Every year, millions of people are killed or injured in motor vehicle accidents in the United States. Although recent improvements to occupant restraint systems, such as seatbelts and airbags, have significantly decreased life threatening injuries, which usually occur to the chest or head, they have done little to decrease the occurrence of lower extremity injuries. Although lower extremity injuries are not usually life threatening, they can result in chronic disability and high psychosocial cost. Of all lower extremity injuries, injuries to the knee-thigh-hip (KTH) region have been shown to be among the most debilitating. This project used a finite element (FE) model of the KTH region to study injury. A parametric investigation was conducted where the FE KTH was simulated as a vehicle occupant positioned to a range of pre-crash driving postures. The results indicate that foot contact force and knee kinematics during impact affects the axial force absorbed by the KTH region and the likelihood of injury. The results of the study could be used to reevaluate the lower extremity injury thresholds currently used to regulate vehicle safety standards. Also, the results could be used to provide guidelines to vehicle manufacturers for developing safer occupant compartments.

BACKGROUND: In order to maintain non-weight bearing restrictions of the lower extremity, an assistive device must be utilized. Currently most devices require the restricted limb to be held in a static position while the contralateral extremity provides forward propulsion. Atrophy and disuse conditions ensue rapidly, slowing healing and prolonging recovery. A hands-free single crutch (HFSC) utilizes both lower extremities, potentially reducing atrophy. The purpose of this study was to examine the Electromyography (EMG) differences between a HFSC and standard axillary crutches (SAC). METHODS: A prospective, crossover study was performed using 21 healthy volunteers from an active duty foot and ankle clinic. Demographic data was obtained and then subjects were fitted with a HFSC and SAC. Wireless surface EMG sensors were applied to the belly of the rectus femoris (RF), vastus lateralis (VL), lateral gastrocnemius (LG), and the gluteus maximus (GM) by a board-certified orthopedic surgeon. Subjects then ambulated at a self-selected velocity for 30 meters, while 15 seconds of the gait cycle was recorded for each device. Mean muscle activity and the maximum voluntary isometric contraction (MVIC) were recorded. RESULTS: The RF, GM, and LG showed statistically significant increased levels of muscle activity while using the HFSC compared to SAC (respectively P = 0.05, P = 0.03, P = 0.03). The VL did not show statistically higher muscle activity while using the HFSC (P = 0.051). The RF, GM, and VL showed statistically significant higher MVIC percentages while using the HFSC compared to using SAC (respectively P = 0.005, P = 0.005, P = 0.013). The LG did not show statistically higher MVIC percentage while using the HFSC (P = 0.076). CONCLUSION: The HFSC subjects demonstrated increased muscle recruitment and intensity while maintaining cyclic contractions consistent with bipedal gait pattern. SAC demonstrated less recruitment and intensity with an isometric pattern regardless of the phase of gait. / 2022-06-04T00:00:00Z

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