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Concise report
Interobserver reliability of ultrasonography in the assessment of cartilage damage in rheumatoid arthritis
  1. Emilio Filippucci1,
  2. Karine Rodrigues da Luz2,
  3. Luca Di Geso1,
  4. Fausto Salaffi1,
  5. Marika Tardella1,
  6. Marina Carotti3,
  7. Jamil Natour2,
  8. Walter Grassi1
  1. 1Clinica Reumatologica, Universitá Politecnica delle Marche, Ancona, Italy
  2. 2Disciplina de Reumatologia, Universidade Federal de São Paulo, São Paulo, Brazil
  3. 3Istituto di Radiologia, Universitá Politecnica delle Marche, Ancona, Italy
  1. Correspondence to Emilio Filippucci, Clinica Reumatologica, Universitá Politecnica delle Marche, Ospedale A. Murri Via dei Colli, 52, 60035 Jesi, Ancona, Italy; emilio_filippucci{at}yahoo.it

Abstract

Objectives To evaluate the interobserver reliability of ultrasonography (US) in the assessment of cartilage damage at metacarpophalangeal (MCP) joint level in patients with rheumatoid arthritis (RA).

Methods US examinations were performed on 80 MCP joints of 20 patients with RA using a MyLab70 XVG (Esaote Biomedica, Genoa, Italy), equipped with a broadband linear probe (6–18 MHz). For each patient, second and third MCP joints of both hands were examined independently on the same day by two rheumatologists (an experienced musculoskeletal sonographer and an investigator with limited US training). A multiplanar scanning technique on dorsal, lateral and volar aspects of the MCP joints was adopted. All US pathological findings were documented on at least two perpendicular scanning planes. Each joint was assessed by quadrant for the presence or absence of cartilage damage. Cartilage damage was also scored per quadrant on a five-grade semiquantitative scoring system on which investigators reached a consensus prior to the study.

Results Exact agreement between investigators was found in 173 out of 200 quadrants (86.5%) with regard to presence or absence of cartilage damage. Percentages of exact agreement for cartilage damage semiquantitative assessment at dorsal, lateral and volar quadrants were 72.5%, 52.5% and 85%, respectively, while unweighted κ values were 0.561, 0.366 and 0.766, respectively.

Conclusions The present study demonstrated moderate to good interobserver reproducibility of a semiquantitative scoring system based on qualitative morphological changes for cartilage damage at MCP joint level in patients with RA.

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Introduction

Rheumatoid arthritis (RA) is a systemic disease characterised by chronic symmetric synovitis leading to progressive destruction of the joint surfaces.1 2 Conventional radiography is the cornerstone imaging modality for assessing and monitoring joint damage in RA.3 4 However, several studies have reported its low sensitivity in the detection of bone erosions and only indirect signs of cartilage damage can be depicted by conventional radiography.3,,8

Over the last 10 years, while ultrasonography (US) was found to be a sensitive and reliable imaging technique for the detection of bone erosions at small joints of hands and feet in patients with RA, only few studies investigated the ability of US in the assessment of articular cartilage.

The available evidence indicates that US has the potential to provide for a detailed imaging of the hyaline cartilage, showing even minimal cartilage abnormalities in patients with RA.9,,11

Metacarpophalangeal (MCP) joints are frequently involved joints in patients with RA and wide portions of the metacarpal head cartilage of the second and third fingers can be visualised by US.9 10 12

The main aim of this study was to evaluate the interobserver reliability of US in the assessment of cartilage damage at MCP joint level in patients with RA.

Materials and methods

Patients

A total of 20 consecutive patients with a diagnosis of RA according to the American College of Rheumatology (ACR) criteria13 underwent a bilateral US examination of the second and third MCP joints. Patients were recruited from the Department of Rheumatology of the Università Politecnica delle Marche at Jesi (Ancona, Italy) between 15 September 2007 and 15 December 2007.

Radiographic image interpretation

x-Rays of the hands in posteroanterior view were assessed by an experienced musculoskeletal radiologist who was blinded to clinical and US imaging data.

Joint space narrowing was scored at the level of the second and third MCP joints using the Sharp scoring system.14

US image acquisition

All patients were scanned independently on the same day by two rheumatologists (an experienced musculoskeletal sonographer and an investigator with limited US training). US examinations were focused on the assessment of the hyaline cartilage of the metacarpal heads. The metacarpal head of the second finger was divided into three quadrants: dorsal, radial and volar; while the head of the third finger was divided into two quadrants: dorsal and volar. Each quadrant was scanned in longitudinal and transverse views, from radial to ulnar and from proximal to distal to ensure the maximal exploration of the hyaline cartilage. Particular attention was paid on maintaining the probe in a position providing an angle of 90° between the direction of the US beam and the cartilage surface. While lateral and volar aspects were explored with the hand in neutral position,15 the dorsal aspect of the metacarpal heads was scanned with the MCP joint in maximal flexion (more than 45°) to increase the extent of the cartilage explorable by US.

US examinations were performed using a MyLab70 XVG (Esaote Biomedica, Genoa, Italy), equipped with a broadband linear probe (frequency ranging from 6 to 18 MHz) and lasted less than 5 min per patient.

US image interpretation

Before the start of the study, the investigators examined together a total of 20 patients with RA at different stages of the disease, fulfilling the ACR criteria13 and 15 healthy subjects who had no history or signs of hand disease and reached a consensus on the scanning protocol and on the interpretation of normal and pathological US findings.

Normal features of the hyaline cartilage at the metacarpal head included two hyperechoic sharp, regular and continuous margins delimiting a homogenous anechoic band (figure 1A,A′).9,,11

Figure 1

Pictorial reference of the ultrasound (US) scoring system for semiquantitative assessment of the cartilage damage at metacarpal head level. Images were obtained on the dorsal aspect on longitudinal (A–E) and transverse (A′–E′) views with the metacarpophalangeal (MCP) joint in maximal flexion. A. Score=0: there is no evidence of cartilage abnormalities. B. Score=1: loss of the sharpness of the superficial margin of the hyaline cartilage. C. Score=2: partial thickness defect of the cartilage layer. D. Score=3: full thickness defect of the cartilage layer with a normal subchondral bone profile. E. Score=4: complete loss of the cartilage layer and subchondral bone involvement.

Cartilage damage was evaluated using the following semiquantitative scoring system based on qualitative morphological changes introduced by Disler and colleagues11: 0=normal hyaline cartilage; 1=loss of the sharpness of the superficial margin of the hyaline cartilage; 2=partial thickness defect of the cartilage layer; 3=full thickness defect of the cartilage layer with a normal subchondral bone profile; 4=complete loss of the cartilage layer and subchondral bone involvement. The presence or absence of at least one of these abnormalities was also evaluated. All US pathological findings were documented on at least two perpendicular scans and recorded per quadrant of metacarpal head. A pictorial reference of the scoring system including all the cartilage abnormalities was obtained on the dorsal aspect of the metacarpal head and shown in figure 1.

Total additive scores per MCP joint were calculated, as result of the sum of the scores obtained at the different quadrants from either the detection or the semiquantitative assessment of the cartilage damage.

Statistical analysis

Statistical analysis was performed using the MedCalc software (V.9.2 for Windows; Mariakerke, Belgium). Interobserver reproducibility was determined using κ statistics (unweighted κ for dichotomous evaluation and weighted κ for semiquantitative scoring) and percentage of exact agreement. κ values lower than 0.20 were considered poor, between 0.21 and 0.40 fair, between 0.41 and 0.60 moderate, between 0.61 and 0.80 good and between 0.81 and 1 excellent.16

Results

A total of 20 patients, (80% women) with a mean±SD age of 51.3±16.8 years (range 25–78) and a mean±SD disease duration of 103.8±95.4 months (range 6–300), were assessed. In all, 80 metacarpal heads and 200 quadrants (80 dorsal quadrants, 40 radial quadrants and 80 volar quadrants) were scanned.

Patient demographic and clinical characteristics acquired by the rheumatologist who performed the clinical examinations are reported in table 1, together with the US and radiographic findings.

Table 1

Patients clinical characteristics and ultrasound (US) and x-ray findings

A total of 47 (59%) out of 80 MCP joints were found to be positive for cartilage damage in at least 1 of the 3 quadrants used to examine metacarpal heads by US. While in 33 (41%) out of 80 MCP joints, no US findings indicative of cartilage involvement were detected.

Exact agreement between investigators with regard to presence or absence of cartilage damage was found in 173 (86.5%) out of 200 quadrants, of which 70 (87.5%) out of 80 were dorsal quadrants, 26 (65%) out of 40 were radial quadrants and 77 (96.2%) out of 80 were volar quadrants.

Percentages of exact agreement for cartilage damage semiquantitative assessment at dorsal, lateral and volar quadrants were 72.5%, 52.5% and 85%, respectively, while unweighted κ values (SE, 95% CI) were 0.561 (0.080, 0.404 to 0.717), 0.366 (0.105, 0.159 to 0.572) and 0.766 (0.062, 0.643 to 0.888), respectively and weighted κ values were 0.672, 0.537 and 0.832 respectively.

Disagreement between the sonographers was found in 53 (26.5%) out of 200 semiquantitative assessments of cartilage damage, being the loss of the sharpness of the superficial margin of the hyaline cartilage the most frequent reason of lack of agreement (16 out of 53 disagreements in scoring cartilage damage).

Weighted κ values for total additive scores per joint were 0.729 and 0.733, respectively, for the detection and for the semiquantitative assessment of cartilage damage.

Discussion

In patients with RA, joint damage is the result of a variable combination of bone erosion and cartilage lesion.12 In daily clinical practice, the assessment of joint damage is currently performed using conventional radiography, which is relatively insensitive in detecting bone erosions and can only visualise indirect signs of cartilage involvement.3 4 Over the last 10 years, evidence has been gathered supporting the sensitivity of US to detect bone erosions and an increasing number of rheumatologists have started to scan patients in the clinical setting of early arthritis. Despite high-resolution US allowing for a detailed visualisation of the hyaline cartilage, its use is still bound to research, due the substantial lack of the acquisition and interpretation US criteria for cartilage involvement in RA.

The main aim of the present report was to evaluate the interobserver reliability of US in the assessment of cartilage damage at MCP joint level in patients with RA and reliable detection and semiquantitative scoring of cartilage damage were demonstrated. To the best of our knowledge, only another recent study by Möller and colleagues10 has investigated this topic. However, in that study only the dorsal aspect of MCP and proximal interphalangeal joints was investigated and the hyaline cartilage was assessed measuring the maximal distance between the margins. Latest generation US equipment allows for a detailed assessment of qualitative findings indicative of cartilage damage. At the focal area, the probe used in the present study provides an axial resolution of 30 μm and a lateral resolution of 60 μm, with an excellent contrast resolution. We believe that this kind of approach can avoid an underestimation of cartilage damage with respect to the measurement of the cartilage thickness. Since to the best of our knowledge there is no previous similar study, we decided to test the interobserver reliability of qualitative cartilage changes.

In the present study, moderate to good interobserver agreement for US qualitative morphological changes indicative of cartilage damage was obtained by two rheumatologists (an experienced musculoskeletal sonographer and a sonographer with limited experience). While a very long period of training is required to achieve competency in musculoskeletal US, adequate skill for a careful assessment of specific target, such as articular cartilage, can be obtained in a shorter time even by a sonographer with limited US training.

From the analysis of the interobserver agreement levels according to the different quadrants, the lateral aspect of the second metacarpal head resulted the most difficult to score. A possible explanation relies on the physiological thinning of the cartilage at that level, which makes the cartilage even more difficult to evaluate. According to the analysis of the disagreements between the sonographers, the most difficult US finding to assess was the loss of the sharpness of the superficial margin of the hyaline cartilage, being responsible for 16 (30%) out of 53 disagreements in scoring cartilage damage. After rereading the US images, it was clear that the sonographer with limited US training either missed the superficial margin because the cartilage surface was not insonnated perpendicularly (this occurred 10 times) or misinterpreted the lower margin of the finger extensor tendon as the superficial margin of the cartilage when the superficial margin had lost its sharpness (this occurred 6 times).

The rationale for the development of a semiquantitative scoring system is mainly based on the fact that its use during US short-term monitoring may enable the rheumatologists to identify fast progression of the cartilage damage in patients with RA. While limitations are related to the acoustic barriers and to the operator experience and expertise, the additional value of US is related to its non-invasive, inexpensive and detailed imaging. Thus, despite the technical limitations other studies are required to further evaluate the US validity in the assessment of cartilage damage in patients with RA. These studies should involve a higher number of sonographers and patients.

In conclusion, the present study demonstrated moderate to good interobserver reproducibility of a semiquantitative scoring system based on qualitative morphological changes for cartilage damage at MCP joint level in patients with RA.

References

Footnotes

  • Competing interests None.

  • Provenance and peer review Not commissioned; externally peer reviewed.

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