220 Radiological aspects of osteoarthritis 1 3

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Radiologische Aspekte der Arthrose

Zusammenfassung Aufgrund der Bevölkerungsalte-rung wurde die Arthrose kontinuierlich zu einer der häufigsten Indikationen in der muskuloskelettalen Bild-gebung. Die Arthrose geht mit einem hohen Maß an krankheitsbedingter Funktionsbeeinträchtigung und so-mit reduzierter Lebensqualität einher. Ihre Pathogenese ist – in Abhängigkeit vom betroffenen Gelenk – mitunter komplex und erfordert die Diskriminierung einzelner prädisponierender Erkrankungen. In diesem Artikel wird auf die radiologischen Aspekte in der Arthrose-diagnostik eingegangen. Zusätzlich wird der Stellenwert der einzelnen Modalitäten der Bildgebung für die wich-tigsten Arthrose-Lokalisationen Hand, Hüfte und Knie ermittelt.

Schlüsselwörter: Arthrose, Indikation, Bildgebung

Summary Osteoarthritis (OA) is one of the most fre-quent indications in musculoskeletal imaging because OA is the most prevalent musculoskeletal disease in developed countries. As the population becomes older and older, the need for adequate imaging techniques also increases. The various forms of osteoarthritis are as-sociated with a high degree of illness-induced physical disability and reduced life quality. In some forms, the pathogenesis is complex and can require the discrimi-nation of a variety of predisposing diseases. The specific forms of osteoarthritis will be highlighted in this article. In addition, the value of each imaging modality will be assessed, with special regard to the most common sites: hand, hip, and knee.

Keywords: Osteoarthritis, Indication, Imaging techniques

Introduction

Osteoarthritis (OA) is one of the most common patho-logic conditions in the elderly population, and a leading cause of disability among the elderly [1]. Pain and radio-graphic changes are common in people with OA, but the relative contributions of pain and the observed radio-graphic changes to quality of life (QOL) are unknown. QOL is a measure of health status and predicts the use of health care resources and also predicts the mortality [2]. Although radiographic markers of OA are weakly associ-ated with pain, both are associated with poor QOL. It is still unclear whether radiographic findings are indepen-dent of pain or of a diagnosis of OA [3–5].

With regard to the steadily growing percentage of old and very old people in the developed world, OA is—just as is osteoporosis—also a growing socioeconomic issue [6]. This underlines the increasing importance of imag-ing modalities and techniques for the various forms of OA.

Still, the baseline imaging modality is the conventional radiograph (CR) in two different projections, e.g., antero-posterior (AP) and the axial projection (Lauenstein for the hip joint) [7]. Obtaining an image under weight-bear-ing conditions, e.g., when the patient is standing, offers the opportunity to detect malposition of the limbs. The advantages of CR include: a standardized method that is important for follow-up examinations; its wide availabil-ity; the exclusion of relevant differential diagnoses, such as bone tumors; and lastly, its cost-effectiveness.

Further evaluation of the joints, especially of the intraarticular structures, should be performed with mag-netic resonance imaging (MRI). The domain of MRI is cartilage imaging. The delineation of labroligamentous structures should be performed with MR arthrography. Other imaging modalities, in particular sonography, performed by an experienced investigator, provide a high resolution of the superficial structures, especially of nerves. Sonography also enables the differentiation between joint effusion, and between active and inactive

Wien Med Wochenschr (2013) 163:220–227DOI 10.1007/s10354-013-0184-6

Radiological aspects of osteoarthritisJudith Sautner, Claudia Schueller-Weidekamm

Dr. J. Sautner ()Landesklinikum Weinviertel Stockerau, 2. Medizinische Abteilung, Karl Landsteiner Institut für klinische Rheumatologie, Landstraße 18, 2000 Stockerau, Austriae-mail: judith.sautner@stockerau.lknoe.at

PD Dr. C. Schueller-WeidekammUniv. Klinik für Radiodiagnostik und Muskuloskelettale Radiologie, AKH Wien, Währinger Gürtel 18–20, 1090 Vienna, Austriae-mail: claudia.schueller-weidekamm@meduniwien.ac.at

Received: 19 October 2012 / Accepted: 16 January 2013 / Published online: 15 February 2013© Springer-Verlag Wien 2013

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Radiological aspects of osteoarthritis 2211 3

synovitis by Doppler sonography, which is important for secondary OA.

Pathogenesis

Although there is no doubt that mechanics play a key role in OA, the pathogenesis is a complex issue and cannot be explained by degeneration alone. The cartilage and the subchondral region is influenced by chronic strains like pressure, tension, and shear [8]. These forces are as relevant for the development of OA as for individually different patterns in the vascularization and flexibility of the deeper layer of the osteochondral compartment. The English term “osteoarthritis” describes very accurately, the chronic inflammatory condition in OA. In the joint, especially in the cartilage, a constant remodeling, bal-ancing, degeneration and regeneration take place, even as early as adolescence. Once the regeneration process diminishes, constant cartilage loss sooner or later leads to OA.

Primary, purely degenerative OA can be distinguished from the secondary form following trauma or an inflam-matory joint condition.

In this article, we focus on the three most often affected joints: hand, hip and knee.

1) Hand osteoarthritis

The hands are frequently involved in generalized OA. The age-standardized prevalence of hand osteoarthritis (HOA) is only modestly higher in women than in men

(44 vs. 38 %), whereas erosive or symptomatic HOA affects women more often than men [9]. One major problem is the definition of HOA, which comprises a very heteroge-neous group of several sites of OA: a) OA of the wrist; b) OA of the thumb base; c) OA of the metacarpophalangeal joints; d) OA of the proximal interphalangeal joints; and e) OA of the distal interphalangeal joints. As for other forms of OA, the European League Against Rheumatism (EULAR) has published evidence-based recommenda-tions for the management and diagnosis of HOA, also incorporating the imaging modalities used to image these types of OA [10, 11]. CR is still the gold standard for the morphological assessment of HOA due to its high availability, good feasibility, and low costs. However, currently there is no established gold standard for the definition of radiographic HOA, because definitions and grading systems in the literature differ considerably [12].

Typical HOA-CR demonstrates the presence of osteo-phytes (“true” intraarticular osteophytes and traction spurs), erosions, cysts, sclerosis, and joint space narrow-ing (JSN) (Fig. 1).

The HOA-CR is currently recommended as the imag-ing endpoint for clinical trials of Symptomatic slow act-ing drugs in osteoarthritis (SYSADOA) in HOA [13]. In addition, sonography is an interesting imaging modality, especially for the hands, providing a dynamic picture, assessing osteophytes, visualizing (secondary) inflam-mation in the HOA finger joints by Power Doppler, and also ruling out rheumatoid arthritis (RA) and psoriatic arthritis (PsA) as primary inflammatory differential diag-noses [14]. In contrast to inflammatory conditions in the hands, MRI is not an established imaging modality for

Fig. 1 a, b Conventional ra-diographs in dorsovolar and oblique plane show polyar-throsis of the left hand in an 86-year-old woman. Note the overhanging osteophytes (arrow) and the joint space narrowing predominantly in the distal and proximal interphalangeal joints. The metacarpophalangeal joints are less involved

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the assessment of HOA yet; it is currently mainly per-formed for research purposes.

2) Hip osteoarthritis

Due to cartilage loss, the femoral head changes its posi-tion relative to the acetabulum. It primarily moves upward, and, in rare cases, axially or toward the middle [15]. Particularly in the case of a cranial movement of the femoral head, an accentuated subchondral sclerosis and subchondral cysts at the lateral edge of the head and at the acetabulum can be observed. This might result in an overcoverage with retroversion and a deep acetabulum (Fig. 2).

There are two different types of femoroacetabular impingement (FAI). The first, the pincer impingement, is caused by a protrusio acetabuli or an overcoverage of the acetabulum which causes an impingement of the lateral acetabulum against the femoral neck. This entity is more often seen in elderly women. The second type of hip impingement is the cam impingement which pre-dominantly occurs in younger male patients. The cam impingement is characterized by an osseous bump at the femoral neck (“pistol grip deformity”) that results in an outside-in delamination of the acetabular cartilage. Most femoroacetabular impingements are of mixed type [16].

Analogous to the Milwaukee shoulder, the pres-ence of calcium-pyrophosphate deposition disease and insufficiency fractures in the hip are associated with a rapidly progressive form of destructive OA [17]. Within a few weeks of presentation, a fulminant joint destruction can be observed, with no osteophytes or subchondral cysts.

Secondary coxarthrosis

Various types of diseases may lead to a secondary coxar-throsis. The diagnosis of the underlying disease must be based on both radiological imaging and clinical features. An early diagnosis is crucial for the management of the specific disease, as are early interventions in order to pre-vent secondary coxarthrosis.

Predisposing conditions for coxarthrosis in childhood

a) Dysplasia

Dysplasia involves inborn or acquired malpositions and malossification of the newborn. If severe forms of dyspla-sia are not treated, the consequence will be permanent damage of the joint, leading to walking deficits and pain. This underlines the importance of pediatric and orthope-dic sonography of the hip of the newborn [18]. Hip dys-plasia, as well as congenital luxation, can be excluded. Dysplasia can cause coxarthrosis with anterocranial movement of the femoral head.

b) Morbus Perthes

Morbus Perthes is the second important hip disease in childhood, with an incidence of 1:1200, starting primar-ily at the age of five to seven [19]. A blood circulation problem in the proximal femoral epiphysis leads to a failure in endochondral ossification of the femoral head (Fig.  3). There is a chance of complete healing, as well as severe deformities of the femoral head. The Herring classification is of prognostic value in this regard [20]. Diagnosis can be made by AP CR and the axial view, com-pleted by sonography. CT, as well as scintigraphy, should be avoided because of radiation concerns, whereas MRI shows pathologic features in the femoral epiphysis very early. However, MRI is not always available.

Fig. 2 a–c Conventional radiograph of the pelvis in antero-posterior view (a) of a 60-year-old man with right hip pain. The joint space is moderately narrowed; osteophytes are lo-cated at the lateral site of the femoral head; and subchon-dral sclerosis of the acetabulum with a centrally-located lu-

cency is seen (arrow). The corresponding short tau inversion recovery (STIR) magnetic resonance images in coronal plane (b, c) show a large subchondral cyst (short arrow) in the ac-etabulum and thinning of the cartilage (long arrow). Labral le-sions are often associated in coxarthrosis (open arrow)

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Radiological aspects of osteoarthritis 2231 3

c) Epiphysiolysis capitis femoris

This is the third important underlying pathological hip condition in childhood and adolescence, with an inci-dence of 0.2–10 of 10,000, mainly affecting male youth up to the age of 14. It is characterized by an anteroinfe-rior dislocation of the femoral neck and a posteroinferior slipping of the epiphyseal gap [21].

Diagnosis can be made by AP CR and an axial view, which shows the dislocated femoral neck near the epiph-yseal gap. The head shows a normal congruence with the acetabulum. In case of a longer-lasting epiphysiolysis, a

repairing callus can often be seen on the dorsomedial part of the head–neck zone. MRI is a good technique to show the slipping of the epiphysis and to help diagnose the initial stage of the slipping, the so-called “preslip” [22, 23] (Fig. 4).

Early diagnosis of cartilage and labrum acetabulare damage

From adolescence onwards, diseases of the joint carti-lage and of the labrum acetabulare predispose a patient

Fig. 3 a–c Conventional radiographs in anteroposterior view (a) of the hip and axial view of the right hip (Lauenstein) (b) in a 28-year-old woman with progressive pain in the right hip. The axial view of the right hip shows a subchondral lucency of the femoral head indicating a subchondral fracture (arrow).

The corresponding crescent sign (open arrow) that is patho-gnomonic for the avascular necrosis of the hip (Legg-Calve-Perthes disease) is seen on the axial proton density magnetic resonance image (c)

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for the development of coxarthrosis. The imaging of the cartilage, labrum, synovialis, and the periarticular soft tissue is obtained from MRI today [24].

The hip cartilage resembles a horseshoe, formed by a central, cartilage-free zone surrounded by the lig. transversum. Changes in hydration and proteoglycans are responsible for the damage to the cartilage, starting with cracking of the cartilage, then rupturing, and finally, formation of subchondral cysts [25]. Sometimes, MR arthrography is needed for a precise assessment of actual cartilage damage [26].

Indications for imaging in coxarthrosis and predispos-ing conditions are summarized in Table 1 [27].

3) Knee osteoarthritis

OA in the knee is very common, with an increasing prev-alence in the elderly population. The prevalence is 9 % in the second decade of life, 30 % in the sixth decade, and over 90 % in the seventh decade [28]. The Kellgren–Law-rence score graduates OA of the knee on CR and takes the following parameters into account: osteophytes, joint

space narrowing (JSN), subchondral pseudocystic areas with subchondral sclerosis, and deformity [29] (Table 2).

The most important radiographic criterion for OA is the JSN. In the knee, JSN is represented by loss of cartilage coverage, meniscal extrusion, and meniscal degenera-tion, whereas, in the hip, the joint space is the correlate of cartilage thickness [30]. In the knee, there is an asso-ciation between medial meniscus tears and changes in cartilage and subchondral trabecular bone [31]. In con-trast to MRI, CR cannot identify the cause of JSN in the knee (Fig. 5).

In 2011, the Imaging of Osteoarthritis Research Society International (OARSI) defined new criteria for the defini-tion of OA [13], including MRI criteria such as cartilage coverage reduction, bone marrow edema, subarticular sclerosis, and meniscal lesion.

Using MRI, it is possible to accurately and feasibly measure changes in cartilage morphology and cartilage thickness. The biomechanical quality of the cartilage can be assessed by dedicated cartilage sequences, such as T2-mapping or delayed gadolinium-enhanced MR imag-ing of cartilage (dGEMRIC) [32, 33] (Fig. 6).

Fig. 4 a, b In a 12-year-old girl with epiphysiolysis femoris capitis in the right hip, the femoral head is dislocated medially and slipped (arrow) seen on the axial conventional radiographs (a). Three-dimensional echo-gradient sequence in paraxial refor-mation demonstrates the posteroinferior dislocation of the epiphysis

Table 1. Indications for imaging in coxarthrosis and predis-posing conditions

CR Sonography CT MRI MR arthrography

Coxarthrosis + − − − −

Dysplasia − + − − −

Morbus Perthes + + − a −

Epiphysiolysis + − − + −

Cartilage − − − + +

Labrum ac-etabulare

− − − − +

Femoroacetabu-lary impinge-ment

+ − +/–b + −

Posttraumatic coxarthrosis

+ − + − +c

Osteonecrosis +d − − + −

CR conventional radiograph, CT computed tomography, MRI magnetic resonance imagingaMRI is not yet the gold standard for this indicationbOnly in case of lacking MRIcMRI to diagnose ligamentum capitis lesionsdNot suitable for an early stage of disease

Table 2. Kellgren-Lawrence score for assessing the grade of arthrosis

Criteria Points Definition

Osteophytes 0 None

1 Present

2 Large

Joint space width 0 Normal

1 Definitely narrowed

2 Severely narrowed

3 Completely obscured

Subchondral sclerosis 0 None

1 Mild

2 Mild with cysts

3 Severe with cysts

Deformity 0 None

1 Mild

2 Strong

Grade 1: 1–2 points, grade 2: 3–4 points, grade 3: 5–9 points, grade 4: 10 points

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This is an important issue for the detection of early OA and might bear the potential to avoid the total joint replacement in end-stage OA. Furthermore, the sub-chondral bone plays an important role in the prognosis of OA. Subchondral bone marrow edema (BME), as well as subchondral cysts, are associated with the progression of articular cartilage loss and fluctuation of pain in knee OA. These observations result in the conclusion that

BME is a predictor for the development and impairment of OA [34]. Although a correlation between pain and BME could be shown, care must be taken to interpret bone marrow lesions, because there is a wide spectrum of dif-ferential diagnoses [35]. Ultrasound is the most promis-ing tool for evaluating OA synovitis and might be able to exclude pathologies that are associated with current OA symptoms [36].

Fig. 5 a–d The conventional radiographs in anteroposte-rior (a) and lateral (b) view in the 75-year-old man show a significant joint space narrowing of the medial femorotibial compartment (arrow). On the correspond-ing sagittal (c) and coronal (d) proton density fat satu-rated magnetic resonance images, an associated bone marrow edema, predomi-nantly in the medial femoral condyle is seen (star). Joint space narrowing is caused by a total loss of cartilage in the medial compartment and meniscectomy of the medial meniscus (open arrow). Note the horizontal tear and the subluxation of the lateral meniscus (short arrow), both are typically seen in gonarthrosis with meniscal degeneration

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Conclusion

For the assessment of OA, CR is still the gold standard, due to its standardized technique, its high availability and cost-effectiveness. It is the method of choice for the initial assessment of a joint. Sonography is superior in the demonstration of superficial soft tissue structures and nerves. In addition, sonography makes it possible to assess inflammatory activity by Power Doppler without contrast media application. For the assessment of early diagnosis of OA, MRI is superior in the evaluation of early cartilage defects and cartilage quality and enables the detection of bone marrow edema. Taking its high costs into account, MRI should preferably be applied in younger patients with chronic joint pain. In doubtful cases, MRI is helpful to optimize a patient’s treatment, especially for the preoperative planning.

Conflict of interestThe authors declare that there is no conflict of interest.

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