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Basic Prosthetics I

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Basic Prosthetics I

  1. 1. Normal Gait vs. Prosthetic Gait Clinical Course R&D 8/23/12
  2. 2. Normal Gait Cycle – 2 phases • Stance Phase Time the foot is in contact with the floor • Swing Phase Time the foot is in the air Stance Phase 60% 8/23/12 Swing Phase 40%
  3. 3. Divisions of the Gait Cycle- 8 phases Stride (Gait Cycle) Periods Stance Swing Tasks Weight Acceptance Single Limb Support Limb Advancement Phases Initial Loading Mid Contact Response Stance 8/23/12 Terminal Stance Pre Swing Initial Swing Mid Swing Terminal Swing
  4. 4. Normal Gait Cycle Perry 1992 Inman 1981 1. Initial Contact Heel strike (0 - 2% of the GC) 2.Loading Response Foot Flat (2 -12% of the GC) 3.Mid-Stance Mid Stance (12 - 30% of the GC) 4.Terminal Stance Heel Off (30 – 50 % of the GC) 5.Pre-Swing Heel Off - Toe Off (50 – 60 % of the GC) 6.Initial Swing Toe Off - Early Accl. (60 – 73 % of the GC) 7.Mid-Swing Mid Swing (73 – 87 % of the GC) 8.Terminal Swing Deceleration (87 -100 % of the GC) 8/23/12
  5. 5. Loading Response Loading reponse phase GRF 100% BW • 60% of the body weight is transferred in 0,2 sec time 12% 8/23/12
  6. 6. Loading Response •In normal gait the body weight has a free fall in the end of terminal swing •The body weight falls about 1 cm causing high impact •The human body immediately reacts with controlled plantar flexion •The quadriceps controls knee flexion in early stance 8/23/12
  7. 7. Stance phase vs speed • Increasing speed results in increased impact. Walk Slow Walk 200 Run • Shock absorbing systems assist to achieve natural gait and reduce impact 100 0 0 8/23/12 62%
  8. 8. Terminal Stance • Maximum angle in the toe joint shows 55° in pre swing 8/23/12
  9. 9. Terminal Stance The forefoot lever arm stabilizes the knee and supports the center of mass 8/23/12
  10. 10. Terminal Stance •Full length toe lever prevents: - pelvis from droping - knee instability •Resulting in: - symmetrical gait - more equal stride length - reduced impact on the sound side 8/23/12
  11. 11. Rotation 8/23/12
  12. 12. Speed and Gait Stance Phase Swing Phase 60% 40% 5 km/h 7 km/h 8/23/12
  13. 13. Speed and Gait • Swingtime related to walking speed 0,55sec 0,40sec 0,8 m/sec 8/23/12 1,8m/sec
  14. 14. TT Typical Prosthetic Gait 1. 2. 3. 4. 5. 6. Shortened midstance Reduced stance flexion Early heel off Early toe off Reduced stance phase time Reduced knee flexion in swing (Breakey 1976) 8/23/12
  15. 15. Prosthetic issues resulting in pathologic gait - TT Typically prosthetics are too short! WHY? •Lack of suspension •Potential Clinical issue: shorter prosthetic leg (Lilja et al. 1994) •Increased hip to toe distance: •Lack of dorsiflexion •single axis knee design (Gard et al. 1996) 8/23/12
  16. 16. Prosthetic issues resulting in pathologic gait - TF • Average ground clearance 1,29cm Winter DA. Foot trajectory in human gait: a precise and multifactorial motor control task. Phys Ther 1992; 72:1:55-66 • Average socket pistoning 10mm Erikson, Roentgenological Study of certain Stump-Socket Relationship in Above-knee Amputees with Regard to Tissue Proportios, Socket Fit and Attachment Stability. Upsala J Med Sci, 1973. 78: p. 203-214. 8/23/12
  17. 17. Pathologic Gait TF Circumduction Vaulting 8/23/12 Hip Hiking Duchenne
  18. 18. Pathologic Gait TT 8/23/12
  19. 19. Plantar Dorsiflex. in ° Plantar Dorsiflex. in ° Ankle motion in stair walking Ascent Stance Swing Descent Swing Stance Normal (Andriacchi et al.1991) 8/23/12 Prosthetic (Powers et al. 1997)
  20. 20. Shortcomings of prosthetic foot design with respect to kinematics •Kinematics: The angular ranges are generally larger during stair walking than during level walking. Ascend: IC in dorsiflexion TS in plantarflexion Descend: IC in plantarflexion TS in neutral R. Riener et al. / Gait and Posture 15 (2002) 32–44 8/23/12
  21. 21. Shortcomings of prosthetic foot design with respect to kinematics •Decline: IC in slight plantarflexion TS in dorsiflexion M. Kuster,S. Sakurai, G A Wood PhD Kinematic and Kinetic Comparision of downhill and level ground walking Clinical Biomechanics Vol. 10,No. 2, pp. 79-84, 1995 8/23/12

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