ARUP; ISBN: 978-0-9562121-5-3 - CMBBE 2012 - Cardiff University

expected. In our graph it is possible to recognize two distinct linear tracts characterized
by a low slope up to 40° and a higher slope above 50° of flexion (Fig. 2).
Force [N]
Figure 2 - Quadriceps muscle force computed during ‘quasi-static’ simulations.
The maximum value of muscle force, that was obtained at 90° of flexion, was 2760 N
which corresponds to 3.88 BW.
3.2 Ligament forces and lengthening-shortening patterns
Starting from a reference length, at full extension, of about 34.5 mm, the ACL was
found to lengthen reaching a peak at 15° of flexion; the ACL then gradually shortened
and reduced its length by 21% of its reference length at 90° of flexion (Fig. 3).
Length [mm]
3000
2500
2000
1500
1000
500
40
36
32
28
24
20
0
Quadriceps Muscle Force
0 10 20 30 40 50 60 70 80 90
Flexion angle [deg]
ACL Length
0 10 20 30 40 50 60 70 80 90
Flexion angle [deg]
Figure 3 - ACL length depicted as a function of the knee flexion angle.
The correspondent ACL force pattern was characterized by a considerable decrease,
from 130 N to 40 N, in the angle range from 0° to 40° of flexion; then the ACL
ligament force progressively approached a zero level near 60° of flexion (Fig. 4).
The PCL length pattern showed a small decrease up to 30° of flexion with a subsequent
elongation from 26 mm to 36 mm at 90° of flexion. Correspondent ligament force (Fig.
4) increased up to 400 N with an exponential growth (R 2 =0.983).
The LCL and MCL were characterized, on average, by a 10.5% shortening and a 5%