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Interface pressures and shear stresses: sagittal plane angular alignment effects in three trans-tibial amputee case
1Department of Bioengineering, University of Washington, Seattle 98195, USA. sanders@limbs.bioeng.washington.edu
Prosthetics and Orthotics International
|June 4, 1999
Summary
Adjusting prosthetic alignment minimally impacts interface pressures for trans-tibial amputees. However, significant changes in shear stress were observed, with session-to-session variations exceeding alignment effects, indicating user compensation.
Area of Science:
- Biomechanics
- Prosthetics and Orthotics
- Rehabilitation Engineering
Background:
- Patellar-tendon-bearing (PTB) total contact prostheses are commonly used for trans-tibial amputees.
- Understanding the biomechanical effects of socket-shank alignment is crucial for optimizing prosthesis function and user comfort.
- Interface pressures and shear stresses are key indicators of prosthetic fit and potential for tissue damage.
Observation:
- Measurements of interface pressures and shear stresses were conducted on three trans-tibial amputee subjects during ambulation.
- Subjects utilized patellar-tendon-bearing (PTB) total contact prosthetic devices.
- Sagittal plane angular alignment settings of the prosthesis were systematically varied.
Findings:
- Substantial modifications in sagittal plane socket-shank angular alignment had minimal impact on peak interface pressures during the stance phase.
- However, these alignment changes exerted more substantial effects on peak resultant shear stresses during the stance phase.
- No consistent pattern emerged indicating higher stress at misaligned versus nominally aligned settings.
Implications:
- Prosthetic alignment adjustments in the sagittal plane may not significantly alter peak interface pressures, suggesting a degree of inherent tolerance or adaptation.
- The observed variability in shear stress highlights the importance of considering alignment, but also points to other factors influencing stress.
- Greater session-to-session variations in interface stresses compared to alignment changes suggest that amputees may effectively compensate for minor misalignments, but struggle with day-to-day consistency, necessitating further investigation into factors affecting gait stability and comfort.