Radiographic Analysis of Trochlear Notch Sclerosis in the Diagnosis of Osteoarthritis Secondary to Medial Coronoid Disease

Original Research 7 © 2009 Schattauer GmbH Radiographic analysis of trochlear notch sclerosis in the diagnosis of osteoarthritis secondary to medial coronoid disease D. Draffan1; I. Carrera1; S. Carmichael1; J. Heller1; G. Hammond2 1Institute of Comparative Medicine Faculty of Veterinary Medicine, University of Glasgow, UK; 2Hospital for Small Animals, Easter Bush Veterinary Centre, Roslin, Midlothian, UK 1) Increased density of the bone (e.g. en- Summary Introduction largement of the trabeculae, reduced Trochlear notch sclerosis (TNS) as assessed by radiogra- phy has been shown to be increased in elbow dysplasia inter-trabecular bone marrow spaces and (ED) associated medial coronoid process disease (MCD). Medial coronoid process disease (MCD) is subchondral compaction); The aims of this study were to investigate whether two a term that represents a spectrum of pathol- 2) Superimposed osteophytes, and peri- defined radiographic tests evaluating TNS would in- ogies which affect the medial coronoid pro- osteal/endosteal new bone; crease the sensitivity of detecting osteoarthritis second- cess, including fragmentation of the medial 3) Superimposed soft tissue mineralisation. ary to MCD, and to assess whether there was a cor- coronoid process (1, 2). MCD is one of the relation between increasing TNS with severity of MCD. abnormalities seen in elbow dysplasia (ED); Radiographic evidence of TNS secondary to Sixty-one dogs with MCD (121 elbows) were selected the other lesions regularly included are unu- MCD has been described (25) and the inter- from the imaging database. The controls were nine ca- nited anconeal process, and osteochondro- national elbow working group (IEWG) in- davers (18 disease-free elbows). Standard Inter- sis or osteochondritis dissecans of the medi- clude the use of TNS as part of their grading national Elbow Working Group radiographs and CT al humeral condyle (3). Some authors also system for elbow arthrosis. The purpose of scans were taken of each elbow. Plain radiographs were analysed using various assessments: osteophyte include elbow joint incongruency (4, 5). this study was to evaluate the reliability of grade (0–3), coronoid grade (0–3), TNS descriptive MCD is the most common manifestation of qualitative and quantitative radiographic grade (0–3) and TNS ratio. The TNS ratio was calcu- ED (6–9), and, according to many studies, it TNS assessment that could be easily trans- lated from the depth of ulnar sclerosis at the level of is the most frequent cause of thoracic limb ferred to general practice in order to in- the disto-cranial margin of the humeral condyles di- lameness in young, large breed dogs crease the sensitivity of the radiographic di- vided by the cranio-caudal ulna depth. The TNS de- (10–18). ED is the most common cause of agnosis of arthrosis secondary to MCD. The scriptive assessment and ratio both increased the over- elbow osteoarthritis (19). It is therefore of primary hypothesis was that radiographic all sensitivity of diagnosing osteoarthritis secondary to paramount importance that this disease is TNS tests increase the sensitivity of detect- MCD above the other radiographic tests. The sensitivity diagnosed in general practice in order to ing MCD. The second hypothesis was that of the TNS ratio at <0.3 mm was 91%-96% and the allow appropriate therapy, specialist referral increasing TNS correlates with increasing TNS descriptive assessment was 77%-96%. Radio- (if required) and client education to be com- severity of MCD as evaluated by CT. graphic TNS significantly increased with increasing severity of coronoid disease grade as evaluated by CT menced as early as possible. Radiographic p<0.01. The finding that TNS increases the sensitivity signs of MCD are well documented and are of diagnosing osteoarthritis secondary to MCD is valu- based on the early signs of osteoarthritis able to those that have neither a CT scanner nor arth- (13, 20). It is known that the radiographic Materials and methods roscopy readily available. The assessments described in diagnosis of MCD is difficult, with poor this study are easy to apply and do not require any sensitivity compared to advanced imaging In this retrospective study the clinical data- sophisticated technology in order to detect sclerosis. modalities, such as computed tomography base at the University of Glasgow Small (CT) and magnetic resonance imaging Animal Hospital was reviewed from Keywords (MRI) (20–23), but radiology still remains 2004–2007 in order to identify dogs that had Trochlear notch sclerosis, medial coronoid disease, the primary imaging modality in general undergone both CT and radiographic evalu- elbow dysplasia practice. Trochlear notch sclerosis (TNS) is ation of the elbow joint. Additional recorded a radiological term which describes in- clinical information included: age, breed, Vet Comp Orthop Traumatol 2009; 22: 7–15 creased bone radio-opacity in the region of sex, weight, duration of lameness, and the Prepublished online: December 10, 2008 the ulnar trochlear notch, although the term results of arthroscopy, if performed. The in- doi:10.3415/VCOT-07–12–0110 sclerosis means a hardening. It is thought to clusion criteria for each dog were; 1) tho- be due to three different pathological pro- racic limb lameness localised to the elbow cesses (24): joint, 2) diagnostic quality radiographs Received: December 8, 2007 Accepted: May 13, 2008 Vet Comp Orthop Traumatol 1/2009 Downloaded from www.vcot-online.com on 2011-11-23 | ID: 1000542141 | IP: 137.166.68.75 For personal or educational use only. No other uses without permission. All rights reserved. 8 Draffan et al. Table 1 numbers were covered and every elbow was Assessment Grade Description Descriptions of the assess- assigned a number. Each observer analysed ments made for CT and 0 normal coronoid as detected by CT radiographic analyses. the radiographs independently and one 1 altered attenuation week later they analysed the CT scans. CT Coronoid disease grade 2 fissured coronoid For radiographic analyses, osteophyte grade, medial coronoid process disease 3 fragmented coronoid grade and TNS sclerosis grade were assessed 0 no osteophytes on a categorical scale (Table 1). Continuous 1 largest osteophyte <2mm Radiographic osteophyte grade measures of TNS ratio were obtained using 2 largest osteophyte 2–5mm the medio-lateral radiographic projection 3 largest osteophyte >5mm (Fig. 1A, B) and the following standardised 0 normal coronoid measurements and calculations: the depth of sclerosis was measured at the level of the Radiographic medial coronoid 1 mild change in coronoid shape cranio-distal margin of the humeral condyle disease grade 2 marked change in coronoid shape in millimetres (A) and the cranio-caudal 3 fragmented coronoid ulnar depth was measured in millimetres 0 no sclerosis (outer cortex-outer cortex) (B) at the same 1 mild sclerosis, trabecular pattern still level (Fig. 1A, B) 90° to the caudal ulnar Trochlear notch sclerosis (TNS), easily seen shaft. The overall TNS ratio of sclerosis to medio-lateral projection, qualitative 2 moderate sclerosis, trabecular pattern ulnar depth was then calculated as A/B. (descriptive) grade slightly unclear Computed tomograms were assessed for 3 severe sclerosis, trabecular pattern the grade of MCD on a categorical scale cannot be seen (Table 1). A group consensus was also obtained using a combination of the assessments of the CT scans for all of the observ- ers for MCD. By simple majority, the con- (standard IEWG views) and CT scans taken coronoid process. One millimetre sequen- sensus CT coronoid disease grade was used within one week of each other, and 3) evi- tial slices with a slice thickness of 1.2 mm, as the criteria for the diagnosis of MCD to dence of MCD on CT scan in at least one (slice overlap 0.2 mm), were obtained. The which all radiographic assessments were re- elbow. images were reviewed by all of the observ- lated. This categorisation was termed ‘con- Cases with incomplete medical records ers using a bone window (window width sensus’ and is treated as the gold standard or any other pathology within the elbow 3500 Hounsfield units, window level 500 for the diagnosis of presence and extent of were excluded. Elbows demonstrating Hounsfield units). MCD in this paper. MCD with concurrent incongruency were A control population of nine adult cross included. breed canine cadavers, (euthanatised for hu- Standard IEWG radiographic views of mane reasons unrelated to the elbow), with each elbow were obtained (neutral and flex- the same median weight (28 kg) and age Statistical analysis ed mediolateral and extended craniocau- (one year) as the disease population, were Initial graphical analyses of the data were dal), using a rare earth cassette (Quanta de- selected. The forelimbs were collected by undertaken for each radiographic measure- tail; DuPont) and high detail film (Cronex shoulder disarticulation, wrapped in saline- ment and for each observer. Kruskal-Wallis 10T; Agfar). Table top exposures were per- soaked towels and stored at –20°C until the analyses were used in order to compare the formed without the use of a grid and settings time of examination. Before examination, TNS ratio results between levels of consen- were adjusted depending on tissue thick- the limbs were thawed for 24 hours at room sus for each observer and follow-up compari- ness, according to pre-existing exposure temperature remaining in the saline-soaked sons were undertaken using Mann-Whitney charts. CT scans were obtained using a third towels.

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