Thesis
Investigation into the load sharing and joint stabilising functions of a knee-ankle-foot orthosis
- Creator
- Rights statement
- Awarding institution
- University of Strathclyde
- Date of award
- 1997
- Thesis identifier
- T9048
- Qualification Level
- Qualification Name
- Department, School or Faculty
- Abstract
- Knee-ankle-foot orthoses (KAFOs) are commonly prescribed in the management of knee instability and in a limited capacity, to reduce the loading on the pathological anatomy. Conventional leather and metal KAFOs provide poor cosmesis but provide a wide choice for orthotic prescription. In contrast, the more cosmetic plastic and metal KAFOs now customarily administered provide a more lightweight design but with reduced stiffness and loading capabilities. As such mechanical failure, usually due to fracture of one of the metal uprights, is a common occurrence. To date, design of KAFOs has been largely empirical, with only limited evaluations into the their biomechanical performance. This research evaluated the loads applied to the medial and lateral uprights at the orthotic knee joint of two cosmetic KAFOs, during normal level walking. A further investigation employing kinetic and kinematic data recording equipment was used to calculate total intersegmental loads. This information, together with the orthotic loading data, enabled a full biomechanical analysis of the joint stabilising and weight bearing capacity of the orthoses to be completed. Two custom built, six-channel load transducers, designed during previous work at the Bioengineering Unit were used to replace the medial and lateral knee joints of the KAFOs. A computerised video system (VICON) recorded the 3D co-ordinates of body markers while a force plate measured the total ground reaction forces for the leg/KAFO complex. This allowed the derivation of gait characteristics like timing parameters and intersegmental forces and moments at the knee joint. Meanwhile the transducers measured the six loads applied to the KAFO at the orthotic knee joint. Conversion of the orthotic and total loads into the local reference system of the shank using the kinematic data enabled the loading data to be compared and allowed the biomechanical performance of the orthosis to be studied. The results obtained from the two subjects tested varied in both the magnitude of the loads and the nature of the loading patterns. However, comparison of the total and orthotic moments for both patients clearly indicated that the KAFO adequately performs it joint stabilising function, by preventing the knee joint from buckling during the early part of stance. For the first patient wearing a high brimmed KAFO, the axial force results suggest that the orthosis relieved the anatomy by up to 90% during early stance, declining to approximately 20% during late stance. The other patient exhibited intense lateral trunk bending which caused a tensile force on the medial upright but a compressive force on the lateral one. When vectorially added the results showed that practically no weight bearing relief was offered by the KAFO of this patient. The high loads recorded for the patient wearing the high brimmed KAFO occasionally exceeded the maximum design loads for the transducer in the medio-lateral direction, indicating the need for stronger transducers to be constructed.
- Advisor / supervisor
- Solomonidis, Stephan
- Resource Type
- DOI
- Funder
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