Changes in micro-architecture of subchondral bone in knee

osteoarthritis Sam de Groen

Supervisors: Prof Karen J Reynolds, Dr Egon Perilli

Associates: Bryant C Roberts (Hons)

Introduction

• Osteoarthritis (OA): painful, disabling disease

• Estimated cost AU$1.2 billion dollars in 2004-20051

• OA in the knee or hip is associated with altered walking gait patterns2

1. Mehrotra C, Remington P, Naimi T, et al. (2005) 2. Astephen J.L, Deluzio K.J (2007)

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Background OA: Bone and cartilage

• Pathogenesis of OA is complex• Initially thought as a wear and tear

disease of the cartilage 1

• However, changes in subchondral bone structure were also found 2

• Subchondral bone is an effective shock absorber 3

1. Radin E.L, Rose R.M (1986) 2. Lajeunesse D, Reboul P (2003)3. Goldstein S.A (1983)

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Jacquelyn Gilchrist (2003) http://www.interactive-biology.com/wp-content/uploads/2012/07/Osteoarthritis-of-Knee-Joint-1024x1024.jpg

Background Imaging of bone micro-architecture• Traditionally subchondral bone micro-architecture was

studied by histology (2D method) or micro-CT (3D method) on small biopsies from excised tibia

• Biopsies showed regional changes in subchondral bone and plate structure

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Bobinac D, et al. (2003)

8mm

Cartilage

Sub. Plate

Sub. Bone

Milz, et al. (1994)

Aim

• To develop a method for 3D subregional analysis of the micro-architecture in the knee subchondral bone, on entire excised tibia plateau scanned with micro-CT

• Bigger project: To explore, on patients undergoing total knee arthroplasty, the relationships between the variations in subchondral bone micro-architecture measured in their excised tibial plateau, and the loading measured in vivo during walking prior to surgery.

• Project funded by Arthritis Australia (Grant in Aid, 2013 Perilli E, Thewlis D, Reynolds KJ)

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Hypothesis• The micro-architecture of the subchondral bone and

thickness of subchondral plate, as measured by micro-CT, will differ among four anatomical sub-regions (anterior, posterior, medial, lateral)

ACL

PCL

Posterior

LateralMedial

Anterior

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Method

• Tibial plateau harvested during TKA (Burnside Hospital)*

• Micro-CT imaging (Skyscan1076) at Adelaide Microscopy

• In the micro-CT cross-section images of entire plateau, subregions for analysis were created via software (sw CTAn, Skyscan), in two ways

• Bone volume and plate thickness were measured in these subregions (software CTAn, Skyscan)

*Ethics Approval granted in July 2013

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Subchondral Bone and Plate

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2D Micro-CT cross-section images, 17µm/pixel

Selection of Regions of Interest• 3 mm-thick ROIs (176 slides) in subchondral bone

Irregular shaped ROIs 18mm diameter circular ROIs

9Micro-CT cross-section images, 17 µm/pixel

18mm

26mm

Results

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26mm

18mm

Part II: Spatial Mapping

• Systematic mapping of the spatial variations in microarchitecture of both subchondral plate and subchondral bone, in 3D, without coring

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Subchondral Bone and Plate

122D Micro-CT images, 17µm/pixel

Subchondral Plate

Subchondral Bone

Subchondral Bone and Plate

132D Micro-CT images, 17µm/pixel

Subchondral Plate

Subchondral Bone

3D Analysis over VOI 5 x 5 x 21 mm3

• Separated subchondral bone and subchondral plate• VOIs: 5 x 5 mm grid, 21 mm high• 104 VOIs in total

143D Micro-CT images, 17µm/pixel

Subchondral bone and plate in 3D

153D Micro-CT images, 17µm/pixel

Subchondral bone and plate in 3D

163D Micro-CT images, 17µm/pixel

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• Morphometric analysis over all VOIs (CTAn)• Results into Excel spread sheet• For graphic representation a MATLAB script was

developed to generate ‘heat maps’

Sub. Bone BV (mm^3) ROIs Width =5mm Length = 5mm Height = 21.4mm1 2 3 4 5 6 7 8 9 10 11

A 30.4 21.4 15.4 14.8 8.1 7.5 6.4B 2.9 41.0 42.6 44.7 31.5 20.9 16.8 22.0 19.2 12.5C 54.7 53.4 45.9 45.1 26.7 23.0 22.4 24.0 19.3 19.9 4.6D 45.0 40.5 36.1 41.7 35.2 26.8 22.5 25.4 17.6 20.0 5.6E 34.5 38.9 28.8 46.7 42.3 40.1 41.4 30.6 23.9 21.5 5.9F 38.1 41.9 29.4 55.0 56.3 42.7 46.3 41.9 29.8 29.0 6.6G 42.8 45.8 32.0 39.6 52.0 46.3 46.4 41.8 35.2 28.5 7.4H 36.4 39.8 25.9 24.5 48.4 51.0 35.3 35.7 31.6 24.9 4.5I 13.6 27.2 20.8 25.9 20.9 23.1 31.1 29.9 16.2 7.6J 9.6 19.0 19.6 30.4 10.3 5.0 7.2 4.3K 4.5 6.0 13.6

Analysis over VOI 5 x 5 x 21 mm3

Subchondral bone (5x 5 x 21 mm3 VOI)Bone Volume (mm3) Tb.Th (µm)

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(µm)(mm3)

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Plate Th. (µm)

Bone Volume (mm3)

(µm)(mm3)

Subchondral plate (5x 5 x 21 mm3 VOI)

Plate.Th (µm)

Plate.Th (µm)

Summary 2

• First micro-CT study that quantifies regional differences in entire human tibial plateau without coring the bone

• First method carrying out a 3D mapping of subchondral bone and subchondral plate microarchitecture

• Medial compartment showed highest bone volume in both subchondral bone as also in plate

• Medial compartment showed highest plate thickness

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Future Directions

• Do the analysis on more samples (N=7 for pilot study) for looking at statistical significant differences among regions

• Select uniform VOI size for subchondral bone analysis– 3x5x5mm ROIs across entire bone

• Automating processes– Edge detection for separation of subchondral bone and

subchondral plate from micro-CT images– MATLAB script to generate results

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Changes in micro-architecture of subchondral bone in knee osteoarthritis

Sam de GroenSupervisors: Prof KJ Reynolds, Dr E Perilli, Assoc: BC Roberts (Hons)

Thank you

Subchondral bone (5x 5 x 21 mm3 VOI)Bone Volume (mm3)

Tb.Th (µm)

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(µm)

(mm3)

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Plate Th. (µm)

Bone Volume (mm3)

(µm)

(mm3)

Subchondral plate (5x 5 x 21 mm3 VOI)

Plate.Th (µm)

Future Directions

-To look for statistical significant differences among 4 regions (or n x n):

1 ANOVA for repeated measurements

2 Post hoc analysis (Fishers, Scheffe or Bonferroni)

-to look for correlations between joint moments and microarchitecture, in the 4 regions: correlation analysis.

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