A NOVEL APPROACH TO QUANTIFY PATELLOFEMORAL JOINT CONTACT STRESS

Kamrul Islam (1), Tanvir Mustafy (1), Samer M. Adeeb (1), Marwan El-Rich (1), J.L. Ronsky (2), Jesse Anderson (3)

(1)Department of Civil and Environmental Engineering, University of Alberta, Canada; (2) Department of Mechanical and Manufacturing Engineering, University of

Calgary, Canada; (3) Department of Orthopaedic Surgery, University of Alberta

Introduction Patellofemoral pain syndrome (PFPS) is one of the

most common knee disorders, an ailment which

affects more than 25% of the population

[Devereaux et al., 1984]. Abnormal stresses are

often cited as a prime cause of different instabilities

in the patellofemoral (PF) joint including PFPS. It

affects people who are active or participating in

sports [Devereaux et al., 1984]. Nevertheless, exact

reasons of PFPS are still unknown. Researchers

have used different experimental and numerical

techniques to assess PFPS [Draper et al., 2009;

Farrokhi et al., 2011]. However, none of those

techniques have been established as a gold standard

to assess PFPS accurately. Therefore we are using a

new geometric measurement technique to

investigate the healthy and symptomatic PF joints.

We implemented a computational modelling

approach using 3-D registration technique and

linear mapping to investigate the PF joint contact

stress in terms of depth of penetration (PD) of

patellar cartilage surface into the femur cartilage

surface; as PD is the indirect measure of stress. The

aim of the current work is to quantify the

penetration depth of the healthy and symptomatic

PF joints using five different methods (PD1-PD5),

and the difference between the lateral and medial

side of the PF joints.

Methods This study used experimental data from the left

knee of healthy (female, 26±4y, 167.0±7.9cm,

64.4±5.7kg) and pathological (PFPS) subjects

(female, 28±8y, 167.0±4.7cm, 59.0±5.5kg) which

were scanned using 3.0T MRI at 15, 30, and 45° knee flexion angles. 3-D reconstructed geometry of

the patella and femur were created using MIMICS.

Following the digitization, two data sets of 3-D

geometry for the patella and femur were imported

into the Geomagic Studio 12 for registration. Using

the registration method, the patella at 15° is linearly

transformed from its original (reference) position to

a weight-bearing position (30° and 45°) in order to

identify the complex interaction between the patella

and femur surfaces. In this study, PD was defined

as: (a) PD1: Cubic root of intersection volume, (b)

PD2: Highest thickness of intersection, (c) PD3:

Ratio of the intersection volume to the projected

surface area in contact, (d) PD4: Ratio of the

intersection volume to the total volume of patella

(non-dimensional), and (e) PD5: Shortest

translational distance required which brings two

objects in contact.

Results

Knee

Angle H.S. PD1 PD2 PD3 PD4 PD5

30°

1 6.08 1.95 1.10 0.97 2.20

2 6.97 1.98 1.54 1.95 2.80 3 6.50 1.90 1.16 1.81 2.40

45°

1 6.88 2.20 1.10 1.41 2.60

2 7.50 2.10 1.24 2.43 3.00 3 7.32 1.98 1.10 2.58 2.50

Knee

Angle PFPS PD1 PD2 PD3 PD4 PD5

30°

1 7.13 3.18 1.33 2.27 2.95

2 6.93 3.00 1.52 1.46 2.90 3 5.30 2.00 0.67 1.04 1.90

45°

1 7.59 3.36 1.36 2.75 3.10

2 8.25 3.38 1.39 2.50 2.92

3 7.68 2.20 1.36 3.10 2.90

Table 1: PD (mm) for healthy (H.S.) and PFPS

subjects at different knee position

Figure 1: PD (mm) in lateral (L) and medial (M)

side of the PF joint for healthy and PFPS subjects

at 30° and 45° knee position using method PD2

Discussion PD estimated by using method PD2, PD4, and PD5

is greater in PFPS subjects which may generate

higher contact stress. In 30° knee position, for

healthy subjects PD is higher in the lateral side

when compared to PFPS subjects but the situation

is reverse in medial side. In future finite element

analysis will be performed to confirm or disconfirm

this finding.

References Devereaux, MD et al, Br J. Sports Medicine, 18:18-

21, 1984.

Draper, C.E. et.al, J Orthop Res, 27:571-577, 2009.

Farrokhi, S. et al, Osteoarthritis and Cartilage,

19:287-294, 2011.

S396 Presentation 1724 − Topic 29. Knee biomechanics

Journal of Biomechanics 45(S1) ESB2012: 18th Congress of the European Society of Biomechanics