THE ROOTS OF MODERN motion analysis can be traced back to photographer Eadweard Muybridge who used his invention, the zoopraxiscope, to project sequential motions onto a screen so they appeared in motion. At the University of Pennsylvania, he studied animals and human volunteers. To gain insight into uncommon human motion he also recruited patients with physical disabilities from a nearby hospital. The integration of elegant mathematics and engineering, advances in instrumentation and imaging techniques and the evolution in computer technology have propelled the art and science of human motion analysis beyond basic description towards prominent roles in surgical decision making, rehabilitation, prosthetics, orthotics, ergonomics, and athletic performance.
GAIT ANALYSIS AT CHILDREN’S MEMORIAL Hospital of Chicago
Since the Children’s Motion Analysis Center opened its doors in 1989, we have examined the pathological gait of more than 2,000 children to direct their surgical, orthotic and therapeutic intervention. The patients seen in the gait analysis laboratory present with various neuromuscular disorders, but the vast majority of the children carry a diagnosis of cerebral palsy or spina bifida. Gait analysis at Children’s includes a complete lower-extremity physical examination, videotaped walking, three-dimensional joint motion or kinematics, joint moments, joint powers, dynamic electromyography, and foot pressure analysis.
The physical exam provides information regarding muscle strength and joint range of motion. Despite the valuable information that is garnered from the physical exam, it is somewhat limited because it is predominantly a horizontal exam. The vertical exam as the patient walks includes the rudimentary observational gait analysis which includes systematically focusing on one body part and then another. Since tasks such as walking are comprised of simultaneous movement of multiple body parts, simple observation is limited. For instance, what appears to be an equinus ankle posture may in fact be a crouch gait in combination with a neutral ankle position. In addition, events that occur faster than 1/12 of a second cannot be perceived by the human eye. This can be overcome easily with a videotape and slow motion replay of the events. The limitation of videotape is that three-dimensional motion is confined to two dimensions, which can be grossly misleading to the clinician. For example, a patient viewed from the coronal plane with a combination of internal femoral rotation and external tibial rotation may be misinterpreted as having knee valgus.
To assess three-dimensional joint rotations, passive reflective markers are placed on the patient at specific anatomical landmarks as depicted in Figure 1. As the patient walks through the lab, the three-dimensional location of each marker is detected by multiple infrared cameras. A biomechanical model is applied to the marker series to calculate the three-dimensional motion of each body segment. The processed data generates a graphical representation of each joint in all three planes and is expressed in terms of the gait cycle (Figure 2). Read the complete article.
By Stephen Vankoski, MS and Luciano Dias, MD