USG of Osteoarthritis

서울대학교 의과대학 재활의학교실

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Contents

• General Principles of USG on OA

• USG of Normal Joints

• USG of OA (Cartilage, Bone etc)

• USG of Individual Joints (Knee, Hand, Hip)

Introduction

• Osteoarthritis

– Most common joint disease

– 50% of elderly person complain joint pain

• Pathology

– Progressive degeneration & thinning of cartilage

– Changes of adjacent subchondral bone

Pros of USG on OA

• Noninvasive

• Cheap

• Performed in exam room minimizing the discomfort and inconvenience

• Repeated exam is possible

• Dynamic assessment of joint

• Show adjacent soft tissues

Cons of USG on OA

• Limited acoustic window

– Some part of weight bearing areas can not be visualized

• Lack of universal grading system

• Operator dependent results

• Needs more clinical validation

– No studies comparing US with arthroscopy (gold standard for dx of cartilage degeneration)

General Principles of US on OA

• Highest frequency that allows visualization of the target area

– MCP: 13 MHz or higher

– Hip : 10 MHz or lower

• Multiplanar scanning technique

• Dynamic examination during flexion-extension

Things to See

• Articular cartilage

• Osteophytes

• Joint inflammation

US of Normal Joints

• Uniformity of bone profile

• Homogenous echogenecity of periarticular soft tissues

• Minimal amount of fluid in joint or bursae

Hyaline Cartilage by USG

• Lack of echos with sharp margins

– Well defined anechoic or homogenously hypoechoic band

• Between chondrosynovial and osteochodral margins

Other Structures

• Bone – Regular echogenecity

– Hyperechoic band with anechogenesity below

• Meniscus – Between the bones

– Homogenously echogenic triangle-shaped structure

Cartilage in OA by USG

• Loss of sharp contour

• Variable echogenecity

• Asymmetric narrowing of the cartilaginous layer

Bone Changes in OA by USG

• Hyperechoic signal in the area of joint capsular attachments

• Osteophytes, at later stage

US EXAM IN KNEE OA

Position

• Full flexion

Scan Method

• Identify intercondylar notch area

• Evaluate cartilage in sulcus area

• Cartilage of medial condyle

• Cartilage of lateral condyle

• Keep US beam perpendicular to the femoral surface all the time

Normal Knee Cartilage

OA Knee I

OA Knee II

Saarakkala et al. Osteoarth Cart 2012 (in press)

Normal

Degenerative (mild) Loss of sharp margin Increased echo

Moderate Local thinning < 50%

Moderate Local thinning > 50%

100% loss of cartilage

Meniscus Changes

• Meniscal subluxation

– Commonly associated in OA

Supine

Upright

US EXAM IN HAND OA

Equipment, Scan Technique

• Probe: Hocky stick

• Scanning plane

– Longitudinal

– Transverse

– Dorsal & palmar surface

– Medial & lateral regions

Position

• Volar side: Neutral position

• Dorsal side: Full flexion, sometimes extension

Gel Pad

Findings

• Osteophytosis

• Joint space narrowing

• Erosion

Osteophytes

• Cortical protrusion at the joint margin

Joint Space Narrowing

Use of Power Doppler

Erosion

• Less sensitive with USG

• Reason

– Central location of lesion

– Overhanging osteophytes

USG has poor correlation with clinical features of erosive OA -> Early detection of preclinical OA ?

US EXAM IN HIP OA

Equipment, Position

• 5 MHz, Convex array type

• Extension of hip

• 10-15 external rotation

USG findings

• Cartilage evaluation is usually impossible

• Diagnosis with intra-articular fluid collection

• Koski’s definition

– Longest intra-articular distance >7 mm

– Side to side difference > 1mm

Validity of USG

• Correlation between US-detected cartilage thickness and histological thickness

– McCune WJ et al. Clin Orthop Relat Res 1990

– Martino F et al. Clin Rheumatol 1993

• Correlation with MRI

– Ostergaard M et al. Acta Radiol 1995

Summary

• USG is a useful imaging modality in OA

• Limited acoustic window

• Clinical validation is necessary.