Biomechanics of BKA

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Biomechanics of BKA

• Renee Kitto
• Port Macquarie Base Hospital

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Contents

• Normal gait
• Prerequisites of Normal Gait
• Gait characteristics of BKA
• Other causes of gait abnormalities

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Normal gait

• Analysing pathological gait, compare to normal
• Identifying gait deviation, you can work towards
  normal gait
• Normal gait is the most energy efficient

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Stance Phase

• Begins at heel strike on one leg and ends at toe
  off on the same leg
• Initial contact (heel Strike)
• Loading response (0-10)
• Mid-stance (10-30)
• Terminal stance (push off) (30-50)
• Pre swing (toe off) (50-60)

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Swing Phase

• Begins where stance ends and is the period
  between toe off on one leg and heel strike on the
  same leg
• Initial swing (60-73)
• Mid-swing (73-87)
• Terminal-swing (87-100)

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Prerequisites of normal gait

• Stability in Stance
• Clearance in swing
• Pre-position of the foot in terminal swing
• Adequate step length
• Energy conservation

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Gait characteristics

• BKA gait is asymmetrical

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Gait Characteristics

• Temporal and distance factors
• Stance phase shorter on prosthetic side
• Step length of the prosthetic side longer and
  faster
• Self selected walking velocity is lower
• Decreased Cadence
• Average stride length is shorter

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Gait Characteristics

• Joint Angles
• Decreased knee flexion (prosthetic side) during
  early stance
• Decreased knee flexion (prosthetic side) during
  late stance
• Larger relative knee angle range on the
  prosthetic side compared to the unaffected side
• Greater than normal positions of maximum hip
  flexion (prosthetic side)
• Increased knee flexion (unaffected side) during
  early stance

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Gait Characteristics

• Joint moments
• Unaffected side
• Higher hip extensor moment during stance
• Higher hip flexor moment during early swing
• Higher knee extension moment during stance
• Prosthetic side
• Ankle D/F moment longer in duration and larger in
  amplitude during early stance

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Gait Characteristics

• Joint Power
• Heel Contact (unaffected side)
• Increased hip extensor activity (unaffected side)
• Heel Contact (prosthetic side)
• Increased hip abductor activity (unaffected side)
• Increased knee extensor activity (unaffected
  side)
• Increased hip extensor muscle bursts on both
  sides

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Gait Characteristics

• Joint Power
• Midstance
• Increased hip abductor activity (prosthetic side)
• Push-off
• Increased hip flexor power generation (prosthetic
  side)

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Other causes of gait abnormalities
Prosthesis Patients capability and general
condition Shape, length and size of the residual
limb Discomfort Inadequate or incorrect
re-education Psychological, social or economic
reasons
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References

• Bateni, H et al (2002) Kinematic and Kinetic
  Variations of Below-Knee Amputee Gait. Journal of
  Prosthetics and Orthotics, 14, 2-10.
• Engstrom, B, Van de Ven, C (1999) Therapy for
  Amputees. London Churchill Livingstone.,
  115-136.
• Robinson, J et al (1977) Accelerographic,
  Temporal, and Distance Gait Factors in Below-Knee
  Amputees. Physical Therapy, 57, 898-904.

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References

• Sadeghi, H et al (2001)Muscle Power Compensatory
  Mechanisims in Below- Knee Amputee Gait. American
  Journal of Physical Medicine and Rehabilitation,
  80, 25-32.
• Ruud, W et al (2004) Adaptions to Mass
  Perturbations in Transtibial Amputees Kinetic or
  Kinematic Invariance. Archives of Physical
  Medicine and Rehabilitation, 85, 2046-2052.