Page 171 - Biomedical Engineering and Design Handbook Volume 1, Fundamentals

148 BIOMECHANICS OF THE HUMAN BODY

panel depicts a varus-aligned knee (i.e., genu varum). Genu varum is more commonly known as
bow-leggedness. Because the net moment is the result of all muscles acting about the joint, it is a
reasonable assumption that the medial compartment forces will be greater for the genu varum knee
than forces for the normally aligned knee. These increased forces coupled with reduced joint contact
area (the area being substantially less as it is mostly over the medial side) will lead to greater stresses
in the joint, which may predispose an individual to knee osteoarthritis. The abduction moments for
an unimpaired and a genu varum knee are shown in Fig. 6.20. Note how the mid-stance abduction
moment is significantly greater for the presurgical genu varum knee. The dashed line is the average
postsurgical mid-stance moment for patients who underwent high tibial osteotomy surgery, which is
a surgical procedure in which a wedge of bone is removed to better align the joint. Note that the mid-
stance knee abduction moment for these subjects has returned to near normal following surgery.

Knee Abduction Moment
Abduction
60
Presurgery
40
N-m 20 Normal

0
Mid stance
Heelstrike Toe off
–20
0 6 12 18
Stance phase
FIGURE 6.20 Stance phase knee abduction moment for a normally aligned and a
genu varum knee. Note the difference during mid-stance. The dashed grey line is the
postsurgical mean data for patients undergoing high tibial osteotomy to correct the genu
varum. The mean postsurgical mid-stance abduction moment (mean = 16 N . m) has
returned to a near normal level. [Data taken from Weidenhielm et al. (1995).]

These examples demonstrate how, using human movement analysis, we can calculate the
kinematics and kinetics during complex motions and how these, in turn, can be used to provide infor-
mation about clinical efficacy and athletic performance.
Kinematic and kinetic data reported in this chapter were calculated after the movements of
interest were collected. That is, the data were postprocessed. The study of human movement is a
dynamic field and advances in both hardware and software are providing new possibilities for the
way data are processed and displayed. This has opened up exciting new applications for video-based
motion analysis, including computing joint kinematics in real time. In the following section we
provide an overview of the processing flow in realtime motion analysis and present an example of
work we are conducting in our laboratory.

6.4.7 Real-Time Motion Capture and Data Visualization
Real-time motion capture and data visualization has become a reality in recent years due to improve-
ments in hardware, software, and ever increasing computing power. It is now possible to view a
recorded motions and resulting kinematics at almost exactly the same time the movement was
performed. There are numerous advantages of real-time data capture and visualization for those in
the entertainment industry, researchers, and clinicians. Animators and directors benefit because they
can decide if movements were done as the scene had intended rather than waiting hours or days only