Page 199 - Advances in Biomechanics and Tissue Regeneration

9.6 FUTURE DIRECTIONS 193

FIG. 9.7 Ensemble averaged normalized surface EMG [127] and estimated muscle forces normalized to their isometric maximal values (taking the
maximum muscle stress at 0.6 MPa) during the stance phase for various knee muscles. For uniformity, the estimated values at 0% and 5% periods of
stance are averaged to present a single data point at HS. Coefficients of determination as a measure on the goodness of fit are also listed at each period.

9.6 FUTURE DIRECTIONS

In our MS model of the lower extremity, only the knee joint was represented in details. On the other hand, hip and
ankle joints were modeled as frictionless spherical joints. To improve the accuracy of estimations, it is preferable to
incorporate also these articulations with accurate passive properties as much as possible. In addition, due to the
expected variations in morphology, musculature, and material properties, subject-specific models taking account
of individual characteristics are recommended to compute personalized response [193]. The resulting predictions will
then help establish more personalized protocols for effective injury prevention, treatment, and postoperative rehabil-
itation. Toward this goal, statistical modeling and sensitivity analyses will be of great help.
With the rising incidence of medial knee joint OA, knee adduction moment (KAM) is commonly introduced as a
surrogate measure of load on the medial plateau and hence as a marker where its reduction is the main focus of various
interventions (e.g., orthoses, shoe insoles, gait modification, and osteotomy) that aim to prevent the development and
progression of OA. However, some recent in vivo studies using instrumented implants have questioned such direct
relationship and qualified the correlation between KAM and the medial compartment load as poor to average [194].
Similarly, questions have been raised on the association between pain/symptoms and reduction in KAM when wear-
ing wedged insoles [195]. The internal load distribution is however influenced mainly by changes in the knee adduc-
tion rotation (rather than in KAM) as demonstrated in our earlier simulations at mid-stance phase of gait [35].
Confirmation of this finding during the entire stance phase of gait is, however, essential to back up and generalize
such conclusion. Knee adduction rotation and moment should hence be altered within reported measurements one
at a time at each stance period [196].
Quantification of the stability margin (reserve) of the intact/injured/reconstructed human knee joints is crucial in
performance evaluation, injury prevention, implant design, and treatment managements. Joint hypermobility (insta-
bility) has been associated with pain, implant failure, injury, and OA [197]. Dynamic stability of the knee joint in daily

I. BIOMECHANICS