring, contact, comfort;
Level of ischial containment will determine level of socket/prosthetic control |
What are the 4 T's of socket design/comfort? | Total Contact;
Total Contouring;
Total Control;
Total Comfort |
Structural Goals | Replace structural support to skeletal system;
Xfer support forces thru residual soft tissue to femur;
Stabilize femur into hip in natural position for posture & force |
Hip Geometry- Anterior | Acetabulum is functional center of rotation of hip joint;
Ischial tub & greater trochanter are relatively equidistant from center of femoral head |
Hip Geometry- Lateral | Acetabulum is fxnal center of rotation of hip joint |
Socket Geometry- Soft Tissue Containment | Controls mm tissue;
Provides counter support to contain ischium in place;
Must be flexible to allow for mvmt & seating comfort |
Socket Geometry- Bony Lock | Medial lock contains & supports ischial tuberosity;
Lateral lock supports sub-trochanter & maintains femoral control |
Plug Fit | Provides limited concentration of forces on acetabulum;
Lacks rotational control;
No bony lock |
Quadrilateral Socket | Controls rotation by restricting mm & tendon mvmt;
Excessive soft tissue containment;
No bony lock |
Quad Socket- Medial | Contain tissue;
Counter pressure to lateral wall;
Same height as posterior wall to prevent adductor roll;
Proximal brim horizontal & parallel to floor |
Quad Socket- Lateral | Adequate lateral support to femur at mid-stance;
Socket adducted (prevent abd & stabilize pelvis; provide stretch to glut med);
2.5" above ischial shelf;
Stabilize greater trochanter |
Quad Socket- Anterior | Blocks fwd motion of residual limb;
Ant/Med channel- relief for adductor longus & gracilis;
Scarpa's triangle modification;
2.5" above ischial seat- too high impinges ASIS |
Quad Socket- Posterior | WB surface for ischial tub;
Ischial tub 1" medial from medial wall & .5" posterior;
Wall slopes 5-7 deg medially (easier access to ischial tub; places hip extensors on stretch) |
Problems with Quad Socket | Femur abd due to loss of adductor strength- compensated Trendelenburg;
Uncomfortable due to excess pressure over ischial tub;
Short limbs- harder to distribute pressure= worse fit |
Ischial Containment Socket | Wider AP, Narrow ML;
Controls femoral adduction;
Contains ischial tuberosity & pubic ramus;
More optimal distribution forces along femoral shaft |
Ischial Containment Socket | More containment of residual limb = larger volume = better distribution of forces/pressure;
Post. brim- prox & post to ischium;
Ischial tub contained in socket = bony lock;
Provides ML & rotational control |
Anatomical Socket | Focused bony lock to stabilize ischium;
Femur supported in fxnal position;
Uniform soft tissue compression maintains support, comfort, containment;
Balanced geometry |
Anatomical Socket- Lateral View | Control of the femur;
Stabilize the hip |
Anatomical Socket- Medial View | Contain ischium;
Stabilize medial mm group;
Provide counterforce for femur;
Allow mm mvmt |
Anatomical Socket- Anterior View | Flexible at proximal aspect to provide walking/sitting comfort;
Allow for blood flow;
Provide relief for mm mvmt |
Anatomical Socket- Posterior View | Flexible at proximal aspect to provide walking & sitting comfort;
Support gluteal mm;
Provide relief for mm mvmt |
Anatomically Contoured Socket | Custom designed to individual residual limb shape;
Mm & bone contoured;
Flexible interface works with mm to enhance fxn;
Enhanced comfort for specific lifestyle |
Suction Suspension | Pts who have stable volume residual limb;
Wet-fit;
Tradition fit;
Advantages- cosmetic, intimate fit;
Disadvantages- scarring, volume fluctuation |
Lanyard Suspension | String attached to end;
Pulled down into socket;
Advantages- cosmetic, intimate fit;
Disadvantages- need good hand dexterity |
Locking Linear | Gel liner with locking mechanism;
Pin attached to bottom;
Slide into socket- locks; press button to release
Advantages: comfort, ease of donning;
Disadvantages: less durable, perspiration, limited on length |
Waist Belt | Total Elastic Suspension (TES);
Silesian bandage;
Advantages: add'l suspension, controls rotation;
Disadvantages: not cosmetic, uncomfortable around waist |
Pelvic Belt | Includes metal hip joint;
Goes around waist for suspension;
Advantages: controls hip, looser fit;
Disadvantages: increased weight, not cosmetic, restricts hip |
Check-Out: Standing Exam | Foot flat on floor (with shoe);
Correct height;
No leaning pylon;
Stable knee;
Ischial tuberosity contained |
Check-Out: Sitting Exam | Remain on limb;
Knees aligned (as close as possible) |
Check-Out: Walking Exam | Note gait deviations;
Pistoning minimal;
No leaning pylon |