Summary of background: Intertrochanteric varus osteotomy of the femur for hip osteoarthritis is expected to bring improved congruity and increased weight-bearing surface area of the hip joint. Before surgery, we usually make a tracing on a paper using an anteroposterior roentgenogram of the hip to simulate the operating procedures and obtain better conditions in the hip. Nevertheless, there have been some cases in which this procedure does not provide satisfactory postoperative results in terms of relief of pain or locomotion, with long-term limp due to weakness of the hip abductor muscle group and shortening of the leg.
Objectives: To confirm if the improved congruity and increased covering of the weight-bearing surface area obtained by varus osteotomy can be actually reproduced during walking, and to evaluate the kinetic mechanism of the effects of this procedure using gait analysis.
Methods: We measured the strength ratio of the hip abductor muscles as the percent of the opposite side, and analyzed the pelvic movement and data of dynamic electromyography (EMG) recorded during locomotion in 24 female patients who underwent unilateral intertrochanteric varus osteotomy of the femur for hip osteoarthritis, 30 non-surgically-treated female patients with hip osteoarthritis, and 54 healthy women. In the operated patients, the roentgenograms obtained during one-legged stance on the affected side disclosed that 10 were positive for Trendelenburg's phenomenon (T(+) group) and 14 were negative for Trendelenburg's phenomenon (T(-) group). All subjects walked with bare feet at a comfortable pace on a walkway containing a force plate. Photo switches were placed in a walkway to measure the gait velocity and to determine the stance phase time of one gait cycle. Frontal and sagittal trajectories of body surface markers for computerized joint-angle motion analysis were acquired using the Quick-MAG system. EMG data for the gluteus maximus, gluteus medius, tensor fascia latae, and lateral hamstrings recorded using surface electrodes were integrated to quantify as the percent of maximum voluntary contraction (% MVC).
Results: This study disclosed that the stance phase time was shorter and the strength ratio of the hip abductor muscles was lower in the operated patients than those in the other 2 groups, and the change of the pelvic obliquity was smaller and the % MVC of the gluteus medius and tensor fascia latae were greater than those in the normal subjects. The change of the pelvic tilt showed the same pattern with those of the pelvic obliquity. The T(+) group showed decreased strength ratio of the hip abductor muscles and increased % MVC for the gluteus medius and the tensor fascia latae compared to the T(-) group, but the changes of both the pelvic obliquity and pelvic tilt did not significantly differ in the 2 groups.
Conclusion: This study showed the postoperative reappearance of the simulated conditions in the hip before varus osteotomy of the femur, providing evidence that the pelvis was horizontally maintained during walking due to decreased stance phase time and increased performance of the hip abductor muscles after this procedure.