A NOVEL DESIGN OF A HIP BRACE MECHANISM FOR REHABILITATION OF LIMITED RANGE OF MOTION
Osteoarthritis (OA) and femoroacetabular impingement (FAI) are both conditions that can cause destruction of the hip joint – resulting in pain, limited range of motion, and gait imbalances. The purpose of this study is to analyze the gait and muscle activity in patients with OA and FAI and propose and test the effectiveness of a rehabilitative mechanism that aims to help balance muscle activity to improve gait. Each of the three subjects (one baseline, one with FAI, and one with OA) underwent electromyographic (EMG) analysis and 2-D gait analysis for three conditions: with no brace, with just the brace, and with the mechanism. The FAI subject showed low peak gluteal activity in the affected side compared to the unaffected (14.70% less affected gluteus medius (GMD), 11.77% less affected gluteus maximus (GMX)). The device increased GMD activity on the affected side to be closer to that of the unaffected side at 5.5% less. The GMX peak activity increased by 21.83%, even though the affected side was still less by 11.51%. The OA subject showed higher mean gluteal activity on the affected side when compared to the unaffected side. The GMD and GMX activity was 9.6% and 0 7% greater, respectively. With the device added, the GMD and GMX means on the affected side was 13.6% and 0.7% greater, respectively. The subject with FAI showed at 14.57o less hip range of motion (ROM) on the affected side when compared to the baseline value of 50o. When the device added, the ROM decreased further by 1.79o. The FAI subject showed 2.42o more pelvis ROM than that of the baseline subject. With the device, the difference between the FAI subject and the baseline subject was only 0.61o. The OA subject showed a percent difference less of 33.06% between his double step length on the affected side and the normal value of 1.41 m. With the device, the percent difference less becomes 29.27%. With no brace or device, this subject shows 7.7% less time in stance phase than the normal value of 60% and only 0.83% more when the device is worn. Finite element analysis (FEA) was conducted to determine the mechanical integrity and fatigue life of the mechanism and free body diagrams (FBDs) with calculations were done to estimate the change in muscular forces with the mechanism. The FEA found a maximum stress of 32.51 ksi. The margin of safety for fatigue of an unnotched condition was calculated to be 2.46. In a notched case, the cycles until failure was determined to be 213,797 cycles. The FBDs found that there is a muscle activity increase of 4.3% and 2.6% for extension and flexion, respectively. Future studies would need to be done with a larger pool of subjects, different design ideas (to optimize results), and trials done after the subjects have used the device for a time.