A Novel Approach to Quantify Patellofemoral Joint Contact Stress

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Presentation 1724 − Topic 29. Knee biomechanics

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.

(non-dimensional), and (e) PD5: Shortest translational distance required which brings two objects in contact.

Results Knee Angle 30°

45° Knee Angle

H.S.

PD1

PD2

PD3

PD4

PD5

1 2 3 1 2 3

6.08 6.97 6.50 6.88 7.50 7.32

1.95 1.98 1.90 2.20 2.10 1.98

1.10 1.54 1.16 1.10 1.24 1.10

0.97 1.95 1.81 1.41 2.43 2.58

2.20 2.80 2.40 2.60 3.00 2.50

PFPS

PD1

PD2

PD3

PD4

PD5

3.18 1.33 2.27 3.00 1.52 1.46 2.00 0.67 1.04 7.59 3.36 1.36 2.75 45° 8.25 3.38 1.39 2.50 7.68 2.20 1.36 3.10 Table 1: PD (mm) for healthy (H.S.) and subjects at different knee position 30°

1 2 3 1 2 3

7.13 6.93 5.30

2.95 2.90 1.90

3.10 2.92 2.90 PFPS

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 Journal of Biomechanics 45(S1)

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, 18:1821, 1984. Draper, C.E. et.al, J Orthop Res, 27:571-577, 2009. Farrokhi, S. et al, Osteoarthritis and Cartilage, 19:287-294, 2011.

ESB2012: 18th Congress of the European Society of Biomechanics