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UBC Theses and Dissertations

Control of subtalar motion with the use of ski-boot footbeds Greenberg, Susan B


Research shows that up to 80% of recreational skiers have lower limb alignments which can impede their ability to turn their skis properly (Subotnick,1982). The most difficult of these alignment problems to control within a ski-boot is the varus alignment of the subtalar joint (Macintyre and Matheson, 1988). The use of custom molded footbeds made specifically for use inside of ski boots has been suggested as one method of compensating for a varus aligned foot. This study compared the effectiveness of one brand of custom molded ski boot footbed with that of a noncustom insole in controlling the motions of the lower limb associated with subtalar varus. Specifically these motions were those of the rearfoot and the navicular tubercle, along with the alignment of the tibial tuberosity with respect to the mid-line of the ski boot. In addition, subjects were given the opportunity to assess their subjective feelings of edge control, pain, and fatigue while skiing with both the custom molded footbeds and non-custom insoles. The subject group for this study consisted of 13 advanced level adult skiers who demonstrated more than three degrees of subtalar varus when non-weight bearing. Each subject received a pair of custom molded ski boot footbeds at the beginning of the study. Ski boots that had been cut away at the rear and the medial side were used in the laboratory in order to observe the motions of the navicular tubercle and the rearfoot as the subject transferred their weight in a simulated skiing motion. The right and left navicular tubercle, tibial tubercle, and the insertion of the Achilles at the calcaneus of each subject were located by palpation and marked. After sufficient practice of the weight transfer motion, two trials of each landmark were photographed using 35mm slide film. The subjects were first photographed while using the non-custom insoles and again using the custom molded footbeds. The slides were digitized and comparisons were made between the two types of insoles for both the start and end locations of the landmarks as well as for the ranges of motion through which the landmarks traveled. Statistical analyses of the group results indicated that there was significantly less (p=0.000) navicular motion during the shift from the start to the end positions with the use of the custom molded footbeds as compared to the non-custom insoles. The rearfoot angle was significantly less at both the start (p=0.000) and end (p=0.000) positions with the use of the custom footbeds as compared to the noncustom insoles. There was no statistical difference between the amount of rearfoot motion allowed by either type of insole. The tibial tubercle was positioned significantly (p=0.000) closer to the mid-line of the ski boot when using the custom footbeds than with the use of the non-custom insoles. These results indicate that the custom footbeds domaintain the subtalar joint in a more neutral position than do non-custom insoles. During the skiing section of the study the subjects rated the custom footbeds as providing better edge control (p=0.000) and resulting in less fatigue (p=0.000) than noncustom insoles. There was no statistical significance when comparing the ratings given by the group for the level of pain experienced with the use of either type of insole. There was a statistically significant improvement (p=0.000) in race times for the group when using the custom footbeds as compared to the non-custom insoles. The results of this study indicate that custom molded ski boot footbeds are able to control subtalar motion more effectively than a non-custom insole. It appears that this control of subtalar motion enhances the skiing experience by increasing edge control and reducing the amount of fatigue experienced.

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