Page 198 - Advances in Biomechanics and Tissue Regeneration

192 9. COMPUTATIONAL MUSCULOSKELETAL BIOMECHANICS OF THE KNEE JOINT

FIG. 9.6 Instantaneous (tangent) F-E (A) and add-abd (B) angular rigidities of the passive tibiofemoral joint as a function of the compression
preload and joint flexion angle (+: results by a less refined version of the same model) [37].

initiation of contact (HS at 0% stance), estimated values are overall smaller than measurements that could partly be due
to the absence of coactivity in the model employed here. Moreover, concerns on collected surface EMG measurements
in larger and deeper muscles, cross-talk effects, processing and normalization of signals, and finally force-EMG rela-
tions should be taken into account whenever comparing force estimations with collected EMG data.
Apart from the early periods of stance (0% and 5%) and due mainly to add-abd rotations, the medial plateau carried
a larger portion of contact forces than did the lateral plateau [15, 20, 22], which agrees with earlier estimates [104, 184].
In accordance with our predictions, others also reported small forces or none at all on the lateral compartment at the
toe-off period at the end of stance [132, 185]. In vivo measurements of knee contact forces provide a valuable oppor-
tunity for the global validation of MS models by direct comparison between predicted/measured contact forces that
could also indirectly validate estimated muscle forces and algorithm used. Some studies have measured in vivo knee
contact forces of patients by instrumented knee implants during gait on treadmill [186–188] and over ground [1,
189–191]. Maximum total contact force ranged from 1.8 to 3.0 BW, typically remaining between 2.0 and 2.5 BW.
For the most part, MS model studies overestimate tibial contact forces during gait with maximum total contact forces
ranging from 1.8 to 8.1 BW with most estimates falling in the range of 3.0–3.5 BW [15, 19, 20, 22, 25, 110, 132, 181, 182,
192]. With our MS model during the stance phase of gait in asymptomatic subjects, the maximum contact forces (up to
4 BW) were found at 25% and 75% stance periods that are larger than 2.5–3 BW measured in vivo in patients with
instrumented knee implants [1].

I. BIOMECHANICS