Knee Joint Models for Kneeling Biomechanics - Computational Biomechanics of the Musculoskeletal System - page 88

table 7.2
Initial Strain of the ligaments (Percent)

aaCl paCl aPCl pPCl alCl plCl amCl pmCl

0.06 0.1 0.0 0.0 0.0 0.0 0.04 0.04

7.3 determInIng the meChanICal StatuS oF kneelIng
Because the purpose of this model was to determine the mechanical status of the knee joint under
kneeling, the stress distributions of cartilages, menisci, and ligaments were determined.

7.3.1 S treSS d iStriBution of c artilaGe
The largest von Mises stress occurred at the point of contact between the tibia and patellar carti-
lages (Figure 7.4). The peak von Mises stress reached 1.875 MPa under a 300-N compressive load.
It then increased to 2.008 MPa at 600 N and 2.471 MPa at 1000 N. Li, Lopez, and Rubash (2001)
calculated von Mises stress distribution and ran a parametric analysis on their standing model.
They found the peak von Mises stress to be 1.57 MPa for a standing position. Using the same
cartilage material properties (elastic modulus of 10 MPa and Poisson's ratio of 0.45) and similar
boundary conditions (1000-N compression force with 300-N muscle force), the von Mises stress
was found to be 2.471 MPa. This indicated that kneeling would increase the von Mises stress by
approximately 57%.
The trend for the peak cartilage contact pressure is similar, reaching 4.358 MPa under 300-N
compressive loads, and increasing to 4.805 MPa at 600 N and 5.581 MPa at 1000 N. The contact
area also increased from 315.34 mm 2 to 379.104 mm 2 and to 424.842 mm 2 , with the loads changing
from 300 N to 600 N and to 1000 N. With increasing loads, the location of maximum stress also
changed, migrating toward the lower part of the patella.
Some researchers have used the largest contact pressure to illustrate the risks to the cartilage.
Donahue et al. (2002) showed the peak contact pressure on knee cartilage while standing fluctuated
from 2.10 to 2.51 MPa and was influenced by different material properties and boundary conditions.
In this research, the peak pressure reached 5.581 MPa, suggesting that kneeling carries a greater
risk of injuries than normal standing. If we use a 4.5-MPa peak contact pressure as the criterion for

S, Mises
(Avg: 75%)
+ 2.200e + 00
+ 2.017e + 00
+ 1.833e + 00
+ 1.650e + 00
+ 1.467e + 00
+ 1.283e + 00
+ 1.100e + 00
+ 9.167e - 01
+ 7.333e - 01
+ 5.500e - 01
+ 3.667e - 01
+ 1.833e - 01
+ 0.000e + 00

FIgure 7.4 (See color insert.) The von Mises stress on the cartilages of the knee joint in a kneeling posture

under 1000 N.